The variable and changing southern ocean silicate front: Insights from the CESM large ensemble

TitleThe variable and changing southern ocean silicate front: Insights from the CESM large ensemble
Publication TypeJournal Article
Year of Publication2018
AuthorsFreeman N.M, Lovenduski N.S, Munro D.R, Krumhardt K.M, Lindsay K., Long M.C, Maclennan M.
JournalGlobal Biogeochemical Cycles
Date Published2018/05
Type of ArticleArticle
ISBN Number0886-6236
Accession NumberWOS:000434413500002
Keywordsantarctic; antarctic circumpolar current; antarctic polar front; biogenic silica; characteristics; circumpolar current; Climate variability; dissolved iron; drake passage; earth system; Environmental Sciences & Ecology; Geology; line simulation; Meridional overturning circulation; Meteorology & Atmospheric; model; natural; polar front; sciences; sea-surface temperature; Silicate Front; Southern Ocean; variability

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 approximate to 3 degrees 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.

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