Recent Glacially Influenced Sedimentary Processes on the East

Quaternary Science Reviews 49 (2012) 64e81

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Quaternary Science Reviews

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Recent glacially inﬂuenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin

Marga García a,*, Julian A. Dowdeswell a, Gemma Ercilla b, Martin Jakobsson c a Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK b Instituto de Ciencias del Mar, CSIC, Grupo de Márgenes Continentales, Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Spain c Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden article info abstract

Article history: This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of Received 10 January 2012 landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and Received in revised form sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent 19 June 2012 sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of Accepted 27 June 2012 landform development points to a predominantly glacial origin of the sediment supplied to the Available online xxx continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes Keywords: Greenland Basin along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest Glacially influenced sedimentary processes a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led Debris flows to the development of scarps and channels on the slope and debris flows on the continental rise. The Turbidite systems more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction last glaciation (Evans et al., 2002; Ó Cofaigh et al., 2002, 2004; Hakånsson et al., 2007). Recent studies further north, between The large-scale morphology and landforms of high-latitude 76N and 81.5N, also support an ice sheet grounding as far as the continental margins and basins are in most cases products of the shelf edge during the Last Glacial Maximum (Evans et al., 2009; major recent sedimentary processes that have shaped the present- Winkelmann et al., 2010). The understanding of past variations in day seafloor. They have therefore been used widely for recon- the dynamics of the Greenland Ice Sheet, and especially the structing sedimentary environments during the last glacial cycle. behaviour of fast-flowing ice streams, can provide important Reconstructions of the eastern Greenland Ice Sheet have been constraints on the likely dynamics of modern Greenland ice based on studies of the continental margin off Scoresby Sund and streams. These ice streams are, in turn, an important control on the Kejser Franz Joseph Fjord (68Nto74N) (e.g. Dowdeswell et al., rate of global sea-level rise today (Gregory et al., 2004; Rignot and 1994a,b; Evans et al., 2002; Ó Cofaigh et al., 2002; Wilken and Kanagaratnam, 2006). Mienert, 2006); two different scenarios have been proposed. In High-latitude continental shelves, unless reworked by the the first, glacier fluctuations were relatively limited during the last ploughing action of iceberg keels (e.g. Woodworth-Lynas et al., glacial cycle with the ice sheet inferred to have reached only the 1985; Dowdeswell et al., 2002; Dowdeswell and Bamber, 2007), outer fjords or the inner shelf during full-glaciation (Funder, 1989; often preserve assemblages of glacially produced landforms that Funder and Hansen, 1996; Elverhøi et al., 1998; Funder et al., 1998, allow the reconstruction of the form and flow of Late Quaternary 2011). A second scenario suggested that the outer shelf, or even the ice sheets (e.g. Canals et al., 2000; Ottesen et al., 2005; Evans et al., shelf-edge, was the maximum extent for the ice sheet during the 2006; Mosola and Anderson, 2006). By contrast, continental slopes and deep basins in the polar seas are complex sedimentary settings recording the interplay of glacial, glacimarine, marine and mass- * Corresponding author. Instituto Andaluz de Ciencias de la Tierra, wasting processes (e.g. Laberg and Vorren, 1995; King et al., 1996; CSIC-Universidad de Granada, Avda. de las Palmeras n 4, 18100 Armilla, Granada, Spain. Tel.: þ34 958 230000x190139; fax: þ34 958 552620. Hesse et al., 1999; Dowdeswell et al., 2004; Li et al., 2011). This E-mail addresses: [email protected], [email protected] (M. García). paper presents a detailed description and interpretation of the

0277-3791/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.quascirev.2012.06.016 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 65 landforms that characterize a sector of the East Greenland conti- and production of maps were performed with Caris and Fle- nental slope and the Greenland Basin. We analyze landforms on the dermaus software. continental slope between 74N and 76N, and provide a new Bathymetric and backscatter mosaics for the Greenland Basin interpretation of landforms in the deep Greenland Basin (Fig. 1). are illustrated in Fig. 2. Fig. 2A shows the topography of the seafloor The geological significance and timing of the recent sedimentary from the upper slope to the deep basin. The data cover depths processes are interpreted in terms of their relation with the last ranging from 147 to 3730 m. Minimum depths occur at the Vesteris glacialeinterglacial cycle, in order to assess previously proposed Seamount, and maximum values are in the deep basin in the hypotheses from adjacent margins regarding the extent of the East easternmost part of the study area. Greenland Ice Sheet during the Last Glacial Maximum. Backscatter imagery was produced using FM Geocoder (Fonseca and Calder, 2005)(Fig. 2B). Values of mean backscatter range 2. Methods and datasets from 20 to 55 dB. Backscatter represents the strength of the returning sound signal transmitted from the multibeam system, This work is based on mapping carried out during cruise JRC-51 and is dependent on the grain size, insonification-orientation and of RRS James Clark Ross (Fig. 1A). Swath bathymetry and associated sea-surface conditions during the survey (e.g. Keeton and Searle, backscatter data were obtained with a hull-mounted Kongsberg- 1996; Fonseca and Mayer, 2007; Kagesten, 2008; De Falco et al., Simrad EM120 multibeam system, operating with a nominal 2010), and also on seafloor morphology and near-surface stratig- frequency of 12 kHz and 191 beams, with a 11 beam configu- raphy. In general, coarser sediments will give a stronger reflected ration. This provided a resolution of approximately 50 m in 3000 m signal, with surface shape and roughness important in controlling water depth (the maximum depth in the study area being 3700 m). backscatter for coarse sediments (Kagesten, 2008). In the Navigation data were obtained from DGPS and the data processing Greenland Basin, the mean backscatter pattern allows the

