Ingólfsson, Ó. 2011. Fingerprints of Quaternary Glaciations on Svalbard

Geological Society, London, Special Publications

Fingerprints of Quaternary glaciations on Svalbard

Ó. Ingólfsson

Geological Society, London, Special Publications 2011; v. 354; p. 15-31 doi: 10.1144/SP354.2

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O´ . INGO´ LFSSON Faculty of Earth Sciences, University of Iceland, Sturlugata 7, Is-101 Reykjavı´k, Iceland and The University Centre in Svalbard (UNIS) (e-mail: [email protected])

Abstract: Marine and terrestrial archives can be used to reconstruct the development of glacially influenced depositional environments on Svalbard in time and space during the late Cenozoic. The marine archives document sedimentary environments, deposits and landforms associated with the Last Glacial Maximum (LGM) when Svalbard and the Barents Sea were covered by continental-scale marine-based ice sheet, the last deglaciation and the work of tidewater glaciers in interglacial setting as today. The terrestrial archives record large-scale Quaternary glacial sculpturing and repeated build-up and decay of the Svalbard–Barents Sea ice sheet. The fingerprinting of Quaternary glaciations on Svalbard reflects the transition from a full-glacial mode, with very extensive coverage by the Svalbard–Barents Sea ice sheet and subsequent deglaciation, to an interglacial mode with valley, cirque and tidewater glaciers as active agents of erosion and deposition. Conceptual models for Svalbard glacial environments are useful for understanding developments of glacial landforms and sediments in formerly glaciated areas. Svalbard glacial environments, past and present, may serve as analogues for interpreting geological records of marine-terminating and marine-based ice sheets in the past.

Svalbard is an archipelago in the Arctic Ocean that Nordaustlandet, but large valley glaciers and comprises all islands between 748N–818N and cirque glaciers are frequent along both the west 108E–358E (Fig. 1). The principal islands are Spits- and east coasts of Spitsbergen. Small ice caps also bergen, Nordaustlandet, Barentsøya, Edgeøya, exist on the eastern islands, Edgeøya and Barentsøya Kong Karls Land, Prins Karls Forland and Bjørnøya (Fig. 1). On Spitsbergen, glaciation is most extensive (Bear Island). The total area of Svalbard is in areas near the eastern and western coasts, where 62 160 km2. The West Spitsbergen Current, which many glaciers terminate in the sea. In contrast, gla- is a branch of the North Atlantic Current, reaches ciers in the central part of the island are smaller, the west coast of Svalbard, keeping water open mainly because of low precipitation (Humlum most of the year. The present climate of Svalbard 2002). A significant number of glaciers in Svalbard is Arctic, with mean annual air temperature of are of the surging type. The surges are relatively c. 26 8C at sea level and as low as 215 8Cin short intervals (,1to.10 a) of extraordinary fast the high mountains. Most of Svalbard is situated flow which transfer mass rapidly down-glacier, within the zone of continuous permafrost (Humlum punctuating much longer quiescent periods (,10 et al. 2003). Precipitation at sea level is low, only to .200 a) characterized by stagnation when ice c. 200 mm water equivalent (w.e.) in central Spits- builds up in an upper accumulation area forming a bergen and c. 400–600 mm w.e. along the western reservoir of mass for the next surge (Dowdeswell and eastern coasts of the island. The Svalbard et al. 1991, 1999; Lønne 2004; Sund 2006). Lefau- landscape, in particularly the island of Spitsbergen, connier & Hagen (1991) suggested that the majority is generally mountainous with the highest eleva- of Svalbard glaciers surged. The mass balance of tion of c. 1700 m a.s.l. on north-eastern Spitsbergen. many glaciers in Svalbard is partly controlled by Large glacially eroded fjords are numerous, parti- snowdrift during the winter (Humlum et al. 2005). cularly at the northern and western coasts of Spits- The equilibrium-line altitude (ELA) rises on a trans- bergen where the Wijdefjorden, Isfjorden and Van ect from west to east across Spitsbergen (Fig. 1), Mijenfjorden fjords have lengths of 108, 107 and reflecting the distribution of precipitation very well. 83 km, respectively. Some coastal areas are charac- On Prins Karls Forland and along the central west terized by strandflat topography: low-lying bedrock coast it lies at 300 m a.s.l., but reaches .700 m in plains often blanketed by raised beaches. the highlands of north-eastern Spitsbergen. About 60% of Svalbard is covered by glaciers There are two end-member modes of glacieri- (Hagen et al. 1993, 2003), with many outlet glaciers zation on Svalbard: a full-glacial mode, when terminating in the sea. Svalbard ice caps and gla- Svalbard and the Barents Sea were covered by a ciers cover about 36 600 km2, with an estimated large marine-based ice sheet, and an interglacial total volume of c. 7000 km3 (Hagen et al. 1993). mode (like today) when the Svalbard glacial Most of the ice volume is contained in the high- system is dominated by highland ice fields, ice land ice fields and ice caps on Spitsbergen and caps and numerous valley and cirque glaciers. The

