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

Abstract

Abstract. 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 Emiliania huxleyi, 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 (between South America and the Antarctic Peninsula) of coccolithophore distribution, CP, primary production, chlorophyll a and macronutrient concentrations, irradiance and carbonate chemistry. Although CP represented less than 1 % of total carbon fixation, coccolithophores were widespread across Drake Passage. The B/C morphotype of E. huxleyi was the dominant coccolithophore, with low estimates of coccolith calcite ( ∼ 0.01 pmol C coccolith −1 ) from biometric measurements. Both cell-normalised calcification (0.01-0.16 pmol C cell −1 d −1 ) and total CP (< 20 µmol C m −3 d −1 ) were much lower than those observed in the subpolar North Atlantic where E. huxleyi morphotype A is dominant. However, estimates of coccolith production rates were similar (0.1-1.2 coccoliths cell −1 h −1 ) 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 ρ = 0.4, p < 0.01). Rates of calcification per cell and coccolith production, as well as community CP and E. huxleyi abundance, were all positively correlated (p < 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 E. huxleyi, 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 2 concentrations.

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment

“…This problem of correlations among drivers has been noted before in examining transect data across the Drake Passage, where more detailed measurements of coccolithophore properties augmented with incubation studies found that temperature and light were the most probable drivers of coccolithophore abundance and calcification rates (Charalampopoulou et al, 2016). Our lack of information on the availability of light (mixed layer depth was determined only on the two hydrographic sections), iron, or individual species and strains makes deducing a possible influence of ocean acidification on coccolithophore distributions from our spatial distribution data even more difficult.…”

“…Further progress in understanding the controls on coccolithophore abundances in the Southern Ocean is clearly needed. At present, temperature, light and competition with diatoms for iron appear to be the strongest candidates (at least for southward expansion (Charalampopoulou et al, 2016;Gafar et al, 2017; with nitrate a strong influence on the location of the northern oligotrophic boundary : Feng et al, 2016).…”

“…Work to check these efforts for the Southern Ocean has begun but remains sparse. Early work in the South Atlantic found that SPIC values appeared to exceed ocean PIC by a factor of 2-3 (Balch et al, 2011), and based on a handful of samples, it was suggested that this might reflect a lower amount of PIC per coccolith (Holligan et al, 2010), and it has since been confirmed that polar coccolithophores can have low PIC contents (Charalampopoulou et al, 2016;Muller et al, 2015;Poulton et al, 2011). Two dedicated voyages to investigate the Great Calcite Belt in the SAZ and PFZ across the South Atlantic and south Indian oceans attempted a comparison of acid-labile backscatter (as a proxy for PIC) and MODIS SPIC values, but there were no matchups in the South Atlantic owing to cloudy conditions (Balch et al, 2016).…”

Simultaneous shifts in elemental stoichiometry and fatty acids of &lt;i&gt;Emiliania huxleyi&lt;/i&gt; in response to environmental changes

“…Evidence from in situ and satellite observations indicates that E. huxleyi has been increasingly expanding its range poleward in both hemispheres over the last two decades, and contributing factors to this poleward expansion may differ between regions and hemispheres (Winter et al, 2014). For example, warming and freshening have promoted E. huxleyi blooms in the Bering Sea since the late 1970s (Harada et al, 2012), while temperature and irradiance were best able to explain variability in E. huxleyi-dominated coccolithophore community composition and abundance across the Drake Passage (Southern Ocean) (Charalampopoulou et al, 2016). Hence, empirical data on the responses of E. huxleyi to different environmental drivers would be critical for fully understanding the roles of this prominent coccolithophore species in marine ecosystems.…”

Spatial patterns of phytoplankton composition and upper-ocean biogeochemistry do not follow carbonate chemistry gradients in north-west European Shelf seas

“…Some earlier field studies have also analyzed linkages between carbonate chemistry and species composition in an OA context using multivariate statistics (e.g. Charalampopoulou et al (2011);Charalampopoulou et al (2016)). Frigstad et al (2013) reported the need for comprehensive studies on all available environmental data (with lots of variables) to determine causal relationships.…”