An origin for laminated glacimarine sediments through sea-ice build-up and suppressed iceberg rafting

Laminated glacimarine sediments are observed in visual core logs and x-radiographs from Scoresby Sund and Nansen Fjord, east Greenland. They are mostly underlain and overlain by massive or stratified glacimarine diamicton (Dmm or Dms), which is a product of iceberg delivery of heterogeneous debris and, in Scoresby Sund, reworking by deep-drafted iceberg keels. The laminated sediments are AMS radiocarbon dated to two cold periods since the last, Late Weichselian deglaciation: the Younger Dryas stadial (Milne Land Stadial in east Greenland) and the Little Ice Age. During cold climatic events, multiyear shorefast sea ice ('sikussak') formed in these fjords and trapped the icebergs. Fine-grained, laminated muds (Fl) were deposited in Scoresby Sund when the flux of icebergs was suppressed, but turbid meltwater continued to provide some sediment flux to the fjord systems, varying through time to produce laminations. In Nansen Fjord, thinner and often massive mud layers (Fm) resulted from shorter intervals of sea-ice cover with no ice rafting. Stratified diamicton layers (Dms), which alternate with mud deposition to produce a laminated unit, probably represent intervening times of more open conditions with iceberg rafting. In Scoresby Sund, foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition. The absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites. There is no evidence of macrofaunal activity, and bioturbation is absent from the laminated sediments. Satellite data show that multiyear shorefast sea ice is present in several areas of the high Arctic today, and this traps icebergs calved from interior ice-cap drainage basins. Thus, the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and Quaternary Arctic.     

The Late Quaternary sedimentary record in Scoresby Sund, East Greenland

Until recently, little was known about the Quaternary marine sedimentary record in East Greenland. Geophysical and geological investigations in Scoresby Sund were undertaken to characterize the nature and chronology of this record. Seismic records show that almost 70% of the outer fjord system is covered by about 10 m of unlithified sediments, making direct correlation with the Quaternary records on land and the adjacent continental margin difficult. These acoustically unstratified sediments are scoured by icebergs above 550 m water depth. Almost 90% of core material is massive diamicton of Holocene age, deposited mainly from iceberg rafting and turbid meltwater. Sedimentation rates are 0.1 -0.3 m 1000 yr-¹. Thicker accumulations of unlithified Quaternary sediments in Scoresby Sund occur as sediment ridges and in two other major depocentres. A low sediment ridge runs across the mouth of Scoresby Sund, and is interpreted as an end moraine of Late Weichselian Flakkerhuk stadial age. The very restricted sediment thickness suggests that grounded ice filled the fjord during the Flakkerhuk and an ice shelf was not present. High inputs of ice rafted debris to the continental margin at about 18 000 BP indicate this as a probable age for the moraine. During the Allerød Interstadial, ice probably retreated from the outer fjord system, since massive diamictons similar to those of Holocene age are present at the base of most cores. A major depocentre of acoustically stratified sediments at the head of Hall Bredning is interpreted to represent ice proximal deposits from a glacier margin extending across the fjord. It is adjacent to dated moraines on land and is inferred to be of Milne Land stadial age (about 10 000 BP). A similar age is interpreted for acoustically laminated sediments and a moraine at the entrance of Vikingebugt, on the south side of Scoresby Sund. Dated kame terraces in the inner fjord system indicate that ice retreated to its present position 6–7000 years ago.     

10Be ages from central east Greenland constrain the extent of the Greenland ice sheet during the Last Glacial Maximum

Traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the East Greenland continental margin during the Last Glacial Maximum (LGM): ice to the shelf break south of Scoresby Sund and ice extending no further than to the inner shelf at and north of Scoresby Sund. We report new ¹⁰Be ages from erratic boulders perched at 250 m a.s.l. on the Kap Brewster peninsula at the mouth of Scoresby Sund. The average ¹⁰Be ages, calculated with an assumed maximum erosion rate of 1 cm/ka and no erosion (respectively, 17.3±2.3 ka and 15.1±1.7 ka) overlap with a period of increased sediment input to the Scoresby Sund fan (19–15 ka). The results presented here suggest that ice reached at least 250 m a.s.l. at the mouth of Scoresby Sund during the LGM and add to a growing body of evidence indicating that LGM ice extended onto the outer shelf in northeast Greenland.     

