Variability of primary production and air‐sea CO₂ flux in the Southern Ocean

Abstract

[1] Biogeochemical cycling in the Southern Ocean (SO) plays a key role in the global sea-air CO 2 balance and in the ocean anthropogenic carbon inventory (Ito et al., 2010;Khatiwala et al., 2009;Sarmiento et al., 2004). Some previous studies suggest a decreasing trend in the Southern Ocean carbon sink (Le Quéré et al., 2007;Lovenduski et al., 2007;Wetzel et al., 2005). We investigate the interannual and decadal variations in sea-air CO 2 flux and phytoplankton production in the SO with hindcast simulations by an ocean biogeochemical model. Decreasing trends in sinking POC and primary production are found from 1979 to 2003, concurrent with a decreasing trend in carbon uptake from the atmosphere. Simulations show substantial interannual and decadal variability in productivity. The sea-air CO 2 flux is significantly correlated with sinking POC, especially in high productivity regions of the Southern Ocean. Both mixed layer depths and iron concentrations are important to the long-term trends in production and phytoplankton community structure. Sea ice cover also plays an important role at high latitudes. Variability in dust deposition in recent decades has little influence on total SO productivity and carbon uptake, however, there are regional impacts near dust source regions. Accurately representing mixed layer depths and their impacts on phytoplankton light stress are critical for understanding how climate change impacts SO ecosystems and biogeochemistry.

Interannual drivers of the seasonal cycle of CO<sub>2</sub> in the Southern Ocean

“…Our finding that Chl a is the dominant driver of interannual pCO 2 variability should not be surprising given that models and observations support this notion (Hoppema et al, 1999;Bakker et al, 2008;Mahadevan et al, 2011;Wang et al, 2012;Hauck et al, 2013Hauck et al, , 2015Shetye et al, 2015). However, our data show that the dominance of interannual Chl a variability over pCO 2 is largely limited to regions where Chl a is high, such as the Atlantic, the Agulhas retroflection and south of Australia and New Zealand (Fig.…”

Interannual drivers of the seasonal cycle of CO<sub>2</sub> fluxes in the Southern Ocean

“…given that models and observations support this (Hoppema et al 1999;Bakker et al 2008;Mahadevan et al 2011;Wang et al 2012;Hauck et al 2013;Shetye et al 2015). However, our data show that the dominance of interannual Chl-a variability over ∆pCO 2 is largely limited to regions where Chl-a is high, such as the Atlantic, the Agulhas retroflection and south of Australia and New Zealand (Figure 9).…”

Distributions, trends and inter-annual variability of nutrients along a repeat section through the Weddell Sea (1996–2011)

“…Phytoplankton blooms are frequent in the Weddell Sea (e.g., Lancelot et al, 1993;Krell et al, 2005), but trends in biological activity have to our knowledge as yet not been reported. Trends in the wider Southern Ocean, on the other hand, have been observed (e.g., Atkinson et al, 2004) and several studies suggest that the recent positive trend in the Southern Annular Mode (SAM) must be followed by changes in physical forcing and subsequent changes in the biological systems (e.g., Arrigo et al, 2008;Wang and Moore, 2012;Hauck et al, 2013). Hence, although changes in biological activity are likely, there is presently no evidence for it in the Weddell Sea.…”