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 Coccolithophore blooms are significant contributors to the global production and export of calcium carbonate (calcite). The Patagonian Shelf is a site of intense annual coccolithophore blooms during austral summer. During December 2008, we made intensive measurements of the ecology, biogeochemistry, and physiology of a coccolithophore bloom. High numbers of Emiliania huxleyi cells and detached coccoliths (>1 × 103 mL−1 and >10 × 103 mL−1, respectively), high particulate inorganic carbon concentrations (>10 mmol C m−2), and high calcite production (up to 7.3 mmol C m−2 d−1) all characterized bloom waters. The bloom was dominated by the low-calcite-containing B/C morphotype of Emiliania huxleyi, although a small (<10 µm) Southern Ocean diatom of the genus Fragilariopsis was present in almost equal numbers (0.2–2 × 103 mL−1). Estimates of Fragilariopsis contributions to chlorophyll, phytoplankton carbon, and primary production were >30%, similar to estimates for E. huxleyi and indicative of a significant role for this diatom in bloom biogeochemistry. Cell-normalized calcification rates, when corrected for a high number of nonactive cells, were relatively high and when normalized to estimates of coccolith calcite indicate excessive coccolith production in the declining phase of the bloom. We find that low measures of calcite and calcite production relative to other blooms in the global ocean indicate that the dominance of the B/C morphotype may lead to overall lower calcite production. Globally, this suggests that morphotype composition influences regional bloom inventories of carbonate production and export and that climate-induced changes in morphotype biogeography could affect the carbon cycle.
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 The coccolithophore Emiliania huxleyi frequently forms large-scale blooms in subpolar waters, where the overproduction and shedding of cellular scales (coccoliths) into the surrounding waters causes high reflectance and a milky appearance. Such blooms occur in several oceanic (e.g., Iceland Basin) and coastal (e.g., North Sea, Patagonian Shelf) regions of the world's ocean [Brown and Yoder, 1994; Iglesias-Rodriguez et al., 2002]. The Patagonian Shelf in the southwest Atlantic Ocean is one of the most prominent and largest of regular high-reflectance blooms [Brown and Podesta, 1997; Garcia et al., 2011; Signorini et al., 2006]. Coccolithophore blooms on the Patagonian Shelf peak in austral summer (November to January) each year [Signorini et al., 2006] and develop in a north to south direction [Painter et al., 2010]. The Patagonian Shelf is a complex hydrographic regime, where warm, low-nutrient subtropical waters from the north mix with cold, high-nutrient waters from the south [Painter et al., 2010]. The area also acts as a significant seasonal sink of CO2 associated with highly productive shelf waters, with the shelf break front dominant and associated with intense biological activity [Signorini et al., 2006; Schloss et al., 2007; Bianchi et al., 2009].
 Coccolithophore blooms in the North Atlantic (e.g., Iceland Basin) are thought to be formed through a combination of high sea-surface temperatures, shallow mixed layers (<20 m), and high-irradiance conditions (>1500 μE m−2 s−1), as well as reduced microzooplankton grazing [Holligan et al., 1993a; Tyrrell and Merico, 2004]. Blooms of E. huxleyi are generally believed to follow those of diatoms in waters which have become seasonally depleted in inorganic nutrients (e.g., silicic acid) and are becoming more stable in terms of vertical mixing (i.e., a seasonal thermocline) [Holligan et al., 1993a, 1993b]. Nitrate to phosphate ratios have been linked to bloom formation [Tyrrell and Merico, 2004], although blooms often form in waters with both high and low ratios of nitrate to phosphate [Townsend et al., 1994; Lessard et al., 2005; Painter et al., 2010]. On the Patagonian Shelf, coccolithophore blooms have been linked with high mixed layer irradiances [Signorini et al., 2006; Painter et al., 2010; Garcia et al., 2011], with the bloom in 2008 in colder (<10°C) and more nutrient-rich waters (e.g., nitrate >10 µmol kg−1) than found in the Iceland Basin [Poulton et al., 2011].
