East Antarctic Margin Research Articles

Productivity Proxies in Surface Sediment of the East Antarctic Margin: A Focus on Excess Ba

AbstractComponents such as organic carbon (Corg), carbonate, opal or barite are valuable paleoceanographic proxies, enabling the reconstruction of past changes in carbon cycling under various climate regimes, particularly when 230Th‐normalization is used to reconstruct particulate vertical rain rates. However, these components can be affected by poor preservation in the sediment. Barite is generally better preserved compared to other productivity proxies, but its estimates using “excess barium” (xsBa) calculations or Ba/Al ratios may not always be reliable, especially near the continental margin. This study presents a multi‐proxy investigation of surface sediments from the East Antarctic margin to assess the robustness of xsBa as a paleo‐productivity proxy. 230Th‐normalized fluxes of Corg and opal record consistent variations within the sediment, while xsBa appears to be affected by different processes. Results suggest that xsBa may not robustly reflect marine barite in sediment close to the Antarctic Ice Sheet, because (a) the authigenic signal is overprinted by large lithogenic inputs; and (b) other mineral phases (e.g., Fe oxides) may be important Ba carrier phases in the region. 230Th‐normalized Ba concentrations in the oxide‐free sediment fraction, which was reductively leached to remove Fe‐Mn oxides, aligns with the other biogenic fluxes, implying that specific leaching for barite isolation might be required in sediment proximal to the Antarctic Ice Sheet, rather than using the standard “xsBa” calculation or Ba/Al ratios. This study gives new insights into the sedimentary cycle of Ba in East Antarctic sediment and confirms the importance of using multi‐proxy records to perform paleo‐reconstructions.

Revisiting circulation and water masses over the East Antarctic margin (80–150°E)

Full-depth hydrographic sections of the BROKE experiment in 1996 (across the Antarctic margin from 80 to 150°E; Bindoff et al., 2000) were revisited for the first time during the 2018/2019 austral summer. We describe the subsurface physical oceanography in 2019 and the hydrographic changes between 1996 and 2019 not documented in earlier studies. The survey captured decadal changes in ocean structure from the southern flank of the Antarctic Circumpolar Current (ACC) to the continental shelves. In five cross-slope meridional sections, where 1996 and 2019 measurements are comparable (112, 120, 128, 140, and 150°E), the poleward shift of the southern boundary of the ACC (50–120 km) prevailed near the continental rise. The simultaneous displacement of barotropic ACC fronts and poleward migration of deep water contributed to full-depth warming (0.1–1.6 °C) and potentially to a reduction in the bottom water volume. Freshening was widely observed from the deep to bottom layers (∼0.02 g/kg), with the signal extending from the upper continental slope. Bottom-intensified freshening was accompanied by an oxygenation of 10–20 μmol/kg, indicating that freshening-driven oxygenation of bottom layers counteracted the deoxygenation effect of the poleward barotropic frontal shift. Westward transport of the Antarctic Slope Current decreased by more than 10 Sv from 1996 to 2019 in the five cross-slope sections; its frontal features and current axis shifted offshore by more than 20 km in 112–140°E. Additionally, subsurface warming along modified Circumpolar Deep Water by up to 0.4 °C was commonly detected across the upper continental slope. For the 2019 hydrography, shelf water sufficiently dense to form bottom water (>28.35 kg/m3) was found to the east of Mertz Polynya (142–148°E), implying a pathway for dense shelf water export from the eastern margin of Mertz Polynya. Our findings underscore the importance of sustained efforts for in-situ observations that widely cover the East Antarctic margin.

