Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO2 from 10 years of satellite Earth observation data

• Published in: Biogeosciences
• Main Authors: Shutler, J. D., Land, P. E., Brown, C. W., Findlay, H. S., Donlon, C. J., Medland, M., Snooke, R., Blackford, J. C.
• Format: Text
• Language: English
• Published: 2018
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/bg-10-2699-2013; https://www.biogeosciences.net/10/2699/2013/

Coccolithophores are the primary oceanic phytoplankton responsible for the production of calcium carbonate (CaCO 3 ). These climatically important plankton play a key role in the oceanic carbon cycle as a major contributor of carbon to the open ocean carbonate pump (~50%) and their calcification can affect the atmosphere-to-ocean (air-sea) uptake of carbon dioxide (CO 2 ) through increasing the seawater partial pressure of CO 2 ( p CO 2 ). Here we document variations in the areal extent of surface blooms of the globally important coccolithophore, Emiliania huxleyi, in the North Atlantic over a 10-year period (1998–2007), using Earth observation data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). We calculate the annual mean sea surface areal coverage of E. huxleyi in the North Atlantic to be 474 000 ± 104 000 km 2 , which results in a net CaCO 3 carbon (CaCO 3 -C) production of 0.14–1.71 Tg CaCO 3 -C per year. However, this surface coverage (and, thus, net production) can fluctuate inter-annually by −54/+8% about the mean value and is strongly correlated with the El Niño/Southern Oscillation (ENSO) climate oscillation index ( r =0.75, p <0.02). Our analysis evaluates the spatial extent over which the E. huxleyi blooms in the North Atlantic can increase the p CO 2 and, thus, decrease the localised air-sea flux of atmospheric CO 2 . In regions where the blooms are prevalent, the average reduction in the monthly air-sea CO 2 flux can reach 55%. The maximum reduction of the monthly air-sea CO 2 flux in the time series is 155%. This work suggests that the high variability, frequency and distribution of these calcifying plankton and their impact on p CO 2 should be considered if we are to fully understand the variability of the North Atlantic air-to-sea flux of CO 2 . We estimate that these blooms can reduce the annual N. Atlantic net sink atmospheric CO 2 by between 3–28%.