The Variable and Changing Southern Ocean Silicate Front: Insights From the CESM Large Ensemble

The Variable and Changing Southern Ocean Silicate Front: Insights From the CESM Large Ensemble The location of the Southern Ocean Silicate Front (SF) is a key indicator of physical circulation, biological productivity, and biogeography, but its variability in space and time is currently not well understood due to a lack of time‐varying nutrient observations. This study provides a first estimate of the spatiotemporal variability of the SF, defined using the silicate‐to‐nitrate (Si:N) ratio as simulated by the Community Earth System Model (CESM) Large Ensemble (1920–2100), and its response to a changing Southern Ocean. The latitude where Si:N = 1 largely coincides with regions of high gradients in silicate and the observed position of the Antarctic Polar Front (PF) and serves as an indicator of waters with adequate nutrients available for diatom growth. On seasonal to interdecadal time scales, variability in the location of the SF is largely determined by biological nutrient utilization and Southern Ocean bathymetry, respectively. From 1920 to 2100, under historical and RCP8.5 forcing, the zonally averaged SF shifts poleward by ∼3° latitude, with no discernible shift in the position of the simulated location of the PF or the core of the Antarctic Circumpolar Current. A more poleward SF is primarily driven by long‐term reductions in silicate and nitrate concentrations at the surface as a consequence of greater iron availability and a warmer, more stratified Southern Ocean. These results suggest a decoupling of the SF and PF by the end of the century, with implications for local biogeography, global thermocline nutrient cycling, and the interpretation of paleoclimate records from deep sea sediments. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Global Biogeochemical Cycles Wiley

The Variable and Changing Southern Ocean Silicate Front: Insights From the CESM Large Ensemble

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Publisher
Wiley
Copyright
©2018. American Geophysical Union. All Rights Reserved.
ISSN
0886-6236
eISSN
1944-9224
D.O.I.
10.1029/2017GB005816
Publisher site
See Article on Publisher Site

Abstract

The location of the Southern Ocean Silicate Front (SF) is a key indicator of physical circulation, biological productivity, and biogeography, but its variability in space and time is currently not well understood due to a lack of time‐varying nutrient observations. This study provides a first estimate of the spatiotemporal variability of the SF, defined using the silicate‐to‐nitrate (Si:N) ratio as simulated by the Community Earth System Model (CESM) Large Ensemble (1920–2100), and its response to a changing Southern Ocean. The latitude where Si:N = 1 largely coincides with regions of high gradients in silicate and the observed position of the Antarctic Polar Front (PF) and serves as an indicator of waters with adequate nutrients available for diatom growth. On seasonal to interdecadal time scales, variability in the location of the SF is largely determined by biological nutrient utilization and Southern Ocean bathymetry, respectively. From 1920 to 2100, under historical and RCP8.5 forcing, the zonally averaged SF shifts poleward by ∼3° latitude, with no discernible shift in the position of the simulated location of the PF or the core of the Antarctic Circumpolar Current. A more poleward SF is primarily driven by long‐term reductions in silicate and nitrate concentrations at the surface as a consequence of greater iron availability and a warmer, more stratified Southern Ocean. These results suggest a decoupling of the SF and PF by the end of the century, with implications for local biogeography, global thermocline nutrient cycling, and the interpretation of paleoclimate records from deep sea sediments.

Journal

Global Biogeochemical CyclesWiley

Published: Jan 1, 2018

Keywords: ; ; ; ;

References

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