From:Martini, I. P., French,H.M.&Pe´rez Alberti, A. (eds) Ice-Marginal and Periglacial Processes and Sediments. Geological Society, London, Special Publications, 354, 15–31. DOI: 10.1144/SP354.2 0305-8719/11/$15.00 # The Geological Society of London 2011. 16 O´ . INGO´ LFSSON

Fig. 1. The Svalbard archipelago with distribution pattern of the equilibrium-line altitude (ELA) given as 100 m contour intervals (modified from Hagen et al. 2003). The islands of Hopen (SE from the Svalbard archipelago) and Bjørnøya (midway between Norwegian mainland and Spitsbergen) are not on the map. full-glacial mode leaves pronounced fingerprints on Full-glacial-mode sediments and the continental shelf margins and slopes, and during landforms deglaciation sediments and landforms are deposited on the continental shelf and in fjords around The timing of the onset of Cenozoic Northern Hemi- Svalbard. Most sedimentation occurs subglacially sphere high-latitude glaciations is not well known. in fjords and on the shelf, and ice-marginally on Ice rafted debris (IRD) and foraminiferal data from the continental break and slope. There is prevailing Arctic basin deep-sea sediment cores suggests that erosion inside the present coast, but a strong sig- episodical perennial sea ice might have occurred nal of glacial isostasy in response to deglaciation as early as the middle Eocene 47.5 million years where sets of raised beaches mark deglaciation ago (Ma) (Stickley et al. 2009). It is recognized and marine transgression. The interglacial mode is that sea-ice cover existed in the central Arctic basin characterized by fjord and valley sedimentation by the middle Miocene (Darby 2008; Krylov et al. below and in front of polythermal and surging 2008), but ice-sheet build-up over the Svalbard– glaciers. The interglacial mode of glacierization Barents Sea region probably did not initiate produces landform-sediment assemblages that can until the Pliocene–Pleistocene, 3.6–2.4 Ma (Knies be related to the tidewater glacier landsystem et al. 2009). Sejrup et al. (2005) suggested that (Ottesen & Dowdeswell 2006), the glaciated valley extensive shelf glaciations started around Svalbard landsystem (Eyles 1983) and the surging glacier at 1.6–1.3 Ma. The number of full-scale ice-sheet landsystem (Evans & Rea 1999). The glacial finger- glaciations over Svalbard–Barents Sea is not printing on Svalbard is primarily reflecting the known, but Solheim et al. (1996) suggest at least transition from a full-glacial mode to an intergla- 16 major glacial expansion events occurred over cial mode. the past 1 Ma. Laberg et al. (2010) reconstructed the FINGERPRINTS OF GLACIATIONS ON SVALBARD 17 late Pliocene–Pleistocene history of the Barents Sea are separated by shallow bank areas. Less dynamic ice sheet, based on three-dimensional seismic data ice probably existed on shallower banks (Landvik from the south-western Barents Sea continental et al. 2005; Sejrup et al. 2005; Ottesen et al. 2007). margin. They inferred that a temperate Barents Studies of large-scale margin morphology and Sea ice sheet with channelized meltwater flow seismic profiles have identified large submarine developed during the late Pliocene–Early Pleisto- trough-mouth fans (TMF) at the mouths of several cene. More polar ice conditions and a Barents major cross-shelf troughs (Fig. 2) (Vorren et al. Sea ice sheet that included large ice streams, with 1989; Sejrup et al. 2005). These are stacked units little or no channelized meltwater flow, occurred of glaciogenic debris flows interbedded with hemi- in the Middle and Late Pleistocene. There are both pelagic sediments displaying thickness maxima marine and terrestrial geological archives that high- along the shelf edge, and reflect direct sediment light full-glacial-mode conditions and subsequent delivery from an ice stream reaching the shelf deglaciation. edge (Vorren et al. 1989; Vorren & Laberg 1997). Andersen et al. (1996) defined five lithofacies Marine archives groups from cores retrieved from the western Svalbard continental slope. Laminated-to-layered The dimensions and dynamics of the Last Glacial mud and turbidites reflect post-depositional rework- Maximum (LGM) Svalbard–Barents Sea ice sheet ing of the shelf banks, caused by eustatic sea-level are reflected in the submarine sediments and land- fall during ice growth. Hemipelagic mud represents forms preserved on the seafloor of the deglaciated the background sediments and is evenly dispersed shelves and fjords (Ottesen et al. 2005). Marine over the entire continental margin. Homogeneous archives that contain information on former and heterogeneous diamictons were deposited ice-extent and ice dynamics include the following. during glacial melt events (hemipelagic mud with ice-rafted debris) and during peak glaciation on the Shelf bathymetry. Landforms include glacial submarine fans (debris-flow deposits). Large-scale troughs, submarine transverse ridges, mega-scale slope failures have affected the glaciogenic deposits glaciallineations,elongateddrumlinsandrhombohe- along the western Barents Sea margin (Kuvaas & dral ridge systems. These delineate the drainage of Kristoffersen 1996; Laberg & Vorren 1996). The glaciers and show that the shelf areas have largest TMFs occur in front of the Storfjorden been shaped by erosion and deposition below and in and Bear Island trough mouths (Fig. 2), probably front of moving outlet glaciers and ice streams. reflecting where the largest Svalbard–Barents High-resolution seismic records. These show Sea palaeo-ice streams entered the western shelf glacial unconformities and give information on break (Faleide et al. 1996; Vorren & Laberg 1997; thickness, extensions and architecture of sediments Andreassen et al. 2008). The oldest Storfjorden above basement rocks. These records signify the and Bear Island TMF sediments have been esti- extent of glacial erosion and subsequent deposition mated to be c. 1.6 Ma (Forsberg et al. 1999; Butt on the shelf. et al. 2000). Whereas TMFs can be regarded as archives Sediment cores. These include sedimentological and of numerous glaciations, most sediments and land- petrographic analyses for identifying tills and gla- forms on the shelf and in the fjords relate to the ciomarine sediments. Sediment cores are used to LGM and subsequent deglaciation. End-moraines verify seismic records. The tills are first-order have been identified at several locations on the shelf evidence on former ice extent, and 14C dates from (Ottesen et al. 2005, 2007; Ottesen & Dowdeswell glaciomarine sediments provide constraining mini- 2009), suggesting outlet glaciers and ice streams mum dates for deglaciation of the shelf areas. draining the Svalbard fjords and a shelf-edge glacia- The seafloor morphology of the Svalbard margin tion along the major part of the margin during the west and north of the archipelago is characterized LGM. Ottesen et al. (2005, 2007) and Ottesen & by a series of deep fjord-trough systems separated Dowdeswell (2009) recognized an assemblage of from one another by intervening shallow banks. sediments and landforms that can be used to infer This is caused by the actions of ice sheets and ice the flow and dynamics of the last ice sheet on streams during the Pleistocene, where the extent of Svalbard (Fig. 3). They distinguished between the Svalbard–Barents ice sheet during peak gla- inter-ice-stream and ice-stream glacial landform ciations was repeatedly limited by the shelf edge assemblages, which reflect different glacial (Solheim et al. 1996; Vorren et al. 1998). Sejrup dynamics associated with ice streams in fjords and et al. (2005) concluded that the morphology troughs and slower moving ice between the strongly reflected that fast-moving ice streams troughs and ice streams. They identified five had repeatedly entered the continental shelf areas, subsets of landforms that make up the inter-ice- creating numerous glacial troughs/channels that stream glacial landform assemblage, and labelled 18 O´ . INGO´ LFSSON

