Coccolithophore surface distributions in the North Atlantic and their modulation of the air-sea flux of CO<sub>2</sub> from 10 years of satellite Earth observation data

Abstract

Abstract. Coccolithophores are the primary oceanic phytoplankton responsible for the production of calcium carbonate (CaCO3). 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 (CO2) through increasing the seawater partial pressure of CO2 (pCO2). 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 km2, which results in a net CaCO3 carbon (CaCO3-C) production of 0.14–1.71 Tg CaCO3-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 pCO2 and, thus, decrease the localised air-sea flux of atmospheric CO2. In regions where the blooms are prevalent, the average reduction in the monthly air-sea CO2 flux can reach 55%. The maximum reduction of the monthly air-sea CO2 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 pCO2 should be considered if we are to fully understand the variability of the North Atlantic air-to-sea flux of CO2. We estimate that these blooms can reduce the annual N. Atlantic net sink atmospheric CO2 by between 3–28%.

Exploiting satellite earth observation to quantify current global oceanic DMS flux and its future climate sensitivity

“…Also, it should be noted that the method of Shutler et al . [] specifically targets anomalously high reflectances, and so does not detect any background concentration of coccolithophores, which may also contribute a DMS flux.…”

“…Shutler et al . [] used this approach to estimate the proportion of time and space that coccolithophore blooms are present within the North Atlantic (75°W–11°E, 35–68°N), see Table .…”

“…We combined satellite‐derived spatial coverage of North Atlantic coccolithophore blooms (calculated using the methods of Shutler et al . [] and summarized in Table ) with a range of estimates of the increase in DMS levels due to the bloom and the duration of the increased DMS, to estimate coccolithophore bloom‐driven sea‐to‐air DMS flux over plausible ranges of bloom DMS enhancement and duration, in the hope that future work will constrain these ranges. We calculated the increase in annual DMS flux assuming that blooms increase DMS by 5, 15, and 25 nM while a bloom is identified from satellite in a given pixel, and this effect is assumed to continue for 1–20 days, day 1 being the day of satellite detection.…”

Carbon on the Northwest European Shelf: Contemporary Budget and Future Influences

“…It is important to note that over long timescales this PIC stock represents a large carbon store (subduction being the long-term sink for atmospheric CO 2 in the global carbon cycle). However, the production of PIC indirectly results in release of CO 2 to the atmosphere on short timescales (Frankignoulle et al, 1994), due to the consumption of alkalinity, and so PIC production also modulates the oceanic sink of CO 2 (Shutler et al, 2013).…”

How Can Present and Future Satellite Missions Support Scientific Studies that Address Ocean Acidification?

“…Algorithms developed for detection of coccolithophores (e.g., Balch et al, 2005) provide a basis for detection and quantification of coccolithophore PIC from satellite observations. Such observations, in turn, are invaluable to carbonate system research in that they provide spatiotemporal information about the conversion of T CO2 to PIC (Balch and Utgoff, 2009;Shutler et al, 2013).…”