Satellite estimates of net community production indicate predominance of net autotrophy in the Atlantic Ocean

• Published in: Remote Sensing of Environment
• Main Authors: Tilstone, Gavin H., Xie, Yu-yuan, Robinson, Carol, Serret, Pablo, Raitsos, Dionysios E., Powell, Timothy, Aranguren-Gassis, Maria, Garcia-Martin, Enma Elena, Kitidis, Vassilis
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2015
• Subjects: Antarctic; The Antarctic; Austral; Greenland; Antarc*; North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/525303/; https://doi.org/10.1016/j.rse.2015.03.017

There is ongoing debate as to whether the oligotrophic ocean is predominantly net autotrophic and acts as a CO2 sink, or net heterotrophic and therefore acts as a CO2 source to the atmosphere. This quantification is challenging, both spatially and temporally, due to the sparseness of measurements. There has been a concerted effort to derive accurate estimates of phytoplankton photosynthesis and primary production from satellite data to fill these gaps; however there have been few satellite estimates of net community production (NCP). In this paper, we compare a number of empirical approaches to estimate NCP from satellite data with in vitro measurements of changes in dissolved O2 concentration at 295 stations in the N and S Atlantic Ocean (including the Antarctic), Greenland and Mediterranean Seas. Algorithms based on power laws between NCP and particulate organic carbon production (POC) derived from 14C uptake tend to overestimate NCP at negative values and underestimate at positive values. An algorithm that includes sea surface temperature (SST) in the power function of NCP and 14C POC has the lowest bias and root-mean square error compared with in vitro measured NCP and is the most accurate algorithm for the Atlantic Ocean. Nearly a 13 year time series of NCP was generated using this algorithm with SeaWiFS data to assess changes over time in different regions and in relation to climate variability. The North Atlantic subtropical and tropical Gyres (NATL) were predominantly net autotrophic from 1998 to 2010 except for boreal autumn/winter, suggesting that the northern hemisphere has remained a net sink for CO2 during this period. The South Atlantic sub-tropical Gyre (SATL) fluctuated from being net autotrophic in austral spring-summer, to net heterotrophic in austral autumn–winter. Recent decadal trends suggest that the SATL is becoming more of a CO2 source. Over the Atlantic basin, the percentage of satellite pixels with negative NCP was 27%, with the largest contributions from the NATL and SATL during boreal ...