Tracking deep-water flow on Eirik drift over the past 160 kyr: linking deep-water changes to freshwater fluxes

This dissertation uses surface and deep ocean proxies to understand changes in North Atlantic deep-water production associated with periods of increased freshwater input throughout the Late Pleistocene and Holocene. Coring sites on Eirik Drift have long-term sedimentation rates exceeding 15 cm/kyr., allowing for paleoceanographic reconstructions on Milankovitch and millennial time scales. The transition from glacial North Atlantic Intermediate Water (gNAIW) of marine isotope chron (MIC) 2 to North Atlantic Deep Water (NADW) during the Holocene is examined in Chapter 1. Early Holocene (9000-10,500 ka), sedimentation rates in core 21GGC (3471 m) are >100 cm/kyr., indicating gNAIW winnowed upstream glacial sediments, depositing at 21GGC. Enhanced sediment deposition persisted until ~9ka when long-term rates leveled off at 40 cm/kyr., indicating NADW density had stabilized. From 8.6 to 8.2 ka, catastrophic drainage of glacial Lake Agassiz poured freshwater into the North Atlantic disrupting deep-ocean circulation. Chapter 2 focuses on the past 160 kyr at Site 1306 (2272 m) on the Eirik Drift where highest sedimentation rates occurred during MIC 2- 5d. Mean sortable silt (SS) and ?18O of N. pachyderma (s) are inversely related during this interval, indicating that changes in surface conditions above the Eirik Drift are propagated into the deep ocean. During the past 40 kyr., SS decreases are concomitant with instances of surface ocean freshening. These intervals correlate with Heinrich Events, suggesting that massive ice flows released from the continents altered deep ocean circulation. The final chapter examines deep-ocean response during Terminations 1 and 2. Higher insolation forcing across Termination 2 is postulated to promote rapid melting of continental glaciers, leaving little opportunity for continental storage of freshwater. Conversely, lower insolation across Termination 1 allowed continental ice to linger, allowing for the routing and rapid release of freshwater creating abrupt climate reversals (H1, YD and 8.2 kyr Event). Deep-ocean circulation during MIC 5e loses buoyancy in a fashion similar to the Holocene; however, maximum flow velocities are curtailed for ~7 kyr after the onset of interglacial conditions. This lag is best explained by the melting of Greenland into areas of NCW convection due to increased insolation forcing.Ph.D.Includes bibliographical references.by Samuel Straker Henderso