Deciphering the role of varying iceberg source in abrupt climate change

North, Rachel 2016. Deciphering the role of varying iceberg source in abrupt climate change. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Heinrich events involve the massive release of icebergs from continental ice sheets into the sub-polar North Atlantic, which travel as far south as 40°N and deposit large quantities of Ice Rafted Debris (IRD) in marine sediments. Determining the distribution of IRD sources across the Atlantic during Heinrich events is a vital step in ascertaining the sequence of iceberg rafting, and the relative involvement of circum-North Atlantic ice sheets in this release of freshwater to the North Atlantic. This study examines evidence from multiple radiogenic isotope (Nd, Sr and Pb) analyses on the detrital clay size fraction (<2μm), and stable isotopes in the detrital <63 μm fraction of a Hudson Strait (HS) source (δ18O of <-2.5 and εNd of <-19) in the clay and fine fraction deposited at the IRD belt site during Heinrich events. At the north-eastern British margin changes in detrital δ18O and εd are related to small inputs of HS derived material during H4, however during H2 there is no discernible HS source to the fine fraction this is contrary to previous coarse fraction studies at the site. It is proposed that the dominance of the British and Irish Ice Sheet (BIIS) source at the site during H2 is due to the increasing size of the British Ice sheet over the course of the last glacial. Endmember modelling of particle size distributions demonstrate a coarsening of the silt fraction over the Heinrich events at the IRD belt site. At the margin of the BIIS there is a correspondence between millennial scale IRD events and coarse particle size distributions which is superimposed on increases in the finest endmember over the last glacial in response to the BIIS reaching the shelf edge. Changes in stable isotopes of surface dwelling foraminifera demonstrate that the surface waters were fresher during H2 and H4 coinciding with fine fraction IRD inputs. At the British ice sheet margin, increasing surface water stratification after 27 ka BP coincides with increases in fine particle size endmember and δ18O of the fine fraction further indicating the consistent presence of the BIIS at the shelf edge after 27 ka BP.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QD Chemistry Q Science > QE Geology
Date of First Compliant Deposit:	6 May 2016
Last Modified:	10 Aug 2021 13:23
URI:	https://orca.cardiff.ac.uk/id/eprint/90591

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