Combined effects of warming, acidification and changing ocean circulation on the marine carbon cycle during the PETM

Abstract:

We are studying the ocean biogeochemistry during the Paleocene-Eocene Thermal Maximum (PETM; 55 million years ago) with an Earth System Model (ESM). During this period of abrupt environmental change the climate underwent a significant transformation within short geological timescales (~10 ky). The PETM is globally recorded in proxy-data by a negative δ¹³C carbon isotope excursion and carbonate dissolution in the ocean, suggesting that the occurred warming was caused by massive carbon release. To investigate the marine biogeochemistry before and during the onset of the PETM we use the ESM of the Max Planck Institute for Meteorology to simulate scenarios with different rates of carbon release over several thousand years. Starting from an already warmer background climate than present, the atmospheric CO₂ increase and concomitant warming lead to acidification and deoxygenation of mid and deep ocean waters. Our results indicate that a weakening of deep water formation, caused by global warming, plays a major role in producing inhospitable conditions for benthic organisms during the PETM. We show how the interaction between biological and physical responses to the carbon perturbation lead to the observed calcite sediment dissolution in the deep ocean. At the surface a weakening of the physical and biological carbon pump restricts the oceanic uptake capacity of atmospheric CO₂ which helps to maintain elevated atmospheric CO₂ concentrations and temperatures throughout the event.