Cold-Water Corals as Archives for Ocean Dynamics, Environmental Conditions and Glacial Reef Accumulation

• Main Author: Hemsing, Freya
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: 500; 500 Natural sciences and mathematics; 530; 530 Physics; 550; 550 Earth sciences; Antarc*; Antarctic; North Atlantic
• Online Access: https://archiv.ub.uni-heidelberg.de/volltextserver/23858/; https://archiv.ub.uni-heidelberg.de/volltextserver/23858/1/PhDThesisFHemsing2017.pdf; https://doi.org/10.11588/heidok.00023858; https://nbn-resolving.org/urn:nbn:de:bsz:16-heidok-238586

Paleoceanographic reconstructions are fundamental for our understanding of past climate variabilities and have mainly focused on changes of circulation and environmental conditions in the surface or deep ocean. The thermocline (100 – 1000 m), acting as a link and buffer between the well-mixed warm surface and the slow and cold deep water, has been largely overlooked. In this study two cold-water coral (CWC) bearing cores from two depths in the thermocline of the southern Gulf of C´adiz (sGoC) were analysed in a mutli-proxy approach. U-series dated glacial CWCs were analysed for recorded Li/Mg temperatures, water mass 14C reservoir ages and radiogenic Nd isotope signatures (epsilonNd). For the first time, a CWC epsilonNd record was extended by two independent co-located hemipelagic sediment records. A seesaw pattern for the glacial sGoC intermediate waters alternating between predominant Eastern North Atlantic Central Water (ENACW) and Eastern Antarctic Intermediate Water (EAAIW) is proposed. Glacial ENACW and EAAIW both exhibited polar temperatures (~0°C) and more radiogenic epsilonNd signatures (~-9) than nowadays and were distinguishable by their reservoir ages, with better ventilated glacial ENACW than EAAIW. A compilation of existing CWC mound aggregation records allowed for a first estimate of initial CWC settlement in the ocean around 3.4Ma ago, coinciding with the mid-Pliocene warm period and the onset of Northern Hemisphere glaciation. Additionally, Ba isotopes (delta138/134Ba) recently introduced for seawater, was calibrated for the use in CWCs. This lays the foundation for the missing nutrient or surface biological productivity proxy in fossil CWCs.