Millennial-scale ice-ocean-climate variability during the last glacial : high-resolution records from the NE Atlantic

• Main Author: Peck, Victoria Louise
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Cardiff 2006
• Subjects: Ice Sheet; Ice Shelf; Neogloboquadrina pachyderma; North Atlantic; North atlantic Thermohaline circulation
• Online Access: https://archimer.ifremer.fr/doc/00505/61712/65680.pdf; https://archimer.ifremer.fr/doc/00505/61712/

Marine sediment core MDO1-2461 recovered from the European Margin, SW of Ireland (51° 45’ N, 12° 55’ W) at a water depth of 1153m provides material for multi-decadal to centennial scale investigation into ice-ocean-climate variability during the period 60 to 8 kyrs BP. Particular focus is placed on the oceanic and climatic conditions under which periodic collapse of the North American Laurentide ice sheet (LIS) occurred, so called Heinrich (H) events, and the involvement of the NW European ice sheets (NWEIS) within episodes of abrupt climate change. Presented here are records of circum-North Atlantic ice sheet growth, dynamics and decline from lithological and geochemical analysis of ice-rafted debris. Paired Mg/Ca and 6180 data from the surface dwelling Globigerina bulloides and subsurface dwelling Neogloboquadrina pachyderma sinistral are used to determine late-glacial variability of temperature, salinity and stratification o f the upper water column, and benthic 813C records from C. wuellerstorfi documents the interchange of glacial northern and southern-sourced intermediate water signatures along the European Margin when compared to similar records from the Portuguese Margin and high-latitude North Atlantic basin. A picture emerges that the BIS was in a continuing state of readjustment and never fully reached steady state. Persistent 2 kyr instability of the BIS fluxes throughout the late glacial (26.5-10 kyr BP) suggests that ‘precursor events’ were not directly implicated in the collapse of the LIS. However, negative salinity excursions of up to 2.6 indicate significant incursions of meltwater associated with peaks in NWEIS instability, stratifying the upper water column. Such events are associated with reduced ventilation of intermediate waters, recorded in depleted epibenthic 813C suggesting that instability and meltwater forcing of the NWEIS temporarily weakened Glacial North Atlantic Intermediate Water formation, allowing transient advance of southern-sourced waters to the site of MDO1-2461. NWEIS-instability and associated perturbation to the North Atlantic thermohaline circulation may have set the stage for H event initiation; regional cooling associated with a preliminary reduction in MOC may have promoted the growth of a LIS-fringing ice-shelf and subsequent subsurface warming and sea level rise may have destabilised the ice margin. Additionally, high-resolution summer sea surface temperature records based on the Mg/Cac. buiioides suggest that mild, even warm summer months may be a have been a feature of H events.