 As sites of intense calcite production, coccolithophore blooms are marked regions of unique biogeochemistry, where calcite production (CP) is high and organic carbon production is typically low [Fernandez et al., 1993; Harlay et al., 2011]. As E. huxleyi cells are relatively small (~5–6 µm), individual cells contain low amounts of chlorophyll-a (0.1–0.2 pg cell−1 [Haxo, 1985]), and so despite high cell densities (>1000 cells mL−1), coccolithophore blooms are associated with low chlorophyll-a (Chl) concentrations (<1–2 mg m−3 [Balch et al., 1991; Holligan et al., 1983, 1993a, 1993b; Garcia et al., 2011]). While E. huxleyi may dominate cell numbers, other coccolithophore species (e.g., Coccolithus pelagicus) and phytoplankton are often present [Fernandez et al., 1993; Harlay et al., 2011], although their net influence on bloom biogeochemistry is unclear. Coccolithophores are potentially sensitive to climate change, especially ocean acidification, whereby seawater takes up elevated atmospheric CO2, fundamentally changing ocean pH and carbonate chemistry. Laboratory work has shown considerable intraspecies variability in E. huxleyi responses to changes in carbonate chemistry [Langer et al., 2009, 2011], and there is a need to examine natural populations along environmental gradients [e.g., Cubillos et al., 2007; Beaufort et al., 2011].
 In laboratory cultures, E. huxleyi produces and sheds excess coccoliths from its outer covering of coccoliths (coccosphere) when it experiences severe nutrient or light limitation [Paasche, 2002] and as growth rates slow. This continued production of coccoliths while resources limit cell division and organic production [e.g., Müller et al., 2008] is thought to be the main mechanism by which E. huxleyi forms large-scale high-reflectance blooms in the open ocean [Balch et al., 1996a; Tyrrell and Merico, 2004]. With each E. huxleyi cell able to produce two to three coccoliths per hour [Paasche, 1962; Balch et al., 1996b], high coccolith numbers (attached and detached) may be formed relatively rapidly, although coccolith production and detachment rates scale with rates of cellular division [Fritz and Balch, 1996; Fritz, 1999]. However, relatively few measurements of coccolith production currently exist with which to assess coccolithophore physiology in field populations.
 During December 2008, intensive interdisciplinary measurements were made of the hydrography, ecology, biogeochemistry, and coccolithophore physiology along the Patagonian Shelf, as part of the Coccolithophores Of the Patagonian Shelf (COPAS'08) expedition. Analysis of satellite images has shown that the large-scale calcite feature (Figure 1a) developed from north to south, with calcite (particulate inorganic carbon) rich waters carried north via the northward flow of the Falklands Current, and the decline of the bloom during in situ sampling was associated with an increase in sea-surface temperature [Painter et al., 2010]. Examination of detached coccoliths by Poulton et al.  highlighted that E. huxleyi morphotype B/C (herein E. huxleyi B/C) dominated bloom waters and that this morphotype has a lower coccolith calcite content than other E. huxleyi morphotypes. The present study examines the ecological (phytoplankton community), biogeochemical (stocks and rates), and physiological (cellular calcification, coccolith production rates) characteristics of the 2008 Patagonian Shelf bloom. The two interlinked goals of the present study are to (1) assess how the characteristics of the 2008 bloom compare with other well-studied global blooms (e.g., in the Iceland Basin, Bay of Biscay) and (2) examine whether the dominance of the low coccolith-calcite E. huxleyi B/C affects the characteristics of the bloom.
Figure 1. The 2008 Patagonian Shelf bloom. (a) Cruise track (white line) and predawn sampling stations superimposed on a December 2008 composite of surface calcite; (b) temperature versus salinity plots (full-depth CTD data) for sampling stations with hydrographic provinces separated following the analysis of Painter et al. ; (c) scanning electron microscope (SEM) image of Emiliania huxleyi coccosphere showing B/C morphotype characteristics; and (d) SEM image of Fragilariopsis cells (likely F. pseudonana). Stations 060, 094, and 102 were in identical positions (Table 1). Hydrographic provinces in Figure 1b are color coded and include BC, Brazil Current; T, transitional waters; SW, shelf waters; ASW, sub-Antarctic shelf waters; NFC, Northern Falklands Current; SFC, Southern Falklands Current. White scale bars in Figures 1c and 1d are 1 µm.
