Pliocene-Pleistocene evolution of the Laurentide Ice Sheet and North Atlantic ocean circulation

Abstract

The high sensitivity of the North Atlantic to climate change makes it an ideal region to study in palaeoclimate research to understand better the workings our planet’s climate system. To this end, this thesis reports new authigenic lead (Pb) isotope and fish debris neodymium (Nd isotope; Nd) records from northwest North Atlantic IODP sites U1302/3 (~50˚N) and IODP Site U1313 (~41˚N), which are used to investigate the evolution of the North American Laurentide Ice Sheet (LIS) and North Atlantic ocean circulation during the Plio-Pleistocene. Authigenic Pb isotope records from sites U1302/3 track chemical weathering on North America, which varies as a function of LIS extent. In Chapters 3 and 4, data of this sort spanning the past ~500 kyr are used to demonstrate that the timescale of LIS retreat during each of the largest three glacial terminations of the mid- to late-Pleistocene – Terminations (T) 5 (~424 ka), T2 (~130 ka) and T1 (~14 ka) – is different; a fact that should be taken into consideration when using models of glacio-isostatic adjustment to correct estimates of sea-level highstand during interglacial marine isotope stages (MIS) 11 (~410 ka) and 5e (~124 ka), which are widely considered to represent the most recent geological analogues for near-future changes in Earth’s climate. The early timing inferred in Chapter 4 for LIS (and Greenland Ice Sheet) break-up during T5 (by ~ 418 ka) also makes it likely that the sea-level highstand associated with MIS 11 (by ~405 ka) reflects ice loss from Antarctica, and thus lies in the upper end of estimates (~+1–13 m above present). In Chapter 5, a new Nd record from Site U1313 is used to track the evolution of the end-member composition of Northern Sourced Waters bathing the deep North Atlantic during the Last Glacial Cycle (~124–0 ka). The history of high-latitude changes in climate inferred here to be responsible for this evolution is applied to older Nd records from this region to infer climate changes in the high northern latitude during the last two major transitions in Earth’s climate – the intensification of Northern Hemisphere Glaciation (3.6–2.5 Ma) and the Mid-Pleistocene Transition (1.2–0.8 Ma).