The Oligotrophic Ocean Is Autotrophic

• Published in: Annual review of marine science 2013-01, Vol.5 (1), p.535-549
• Main Authors: Williams, Peter J. le B, Quay, Paul D, Westberry, Toby K, Behrenfeld, Michael J
• Format: Article
• Language: English
• Subjects: Autotrophic Processes - physiology; carbon balance; Ecosystem; Environmental Monitoring - methods; isotopic tracers; Oceans and Seas; organic balance; oxygen budgets; Plants - metabolism; productivity
• ISSN: 1941-1405; 1941-0611
• DOI: 10.1146/annurev-marine-121211-172335

In vitro observations of net community production (NCP) imply that the oligotrophic subtropical gyres of the open ocean are net heterotrophic; in situ observations, in contrast, consistently imply that they are net autotrophic. At least one approach must be returning an incorrect answer. We find that ( a ) no bias in in situ oxygen-based production estimates would give false-positive (net autotrophy) rates, ( b ) observed 13 C enrichment of surface water dissolved inorganic carbon (DIC) can be explained only by positive NCP (net autotrophy), ( c ) lateral and vertical inputs of organic carbon are insufficient to sustain net heterotrophy, and ( d ) atmospheric input of organic material is too small to support in vitro rates of net heterotrophy and would yield δ 13 C depletion of surface DIC, quite the opposite of what is observed in the subtropical gyres. We conclude that the in vitro observations, implying net heterotrophy, must contain a bias that is due to an underestimate of photosynthetic rate and or an overestimate of respiration rate.