Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

Emilie Capron; Aline Govin; Emma J. Stone; Valérie Masson-Delmotte; Stefan Mulitza; Bette Otto-Bliesner; Tine L. Rasmussen; Louise C. Sime; Claire Waelbroeck; Eric W. Wolff

doi:10.1016/j.quascirev.2014.08.018

Capron, Emilie;Govin, Aline;Stone, Emma J.;Masson-Delmotte, Valérie;Mulitza, Stefan;Otto-Bliesner, Bette;Rasmussen, Tine L.;Sime, Louise C.;Waelbroeck, Claire;Wolff, Eric W.

2014-10-03 00:00:00

Quaternary Science Reviews 103 (2014) 116e133 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial a, * b c d Emilie Capron , Aline Govin , Emma J. Stone , Valerie Masson-Delmotte , b e f a Stefan Mulitza , Bette Otto-Bliesner , Tine L. Rasmussen , Louise C. Sime , d g Claire Waelbroeck , Eric W. Wolff British Antarctic Survey, High Cross, Madingley Road, CB3 0ET Cambridge, UK MARUM/Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, 28359 Bremen, Germany BRIDGE, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK Institut Pierre-Simon Laplace/Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212, CEA-CNRS-UVSQ, 91191 Gif-sur-Yvette, France Climate and Global Dynamics Division, National Center for Atmospheric Research (NCAR), Boulder, CO 80305, USA CAGE-Centre for Arctic Gas Hydrate, Environment and Climate, UiT, the Arctic University of Norway, Tromsø, Norway Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, CB2 3EQ Cambridge, UK article i nf o abstract Article history: The Last Interglacial (LIG, 129e116 thousand of years BP, ka) represents a test bed for climate model Received 31 March 2014 feedbacks in warmer-than-present high latitude regions. However, mainly because aligning different Received in revised form palaeoclimatic archives and from different parts of the world is not trivial, a spatio-temporal picture of 20 August 2014 LIG temperature changes is difﬁcult to obtain. Accepted 22 August 2014 Here, we have selected 47 polar ice core and sub-polar marine sediment records and developed a Available online strategy to align them onto the recent AICC2012 ice core chronology. We provide the ﬁrst compilation of high-latitude temperature changes across the LIG associated with a coherent temporal framework built Keywords: between ice core and marine sediment records. Our new data synthesis highlights non-synchronous Last Interglacial period maximum temperature changes between the two hemispheres with the Southern Ocean and Marine sediment cores Antarctica records showing an early warming compared to North Atlantic records. We also observe Ice cores warmer than present-day conditions that occur for a longer time period in southern high latitudes than Data synthesis Climate model simulations in northern high latitudes. Finally, the amplitude of temperature changes at high northern latitudes is larger compared to high southern latitude temperature changes recorded at the onset and the demise of the LIG. We have also compiled four data-based time slices with temperature anomalies (compared to present- day conditions) at 115 ka, 120 ka, 125 ka and 130 ka and quantitatively estimated temperature un- certainties that include relative dating errors. This provides an improved benchmark for performing more robust model-data comparison. The surface temperature simulated by two General Circulation Models (CCSM3 and HadCM3) for 130 ka and 125 ka is compared to the corresponding time slice data synthesis. This comparison shows that the models predict warmer than present conditions earlier than documented in the North Atlantic, while neither model is able to produce the reconstructed early Southern Ocean and Antarctic warming. Our results highlight the importance of producing a sequence of time slices rather than one single time slice averaging the LIG climate conditions. Crown Copyright © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). 1. Introduction Members, 2006; Masson-Delmotte et al., 2013; Nikolova et al., 2013). During the last decade, the Arctic has experienced the Due to numerous positive feedbacks, polar regions act as am- strongest warming trend observed at the Earth's surface, and pliﬁers of climate change (e.g. CAPE Last Interglacial Project further climate change is expected to produce large environmental changes in the near future including Arctic glaciers and Greenland ice sheet contributions to projected sea level rise (Church et al., 2013). By contrast, recent sea ice and temperature trends in and * Corresponding author. Tel.: þ44 1223 221 368; fax: þ44 1223 362 616. around Antarctica appear more complex, and this area is expected E-mail address: [email protected] (E. Capron). http://dx.doi.org/10.1016/j.quascirev.2014.08.018 0277-3791/Crown Copyright © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 117 to respond on longer time scales to increased greenhouse gas comparison of temperature rates of change inferred from transient emissions, with large uncertainties on associated sea level risks. simulations as well as sea surface temperature (SST) from alkenone The ability of climate models to correctly capture feedbacks data and polar temperature syntheses, albeit without common involved in polar ampliﬁcation remains uncertain and past climatic chronologies. Both studies stress uncertainties associated with changes provide benchmarks against which the realism of climate chronologies and temperature-averaging procedures. A temporal models can be assessed (Braconnot et al., 2012; Schmidt et al., description of the LIG climate rather than an asynchronous 2014). In particular, studying past warm periods such as recent compilation of LIG temperature optima could allow a detailed interglacial periods, provide unique insights to assess polar evaluation of these model simulations. ampliﬁcation feedbacks in a range of temperature changes com- Indeed, current temporal representations inferred from marine parable to projected future changes (e.g. Otto-Bliesner et al., 2013). sediment and ice core records remain limited so far by the lack of a The Last Interglacial period (hereafter LIG; 129e116 thousand of common robust age scale over the LIG. Existing LIG syntheses are years BP, hereafter ka) is of particular interest since large parts of the currently based on records taken on their original timescale, globe were characterised by a warmer-than-present day climate introducing absolute dating uncertainties that can reach several (e.g. CAPE Last Interglacial Project Members, 2006; Turney and thousand years (e.g. Waelbroeck et al., 2008; Bazin et al., 2013; Jones, 2010). While orbital insolation was distinctly different to Veres et al., 2013). However, there is evidence that surface tem- present-day (Laskar et al., 2004), atmospheric CO concentration perature peaks are not globally coincident. In particular, there is a levels were close to pre-industrial values (Lüthi et al., 2008). The LIG signiﬁcant delay in the establishment of peak interglacial condi- is not an analogue for future climate change because orbital forcing tions in the North Atlantic and Nordic Seas as compared to the is fundamentally different from anthropogenic forcing, and because Southern Ocean (Cortijo et al., 1999; Bauch and Erlenkeuser, 2008; the geographical pattern of LIG temperature changes strongly differ Bauch et al., 2011; Van Nieuwenhove et al., 2011; Govin et al., 2012). from those expected in the future (Masson-Delmotte et al., 2011a). Also, an early Antarctic warming has been reported (Masson- Nonetheless, it offers an opportunity to assess the effect of warmer- Delmotte et al., 2010). Thus, a compilation with a dynamic repre- than-present-day polar climate on climate-sensitive parts of the sentation of the sequence of climatic events (several time slices) Earth system, most notably polar ice sheets and sea level. Previous taking into account potential asynchronous temperature changes work suggests that global sea level was 5.5e9 m higher than today between the two hemispheres during the LIG is necessary. This (e.g. Kopp et al., 2009; Thompson et al., 2011). Combined with earlier requires synchronising palaeoclimatic records from different ar- evidence for LIG ice at the bottom of the Greenland ice sheet (e.g. chives (e.g. ice cores and marine sediments). GRIP members, 1993), the NEEM ice core data demonstrate the The objectives of this study are twofold. First we document the resilience of the central Greenland ice sheet to LIG local warming magnitude and spatio-temporal structure of LIG temperature (NEEM community members, 2013). Ice sheet simulations changes in the high latitudes of the two hemispheres. For that compatible with NEEM elevation estimates suggest that the purpose, we describe a new data synthesis of air and sea surface Greenland ice sheet contribution to the sea level rise should be in the temperature changes across the LIG in polar and sub polar regions range of 1.4e4.3 m (Robinson et al., 2011; Born and Nisancioglu, associated with a coherent temporal framework between ice core 2012; Masson-Delmotte et al., 2013; Quiquet et al., 2013; Stone and marine sediment records. Second, based on this new high et al., 2013). However, different input climates arising from climate latitude data compilation, we produce four data-based surface simulations have been used as inputs for these ice sheet simulations. temperature anomaly time slices at 115 ka, 120 ka, 125 ka and Also, the study of the LIG beneﬁts from numerous snapshot and 130 ka for which we propagate relative dating uncertainties and transient climatic simulations with state of the art General Circula- reconstructed temperature errors into the ﬁnal temperature tion Models (GCMs; e.g. Bakker et al., 2013; Lunt et al., 2013; anomaly estimates. Using snapshot simulations performed for the Nikolova et al., 2013; Otto-Bliesner et al., 2013; Langebroek and 125 ka and 130 ka climatic conditions by the CCSM3 and HadCM3 Nisancioglu, 2014; Paleoclimate Modelling Intercomparison Project, models, we illustrate how these new time slices enable more robust http://pmip3.lsce.ipsl.fr/). Altogether, this further motivates the model-data comparison to be performed in order to test state-of- evaluation of these GCMs against LIG climate reconstructions. In the-art GCMs also used to perform future climate projections. particular, data syntheses are required to document the magnitude and spatio-temporal structure of LIG temperature changes. 