Fig. 2. Location of large submarine trough-mouth fans (TMF), reflecting where the largest Svalbard–Barents Sea palaeo-ice streams entered the western shelf break (modified from Vorren et al. 1989). them 1 to 5 by their relative age of deposition in fjords prior to deglaciation). The crag-and-tail (Fig. 3a). landforms (3 on Fig. 3a) are streamlined features with an upstream core of bedrock and glacial Landforms relating to ice advance to the shelf edge. sediments deposited in lee of the bedrock knob, pro- These are glacial lineations orientated in the direc- duced at the bed of moving ice. tion of ice flow across the shelf, and a well-defined The sediment-landform sets (4) and (5) (Fig. 3a) linear belt of hummocky terrain inferred to represent defined by Ottesen & Dowdeswell (2009) were the shelf-edge ice grounding zone (1 on Fig. 3a). produced during the Holocene and belong to The glacial lineations are sets of parallel subdued interglacial-mode tidewater glacier sediment- ridges that have amplitudes of less than 1 m and a landform assemblages. These include basin fills wavelength of several hundred metres. The hum- within fjords (4), representing fine-grained sediment mocky belt is a well-defined, continual and linear deposition linked to the discharge of turbid melt- belt of irregular hummocky terrain about one kilo- water from tidewater glacier margins and submarine metre in width, where hummocks and ridges have slides from steep fjord walls, demonstrating slope amplitudes of c. 5 m. The belt terminates abruptly instability. Landforms of recent ice re-advance and at the shelf edge (Fig. 3a), and Ottesen & Dowdes- retreat at fjord heads (5) include large terminal well (2009) suggest that this terrain represents the moraines within a few kilometres of present tide- grounding zone of an ice margin. water glacier margins, recording re-advance associated with the Little Ice Age and subsequent retreat Landforms of ice retreat across the shelf during marked by deposition of small, sometimes annual deglaciation. These are large and small transverse transverse ridges. moraine ridges; small ridges are interpreted to be The ice-stream glacial landform assemblage retreat moraines whereas the larger ridges probably (Fig. 3b) of Ottesen & Dowdeswell (2009) recog- mark stillstands during retreat of a grounded ice nizes sediment-landform subsets that characterize margin (2 on Fig. 3a). The lateral continuity of the the action of active ice streams in cross-shelf ridges over a number of kilometres also implies troughs. systematic retreat along a wide ice front. Mega-scale glacial lineations and lateral ice- Landforms of ice retreat from fjord mouths to fjord stream moraines. The mega-scale glacial lineations heads. These are arcuate moraines (suggesting poss- are streamlined linear and curvilinear submarine ible glacial re-advance to fjord mouths and/or still- features elongated in the direction of the long axis stands during deglaciation), crag-and-tail features of the depressions, observed in several major and small transverse ridges (suggesting active ice fjords and cross-shelf troughs on the Svalbard FINGERPRINTS OF GLACIATIONS ON SVALBARD 19

