ENVIRONMENTAL IMPACTS ON FORAMINIFERAL CALCIFICATION IN THE PLIOCENE
The aim of the research project was to understand better the changes in calcification observed in planktic foraminifera in response to warmer temperatures and higher carbon dioxide (CO2). Size assemblage through automated microscopy; size normalised weight; shell thickness and calcite:volume ratios via micro-CT scanning.
Anthropogenic atmospheric carbon dioxide (pCO2atm) is rapidly rising. This increase impacts the ocean, affecting ocean chemistry, the biological pump, and marine organisms. Marine calcifiers are predicted to be affected by increased CO2, but future consequences remain relatively unknown. To assess potential impacts, this project established the relationship between changing environmental conditions and calcification in foraminifera, a group essential to the carbon cycle. The Pliocene was the last time interval when pCO2atm concentrations were comparable to today.
The test size and weight of the dominant species, Globigerinoides ruber (white), was quantified through the Pliocene at Ocean Drilling Program Site 999 in the Caribbean to assess impacts on carbonate production. Test size shows high-frequency variability not related to carbonate chemistry or temperature. During the cold interval marine isotope stage (MIS) M2, foraminiferal test size increased, potentially linked to intensified stratification in response to the closure of the Central American Seaway (CAS).
The foraminiferal size-normalised weight (SNW) of G. ruber decreases during MIS M2 and is heavier at higher temperatures and thereby for inference higher pCO2atm, challenging the view of oceanic partial pressure of carbon dioxide (pCO2) as a simple driver for calcification. To better understand the drivers of changes in SNW, CT scans were used to calculate calcite-to-volume (CV) ratios and test thickness in the penultimate chamber (see figure below). This data suggests the driver of weight change in foraminifera is unlikely due to increased pCO2atm, but rather biotic factors, despite reduced CV ratios during warmer interglacial periods.