Detection and mapping of supraglacial lakes on East Antarctic margin using Landsat 8 OLI during 2014–2023

Using an optical band index generated from Landsat 8 OLI data, an inventory of Antarctic supraglacial lakes (size >0.01 km2) during 2014–2023 is presented. Shaded snow, cloud and rock shadow were removed by using a band-based filter. Over the north Antarctica, we identified 639 lakes covering an area of 520.79 km2, 1025 lakes covering 272.82 km2 over the East Antarctica, and 1045 lakes covering 93 km2 over the Transantarctic Mountains. The influence of air temperature, 10-m zonal/meridional wind components and climate indices on surface melt were investigated. Over the Dronning Maud Land, air temperature promoted melt, while Föhn and katabatic winds warmed adiabatically along the leeward side of the elevated features and initiated melt in south Antarctica. Nearly all areas have exhibited a decrease in melt over the past few years, and the number of melt cases dropped after 2020. Negative SAM index favoured melt over the Dronning Maud Land. This study identified new SGLs, which will be a benchmark for further studies. The undulating terrain posed a difficulty for collecting and interpreting satellite data, which should be addressed using advanced technologies and algorithms.

Oceanic Regime Shift to a Warmer Continental Shelf Adjacent to the Shackleton Ice Shelf, East Antarctica

AbstractThe long‐held view that the East Antarctic margin is isolated from warm offshore waters has been challenged by recent observations showing incursions of warm modified Circumpolar Deep Water (mCDW) reaching several East Antarctic ice shelves. However, large areas of the East Antarctic continental shelf remain poorly observed, making it challenging to determine if the supply of oceanic heat to the ice shelves is changing. Here, we use temperature and salinity profiles to the west of the Shackleton Ice Shelf (SIS; ≈100°E) spanning 60 years to assess the variability of the water masses in the context of a changing climate. We document warming and freshening of shelf waters. Prior to 1996, cold mCDW water (θ < −1.6°C) was found below the surface mixed layer and cold Dense Shelf Water (DSW) with a salinity of >34.5 dominated the water column. After 2010, warm mCDW (≥−1.0°C) was widespread over the continental shelf and DSW with salinity over 34.5 was no longer present. The mixing ratio of glacial meltwater indicates that warm mCDW observed in 2011 caused basal melting of the SIS, possibly reducing the salinity of DSW. Increased access of warm waters to the continental shelf may have also occurred on the eastern side of the ice shelf, where glaciological evidence shows the grounding line has retreated. These observations suggest a shift occurred prior to 2011 that has increased the ocean heat supply to the continental shelf and to the SIS, increasing basal melt and reducing DSW formation.

Outboard Onset of Ross Orogen Magmatism and Subsequent Igneous and Metamorphic Cooling Linked to Slab Rollback during Late-Stage Gondwana Assembly

Changes in magmatism and sedimentation along the late Neoproterozoic-early Paleozoic Ross orogenic belt in Antarctica have been linked to the cessation of convergence along the Mozambique belt during the assembly of East-West Gondwana. However, these interpretations are non-unique and are based, in part, on limited thermochronological data sets spread out along large sectors of the East Antarctic margin. We report new 40Ar/39Ar hornblende, muscovite, and biotite age data for plutonic (n = 13) and metasedimentary (n = 3) samples from the Shackleton–Liv Glacier sector of the Queen Maud Mountains in Antarctica. Cumulative 40Ar/39Ar age data show polymodal age peaks (510 Ma, 491 Ma, 475 Ma) that lag peaks in U-Pb igneous crystallization ages, suggesting igneous and metamorphic cooling following magmatism within the region. The 40Ar/39Ar ages are similar to ages in other sectors of the Ross orogen, but younger than detrital mineral 40Ar/39Ar cooling ages indicative of older magmatism and cooling of unexposed inboard areas along the margin. Detrital zircon trace element abundances suggest that the widespread onset of magmatism in outboard localities of the orogen correlates with a ~560–530 Ma decrease in crustal thickness. The timing of crustal thinning recorded by zircon in magmas overlaps with other evidence for the timing of crustal extension, suggesting that the regional onset of magmatism with subsequent igneous and metamorphic cooling probably reflects slab rollback that coincided with possible global plate motion changes induced during the final assembly of Gondwana.

