Surface and deep water variability on the Agulhas Plateau over the past 170 ka

• Main Author: Molyneux, Elizabeth Grace
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: GC Oceanography; Antarctic; Indian; Southern Ocean; The Antarctic; Antarc*; NADW; North Atlantic Deep Water; North Atlantic; Planktonic foraminifera
• Online Access: https://orca.cardiff.ac.uk/id/eprint/54751/; https://orca.cardiff.ac.uk/id/eprint/54751/1/U585140.pdf

High resolution multi-proxy analysis was undertaken on core MD02-2589 (41 26.03'S, 25 15.30'E, 2660 m water depth) from the Agulhas Plateau, Indian to Atlantic throughflow region, for the past 170 ka in order to provide a detailed record of both deep and surface ocean-climate interactions in the region. Particular focus was on Terminations I and II and Marine Isotope Stage (MIS) 5a-4 transition. Planktonic foraminifera assemblage counts and inferred sea surface temperature calculations combined with planktonic stable carbon and oxygen isotopes and ice rafted debris counts were used to show that towards the end of glacial periods MIS 6 and 2 there was a pooling of heat and salt in the throughflow region, transported to the area by the Agulhas Current. These waters were unable to be transported into the Atlantic Ocean due to the northwards position of the frontal systems associated with the Antarctic Circumpolar Current (ACC). Wider Southern Ocean warming towards the end of MIS 6, during maximum global ice volume, also shown by the benthic proxies, is seen to release a pulse of the pooled waters through the Agulhas throughflow region, some 6 ka before a Southern Ocean wide cold reversal linked to the resumption of North Atlantic Deep Water (NADW) convection to interglacial levels. This is significantly longer than ages suggested through modelling for the resumption of the thermohaline circulation interglacial mode following the recommencement of Agulhas leakage. Additional planktonic carbon isotope data from core MD02-2588 (41 19.90'S, 25 49.40'E, 2907 m water depth) show the development of a Carbon Isotope Minima Event during Terminations I and II, probably linked to the breakdown of stratification of the water column following glacial periods. Benthic stable carbon and oxygen isotope measurements combined with the sortable silt mean grain size sedimentological proxy are used to show the phasing of bottom water changes over terminations, with changes in chemical ventilation being largely decoupled from ...