2. Material and methods Several climatic data compilation initiatives have been con- ducted for the LIG (CLIMAP, 1984; Kaspar et al., 2005; CAPE Last 2.1. Palaeoclimatic data selection Interglacial Project Members, 2006; Clark and Huybers, 2009; Turney and Jones, 2010; McKay et al., 2011). Turney and Jones We selected sites presenting a mean time-resolution of tem- (2010) averaged temperature estimates across the benthic forami- perature reconstruction better than 2 ka and sufﬁcient additional 18 18 18 nifera d O and ice d O plateau in marine and ice core records information (e.g. benthic and/or planktic d O records, ash layers) respectively, and across the period of maximum warmth in to help integrate them with conﬁdence into the common temporal terrestrial sequences. They deduced a global annual LIG framework. We selected ﬁve records of surface air temperature “maximum” warming above pre-industrial of about 2 C and they deduced from water stable isotopes measured along polar ice cores identiﬁed earlier warming in Antarctica. McKay et al. (2011) used an and 42 SST records from marine sediment cores located above 40 N alternative temperature-averaging method and calculated the and 40 S of latitude (Fig. 1). We obtained data through the PAN- mean sea surface temperature (SST) over a 5 ka period centred on GAEA database, from individual papers provided by principal in- the warmest temperature observed between 135 ka and 118 ka in vestigators or extracted from published ﬁgures through digital marine records. They estimated a global annual mean SST warming image processing. Details for each selected record are given in of þ0.7 ± 0.6 C relative to the late Holocene. Table A1. Otto-Bliesner et al. (2013) used these existing LIG temperature compilations to benchmark snapshot simulations performed at 125 # Ice core records: and 130 ka with the CCSM3 GCM. However, both time slices are compared to a single data synthesis built assuming explicitly syn- We include local surface air temperature reconstructions for the chronous peak warmth. Recently, Bakker et al. (2014) proposed a East Antarctic EPICA Dome C (EDC), EPICA Dronning Maud Land 118 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 Fig. 1. Location of marine sediment and ice core sites in a. the Northern Hemisphere and b. the Southern Hemisphere included in this study. The compilation contains surface air temperature records from Greenland (black square) and Antarctic (red square) ice cores and SST reconstructions (diamond) based on Mg/Ca (blue), alkenones (grey), diatoms assemblages (orange), radiolarians (green) and foraminifera assemblages (MAT method, purple; NPS percentage, pink). Numbers refer to record labels indicated in Table A1 from the Appendix. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) (EDML), Vostok and Dome F ice cores based on the stable isotopic reconstructions are based on foraminiferal Mg/Ca ratios (three re- composition of the ice (Masson-Delmotte et al., 2011b and references cords), alkenone unsaturation ratios (three records) and faunal therein). Reconstructions of local surface temperature in Antarctic ice assemblage transfer functions (24 records based on foraminifera cores are based on the present day spatial relationship between the assemblages, two records based on radiolarian assemblages and ice isotopic composition of the snow and surface temperature (“iso- four records based on diatom assemblages) and the percentage of topic thermometer”). While in principle they should reﬂect the polar foraminifera species Neogloboquadrina pachyderma precipitation-weighted temperatures, they are considered here as sinistral (six records) (Fig. 1, Table A1). Therefore, our data compi- annualmeans.Precipitationintermittency,changesinmoisture origin lation mostly includes SST reconstructions based on faunal as- as well as site elevation and ice origin changes (Jouzel et al., 2003; semblages, which reﬂects the low amount of high-resolution SST Masson-Delmotte et al., 2006; Vinther et al., 2009; Stenni et al., records produced with alternative geochemical methods (e.g. 2010) affect the quantiﬁed temperature changes from ice cores. In alkenone paleothermometry, foraminiferal Mg/Ca) throughout the particular, a modelling study of projected climate and precipitation LIG. isotopic composition suggests that using such a method could result We use these records as representing annual or summer SST as in an underestimation of past temperatures for periods warmer than given by the authors of the respective papers. Note that in the case present day conditions (Sime et al., 2009). It results in an uncertainty of core MD97-2121, both summer SST (record [27] on Fig. 1 and associated with the different ice-core-based Antarctic absolute tem- Table A1, hereafter records are only designated such as [27]) and " " perature reconstructions from ±1 Cto ±2 C(Stenni et al., 2010; annual mean SST [28] have been reconstructed from the same Masson-Delmotte et al., 2011b). source data while for core SU90-08 a summer SST record has been Ice cores retrieved in Greenland are deﬁcient in providing a deduced from foraminifera assemblages ([23]; Cortijo, 1995) and an continuous or/and complete record of the LIG (GRIP members,1993; annual SST record has been deduced based on alkenone paleo- Grootes et al.,1993; NorthGRIP community members, 2004; NEEM c. thermometry ([22]; Villanueva et al., 1998). Uncertainties on each m. 2013). Here, we use the NGRIP d O for record alignment pur- reconstructed SST record were estimated from (1) the uncertainty ice poses between 123 and 110 ka as it represents the only continuous on measurement and (2) the calibration of geochemical and Greenlandic record covering this time interval. In Greenland, iso- microfossil proxies against modern conditions and range between topeetemperature relationships vary through time and have 0.6 and 2.1 C depending on the SST proxies (uncertainties for in- smaller slopes than the modern spatial gradient. We use here the dividual records are given in Table A1). precipitation-weighted temperature estimate corrected for eleva- tion and upstream effects deduced from the NEEM ice core between 2.2. Strategy for aligning climatic records over the Last Interglacial 116 and 128 ka (NEEM c. m., 2013). Note that while elevation effects are commonly considered to be negligible for Antarctic ice cores Beyond the applicable range of radiocarbon dating, LIG re- (Bradley et al., 2012, 2013), this is not the case for Greenland. constructions beneﬁt from few absolute markers. Large discrep- ancies of up to several thousand years exist between time scales # Marine sediment cores: used to display marine sediment cores and ice core timescales. As an example, Parrenin et al. (2007) report a 2 ka age difference The marine sediment records included in our data synthesis are across this time period between the LR04 time scale classically mostly located in the North Atlantic region for the Northern taken as a reference chronology to establish age models of marine Hemisphere and in the Indian and Atlantic sectors of the Southern sediment cores (Lisiecki and Raymo, 2005) and the EDC3 ice core Ocean for the Southern Hemisphere. The coverage of selected sites chronology. Thus, the construction of a common chronostratig- reﬂects the lack of high-resolution SST records covering the LIG in raphy between ice core and marine records is critical to compare other high-latitude regions and emphasises the need for obtaining the LIG climate evolution in both the Northern and Southern future SST records in particular in the Paciﬁc Ocean. SST Hemispheres. E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 119 2.2.1. AICC2012, a new ice core dating and a reference chronology alignment and reﬂects how robust the tie-point is regarding its We use the new AICC2012 ice core chronology (Bazin et al., location (e.g. situated at the mid-point of a well-marked transition) 2013; Veres et al., 2013) as a reference chronology to display the and how synchronous the records used for the alignment become selected marine sediment and ice core records. The AICC2012 after deﬁning the tie-point. A list of deﬁned tie-points, corre- chronology is the ﬁrst integrated timescale over the LIG, based on a sponding rationale and relative 1s age uncertainties on the multi-site approach including both Greenland (NGRIP) and Ant- AICC2012 timescale is given for every selected sediment core in arctic ice cores (EDC, EDML, TALDICE, Vostok). The new chronology Table A2. shows only small differences, well within the original uncertainty range, when compared with the EDC3 age scale over the LIG. # Southern Ocean cores: We align each SST record from the However, the numerous new stratigraphic links signiﬁcantly Southern Ocean onto the EDC deuterium record (dD, Jouzel et al., reduce the absolute dating uncertainty down to ±1.6 ka (1s) over 2007; site [45] on Fig. 1) displayed on AICC2012. Our decision to the LIG (Bazin et al., 2013) making it the most appropriate age scale align marine cores from all Southern Ocean sectors onto the EDC to date with which to compare our synchronised records with record is justiﬁed by the fact that the Dome F, EDML and EDC model runs and other dated records. water stable isotope records show similar variations, with The Dome F and the NEEM ice cores have not been included to approximately simultaneous climatic transitions (Masson- construct the AICC2012 chronology (Bazin et al., 2013; Veres et al., Delmotte et al., 2011b). Also considering either the EDC dD re- 2013). However, both the Dome F and the NEEM ice cores have been cord or the EDC site temperature estimate as a reference curve previously transferred onto the EDC3 timescale (Parrenin et al., for aligning marine sediment records onto AICC2012 does not 2007; NEEM c. m., 2013). Thus by using published EDC3- affect the timing of the glacial inception and the start of AICC2012 age relationships (Bazin et al., 2013; Veres et al., 2013), Termination II (Masson-Delmotte et al., 2011b). Termination II is we transfer the temperature records from the Dome F and the slightly more abrupt in the site temperature record than in the NEEM ice cores onto the AICC2012 chronology. dD record but it only leads to an age difference for the two corresponding mid slope points of less than 500 years. 