OSTRACOD BODY SIZE VARIABILITY LINKED TO ARCTIC OCEAN VENTILATION DURING QUATERNARY CLIMATE CHANGES

Mechanistic models of aquatic metabolism have recently advanced our understanding of the role of thermal and hypoxia tolerance in body-size variation in laboratory experiments. Here we combine mechanistic models and ostracod fossil records to explore climatic factors driving body size variability over the past 2.75 million years in the Arctic Ocean. We used samples that have bottom-water temperature estimates based on Mg/Ca ratios of ostracods and analyzed the shell sizes of over 2000 adults and late juveniles of two ostracod species, Krithe hunti and Krithe minima. Preliminary results show that (1) the adult sizes increased along with the Pliocene-Pleistocene development of sea ice and ice shelves from 2.75 – 0.45 Ma, (2) the sizes decreased during episodes of enhanced Atlantic warm water inflow post-Mid Brunhes Event (a major climate transition ~ 400–350 ka), and (3) both temperature and oxygen availability likely play important roles in size evolution over the geological timescales. While the Arctic Ocean today is experiencing rapid changes in temperature, sea-ice loss, and deep ocean circulation, our study brings forth important information on the magnitude of metazoan’s metabolic scaling and suggests the potential of ostracods as a paleo-oxygen proxy.