Date of Award

8-2020

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Sandra Passchier

Committee Member

Stefanie Brachfeld

Committee Member

Jorge Lorenzo Trueba

Abstract

IODP 347 Site M0065 was drilled to assess the last deglaciation of the Scandinavian Ice Sheet (SIS) within the southern Baltic Sea Basin (BSB) from ~20 ka BP. Site M0065 was drilled in the Baltic Sea within the Bornholm Basin in a water depth of 87m. It provided the opportunity to study the development of the Baltic Ice Lake (BIL), which occupied the southern BSB between ~17 and 11 ka. Previous studies in this area looking at glacial till and surface exposure dates have dated the deglaciation of Bornholm Island, and consequently Site M0065, at ~16.3 ka BP. A visual inspection of the high-resolution images of cores from site M0065B indicates clay size fraction sediment was deposited from Core 1H down to Core 12H, 36 mbsf, where glacial sand/silt and clay varves are introduced. Within the clay sections color variations are observed indicating a compositional or chemical change. Glacial varve counting determined that the site was influenced directly by seasonal glacial melting for approximately 50 years. Sixty-seven samples were taken from core M0065B (3.2 to 49.1 mbsf) to analyze particle size distributions from 0.02μm to 2mm, and 23 of them were analyzed as part of this study. Grain size and geochemical XRF and ICP-MS data was used to indicate the cause of color variation and determine whether site M0065 was influenced by proximal seasonal ice sheet melting within the BIL, followed by sediment deposition within a stagnant, non-circulating, BIL with changing provenance and lake anoxic conditions. The succession of the rapid retreat of the SIS and transition from a proximal to distal glaciolacustrine environment to the drainage events of the BIL is seen within Bornholm Basin and is marked with changes in grain size and geochemistry of the sediment deposited. Al/Ti and Mn/Al ratios do not indicate a provenance or bottom water oxidation change, but Zr/Al ratios do indicate an increase in meltwater strength. Br/Al and a dramatic increase in sulfur, both proxies for organic content, further indicate reworking of previously deposited sediment due to the BIL drainage event at 12.9 ka BP. The marine incursion into deep lacustrine depositional environment of the BIL Yoldia Sea (YS) at 10.5 ka BP and transition to the freshwater stage of the (YS) is seen with an increase in Mn/Al ratios and the change in grain size along with the emerging presence of brackishfreshwater diatoms.

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