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Seafloor Geomorphology of Western Antarctic Peninsula Bays

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Seafloor Geomorphology of Western Antarctic Peninsula Bays The Cryosphere, 12, 205–225, 2018 https://doi.org/10.5194/tc-12-205-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Seafloor geomorphology of western Antarctic Peninsula bays: a signature of ice flow behaviour Yuribia P. Munoz and Julia S. Wellner Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA Correspondence: Yuribia P. Munoz ([email protected]) Received: 12 June 2017 – Discussion started: 22 June 2017 Revised: 4 November 2017 – Accepted: 13 November 2017 – Published: 22 January 2018 Abstract. Glacial geomorphology is used in Antarctica to 1 Introduction reconstruct ice advance during the Last Glacial Maximum and subsequent retreat across the continental shelf. Analo- While warming temperatures in the Antarctic Peninsula (AP) gous geomorphic assemblages are found in glaciated fjords have resulted in the retreat of 90 % of the regional glaciers and are used to interpret the glacial history and glacial dy- (Cook et al., 2014) and the collapse of ice shelves (Morris namics in those areas. In addition, understanding the distri- and Vaughan, 2003; Cook and Vaughan, 2010), recent stud- bution of submarine landforms in bays and the local con- ies have shown that since the late 1990s this region is cur- trols exerted on ice flow can help improve numerical models rently experiencing a cooling trend (Turner et al., 2016). The by providing constraints through these drainage areas. We AP is a dynamic region that serves as a natural laboratory present multibeam swath bathymetry from several bays in to study ice flow and the resulting sediment deposits. As the the South Shetland Islands and the western Antarctic Penin- ice retreats, it leaves behind glacial geomorphic features on sula. The submarine landforms are described and interpreted the seafloor; these submarine landforms have been mapped in in detail. A schematic model was developed showing the fea- glaciated environments in Antarctica (Anderson et al., 2001; tures found in the bays: from glacial lineations and moraines Wellner et al., 2001, 2006; Evans et al., 2004; Heroy and An- in the inner bay to grounding zone wedges and drumlinoid derson, 2005; Larter et al., 2009; Livingstone et al., 2013; features in the middle bay and streamlined features and melt- Hodgson et al., 2014), southern Chile (Dowdeswell and water channels in the outer bay areas. In addition, we anal- Vasquez, 2013), North America (Dowdeswell et al., 2016), ysed local variables in the bays and observed the following: and northern Europe (Ottesen et al., 2005; Ottesen and (1) the number of landforms found in the bays scales to the Dowdeswell, 2006, 2009; Dowdeswell et al., 2010), giv- size of the bay, but the geometry of the bays dictates the ing insight into the glacial history of each region. Sev- types of features that form; specifically, we observe a corre- eral seafloor features have been mapped west of the AP on lation between the bay width and the number of transverse the continental slope and continental shelf (Dowdeswell et features present in the bays. (2) The smaller seafloor fea- al., 2004; Graham and Smith, 2012; Gales et al., 2013), tures are present only in the smaller glacial systems, indicat- the South Shetland Islands (Milliken et al., 2009; Simms ing that short-lived atmospheric and oceanographic fluctua- et al., 2011), South Georgia Island (Hodgson et al., 2014; tions, responsible for the formation of these landforms, are Graham et al., 2017), Bransfield Strait (Canals et al., 2000, only recorded in these smaller systems. (3) Meltwater chan- 2002), Gerlache Strait (Evans et al., 2004), south of Anvers nels are abundant on the seafloor, but some are subglacial, Island (Domack et al., 2006), and Marguerite Bay (Ó Co- carved in bedrock, and some are modern erosional features, faigh et al., 2002; Anderson and Fretwell, 2008; Livingstone carved on soft sediment. Lastly, based on geomorphological et al., 2013). However, the seafloor geomorphology in west- evidence, we propose the features found in some of the prox- ern AP bays has not been described in detail, except for a imal bay areas were formed during a recent glacial advance, few locations (Garcia et al., 2016; Munoz and Wellner, 2016; likely the Little Ice Age. Wölfl et al., 2016). Although most of the data we present are publicly available, this is the first instance, to our knowledge, Published by Copernicus Publications on behalf of the European Geosciences Union. 