2.2.2. Transfer of marine records onto AICC2012 We follow the strategy of Govin et al. (2012) to align marine Fig. 2 (left panel) illustrates the alignment of core MD88-769 records onto the AICC2012 ice core chronology. It is based on the [37] onto AICC2012 based on four tie points. We deﬁne a ﬁrst tie assumption that surface-water temperature changes in the sub- point by aligning the ﬁrst SST increase with the EDC dD increase at Antarctic zone of the Southern Ocean (respectively in the North the beginning of Termination II (138.2 ± 2 ka). Then, we deﬁne a Atlantic) occurred simultaneously with air temperature variations mid-slope tie point in the course of the glacialeinterglacial tran- over inland Antarctica (respectively Greenland). Such a link be- sition (131.4 ± 1 ka) and another mid-slope tie point during the tween air above the polar ice sheets and surrounding surface wa- glacial inception (116 ± 1.5 ka). Finally, a last relative age constraint ters has been observed during the abrupt climate changes over the is determined by tying the mid-slope of the dD increase corre- Last Glacial period and during Termination I which beneﬁt from sponding to the Antarctic Isotopic Maxima 24 and its counterpart robust radiocarbon dating constraints (Bond et al., 1993; Calvo identiﬁed in the SST record (106.7 ± 2 ka). We are conﬁdent in our 14 18 et al., 2007). For instance, SST changes at site NA87-22 ( C-dated alignment since it results in simultaneous benthic d O variations record, Waelbroeck et al., 2008, 2011) are synchronous within recorded in cores MD88-769 and MD02-2488 [38] (which was dating uncertainties with both the NorthGRIP d O and CH retrieved at a similar water depth and previously transferred onto ice 4 concentration changes over the last 25 ka (Fig. 1 from Masson- AICC2012 following a similar strategy) (Fig. 2, left panel). Delmotte et al., 2010). Benthic foraminiferal d O is often used as a stratigraphic tool to # North Atlantic cores: We align the SST proxy records from the place marine records on a common age model (e.g. Lisiecki and North Atlantic cores to the ice d O record from the NGRIP Raymo, 2005). We prefer avoiding using this strategy for all the Greenland ice core during the Last Glacial inception. We favour selected marine records since there is evidence for signiﬁcant off- the NGRIP ice core to the NEEM ice core as the Greenland sets (from 1 ka to up to 4 ka) between benthic d O records from reference ice core because (1) the NGRIP ice core is one of the ice different water masses and oceanic basins during deglaciations (e.g. records used to constrain the AICC2012 chronology and (2) the Skinner and Shackleton, 2005; Lisiecki and Raymo, 2009). However, NGRIP ice core represents a continuous record up to 123 ka no clear benthic d O offsets (within dating uncertainties, ~2 ka) are (NorthGRIP c. m. 2004) while the NEEM ice core record presents observed during the penultimate deglaciation between North stratigraphic discontinuities at the end of the LIG (NEEM c. m. Atlantic sites located at different water-depth within the same 2013). Since the NGRIP ice core does not cover the early LIG, North Atlantic Deep Water mass (Govin et al., 2012). Therefore, we alternative strategies are followed to align marine and ice core use benthic foraminiferal d O records to verify the overall agree- records prior to 122 ka. First, we assume that the global abrupt ment of chronologies deﬁned in North Atlantic or Southern Ocean methane increase during Termination II reﬂects synchronous sites located in the same water mass. For this purpose, we use cores abrupt warming of the air above Greenland. This is indeed MD02-2488 [38] and ODP980 [14] as Southern Ocean and North observed during Termination I as well as during millennial-scale Atlantic references, respectively, because of the high temporal DansgaardeOeschger events (e.g. Chappellaz et al., 1993; Huber resolution of their SST records and the availability of multi-proxy et al., 2006; Baumgartner et al., 2013). On Fig. 2, the right panel records (i.e. planktic and benthic foraminiferal stable isotopes). illustrates the alignment of core SU90-44 [19] onto AICC2012 To align marine sediment cores onto the AICC2012 chronology, using four tie-points. The beginning of the LIG is relatively well we use the software AnalySeries 2.0 (Paillard et al.,1996) and deﬁne constrained in all North Atlantic cores with a tie point linking the minimum number of tie points which produces the best the ﬁnal SST increase with the abrupt methane increase recor- possible alignment. Age models are constructed by linear interpo- ded in the EDC ice core (128.7 ± 0.5 ka). However, in order to lation (i.e. constant sedimentation rate) between tie-points. The constrain the 130 ka time slice, it is necessary to deﬁne a tie relative uncertainty attached to each tie point is graphically esti- point prior to 131 ka (see Section 2.3). Thus, we deﬁne a ﬁrst tie mated through multiple alignment possibilities. It takes into ac- point during the preceding glacial period using the assumption count the time resolution of the records used to perform the that the establishment of the very cold glacial conditions related 120 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 Fig. 2. Deﬁnition of age models in the Southern Ocean MD88-769 core [34] (red curves) and the North Atlantic SU90-44 core [17] (blue curves). Numbers between brackets correspond to of the core location on Fig. 1. Triangles (with error bars representing associated relative 1s dating uncertainties) and vertical dotted lines highlight the tie-points deﬁned between (left panel) the MD88-769 Summer SST record and the Antarctic EDC dD record (Jouzel et al., 2007; black) and (right panel) between the SU90-44 Summer SST record and the NGRIP ice d O record (NorthGRIP c. m. 2004; black), the CH concentration measured in the air trapped in the EDC ice core (Loulergue et al., 2008; grey) and the percentages of N. pachyderma sinistral (LSCE database). The resulting agreement between Summer SST and benthic d O records from MD88-769 and MD02-2488 (Govin et al., 2012; grey) both displayed on AICC2012 is shown as well as resulting sedimentation rate variations and associated relative age uncertainty of the tie points for each core. Grey shaded areas mark non-parametric 2s (2.5th and 97.5th percentiles) conﬁdence intervals of Monte Carlo iterations (see text for details). (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) to Heinrich event 11 is synchronous within the North Atlantic onto AICC2012. Note that in the rest of the manuscript, we region. As a result, we tie the increase of the percentage of differentiate the North Atlantic high latitude region from the N. pachyderma sinistral in core SU90-44 with the one recorded Labrador Sea area. at 133.8 ± 2 ka in core ODP980 previously transferred onto # Nordic Seas and Labrador Sea cores: Climatic alignments of re- AICC2012 (Table A2). Then, at the end of the LIG, the ﬁrst pro- cords retrieved in the Labrador Sea and the Nordic Seas are more nounced North Atlantic cooling is tied to the corresponding equivocal for two main reasons. First, most of the SST estimates enhanced cooling in the NGRIP ice core (116.8 ± 1.5 ka). We have been derived from the percentage of N. pachyderma ﬁnally deﬁne a tie point that links SST and Greenland air tem- sinistral which is not suitable to record SST variations below perature at the end of the ﬁrst abrupt event, Dans- 6.5 C(Tolderlund and Be, 1971; Kohfeld et al., 1996). Indeed, gaardeOeschger 25 (107.3 ± 1.5 ka). We are conﬁdent in the while the percentage of this species is linearly related to SST choice of these tie points since they lead to simultaneous in- changes for water of ~6.5e15 C, the abundance of creases in the percentage of N. pachyderma sinistral recorded in N. pachyderma sinistral already accounts for ~95% of forami- cores SU90-44 and ODP980 (Fig. 2, right panel). A similar pro- nifera faunal assemblages at 6.5 C, thus any temperature cedure is followed for all other North Atlantic high latitude sites change below this value cannot be tracked with this method except for the site EW9302-JPC2 [21] located in the Labrador Sea (Kohfeld et al., 1996; Govin et al., 2012). Also, potential issues in and for which it is less straightforward to deﬁne the alignment the preservation of the planktic foraminifera shells may affect E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 121 the SST reconstructions (e.g. Zamelczyk et al., 2012). Unfortu- difﬁculty of performing these alignments is reﬂected in the rela- nately to our knowledge, there are very few alternative quan- tively high relative dating uncertainties associated to each tie titative SST estimates available for the LIG in the Labrador Sea point (Table A2). In three of these high northern latitude sites, (only [11], [12], [13] and [21]) and in the Nordic Seas (only [7]) temperature anomalies cannot be reconstructed for the 130 and based on alternative SST reconstruction methods. 