Unradiogenic reactive phase controls the εNd of authigenic phosphates in East Antarctic margin sediment

Determining past changes in ocean circulation on the Antarctic margin is important for understanding the interactions between climate, circulation, and ice sheet retreat. However, the application of neodymium isotopes (εNd), a well-known proxy of ocean circulation, is limited on the Antarctic margin, due to the lack of carbonate preservation and inconsistency in authigenic εNd leached from bulk sediment. Here we assess the use of the εNd proxy along the continental rise of Wilkes Land, by combining analyses of seawater with phases extracted using a 10-second reductive leach in co-located surface sediments. Dissolved seawater εNd values displayed the following water mass signatures; εNd = −8.8 ± 0.2 (n = 1) for Antarctic Surface Water; εNd = −9.7 ± 0.2 (n = 2) for Winter Water; and εNd = −8.7 ± 0.3 (n = 6) for modified Circumpolar Deep Water. The sediment leachate did not reproduce a bottom water Nd signature and yielded a very variable εNd, ranging from −10.4 to −14.4. In contrast, the bulk detrital sediment εNd fell within a narrow range of −13.1 ± 0.5 (n = 29). Examination of elemental ratios and rare earth element (REE) anomalies indicates that the leaching procedure extracts exclusively authigenic phases. The strong relationship found between phosphorus (P) and REE suggests that a P-associated phase is the main REE host-phase leached, as opposed to ferromanganese oxyhydroxides. The leached europium anomalies and εNd indicate that the extracted Nd signature is influenced by two end members, one with a seawater-like εNd (∼-8) and one more negative than the bulk detritus (εNd ∼−14). Finally, the decoupling between [Nd] and εNd, as well the distinct middle-REE enrichments measured in the leach implies the authigenic εNd is controlled by diagenesis. We thus infer that the Nd signature of the leached phosphates is derived from porewater and influenced by the presence of a reactive detrital component in the sediment. Unradiogenic reactive sedimentary phases which easily dissolve into porewaters are likely sourced from the subglacial erosion of ancient metasediments and crustal remnants on the Wilkes Land coast. These new εNd data contribute to the evaluation of the εNd proxy at complex, dynamic and under-studied interfaces such as the East Antarctic margin. However, further work is still needed to develop reliable proxies of past Antarctic water masses.

Ediacaran mafic magmatism recorded in Cambrian eclogites of the Ross orogen, Antarctica: Implications for the Neoproterozoic rifting episodes along the Pacific‐Gondwana margin

AbstractWe report the first finding of Ediacaran mafic magmatism in northern Victoria Land of the Ross orogen, Antarctica, based on ca. 600–590 Ma magmatic zircon cores in Cambrian eclogites. The mafic magmatism could be either linked to ca. 615–590 Ma incipient convergent margin magmatism in central segment of the Ross orogen, or ca. 600–580 Ma continental rift‐related volcanism widespread in eastern Australia. The latter is preferred based on the trace‐element compositions distinctive from those of arc‐related basalts and the depleted mantle‐like Hf isotopic compositions of zircon. Our results suggest dual rifting episodes during both the Ediacaran and Cryogenian (ca. 670–650 Ma) in the East Antarctic margin, correlative with those in eastern Australia. A spatial distribution of coeval rifting and subduction along the Ediacaran margin of East Antarctica is readily accounted for by rift inheritance; the upper‐ and lower‐plate geometry resulting from detachment and transform faulting.