Fig. 1. A) Location of the study area on the regional IBCAO bathymetric map (Jakobsson et al., 2008), showing the location of the sub-bottom TOPAS profiles, swath bathymetry data and cores obtained during the JRC-51 cruise that have been interpreted in this work. Blue dotted lines mark the trend of former glacial troughs. F.Z.: Fracture zone; Norske T.: Norske Trough; S.K. I.: Store Koldeway Island; Hochst: Hochstetterbugten; Dove B.: Dove Bugt; KFJ F.: Kejser Franz Josef Fjord. B) Profiles along the East Greenland margin. Legend: Csh: Continental shelf; CS: Continental slope; CR: Continental Rise; B: Basin. Profiles are located in A. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 66 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81

frequency in the range of 0.5e5 kHz. It is capable of providing a vertical resolution better than 1 m. Processing of the data was carried out with TOPAS software. Side-scan sonar imagery was obtained with the Towed Ocean Bottom Instrument (TOBI) system (Flewellen et al., 1993). TOBI included a 30 kHz deep-tow side-scan sonar with swath bathymetry capability, an 8 kHz chirp profiler sonar, gyrocompass and pitch and roll sensor. Acoustic facies have been defined based on the acoustic amplitude, lateral continuity, geometry and internal configuration of reflections on sub-bottom TOPAS profiles (Damuth, 1980), and on mean backscatter values (Fig. 2B). The interpretation of acoustic facies is based on their seismic characteristics and distribution, and follows the work of several authors (e.g. Damuth, 1980; Hong and Chen, 2000; Zaragosi et al., 2000; Droz et al., 2001; Loncke et al., 2002; Kottke et al., 2003). Published regional datasets have been used to complete our interpretations. These include the IBCAO Version 2.0 bathymetric chart for offshore East Greenland (Jakobsson et al., 2008), a GLORIA 6-kHz side-scan sonar mosaic (Mienert et al., 1993; Dowdeswell et al., 1996; Wilken and Mienert, 2006) and sedimentological information from cores retrieved from the Greenland Basin margin (Ó Cofaigh et al., 2002, 2004; Wilken and Mienert, 2006).

3. Study area: geological background and glacial history

The initial breakup of the Norwegian-Greenland Sea started in Early Eocene time, through the activity of the Mid-Atlantic Ridge. Geodynamic evolution since then has included stages of compression, extension, magmatism, uplift and subsidence (Johnson and Heezen, 1967; Price et al., 1997; Lundin and Doré, 2002; Voss and Jokat, 2009). The onset of glaciations in the northern hemisphere has been documented from the occurrence of ice-rafted debris (IRD) in deep-sea sediments (Eldrett et al., 2007; Tripati et al., 2008; Jakobsson et al., 2010). The Greenland Ice Sheet (GIS) dates from Eocene/early Oligocene and its glacial history includes a succession of at least four cooling pulses during the late Miocene, and a major intensification of glaciation during the Plio-Pleistocene. Glacial sediments were deposited on the outer shelf and continental slope of the Greenland Basin during the early Pliocene and late Pliocene, and a younger depositional event occurred during the Quaternary, probably corresponding to the last major advance of the GIS during the Saalian (Vanneste et al., 1995; Solheim et al., 1998; Hakånsson et al., 2008). Large-scale trough mouth fans have not developed on the East Greenland margin due to a combination of factors, including sediment characteristics and delivery rate, meltwater volume and the size of the ice-sheet drainage basins (Ó Cofaigh et al., 2004). During the Late Weichselian, full-glacial ice-sheet advance in East Greenland was until recently thought to have been restricted mainly to fjord and inner-shelf locations (Funder, 1989; Funder and Hansen, 1996; Funder et al., 1998, 2011). New swath-bathymetric observations, however, have shown the presence of subglacially produced mega-scale glacial lineations and moraine ridges on the outer shelf, providing clear evidence of ice advance across the shelf (Evans et al., 2009; Dowdeswell et al., 2010; Winkelmann et al., Fig. 2. A) Swath bathymetric map of the study area, showing the Norske margin in the fi northern area, off the Norske Trough; the KFJ margin, off the Kejser Franz Joseph Fjord 2010). These ndings provide direct support for earlier indirect (KFJ fjord); and the deep basin, where volcanic edifices are the most prominent inferences of an extensive Late Weichselian ice sheet, reaching at seafloor features. B) Backscatter map of the Greenland Basin, reflecting the charac- least the outer continental shelf (Fleming and Lambeck, 2004; Ó teristics of the shallow sediment. Backscatter values are one of the criteria used to Cofaigh et al., 2004; Wilken and Mienert, 2006; Hakånsson et al., define acoustic facies. 2007). Deglaciation of the East Greenland shelf commenced about 17,000e18,000 years ago (Evans et al., 2002; Ó Cofaigh et al., in recognition of sedimentary features and has been used as a key press), and hemipelagic sedimentation has been predominant on parameter for the definition of acoustic facies. the margin subsequent to ice retreat (Ó Cofaigh et al., 2002, 2004; The TOPAS PS 018 system used to obtain sub-bottom profiles Wilken and Mienert, 2006). The timing of the deglaciation has been operates with a primary frequency of 15 kHz and a secondary established by radiocarbon dating of sediment cores from the M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 67

