Nutrient Controls on Export Production in the Southern Ocean. Issue 8 (5th August 2019)

• Record Type: Journal Article
• Authors: Arteaga, Lionel A.; Pahlow, Markus; Bushinsky, Seth M.; Sarmiento, Jorge L.
• Is Part Of: Global biogeochemical cycles. Volume 33:Issue 8(2019:Aug.)
• Page Start: 942
• Page End: 956
• Publication Date: 2019-08-05
• Subjects: carbon -- export -- nutrient -- limitation -- phytoplankton; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2019GB006236
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract : We use observations from novel biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling program to estimate annual net community production (ANCP; associated with carbon export) from the seasonal drawdown of mesopelagic oxygen and surface nitrate in the Southern Ocean. Our estimates agree with previous observations in showing an increase in ANCP in the vicinity of the polar front (∼3 mol C m −2 y −1 ), compared to lower rates in the subtropical zone (≤ 1 mol C m −2 y −1 ) and the seasonal ice zone (<2 mol C m −2 y −1 ). Paradoxically, the increase in ANCP south of the subtropical front is associated with elevated surface nitrate and silicate concentrations, but decreasing surface iron. We hypothesize that iron limitation promotes silicification in diatoms, which is evidenced by the low silicate to nitrate ratio of surface waters around the Antarctic polar front. High diatom silicification increases the ballasting effect of particulate organic carbon and overall ANCP in this region. A model‐based assessment of our methods shows a good agreement between ANCP estimates based on oxygen and nitrate drawdown and the modeled downward organic carbon flux at 100 m. This agreement supports the presumption that net biological consumption is the dominant process affecting the drawdown of these chemical tracers and that, given sufficient data, ANCP can be inferred from observations of oxygen and/or nitrate drawdown in the Southern Ocean. Key Points: Organic carbon export is inferred from float‐based observations of mesopelagic oxygen and surface nitrate drawdown in the Southern Ocean Our estimates agree with previous observations showing an increase in inferred export in the vicinity of the polar front We hypothesize that iron limitation enhances silicification by diatoms, thereby increasing the ballasting effect of biogenic carbon export