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Dissertation zugänglich unter
Using seafloor characteristics as indicators for past, modern and future marine environments in Potter Cove, King George Island, Antarctica
Eigenschaften des Meeresbodens als Indikatoren für vergangene, rezente und zukünftige marine Lebensräume in Potter Cove, King George Island, Antarktis
Dokument 1.pdf (8.420 KB)
Freie Schlagwörter (Englisch):
Antarctica , Hydroacoustics , Seafloor Classification , Deglaciation History , Climate Change
Betzler, Christian (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
The objective of this PhD thesis is to delineate past, modern and future environments in Potter Cove, a small tributary embayment on King George Island, South Shetland Islands, Antarctica. It is aimed to assess past and modern impacts of climate change on this representative coastal system and to suggest future developments under the recent climatic trend. Seafloor characteristics have been investigated using hydroacoustics, underwater video recordings and sediment samples. Multivariate analyses were applied to faciliate and improve the data processing and the objective interpretation of the data sets. The majority of the data was acquired during two field campaigns within the international research programme IMCOAST during the austral summer season of 2010/2011 and 2011/2012.
The deglaciation history of King George Island is still debated and subject of numerous scientific studies. In this thesis, high-resolution swath bathymetry, shallow seismics and one sediment core allowed the delineation of submarine landforms and sub-bottom characteristics in Potter Cove that are instrumental to reconstruct glacial dynamics during the Late Holocene. Furthermore, ancient and modern environmental processes are described and interpreted. The results reveal the occurrence of moraine deposits and glacial lineations in the inner part of the cove. The seafloor is made up of glacial debris that has been deposited underneath or in direct vicinity of grounded ice. This deposit is covered by a thin layer of meltwater-derived sediments. The moraine ridges evidence the occurrence of glacial stillstands and potential readvances since 2.6 cal kyr BP. Landforms on the slope in the outer cove include channel structures, ice plough marks and pockmarks. The seafloor consists of gravity flow deposits that result from sediment disturbance by deep-keeled icebergs and from sediment overload. The latter was most likely caused by the accumulation of glacial debris on top of the slope, when the glacier was situated in direct proximity. Furthermore, submarine channel structures that were eroded by meltwater discharge or turbidity currents, transport until today large amounts of sediments onto the slope.
The modern habitat distribution in Potter Cove was assessed with an acoustic seabed discrimination system that was validated by underwater video images using a linear discriminant approach. Due to the absence of wave and current measurements in the study area, bed shear stress estimates were calculated to delineate zones prone to sediment erosion. On the basis of the investigations, two habitat classes were identified in Potter Cove. The soft-sediment habitat consists of fine sediments with a scattered occurrence of echinodermata, ascidians and pennatulids. The stone habitat is instead characterised by the occurrence of stone and boulder fields with occasional sediment patches and various abundances of different macroalgae species. The habitat distribution is mainly controlled by erosion processes besides sediment supply and coastal morphology. Furthermore, seafloor characteristics in the soft-sediment habitat have been assessed in detail and subsequently attributed to environmental processes present in the study area. Sediment cores were used to identify depositional trends. A fuzzy cluster analysis was applied to classify this habitat into different marine deposition zones, including the central depressions, the transitional environment, the shallow water environment and the glacier-proximal setting.
Predictions for the future development of Potter Cove have been made based on global climate scenarios. Rapid glacial retreat has caused the establishment of the Fourcade Glacier at the land-sea interface. The predicted warming trend will sooner or later result in a complete retreat on land and change the glacier-proximal cove environment into a glacier-distal setting. Enhanced precipitation rates and stronger south-westerly winds will additionally relocate and enhance terrestrial discharge and furthermore result in changes within the water circulation system. A rather calm seafloor environment is assumed for the deeper innermost part of the cove, whereas energy conditions will be increased in the outer part and along the shallow rims of the cove. The seafloor in the outer cove will be subject to enhanced mass flow events and disturbance by ice. Regarding the habitat distribution, an expansion of the stone habitat into the cove and into deeper waters is predicted with long-term effects on the marine ecosystems in Potter Cove. The marine zonation in the soft-sediment habitat will experience a change in sediment characteristics and will shift according to new meltwater pathways and the relocation of the erosion-prone areas.