Eugene W Domack

Foehn winds link climate‐driven warming to ice shelf evolution in Antarctica

Rapid warming of the Antarctic Peninsula over the past several decades has led to extensive surface melting on its eastern side, and the disintegration of the Prince Gustav, Larsen A, and Larsen B ice shelves. The warming trend has been attributed to strengthening of circumpolar westerlies resulting from a positive trend in the Southern Annular Mode (SAM), which is thought to promote more frequent warm, dry, downsloping foehn winds along the lee, or eastern side, of the peninsula. We examined variability in foehn frequency and its relationship to temperature and patterns of synoptic-scale circulation using a multidecadal meteorological record from the Argentine station Matienzo, located between the Larsen A and B embayments. This record was further augmented with a network of six weather stations installed under the U.S. NSF LARsen Ice Shelf System, Antarctica, project. Significant warming was observed in all seasons at Matienzo, with the largest seasonal increase occurring in austral winter (+3.71°C between 1962–1972 and 1999–2010). Frequency and duration of foehn events were found to strongly influence regional temperature variability over hourly to seasonal time scales. Surface temperature and foehn winds were also sensitive to climate variability, with both variables exhibiting strong, positive correlations with the SAM index. Concomitant positive trends in foehn frequency, temperature, and SAM are present during austral summer, with sustained foehn events consistently associated with surface melting across the ice sheet and ice shelves. These observations support the notion that increased foehn frequency played a critical role in precipitating the collapse of the Larsen B ice shelf.

Boundary condition of grounding lines prior to collapse, Larsen-B Ice Shelf, Antarctica

Top-down rather than bottom-up change The Larsen-B Ice Shelf in Antarctica collapsed in 2002 because of a regional increase in surface temperature. This finding, reported by Rebesco et al., will surprise many who supposed that the shelfs disintegration probably occurred because of thinning of the ice shelf and the resulting loss of support by the sea floor beneath it. The authors mapped the sea floor beneath the ice shelf before it fell apart, which revealed that the modern ice sheet grounding line was established around 12,000 years ago and has since remained unchanged. If the ice shelf did not collapse because of thinning from below, then it must have been caused by warming from above. Science, this issue p. 1354 Surface warming caused the disintegration of the Larsen Ice Shelf in 2002. Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf.

The seafloor imprint of the Gerlache–Boyd Ice Stream (65–62° S), northern Antarctic Peninsula

The northern Antarctic Peninsula (NAP) forms a narrow stretch of land that extends to a relatively low latitude (63° S) and is subject to a humid, maritime-influenced climate, especially on its western side. During the Last Glacial Maximum (LGM), the NAP was covered by the northern part of the Antarctic Peninsula Ice Sheet (APIS) (Lavoie et al. 2015). The APIS fed ice streams flowing on both sides of the NAP, including the Gerlache–Boyd Ice Stream (GBIS) (Canals et al. 2000). Fast-flowing ice streams are the most dynamic components of ice sheets and largely determine ice-sheet mass loss and stability (Bentley 1987; Bamber et al. 2000). They transport large volumes of sediments both subglacially and englacially, and shape a variety of landforms both on land and the seafloor (e.g. Dowdeswell & Elverhoi 2002). During the LGM and throughout deglaciation, the role of ice streams was particularly significant. We describe the landforms associated with the GBIS based on a comprehensive compilation of multibeam bathymetry. The set of landforms and deposits left by the GBIS ranges in age from LGM to present, and illustrates both the products of ice-stream dynamics and how post-glacial processes can mask this glacial imprint. Our aim is to understand the dynamics of the GBIS and its temporal evolution since the LGM. In addition, the role of underlying geological control on the overall physiography of the GBIS is assessed. The study area extends 365 km from the southern end of Gerlache Strait (GS) to the South Shetland deep-sea trench and is fed by a glacierized catchment of about 23 000 km2 (Fig. 1a) (Canals et al. 2000). The height difference from the ice divide to the deep-sea trench is c. 6700 m. The GBIS system was the main drainage pathway of this catchment (O Cofaigh et …

Bedrock meltwater channels in Palmer Deep, Antarctic Peninsula

The Antarctic Peninsula inner shelf has been deeply scoured by glacial erosion resulting in numerous deep troughs that funnelled ice flow out across the shelf. Palmer Deep is one of these erosional troughs located at the convergence of three distinct ice accumulation centres: Anvers Island, Bruce Plateau and the Graham Coast (Fig. 1a). A distinctive channelized morphology observed in swath-bathymetric data from the trough-outlet sill reflects a combination of subglacial meltwater scour and underlying structural weakness within the bedrock. The origin of these features can be linked to the development of a subglacial lake basin within Palmer Deep during or prior to the Last Glacial Maximum (LGM), its subsequent drainage and the recession of the Palmer Deep ice-stream system (Domack et al. 2006). Fig. 1. Multibeam bathymetry of Palmer Deep collected during NB Palmer cruises NBP9903 and NBP0107 (US Antarctic Program). Aquisition system Seabeam 2100. Frequency 12 kHz. Grid-cell size 50 m. ( a ) Multibeam image. VE×3. Land area from …

