BIOLOGICAL CARBON PUMP

Net Community Production (NCP) of organic matter, defined as primary production minus respiration at all trophic levels in the upper ocean, removes dissolved inorganic carbon from surface waters and converts it into particulate organic carbon. These particles are removed from the surface by sinking or migrating organisms. This process, known as the biological pump [Buesseler and Boyd, 2009], reduces the surface ocean CO₂ partial pressure resulting in a lowering of atmospheric CO₂. Numerical models indicate that the biological pump reduces atmospheric CO₂ by about 200 ppm, relative to the value expected for an abiotic ocean ([Sarmiento et al., 2011]; [Watson and Orr, 2003]; [Parekh et al., 2006]). The IPCC found “It is difficult to project how the pump might be altered and whether it would represent a positive or negative feedback to climate change” [Portner et al., 2014]. [Riebesell et al., 2009] illustrated the various sensitivities of marine carbon fluxes and highlighted the fact that the sign and magnitude of the various responses and feedbacks in the biological systems are largely unknown. In situ observations are required throughout the ocean to constrain variability in the biological pump. Profiling floats equipped with nitrate, oxygen and pH sensors will allow direct measurement of NCP and the biological pump ([Riser and Johnson, 2008]; [Alkire et al., 2012]; [Plant et al., 2016]). Chemical and biooptical sensors allow estimates of the carbon export component ([Martz et al., 2008]; [Dall'Olmo and Mork, 2014]), changes in the timing of phytoplankton blooms [Boss and Behrenfeld, 2010], and influence of nutrient transport events ([Johnson et al., 2010]; [D'Ortenzio et al., 2014]; [Pasqueron de Fommervault et al., 2015])