115 ka data-based time slices due to the lack of chronological constraints. We update the chronology that was originally deﬁned Second, planktic and benthic foraminiferal d O are charac- in the Labrador Sea core EW9302-JPC2 using the EDC3 timescale terised by highly depleted d O values during Termination II (e.g. as a reference by Govin et al. (2012) in order to transfer the re- Risebrobakken et al., 2006; Bauch and Erlenkeuser, 2008), which cords onto AICC2012. Fig. 3 illustrates how we transfer MD95- makes the identiﬁcation of the LIG climatic optimum in forami- 2009 [7] and HM71-19 [2] records from the Nordic Seas onto niferal stable isotopes difﬁcult. Very low benthic d O during the AICC2012 chronology. First, the North Atlantic core ENAM33 Termination II may derive from intensiﬁed sea ice formation and [8] is transferred onto AICC2012 via the alignment of its SST record brine rejection that transferred to bottom waters the low d O (Rasmussen et al., 2003; this study; Details are given on the SST signal recorded in surface waters in response to strong iceberg reconstruction method in the appendix) to the NGRIP d O and ice melting (e.g. Risebrobakken et al., 2006). Alternatively, Bauch and the EDC CH concentration (see previous section for details on the Bauch (2001) proposed that such low benthic d O values may approach). Second, we deﬁne stratigraphic links between core reﬂect the warming of bottom waters in response to the inﬂow of ENAM33 and the Nordic sea core MD95-2009 to transfer the latter warm subsurface Atlantic waters below fresh and stratiﬁed surface onto AICC2012. A ﬁrst tie point is determined based on the waters in the Nordic Seas. alignment of MD95-2009 benthic d O record with core ODP980 at To overcome these difﬁculties, we combine here several lines of 138.2 ka associated with a relative age uncertainty of 4 ka. Such a evidence (i.e. temperature variations, tephra layers, foraminiferal relative age uncertainty takes into account the difﬁculty in stable isotopes, biostratigraphic constraints) to deﬁne chronolo- deﬁning the tie point and the possible time lags between two gies as robust as possible in the Norwegian and Labrador Seas. The benthic d O records from different oceanic basins. Then, we Fig. 3. Deﬁnition of age models in one North Atlantic (ENAM33 [8], green curves) and two Norwegian Sea sediment cores (MD95-2009 [7] and HM71-19 [2]). Numbers between brackets correspond to the location of records on Fig. 1. ENAM33 core has been ﬁrst transferred onto AICC2012 through climatic alignments (tie points indicated in black triangles). In addition to climatic alignment-based tie points (black triangles and pink square for the tie point proposed by Rasmussen et al., 2003), core MD95-2009 was linked to core ENAM33 thanks to the ash layer 5e-Low/bas-IV identiﬁed in both cores (orange dot). Core HM71-19 was aligned onto core MD95-2009 based on the ash layers 5e-Midt/RHY and 5e- Low/bas-IV identiﬁed in both cores (orange dots) and planktic and benthic d O records (black triangles). Sedimentation rate variations and deﬁned relative age uncertainty are also shown for each core. Grey shaded areas mark non-parametric 2s (2.5th and 97.5th percentiles) conﬁdence intervals of Monte Carlo iterations (see text for details). (For inter- pretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) 122 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 123 include the biostratigraphic link proposed by Rasmussen et al. error. Third, we (1) randomly determined the age of every tie-point (2003) between cores MD95-2009 and ENAM33 dated at within the space of dating error documented in Table A2, (2) 128.0 ± 1.5 ka on AICC2012. These authors aligned in both cores checked for potential age reversals and discarded the iteration in the disappearance of Atlantic benthic foraminifera species groups those cases, (3) assigned an age to every depth with SST values by that are replaced by benthic species associated with the cold linear interpolation between tie-points. On Figs. 2e4, we show SST Norwegian Sea Overﬂow Water, hereby reﬂecting the onset of records associated with a non-parametric 2s conﬁdence interval convection in the Nordic seas (Rasmussen et al., 2003). We use envelope (from the 2.5th to the 97.5th percentiles after resampling also as a stratigraphic link the ash layer 5e-Low/BasIV identiﬁed in every 0.1 ka). both ENAM33 and MD95-2009 cores (Rasmussen et al., 2003). While an older age was reported by Rasmussen et al. (2003) based on a correlation onto the SPECMAP time scale, the ash layer 5e- 2.3. Establishment of data-based time slices at 130 ka, 125 ka, Low/BasIV in core ENAM33 corresponds to a depth level dated at 120 ka and 115 ka 123.7 ± 2 ka based on the deptheage relationship resulting from the alignment of this core onto AICC2012 (Fig. 3, left panel). Thus, In order to provide a dynamical climatic description not only of this age of 123.7 ± 2 ka is used as a third tie point to constrain the the LIG climatic optimum (e.g. Turney and Jones, 2010; McKay et al., age model of core MD95-2009 (Fig. 3, middle panel). At the end of 2011) but also covering of its onset and demise, we choose to the LIG, the pronounced cooling in MD95-2009 SST record is tied calculate temperature anomalies for four time windows: 114e116, to the corresponding enhanced cooling in the NGRIP ice core at 119e121, 124e126 and 129e131 ka, hereafter referred to as the 116.7 ± 2 ka. A ﬁnal tie point at 107.5 ± 4 ka is determined based data-based 115, 120, 125 and 130 ka time slices, respectively. on the alignment of MD95-2009 benthic d O record with core Although, snapshot simulations have also been run for the 128 and ODP980. 126 ka climatic conditions, we consider that the average relative We use two types of tie-points to transfer core HM71-19 from age uncertainties associated with the alignment of marine cores the Nordic Seas onto the AICC2012 timescale. First, the tephra onto AICC2012 prevent us to propose more that 4 time slices within layers 5e-Low/BasIV and 5e-Midt/RHY (Fronval et al., 1998; the 115 kae130 ka time interval. Also, we choose a 2 ka time Rasmussen et al., 2003) dated at 123.7 ± 2 ka and 118.9 ± 3 ka on window for each time slice so that each average temperature AICC2012 and identiﬁed in both cores HM71-19 and MD95-2009 anomaly relies on a sufﬁcient number of data points. To develop a (Fronval et al., 1998; Rasmussen et al., 2003) are used as two tie comparison to present-day summer SST, mean annual or summer points. Note that to deﬁne the age of 118.9 ± 3 ka for the tephra SST for each marine core location are extracted at 10 m depth from layer 5e-Midt/RHY, we follow the same strategy as for the tephra the 1998 World Ocean Atlas (WOA98), as recommended in Kucera layer 5e-Low/BasIV, i.e. the age is deduced based on the depth/age et al. (2005) (Table A1). Summer SST are deﬁned as averaged SST relationship for core MD95-2009 transferred onto AICC2012. As a during the months of July, August and September for the Northern result, uncertainties associated to these tie points include the un- Hemisphere (JAS SST) and as the averaged SST during the months of certainty linked to the respective estimated ages of 5e-Low/basIV January, February and March for the Southern Hemisphere (JFM and 5e-Midt/RHY as deﬁned in cores ENAM33 and MD95-2009, SST). Note that the choice of the WOA database has a negligible respectively, transferred onto the AICC2012 timescale. Second, in impact on the resulting SST anomalies. A root-mean-standard- order to provide additional constraints at the onset and demise of deviation of only 0.2 C is deduced from a comparison of JAS the LIG, we also align the planktic d O record (tie points at present-day summer SST at all marine core locations from WOA98, 134.6 ± 4 ka and 128.7 ± 2 ka) and benthic d O record WOA2001, WOA2005, WOA2009, and WOA2013. In line with (112.5 ± 4 ka) from core HM71-19 onto those from the Norwegian MARGO community members (2009), we neglect here the uncer- Sea core MD95-2009. Indeed, we make the assumption that at the tainty on modern WOA98 SST, which we consider to be much scale of glacialeinterglacial changes, hydrological changes within smaller than the error on reconstructed SST. For ice core records, we the Nordic Seas are occurring at the same time within an uncer- use annual mean surface air temperature given in the literature tainty of a few thousand years based on existing records (e.g. Bauch based on present day instrumental temperature measurements et al., 2000; Bauch et al., 2012). (Masson-Delmotte et al., 2011b; NEEM c. m., 2013). For each marine sediment record, we perform a Monte-Carlo For each marine sediment record, we use the Monte-Carlo analysis to propagate the errors associated with both (1) the un- analysis to determine the temperature anomalies and associated certainty linked to the SST reconstruction method and (2) the age temperature uncertainty for each time slice. Mean SST anomalies