Greenland Basin, where the transition from glacially influenced The continental slope and rise are characterized mainly by two turbidites and debris-flow deposits to the most recent hemipelagic facies: a transparent facies containing thin lenticular bodies (IIB) unit has been dated at about 13,000 years B.P. (Ó Cofaigh et al., and a non-penetrative, wavy seismic facies (IB). In addition, a non- 2004). penetrative, regular acoustic facies (IA) is identified locally on steeper areas. 4. Physiography The floor of the Greenland Basin is generally represented by stratified acoustic facies (Fig. 3). An undulating facies (IIIC) occurs The study area is delimited by the Jan Mayen Fracture Zone to mainly in the shallowest, south-western part of the study area, the south-west and the East Greenland Ridge to the north-east. It where a locally chaotic acoustic facies (IV) is also identified. The covers the upper slope, from 1200 m water depth, to the deep basin deep basin generally presents stratified acoustic facies with parallel at depths of more than 3700 m (Figs. 1 and 2). The physiography and horizontal (IIIB) or deformed reflections (IIID). Lenticular or changes along the margin, from a narrow, less than 200 km-wide mound-shaped bodies of transparent acoustic facies (IIA) charac- margin with a steep and narrow continental slope off Kejser Franz terize part of the deepest basin, locally covered by thin, layered Joseph Fjord in the southern part of the study area (hereafter KFJ deposits (acoustic facies IIIA), in the northern part of the study area. margin), to a much wider margin, up to 450 km wide, with a well- Finally, non-penetrative, irregular facies (IC), with some patches of developed continental rise in the northern part of the study area off transparent acoustic facies (IIB) beyond, characterise volcanic the Norske Trough (hereafter Norske margin). edifices in the basin. The East Greenland continental shelf widens from minimum values of 120 km at the KFJ margin to a maximum width of 300 km at 6. Submarine landforms the Norske margin, where it connects with the Boreas Abyssal Plain to the east (Figs.1 and 2). The continental shelf is cut by four troughs with Submarine landforms in the Greenland Basin have been iden- a general NWeSE trend and widths of tens of kilometres. Glacial tified after examination of data from swath bathymetry, back- troughs in the study area are, from south to north, the basinward scatter, sub-bottom profiles and TOBI imagery. The landforms can continuation of KFJ Fjord, the main trough formed by Hoch- be grouped into four major categories: 1) erosive mass-wasting stetterbugten and Dove Bugt, a trough off Store Koldewey, and the features; 2) depositional lobes; 3) turbidite channel systems; and Norske Trough (Fig.1). The shelf reaches depths of 400 m, except at the 4) bedrock structural features. mouths of glacial troughs where depths increase to more than 500 m. The continental slope extends to 2500e3200 m in water depth. 6.1. Erosive mass-wasting features On the KFJ margin the continental slope is relatively narrow (20e50 km wide), with maximum gradients of 5 (Fig. 1B). On the Erosive mass-wasting features are identified on the continental Norske margin the slope is up to 70 km wide, with gradients of slope mainly in the Norske margin area (Figs. 1 and 4). Several 1.5e3.5 reaching maximum values of 9 on several margin-parallel major slide scars, 30 km long and 1 km wide, give a step-like shape scarps (Fig. 1B). In this area, a 60 km wide continental rise reaches to the continental slope (Fig. 4B). The scars are up to 100 m high and depths of 3500 m, with gentle gradients typically less than 2. The have steep gradients of up to 9. In addition, smaller scars are basin extends to maximum depths of 3700 m. Characteristic identified at a wide range of depths, from 1200 to 3370 m (Fig. 4). features in the basin are volcanic edifices, such as the solitary These scars, 5e15 m high and only few kilometres long, are asso- Vesteris Seamount which is 2850 m high (Haase and Devey, 1994). ciated with depositional lobes. Our new bathymetric data reveals the existence of numerous NE- Divergent channel-like depressions occur at depths of SW-oriented elongated edifices with maximum heights of 500 m 1900e3400 m, where the gradient is 0.1e1.4 (Fig. 4A). Individual above the surrounding seafloor (Fig. 2A). channels are 5e30 m deep, 0.5e3 km wide and can be traced for at least 40 km downslope. They occur basinward of the scars and 5. Acoustic facies display a divergent pattern, suggesting they may be linked to the scars in terms of operating processes. Channels are identified as 5.1. Acoustic facies description scarps on the sub-bottom profiles (profile BeB0 in Fig. 4B). The area of erosive features on the Norske margin is characterized by Four major acoustic facies have been differentiated in the acoustic facies IIB (thin transparent lens-shaped bodies) and locally Greenland Basin. A non-penetrative facies (I) includes three by acoustic facies IA (regular non-penetrative seafloor reflection) subtypes, showing no penetration of the acoustic signal. Regular, (Fig. 3). wavy and irregular seafloor reflections characterize subtypes IA, IB and IC, respectively. A transparent acoustic facies (II) has two 6.2. Depositional lobes subtypes. Subtype IIA is represented by lenticular or mound- shaped bodies, up to 30 ms thick, whereas subtype IIB is charac- Depositional lobes include a number of horizontally and verti- terized by thin lens-shaped bodies, less than 10 ms thick. A strati- cally stacked lobes on the continental rise (Fig. 5A), and two large fied acoustic facies (III) represents parallel-stratified reflectors and isolated lobes on the continental slope (Fig. 5D). The stacked has four subtypes; thin packages of parallel reflectors overlying depositional lobes occur on the Norske margin continental rise, at transparent deposits (IIIA), continuous horizontal reflectors (IIIB), depths of 3300e3600 m, where the gradient averages 0.4 (Fig 5B). continuous undulating reflectors (IIIC), and deformed reflectors They are elongate, up to 25 km long and 2e5 km wide with (IIID). A chaotic acoustic facies (IV) shows a wavy surface and aNWeSE orientation (Fig. 5B). Individual lobes are separated by chaotic internal character with no well-defined reflectors. The four narrow depressions up to 15 m deep, and are characterized by acoustic facies and their characteristics are illustrated in Table 1. a wavy, non-penetrative seafloor reflector of acoustic facies IB. The wavy surface can be recognized on the backscatter imagery as 5.2. Acoustic facies distribution arcuate, concave-upslope stripes of alternating high and low backscatter (Fig. 5B). The lobes form a ridge-and-valley topography, The distribution of acoustic facies in the Greenland Basin is up to 20 m deep and 0.8e1.3 km in wavelength (Fig. 5C). Down- shown in Fig. 3. slope of the depositional lobes, transparent deposits on the lower Table 1 Acoustic facies. Description based on seismic character and backscatter, distribution on the East Greenland margin and deep basin, interpretation and example from the sub- bottom TOPAS profiles.

Acoustic facies Description Distribution Interpretation

I. Non IA. Regular seafloor reflection with no subbottom Locally on the Scars, steep areas penetrative reflections Backscatter: 30/20 dB continental slope

IB. Wavy non-penetrative seaﬂoor reﬂection Norske margin Slide deposits with Backscatter: 40/20 dB continental rise pressure ridges

IC. Irregular seafloor reflection with no Volcanic edifices Volcanic activity subbottom reflections Backscatter: irregular

IIA. Transparent lenticular or mounded-shaped Distal turbidite system bodies, up to 30 ms TWTT thick Deep basin depositional lobes Backscatter: 40/35 dB

II. Transparent IIB. Thin (<10 ms TWTT) transparent lens-shaped Continental slope Mass movement deposits bodies Backscatter: 40/20 dB and rise

IIIA. Thin (w10 ms TWTT) package of continuous Distal part of the Non-channelized turbidite horizontal parallel reﬂections overlying transparent deep basin deposition covering distal deposits Backscatter: 35/25 dB turbidite deposits

IIIB. Continuous, horizontal parallel reﬂections Deep basin Non-channelized turbidite Backscatter: 40/30 dB deposition

III. Stratiﬁed IIIC. Continuous, undulating parallel layered Proximal parts of the Sediment waves on reﬂections Backscatter: 40/30 dB deep basin turbidites

IIID. Parallel layered deformed reflections Deep basin, close to Deep basin, close to Backscatter: 45/30 dB volcanic edifices volcanic edifices

IV. Chaotic facies, wavy surface Foot of the KFJ margin Debris ﬂows Backscatter: 40/35 dB continental slope

IV. Chaotic M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 69

Fig. 3. Map ofacoustic facies distribution on the East Greenland margin and basin, showing the major four types (non-penetrative, transparent, stratiﬁed and chaotic) and subtypes (Table 1).

