In the wake of deglaciation - sedimentary signatures of ice-sheet decay and sea-level change Studies from south-central and the western Arctic Ocean Henrik Swärd Academic dissertation for the Degree of Doctor of Philosophy in Marine Geology at Stockholm University to be publicly defended on Friday 27 April 2018 at 13.00 in William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14.

Abstract Lacustrine and marine sedimentary archives help unravel details concerning the withdrawal of large ice sheets and resulting sea-level changes during the last deglaciation (22 -11 kyr). In a series of four manuscripts, this PhD thesis investigates the sedimentological signatures from deglacial processes at three key locations in the northern hemisphere: (i) Vättern (LV) in south-central Sweden, (ii) Herald Canyon (HC) in the western Chukchi Sea, and (iii) Mackenzie Trough (MT) on the westernmost edge of the Canadian Beaufort Shelf. One lacustrine (LV) and two marine (HC and MT) sediment cores were analyzed using a broad range of methods to describe the physical, chemical, mineralogical and biological characteristics, and used to construct paleoenvironmental interpretations.

Constituting the westernmost part of the during parts of the last deglaciation, LV has long been envisaged as a key region for deglacial studies in southern Scandinavia. Sediments in LV highlight four major lake development stages following the withdrawal of the Fennoscandian Ice Sheet. These include the , the , the and the ultimate isolated lake stage. New radiocarbon dates indicate that the lake became isolated at 9530±50 cal. yr BP. A sharp transition from a varved clay unit to a partly sulfide laminated clay unit marks the final drainage of the Baltic Ice Lake, dated to 11 650±280 cal. yr BP. However, an earlier peak in pore water chlorinity identified in the sediment provides the most compelling evidence to date for an initial drainage of the Baltic Ice Lake (~12.8 cal. kyr BP) near the onset of the Younger Dryas cold event.

Located downstream from where Pacific water flows into the Arctic, HC is a key location for understanding the details of the early Holocene (~11 cal. yr BP) flooding of the Bering Strait, and investigating sedimentological proxies for Pacific water in Arctic Ocean sediment cores. The deglacial transgression of the shelf and opening of the Bering Strait is reflected in the grain size and biogenic silica content from the HC sediment core. However, a clear Pacific water signature is not seen in the clay mineralogy which exhibits increased variability after the opening of the Bering Strait. This is interpreted as a combination of Pacific and East Siberian sources for bottom waters in HC. The absence of a clear Pacific water signature in the clay mineralogy highlights potential limitations to using this proxy in other records from the western Arctic.

Far field studies from the Arctic Ocean have argued that Mackenzie River sediments in Younger Dryas age sediments can be recognized by a unique mineral and isotopic composition, but no detailed proximal study of Mackenzie River sediments exists to support this assertion. The mineral and isotopic (Sr and Nd) studies presented in this thesis from the third of the key regions, the MT, fills this gap. The results show that the mineral assemblage and ɛNd of fine fraction material remained relatively stable during the decay of the . An exception to this exists in a transitional sedimentary unit, deposited immediately after transgression at the site, and might be related to meltwater pulses associated with the drainage of the . The results suggest that the modern mineral and isotopic signature of Mackenzie River sediments may not be a suitable proxy for deglacial meltwater events in far field sedimentary records.

Keywords: paleoenvironmental changes, last deglaciation, sedimentology, Lake Vättern, western Arctic Ocean, Mackenzie Trough, Herald Canyon.

Stockholm 2018 http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-153906

ISBN 978-91-7797-163-4 ISBN 978-91-7797-164-1

Department of Geological Sciences

Stockholm University, 106 91 Stockholm