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Table 1. Hydrographic Characteristics of Sampling Stations Along the Patagonian Shelf a
|Station ID||Dateb||Latitude (°S)||Longitude (°W)||Water Depth||Hydrographic Provincec||ML||Zeup||SST||Salinity||Surface Macronutrients (mmol m−3)||ĒML (mol PAR m−2 d−1)||Carbonate Chemistry|
| || || || ||(m)|| ||(m)||(m)||(°C)|| ||NOx||PO4||dSi|| ||pH||Ωcalcite|
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 Relative to many other coccolithophore blooms in the global ocean, the 2008 Patagonian Shelf bloom was uniquely dominated by the B/C morphotype of E. huxleyi [Poulton et al., 2011] and had high abundances of small (<10 µm) Fragilariopsis diatoms (likely F. pseudonana), and these two made almost equal contributions to total Chl, phytoC, and PP (Table 3). Hence, our observations highlight how coccolithophore blooms differ globally and represent complex mosaics of inorganic and organic production. Both Cook et al.  and Poulton et al.  have suggested that E. huxleyi type B/C is a Southern Ocean specialist and may dominate communities in the Scotia Sea [Hinz et al., 2012]. Small Fragilariopsis are also common throughout the Scotia and Weddell Seas [Cefarelli et al., 2010; Hinz et al., 2012], and it appears that the 2008 coccolithophore bloom, which occurred in cold, macronutrient-rich water, was also dominated by a flora more representative of the Southern Ocean. High residual macronutrient concentrations (i.e., HNLC conditions) at the southern end of the shelf (Table 1) also support a Southern Ocean link and imply a potential role for micronutrient availability in bloom dynamics [Garcia et al., 2008].
 Indices of the degree of cellular calcification, including coccolith calcite content [Poulton et al., 2011], cell-specific calcification, and individual coccolith production rates (Figures 3b and 3c), indicate that the shelf community was producing coccoliths at physiologically high rates, in excess of the number needed to make a new coccosphere daily. When sampled, the 2008 coccolithophore bloom was in decline [Painter et al., 2010], despite high cellular rates of calcification, and therefore, we conclude that the relatively low inventories of calcite present in bloom waters were due to dominance of the low-calcite B/C morphotype.
 High reflectance signals, indicative of coccolithophore blooms, are common features in the Southern Ocean (e.g., South Georgia, Polar Frontal Zone) [Holligan et al., 2010]. The dominance of E. huxleyi type B/C in many parts of the Southern Ocean [e.g., Cubollis et al., 2007; Cook et al., 2011; Poulton et al., 2011; Hinz et al., 2012] implies that this morphotype dominates high-reflectance features in the Southern Hemisphere and these may be characterized by low areal calcite content relative to similar sized features in the Northern Hemisphere which may be dominated by type A. Importantly, our observations from the Patagonian Shelf indicate that bloom morphotype composition has a global significance in terms of coccolithophore bloom dynamics, specifically the magnitude of calcite production and export of these features.
 Establishing that E. huxleyi morphotype variability has a direct impact on the calcite yield of coccolithophores, including blooms, signifies that understanding global morphotype biogeography [e.g., Cubillos et al., 2007] and comparative physiology [e.g., Cook et al., 2011] are key steps in understanding global calcite production. When viewed in the context of climate change, our observations indicate that biogeographical shifts in the morphotypes of E. huxleyi [e.g., Cubillos et al., 2007] will influence oceanic calcite production. Furthermore, strain-specific variability in the sensitivity of E. huxleyi to ocean acidification [Langer et al., 2009, 2011], potentially linked to morphotype variability, could ultimately have important implications for the marine carbon cycle. For example, if morphotypes with lower (or higher) coccolith calcite content are favored by higher pCO2 conditions, then global coccolithophore calcite production may decrease (or increase).