Fig. 3. Schematic models of submarine glacial landforms on Svalbard continental margins. (a) An inter-ice-stream glacial landform assemblage, located between fast-flowing ice streams. (b) An ice-stream glacial landform assemblage, where fast-flowing ice was fed from large interior drainage basins. The landforms are labelled by their relative age of deposition, where 1 denotes the oldest landform (modified from Ottesen & Dowdeswell 2009). 20 O´ . INGO´ LFSSON margin (Ottesen et al. 2007; Ottesen & Dowdeswell of years (Dowdeswell et al. 2008). The diamictic 2009). They vary from hundreds of metres to more grounding-zone wedges were produced by continu- than 10 km in length and up to 15 m in height. ing sediment delivery from the deforming beds of The mega-scale lineations probably result from soft- active ice during the stillstands (Dowdeswell et al. sediment deformation at the base of fast-flowing 2008). The transverse ridges that are observed on ice streams (Dowdeswell et al. 2004). Lateral the continental shelf to the side of the troughs ice-stream moraines (1 on Fig. 3b) are individual (Fig. 3b) have been interpreted to be recessional linear ridges of tens of kilometres in length and up push moraines reflecting stillstands or winter- to c. 40–60 m high that have been observed along summer ice-front oscillations during deglaciation some of the lateral margins of cross-shelf troughs (Ottesen & Dowdeswell 2006). Individual ridges in Svalbard. Ottesen et al. (2005, 2007) described are up to 15 m high, are spaced a few hundred metres linear ridges of tens of kilometres in length and up apart and usually occur in clusters rather than as to 50 m in relative elevation running along the isolated individual features. lateral margins of the Isfjorden and Kongsfjorden Dowdeswell et al. (2008) argued that the mega- cross-shelf troughs as they approach the shelf scale glacial lineations were products of rapid ice break west of Svalbard. Sub-bottom profilers do retreat, whereas the grounding-zone wedges sug- not generally achieve acoustic penetration of these gested episodic retreat. They interpreted suites of ridges, implying that they are made up of relatively transverse ridges to be indicative of relatively slow coarse diamictic sediments. These extensive lateral retreat of grounded ice margins. ridges are interpreted to define the lateral margins Seismic record and sediment core data. These data of fast-flowing former ice streams (Ottesen et al. (Fig. 4) concur with the bathymetric data on the 2005, 2007). glacial origin of landforms and sediments described above. Unconformities caused by glacial erosion Grounding zone wedges and transverse ridges. provide strong reflectors (Solheim et al. 1996). Grounding zone wedges are large seafloor ridges When the marine sequence is penetrated by corers, orientated transverse to the direction of former ice stiff diamictons, interpreted to be subglacial tills flow and occur both at the shelf edge and in the deposited below grounded glaciers in the fjords troughs and fjords of Svalbard. The ridges are and out on the shelf, are retrieved (Svendsen et al. characteristically tens of metres high, up to several 1992, 1996; Landvik et al. 2005). The diamictons kilometres wide and tens of kilometres long. Acous- are overlain everywhere by fine-grained marine or tic stratigraphic records show that the ridges form glaciomarine muds (Elverhøi et al. 1980, 1983; sedimentary wedges lying above strong basal reflec- Sexton et al. 1992). Radiocarbon ages on subfossil tors. Ottesen et al. (2007) concluded that although shells from the muds give constraining ages for the sedimentary wedges sometimes only have rela- the muds as being of deglaciation ages and the dia- tively subtle vertical expression on the sea floor, mictons having been deposited in connection with they may contain a few cubic kilometres of sedi- the LGM expansion of ice. ments. Where these extensive ridges and underlying sedimentary wedges are found in the troughs and Terrestrial records fjords of Svalbard (2 on Fig. 3b) they are interpreted as marking major stillstands of the ice margin during While the marine archives contain evidence of general deglaciation (Landvik et al. 2005; Ottesen repeated expansions of the Svalbard–Barents Sea et al. 2007), lasting for hundreds rather than tens ice sheet to the continental margin around Svalbard,

