“…It accounts for up~50% of calcite raining down on marine sediments, with the other 50% derived from foraminifera (Broecker and Clark, 2009). Export of CaCO 3 is facilitated by its high density (2.7 g cm −3 ), inherent protective organic coatings (Hassenkam et al, 2011), association with particulate organic matter [marine snow, transparent exopolymeric particles and faecal pellets (Pedrotti et al, 2012;Collins et al, 2015)] and supersaturation in the upper water column (Westbroek et al, 1993;Balch et al, 2007;Berelson et al, 2007;Broecker and Clark, 2009). While there are no coccolith-specific estimates, the total PIC sinking-flux below 2000 m may be as much as 50 Tmol C year −1 (Berelson et al, 2007), with associated CaCO 3 :POC ratios (or 'rain ratios') having important implications for POC transport to the deep ocean and biological pump efficiency (Armstrong et al, 2002;Klaas and Archer, 2002;Ridgwell et al, 2009).…”