The last glacial cycles in East Greenland, an overview

Marine, fluvial and glacigene sediments exposed in coastal cliffs and stream-cut sections in East Greenland between latitudes 69° and 78° N display a record of Quaternary climatic and environmental change going back to pre-Saalian times (> 240 ka), but with main emphasis on the last interglacial/glacial cycle. The stratigraphical scheme is based on studies on the Jameson Land peninsula, and contains five glacial stages and stades with the Greenland ice sheet or its outlets reaching the outer coasts. Individual sites are correlated and dated by a combination of biostratigraphy, luminescence dating, amino acid analyses, as well as ¹⁴C- and uranium series dating. The pre-Weichselian Lollandselv and Scoresby Sund glaciations were the most extensive. During the Weichselian the Inland Ice margin in this part of East Greenland was apparently very stable. The Aucellaelv, Jyllandselv and Flakkerhuk stades mark the advance and subsequent retreat of outlet glaciers from the Inland Ice which advanced through the wide Scoresby Sund basin and reached the inner shelf. In-between the glacier advances, three interglacial or interstadial periods have been recognized. During the Langelandselv interglacia-tion (≅ Eemian) the advection of warm Atlantic water was higher than during the Holocene, and the terrestrial flora and insect faunas show that summer temperatures were 3–4°C higher than during the Holocene optimum. There is no unambiguous evidence for cooling in the sediments from this interval. Later, in isotope stage 5, there were apparently two ice-free periods. During the Hugin Sø interstade, stable Polar water dominated Scoresby Sund, and the terrestrial flora suggests summer temperatures 2° -3° lower than the present. The marine and fluvial sediments from the second ice-free period, the Mønselv interstade, are devoid of organic remains.     

Interactions between the Greenland Ice Sheet and the Liverpool Land coastal ice cap during the last two glaciation cycles

The sedimentary record from the Ugleelv Valley on central Jameson Land, East Greenland, adds new information about terrestrial palaeoenvironments and glaciations to the glacial history of the Scoresby Sund fjord area. A western extension of a coastal ice cap on Liverpool Land reached eastern Jameson Land during the early Scoresby Sund glaciation (≈the Saalian). During the following glacial maximum the Greenland Ice Sheet inundated the Jameson Land plateau from the west. The Weichselian also starts with an early phase of glacial advance from the Liverpool Land ice cap, while polar desert and ice‐free conditions characterised the subsequent part of the Weichselian on the Jameson Land plateau. The two glaciation cycles show a repeated pattern of interaction between the Greenland Ice Sheet in the west and an ice cap on Liverpool Land in the east. Each cycle starts with extensive glacier growth in the coastal mountains followed by a decline of the coastal glaciation, a change to cold and arid climate and a late stage of maximum extent of the Greenland Ice Sheet. Copyright © 2005 John Wiley & Sons, Ltd.     

Dating of raised marine and lacustrine deposits in east Greenland using beryllium‐10 depth profiles and implications for estimates of subglacial erosion