Fig. 4. Sketch of seismic section along Isfjorden, Svalbard. A moraine ridge at the shelf edge marks LGM extension of an ice stream in the Isfjorden trough, and stiff diamicton is interpreted to be till deposited by the last major glaciations (modified from Svendsen et al. 1996). FINGERPRINTS OF GLACIATIONS ON SVALBARD 21 the terrestrial record of full-scale glaciations is more fragmentary because of the prevailing erosion at times of major ice-sheet expansion. Volume esti- mates of sediments offshore have been argued to indicate that 2–3 km of rock has been removed from central Spitsbergen since the Eocene (Eiken & Austegard 1987; Vorren et al. 1991). It has been suggested that at least half of this volume was removed during the Pleistocene glaciations (Svendsen et al. 1989; Dimakis et al. 1998; Elverhøi et al. 1998), and it has been assumed that the bedrock geomorphology of Svalbard is predominantly the result of Quaternary sculpturing (Hjelle 1993). The landscapes of Svalbard are characterized by extensive glacial carving of cols, valleys and fjords where the glaciers have enhanced pre-glacial fluvial and tectonic landscapes. Svend- sen et al. (1989) pointed out that erosion of the major fjords below sea level requires large ice sheets with outlet glaciers at the pressure melting point at their base. They also concluded that the pronounced alpine landscape of Svalbard indicated that cirque and valley glaciers, rather than ice sheets, were mainly responsible for carving the valleys and other high-relief landforms and that glacial erosion by polythermal valley glaciers is the most important geomorphic process in the present climate. Fig. 5. Reconstruction of the Svalbard–Barents Sea ice Evidence of more extensive ice cover than today sheet and its fast-flowing ice streams (modified from during the LGM and previous glaciations is present Ottesen et al. 2005). on every ice-free lowland area around Svalbard outside the Neoglacial limits in the form of glacial drift, erratics and striations (Sollid & Sørbel 1988; Svalbard–Barents Sea ice sheet that covered most Salvigsen et al. 1995). Directional evidence gener- of Svalbard and its shelf areas (Fig. 5). ally suggests ice flow offshore towards the shelf As there is overall erosion on land on Svalbard areas on western Svalbard (Kristiansen & Sollid during repeated glaciations, the pre-late Quaternary 1987; Landvik et al. 1998). Evidence on ice thick- (Saalian) glacial history of Svalbard lacks all details ness and ice movements during the LGM include (Svendsen et al. 2004). There are a number of key- ice-abraded ridge crests roche moutonneés, stria- lithostratigraphical sections that contain tills and tions, erratics and glacial drift on nunataks and marine sediments that have been dated or correlated coastal mountains. A number of studies have to late Quaternary Svalbard–Barents Sea ice addressed the thickness of the Svalbard–Barents sheet oscillations (Mangerud et al. 1998) (Fig. 6): Sea ice sheet over Svalbard during the LGM. A Kongsøya (Ingo´lfsson et al. 1995), Kapp Ekholm long-standing debate exists on whether morphological data (such as the existence of pre-LGM sets of raised beaches and large rock glaciers) could be taken to suggest the existence of ice-free enclaves on the lowlands of western and northern Svalbard (Landvik et al. 1998, 2005; Andersson et al. 1999; Houmark-Nielsen & Funder 1999). There is a growing consensus that although some coastal mountains may have protruded as nunataks above the ice-sheet surface at LGM on the outer coast of northern and western Svalbard, there are very little data to support the existence of any lowland ice- free enclaves (Landvik et al. 2003, 2005; Ottesen et al. 2007). Taken together, marine and terrestrial evidence suggest a LGM configuration of the Fig. 6. Location of key stratigraphic sites on Svalbard. 22 O´ . INGO´ LFSSON

