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Quaternary Science Reviews 30 (2011) 3603e3617 Contents lists available at SciVerse ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel, Antarctic Peninsula Stephen J. Robertsa,1, Dominic A. Hodgsona,*,1, Mieke Sterkenb,1, Pippa L. Whitehousec, Elie Verleyenb, Wim Vyvermanb, Koen Sabbeb, Andrea Balboa, Michael J. Bentleyc, Steven G. Moretond a British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK b Laboratory of Protistology and Aquatic Ecology, Ghent University, B-9000 Gent, Belgium c Department of Geography, University of Durham, South Road, Durham DH1 3LE, UK d Natural Environment Research Council Radiocarbon Facility, Scottish Enterprise Technology Park, East Kilbride, UK article info abstract Article history: The recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and Received 4 January 2011 retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic Received in revised form ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass 5 September 2011 change need to be corrected for ongoing glacial isostatic adjustment, a process which must be con- Accepted 13 September 2011 strained by geological data. However, there are relatively little geological data on the geometry, volume Available online 26 October 2011 and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints Keywords: Sea-level on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Ice sheets Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated Deglaciation marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Holocene Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of À À À Palaeolimnology 3.91 mm yr 1 declining to c. 2.11 mm yr 1 between c. 6900e2900 cal yr BP, 1.63 mm yr 1 between c. À Antarctica 2900e1800 cal yr BP, and finally to 0.29 mm yr 1 during the last c. 1800 years. The new Beak Island RSL Satellite-gravity measurements curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some GRACE satellite glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction (Huybrechts, 2002) which is in accord with the 9.5e17.5 m ob- tained by Philippon et al. (2006). The variability in these estimates Since the Last Glacial Maximum (LGM) global sea levels have highlights the problems involved in reconstructing the Last Glacial risen by 125þ/À5m(Fleming et al., 1998). Deglaciation of the Maximum eustatic contributions from Antarctica. northern hemisphere ice sheets contributed w100 m (Clark et al., This is because, of the global ice sheets, the Antarctic Ice Sheet 2002); the Antarctic Ice Sheet and other small ice sheets supplied has least field data to constrain its past volume and its contribution the remainder. Most models predict the Antarctic Ice Sheet to have to global sea-level change (Solomon et al., 2007). Similarly, there is contributed c. 20 m to global sea-level rise with estimates ranging little geological evidence to determine whether dynamical ice from as much as 37 m (Nakada and Lambeck, 1988)to12m discharge or surface melting has dominated the ice sheet mass (Huybrechts, 1992). More recently, an improved three-dimensional balance, a question that is typically explored through ocean general thermomechanical model has suggested a contribution of 14e18 m circulation models (e.g. Holland et al., 2008). A better understanding of how global ice sheets contributed to sea-level change since the LGM is therefore key to predicting how changes in these ice sheets could influence sea-level in a future warming world. This is espe- * Corresponding author. Tel.: þ44 1223 221635; fax: þ44 1223 362616. E-mail address: [email protected] (D.A. Hodgson). cially relevant as in the last Eemian interglacial (Marine Isotope 1 These authors contributed equally to this work. Stage 5e, MIS5e), when temperatures in Antarctica were up to 6 C 0277-3791/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2011.09.009 3604 S.J. Roberts et al. / Quaternary Science Reviews 30 (2011) 3603e3617 higher (Sime et al., 2009), global sea-level peaked at least 6.6 m (95% inlets or basins. Following deglaciation, as isostatic rebound out- probability) higher than today (Jansen et al., 2007; Kopp et al., 2009). paced eustatic sea-level rise, they became isolated and transformed In the current and projected period of warming, modelling suggests into freshwater lakes. The sediment in the