Biological Carbon Pump (BCP)

106 CO2+16 HNO3 + H3PO4 + 122 H2O => light (CH2O)106 (NH3)16 H3PO4 + 138 O2

The vertical transport of organic particles from the euphotic zone to the deeper ocean is vital to the ocean’s ability to sequester atmospheric carbon dioxide. Primary producers in the aquatic ecosystem, mainly phytoplankton, fix CO2 and convert it into organic matter by means of photosynthesis (Eq. 1.1). Phytoplankton and macrophytes account for 94% and 6% of the net primary production in the euphotic zone respectively (Falkowski et al., 2004; Durate et al., 2005; Carr et al., 2006; Rousseaux and Gregg, 2014). The atmospheric carbon that gets converted into organic matter during photosynthesis, is further transformed into different forms by food web processes and physical mixing, and finally gets transported to the deeper oceans via gravitational settling (Fig. 1.3). A fraction of these organic matter sinks into the deeper oceans, mainly in the form of particles known as particulate organic matter. This process of removing organic matter from surface water to the deep ocean via particle settling is known as the oceanic biological carbon pump (BCP). Thus, the biological pump transfers large amounts of atmospheric carbon to deep ocean with primary producers in the surface ocean converting 10-12 Gt of dissolved carbon dioxide into particulate organic carbon (POC) per year (Falkowski et al. 2000; Henson et al., 2012; Stewart et al., 2010; Passow and Carlson, 2012).

Figure. The biological carbon pump (Herndl and Reinthaler, 2013).

The strength of biological pump to drawdown atmospheric carbon into the oceans depends on: i) the mode and speed of particles sinking determines the depth to which the particles are exported and the degree to which they are remineralized in the water column, ii) how fast the sinking particles leave the seasonal mixing layer (Anita et al., 2001), iii) the efficiency at which particulate matters are exported below euphotic zone. This overall all transfer efficiency of carbon by the biological pump is often represented as the ratio of POC exported below euphotic zone to the NPP in the water column. Therefore, it is essential to have a better understanding of the magnitude of particulate export and scavenging in order to quantify the efficiency of biological pump. There are many studies related to carbon export (Buesseler et al., 1998; Buessseler et al., 2001; Puigcorbe et al., 2017, Ramondenc et al., 2016, Black et al., 2018) which are location specific and have used different methods to quantify the carbon export. These studies have clearly indicated that quantifying both the magnitude and variability of the carbon export in the global ocean is challenging and there still exists areas with inadequate carbon export data. Further, with increase in global carbon dioxide from 300 ppm to 410 ppm within a century, it is important to understand the full biogeochemical cycling of carbon including the removal from the ocean and its subsequent export to the deeper ocean.