Here we combine ¹⁰Be depth profile techniques applied to late glacial ice‐contact marine and lacustrine deltas, as well as boulder exposure dating of associated features in the Scoresby Sound region, east Greenland, to determine both the surface age and the magnitude of cosmogenic nuclide inheritance. Boulder ages from an ice‐contact delta in northern Scoresby Sund show scatter typical of polar regions and yield an average age of 12.8 ± 0.5 ka – about 2 ka older than both our average profile surface age of 10.9 ± 0.7 ka from three depth profiles and a radiocarbon‐based estimate. On the other hand, boulder exposure ages from a set of moraines in southern Scoresby Sund show excellent internal consistency for polar regions and yield an average age of 11.6 ± 0.2 ka. The profile surface age from a corresponding ice‐contact delta is 8.1 ± 0.9 ka, while a second delta yields an age of 10.0 ± 0.4 ka. Measured ¹⁰Be inheritance concentrations from all depth profiles are internally consistent and are between 10% and 20% of the surface concentrations, suggesting a regional cosmogenic inheritance signal for the Scoresby Sound landscape. Based on the profile inheritance concentrations, we explore the first‐order catchment‐averaged bedrock erosion under the Greenland ice sheet, yielding estimates of total erosion during the last glacial cycle of the order of 2–30 m. Copyright © 2010 John Wiley & Sons, Ltd.     

The interglacial-glacial record at the mouth of Scoresby Sund, East Greenland

The sedimentary record around outer Scorcsby Sund begins with the Scorcsby Sund glaciation (≅ isotope stage 6), but is incomplete. Both at Kap Hope, headward of the fjord mouth, and at Kikiakajik on the outer coast. there are shallow marine sediments, correlated with the Langelandselv interglaciation (≅ isotope substagc 5e) on the basis of molluse assemblages and luminescence dates. Abundant Balanus crenatus , and several bivalves. show that thc adveetion of warm Atlantic water to the East Greenland coast was higher during that interglacial than during the Holocenc. Glacial striae at Kap Brewster (facing the open ocean) and till on top of the interglacial beds at Kikiakajik show that both an outlet from the Greenland Iee Sheet, and more local glaciers reached the continental shelf during the Weichselian. This glacial event is poorly dated. but tentatively correlated with the Flakkerhuk stade (≅ 19 15 ka BP) when, from marine geological data, it is suggested that thc Scoresby Sund glacier terminated c . 30 km east of Kap Brewster. During the Milne Land stade ( c . 10 ka BP) there was a resurgence of local ice caps in the mountains both north and south of the fjord mouth, but Scoresby Sund and Hall Bredning probably remained free of glaciers. Dating of these events was achieved through Iuminescence- (TL and OSL) and the ¹⁴C-method. and biostratigraphical and amino acid correliition Interglacial shells on thc outer coast show much lower amino acid D/L ratios than shells of the same age within the Scoresby Sund area. This may indicate that the outer coast remained free of ice cover and marine inundation much longer, arid suffered colder temperatures than areas along the fjord.     

The origin of massive diamicton facies by iceberg rafting and scouring, Scoresby Sund, East Greenland

Almost 90% of 39 m of core material recovered from Scoresby Sund and the adjacent East Greenland shelf is massive diamicton, interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring. There is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources. Model calculations suggest that the ¹⁴C derived Holocene sedimentation rate of 0.1-0.3 m 1000 yr⁻¹ in Scoresby Sund can be accounted for mainly by iceberg rafting of debris. A further 4% of core material is of gravel or coarse sand lenses, interpreted to reflect iceberg dumping of debris. Intensive iceberg scouring, which reworks sea floor sediments, is observed on acoustic records from over 30 000 km² of the Scoresby Sund fiord system and the adjacent East Greenland shelf (69-72°N and 75°N). The rate of iceberg production from Greenland Ice Sheet outlet glaciers, and iceberg drift tracks on the shelf, suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km² area above the shelf break. The relatively extensive modern occurrence of massive diamicton, formed by iceberg rafting and scouring, together with suspension settling of fines, suggests that it may also be a significant facies in the glacier-influenced geological record. The recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers.     