lakes records this tran- that a likely upper bound to sea-level by 2100 is 1.4 m (Rahmstorf, sition, and can be dated to determine when the basin sill was at sea- 2007). However, these projected sea-level increases do not include level. By applying this approach to a ‘staircase’ of lakes at increasing potentially large contributions due to the dynamic instability of ice altitudes in one region, or preferably in a single well-defined sheets during the current century (Solomon et al. 2007). Taking such locality, a RSL curve can be reconstructed; often, this is more variables into consideration, Pfeffer et al. (2008) estimate an upper precise than the raised beach approach. bound of 2 m of sea-level rise by 2100. To date, Antarctic RSL curves are limited to the ice free regions of Ice mass loss in Antarctica is strongly dominated by changes in the Scott Coast and Victoria Land Coast (Hall et al., 2004), the Vestfold the Amundsen Sea sector of West Antarctica, with significant loss Hills (Zwartz et al., 1998), Larsemann Hills (Verleyen et al., 2005; also inferred over the Antarctic Peninsula by models such as the Hodgson et al., 2009), and Lützow Holm Bay (Miura et al., 1998)in ICE-5G (VM2) model of Peltier (2004) due to the large value of the East Antarctica. On the Antarctic Peninsula, RSL curves and sea-level GIA correction applied. Limited ice mass loss is inferred for most of constraints exist for Alexander Island (Roberts et al., 2009), Margue- East Antarctica (Rignot et al., 2008). The net rate of ice loss in 2006 rite Bay, and the South Shetland Islands (Bentley et al., 2005; Fretwell À À was À196þ/À92 Gt yr 1, with contributions of À60þ/À46 Gt yr 1, et al., 2010; Hall, 2010; Watcham et al., 2011). There are, however, no À À À132þ/À60 Gt yr 1 and À4þ/À61 Gt yr 1 from the Antarctic RSL curves, and only a limited number of RSL constraints, for the Peninsula, West Antarctica and East Antarctica, respectively north-eastern Antarctic Peninsula region (e.g. Ingólfsson et al., 1992; (Rignot et al., 2008). With a current rate of atmospheric tempera- Hjört et al., 1997) where the recent warming trend is most marked ture increase several times the global mean (3.7þ/À1.6 C (Steig et al., 2009). À À century 1compared to 0.6þ/À0.2 C century 1 (Houghton et al., In this paper, we construct a RSL curve for Beak Island, located in 2001)), the Antarctic Peninsula is a key locality to study the Prince Gustav Channel on the north-eastern side of the Antarctic effects of temperature on the cryosphere. The warming, together Peninsula, using a combination of geomorphological evidence of with changes in the configuration of ocean currents, have resulted former marine limits and radiocarbon-dated marine-freshwater in the catastrophic disintegration of seven ice shelves (Hodgson transitions in three isolation basins. We compare our reconstruc- et al., 2006) and accelerated the discharge of 87% of continental tion with a suite of glacio-isostatic adjustment (GIA) models, and glaciers (Cook et al., 2005). These responses look set to accelerate determine which model is best constrained by the geological field given IPCC predictions that future anthropogenic increases in evidence. greenhouse gas emissions will lead to a 1.4e5.8 C rise in global temperatures by 2100 (Solomon et al., 2007). On the Antarctic 1.1. Site description Peninsula, most of the effects leading to loss of ice are currently confined to the north. Continued warming in this region will lead to Beak Island (63 360S, 57 200W) is the partially submerged a southerly progression of ice shelf disintegrations along both periphery of an inactive volcanic caldera situated in Prince Gustav coasts (Vaughan and Doake, 1996; Hodgson et al., 2006), removing Channel between Vega Island and the Tabarin Peninsula (Fig. 1), on the buttressing effect of the ice shelves and causing accelerated the north-western side of the Weddell Sea Embayment. The island discharge of their feeder glaciers. The total volume of ice on the is composed of Miocene volcanic rocks, mainly porphyritic basalt, Antarctic Peninsula is 95 200 km3, equivalent to 242 mm of eustatic hyaloclastites and pillow lavas belonging to the James Ross Volcanic sea-level rise, or roughly half of all the glaciers and ice caps outside Island group (Bibby, 1966).

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