Coupling of the cryosphere and ocean during intervals of rapid climate change in the palaeo record: a multi-proxy study of the Heinrich events of the last glacial from the Northeast Atlantic

• Main Author: Crocker, Anya Jane
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Ice Sheet; North Atlantic; Northeast Atlantic; Planktonic foraminifera; The Cryosphere
• Online Access: https://eprints.soton.ac.uk/364163/; https://eprints.soton.ac.uk/364163/1/Crocker_PhD_2013.pdf

Determining the response of the global thermohaline circulation to freshwater perturbations is of vital importance for future climate modelling efforts. The Heinrich events of the last glacial provide classic case studies, with major episodic inputs of freshwater associated with large numbers of icebergs flooding the North Atlantic Ocean. Climate modelling experiments and proxy reconstructions have both indicated a significant decrease in the strength of the meridional overturning circulation in response to this fresh water input to the ocean during each Heinrich event. Here, I present high resolution, multi-proxy reconstructions of cryospheric and surface and deep ocean behaviour over the last 40,000 years from Ocean Drilling Project (ODP) Site 980 in the northeast Atlantic, incorporating Heinrich events 1 to 4. Oxygen, carbon and neodymium isotope reconstructions of bottom water chemistry show a unique signature at this site for every Heinrich event, indicating the influence of a different water mass during each event. Bulk sediment leachate neodymium isotope values are strongly offset towards more radiogenic values than both planktonic foraminifera and fish debris throughout the Holocene, however, the agreement between the substrates is much closer under glacial conditions. This observed offset is attributed to modification of the leachate signal by fine material transported by strengthened bottom current activity in the Holocene, suggesting that bulk sediment leachates may not always record bottom water chemistry faithfully at sediment drift sites. Rare earth element profiles suggest that foraminifera without their ferromanganese coatings removed do not undergo significant diagenetic modification in the sediment, making these a better choice for reconstructions of bottom water neodymium isotope signatures. Each Heinrich event shows a different sequence of changes in the lithologies of ice-rafted debris, which argues against a simple repeating pattern of ice sheet destabilisation at each Heinrich event. The ...