Calcification response to climate change in the Pliocene?

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 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 calcification during the high pCO₂ Pliocene or during the transition into an icehouse world. [ABSTRACT FROM AUTHOR]