Fig. 4. Erosive mass-wasting landforms of the Greenland Basin slope (location in Inset). A) Shaded-relief swath image of the Norske Trough margin. B) Sub-bottom profiles showing the non-penetrative seafloor, thin transparent lenses and scars. See the location of profiles in A. Fig. 5. Depositional mass-wasting features in the Greenland Basin (locations Inset). Shaded relief swath image (A) and backscatter map (B) of the Norske Trough margin showing the distribution of stacked lobes in the profile CeC0. D) Shaded relief swath image of the KFJ margin and location of sub-bottom profile DeD0, with isolated lobe. M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 71 continental rise (acoustic facies IIB) connect with turbidite chan- shallower set, which affects the upper 40 m of the sediment column nels (Fig. 5A). and is composed of more asymmetrical waves (average upslope In addition, two large isolated depositional lobes have been flank length:downslope flank length 1:3.3). identified at the foot of the slope on the KFJ margin, at depths of A second family of sediment waves is composed of much smaller 1800e2100 and 2450e2550 m (Fig. 5C). Only the more westerly features that can be clearly identified on the TOBI side-scan sonar lobe can be mapped in its entirety. It is elongate downslope, and is images at the distal terminations of the small channels (Fig. 6, 22 km long and 8 km wide, with a maximum relief of 30 m. It profile CeC0). These waves only affect the upper 10e20 m of the displays a characteristic highly irregular surface in the bathymetry sedimentary record, are relatively irregular in shape and trend, only and chaotic acoustic facies IV in sub-bottom profiles and is affected tens of metres long and typically 5e10 m high; they sometimes by the excavation of channels on its northern side (Fig. 5C). displaying barchan-shapes. Individual sediment waves appear to be oriented oblique to the regional gradient, but they display a high 6.3. Turbidite systems variability in orientation. The predominant acoustic facies on the channels and sediment- Two major turbidite systems have been identified on our swath- wave fields is type IIIC (continuous, undulating parallel layered bathymetric dataset. The first is a channel at the foot of the conti- reflections, Table 1), but acoustically transparent deposits can also nental rise on the Norske margin, with a WSWeENE orientation be observed underlying most of the sediment-wave fields. and maximum width of 3.7 km (Figs. 2A, 5A). The data only cover a 50 km-long part of this system, revealing a strongly asymmetrical 6.3.3. Channel-levee system profile, with steep SE walls (25 m high, up to 4) and smoother, In the more proximal part of the Greenland Basin, a channel- almost diffuse NW walls. The second is a complete turbidite system levee system is present for more than 150 km at depths ranging that extends for more than 500 km from the KFJ margin continental from 2600 to 3200 m and gradients of 0.1e0.25 (Fig. 7). The slope to the deep basin (Figs. 2A, 6 and 7). Although this turbidite morphology of the main channel changes abruptly at 2660 m water system has already been reported (Mienert et al., 1993; depth, becoming deeper (50e60 m deep) and asymmetrical, Dowdeswell et al., 2002; Ó Cofaigh et al., 2004; Wilken and showing a 20e30 m higher leveed southern wall (Fig. 7A). The Mienert, 2006), the new data analyzed in this work allow profile is generally smooth, with marked rims and steep flanks of a detailed characterization of the complete system. Four sub- up to 5 and a general trend parallel to the regional gradient. A systems are identified, forming a continuum from the upper second leveed channel merges with the main channel from its slope to the distal part of the Greenland Basin; tributary channels, northern flank at w2820 m water depth and sinuosity increases channels with sediment-wave fields, channel-levee complexes, and basinwards in the vicinity of several volcanic edifices (Fig. 7A). TOBI distal channels and associated depositional lobes. side-scan sonar images show terraces, up to 40 m high, instabilities affecting the rims of the channel, braided channel floors and over- 6.3.1. Tributary channels excavations within the thalweg (Fig. 7B). The channel width A series of tributary channels is observed on the KFJ margin increases from w1 km to 2.8 km in the distal, sinuous part of the continental slope, at 1350e2000 m water depth, where the average channel. A small sediment-wave field covers an area of w40 km2 at gradient is 1.2 (Figs. 5D, 6A, C). These channels have a general the southern side of the channel, at w2700 m water depth (Fig. 7A). WNWeESE to EeW trend, are spaced less than 1 km apart and Waves are 5e15 m high and wavelength is 0.7e1.6 km. Continuous display a convergent pattern downslope. The channels are and deformed parallel stratified acoustic facies (IIIB and IIID, 0.8e1.6 km wide and 5e25 m deep. Acoustic facies IC is typical of respectively) predominate in this area, whereas the thalweg of the these tributary channels, which have an irregular, non-penetrative channel shows high-amplitude reflections or infilling by trans- seafloor reflector. parent deposits. Transparent deposits occur buried at the channels flanks, and also fill the thalweg in distal areas (Fig. 7D). 6.3.2. Channels and sediment-wave fields Tributary channels continue basinward through sediment-wave 6.3.4. Distal channel and depositional lobes fields, which are present for about 100 km downslope at depths of The distal part of the turbidite system occurs in the deep basin, 2000e2600 m, where the regional gradient averages 0.35 (Figs. 6, at water depths >3200 m, where the regional gradient is very low, 7). Channels are relatively straight, WSWeENE to SWeNE- typically <0.15 (Fig. 8). Narrow (1e1.6 km wide) and relatively oriented, and up to 60 km long (Fig. 6A). They are 10e30 m deep, shallow (5e30 m deep) channels are identified on this flat area, 1e2 km wide and have V-shaped profiles. Most channels end displaying SWeNE to WeE trends and symmetrical, V- or U-shaped abruptly in the proximity of a major trunk channel, whereas some profiles. Channels usually present relatively low values of back- others seem to open directly into it. The WeE-trending trunk scatter (45 to 40 dB) (Fig. 8B). The channels lose their channel is relatively straight, and wider (up to 3.5 km) and deeper morphological identity at about 3580 m water depth. The flat, (up to 35 m) than the smaller tributary channels. deepest areas where channels disappear show higher backscatter Sediment-wave fields develop at depths ranging between about values of 25 to 20 dB (Fig. 8B). The predominant acoustic facies 2000 and 2600 m (Fig. 6). Two families of sediment waves are at the termination of channels are transparent lens- or mound- differentiated. The first family corresponds to large waves that shaped bodies (IIA), thin packages of continuous parallel reflec- affect the upper 100 m of the sedimentary record and are roughly tions overlying transparent deposits (IIIA) in the northernmost part parallel to the regional gradient (Fig. 6E). They occupy an area of at of the deep basin, and continuous parallel reflections (IIIB) in the least 1170 km2. The waves are up to 25 m high and have a wave- relatively higher areas surrounding volcanic edifices (Fig. 8). length of 1e2.6 km and an upslope-migration trend (Fig. 6, profile BeB0). Individual sediment waves are laterally continuous for tens 6.4. Structural features of kilometres, and some of them seem to be continuous across the channels. Vertically, two sets of waves are identified on the TOPAS Landforms on the seafloor of the Greenland Basin also include profiles (Fig. 6E). The deeper set (at least 20 m thick) is composed of two types of structural features: structural scarps and volcanic relatively symmetrical waves (average upslope flank length:- edifices (Figs. 1, 8A). Structural scarps occur in the deep basin, and downslope flank length 1:1.1) with a higher migration than the produce a step-like morphology, becoming steeper in a north- 72 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81