uncertainties on the tie points that we deﬁned during the record for each time window were calculated after resampling every alignment. The error on the SST reconstruction is set to the value 0.1 ka. From the 1000 slightly different SST anomalies obtained for attributed for each SST record in its original publication (listed in each time slice, the median SST anomaly and the associated non- " " Table A1). It varies from 0.6 C to up to 2.1 C and it is on average parametric 2s uncertainties (2.5th and 97.5th percentiles) were 1.4 C. To include uncertainties linked to the temporal alignment of calculated (Fig. 5). The uncertainty on temperature anomalies is records, we ﬁrst estimate dating uncertainties associated with " ± 2.6 C on average. It increases for the time slices 115 and 130 ka deﬁned tie-points (Table A2). Second, we propagated these errors since they are within large climatic transitions. As a result, even by applying to all cores a Monte-Carlo analysis performed with small dating uncertainties can lead to larger differences in tem- 1000 age model simulations. For every iteration, we add random perature anomalies deduced for one given time slice from the noise to SST values within the space of temperature reconstruction various Monte Carlo simulations. Fig. 4. Air and summer sea surface temperature records displayed on the AICC2012 timescale between 110 ka and 135 ka (red colours for the Southern Hemisphere records and blue colours for the Northern Hemisphere records). Note that y axes display the same temperature amplitude of 20 C to allow visual comparison between sites. Grey shaded areas mark non-parametric 2s (2.5th and 97.5th percentiles) conﬁdence intervals of Monte Carlo iterations (see text). Note that two SST records have been produced for sites MD03-2664 [12, 13], SU90-08 [22, 23] and MD-2121 [27, 28]. Annual signals [22, 28] are displayed in black and spring signal is displayed in grey. Dashed black lines mark their non-parametric 2s (2.5th and 97.5th percentiles) conﬁdence intervals of Monte Carlo iterations (see text). (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) 124 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 Fig. 5. Temperature anomalies estimated for four time-slices at 115 ka, 120 ka, 125 ka and 130 ka. a. Northern Hemisphere air temperature and SST anomalies. SST anomalies are calculated relative to modern summer SST taken at 10 m water-depth from the World Ocean Atlas 1998 (following the MARGO recommendations, Kucera et al., 2005, months used to estimate modern SST at site locations are July, August and September). b. 2s uncertainties of temperature anomalies in the Northern Hemisphere taking into account the error on the temperature reconstruction and the propagated dating errors. c and d. Same as a. and b. for the Southern Hemisphere. Summer months used to estimate modern SST at site locations are January, February and March. The bigger the dot is, the larger the anomaly is. Warming (cooling) vs modern temperature is represented in orange (blue). 2.4. Model simulations CCSM3 climatologies are calculated from the last 30 years of a 950 year-long pre-industrial simulation and of 350 year-long simula- To illustrate the potential of our new LIG data synthesis in tions at 125 and 130 ka (continued from previously run LIG simu- model-data comparisons, we use two snapshot simulations at lations). HadCM3 climatologies are calculated from the last 50 years 125 ka and 130 ka performed with two fully coupled global of a >1000 year pre-industrial simulation and the last 50 years of atmosphere-land surface-ocean-sea ice general circulation models 550 year-long simulations at 125 and 130 ka. The lengths of the two (GCM): the Community Climate System Model, Version 3 (CCSM3, simulations are different because they result at ﬁrst from inde- Collins et al., 2006) and the HadCM3 MOSES 2.1 model (Gordon pendent initiatives but in both cases, the surface diagnostics are in et al., 2000). These two GCMs have been previously used to simu- reasonable equilibrium with the modiﬁed climate although neither late the LIG and pre-industrial climates and details on the model model has reached equilibrium in the deep ocean. For the prein- components and the methodology of coupling are given by Otto- dustrial CCSM3 shows trends of less than 0.1 C per century in the Bliesner et al. (2013) and Lunt et al. (2013) respectively. Whilst Southern Ocean while HadCM3 shows a trend of 0.02 C per cen- biases in SST estimates arise in climate models for several reasons tury for summer SST at high southern latitudes. In order to compare including poor representations of sea ice variability and the Atlantic the model temperature anomalies for the deﬁned data-based time Meridional Overturning Circulation, Lunt et al. (2013) have shown slices, it is necessary to account for the discrepancy between the that CCSM3 and HadCM3 models have the best skill (or smallest pre-industrial reference used for the model and the modern error) for the simulation of pre-industrial surface air temperature, reference used for the data. To correct for this effect, we calculate as compared to the NCEP climatology within all models used to the difference between the gridded NODC WOA98 dataset (repre- simulate the LIG period. sentative of the modern reference) and the gridded HadISST data- Boundary conditions are summarised in Table 1. The Earth's set (Rayner et al., 2003) (representative of a pre-industrial orbital conﬁguration constitutes the dominant forcing for the [1870e1899 AD] reference) and add this to the model anomaly 125 ka and 130 ka climate compared with pre-industrial conditions. (LIG minus pre-industrial). The average correction at the core E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 125 Table 1 conﬁdence the timing of maximum surface temperature peaks in Forcing and boundary conditions used in CCSM3 and HadCM3 simulations (Otto- this region. No signiﬁcant maximum temperature peak is identiﬁed Bliesner et al., 2013; Lunt et al., 2013 for more details). Greenhouse gas concentra- in records [2], [3], and [4] located at the highest latitudes (between tions used for the HadCM3 simulations are those speciﬁed by PMIP3. They were " " 68 N and 70 N; Fig. 4). Still, the establishment of interglacial deduced from records measured on the EDC ice core displayed on the EDC3 time- scale (Spahni et al., 2005; Loulergue et al., 2008; Lüthi et al., 2008). Similar values are temperature seems to occur at 122.5 ka, and 122.7 ka in MD95- obtained when using the AICC2012 time scale. Greenhouse gas concentrations used 2009 [7] and MD95-2010 [5] respectively. In the Labrador Sea, re- for the CCSM3 simulations are higher than the ones taken in the PMIP3 LIG pro- cords [11] and [12] do not record unambiguously a temperature tocols. They were deduced from the EDC greenhouse gas concentration records maximum while a LIG temperature peak is identiﬁed at 124.4 ka in displayed on the EDC3 timescale but represent the peak overshoot values occurring record [21]. at 128e129 ka. Our data synthesis also reveals large regional climatic vari- CCSM3 HadCM3 ability, in particular in the North Atlantic high latitude region. For 130 ka 125 ka PI 130 ka 125 ka PI example, the summer SST record from core MD95-2014 exhibits a Geography Modern Modern Modern Modern Modern Modern deglacial temperature increase toward a maximum, directly fol- Ice Sheets Modern Modern Modern Modern Modern Modern lowed by a smooth temperature decrease (Fig. 4, [10]). At other Vegetation Modern Modern Modern Modern Modern Modern sites, such as the coring sites of ENAM33 and ODP980, maximum CO (ppmv) 300 273 289 257 276 280 summer SSTs prevail for 7e13 ka before cooling and glacial CH (ppbv) 720 642 901 512 640 760 N O (ppbv) 311 311 281 239 266 270 inception take place (Fig. 4, [8] and [14]). Also M23414-9 and Solar constant 1367 1367 1365 1365 1365 1365 SU90-39 SST records clearly exhibit a two-step deglaciation $2 (W m ) interrupted at 130 ka (Fig. 4, [16] and [18]). Such a pattern has also Orbital 130 ka 125 ka 1990 130 ka 125 ka 1950 been recently shown and discussed in a new SST record from the " 0 Alboran Sea located at 36 12.3 N (core ODP976; Martrat et al., locations is of 0.44 C. Similar to the calculations of temperature 2014) while this is not a feature that is unambiguously observed anomalies in marine records (Section 2.3), we show here simulated in the other records included in our synthesis (located above summer SST anomalies deﬁned as JAS for the Northern Hemisphere 40 N). However, the likelihood of recording such a millennial- and JFM for the Southern Hemisphere. For polar ice cores, we scale feature is highly dependent on the temporal resolution of consider annual temperature anomalies at the locations of the the records. Regional variability is observed in the Southern Antarctic ice cores and the precipitation-weighted temperature Hemisphere with a clear temperature overshoot in Antarctic sur- anomaly at the location of the NEEM Greenlandic ice core face air temperature records (records [44]e[47]) and possibly in (Figs. 6e7). DSDP-594 [34]. This overshoot is not visible in other Southern Ocean marine records. 