Estimates of net community production in the Southern Ocean determined from time series observations (2002-2011) of nutrients, dissolved inorganic carbon, and surface ocean pCO2 in Drake Passage

In remote regions such as the open Southern Ocean, satellite observations often provide the only available tool with which to evaluate large-scale biogeochemical processes. However, these observations need to be carefully evaluated with in situ measurements. With an average of 20 crossings per year from 2002 to 2011, the Drake Passage Time-series (DP) represents one of the most complete datasets of biogeochemical measurements in the open Southern Ocean. This dataset offers a unique opportunity to validate satellite-based productivity algorithms and to improve understanding of the role of this region in the global carbon cycle. Net community production (NCP) was estimated using discrete measurements of total dissolved inorganic carbon (TCO2) and phosphate (PO43-), and high-frequency underway measurements of the partial pressure of carbon dioxide in the surface ocean (pCO2(surf)) from the DPT, combined with estimates of gas exchange, Elcman transport wind stress curl, and vertical entrainment We estimate annual NC!' using seasonal PO43- (NCPPO43-) and TCO2 (NCPTCO2,) budgets of 12 +/- 0.7 and 1.6 +/- 0.4 mol C m(-2) yr(-1), respectively. Budget terms for gas exchange, entrainment, and advective supply indicate that a closed system seasonal-drawdown approach that does not consider additional terms may underestimate NCP in this region by nearly 35%. NCP estimates are compared to satellite algorithms commonly used to estimate both net primary production (NPP) and organic carbon export Budget-based NCP approaches indicate high rates of NCP during austral spring with little additional NCP over austral summer. In contrast, satellite approaches suggest a more gradual increase and decline in NCP rates over the growing season with approximately 40% of NCP accumulating during austral summer. (C) 2015 Elsevier Ltd. All rights reserved.