(Mangerud & Svendsen 1992), Skilvika (Landvik et al. 1992), Linneélva (Lønne & Mangerud 1991), Site 15 (Miller et al. 1989), Kongsfjordhallet (Houmark-Nielsen & Funder 1999) and Poole- pynten (Andersson et al. 1999). Most stratigraphic key sites are on the west coast of Svalbard, but the recently described site from Murchisonfjorden, Nordaustlandet (Fig. 6) (Kaakinen et al. 2009) adds to our understanding of late Quaternary glacial events on Svalbard. One striking characteristic of the lithostratigraphical records from coastal Sval- bard is that sections often reflect glaciation events in the form of repeated regressional sequences (Figs 7 & 8). Each cycle consists of a basal till (Fig. 8a) deposited during a regional glaciation large enough for isostatic depression to cause transgression and deposition of glaciomarine–marine sediments on top of till as the ice sheet retreats (Fig. 8b, c). Glacial unloading and isostatic rebound causes a coarsening-upwards sequence where sublittoral sediments and beach foresets reflect regression (Fig. 8d, e). This is particularly well expressed in the stratigraphic record from Kapp Ekholm (Fig. 7). Raised beaches around Svalbard can generally be regarded as isostatic fingerprinting of earlier expanded ice volumes compared to present. Post- glacial raised beaches have been described from most ice-free coastal areas (Forman 1990; Landvik et al. 1998), and the elevation of the postglacial marine limit and history of relative sea-level changes are well known (Fig. 9) (Forman 1990; Forman et al. 2004). The isostatic fingerprinting (Fig. 10) reflects the heaviest glacial loading in the central Barents Sea and clearly expresses the differential ice load of the Svalbard–Barents Sea ice sheet at LGM.

Interglacial-mode sediments and landforms Svalbard did not completely deglaciate during the Holocene (Hald et al. 2004). Salvigsen et al. (1992) and Salvigsen (2002) documented warmer conditions in Svalbard during the early and mid Holocene compared to the present-day climate. Glacier volumes were probably considerably smaller than present (Svendsen & Mangerud 1997; Forwick & Vorren 2007) and some valley/cirque glaciers may have melted away completely. Because of the Neoglacial expansion of glaciers that started some time after mid-Holocene (Svendsen & Mangerud 1997) and culminated by the end of the Little Ice Age around 1890–1900 AD (Werner 1993; Man- Fig. 7. Composite stratigraphy of the Kapp Ekholm gerud & Landvik 2007), the timing, extent and section. Each coarsening-upwards sequence reﬂects volume of ice at the early Holocene glacial glaciation (till) and deglaciation (marine-to-littoral minima is not well known (Humlum et al. 2005). sediments) (modiﬁed from Mangerud & Svendsen Interglacial-mode glacial landforms and sediments 1992). FINGERPRINTS OF GLACIATIONS ON SVALBARD 23

