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

Anastasia Charalampopoulou, Alex J. Poulton, Dorothee C. E. Bakker, Mike I. Lucas, Mark C. Stinchcombe, Toby Tyrrell
2016 Biogeosciences  
<p><strong>Abstract.</strong> Although coccolithophores are not as numerically common or as diverse in the Southern Ocean as they are in subpolar waters of the North Atlantic, a few species, such as <i>Emiliania huxleyi</i>, are found during the summer months. Little is actually known about the calcite production (CP) of these communities or how their distribution and physiology relate to environmental variables in this region. In February 2009, we made observations across Drake Passage
more » ... ake Passage (between South America and the Antarctic Peninsula) of coccolithophore distribution, CP, primary production, chlorophyll <i>a</i> and macronutrient concentrations, irradiance and carbonate chemistry. Although CP represented less than 1<span class="thinspace"></span>% of total carbon fixation, coccolithophores were widespread across Drake Passage. The B/C morphotype of <i>E. huxleyi</i> was the dominant coccolithophore, with low estimates of coccolith calcite (∼ 0.01<span class="thinspace"></span>pmol<span class="thinspace"></span>C<span class="thinspace"></span>coccolith<sup>−1</sup>) from biometric measurements. Both cell-normalised calcification (0.01–0.16<span class="thinspace"></span>pmol<span class="thinspace"></span>C<span class="thinspace"></span>cell<sup>−1</sup><span class="thinspace"></span>d<sup>−1</sup>) and total CP (&amp;lt;<span class="thinspace"></span>20<span class="thinspace"></span>µmol<span class="thinspace"></span>C<span class="thinspace"></span>m<sup>−3</sup><span class="thinspace"></span>d<sup>−1</sup>) were much lower than those observed in the subpolar North Atlantic where <i>E. huxleyi</i> morphotype A is dominant. However, estimates of coccolith production rates were similar (0.1–1.2<span class="thinspace"></span>coccoliths<span class="thinspace"></span>cell<sup>−1</sup><span class="thinspace"></span>h<sup>−1</sup>) to previous measurements made in the subpolar North Atlantic. A multivariate statistical approach found that temperature and irradiance together were best able to explain the observed variation in species distribution and abundance (Spearman's rank correlation <i>ρ</i> = <span class="thinspace"></span>0.4, <i>p</i><span class="thinspace"></span>&amp;lt;<span class="thinspace"></span>0.01). Rates of calcification per cell and coccolith production, as well as community CP and <i>E. huxleyi</i> abundance, were all positively correlated (<i>p</i><span class="thinspace"></span>&amp;lt;<span class="thinspace"></span>0.05) to the strong latitudinal gradient in temperature, irradiance and calcite saturation states across Drake Passage. Broadly, our results lend support to recent suggestions that coccolithophores, especially <i>E. huxleyi</i>, are advancing polewards. However, our in situ observations indicate that this may owe more to sea-surface warming and increasing irradiance rather than increasing CO<sub>2</sub> concentrations.</p>
doi:10.5194/bg-13-5917-2016 fatcat:d6iotorabjhwnj2hkrs7uyirni