Planktonic foraminiferal response to ocean acidification in the Santa Barbara Basin over the last century

Abstract:

Since the onset of the industrial revolution, atmospheric CO₂ concentrations have increased by more than 40% (120 ppm) due to anthropogenic activities. While nearly half of these carbon emissions remain in the atmosphere, the ocean has absorbed approximately 30% of the excess CO₂. The increase in the ocean aqueous CO₂ inventory has resulted in a significant change in seawater chemistry, most notably the decline of mean seawater pH (0.1 units since 1750). Some marine calcifiers, such as planktonic foraminifera, have shown an adverse response to ocean acidification exhibited as a reduction in calcification efficiency. Estimates indicate that planktonic foraminifera are responsible for up to 55% of the total open marine calcium carbonate flux and also serve as low tropic food web members making them an important constituent for chemical and biological processes in the oceans. This study utilizes morphometric (area density) and geochemical (B/Ca) analyses of planktonic foraminifera to calibrate species-specific responses to changes in modern ocean carbonate chemistry. These proxy methods have been applied to down-core records with nearly annual to sub-annual resolution to reconstruct past changes that have occured since the onset of the Industrial Revolution. The sediments used for this study were collected in the Santa Barbara Basin within the California Current System (CSS), which has been identified as a region of rapidly increasing ocean acidification due to natural upwelling processes and increasing atmospheric CO₂. This study will evaluate the effect of ocean acidification on several species of planktonic foraminifera to improve our understanding of the response of these organisms to modern changes in atmospheric CO₂.