3. Results Finally, our synthesis suggests a larger magnitude of tem- perature changes over Antarctica (3.5 C temperature change on 3.1. LIG timeseries average in ice core records between 130 and 115 ka) than at the surface of the surrounding Southern Ocean. Contrasts are also The evolution of synchronised surface air and sea surface tem- observed within the Southern Ocean with marine records at the perature records over the LIG (Fig. 4) highlights several major highest latitudes (up to 50 S) showing a smaller amplitude of features. We highlight an asynchronous establishment of peak temperature change between 130 and 115 ka (1.2 C on average) " " interglacial temperatures between the two hemispheres across the than for marine records north of 50 S(2.5 C on average). LIG by calculating the average date at which the maximum LIG Similarly, Nordic Seas records north of 67 N only exhibit less temperature peaks occurs for the Southern Hemisphere records on than a 2 C amplitude in the temperature change while MD95- one side (Fig. 4; records [27]e[47]; note that when a maximum 2009 [7] records up to a 10 C temperature change over Termi- value was not clearly identiﬁed in the record, we took the date nation II. However, because SST variations below 6.5 C are not where a clear change of slope is marked) and for the North Atlantic well captured by the percentages of the polar species high latitude region records on the other side (Fig. 4; records [10] N. pachyderma sinistral (Govin et al., 2012), the amplitude of and [14]e[26], excluding the record from site CH69-K09 [24] for temperature changes may be underestimated in the Nordic Seas. which it is difﬁcult to unambiguously identify a temperature Still, overall the strongest amplitudes of temperature changes are maximum). For the Southern hemisphere records, we obtain a date recorded in the Northern Hemisphere high latitudes compared to of 129.3 ka associated with a standard deviation of 0.9 ka while we the Southern Hemisphere high latitudes (e.g. SU90-39 [18] and obtain a younger date of 126.4 ka associated with a standard de- SU90-08 [22]). viation of 1.9 ka for the North Atlantic high latitude records. This result hence illustrates the hemispheric differences highlighted in our database. Air temperature maximum conditions at the NEEM 3.2. LIG data-based time slices site [1] in Greenland occur at 126.9 ka, synchronously within dating uncertainties with the warmest conditions in the North Atlantic Our four data-based time slices capture the major features high latitudes. Although concerns about the synchronisation pre- characterising the spatial sequence of events described in Section cluded our use of European vegetation data here, we note that the 3.1 (Fig. 5). In particular, the 130 ka time slice clearly illustrates the time of maximum temperature (in both the warmest and coldest asynchrony previously reported between the Northern and the month) across Europe was also deduced to be around 127 ka Southern Hemisphere high latitudes (e.g. Masson-Delmotte et al., (Brewer et al., 2008). In the Nordic Seas, SST records (records [2]e 2010; Govin et al., 2012). It also reveals SST signiﬁcantly cooler- [7]) are characterised by small amplitude temperature changes than-present-day sea surface conditions (e.g. up to 7.5 ± 3 C across the LIG, in particular because of the limitation of cooler for [20]) in the high latitudes of the Northern Hemisphere N. pachyderma sinistral percentages to record STT variations at low while temperatures were slightly warmer than today (1.7 ± 2.5 C temperatures (see Section 2.2). Because the temperature uncer- on average) in most of the Southern Hemisphere sites. tainty associated with each record after being aligned onto Warmer than present day climatic conditions are visible on the AICC2012 is about 3e4 C, it is difﬁcult to determine with 130, 125 and 120 ka time slices in the Southern Hemisphere, while 126 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 Fig. 6. 130 ka Model-data comparison for the time slice at 130 ka, using the (left panel) CCSM3 and (right panel) HadCM3 models. a. Summer SST temperature anomalies from the marine sediment data (dots) superimposed onto model JulyeAugusteSeptember SST simulation in the Northern Hemisphere; b. Summer SST temperature anomalies from the marine sediment data (dots) superimposed onto the model JanuaryeFebruaryeMarch SST simulation in the Southern Ocean; c. Annual surface air temperature anomalies from the ice core data (dots) superimposed onto the model annual simulation. they are only unambiguously observed on the 125 and 120 ka data- conditions compared to present day. Note also that the CCSM3 based time slices in the Northern Hemisphere. 130 ka simulation is warmer than the HadCM3 130 ka simulation. This is predominantly due to the difference in GHG concentration values used where CCSM3 has a CO value ~50 ppmv higher than 3.3. Model-data comparison at 130 ka and 125 ka HadCM3, though also inﬂuenced by the different sea ice sensitiv- ities of the two models (Table 1). Figs. 6 and 7 display the model-data comparison for the 130 ka In the Southern Ocean, the discrepancy between simulated and time-slice and the 125 ka time slice respectively. Absolute dating reconstructed summer SST is smaller than in the Northern Hemi- should be considered when comparing our new LIG synthesis to sphere high latitudes. Still, LIG modelled summer SST are similar to model outputs. Because the data-based time slices represent 2 ka present-day ones in both model simulations while the data from time windows that have been calculated every 5 ka from 130 to the Southern Ocean illustrate surface oceanic conditions warmer by 115 ka, dating errors affecting the palaeoclimatic records un- to up to 3.9 ± 2.8 C compared to present day (i.e. [29]). Modelled certainties (including the absolute dating error of the AICC2012 annual air temperatures above Antarctica are similar to present- time scale, i.e. less than 1.6 ka during the LIG, Bazin et al., 2013) day at 130 ka in both CCSM3 and HadCM3 simulations. However, should have a limited impact on the main patterns highlighted in all reconstructions from Antarctic ice cores suggest temperatures the model-data comparison. " " 1.5 ± 1.5 Ce2.5 ± 1.5 C warmer than for present-day. Thus, our In the Northern Hemisphere high latitudes, both the HadCM3 model-data comparison at 130 ka illustrates that these two models and CCSM3 simulations exhibit at 130 ka signiﬁcantly warmer correctly simulate neither the cooler-than-present-day conditions summer sea surface conditions compared to present-day. In in the northern high latitudes nor the warmer-than-present-day contrast, reconstructed summer temperatures display cooler E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 127 Fig. 7. 125 ka Model-data comparison for the time slice at 125 ka, using the (left panel) CCSM3 and (right panel) HadCM3 models. a. Summer SST temperature anomalies from the marine sediment data (dots) superimposed onto model JulyeAugusteSeptember SST simulation in the Northern Hemisphere; b. Precipitation-weighed temperature anomaly reconstructed from the NEEM ice core (dot) superimposed onto precipitation-weighed temperature simulated above Greenland; c. Summer SST temperature anomalies from the marine sediment data (dots) superimposed onto the model JanuaryeFebruaryeMarch SST simulation in the Southern Ocean; d. Annual surface air temperature anomalies from the ice core data (dots) superimposed onto the model annual simulation. conditions in the southern high latitudes. In other words, the linear latitudes SST data for 125 ka. However, both models fail at repro- response to summer insolation changes in the Northern Hemi- ducing the reconstructed temperature anomalies at the sites sphere and the lack of response to orbital forcing in the Southern characterised by cooler than present day sea surface conditions ([5], Hemisphere are not consistent with air and sea surface tempera- [6], [7], [21] and [24]). Note that the differences observed between ture reconstructions. the CCSM3 and HadCM3 simulations are likely related to their sea In the Northern Hemisphere high latitudes, the CCSM3 125 ka ice sensitivities with CCSM3 being more sensitive in the Northern simulation exhibits higher computed than reconstructed SST by up Hemisphere and less sensitive in the Southern Hemisphere than to 6 C in speciﬁc locations (e.g. [16], [17] and [18]). It is in agree- HadCM3 (Otto-Bliesner et al., 2013). ment within less than 2 C with the reconstructed data records at Although they simulate warmer conditions over the some other locations (e.g. [22], [23], [25] and [26]). Considering the Greenland ice sheet, neither of the 125 ka simulations are able to uncertainty range associated with SST estimates, HadCM3 results produce a warming as strong as that estimated from the NEEM are generally in good agreement with Northern Hemisphere high ice core (7 ± 4 C at 125 ka) in precipitation-weighted air 128 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 temperature (Fig. 7b). However, an uncertainty of ±4 Cis over Antarctica (simulation data not shown). This seasonal aspect associated with the NEEM precipitation-weighted temperature would deserve further investigations. anomaly. Furthermore, interpretation of Greenland water iso- Fig. 8 represents the difference between the 125 ka and the topic proﬁles in terms of temperature remains challenging due to 130 ka climatic conditions. It strengthens our observations about the the seasonality affecting the precipitations, changes in ice sheet climatic changes in the course of Termination II in the Northern topography (e.g. Vinther et al., 2009; NEEM c. m. 2013), and the Hemisphere. Indeed, it provides a model-data comparison free from possible effects of boundary conditions such as sea ice extent on the uncertainty associated with the choice of the reference tem- the relationship between temperature and isotopic content (Sime perature in both the models and the data for present day conditions et al., 2009). (Section 2.4). This comparison highlights that the magnitude of In the Southern Ocean, data and simulations