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Relationship Between Continental Rise Development and Palaeo-Ice Sheet Dynamics, Northern Antarctic Peninsula Pacific Margin

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Relationship Between Continental Rise Development and Palaeo-Ice Sheet Dynamics, Northern Antarctic Peninsula Pacific Margin ARTICLE IN PRESS Quaternary Science Reviews 25 (2006) 933–944 Relationship between continental rise development and palaeo-ice sheet dynamics, Northern Antarctic Peninsula Pacific margin David Amblasa, Roger Urgelesa, Miquel Canalsa,Ã, Antoni M. Calafata, Michele Rebescob, Angelo Camerlenghia, Ferran Estradac, Marc De Batistd, John E. Hughes-Clarkee aGRC Geocie`ncies Marines, Universitat de Barcelona, Martı´ i Franque`s s/n, E-08028 Barcelona, Spain bIstituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/c, 34010 Sgonico, Trieste, Italy cCSIC Institut de Cie`ncies del Mar, Passeig Marı´tim Barceloneta 37-49, 08003 Barcelona, Spain dRenard Centre of Marine Geology, Ghent University, Krijgslaan 281 S8, B-9000 Gent, Belgium eOcean Mapping Group, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3 Received 17 December 2004; accepted 10 July 2005 Abstract Acquisition of swath bathymetry data west of the North Antarctic Peninsula (NAP), between 631S and 661S, and its integration with the predicted seafloor topography of Smith and Sandwell [Global seafloor topography from satellite altimetry and ship depth soundings. Science 277, 1956–1962.] reveal the links between the continental rise depositional systems and the NAP palaeo-ice sheet dynamics. The NAP Pacific margin consists of a wide continental shelf dissected by several troughs, tens of kilometres wide and long. The Biscoe Trough, which has been almost entirely surveyed with multibeam sonar, shows spectacular fan-shaped streamlining sea-floor morphologies revealing the presence of ice streams during the Last Glacial Maximum. In the study area the continental rise comprises the six northernmost sediment mounds of the NAP Pacific margin and the canyon-channel systems between them. These giant sediment mounds have developed since the early Neogene by southwest flowing bottom currents, which have redistributed along the margin the fine-grained component of the turbiditic currents flowing down canyon-channel systems. The widespread evidence of shallow slope instability within the sediment mounds has been identified from both swath bathymetry and topographic parametric sonar seismic reflection profiles. Bathymetric data show that the heads of all the rise canyon-channel systems coincide geographically with the mouths of the major glacial troughs on the continental shelf edge. This suggests a close genetic link between these morphological features and allows considering a glacio-sedimentary model for the western NAP outer margin seascape development. This model considers the availability of depositional space on the continental rise as the limiting factor for mound development. The depositional space, in turn, is controlled by the spacing between glacial maxima shelf-edge reaching ice streams. This model takes into account both glacial and interglacial scenarios and gives new insights on evaluating the palaeoenvironmental record of the continental rise sediment mounds. r 2005 Elsevier Ltd. All rights reserved. 1. Introduction sensitive glacial systems (Canals et al., 2000, 2002, 2003; O´ Cofaigh et al., 2002). Local ice caps form the present The location of the boundary from sub-polar to polar day glacial cover of islands around the peninsula, climatic conditions in the Northern Antarctic Peninsula whereas an ice sheet of variable thickness covers most (NAP) and its relatively warm maritime setting (Griffith of the Antarctic Peninsula itself. Currently, the ice and Anderson, 1989) have led to very dynamic and drains perpendicular to the Peninsula axis through valley glaciers and ice streams that erode and transport ÃCorresponding author. Tel.: +34 93 402 13 60; sediment to the coast and the inner shelf. In contrast, fax: +34 93 402 13 40. during glacial periods grounded ice sheets reached the E-mail address: [email protected] (M. Canals). shelf edge (Bentley and Anderson, 1998; Anderson et al., 0277-3791/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2005.07.012 ARTICLE IN PRESS 934 D. Amblas et al. / Quaternary Science Reviews 25 (2006) 933–944 2002) eroding deep troughs beneath fast flowing ice first stage, recorded by a basal regional unconformity, streams on the NAP inner shelf (Alley et al., 1989; Pope has been interpreted as having been caused by an and Anderson, 1992; Pudsey et al., 1994; Rebesco et al., enhancement in near-bottom currents associated with 1998; Canals et al., 2000; Domack et al., in press) and the opening of the Drake Passage during the Late depositing prograding sequences on the outer shelf Oligocene (Tucholke, 1977). This critical geodynamic (Larter and Barker, 1989; Larter and Cunningham, event facilitated the establishment of Neogene glaciation 1993). During these cold periods, large volumes of in Antarctica (Kennet, 1977) and hence, led to increased unsorted glacigenic sediments were delivered to, and sediment supply to the Antarctic margins. Sediment