Late Quaternary Glacier and Sea‐Ice History of Northern Wijdefjorden

bs_bs_banner Late Quaternary glacier and sea-ice history of northern Wijdefjorden, Svalbard LIS ALLAART , JULIANE MULLER,€ ANDERS SCHOMACKER, TOM A. RYDNINGEN, LENA HAKANSSON, SOFIA E. KJELLMAN , GESINE MOLLENHAUER AND MATTHIAS FORWICK Allaart,L., Muller,J.,Schomacker,A.,Rydningen,T.A.,H€ akansson, L.,Kjellman,S.E., Mollenhauer,G.&Forwick, M.: Late Quaternary glacier and sea-ice history of northern Wijdefjorden, Svalbard. Boreas. https://doi.org/10.1111/ bor.12435. ISSN 0300-9483. The deglaciation history and Holocene environmental evolution of northern Wijdefjorden, Svalbard, are reconstructed using sediment cores and acoustic data (multibeam swath bathymetry and sub-bottom profiler data). Results reveal that the fjord mouth was deglaciated prior to 14.5Æ0.3 cal. ka BP and deglaciation occurred in a stepwise manner. Biomarker analyses show rapid variations in water temperature and sea ice cover during the deglaciation, and cold conditions during the YoungerDryas, followed by minimum sea ice coverthroughout the Early Holocene, until c. 7 cal. ka BP.Most of the glaciers in Wijdefjorden had retreated onto land by c. 7.6Æ0.2 cal. ka BP. Subsequently, the sea-ice extent increased and remained high throughout the last part of the Holocene. We interpret a high Late Holocene sediment accumulation rate in the northernmost core to reflect increased sediment flux to the site from the outlet of the adjacent lake Femmilsjøen, related to glacier growth in the Femmilsjøen catchment area. Furthermore, increased sea ice cover, lower water temperatures and the re-occurrence of ice-rafted debris indicate increased local glacier activityand overall coolerconditions in Wijdefjorden afterc. 0.5 cal. ka BP.Wesummarize our findings in a conceptual model for the depositional environment in northern Wijdefjorden from the Late Weichselian until present. Lis Allaart ([email protected]), Anders Schomacker, Tom A. Rydningen, Sofia E. Kjellman and Matthias Forwick, Department of Geosciences, UiT The Arctic University of Norway, Tromsø N-9037, Norway; Juliane Muller€ and Gesine Mollenhauer, Helmholtz Centre for Polar and Marine Research, Alfred Wegener Institute, Bremerhaven D-27568, Germany; Lena Hakansson, Department of Arctic Geology, The University Centre in Svalbard (UNIS), Longyearbyen N-9171, Norway; received 30th August 2019, accepted 13th February 2020. Ocean-induced ice melt plays a major role in accelerated In order to understand how the present and projected mass loss and instability along the margins of glaciers futureglobalwarming will affect the glaciersin Svalbard, and ice sheets (e.g. Bindschadler 2006; Straneo et al. and to extend the knowledge of the past climate on 2010; Straneo & Heimbach 2013; Cook et al. 2016). In Svalbard beyond instrumental records, high-resolution Svalbard (74–81°N, 10–35°E), submarine melt, collapse climate records from the Late Pleistocene and Holocene and frontal ablation of modern tidewater glaciers have are needed (Hald et al. 2004; Renssen et al. 2005; been shown to be controlled primarily by ocean temper- Jakobsson et al. 2014; McKay & Kaufman 2014). Fjord ature (Luckman et al. 2015). sediments and submarine geomorphology can provide The Svalbard region and neighbouring high-latitude such information about past glacier and climate fluctu- areas are more strongly affected by the current climate ations and, seen in relation to variations in seawater warming than lower latitudes, an effect often referred to temperatures, allow us to place the current glacier retreat as the Arctic amplification (Screen & Simmonds 2010; into a broader perspective (e.g. Howe et al. 2003; Serreze & Barry 2011). Currently, the extent and thick- Forwick & Vorren 2009). ness of the perennial sea ice cover in the Arctic Ocean The Fram Strait, west of Svalbard, is the main gateway north of Svalbard decreases every year, the glaciers in of oceanic and atmospheric heat exchange between the Svalbard experience unprecedented mass loss, and the Arctic and the Atlantic Oceans (Aagaard et al. 1987; sea surface and air temperatures of Svalbard are Jakobsson et al. 2007; Beszczynska-Moller€ et al. 2011). increasing (Adakudlu et al. 2019). The distal branch of the North Atlantic Drift, the West Fifty-seven percent of the land area of Svalbard is Spitsbergen Current, transports warm saline Atlantic covered by glaciers (Nuth et al. 2013) and more than 60% Water masses (temperature >3 °C and salinity >34.9 ofglaciersinSvalbardhavetidewater margins,allofwhich PSU) northward along the west coast of Svalbard, are affected by warming sea surface temperatures whereas the East Spitsbergen Current carries cold and (Błaszczyk et al. 2009). Furthermore, 13–90% of the less saline water-masses from the Arctic Ocean into the glaciers have been estimated to be of surge-type (e.g. Barents Sea and up along thewest coast of Spitsbergen as Hagen et al. 1993; Jiskoot et al. 1998; Sevestre & Benn the Spitsbergen Coastal Current (Fig. 1). The