Fig. 8. Examples of Svalbard glacial-deglacial sediments in coastal sections: (a) subglacial till, unit A, Kapp Ekholm (Figs 6 & 7) (pocket knife for scale); (b) dropstones in shallow-marine sediments (pocket knife for scale), site 15 (Fig. 6); (c) stratiﬁed shallow-marine sediments with subfossil kelp (35 cm scrape for scale), Poolepynten (Fig. 6); (d) a whale rib at the contact between sublittoral marine sediments and gravelly beach foresets (1 m stick for scale), site 15 (Fig. 6); (e) sublittoral marine sediments with in situ subfossil molluscs, Skilvika (Fig. 6). All photographs by O´ . Ingo´lfsson in 2008. on Svalbard primarily relate to the Neoglacial maxima, and many glaciers have retreated 1–2 km expansion of glaciers. Most glaciers in Svalbard or more. It has been calculated that the net mass are presently retreating from their 1890–1900 AD balance of Svalbard glaciers has been negative 24 O´ . INGO´ LFSSON

Fig. 9. Relative sea-level curves from Svalbard (modiﬁed from Forman et al. 2004).

Fig. 10. The pattern of postglacial raised beaches combined with well-dated relative sea-level curves fingerprints the isostatic depression caused by the Svalbard–Barents Sea ice sheet (modified from Bondevik 1996). FINGERPRINTS OF GLACIATIONS ON SVALBARD 25 most years for the past .100 years, and that the morainal ridges and hummocky moraines, bounded glacial systems of Svalbard may have lost up to by terminal moraines marking the maximum Neo- 30% of their volume since 1900 AD (Lefauconnier glacial ice extent. The distal basins are characterized & Hagen 1990; Glasser & Hambrey 2003). by debris lobes and draping stratified glaciomarine sediments beyond and, to some extent, beneath Tidewater glacier/fjord environments and above the lobes. Distal glaciomarine sediments comprise stratified clayey silt with ice-rafted debris There are a number of conceptual models proposed content (Forwick & Vorren 2009). for tidewater glaciers (Fig. 11a) (Elverhøi et al. Ottesen & Dowdeswell (2006), Ottesen et al. 1980; Bennett et al. 1999), identifying and link- (2008) and Kristensen et al. (2009) identified ing sedimentary processes, deposits and landforms. an assemblage of submarine landforms from the Plassen et al. (2004) proposed a model for sedi- margins of several Svalbard glaciers that they mentation of Svalbard tidewater glaciers (Fig. 12a) linked to glacier surging into the fjord environments based on high-resolution acoustic data and sediment (Fig. 12b). The submarine landforms include: cores and sedimentation patterns in four tidewater streamlined landforms found within the limits of glacier-influenced inlets of Isfjorden, Svalbard. known surges, interpreted as mega-scale glacial Their model shows glaciogenic deposition in proxi- lineations formed subglacially beneath actively mal and distal basins. The proximal basins comprise surging ice (1 on Fig. 12b); large transverse

Fig. 11. Svalbard glaciers: (a) Kongsvegen tidewater glacier, Kongsfjorden; (b) Comfortlessbreen glacier in surge; and (c) Pedersenbreen polythermal glacier, Kongsfjorden. All photographs by O´ . Ingo´lfsson in 2008. 26 O´ . INGO´ LFSSON