then bypassed, the upper slope as small volume but gravity flows funneled by the gullies and canyon-channel frequent events feeding the depositional systems of the systems draining the west of the NAP outer margin NAP Pacific continental rise (McGinnis and Hayes, largely contributed to the supply of fines to the deep 1995; Rebesco et al., 1996). margin and basin environments. Southwesterly flowing Large sediment mounds are characteristic features bottom currents originated in the Weddell Sea redis- along the continental rise of the NAP Pacific margin. tributed such fines along the continental rise (Rebesco Twelve mounds have been studied over the last decade, et al., 1996). This allowed the main drift growth phase including Ocean Drilling Program Leg 178 (Barker (from 15 to about 5 Ma BP) that corresponds with the et al., 1999), mainly because of the presumed value of second stage of drift development (Rebesco et al., 1996, their sediment record for understanding the Neogene 1997). The third stage (from about 5 Ma to present) was Antarctic glaciation. These sediment mounds have been characterised by reduced bottom current activity. These interpreted as sediment drifts produced by bottom three stages have been identified from the seismic currents redistributing the fine-grained component of stratigraphy and can be correlated over large distances channelised turbidity currents (Rebesco et al., 1996). (Rebesco et al., 2002). Numerous erosional unconformities observed in seismic In this paper we present in unprecedented detail, the reflection profiles suggest complex interactions between swath bathymetry of the NAP Pacific margin, including down-slope and along-slope processes throughout the the six northernmost continental rise mounds located history of these mounds. Conceptual models suggest between 631S and 651400S off the Biscoe and Palmer that these deposits formed in three major stages. The archipelagos (Fig. 1). The swath data also cover most of Fig. 1. 3D view of the Northern Antarctic Peninsula region constructed from Smith and Sandwell (1997) predicted topography. View is from southwest (2301) and the illumination is from north–northeast (0201). Scale calculated at 651S. The bold yellow line shows the boundaries of the study area. Colour code is as follows: grey: emerged landmasses; light blue: continental shelf and slope; dark blue: continental rise and deep basin. See also colour bar for altitudes. ARTICLE IN PRESS D. Amblas et al. / Quaternary Science Reviews 25 (2006) 933–944 935 the continental slope and part of the adjacent con- 66,000 km2 (Fig. 2). The Simrad EM 12-S echosounder tinental shelf (Fig. 2). These data have been combined transmits 81 beams across a total swath angle of 1201 with the predicted sea-floor topography of Smith and producing a maximum swath width that is 3.5 times the Sandwell (1997), which on the whole gives an integrated water depth. The system is hull mounted and works at a view of the study area (Fig. 3A). The analysis of the frequency of 12.5 kHz, resolving features of a few meters geomorphic relationships between continental shelf and in height. Multibeam data were logged using Simrad’s rise morphosedimentary features allows proposing a Mermaid system and processed with the Swathed glacio-sedimentary model that links palaeo-ice sheet software. The bathymetry data set was then merged dynamics with outer margin sedimentation. The under- with the predicted sea-floor topography of Smith and standing of such a genetic relationship is significant to Sandwell (1997). Final 100 m grid spacing maps of the interpret the climatic record contained in the large NAP study area were generated using the Generic Mapping Pacific margin sediment mounds. The proposed model Tools (GMT) software (Wessel and Smith, 1991). represents a step forward with respect to former models Topographic parametric sonar seismic reflection (e.g. Rebesco et al., 1998), which were based on fewer profiles (TOPAS) were simultaneously acquired. The and lower resolution data. TOPAS is a hull-mounted sub-bottom profiler based on the parametric interference principle. It uses two primary frequencies of 21.5 and 18 kHz leading to a 2. Material and methods secondary very narrow beam with a frequency of 3.5 kHz, which gives a resolution better than 1 m and a The data set was acquired during BIO Hesperides typical penetration depth between 50 and 200 ms in cruises GEBRAP’96 and COHIMAR’01 with a Simrad deep-sea unconsolidated muds. Pulse triggering of EM EM 12-S multibeam echosounder in the austral sum- 12-S and TOPAS systems was controlled by a Simrad mers of 1996–1997 and 2001–2002, respectively. The synchronicity unit during COHIMAR’01 cruise. The data acquired during both cruises covers an area of absence of such a system during the GEBRAP’96 cruise, Fig. 2. Ship tracks from BIO Hesperides cruises GEBRAP’96 (white dashed lines) and COHIMAR’01 (white lines) on the northern Bellingshausen Sea. Bathymetric contours are plotted from Smith and Sandwell (1997) predicted bathymetry. Contour interval is 100 m. A small box with dotted edges centred at 66.31W and 64.21S corresponds to erroneous Smith and Sandwell (1997) data. ARTICLE IN PRESS 936 D.
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