Is coccolithophore distribution in the Mediterranean Sea related to seawater carbonate chemistry?

Abstract

Abstract. The Mediterranean Sea is considered a "hot spot" for climate change, being characterized by oligotrophic to ultra-oligotrophic waters and rapidly increasing seasurface temperature and changing carbonate chemistry. Coccolithophores are considered a dominant phytoplankton group in these waters. As marine calcifying organisms they are expected to respond to the ongoing changes in seawater carbonate chemistry. We provide here a description of the springtime coccolithophore distribution in the Mediterranean Sea and relate this to a broad set of in situ-measured environmental variables. Samples were taken during the R/V Meteor (M84/3) oceanographic cruise in April 2011, between 0 and 100 m water depth from 28 stations. Total diatom and silicoflagellate cell concentrations are also presented. Our results highlight the importance of seawater carbonate chemistry, especially [CO 2− 3 ] but also ] in unraveling the distribution of heterococcolithophores, the most abundant coccolithophore life phase. Holo-and heterococcolithophores respond differently to environmental factors. For instance, changes in heterococcolithophore assemblages were best linked to the combination of [CO 2− 3 ], pH, and salinity (ρ = 0.57), although salinity might be not functionally related to coccolithophore assemblage distribution. Holococcolithophores, on the other hand, showed higher abundances and species diversity in oligotrophic areas (best fit, ρ = 0.32 for nutrients), thriving in nutrient-depleted waters. Clustering of heterococcolithophores revealed three groups of species sharing more than 65 % similarities. These clusters could be assigned to the eastern and western basins and deeper layers (below 50 m), respectively. In addition, the species Gephyrocapsa oceanica, G. muellerae, and Emiliania huxleyi morphotype B/C are spatially distributed together and trace the influx of Atlantic waters into the Mediterranean Sea. The results of the present work emphasize the importance of considering holo-and heterococcolithophores separately when analyzing changes in species assemblages and diversity. Our findings suggest that coccolithophores are a main phytoplankton group in the entire Mediterranean Sea and can dominate over siliceous phytoplankton. They have life stages that are expected to respond differently to the variability in seawater carbonate chemistry and nutrient concentrations.

Reventilation Episodes During the Sapropel S1 Deposition in the Eastern Mediterranean Based on Holococcolith Preservation

“…Holococcoliths have a distinct preference for warm and oligotrophic water (Oviedo et al, ) and may be able to adapt to ongoing Mediterranean climate change, where surface water would be characterized by relatively high calcite saturation state, high temperature, stratification, and nutrient limitation (D'Amario et al, ). In accordance with their ecological preference, holococcoliths are especially abundant in eastern Mediterranean water samples (D'Amario et al, ; Oviedo et al, ).…”

“…Holococcoliths have a distinct preference for warm and oligotrophic water (Oviedo et al, ) and may be able to adapt to ongoing Mediterranean climate change, where surface water would be characterized by relatively high calcite saturation state, high temperature, stratification, and nutrient limitation (D'Amario et al, ). In accordance with their ecological preference, holococcoliths are especially abundant in eastern Mediterranean water samples (D'Amario et al, ; Oviedo et al, ). Even though the Mediterranean waters are supersaturated with respect to calcite (Schneider et al, ), holococcolith diversity and abundance are reduced in surface sediments (Kleijne, ; Knappertsbusch, ), because of disaggregation into microcrystals and lysocline/seafloor dissolution.…”

“…Holococcoliths are produced by coccolithophores during their haploid life phase. Although belonging to different species, they behave as a homogeneous group (Oviedo et al, ), preferring warm and oligotrophic surface waters (D'Amario et al, ; Kleijne, ; Knappertsbusch, ; Oviedo et al, ).…”

Spatiotemporal variability of alkalinity in the Mediterranean Sea

“…Precipitation and dissolution of calcium carbonate should also be considered in the alkalinity biological equation. However, this process is poorly quantified for the Mediterranean Sea (only sparse measures of calcifiers abundances are available Siokou-Frangou et al, 2010;Oviedo et al, 2015) so it was not possible to include it in the model. Nevertheless, an offline estimate derived by combining information from global studies and models (Poulton et al, 2007;Gregg and Casey, 2007;Jansen et al, 2002), data on sedimentation (Stavrakakis et al, 2013) and our results indicates extra terms of the alkalinity budget up to −0.007 mmol m −3 d −1 in the upper part of the water column and up to about +0.004 mmol m −3 d −1 for the intermediate layer.…”

A 40-year global dataset of visible channel remote sensing reflectances and coccolithophore bloom occurrence derived from the Advanced Very High Resolution Radiometer catalogue

“…Consequently, coccolithophorid blooms are predominantly identified through the removal of likely false positives (e.g river plumes, coastal influences, bathymetry and sea-ice). While coccolithophorid blooms are known to occur across the Eastern (Malinverno et al, 2003) and North Western (Oviedo et al, 2015) and We partially attribute the high R rs values to the sporadic presence of Saharan dust. This requires specific atmospheric correction methods (Moulin et al, 2001) that are not implemented here, and would require ancillary dust information that is of limited availability on the time scale covered by this data set.…”