Southern Ocean nutrient trapping and the efficiency of the biological pump. Issue 5 (21st May 2013)

• Record Type: Journal Article
• Authors: Primeau, François W.; Holzer, Mark; DeVries, Timothy
• Is Part Of: Journal of geophysical research. Volume 118:Issue 5(2013:May)
• Page Start: 2547
• Page End: 2564
• Publication Date: 2013-05-21
• Subjects: phosphate -- biological pump -- Southern Ocean -- data assimilation -- ocean model -- biological production; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/jgrc.20181
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract : [1] We present a data‐assimilated model of the ocean's phosphorus cycle that is constrained by climatological phosphate, temperature, salinity, sea‐surface height, surface heat and freshwater fluxes, as well as chlorofluorocarbon‐11(CFC‐11) and natural Δ 14 C. Export production is estimated to be 5.8±2.0×10 12 mol P/yr of which (26±6)% originates in the Southern Ocean (SO) south of 40°S. The biological pump efficiency, defined as the proportion of the ocean's phosphate inventory that is regenerated, is (39±7)%. Dividing the SO south of 40°S into a sub‐Antarctic zone (SANTZ) and an Antarctic zone (ANTZ) separated by the latitude of maximum Ekman divergence, we estimate that the SANTZ and ANTZ account, respectively, for (23±5)% and (3±1)% of global export production, (17±4)% and (3±1)% of the regenerated nutrient inventory, and (31±1)% and (43±5)% of the preformed nutrient inventory. Idealized SO nutrient depletion experiments reveal a large‐scale transfer of nutrients into circumpolar and deep waters and from the preformed to the regenerated pool. In accord with the concept of the biogeochemical divide, we find that nutrient drawdown in the ANTZ is more effective than in the SANTZ for increasing the efficiency of the biological pump, while having a smaller impact on production in regions north of 40°S. Complete SO nutrient drawdown would allow the biological pump to operate at 94% efficiency by short circuiting the transport of nutrients in northward Ekman currents, leading to a trapping of nutrients in circumpolar and deep waters that would decrease production outside the SO by approximately 44% while increasing it in the SO by more than 725%. Key Points: A data‐assimilated model quantifies export production and regenerated PO4 pool The S. Ocean contributes 75% of the preformed and 20% of the regenerated PO4 Southern Ocean nutrient drawdown traps nutrients in circumpolar deep waters