present fairly Northern Hemisphere SST changes between 130 and 125 ka is not similar summer sea surface conditions at 125 ka compared to represented in both models simulations. The warming observed in 130 ka given the associated temperature uncertainty. As for Ant- the data is underestimated by up to 5 C in the HadCM3 simulation arctic surface air temperature, cooler than present day annual while a slight cooling is produced in the CCSM3 simulation. conditions are observed in the 125 ka CCSM3 simulation. The Both models correctly simulate the absence of signiﬁcant cli- HadCM3 125 ka simulation shows warmer-than-present annual matic changes in the Southern Ocean between 130 and 125 ka. conditions in agreement within 2 C with the climatic conditions Finally, ice core data depict a stable or slightly colder climate (be- " " depicted in ice core data. Note that for both models, simulations tween 0 ± 1.5 C and $1.5 ± 1.5 C) that is reproduced in the CCSM3 represent best the warmer-than-present-day conditions at the [125 ka minus 130 ka] simulation while HadCM3 produces a slight location of ice core data when considering winter air temperature warming (between 0.5 and 1.5 C). Fig. 8. Temperature difference between 125 ka climatic conditions and 130 ka climatic conditions both as recorded in Antarctic ice core and marine sediment data and as simulated by CCSM3 (left panel) and HadCM3 (right panel). In both models, simulated Summer SST are calculated as a temperature average over the months JFM and JAS for the a. Northern Hemisphere and b. the Southern Hemisphere Summer SST respectively. c. Simulated annual air temperatures are compared with air temperature anomalies inferred from Antarctic ice cores. E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 129 4. Discussion In addition, we are aware that considering summer (JAS SST in the Northern Hemisphere; JFM SST in the Southern Hemisphere) 4.1. Potential and limits of the new LIG spatio-temporal data temperature at 10 m water-depth as modern reference might be a synthesis poor representation of the modern habitat of foraminiferal species in terms of season and water-depth (e.g. Tolderlund and Be, 1971; The SST records of our data synthesis have been derived from Kohfeld et al., 1996; Simstich et al., 2003; Jonkers et al., 2010). various methods. The MARGO SST synthesis for the Last Glacial However, we consider that it represents the most appropriate Maximum time period shows that using different microfossil choice here to calculate past temperature anomalies, because it proxies yield discrepancies in SST estimates above 35 N(MARGO corresponds to the calibration depth and season that are included project members, 2009). Unfortunately, quantitatively assessing in the calibration core top database (e.g. Kucera et al., 2005; MARGO the temperature uncertainties related to the use of SST records c. m. 2009) used in SST transfer functions to reconstruct past SST based on different methods in our case is difﬁcult since only two changes. Also, we highlight in the previous paragraph that we cores MD03-2664 and SU90-08 beneﬁt from multiple SST re- observe similar major climatic features and patterns when constructions. For site SU90-08, the comparison of the MAT- comparing temperature anomalies calculated vs WOA or core top based SST reconstruction ([23], Fig. 4) with the alkenone-based values, which suggests that the choice of WOA modern values at SST reconstruction [22] shows that major transitions are recor- 10 m water-depth has little effect on the main results of our study. ded at the same time but higher maximum LIG temperature and Estimated uncertainties are about 2.6 C on average for marine " " larger amplitude changes are observed in the MAT-based sum- sediment cores and set at 1.5 C for Antarctic ice cores and 4 C for mer SST reconstruction compared to the alkenone-based SST the NEEM ice core. This means that they are frequently of the same reconstruction. However, alkenone-based SST is usually inter- amplitude as the calculated temperature anomaly itself. However, preted as reﬂecting annual conditions (Müller et al., 1998; Sachs it is possible to highlight with conﬁdence some climatic patterns in et al., 2000), while MAT-based SST reﬂects summer conditions. the Southern Hemisphere and the North Atlantic region based on SST reconstructions based both on the Mg/Ca ratio [13] and MAT observations made on multiple records. For instance, we consider [12] are available for core MD03-2664. Mg/Ca ratio-based tem- that a warmer than present-day Southern Ocean by about þ2 C is a peratures are systematically lower than MAT-based summer SST robust climatic feature on the 125 and 130 ka data-based time slices but higher than MAT-based winter SST. Irvali et al. (2012) suggest since it is observed in most of the considered marine records even that this pattern illustrates that the Mg/Ca ratio-based SST esti- though taken individually each SST anomaly is associated with an mates might reﬂect spring conditions. As a result, SST signals error of similar magnitude. from those two cores highlight the difﬁculty of comparing SST Although we are conﬁdent in the age models developed for the records from different proxies, because reconstructed SSTs may Southern Ocean and North Atlantic marine records, one should represent different seasonal or annual signals. Previous studies keep in mind that deﬁning robust and coherent chronologies for have already reported this issue and also highlight an additional SST records from the Nordic Seas remains difﬁcult and that the bias derived from the different calibration datasets used in the associated relative uncertainty is large (~3e4 ka). This feature re- SST reconstructions (e.g. de Vernal et al., 2006; Hessler et al., sults from the current limitations associated with SST reconstruc- 2014). Overall, combining LIG SST reconstructions inferred from tion method based on the percentage of the polar species different methods may induce inconsistencies in the recon- N. pachyderma sinistral, and the difﬁculty to identify unambigu- structed SST records, creating difﬁculties when comparing ab- ously stratigraphic markers between cores. Consequently, it is solute values. However, this issue is reduced in our case since SST difﬁcult to identify robust climatic patterns in this region. Future estimates derived from faunal assemblages dominate (30 out of high-resolution SST records based on alternative proxies and the 42 records). Additional high-resolution SST records based on identiﬁcation of new stratigraphic markers (e.g. tephra horizons, various proxy methods would be required to carefully assess Davies et al., 2014) should help to improve chronologies for quantitatively how much the use of various SST reconstruction palaeoclimatic records from in this region. methods inﬂuences the temporal LIG characteristics highlighted While previous compilations already demonstrated warmer- in this study. than-present-day conditions prevailing during the LIG, the Mean annual or summer SST for each marine core location were emphasis of these compilations was on quantifying the maximum extracted at 10 m depth from the 1998 World Ocean Atlas (WOA98) in temperature warmth rather than on the temporal evolution of to develop a comparison to modern time annual and summer SST. the climatic conditions across the time-period. The data synthesis Core top SST reconstructions can diverge from the WOA98 SST of Turney and Jones (2010) reported the early Antarctic warming (Table A1) and this may introduce systematic offsets in temperature but their work was lacking a common temporal framework be- anomaly calculations. Using only core top SST estimates based on tween climatic records. Our work is the ﬁrst LIG compilation the same proxy as LIG SST reconstructions is not possible because associated with a common time frame between marine and ice this top-core information is available in a few selected records only high-latitude records from both hemispheres. This enables to (Fig. A1). Using core top SST values as modern time references is provide a detailed spatio-temporal information on the evolution of also complicated by the perturbation or the loss of most recent high-latitude temperature throughout the LIG. We also propagate sediments during coring procedure. When available, we compare age uncertainties and include SST reconstruction method errors in the temperature anomaly obtained from core top SST and modern order to map for the ﬁrst time high latitude temperature anomalies WOA SST as reference temperatures. Fig. A1 presents the data- for four time slices covering the LIG. based time slices with temperature anomalies calculated with the core-top SSTs as references. It illustrates that the major climatic 4.2. GCM snapshot simulations vs data-based time slices: mismatch features and patterns described on Fig. 5 are also visible when and implications considering core top SST as present-day reference, i.e. an early Southern Hemisphere high-latitude warming compared to the Otto-Bliesner et al. (2013) used the LIG compilations from Northern Hemisphere high-latitudes, longer warmer-than present Turney and Jones (2010) and McKay et al. (2011) to benchmark two conditions in the Southern Hemisphere and larger amplitude of CCSM3 snapshot simulations performed under 125 and 130 ka temperature changes in the high Northern latitudes. conditions for the orbital and greenhouse gas concentration 130 E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 forcing. However, they could not perform a detailed evaluation of polar ice sheet than in the surrounding surface ocean. This is the model simulations for each considered time