Late Weichselian ice-sheet dynamics and deglaciation history of the northern Svalbard margin

Abstract

This thesis presents new results from marine geological and geophysical studies based on sediment gravity cores, airgun, subbottom acoustic and high-resolution swath bathymetric data from fjords, the continental shelf and slope north of Nordaustlandet, Svalbard. From these records, the glacial landform assemblages as well as the glacial and postglacial sedimentary environments were interpreted. Where possible, 14C dating was performed to reconstruct the timing of deglaciation. Research presented in this thesis contributes to a better understanding of the extent, timing and rates of decay of the Svalbard-Barents Sea Ice Sheet (SBIS) during the Late Weichselian, as well as to the understanding of the glacial and interglacial processes that have shaped the northern Svalbard margin.

Kvitøya and Albertini Troughs hosted streaming ice during the Quaternary. While Kvitøya Trough has a well-developed Trough Mouth Fan (TMF) at its mouth, Albertini Trough mouth is withdrawn and lacks a TMF. The extra accommodation space for sediments created by downfaulted bedrock below Albertini Trough mouth is likely the main reason for the lack of a TMF off Albertini Trough, which shows the influence of local structural geology on TMF build-up.

Depth contours of the International Bathymetric Chart of the Arctic Ocean (IBCAO) indicate the presence of cross-shelf troughs off Duvefjorden and Albertinibukta, suggesting the source areas for the repeated ice flows feeding Albertini Trough during the Quaternary. Subglacial landforms in Rijpfjorden and Duvefjorden suggest northerly flowing ice streams in both fjords during the Last Glacial Maximum (LGM). The higher elongation ratio of the subglacial landforms in Duvefjorden and the deeper fjord basin there, suggest a larger and/or more focused ice flow in Duvefjorden compared to in Rijpfjorden.

Listric fault scarps in the Quaternary sediments of Albertini Trough mouth formed during early deglaciation due to a locally unstable sediment stratigraphy there. Overridden terminal moraines with De Geer and push moraines on top, as well as a grounding zone wedge superimposed by glacial lineations indicate multiple readvances of the grounded ice sheet during a generally slow deglaciation of the central Albertini Trough. The deglacial dynamics in Albertini Trough are partly attributed to the shallowing and narrowing of the trough itself, which facilitated ice sheet grounding there. A southwards orientation change from S-N to SSW-NNE of the glacial lineations in Albertini Trough indicates that the ice flow from Duvefjorden became increasingly dominant during deglaciation. Radiocarbon dates from the continental shelf west of Albertini Trough suggest that the retreat of the SBIS front significantly increased with time during deglaciation.

The absence of retreat-related landforms in Rijpfjorden’s deeper areas (>-210 m) as well as in Duvefjorden, suggests the presence of floating glacier fronts influenced by calving during deglaciation. Radiocarbon dates from inner Rijpfjorden and central Duvefjorden indicate that these areas were deglaciated before c. 10.6 ka and 11.0 ka, respectively. The thickness of the deglacial-postglacial sediments in Rijpfjorden and Duvefjorden reaches up to 26 m, which gives linear accumulation rates of c. 66 cm/kyr. The high sedimentation rates and steep slopes in the fjords were important for triggering mass flows, common in both fjords during the Holocene.