intrusion 2015; Farnsworth et al. 2016). These glaciers have quasi- of Atlantic Water from the West Spitsbergen Current is periodic dynamically driven advances that are not directly responsible for an increased heat flux to western related to mass balance (Meier & Post 1969; Sharp 1988; Svalbard fjord systems where it affects the distribution Sevestre & Benn 2015; Aradottir et al. 2019). of surface water-masses, sea ice and, hence, the extents of DOI 10.1111/bor.12435 © 2020 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2 Lis Allaart et al. BOREAS ice caps and glaciers (Nilsen et al. 2008). Spielhagen the area north of the sill at Straumtangen and depths et al. (2011) inferred that the strongest inflowof Atlantic between ~0 and 100 m (for locations see Fig. 1; Nilsen Water into the Arctic Ocean in the past 2.0 ka has taken 2007). The intermediate layer in Wijdefjorden is most place during the last 30 years. The climate of Svalbard is, likely Transformed Atlantic Water, formed by mixing of therefore, highly sensitive to even small changes in the the surface water and intruding Atlantic Water (Fig. 2; configuration of the surrounding water and air masses, e.g. Svendsen et al. 2002). The catchment of the Wijde- making the archipelago a key location for studying the fjorden system is 4375 km2 and the fjord receives runoff impact and interaction of oceanic and atmospheric from four tidewater glaciers (Mittag-Lefflerbreen, forcing on glaciers and climate (Fig. 1; Aagaard 1982; Stubendorffbreen,Midtbreen and Nordbreen) and more Aagaard et al. 1987; Hanssen-Bauer et al. 1990; Rogers than 30 glacier-fed rivers (Fig. 1C; Hagen et al. 1993). et al. 2005; Cottier et al. 2010; Rasmussen et al. 2013; Mittag-Lefflerbreen and Stubendorffbreen drain the Miller et al. 2017). Lomonosovfonnaice capandMidtbreenandNordbreen Spitsbergen is the largest island of the archipelago and drain the Asgardfonna ice cap (Fig. 1C). Mittag- the termination of the Late Weichselian and postglacial Lefflerbreen, Stupendorffbreen and Nordbreen are sug- evolution on northern Spitsbergen remains poorly con- gested surge-type glaciers (Farnsworth et al. 2016). In strained (Slubowska et al. 2005; Bartels et al. 2017). The northern Wijdefjorden, the large lake Femmilsjøen overall objective of this study is to reconstruct the (7.691.3 km) acts as a sediment trap for discharge from postglacial environmental evolution of northern Spits- the northwestern part of Asgardfonna and the outlet bergen based on the integration of swath bathymetry, from the lake supplies the central part of the study area high-resolution seismic data and multi-proxy analyses of with fresh water (Fig. 1C). A surge-type glacier, sediment cores from the outer part of Wijdefjorden Longstaffbreen, terminates in the eastern corner of the (Fig. 1). The specific aims are to (i) reconstruct the lake (Fig. 1C; Hagen et al. 1993). In 1993, the total deglacial dynamics and the postglacial sedimentary number of glaciers in the catchment area was 202, environments; (ii) reconstruct sea-ice extent and water covering an areaof 1831 km2. This number is assumed to temperatures during the deglaciation and the Holocene; be smaller today (Nuth et al. 2013). Aerial and satellite and (iii) identify causal links between glacier retreat, images reveal that the sediment laden meltwater plumes warming sea surface temperatures and sea-ice extent. from these sources are deflected to the south on the western side of the fjord and towards the north on the © Physiographic and geological setting eastern side (TopoSvalbard Norwegian Polar Institute 2019). However, in fjords on Svalbard, changing wind Wijdefjorden is a ~110-km-long, north–south oriented directions and tidal changes can cause both large fjord in northern Spitsbergen (Fig. 1). It is the longest interannual, seasonal and short-term variations in the fjord in the archipelago, and it follows the strike of the surface water distribution (e.g. Svendsen et al. 2002; Billefjorden Fault Zone (Dallmann 2015). The fjord Forwick et al. 2010; Skarðhamar & Svendsen 2010). width increases from 3.3 km at its head to 25 km at its The bedrock of the eastern side of Wijdefjorden is mouth. Vestfjorden, a tributary fjord, joins the western primarily composed of Palaeoproterozoic to Mesopro- side of Wijdefjorden ~30 km north of the fjord head terozoic metamorphic rocks, whereas the bedrockon the (Fig. 1C). A cross-fjord sill, ~8 km wide (in N–S western side contains predominantly Devonian sedi- direction) and with a water depth of ~60 m, is located mentary rocks (Dallmann 2015). These rocks are sepa- ~50 km south of the study site (Fig. 1C). It crosses the rated by the Billefjorden Fault Zone that strikes fjord from Straumtangen to Surtfjellet and divides subparallel to the fjord axis. Wijdefjorden into an outer (northern) and inner (south- ern) basin (Fig. 1C; Kowalewski et al. 1990). Another, Glacial history narrower sill occurs where Vestfjorden and Austfjorden merge (Fig.

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