Late Pleistocene stratigraphy and depositional environments of the Fynselv area, Jameson Land, East Greenland

Deposits of Late Pleistocene age were investigated near the Fynselv river on the southwestern coast of Jameson Land. East Greenland. The deposits are of fluvial, deltaic shallow marine and glacigenic origin. Four stratigraphic units are recorded. Unit I consists of deltaic and shallow marine deposits reflecting a relative sea level of at least 20 m above the present. Elevated fluvial deposits represent the subaerial part of the depositional system. The system existed during full interglacial and subarctic conditions as indicated by remains or flora and Fauna and unit I is correlated with the Langelandselv interglaciation (isotopic substage 5e). Unit II consists of a till deposited by a glacier in the Scoresby Sund Fjord during the beginning of the Early Weichselian referred to as the Aucellaelv stade. The glacier probably melted in a marine environment. Unit III represents a marine delta system during the Hugin Sø interstade. and reveals a relative sea level of at least 62 m above the present. Unit IV consists of till and kame deposits assumed to be deposited by a glacier in the Scoresby Sund Fjord during the Flakkerhuk stade. probably a Late Weichselian glacier advance.     

Seismic stratigraphy records the deglacial history of Jakobshavn Isbræ, West Greenland

Jakobshavn Isbræ is one of the largest ice streams in the Greenland Ice Sheet, presently draining c. 6.5% of the Inland Ice. Here we present high‐resolution Chirp and Sparker sub‐bottom profiles from a seismic survey conducted just outside of the Jakobshavn Isfjord, which provides detailed insight into the glacimarine sedimentary history of the Jakobshavn ice stream during the Holocene. We observe acoustically stratified and homogeneous sediments that drape an irregular substratum and were deposited between ～10 and c. 7.6k cal a BP. The stratified lower units are interpreted as the product of ice‐proximal glacimarine sedimentation deposited rapidly when the grounded ice margin was located close to depositional basins on topographic highs. The upper acoustically homogenous units reflect suspension settling of fine‐grained material and gravitational flows that were extruded from an increasingly unstable ice margin as the ice retreated into the fjord. Proximity to the ice margin and bedrock topography were the dominant controls on sediment accumulation during deglaciation although the 8.2‐ka cooling event probably influenced the position of the ice margin at the fjord mouth. The post‐glacial sedimentary record is characterized by glacimarine and hemipelagic rainout with an increased ice‐rafted detritus fraction that records sedimentation following ice stream retreat into Jakobshavn Isfjord sometime after c. 7.8k cal a BP. Copyright © 2011 John Wiley & Sons, Ltd.     

Marine geophysical evidence for former expansion and flow of the Greenland Ice Sheet across the north‐east Greenland continental shelf

High‐resolution swath bathymetry and TOPAS sub‐bottom profiler acoustic data from the inner and middle continental shelf of north‐east Greenland record the presence of streamlined mega‐scale glacial lineations and other subglacial landforms that are formed in the surface of a continuous soft sediment layer. The best‐developed lineations are found in Westwind Trough, a bathymetric trough connecting Nioghalvfjerdsfjorden Gletscher and Zachariae Isstrøm to the continental shelf edge. The geomorphological and stratigraphical data indicate that the Greenland Ice Sheet covered the inner‐middle shelf in north‐east Greenland during the most recent ice advance of the Late Weichselian glaciation. Earlier sedimentological and chronological studies indicated that the last major delivery of glacigenic sediment to the shelf and Fram Strait was prior to the Holocene during Marine Isotope Stage 2, supporting our assertion that the subglacial landforms and ice sheet expansion in north‐east Greenland occurred during the Late Weichselian. Glacimarine sediment gravity flow deposits found on the north‐east Greenland continental slope imply that the ice sheet extended beyond the middle continental shelf, and supplied subglacial sediment direct to the shelf edge with subsequent remobilisation downslope. These marine geophysical data indicate that the flow of the Late Weichselian Greenland Ice Sheet through Westwind Trough was in the form of a fast‐flowing palaeo‐ice stream, and that it provides the first direct geomorphological evidence for the former presence of ice streams on the Greenland continental shelf. The presence of streamlined subglacially derived landforms and till layers on the shallow AWI Bank and Northwind Shoal indicates that ice sheet flow was not only channelled through the cross‐shelf bathymetric troughs but also occurred across the shallow intra‐trough regions of north‐east Greenland. Collectively these data record for the first time that ice streams were an important glacio‐dynamic feature that drained interior basins of the Late Weichselian Greenland Ice Sheet across the adjacent continental margin, and that the ice sheet was far more extensive in north‐east Greenland during the Last Glacial Maximum than the previous terrestrial–glacial reconstructions showed. Copyright © 2008 John Wiley & Sons, Ltd.     

