Surface biological, chemical, and optical properties of the Patagonian Shelf coccolithophore bloom, the brightest waters of the Great Calcite Belt

Abstract

We report surface observations of a mesoscale coccolithophore bloom at the shelf break of the Patagonian Shelf during December 2008, representing the densest coccolithophore population in the Southern Ocean. The bloom was most intense within the Falklands Current, northeast of the Falkland Islands. Emiliania huxleyi dominated bloom waters, with a mixed E. huxleyi and Prorocentrum sp. dinoflagellate bloom to the west and mixed assemblage of diatoms, dinoflagellates, and flagellates to the east. Optical measurements of coccolith light scattering, analytical measurements of their calcite, and microscopic counts all showed this to be an intense coccolithophore bloom. Average particulate inorganic carbon per coccolith in the bloom was low, typical of the B coccolith morphotype and in agreement with independent measurements made by scanning electron microscopy. Highest particulate inorganic carbon (measured optically and chemically) was observed when residual nitrate (defined as the difference, [NO { 3 ] 2 [Si(OH) 4 ]) was 10-17 mmol L 21 and nitrate to phosphate ratios were close to Redfield values. Elevated particle backscattering was observed in the E. huxleyi bloom, whereas the highest particle scattering occurred in the adjoining Prorocentrum sp. bloom. Backscattering from coccolithophores represented up to 50% of the total backscattering (from organic and inorganic particles) along the main axis of the E. huxleyi bloom. Chlorophyll-specific absorption in the coccolithophore bloom was typical of marine phytoplankton. Residual nitrate plotted vs. temperature showed that the E. huxleyi bloom was associated with waters between 5uC and 15uC, with depleted silicate. Results suggest that previous drawdown of silicate by diatoms occurred prior to the densest E. huxleyi blooms over the Patagonian Shelf. We speculate that such conditions might also be important for annual development of the broader Great Calcite Belt and other coccolithophore blooms.

Environmental drivers of coccolithophore abundance and calcification across Drake Passage (Southern Ocean)

“…The total coccolithophore abundances that we observed (up to ∼ 600 cells mL −1 ) agree with previous observations of maximum abundances of between 200 and 500 cells mL −1 in the Atlantic, Pacific, Indian and Australian sectors of the Southern Ocean (Cubillos et al, 2007;Eynaud et al, 1999;Findlay and Giraudeau, 2000;Gravalosa et al, 2008;Mohan et al, 2008;Hinz et al, 2012;Saavedra-Pellitero et al, 2014;Malinverno et al, 2015;Balch et al, 2016). A previous study across Drake Passage (December, 2006), coinciding with the eastern transect (Transect 2), reported similar abundances of up to 600 cells mL −1 (Holligan et al, 2010).…”

“…nitrate > 10 µmol kg −1 ) and high irradiances (Poulton et al, , 2013Balch et al, 2014). This dominance has now been suggested to result in low integrated calcite concentrations within bloom waters on the Patagonian Shelf (Poulton et al, 2013;Balch et al, 2014).…”

“…Furthermore, the B/C morphotype is physiologically and genetically distinct from morphotype A (Cook et al, 2011(Cook et al, , 2013, and in 2008 it dominated a Patagonian Shelf bloom which occurred in waters with low temperatures (< 8 • C), high macronutrient concentrations (e.g. nitrate > 10 µmol kg −1 ) and high irradiances (Poulton et al, , 2013Balch et al, 2014). This dominance has now been suggested to result in low integrated calcite concentrations within bloom waters on the Patagonian Shelf (Poulton et al, 2013;Balch et al, 2014).…”

Planktic foraminifer and coccolith contribution to carbonate export fluxes over the central Kerguelen Plateau

“…Southern Ocean coccolithophore populations are dominated by the cosmopolitan species Emiliania huxleyi (Saavedra-Pellitero et al, 2014;Winter et al, 2014) that is thought to be the major component of the "great calcite belt" observed in the vicinity of the Subantarctic Front (SAF) and Polar Front (PF) Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsri (Balch et al, 2014). Several studies have reported modern planktic foraminifer abundances and fluxes in the Southern Ocean from net tows (Asioli and Langone, 1997;Mortyn and Charles, 2003;Bergami et al, 2009;Meilland, 2015) and sediment traps (Donner and Wefer, 1994;King and Howard, 2003;Northcote and Neil, 2005;Salter et al, 2014).…”

“…Although neglected for a long time, the presence of coccolithophores in the Southern Ocean has been diagnosed based on an increasing number of direct observations (Winter et al, 2014) and the development of remote sensing methods (Balch et al, 2005(Balch et al, , 2011(Balch et al, , 2014. Southern Ocean coccolithophore populations are dominated by the cosmopolitan species Emiliania huxleyi (Saavedra-Pellitero et al, 2014;Winter et al, 2014) that is thought to be the major component of the "great calcite belt" observed in the vicinity of the Subantarctic Front (SAF) and Polar Front (PF) Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dsri (Balch et al, 2014).…”