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Marine Palynomorphs from the Plio-Pleistocene interval of  the AND-1B Drill-Core McMurdo Sound, Antarctica

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posted on 12.11.2021, 00:08 by Mearns, Rory Matthew

The ANDRILL project recovered over 600 m of Plio-Pleistocene sediments within the Ross embayment, Antarctica. These sediments contain a record of local and regional paleoenvironmental conditions and glacial dynamism. They also provide a proxy for ice dynamics of the West Antarctic Ice Sheet (WAIS) during a period when global temperatures were ~3OC higher than modern. This unique record provides an analogue for future global climate change, which is expected to rise by 3OC by the end of the 21st century. Sixty-one samples from the upper 600 m of the AND-1B core were analysed for their palynomorph content yielding 4 to 5380 grains per sample (with an average frequency of 34 grains per gram). Marine palynomorphs including fossil dinoflagellate cysts, acritarchs, and prasinophyte algae were the focus of this study and fluctuations in their abundance and diversity reflect changes in paleoenvironment and glacial dynamics.  The upper 600 m can be divided into 6 discrete units based on the palynomorph assemblage: The early-Pliocene (~5.0 – 4.6 Ma. Unit 1) is characterised by relatively high abundances of in situ round brown dinoflagellate cysts, microforaminiferal linings, and Leiosphaeridia, suggesting warmer than modern paleoenvironmental conditions and seasonal ice within the Ross embayment. The WAIS was likely small and highly dynamic during Unit 1. The mid-Pliocene (~4.6 – 3.4 Ma. Unit 2) exhibits relatively high abundances of round brown dinoflagellate cysts, microforaminiferal linings, and scolecodonts. The relatively low abundance of Leiosphaeridia (understood to indicate proximal/seasonal ice) suggests that ice free conditions at the drill site may have existed for up to ~1.2 Ma and that this may be the warmest period recorded in the core. During the warm, mid-Pliocene interval a sudden increase in scolecodonts (fossilized polychaete remains) may give indications into the water depth at the drill site because of their dependence on physical disturbance (decreasing with depth) for population growth. Further study of the scolecodonts is required before confident estimates of water depth can be made. The mid- to late-Pliocene (~3.4 – 2.6 Ma. Units 3, 4 & 5) is characterised by a variable palynomorph assemblage indicating variability in paleoenvironmental conditions, ice cover at the drill site, and ultimately a variable WAIS. A spike in the prasinophyte alga Cymatiosphaera (understood to indicate reduced salinity) at the base of a diatomite unit in the late-Pliocene may be a record of algae thriving in meltwater from the collapse of the WAIS. Further highresolution analysis is needed to help resolve this event. The Quaternary interval (~2.6 Ma and younger. Unit 6) is significantly different from previous units and is dominated by reworked Eocene dinoflagellate cysts and acritarchs (the “Transantarctic Flora”). This interval records a period of significant cooling and glacial expansion and the WAIS likely grew to its modern “polar” state. The WAIS may have undergone several collapses during super-interglacial periods in the Pleistocene but if it did it did not persist in its collapsed state for significant periods of time.

History

Copyright Date

01/01/2010

Date of Award

01/01/2010

Publisher

Te Herenga Waka—Victoria University of Wellington

Rights License

Author Retains Copyright

Degree Discipline

Geology

Degree Grantor

Te Herenga Waka—Victoria University of Wellington

Degree Level

Masters

Degree Name

Master of Science

Victoria University of Wellington Item Type

Awarded Research Masters Thesis

Language

en_NZ

Victoria University of Wellington School

School of Geography, Environment and Earth Sciences

Advisors

Hannah, Mike; Naish, Tim