Turbidite deposition on the glacially influenced,canyon‐dominated Southwest Grand Banks Slope,Canada

The deeply dissected Southwest Grand Banks Slope offshore the Grand Banks of Newfoundland was investigated using multiple data sets in order to determine how canyons and intercanyon ridges developed and what sedimentary processes acted on glacially influenced slopes. The canyons are a product of Quaternary ice‐related processes that operated along the margin, such as ice stream outwash and proglacial plume fallout. Three types of canyon are defined based on their dimensions, axial sedimentary processes and the location of the canyon head. There are canyons formed by glacial outwash with aggradational and erosional floors, and canyons formed on the slope by retrogressive failure. The steep, narrow intercanyon ridges that separate the canyons are composite morphological features formed by a complex history of sediment aggradation and degradation. Ridge aggradation occurred as a result of mid to late Quaternary background sedimentation (proglacial plume fallout and hemipelagic settling) and turbidite deposition. Intercanyon ridge degradation was caused mainly by sediment removal due to local slump failures and erosive sediment gravity flows. Levée‐like deposits are present as little as 15 km from the shelf break. At 30 km from the shelf, turbidity currents spilled over a 400 m high ridge and reconfined in a canyon formed by retrogressive failure, where a thalweg channel was developed. These observations imply that turbidity currents evolved rapidly in this slope‐proximal environment and attained flow depths of hundreds of metres over distances of a few tens of kilometres, suggesting turbulent subglacial outwash from tunnel valleys as the principal turbidity current‐generating mechanism.     

Late Quaternary glacial history of the central west coast of Jameson Land, East Greenland

The Late Quaternary ( c . 130,000–10,000 BP) glacial history of the central west coast of Jameson Land, East Greenland, is reconstructed through glacial stratigraphical studies. Seven major sedimentary units are described and defined. They represent two interglacial events (where one is the Holocene). one interstadial event and two glacial events. The older interglacial event comprises marine and fluvial sediments, and is correlated to the Langelandselv interglacial, corresponding to oxygen isotope sub-stage 5e. It is followed by an Early Weichselian major glaciation during the Aucellaelv stade, and subsequently by an Early Weichselian interstadial marine and deltaic event (the Hugin Sø interstade). Sediments relating to the Middle Weichselian have not been recognized in the area. The Hugin Sø interstade deposits have been overrun by a Late Weichselian ice advance, during the Flakkerhuk stade, when the glacier, which probably was a thin, low gradient fjord glacier in Scoresby Sund, draped older sediments and landforms with a thin till. Subsequent to the final deglaciation, some time before 10,000BP, the sea reached the marine limit around 70 m a.s.l., and early Holocene marine, fluvial and littoral sediments were deposited in the coastal areas.     

Recent foraminifera in shelf sediments of the Scoresby Sund fjord, East Greenland

A study of sea-bottom samples from shallow waters in the northern part of Scoresby Sund, off Jameson Land, East Greenland, reveals four different foraminiferal assemblages between 1.3 and 35.6 m water depth. The shallowest samples. Assemblage SA (1.3–2.2 m), contain only very few foraminifera, presumably due to the annual repeated formation of an ice foot. Assemblage SB (3.7 and 4.3 m) is characterized by the calcareous species Haynesina nivea and H. orbiculare , while the arenaceous species Spiropleclammina biformis, Reophax arctica , and Recurvoides turbinatus dominate all the faunas of Assemblage SC (9.3–25.9 m depth). The change in fauna to the succeeding Portatrochammina bipolaris - Spiropleclammina biformis fauna (Assemblage SD, 29.6 and 35.6 m) presumably corresponds to the transition from the shallow Fjord water layer to the deeper and relatively more stable Polar water. Elphidiella hannai (Cushman & Grant) is recorded live for the first time in recent assemblages from the Atlantic Ocean.     