Fig. 6. Tributary channels and channels and sediment-wave field subsystems of the major turbidite system in the Greenland Basin (located in inset). A) Shaded relief swath image showing the location of the sub-bottom TOPAS profiles and TOBI imagery. C) Profile AeA0 showing the tributary channels. D) Sub-bottom profiles showing fields of large (BeB0) and small (CeC0) sediment waves. E) Sub-bottom profile DeD0 showing the two sets of waves. M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 73

Fig. 7. Turbidity-current channel-levee system, distal channels and depositional lobes in the Greenland Basin. A) Shaded relief swath image of the channel-levee system, with cross-profiles showing the levee on the SE side of the channel, and the locations of sub-bottom profile AeA0 and TOBI images. B) and D) TOBI images of the channel, displaying instability features and terraces on the walls. D) Sub-bottom profile crossing the main channel showing the horizontal parallel reflections and acoustically transparent deposits. easterly direction. Individual scarps are up to 30 m high and can be Some of the edifices crop out on the present-day seafloor, forming traced for tens of kilometres on the basin floor. Volcanic edifices are crests up to 700 m high, 5 km wide and 25 km long, whereas others widespread along the deep basin at depths >2800 m (Figs. 1, 2A). are buried by subsequent sedimentation and form smooth, The largest example is Vesteris Seamount (2850 m high, 35 km in 100e200 m high mounds. Outcropping volcanic edifices display diameter), but a series of elongated NE to SW-oriented volcanic irregular, non-penetrative acoustic facies IC (Table 1). Irregular ridges is also identified in the distal part of the basin (Figs. 2A, 8A). patches of relatively high reflectivity (35 to 25 dB) are also 74 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81

Fig. 8. Distal depositional lobes in the deep Greenland Basin (located in inset). A) Shaded relief swath image and B) backscatter map of the deep basin. Proﬁles BeB0,CeC0 and DeD0 show the distal depositional lobes as transparent deposits, locally covered by a thin layered deposit.

identified on the basinward side of some volcanic edifices in the flows at the base of the continental rise. By contrast, the KFJ margin deep basin (Fig. 7C), suggesting relatively recent activity. We do not presents a markedly different set of landforms. Here, a few isolated discuss these bedrock features further here. lobes coexist with the upper reaches of a well-developed turbidite system consisting of tributary channels on the slope that merge, 7. Discussion: recent sedimentary processes within a sediment-wave field, into a major trunk channel (Fig. 9). The basin beyond is dominated by the main turbidite channel and its The landforms identified on the seafloor of the East Greenland levees. In the deepest part of the basin there are more individual continental slope, rise and deep basin are shown in Fig. 9. The map channels that transport sediment to the most distal, north-eastern also includes channels identified beyond our study area by previous areas of the basin. Structural features (scarps and volcanic workers (Mienert et al., 1993; Wilken and Mienert, 2006). The edifices) in the deep basin appear to influence the location of the figure shows the complex distribution of landforms. main channel and the areas of depositional from the most distal part The Norske margin is dominated by large slide scars and of the turbidite system (Fig. 9). The analysis and interpretation of downslope-trending divergent channels on the continental slope, submarine landforms enables discussion of the recent sedimentary and stacked lobes on the continental rise (Fig. 9). A turbidite channel processes operating on the Greenland Basin margin. M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 75

Fig. 9. Map of the Greenland Basin margin showing the distribution of the landforms identiﬁed in this work. The IBCAO regional map and published GLORIA data have been used as background bathymetry.

7.1. Glacigenic mass-wasting processes on the continental slope Several factors may be involved in the location and timing of slides on the Greenland Basin slope (Locat, 2001; Locat and Lee, Slide systems are composed of scars, channel-like depressions 2002). The most important is the likelihood of rapid sediment and lobes, and dominate recent deposition on the Norske margin delivery to the shelf edge at the mouths of cross-shelf troughs, (Fig. 9). Large lobes, with a maximum run-out distance of 130 km linked to the presence of full-glacial fast-flowing ice streams from the most proximal slide scars, are present; they are them- (e.g. Laberg and Vorren, 1995; Dowdeswell et al., 1996, 1997; selves affected by smaller-scale slide processes, as suggested by the Dowdeswell and Siegert, 1999; Ó Cofaigh et al., 2003, 2004; presence of smaller slide scars. The ridge-and-depression shaped Evans et al., 2009). The increased loading due to the rapid surface of the lobes is interpreted as a series of pressure ridges accumulation of glacial sediment would favour the occurrence of (Fig. 4). These morphological characteristics suggest that lobes are slides. In addition, tectonic effects may also be important trig- cohesive masses composed of failed material (Hampton et al., 1996; gers for mass-wasting, including post-glacial seismicity linked to McAdoo et al., 2000). The acoustically transparent deposits isostatic readjustments during and following deglaciation and immediately basinward of the depositional features that evolve to earthquakes (Hampton et al., 1996; Piper et al., 1999; McAdoo stratified deposits towards the turbidite channel (Fig. 5C) are et al., 2000; Lee, 2009; Locat et al., 2009). The most important interpreted as debris flow deposits resulting from disintegrative source of seismicity on the region is related to the Greenland slides, composed of the fluidized part of the failed material fracture zone on the East Greenland Ridge (Fig. 1A), which (McAdoo et al., 2000). Part of the sediment transported by these affects particularly the Norske margin (Bungum and Husebye, debris flows may feed into the turbidite channel at the foot of the 1977; Gregersen, 1986, 2006; Poulsen and Simonsen, 2006; continental rise (Fig. 5A). The two isolated depositional lobes Voss et al., 2007). Finally, the location of slides is probably identified on the KJF margin are also interpreted as debris flows or also influenced by relatively weak stratigraphic layers, suggested disintegrative slides, as suggested by their acoustic facies and by the lateral continuity of slide scars across the continental morphology (Fig. 5D). slope (Fig. 4A). 76 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81