Grounding-zone wedges and mega-scale glacial lineations in the Mertz Trough, East Antarctica

Glacial erosion and deposition have shaped the Mertz Trough, East Antarctica, where seafloor grounding-zone wedges (GZWs) are associated with mega-scale glacial lineations (MSGLs) (McMullen et al. 2006). GZWs form along grounded glacial margins constrained by ice shelves during stillstands and consist of wedge-shaped glacially transported sediment (Powell & Domack 2002). MSGLs are parallel elongate bedforms that typically form in soft sediments beneath rapidly flowing ice streams (Clark 1993; Canals et al. 2000; Clark et al. 2003). They are found in glacial troughs, usually parallel to trough margins. MSGLs are generally 6 to >100 km long, 200–1300 m wide and spaced 0.3–5 km apart, crest-to-crest (Clark et al. 2003; McMullen et al. 2006). Mertz Trough is located perpendicular to George V coast of Wilkes Land, East Antarctica (Fig. 1a, b). Multibeam-bathymetric imagery reveals distinct features on the seafloor including parallel elongate ridge and groove pairs, two sinuous sediment mounds with streamlined bedforms on their surfaces, and depressions (Fig. 1c). Fig. 1. Multibeam-bathymetric image of the central Mertz Trough, East Antarctica. ( a ) Location of study area (red box; map from …

Submarine glacial landforms on the cold East Antarctic margin

The East Antarctic continental margin, which extends from the Weddell Sea to the Ross Sea (Fig. 1h), surrounds the largest and oldest ice mass on Earth; however, it has only been studied at a few locations because of its remoteness and persistent sea ice. The shelf is 100–150 km wide over most of its length but broadens where major crustal structures intersect it, such as in Prydz Bay (Fig. 1a) where the shelf is 200–300 km wide. This paper reviews what is known presently about the geomorphology of the best-studied sectors of the East Antarctic margin: the deep re-entrant of Prydz Bay and the narrower shelves of George V and Mac.Robertson Land (Fig. 1h). Only a small proportion of the East Antarctica shelf has been surveyed with multibeam bathymetry, so this review is also dependent on compilations of single-beam bathymetry, seismic-reflection profiles and side-scan sonar data. In particular, we use George V Digital Elevation Model (GVDEM, Beaman et al. 2011) and International Bathymetric Chart of the Southern Ocean (IBCSO; Arndt et al. 2013). The slope has been more widely studied, with large amounts of seismic-reflection data available (e.g. Kuvaas & Leitchenkov 1992; Escutia et al. 2000; Solli et al. 2007; Close et al. 2007). Fig. 1. ( a ) Prydz Bay and sub-Amery Ice Shelf bathymetry. (IBCSO v. 1.0; Arndt et al. 2013). ( b ) Long profile of Amery Ice Shelf from upstream of the modern grounding zone to the trough-mouth fan on the continental slope. VE×140. ( c ) Cross-section of Amery Ice Shelf valley at its southern end. VE×20. ( d ) Shaded-relief image of multibeam data collected by N. B. Palmer in 2001 (Leventer et al. 2005). The image covers the transition from streamlined bedrock to moulded basin sediment in the Svenner Channel. Image from GEOMAPAPP (www.geomapapp.org). ( e ) Seismic …

A Holocene volcanic knoll within a glacial trough, Antarctic Sound, northern Antarctic Peninsula

Jaegyu Knoll is located in Antarctic Sound, between Trinity Peninsula and islands of the Joinville Island Group, on the northern Antarctic Peninsula (Fig. 1a). Jaegyu Knoll is interpreted as a Holocene submarine intraplate volcano based on its morphology, in situ observations such as bottom videos and high-resolution photographs (Quinones et al. 2005), a rock dredge that recovered fresh volcanic rock (Hatfield et al. 2004) and a measured geothermal anomaly (Hatfield et al. 2004). All aspects of the knoll are consistent with recent volcanic activity, which appears to have been persistent in the northern Antarctic Peninsula region from Mesozoic times to the present (e.g. Baker et al. 1973; Gonzalez-Ferran 1991; Gracia et al. 1997). The knoll, and at least two other smaller volcanic features in Antarctic Sound (Fig. 1a), lie within an overdeepened glacial trough that was presumably sculpted by ice during the Last Glacial Maximum (LGM; 23–19 ka BP). Fig. 1. Jaegyu Knoll (63° 29′ 45″ S, 56° 26′ 45″ W) located on the seafloor of the Antarctic Sound glacial trough, northern Antarctic Peninsula. Jaegyu Knoll was discovered and mapped for the first time in 2001 and named in honour of the young Korean scientist Mr Jun Jaegyu who succumbed …