period since both particularly obvious in the amplitude changes over Termination II compilations present only peak warmth information. Now, we are and over the glacial inception (Fig. 4). Such a difference originates able to investigate in particular, the capability of two GCMs in (i) from the fact that land areas on average change more rapidly reproducing asynchronous climate variations at the beginning of than the ocean (landesea contrast; e.g. Joshi et al., 2008; Braconnot the LIG in polar and sub-polar regions. The warming in the et al., 2012) and (ii) from the polar ampliﬁcation due to feedbacks Southern Ocean and over Antarctica occurred prior to peak warmth related to surface albedo (land ice and sea ice cover), ice sheet in the North Atlantic, Nordic Seas, and Greenland at the beginning elevation and atmospheric processes (e.g. Holland and Bitz, 2003; of the LIG (Masson-Delmotte et al., 2010; Bauch et al., 2011; Govin Masson-Delmotte et al., 2006). et al., 2012; NEEM c. m., 2013). This delay in peak warmth condi- tions between the northern and southern high latitudes illustrated 5. Concluding remarks on the 130 ka time slice is attributed to the “bipolar seesaw” mechanism induced by changes in the intensity of the Atlantic We have selected 47 air and sea surface temperature records Meridional Overturning Circulation (AMOC; Stocker and Johnsen, from ice and marine sediment cores with a temporal resolution of 2003; Masson-Delmotte et al., 2010; Holden et al., 2010). The at least 2000 years covering the LIG. All records have been aligned melting of northern ice sheets during Termination II into the early onto the most recent AICC2012 ice core chronology and this enables LIG has been suggested to delay the full establishment of a vigorous investigation into the temporal evolution of the climate over the AMOC, which coincides with peak Antarctic temperature (Govin LIG in polar and sub-polar regions. This is the ﬁrst synthesis over et al., 2012). the LIG associated with consistent chronologies and a careful The HadCM3 and CCSM3 simulations do not reproduce such a consideration of dating uncertainties. The major features high- bipolar seesaw pattern since they only simulate the climate lighted are (i) non synchronous maximum temperature changes response to the LIG orbital and greenhouse forcing (Table A3), between the two hemispheres with the Southern Ocean and without taking into account physical processes which can redis- Antarctica records showing an early warming compared to North- tribute heat from the north to the south, in particular through the ern Hemisphere high latitude records, (ii) warmer than present-day impact of ice sheet freshwater on the AMOC, absent from these conditions exhibited in Southern Hemisphere records for a longer particular simulations. Simulations introducing freshwater forcing time period compared to records from the Northern Hemisphere, to account for a bipolar seesaw response to persistent iceberg and (iii) larger amplitude of temperature changes at high northern melting at northern high latitudes (Govin et al., 2012) and disin- latitudes compared to high southern latitudes recorded at the onset tegration of the WAIS (Langebroek and Nisancioglu, 2014) better and the demise of the LIG. reproduce the late LIG Northern Hemisphere warming (Holden We provide for the ﬁrst time a spatial and temporal evolution of et al., 2010). A recent modelling study focused on the last deglaci- the LIG climate rather than a snapshot vision on the climatic op- ation (Ritz et al., 2013) showed that inclusion of the Northern timum in the high latitudes of both hemispheres. It allows more Hemisphere remnant ice sheets resulted in a delay in warming at precise model-data comparison over the LIG. For this purpose, we high Northern Hemisphere latitudes by ~2000 years compared have produced four data-based time slices at 115, 120, 125 and with modelling studies which only included the modern ice sheets 130 ka of the temperature anomalies compared to modern condi- (Bakker et al., 2013). In addition, the Ritz et al. (2013) study tions, associated with quantitatively estimated temperature un- included freshwater forcing from the melting ice responding to the certainties including dating errors. We have compared CCSM3 and enhanced warming. HadCM3 surface temperature model simulations for 130 and 125 ka Moreover, the mismatches in term of both the sign and the to the respective 130 and 125 ka data time slices. Our comparison amplitude in temperature changes are likely to originate from the shows that the models predict warmer than present conditions fact that not all appropriate changes in the boundary conditions earlier than documented in the Northern Hemisphere high latitude have been considered in the design of the experiments. In partic- region, while the reconstructed early Southern Ocean and Antarctic ular, both models include present-day vegetation and polar ice warming is not captured by any model. Our results highlight the sheet distribution. Previous modelling of the LIG has shown that importance of producing time slices rather than one representative feedbacks between vegetation and climate enhance the warming at climate for the LIG. They also provide additional evidence that high latitudes (Cruciﬁx and Loutre, 2002; Schurgers et al., 2007). missing processes (ice sheet melt and associated freshwater ﬂuxes, Otto-Bliesner et al. (2013) present also a sensitivity simulation with vegetation feedbacks) likely result in the inability of CCM3 and CCSM3 with the removal of the WAIS. It provides additional local HadCM3 to capture the temporal signal observed in the data (Otto- warming over Antarctica but still not enough to explain the ice core Bliesner et al., 2013). This limits identiﬁcation of potential para- records. Simulations with HadCM3 by Holden et al. (2010) suggest metric or structural errors in the processes that are taken into ac- that in addition to the WAIS retreat, freshwater input to the North count in climate models (e.g. sea ice, polar clouds, snow albedo). Atlantic from the Laurentide and Eurasian ice sheets during Hopefully, this work will encourage more in-depth data-model Termination II is required to agree with the warming indicated by comparison exercises with both snapshots (e.g. Lunt et al., 2013) Antarctic ice core records. Differences between model simulations and transient (e.g. Bakker et al., 2013; Langebroek and Nisancioglu, presented in this paper and data may also be related to model 2014) climate model simulations that will also involve rigorous representations of atmospheric feedbacks (e.g. liquid water in statistical analysis. Arctic clouds) and missing feedbacks linked to sea ice and snow Here, we have focused on air and sea surface temperature. cover processes (e.g. rain and snow melt albedo), and prescribed However, future work should also focused on additional informa- changes in ice sheet topography (e.g. Masson-Delmotte et al., 2006; tion provided by the selected and future new records (e.g. changes Born et al., 2010; Fischer and Jungclaus, 2010; Masson-Delmotte in AMOC intensity, sea ice extent) to move towards a more com- et al., 2011a; Otto-Bliesner et al., 2013). plete picture of environmental changes during the LIG. Finally, Our results illustrate that during the LIG, as-warm or warmer improved model-data comparison techniques such as the use of conditions than today have prevailed for a longer time period in the models which explicitly simulate climate proxies (e.g. ice d O, Southern Hemisphere than in the Northern Hemisphere (Fig. 5). benthic and/or planktic d O, planktic foraminifera assemblage; Larger amplitude temperature changes are also recorded over the Telford et al., 2013) would allow more effective use of the E. Capron et al. / Quaternary Science Reviews 103 (2014) 116e133 131 palaeoclimatic data. Nat. Clim. Change. http://dx.doi.org/10.1038/ paleoclimate information by facilitating a direct comparison be- NCLIMATE1456. tween model and proxy. Bradley, S.L., Siddall, M., Milne, G.A., Masson-Delmotte, V., Wolff, E., 2012. Where might we ﬁnd evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records? Glob. Planet. Change 88e89, 64e75. Acknowledgements Bradley, S.L., Siddall, M., Milne, G.A., Masson-Delmotte, V., Wolff, E., 2013. Combining ice core records and ice sheet models to explore the evolution of the We thank Elsa Cortijo for sharing unpublished SST records, Eli- East Antarctic Ice sheet during the Last Interglacial period. Glob. Planet. Change 100, 278e290. sabeth Michel for participating to the initial marine record syn- Calvo, E., Pelejero, C., de Deckker, P., Logan, G.A., 2007. Antarctic deglacial pattern in thesis effort and Chronis Tzedakis for helpful discussions. E. a 30 kyr record of sea surface temperature offshore South Australia. Geophys. Thomsen (Aarhus University, Denmark) is thanked for the running Res. Lett. 34, L13707 doi:13710.11029/12007GL029937. CAPE Last Interglacial Project Members, 2006. Last Interglacial Arctic warmth of transfer functions based on the 100 mm planktic data of core conﬁrms polar ampliﬁcation of climate change. Quat. Sci. Rev. 25, 1383e1400. ENAM33. 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Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

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Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

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Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

Temporal and spatial structure of multi-millennial temperature changes at high latitudes during the Last Interglacial

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