7.2. Turbidite systems 7.3. Sediment waves

Turbidite systems predominate on the distal continental slope Sediment-wave fields in the Greenland Basin (Fig. 6)are and deep basin (Figs. 6, 7, 8A, 9). The major turbidite system in the attributed to the activity of turbidite processes, as suggested by the Greenland Basin was active during full-glacial and deglacial predominance of laminated sand and mud turbidites in sediment conditions, with activity largely ceasing after about 13,000 years BP cores recovered from the proximal turbidite channel area (Ó according to dating of sediments from the levees beyond the Cofaigh et al., 2002, 2004), and their occurrence in an area domi- channel (Ó Cofaigh et al., 2004; Wilken and Mienert, 2006). The nated by debris flows (Fig. 9)(Belderson et al., 1984; Faugeres et al., implication of the timing of this activity is that it was linked to the 1993). Morphological characteristics such as the upslope migration relatively rapid full-glacial and deglacial delivery of sediments and of sediment waves and the orientation of crestlines parallel to the meltwater when the Greenland Ice Sheet extended across the regional slope also suggest a link to turbidites rather than contour continental shelf (Evans et al., 2009; Winkelmann et al., 2010). currents (Figs. 6 and 9; Normark et al., 1980; Wynn et al., 2000a,b; Physiography is important as it determines the potential for Wynn and Stow, 2002). The observation that some wave crests can transformation of glacially derived sediment on the upper slope be traced across the channels (Fig. 6A) also points to an origin into debris flows and turbidity currents (Migeon et al., 2011). related to unconfined currents rather than related to spillover from Although slope angle has been demonstrated to have small effect the turbidite channels. on the initiation of slides (Hühnerbach et al., 2004; Migeon et al., An alternative hypothesis for sediment waves would be their 2011), it determines the post-failure behaviour of the displaced origin in relation to gravitational deformation processes. This slide masses (Migeon et al., 2011). This may explain why mass- hypothesis is not favoured by the morphological characteristics, wasting deposits conserve their cohesion and form stacked debris such as the upslope migration, the asymmetric reflectivity and the lobes on the continental rise of the Norske margin, where the variations in sediment thickness across the waves. Finally, an gradients are relatively low (Fig. 9). In contrast, on the KFJ margin, ocean-current influence on the origin of sediment waves cannot be higher slope gradients may be linked to translation into turbidity clearly identified in the seafloor morphology of the Greenland currents. The presence of structural features also appears to have an Basin. The East Greenland Current flows along the margin from effect on the distribution of turbidite systems. Structural scarps Fram Strait to Denmark Strait as a strongly directional, south- affect both the trends and location of turbidite channels in the deep westward flow running parallel to the depth contours (Aagaard and basin, whereas volcanic edifices have a control on the location of Coachman, 1968; Swift and Aargaard, 1981; Woodgate et al., 1999; distal turbidite deposits which are restricted to the eastern side of Rudels et al., 2005). Although this current is likely to undergo the deeper edifices (Figs. 4 and 8). intensification due to topographical constraints at the Jan Mayen The detailed morphological study carried out in this work also Fracture Zone (Fig. 1A), its effect on the origin of the sediment enables some discussion of the evolution of the turbidite system. waves is unclear. The tributary channels on the mid-slope were probably produced by If we assume a turbidity-current origin for the sediment waves, intermittent mass-wasting at shallower depths which translated we can use their morphology to make inferences and calculations into turbidity currents. The abrupt morphological change at 2660 m about the characteristics of the flows that generated them. In water depth (Figs. 6A, 7A), where the channel becomes deeper and addition, spatial and temporal changes in morphological parame- asymmetrical with the development of prominent levees, can be ters such as size, symmetry and migration rate provide information explained by either of two processes. The first hypothesis involves about both spatial and temporal variations in turbidity-current a change in flow characteristics due to variations in regional slope. flow regime. Such a change in the regional gradient is observed, marking the The characteristics of a turbidity current can be inferred using termination of the sediment-wave field (0.36e0.05) about 15 km numerical models (Bowen et al., 1984; Wynn et al., 2000a,b; Ercilla proximal to the point where the trunk channel over-deepens et al., 2002). The internal Froude number (Fi), flow thickness and (Fig. 6A). This physiographical effect could have produced flow velocity have been estimated (Fig. 10, Table 2; see model a hydraulic jump, increasing turbidity flow thickness and decreasing details in Appendix 1). These calculations have been applied to velocity; this would favour overspill from the channel and deposi- sectors of the sediment-wave fields that have distinctive slope- tion of levees (Garcia and Parker,1989; Mulder and Alexander, 2001; gradient values (Fig. 10). Transect 1 was traced along an inter- Ercilla et al., 2002; García et al., 2006). While levee deposition may channel area between tributaries on the slope where the small be explained by this effect, it does not explain the sudden increase in sediment waves have been identified. Transect 2 parallels the trunk channel depth that is probably linked to an increase in flow velocity, channel on the main levee in the southernmost part of the system rather than to a decrease. A second hypothesis therefore involves (Fig. 10; Table 2). a change from a predominantly confined turbidity flow, responsible In general, modelled values of Fi decrease with reduction in for the development of a classical turbidite system (including slope gradient, indicating less turbulent flow (Bowen et al.,1984). In channels, levees and distal lobes), to predominantly unconfined the Greenland Basin sediment-wave fields, Fi is in the range turbidity flow that would favour the development of the observed 0.96e1.975, in general agreement with the estimated values of Fi sediment-wave fields and the partial burial and deactivation of the for turbidity currents that have generated coarse-grained sediment proximal part of the turbidite system. The hypotheses are not waves (Fi ranging 1e2; Piper and Savoye, 1993; Mulder et al., 1997; mutually exclusive, and a combination of the two, operating at Wynn et al., 2000a). No sediment waves occur in areas where the different times, could explain the morphology of the system. flow is sub-critical (i.e., significantly Fi < 1). Predicted flow thick- Depositional lobes in the deep basin can alternatively be inter- nesses across the entire wave field are from 27 to 335 m, with preted as debris-flow deposits, as suggested by their thickness, a maximum at the centre of the sediment-wave fields. Values for erosive character at the base and the occurrence of channels Transect 1, on the small sediment-wave field, are significantly lower eroding their upper limit (sub-bottom profile BeB0 in Fig. 8). (25e75 m) than for Transect 2 on the main levee, where they range Debris-flow deposits would be composed of glacigenic sediment from 93 to 335 m. Model-predicted velocities range between 11 and supplied to the continental slope during full-glacial conditions and 72 cm s 1, decreasing downslope. Maximum values may represent early stages of deglaciation, when the ice-sheet reached distal the velocity at the head of the turbidity current, where sediment positions on the continental shelf. concentration is higher, while minimum values would be found at M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 77

