Rapid climate change and bacterial blooms in deep time

Increasing ocean acidification, deoxygenation and bacterial blooms are among the measurable consequences of current and projected trends in atmospheric CO2 and global warming. Such environmental changes prevailed during greenhouse (hothouse) climates in Earth's past that may serve as partial analogues to infer the ecological consequences of future global scenarios.

During Ocean Anoxic Event 2 (OAE-2) at the Cenomanian-Turonian boundary - the warmest interval in the last 100 million years - abrupt widespread ocean stratification has been linked with marine extinctions. However, despite ~40 years of research, the mechanisms responsible for sustaining prolonged periods of anoxia remain contentious. Key questions concern the role of salinity stratification (freshening) in reducing ocean circulation during OAEs and the effects of anoxia in controlling nutrient budgets, nitrogen fixation, and resulting ecosystem structure.

Furthermore, data for the middle and high latitudes are critical for deciphering inter-hemispheric climate synchronicity, but are notably scarce. Recently recovered pelagic cores from IODP Expedition 342 will help fill this important gap. This project will use molecular fossils (biomarkers) to study the physical and biogeochemical evolution of the North Atlantic basin during the Cenomanian by reconstructing variations in water column oxygenation, sea surface temperatures (SST; TEX86 index), organic matter provenance and, in concert with palaeontological data, planktonic ecology.

The overarching goals are to differentiate and test the predictions of competing hypotheses regarding: (a) the role of precipitation and salinity stratification as precursors for ocean deoxygenation; (b) the role of marine productivity and changing ecology on ocean deoxygenation and black shale formation; and (c) the occurrence of elevated SSTs at high latitudes, which might allow proxy and model data to better constrain latitudinal thermal gradients.