Holocene sea ice-ocean-climate variability from Adélie Land, East Antarctica

• Main Author: Gregory, Thomas R
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Cardiff 2012
• Subjects: Dumont d’Urville; East Antarctica; Antarc*; Antarctica; Sea ice
• Online Access: https://archimer.ifremer.fr/doc/00494/60578/64060.pdf; https://archimer.ifremer.fr/doc/00494/60578/

Marine sedimentation from the Adélie Land continental margin of East Antarctica provides unique high resolution records of Holocene environmental change. The subannually resolved sediment cores MD03-2601 (66°03.07’S, 138°33.43’E) and IODP-318-U1357B (66°24.7990′S, 140°25.5705′E) from the Dumont d’Urville Trough,Adélie Land, document atmospheric and oceanic processes impacting on biogenic sedimentation on the Adélie Land continental shelf during the Holocene. Resin embedded, continuous polished thin sections from each core were analysed for diatom content and sediment microfabric using scanning electron microscope backscattered electron imagery. The sediments contained repeating sequences of seasonal diatom-rich laminae which enabled multi-taper method time series analysis. Time series analysis shows that in the Hypsithermal there appears to have been an external (solar) control on interannual sedimentation as well as internal controls (e.g. the southern annular mode, SAM, and El Nino-southern Oscillation, ENSO); whilst in the Neoglacial internal climatic modes exerted a much stronger control. Quasi-biennial (2 – 3 year) peaks commonly occurred in analysis of both Hypsitherml and Neoglacial sequences. The distribution of resting spore-rich laminae in these sections suggests that a multidecadal (>50-years) variation between phasing of the SAM and ENSO systems may exert an important control on interannual environmental variability in the sections analysed. The distribution of diatom-derived biomarker proxies, namely C25 highly branched isoprenoid (HBI) alkenes, was compared to the diatom lamina-based record in core MD03-2601. At the Holocene scale, HBI diene and triene molecules have a positive association to sea ice associated diatom-rich laminae, with greater abundances of both HBI molecules and sea ice associated diatom laminae in the Neoglacial interval. However, at a sub-annual resolution there is no strong association between lamina type and HBI concentrations. This is attributed to a combination of: (i) the HBI alkenes recording a different signal to that of the diatom-rich laminae; (ii) interannual variation in HBI export that is greater than inter-seasonal variation, for which there is little modern data for comparison; (iii) possible diagenetic alteration of the HBI signal.