Fig. 10. Shaded relief swath image of the area of sediment-wave fields (located in inset), showing the position of the long-profile transects. Profiles show the sectors into which transects have been divided based on their gradient, for the analysis of the characteristics of turbidity-current flow (see Table 2). the tail of the current. Calculated values are similar to those of other turbidity-current processes on the continental slope, continental turbidity-current produced wave fields (Normark et al., 1980; rise and deep basin. The timing of deposition of these landforms is Bowen et al., 1984; Piper and Savoye, 1993; Wynn et al., 2000b; interpreted in relation to glacial processes, in particular to the Ercilla et al., 2002). relatively high volumes of sediment supplied by the ice sheet to the Spatial variations can also be inferred from the analysis of the continental margin at the LGM (e.g. Dowdeswell and Siegert, 1999). two distinct families of sediment waves on the Greenland Basin This implies that most of the observed submarine landforms were seafloor (Fig. 6D). Their presence suggests either the coexistence produced during full-glacial conditions, once the ice-sheet of two different mechanisms of wave formations, or a different grounding zone reached its most advanced position, and during degree of maturity between the two types of sediment waves. The the early stages of deglaciation, when sediment supply to the slope second option is favoured: first, there are no significant physio- was still high. This is in agreement with an ice sheet grounded at graphical variations to justify the existence of two coeval flows the outer continental shelf or even at the shelf-edge during the Late with different characteristics; secondly, the smaller sediment Weichselian glaciation of Northeast Greenland (Ó Cofaigh et al., waves develop above a w10 m thick acoustically transparent body 2002, 2004; Wilken and Mienert, 2006; Evans et al., 2009; interpreted as a small slide deposited at depths of 20e25 m below Winkelmann et al., 2010). The development of turbidity currents the seafloor. Sediment waves developed on top of this deposit is linked to both physiography and sediment supply, making this would therefore be more recent in origin, and may not have process likely to be active during both full-glacial and deglaciation reached the same degree of maturity. Temporal variations in the conditions. A temporal change in turbidite processes (from chan- flow characteristics are suggested by the existence of at least two nelised to unconfined flows) could be related to a progressive sets of sediment waves showing distinctive symmetry and decrease in sediment supply as deglaciation proceeds, deactivating migration rates (Fig. 6D). turbidite channels but maintaining sediment transport in the form of unconfined flows and the associated development of sediment- 7.4. Timing waves fields. Submarine mass-wasting would be favoured by both rapid full-glacial sediment delivery and the triggering action of The study of submarine landforms on the East Greenland isostatic movements (Hampton et al., 1996; Piper et al., 1999; margin and basin reveals a clear predominance of debris-flow and McAdoo et al., 2000; Lee, 2009; Locat et al., 2009).

Table 2 Characteristics of the turbidite ﬂow inferred from physiographic and morphologic parameters of the margin and the sediment waves. See Appendix 1 for details on the numerical models used for calculations.

Sector Gradient () H (m) WL (m) Fi (av) Flow thickness (m) Flow velocity (cm/s) Transect 1 1 1 No waves e 2.05 ee 2 0.7 5e15 500e700 1.71 27e38 11e35/13e42 3 0.635 5e10 1000 1.635 59 16e50 4 0.457 5e15 500e900 1.38 41e75 11e35/15e48

Transect 2 1 0.524 15e30 1300e2000 1.485 93e144 18e58/23e72 2 0.227 5e10 1300e2000 1.975 217e335 18e57/23e72 3 0.06 No waves e 0.5 ee 4 0.219 5e15 1000e1500 0.96 173e259 16e50/19e62 5 0.16 No waves e 0.82 e - 78 M. García et al. / Quaternary Science Reviews 49 (2012) 64e81

Fig. 11. A) Synthesis of the major sedimentary processes affecting the East Greenland margin and deep basin. B) Sketch of the differential controls on recent sedimentation on the Norske margin and the KFJ margin.

