Marine bivalve records of Antarctic seasonality and biological responses to environmental change over the Cretaceous-Paleogene mass extinction interval

The Cretaceous-Paleogene mass extinction event occurred 66 million years ago and had a profound effect on the course of evolutionary history, with the extinction of up to 75% of life and larger effects on the broader Earth system. A number of studies posit that the severity of this extinction event may have been amplified by climate variability and destabilisation in the latest Cretaceous – immediately prior to the extinction event. The strong seasonal forcing in the polar high latitudes is likely to have enhanced any such effects during this time period; additionally, the historical mismatch between late Cretaceous proxy data and climate simulations is particularly pronounced at high latitudes and both the effects of a stronger seasonal cycle on proxy temperature conversions, and misrepresentation of seasonality in climate models have been suggested as factors in the mismatch. This makes the Antarctic an extremely valuable location to study with regards to seasonality from a proxy- and model- based perspective. Seymour Island is a rare and valuable Antarctic K-Pg boundary site with a good framework of fossil, stratigraphic and sedimentological study, which makes fossil material ideal for investigation of the effects and impacts of seasonality and environmental change across the mass extinction interval. This thesis presents a detailed study focusing on using fossil bivalve shell material from the Seymour Island section to reconstruct records of Antarctic climate and seasonality across the K-Pg mass extinction event. New data were obtained about the seasonal growth patterns of these bivalves to understand their growth and ontogenetic response to potential climate variability and the effects of the mass extinction. For the first time, sub-annual resolution stable carbon and oxygen isotopic data were produced from Seymour Island’s bivalve shells to show seasonal changes in temperatures and detect changes in biogeochemical cycling and methane influence through the section. These data were integrated with a series of oxygen isotope enabled climate simulations to address potential issues converting from isotopic to temperature data in a highly seasonal environment and provide further information regarding the influence of sea ice. Combining new proxy- and model- based knowledge in a series of sensitivity experiments, it was shown that both sets of data display good agreement under realistic sets of parameters, suggesting that seasonality was important for the development of polar ecosystems. Warm summer temperatures may have been key in permitting the ecological strategy in these bivalves of slow growth to large sizes, which in turn may have contributed to survivorship across the K-Pg boundary.