Earliest Holocene deglaciation of the central Uummannaq Fjord system,West Greenland

Uummannaq Fjord, West Greenland, held the Uummannaq Ice Stream system that drained an estimated ~6% of the Greenland Ice Sheet (GrIS) during the Last Glacial Maximum. Published ages for the final deglaciation in Uummannaq Fjord vary from as early as c. 9.8 ka to as late as c. 5.3 ka. Assessing this variability requires additional chronological controls to improve the deglaciation history of central West Greenland. Here, we combine ¹⁴C dating of lake sediment cores with cosmogenic ¹⁰Be exposure dating at sites adjacent to the present GrIS margin in the central‐inland sector of the Uummannaq Fjord system. We find that ice retreated to or within the present GrIS margin at 10.8±0.2 ka (n = 6). Although this ‘final deglaciation’ to or within the present GrIS margin across the Uummannaq Fjord system varies from c. 10.8 to 5.3 ka, all chronologies indicate collapse from the continental shelf to the inner fjords at c. 11.0 ka, which occurred at a net retreat rate of 300–1100 m a⁻¹. The Uummannaq Fjord system deglaciated c. 1000 years earlier than the major fjord system to the south, Disko Bugt. However, similarly rapid retreat rates of the two palaeo‐ice stream systems suggest that their collapse may have been aided by high calving rates. The asynchronous deglaciation of the GrIS throughout the Uummannaq Fjord system probably relates to the influence of varying fjord geometry on marine glacier behaviour.     

The Aucellaelv stade at Aucellaelv, the first Weichselian glacier advance in Scoresby Sund, East Greenland

The first major Weichselian ice advance in Scoresby Sund, during the Aucellaelv stage, deposited thick till beds along the coast of Jameson Land between > 107 ka and 140 ka. and is correlated with isotope substage 5d in the marine record. This is shown by stream-cut sections at the mouth of the Aucellaelv. Jameson Land, which contain a scquence of shallow marine, fluvial and glacigene sediments extending from the Scoresby Sund glaciation (≅Saalian) to the Flakkerhuk stade (Late Weichselian). The sequence is dated by palaeoceanographic correlation with the deep-sea record, U/Th and luminescence dating, and correlated with the record in adjacent areas by mapping of marker horizons, and by mollusc fauna assemblages and amino acid analyses.     

Facies and stratigraphical analyses of glacial and interglacial sediments at Morgan Bluffs,Banks Island,Canadian Arctic Archipelago

Stratigraphical exposures of both glacial and non‐glacial sediments at Morgan Bluffs, a >6‐km long exposure on the east coast of Banks Island, comprise a discontinuous archive of Quaternary environmental change. A detailed facies analysis of the sediments and a new stratigraphical framework is incompatible with the many climatostratigraphical units proposed previously. Instead, three distinct intervals of sedimentation are recognized. The first records the progradation of a delta, followed by fluvial aggradation of a braided river valley perhaps ～1 Ma. The second documents glacigenic sedimentation, including fluctuations of a tidewater glacier margin, in a marine basin more than 0.78 Ma. The third records till deposition by the NW Laurentide Ice Sheet during the Late Wisconsinan, followed by the progradation of a deglacial, ice‐contact delta into an ice‐dammed lake ～12.8 cal. ka BP. The revised stratigraphical framework adds important new terrestrial observations to a sparse and fragmentary data set of Quaternary environmental change in the Canadian Arctic. This study challenges former references and correlations to the previously proposed climatostratigraphical framework and nomenclature.     