Since about 13,000 years BP, hemipelagic deposition has been interpretation of a Greenland Ice Sheet extending across the the dominant sedimentary process in most of the basin. After this continental shelf during the Last Glacial Maximum, perhaps as an time, mass-movement and turbidity-current activity appears to ice stream in Norske Trough. Mass-wasting would also have been have largely ceased, and an open-marine ice-distal environment favoured by tectonic effects, including both post-glacial seismicity became established in the Greenland Basin (Hebbeln et al., 1998; related to isostatic adjustments during deglaciation and regional Evans et al., 2002; Ó Cofaigh et al., 2004; Wilken and Mienert, seismicity. 2006). Although the resolution of the sub-bottom profiles does By contrast, the more southerly Kejser Franz Josef margin not allow the recognition of a hemipelagic draping layer, these presents small-scale mass-wasting deposits in the form of isolated sediments compose the top of most of the sediment cores recov- debris-flow lobes that most likely developed coevally with an ered from the margin and basin, except on the Norske margin extensive turbidite system composed of tributary valleys, major continental rise and distal basin. Here, corer penetration was pre- channels and sediment-wave fields, channel-levee systems and vented by relatively coarse surficial sediment composed of sandy, distal channels and depositional lobes (Fig. 11B). Turbidite-channel foraminifera-rich mud. This suggests that some downslope transfer systems cover practically the entire Greenland Basin (Mienert et al., of coarser-grained debris may have been active during the Holo- 1993; Ó Cofaigh et al., 2004; Wilken and Mienert, 2006). These cene in this part of the deep basin. systems are the result of two types of flows. Channelised turbidity flows are responsible for the transport of sediment from the 8. Summary and conclusions proximal continental slope to the deep basin through well- developed leveed-channels. Sediment involved in turbidite trans- This paper presents the first study of seafloor landforms on the port is interpreted as being supplied to the continental slope by East Greenland continental slope between 74N and 76N and glacial processes, based on the proposed chronology of the system, provides further morpho-sedimentary interpretations on land- which became largely inactive about 13,000 years BP (Ó Cofaigh forms from the Greenland Basin (Mienert et al., 1993; Ó Cofaigh et al., 2004; Wilken and Mienert, 2006). The channelisation of et al., 2002, 2004; Wilken and Mienert, 2006), based on the anal- sediment into turbidite channels, rather than the development of ysis of swath bathymetry datasets and sub-bottom TOPAS profiles major mass wasting (as in the case of the Norske margin) may be (Fig. 11A). This work has enabled the interpretation of sedimentary related to a relatively lower sediment supply and/or reduced landforms in terms of recent sedimentary processes and their tectonism. Unconfined flows ranging 11e72 cm s 1 produce the timing with relation to glacialeinterglacial cyclicity. The East extensive sediment-wave fields on the levees. Sediment waves Greenland continental margin shows two areas where distinct have developed coevally with small slides, showing different sedimentary processes predominate; the major processes and degrees of maturity, and their morphological characteristics also landforms are summarised in Fig. 11B. point to temporal changes in the characteristics of the flows. The more northerly Norske Trough margin is characterized by This paper demonstrates the glacial influence on recent deep- mass-wasting processes, with scarps and channel-like depressions sea sedimentation in the Greenland Basin. Although continental on the slope and debris-flow lobes deposited on the entire conti- shelves have been the focus of most the studies aiming to recon- nental rise (Fig. 11B). This suggests a relatively high sediment struction of Late Quaternary glacial environments, through identi- supply to the margin during glacial conditions, with the fication of landforms related to ice-sheet grounding on the seafloor, M. García et al. / Quaternary Science Reviews 49 (2012) 64e81 79 the study of more distal continental slope-basin systems which and h is flow thickness. C is a dimensionless number representing have a glacial influence can also provide valuable information about sediment concentration. It is relatively poorly constrained in the extent of past ice sheets. models and can vary depending on the type of flow. For unconfined turbidity currents formed of fine-grained sediments, values of 10 5 4 Acknowledgements and 10 may be suitable (e.g. Bowen et al., 1984; Piper and Savoye, 1993). We thank Neil Kenyon and Colm Ó Cofaigh for their help with data acquisition on Cruise JR51 of the RRS James Clark Ross. The References cruise was funded through UK NERC Grant GST/02/2198 to Julian Dowdeswell. A Marie Curie Intra-European Fellowship (7th Aagaard, K., Coachman, L., 1968. The East Greenland Current North of Denmark Framework Programme, European Commission) has supported the Strait: Part I. Arctic. North Am. 21, 181e200. Belderson, R.H., Kenyon, N.H., Stride, A.H., Pelton, C.D., 1984. A ‘braided’ distributary research of Marga Garcia in the Scott Polar Research Institute, system on the Orinoco deep-sea fan. Mar. Geol. 56, 195e206. University of Cambridge. Writing of the paper was completed while Bowen, A.J., Normark, W.R., Piper, D.J.W., 1984. Modelling of turbidity currents on Julian Dowdeswell was Visiting Cambridge Fellow at Gateway Navy submarine fan, California Continental Borderland. Sedimentology 31, 169e185. Antarctica, University of Canterbury, New Zealand, funded through Bungum, H., Husebye, E.S., 1977. Seismicity of the Norwegian Sea: the Jan Mayen the Erskine Bequest. M. Jakobsson received support from the fracture zone. Tectonophysics 40, 351e360. Swedish Research Council (VR) and the Bert Bolin Centre for Climate Canals, M., Urgeles, R., Calafat, A.M., 2000. Deep sea floor evidence of past ice streams off the Antarctic Peninsula. Geology 28, 31e34. Research at Stockholm University through a grant from FORMAS. We Damuth, J.E., 1980. Use of high-frequency (3.5e12 kHz) echograms in the study of are grateful to the editor and reviewers for their suggestions that near-bottom sedimentation processes in the deep-sea: a review. Mar. Geol. 38, have contributed to improve the quality and clarity of this work. 51e75. De Falco, G., Tonielli, R., Di Martino, G., Innangi, S., Simeone, S., Parnum, I.M., 2010. Relationships between multibeam backscatter, sediment grain size and Pos- Appendix 1. Calculations of turbidity-current characteristics idonia oceanica seagrass distribution. Cont. Shelf Res. 30, 1941e1950. Dowdeswell, J.A., Bamber, J.L., 2007. Keel depths of modern Antarctic icebergs and implications for sea-floor scouring in the geological record. Mar. Geol. 243, First, the internal Froude number is calculated. This value, in 120e131. combination with wavelength of sediment waves, is used to esti- Dowdeswell, J.A., Siegert, M.J., 1999. Ice-sheet numerical modeling and marine mate flow thickness; then, flow velocity is calculated based on the geophysical measurements of glacier-derived sedimentation on the Eurasian Arctic continental margins. Bull. Geol. Soc. Am. 111, 1080e1097. internal Froude number and sediment concentration. Dowdeswell, J.A., Uenzelmann-Neben, G., Whittington, R.J., Marienfeld, P., 1994a. The Late Quaternary sedimentary record in Scoresby Sund, East Greenland. e Internal Froude number (Fi) Boreas 23, 294 310. Dowdeswell, J.A., Whittington, R.J., Marienfeld, P., 1994b. The origin of massive diamicton facies by iceberg rafting and scouring, Scoresby Sund, East Fi for a turbidity current is calculated using (Bowen et al., 1984): Greenland. Sedimentology 41, 21e35. Dowdeswell, J.A., Kenyon, N.H., Elverhøi, A., Laberg, J.S., Hollender, F.-J., Mienert, J., fl 2 ¼ b= þ ; ¼ Siegert, M.J., 1996. Large-scale sedimentation on the glacier-in uenced Polar Fi sin Cf E Fi internal Froude number North Atlantic margins: long-range side-scan sonar evidence. Geophys. Res. e b fi Lett. 23, 3535 3538. where is slope angle, Cf is drag coef cient and E is entrainment Dowdeswell, J.A., Kenyon, N.H., Laberg, J.S., 1997. The glacier-influenced Scoresby coefficient. Sund Fan, East Greenland continental margin: evidence from GLORIA and 3.5 kHz records. Mar. Geol. 143, 207e221. 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The relationship between sediment-wave length (L), ow 17, 1e6. thickness and internal Froude number (Fi), is expressed as (modi- Ercilla, G., Alonso, B., Wynn, R.B., Baraza, J., 2002. Turbidity current sediment waves fied from Normark et al., 1980): on irregular slopes: observations from the Orinoco sediment-wave field. Mar. Geol. 192, 171e187. 2 Evans, J., Dowdeswell, J.A., Grobe, H., Niessen, F., Stein, R., Hubberten, H.-W., h ¼ L=2pFi Whittington, R.J., 2002. Late Quaternary sedimentation in Kejser Franz Joseph Fjord and the continental margin of East Greenland. In: Dowdeswell, J.A., Ó Cofaigh, C. (Eds.), Glacier-influenced Sedimentation on Flow velocity (u) High-Latitude Continental Margins. Geol. Soc. London, Sp. Publ., vol. 203, pp. 149e179. u is calculated based on internal Froude number and sediment Evans, J., Dowdeswell, J.A., Ó Cofaigh, C., Benham, T.J., Anderson, J.B., 2006. 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