Primary production in the Southern Ocean, 1997–2006

TLDR

Primary production estimates in the Southern Ocean are difficult to obtain yet essential for understanding its role in the global carbon cycle. The study aims to provide a nine‑year daily time series of Southern Ocean primary production derived from remote sensing of ocean color, sea‑surface temperature, and sea‑ice concentration. Primary production was calculated using a Southern Ocean‑specific algorithm applied to satellite observations of ocean color, sea‑surface temperature, and sea‑ice concentration. The time series shows an average annual production of 1,950 Tg C a⁻¹—about half previous estimates—with 90 % from the pelagic province, the continental shelf exhibiting the highest area‑normalized rates, marginal ice zone production only slightly higher, the Ross Sea the most productive sector, no long‑term trend, interannual variability mainly driven by sea‑ice and sea‑surface temperature changes, and only 31 % of the variation explained by the Southern Annular Mode, suggesting future increases with stronger winds.

Abstract

Estimates of primary production in the Southern Ocean are difficult to obtain but are essential if we are to understand its role in the global carbon cycle. Here we present a 9‐year time series of daily primary production calculated from remotely sensed ocean color, sea surface temperature, and sea ice concentration using a primary production algorithm parameterized specifically for use in Southern Ocean waters. Results suggest that total annual production in waters south of 50°S averaged 1949 ± 70.1 Tg C a −1 (where a is years) between 1998 and 2006, approximately half that of previous estimates. The large but relatively unproductive pelagic province accounted for ∼90% of Southern Ocean production, while area normalized rates of production were greatest on the much smaller continental shelf (109 g C m −2 a −1 ). Surprisingly, production in the marginal ice zone was only slightly higher than in the pelagic province. The Ross Sea was the most productive sector of the Southern Ocean (mean = 503 Tg C a −1 ), followed closely by the Weddell Sea (mean = 477 Tg C a −1 ). Unlike the Arctic Ocean, there was no secular trend in either sea ice cover or annual primary production in the Southern Ocean during our 9‐year study. Interannual variability in annual production was most closely tied to changes in sea ice cover, although changes in sea surface temperature also played a role. Only 31% of the variation in annual production was explained by the Southern Annular Mode. Annual primary production could increase in the future as stronger winds increase nutrient upwelling.