Fig. 12. Svalbard tidewater glaciers: (a) a model for proglacial sedimentation by Svalbard polythermal tidewater glaciers (modified from Plassen et al. 2004); and (b) landform assemblage model for Svalbard surge-type tidewater glaciers (modified from Ottesen et al. 2008). ridges, interpreted to be terminal moraines formed terminal moraines; (2b) lobe-shaped debris flows; by thrusting at the maximum position of glacier (3) isolated areas of crevasse-fill ridges; (4) eskers surges (2a on Fig. 12b); sediment lobes at the and (5) annual retreat ridges. distal margins of terminal moraines, interpreted as glaciogenic debris flows formed either by failure Terrestrial polythermal and surging glaciers of the frontal slopes of thrust moraines or from deforming sediment extruded from beneath the There are numerous studies of the depositional glacier (2b on Fig. 12b); sinuous ridges, interpreted environments of Svalbard terrestrial polythermal as eskers, formed after surge termination by the and surging glaciers (Fig. 11b, c) which outline sedimentary infilling of subglacial conduits (4 on structural properties, landform-sediment associ- Fig. 12b); concordant ridges parallel to former ice ations and dead-ice disintegration (Boulton 1972; margins, interpreted as minor push moraines pro- Bennett et al. 1996, 1999; Boulton et al. 1999; bably formed annually during winter glacier Hambrey et al. 1999; Lysa˚ & Lønne 2001; Sletten re-advance (5 on Fig. 12b); and discordant ridges et al. 2001). Glasser & Hambrey (2003) gave an oblique to former ice margins and interpreted as overview of sediments and landforms associa- crevasse-squeeze ridges, forming when soft sub- ted with glaciated valley landsystems on Svalbard glacial sediments were injected into basal crevasses (Fig. 13). Characteristics of this landsystem are (3 on Fig. 12b). rockfall debris supply, passive transport and rework- Ottesen et al. (2008) proposed that these sub- ing of a thick cover of supraglacial morainic till, marine landforms were deposited in the following combined with actively transported debris derived sequence based on cross-cutting relationships from the glacier bed. They identified moraine between them, linked to stages of the surge cycle complexes produced by thrusting as the most com- (Fig. 12b): (1) mega-scale glacial lineations; (2a) mon. The sedimentary composition of moraine FINGERPRINTS OF GLACIATIONS ON SVALBARD 27

Fig. 13. A landsystem model for terrestrial Svalbard polythermal glacier (modified from Glasser & Hambrey 2003). complexes varies with source materials and ranges a wide variety of morphological types (often from reworked marine sediments to terrestrial dia- ice cored), linear ridges up to 100 m long or mictons and gravels. Original sedimentary struc- short-crested ridges of several metres and tures or subfossil marine mollusks are commonly near conical mounds. Rectilinear slopes and preserved as a slab of sediments which has been stacking indicate that the moraine-mound stacked by the glacier. The thrusted moraine complex is a result of thrusting in proglacial, complexes often show evidence of glaciotectonic ice-marginal and englacial position. deformations, including low-angle thrust faults (3) Inner zone, between the moraine-mound com- and recumbent folds. Moraine complexes resulting plex and the contemporary glacier snout com- from deformation of permafrost also occur on prising various quantities of foliation-parallel Svalbard. There, stresses beneath the advancing ridges, supraglacial debris stripes, geometrical glaciers are transmitted to the proglacial sediments ridge networks, streamlined ridges/flutes and and can cause proglacial deformation of the perma- minor moraine mounds. Sediment facies are frost layer. This may lead to folding, thrust-faulting predominantly glacial diamicton, commonly and overriding of proglacial sediments. being reworked by proglacial streams. Glasser & Hambrey (2003) suggested that a typical receding Svalbard glacier has three zones The most widespread deposit on the forefields of within its forefield (Fig. 13) as follows. receding valley glaciers on Svalbard is diamicton (Glasser & Hambrey 2003) produced by basal (1) Outer moraine ridge. These are arcuate ridges lodgement processes or meltout. The diamictons rising steeply from the surrounding topo- are in turn reworked by fluvial processes and slump- graphy to heights of 15–20 m. They are com- ing where there is active down-wasting of dead ice monly ice-cored and may be either the result (Schomacker & Kjær 2007). of englacial or proglacial thrusts or be a Christofferson et al. (2005) described landform- product of permafrost deformation. Some gla- sediment assemblages relating to surging Svalbard ciers have large ice-cored lateral moraines. glaciers. They identified ice-flow parallel ridges (2) Moraine-mound complex (Fig. 13), often (flutings), ice-flow oblique ridges (crevasse-fill fea- draped by supraglacial debris stripes. These tures), meandering ridges (infill of basal meltwater), are often present in the form of arcuate belts thrust-block moraines, hummocky terrain and of aligned hummocks or mounds comprising drumlinoid hills. Kristensen et al. (2009) suggested 28 O´ . INGO´ LFSSON that surging glacier ice-marginal landforms on particularly important for our understanding of the land closely resemble the corresponding landforms signatures of surging glaciers, where the recognition on the seabed, including debris-flow mud aprons of palaeosurges within landform and sedimentary in front of surge moraines. They argued that both records is still somewhat capricious. the submarine and the terrestrial mud apron were formed by a combination of ice push and slope Valuable and constructive suggestions from the journal failure. reviewers are acknowledged. The paper was written during a sabbatical visit to Lund University, Sweden.

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