The Influence of Environmental Variability on the Biogeography of
Coccolithophores and Diatoms in the Great Calcite Belt
Helen E. K. Smith1,2, Alex J. Poulton1,a, Rebecca Garley3, Jason Hopkins4, Laura C. Lubelczyk4, Dave T. Drapeau4, Sara Rauschenberg4, Ben S. Twining4, Nicholas R. Bates2,3, and William M. Balch41National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK 2School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK 3Bermuda Institute of Ocean Sciences, 17 Biological Station, Ferry Reach, St. George's GE 01, Bermuda 4Bigelow Laboratory for Ocean Sciences, 60 Bigelow Drive, P.O. Box 380, East Boothbay, Maine 04544, USA apresent address: The Lyell Centre, Heriot-Watt University, Edinburgh, EH14 7JG, UK
Received: 27 Mar 2017 – Accepted for review: 06 Apr 2017 – Discussion started: 13 Apr 2017
Abstract. The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region, provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Water samples for phytoplankton enumeration were collected from the upper 30 m during two cruises, the first to the South Atlantic sector (Jan–Feb 2011; 60 °W–15 °E and 36–60 °S) and the second in the South Indian sector (Feb–Mar 2012; 40–120 °E and 36–60 °S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Sub-Tropical, Polar, and Sub-Antarctic Fronts. The influence of environmental parameters, such as sea-surface temperature (SST), salinity, carbonate chemistry (i.e., pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macro-nutrients (i.e., nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB, was assessed statistically. Nanophytoplankton (cells 2–20 μm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, the coccolithophore Emiliania huxleyi and the diatoms Fragilariopsis nana, F. pseudonana and Pseudonitzschia sp. were the most dominant and widely distributed species. A combination of SST, macro-nutrient concentrations and pCO2 were the best statistical descriptors of biogeographic variability of biomineralizing species composition between stations. Emiliania huxleyi occurred in the silicic acid-depleted waters between the Sub-Antarctic Front and the Polar Front, indicating a favorable environment for this coccolithophore in the GCB after spring diatom blooms remove silicic acid to limiting levels. After full consideration of variability in carbonate chemistry and temperature on the distribution of nanoplankton in the GCB, we find that temperature remains the dominant driver of biogeography in a large proportion of the modern Southern Ocean.
Smith, H. E. K., Poulton, A. J., Garley, R., Hopkins, J., Lubelczyk, L. C., Drapeau, D. T., Rauschenberg, S., Twining, B. S., Bates, N. R., and Balch, W. M.: The Influence of Environmental Variability on the Biogeography of
Coccolithophores and Diatoms in the Great Calcite Belt, Biogeosciences Discuss., doi:10.5194/bg-2017-110, in review, 2017.