Be data from meltwater channels suggest that Jameson Land, east Greenland, was ice-covered during the last glacial maximum

Along the northeast Greenland continental margin, bedrock on interfjord plateaus is highly weathered, whereas rock surfaces in fjord troughs are characterized by glacial scour. Based on the intense bedrock weathering and lack of glacial deposits from the last glaciation, interfjord plateaus have long been thought to be ice-free throughout the last glacial maximum (LGM). In recent years there is growing evidence from shelf and fjord settings that the northeast Greenland continental margin was more extensively glaciated during the LGM than previously thought. However, little is still known from interfjord settings. We present cosmogenic ¹⁰Be data from meltwater channels and weathered sandstone outcrops on Jameson Land, an interfjord highland north of Scoresby Sund. The mean exposure age of samples from channel beds (n = 3) constrains on the onset of deglaciation on interior Jameson Land to 18.5 ± 1.3–21.4 ± 1.9 ka (for erosion conditions of 0–10 mm/ka, respectively). This finding adds to growing evidence that the northeast Greenland continental margin was more heavily glaciated during the LGM than previously thought.     

Late Quaternary changes in sediment composition on the NE Greenland margin (~73° N) with a focus on the fjords and shelf

In order to document changes in Holocene glacier extent and activity in NE Greenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 and PS2640), across the shelf (PS2623 and PS2641), to the Greenland Sea (JM07‐174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X‐ray diffraction of the <2 mm sediment fraction). Fjord core PS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain‐size modes are distinguished of which only one is associated with a coarse ice‐rafting signal – this mode is rare in the mid‐ and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down‐core changes in sediment composition based on the upper late Holocene sediments from cores PS2640 (Sofia Sund), PS2631 (Kaiser Franz Joseph Fjord) and PS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centred c. 2.5, 4.5 and 7.5 cal. ka BP (±0.5 ka) but are rarely linked with changes in the grain‐size spectra. Coarse IRD (>2 mm) and IRD‐grain‐size spectra are rare in the last 9–10 cal. ka BP and, in contrast with areas farther south (~68° N), there is no distinct IRD signal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.     

Glacimarine lithofacies,provenance and depositional processes on a West Greenland trough‐mouth fan

Along the West Greenland continental margin adjoining Baffin Bay, bathymetric data show a series of large submarine fans located at the mouths of cross‐shelf troughs. One of these fans, termed here ‘Uummannaq Fan’, is a trough‐mouth fan built largely by debris delivered from a fast‐flowing outlet of the Greenland Ice Sheet during past glacial maxima. Cores from this fan provide the first information on glacimarine sedimentary facies within a major West Greenland trough‐mouth fan and on the nature of Late Weichselian–Holocene glacigenic sediment delivery to this region of the Baffin Bay margin. Glacigenic debris flows deposited on the upper slope and extending to at least 1800 m water depth in front of the trough‐mouth are related to the remobilization of subglacial debris that was delivered onto the upper slope at times when an ice stream was positioned at the shelf edge. In contrast, sedimentary facies from the northern sector of the fan are characterized by hemipelagic and ice‐rafted sediments and turbidites; glacigenic debris flows are notably absent in cores from this region. Quantitative X‐ray diffraction studies of the <2‐mm sediment fraction indicate that the bulk of the sediment in the fan is derived from Uummannaq Trough but there are distinct intervals when sediment from northern Baffin Bay sources dominates, especially on the northern limit of the fan. These data demonstrate considerable variation in the nature of sediment delivery across the Uummannaq Fan when the Greenland Ice Sheet was at the shelf edge. They highlight the variability of glacimarine depositional processes operating on trough‐mouth fans on high‐latitude continental margins during the last glacial maximum and indicate that glacigenic debris flows are just one of a number of mechanisms by which such large depocentres form. Copyright © 2012 John Wiley & Sons, Ltd.