206 Y. P. Munoz and J. S. Wellner: Geomorphology of Antarctic Peninsula bays Figure 1. Map of the northern Antarctic Peninsula (AP) and South Shetland Islands; red boxes indicate Figs. 2–5. Inset shows the location of the AP in Antarctica. KGI: King George Island; (1) Cierva Cove, (2) Brialmont Cove, (3) Fournier Bay, (4) Charlotte Bay, (5) Andvord Bay, (6) Moser Glacier, (7) Lester Cove, (8) Briand Fjord, (9) Flandres Bay, (10) Etienne Fjord, and (11) Collins Bay. Individual maps of bays 1–11 found in the Supplement. AP map from Polar Geospatial Center; bathymetry and inset from IBCSO (Arndt et al., 2013). that a detailed description of the seafloor geomorphology of formed over several glacial–interglacial cycles (Wellner et a large number of western AP fjords has been completed. al., 2001; Campo et al., 2017). We map the glacial landforms We combine multibeam swath bathymetry data collected and analyse local variables including bay length and width, during seven cruises to the Antarctic Peninsula. The multi- glacier drainage size flowing into the bays, seafloor lithol- beam bathymetry data presented in this study expose geo- ogy, and water depth in order to understand the controls of morphic features formed during past ice flow in several bays ice flow and retreat dynamics in these locations. in the western Antarctic Peninsula, the South Shetland Is- lands, and Anvers Island (Fig. 1). We focus this study on four bays throughout the AP: Maxwell Bay, located on King 2 Study area George Island (KGI), north of the AP; Hope Bay, located on the northernmost tip of the AP known as the Trinity Penin- The AP is the northernmost extent of the Antarctic conti- sula; Lapeyrère Bay, on Anvers Island, west of the AP; and nent. The AP is a long (∼ 1200 km), thin (∼ 250 km) strip finally Beascochea Bay, located in the Graham Land Coast of of mountains of up to 3500 m in elevation. The geological the western AP (Fig. 1). Data from additional bays through- setting of the AP is characterized by Cenozoic tectonic ex- out the AP (found in supplementary material) have been inte- tension and active volcanism (Griffith and Anderson, 1989). grated in the results section to support this investigation. The Glacial ice flow over crystalline bedrock has preferentially glacial seafloor features reveal flow behaviour of grounded eroded over joints and faults, accentuating their appearance ice; structures formed in a deformable sedimentary substrate (Domack et al., 2006). The predominant rock types are meta- likely represent subglacial conditions shortly before ice de- morphic and intrusive and extrusive igneous rocks (Griffith coupling from the seafloor, and structures in bedrock likely and Anderson, 1989). Ice covers about 80 % of the AP, where The Cryosphere, 12, 205–225, 2018 www.the-cryosphere.net/12/205/2018/ Y. P. Munoz and J. S. Wellner: Geomorphology of Antarctic Peninsula bays 207 Figure 2. Multibeam swath bathymetry of Maxwell Bay (a), Marian Cove (b), and Potter Cove (c); vertical exaggeration is 5× in all images. (d) Interpretation of geomorphic features with hillshade as background. Cross sections A–A0 and D–D0 show transverse ridges in Potter Cove (c) and Marian Cove (b) respectively, B–B0 shows elongated ridges in the bay, and C–C0 shows the U-shaped fjord valley. ice thickness ranges between 400 and 800 m (Fretwell et dicate an annual average of 524 mm (Lee et al., 2008; KO- al., 2013) and averages about 500 m. The ice cap covering PRI, 2014; Moon et al., 2015; Fernandez et al., 2016). On Anvers Island reaches up to 600 m, similar to the western AP Anvers Island (west of the AP, Fig. 1), summer air temper- (Ashley and Smith, 2000), while in KGI, the ice cap is only atures reach up to 6–7.5 ◦C, while in the winter the average 150–200 m thick (Simms et al., 2011). is −5 ◦C (Ashley and Smith, 2000). Precipitation in Anvers The high peaks of the AP form a topographic barrier to Island is on average approximately 1200 mm annually (Grif- the westerly winds resulting in a warmer, wetter western AP, fith and Anderson, 1989; Ashley and Smith, 2000) and up and a cooler, dryer eastern AP (Ó Cofaigh et al., 2014). The to 2000 mm yr−1 in Lapeyrère Bay, northern Anvers Island climate in Hope Bay (northern AP, Fig. 1) is cold, dry semi- (Fernandez et al., 2016). polar (Pereira et al., 2013). Annual air temperature at Esper- anza Research Station (located in Hope Bay) range between 2.1 Maxwell Bay − ◦ − ◦ 30.6 and 11.8 C, with an average of 5.1 C and an an- ◦ 0 ◦ 0 nual precipitation of 250 mm measured between 1952 and Maxwell Bay (62 13.7 S, 58 50.9 W) (Fig. 2) is located in 2010 (Pereira et al., 2013; Schaefer et al., 2016). In contrast, the western end of KGI. Maxwell Bay is about 15 km long, the western AP receives an average of 1100 mm yr−1, mea- between 6 and 15 km wide, and has an approximate area of 2 sured between 1997 and 2006 (Thomas et al., 2008), and up 140 km . Maxwell Bay has several embayments: Edgell Bay, to 2900 mm yr−1 in some bays (Fernandez et al., 2016).
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