Environmental responses of the Northeast Antarctic Peninsula to the Holocene climate variability

In this study, we present a unique high-resolution Holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the Vega Drift, eastern Antarctic Peninsula (EAP). These data add to the climate framework already established by high-resolution marine sedimentary records from the Palmer Deep, western Antarctic Peninsula (WAP). Heavy sea ice conditions and reduced primary productivity were observed prior to 7.4 ka B.P. in relation with the proximity of the glacial ice melt and calving. Subsequent Holocene oceanographic conditions were controlled by the interactions between the Westerlies-Antarctic Circumpolar Current (ACC)-Weddell Gyre dynamics. A warm period characterized by short seasonal sea ice duration associated with a southern shift of both ACC and Westerlies field persisted until 5 ka B.P. This warm episode was then followed by climate deterioration during the middle-to-late Holocene (5 to 1.9 ka B.P.) with a gradual increase in annual sea ice duration triggered by the expansion of the Weddell Gyre and a strong oceanic connection from the EAP to the WAP. Increase of benthic diatom species during this period was indicative of more summer/autumn storms, which was consistent with changes in synoptic atmospheric circulation and the establishment of low- to high-latitude teleconnections. Finally, the multicentennial scale variability of the Weddell Gyre intensity and storm frequency during the late Holocene appeared to be associated with the increased El Nino–Southern Oscillation frequency.

Sub-ice shelf sediment geochronology utilizing novel radiocarbon methodology for highly detrital sediments

Sub-ice shelf sediments near Larsen C ice shelf (LIS-C) show fine-scale rhythmic laminations that could provide a near-continuous seasonal-resolution record of regional ice mass changes. Despite the great potential of these sediments, a dependable Late Quaternary chronology is difficult to generate, rendering the record incomplete. As with many marginal Antarctic sediments, in the absence of preserved carbonate microfossils, the reliability of radiocarbon chronologies depends on presence of high proportions of autochthonous organic carbon with minimized detrital organic carbon. Consequently, acid insoluble organic (AIO) 14C dating works best where high productivity drives high sediment accumulation rates, but can be problematic in condensed sequences with high proportions of detrital organic carbon. Ramped PyrOx 14C dating has progressively been shown to improve upon AIO 14C dates, to the point of matching foraminiferal carbonate 14C dates, through differential thermochemical degradation of organic components within samples. But in highly detrital sediments, proportions of contemporaneously deposited material are too low to fully separate autochthonous organic carbon from detrital carbon in samples large enough to 14C date. We introduce two modifications of the Ramped PyrOx 14C approach applied to highly detrital sediments near LIS-C to maximize accuracy by utilizing ultra-small fractions of the highly detrital AIO material. With minimization of the uncertainty cost, these techniques allow us to generate chronologies for cores that would otherwise go undated, pushing the limits of radiocarbon dating to regions and facies with high proportions of pre-aged detritus. Wider use of these techniques will enable more coordinated a priori coring efforts to constrain regional glacial responses to rapid warming where sediments had previously been thought too difficult to date.

Tree-Ring Investigation of Holocene Flood-Deposited Wood From the Oneida Lake Watershed, New York State

ABSTRACT Glacial deposition and fluvial/lacustrine sedimentation interact over terrains in central New York State to preserve a history of geological and hydrological events as well as hydroclimatic transitions. The lower reach of Fish Creek draining the eastern watershed of Oneida Lake, NY, is an area with prominent wood remains. This study explores a collection of 52 logs encased in organic-rich deposits exposed by bank erosion at three locations along Fish Creek near Sylvan Beach, NY, with respect to radiocarbon ages, species, and the crossdating potential of tree rings. Radiocarbon ages and successful tree-ring crossdating document what we interpret as seven major hydrologic episodes ca. 10 ka (i.e. ca. 10,000 cal yr BP), 7.4 ka, 6.8 ka, 6.4 ka, 5.5 ka, 3.1 ka and 2.2 ka cal BP, during which channel aggradation and tree burial may have been associated with abruptly increased flood frequency and/or high water tables. This pilot study establishes four floating tree-ring records: [1] early Holocene hemlock (Tsuga), mid-Holocene [2] walnut (Juglans sp.) and [3] sycamore (Platanus), and [4] late Holocene elm (Ulmus sp.), with sample sizes of 8–14 series of 55–135 years length. Despite the complexity of distribution of radiocarbon ages at each site, the wealth of well-preserved wood demonstrates great promise for understanding the paleoflood history of the Oneida watershed by documenting the magnitude, location, and timing of floods. Further additional systematic sampling can add and strengthen tree-ring dating and tree-ring based flood records, confirm results, and contribute to the Holocene hydrological history of the region.