The role of ocean acidification in Emiliania huxleyi coccolith thinning in the Mediterranean Sea

[摘要] Ocean acidification is a result of the uptake of anthropogenic CO₂ fromthe atmosphere into the ocean and has been identified as a majorenvironmental and economic threat. The release of several thousands ofpetagrams of carbon over a few hundred years will have an overwhelming effecton surface ocean carbon reservoirs. The recorded and anticipated changes inseawater carbonate chemistry will presumably affect global oceanic carbonateproduction. Coccolithophores as the primary calcifying phytoplankton group,and especially Emiliania huxleyi as the most abundant species haveshown a reduction of calcification at increased CO₂ concentrations forthe majority of strains tested in culture experiments. A reduction ofcalcification is associated with a decrease in coccolith weight. However, theeffect in monoclonal cultures is relatively small compared to the strongvariability displayed in natural E. huxleyi communities, as theseare a mix of genetically and sometimes morphologically distinct types.Average coccolith weight is likely influenced by the variability in seawatercarbonate chemistry in different parts of the world's oceans and onglacial/interglacial time scales due to both physiological effects andmorphotype selectivity. An effect of the ongoing ocean acidification onE. huxleyi calcification has so far not been documented in situ.Here, we analyze E. huxleyi coccolith weight from the NWMediterranean Sea in a 12-year sediment trap series, and surface sediment andsediment core samples using an automated recognition and analyzing software.Our findings clearly show (1) a continuous decrease in the average coccolithweight of E. huxleyi from 1993 to 2005, reaching levels belowpre-industrial (Holocene) and industrial (20th century) values recorded inthe sedimentary record and (2) seasonal variability in coccolith weight thatis linked to the coccolithophore productivity. The observed long-termdecrease in coccolith weight is most likely a result of the changes in thesurface ocean carbonate system. Our results provide the first indications ofan in situ impact of ocean acidification on coccolithophore weight in anatural E. huxleyi population, even in the highly alkalineMediterranean Sea.

[学科分类] 地球化学与岩石