Deep-sea coral records of the intermediate Atlantic Ocean during the last glacial cycle

Cold-water corals are found extensively throughout the world's oceans and thus represent a valuable paleoceanographic archive - particularly at the intermediate depths. In Chapter 2 I investigate the temporal and spatial distribution of cold-water corals in the Northeast Atlantic over the past 150 thousand years (kyr). These data revealed that corals were thriving at low and mid-latitudes during the last glacial and deglacial intervals, but their presence at higher latitudes occurred only during warmer climates. Food supply and dissolved oxygen associated with oceanic dynamics (e.g., currents, fronts, upwelling) changed with similar timing to coral occurrence patterns suggesting a strong causal link with climate. In Chapters 3 and 4 I reconstructed seawater ¹⁴C and temperature of intermediate depths in the Northeast and Southwest Atlantic. During the Last Glacial Maximum, the intermediate waters at both sites were colder than present, and the similar ¹⁴C signature suggests an extension of southern-sourced waters into the Northeast Atlantic. During the early deglaciation, a pronounced warming and an increase in ¹⁴C at both locations were interpreted as a result of weakened Atlantic Meridional Oceanic Circulation (AMOC) and heat export from the Southern Ocean and downwelling diffusion. Together the precisely dated coral data revealed that changes at intermediate depths are linked to perturbations in AMOC and global climate shifts.