Abstract
Abstract. As a result of anthropogenic pCO2 increases, future oceans are growing warmer and lower in pH and oxygen, conditions that are likely to impact planktic communities. Past intervals of elevated and changing pCO2 and temperatures can offer a glimpse into the response of marine calcifying plankton to changes in surface oceans under conditions similar to those projected for the future. Here we present new records of planktic foraminiferal and coccolith calcification (weight and size) from Deep Sea Drilling Project Site 607 (mid-North Atlantic) and Ocean Drilling Program Site 999 (Caribbean Sea) from the Pliocene, the last time that pCO2 was similar to today, and extending through a global cooling event into the intensification of Northern Hemisphere glaciation (3.3 to 2.6 million years ago). Test weights of both surface-dwelling Foraminifera Globigerina bulloides and thermocline-dwelling Foraminifera Globorotalia puncticulata vary with a potential link to regional temperature variation in the North Atlantic, whereas in the tropics Globigerinoides ruber test weight remains stable. In contrast, reticulofenestrid coccoliths show a narrowing size range and a decline in the largest lith diameters over this interval. Our results suggest no major changes in plankton calcite production during the high pCO2 Pliocene or during the transition into an icehouse world.
Highlights
Over the last 250 yr atmospheric pCO2 levels have increased from pre-industrial levels of 280 parts per million to 393 ppm in 2012 (Dlugokencky and Tans, 2013)
There is an orbital variability in the carbonate mass accumulation rates (MARs) at Site 607 while, in contrast, at Site 999 the carbonate MAR is more stable, in line with less environmental variability
At neither site did fragmentation couple with the foraminiferal / coccolithophores ratio, which we deem to be influenced by differing abundances of these two calcifiers and not by preferential dissolution of foraminifers
Summary
Over the last 250 yr atmospheric pCO2 levels have increased from pre-industrial (pre-1750) levels of 280 parts per million (ppm) to 393 ppm in 2012 (Dlugokencky and Tans, 2013). The environmental impacts of anthropogenic atmospheric pCO2 and resultant climatic changes are predicted to be widespread across all ecosystems with potential influences on biogeochemical cycles and ecosystem services (Turley et al, 2010). Previous research has largely focused on documenting the response of marine calcifiers to environmental parameters in laboratory culture experiments (Spero et al, 1997; Bijma et al, 1999; Riebesell et al, 2000; Langer et al, 2006; Iglesias-Rodriguez et al, 2008). The plasticity within the population, the selection of ecophenotypes and genotypes with different environmental preferences, their migration, adaptation and evolution are possible mechanisms which may act to dampen the effect of ocean acidification on marine organisms and the processes they influence. Laboratory culture experiments incompletely represent whole ecosystem responses to environmental change
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