Anthropogenic atmospheric carbon dioxide (pCO₂ᵃᵗᵐ) is rapidly rising. This increase is impacting on the ocean, affecting ocean chemistry, the biological pump, and marine organisms. Marine calcifiers are predicted to be affected by increased CO₂, but future consequences are still 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. 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. This data suggests the driver of weight change in foraminifera is unlikely due to increased pCO₂, but rather biotic factors; despite reduced CV ratios during warmer interglacial periods.
Environmental impacts on foraminiferal calcification during the Pliocene
Todd, C. L. (Author). 22 Jun 2018
Student thesis: Master's Thesis › Master of Science (MSc)