Deep water sedimentary processes in the Enderby Basin (East Antarctic margin) during the Cenozoic

AbstractThe thick sequence of mid‐late Cenozoic sediments preserved within the Enderby Basin of the East Antarctica margin contains key information regarding glacial history and palaeo‐oceanographic conditions during the last 34 My. The interplay between glacial processes and ocean circulation can be reconstructed from seismic stratigraphic studies. Here, interpretation of seismic sequences and geomorphology from an extensive 2D seismic dataset (∼75,000 km) are correlated with lithological data of the ODP site 1165 drilled on the continental rise, and used to assess the age and origin of the sediment, and the possible influence of oceanic currents on its distribution. Mapping of seismic units and facies reveals that, in addition to glacial sediments derived from the Antarctic mainland, the upper Cenozoic succession includes drift units with prograding sequences building out from the Mac. Robertson Land margin, west of the Prydz Bay. Three contourite drifts grew on the western side of submarine channels and large sediment wave fields suggest a mixed system of turbidity currents influenced by west‐flowing bottom currents. The drifts are composed of four seismic units representing stages of onset (Lower Oligocene), main growth (Early‐Middle Miocene), maintenance (Middle‐Late Miocene) and burial (Pliocene). The internal geometry and reflection patterns of the drifts imply an intensified current activity from the Early to Middle Miocene. The results plausibly reflect that the formation of proto Antarctic Bottom Water (AABW) started around the Eocene–Oligocene boundary and intensified episodically from the early to middle Miocene.

Water masses distribution offshore the Sabrina Coast (East Antarctica)

Abstract. Current glacier melt rates in West Antarctica substantially exceed those around the East Antarctic margin. The exception is Wilkes Land, where for example Totten Glacier underwent significant retreat between 2000 and 2012, underlining its sensitivity to climate change. This process is strongly influenced by ocean dynamics, which in turn changes in accordance with the evolution of the ice caps. Here, we present new oceanographic data (temperature, salinity, and dissolved oxygen) collected during austral summer 2017 offshore the Sabrina Coast (East Antarctica) from the continental shelf break to ca 3000 m depth. This area is characterized by very few oceanographic in situ observations. The main water masses of the study area, identified by analysing thermohaline properties, are the Antarctic Surface Water with potential temperature θ>-1.5 ∘C and salinity S<34.2 (σθ<27.55 kg m−3), the Winter Water with -1.92<θ<-1.75 ∘C and 34.0<S<34.5 (potential density, 27.55<σθ<27.7 kg m−3), the modified Circumpolar Deep Water with θ>0 ∘C and S>34.5 (σθ>27.7 kg m−3), and Antarctic Bottom Water with -0.50<θ<0 ∘C and 34.63<S<34.67 (27.83<σθ<27.85; neutral density γn>28.30 kg m−3). The latter is a mixture of dense waters from the Ross Sea and Adélie Land continental shelves. Such waters are influenced by the mixing processes they undergo as they move westward along the Antarctic margin, also interacting with the warmer Circumpolar Deep Water. The spatial distribution of water masses offshore the Sabrina Coast also appears to be strongly linked with the complex morpho-bathymetry of the slope and rise area, supporting the hypothesis that downslope processes contribute to shaping the architecture of the distal portion of the continental margin. Oceanographic data presented here can be downloaded from https://doi.org/10.25919/yyex-t381 (CSIRO; Van Graas, 2021).

Holocene sedimentology in an isolation basin in the Larsemann Hills, East Antarctica

Holocene paleoenvironmental changes along the East Antarctic margin have been reconstructed using marine and lake sediment cores. Isolation basins in the coastal ice-free regions offer continuous sedimentary sequences to reconstruct marine-freshwater transitions and its environmental changes. In this study, we present the grain size (sand-silt-clay) and organic matter variations in a 51 cm radiocarbon-dated sediment core from Pup Lagoon, an isolation basin in Larsemann Hills (East Antarctica). The sediment core spans the last 6109 years and provides information on environmental changes in two different settings, i.e., (a) under the marine influence, and (b) as an isolated lake. Three cluster zones were identified viz., LZ1 (6109–2427 y BP: marine environment), LZ2 (2427–2101 y BP: transition zone) and LZ3 (2101–116 y BP: freshwater environment). Fine grain sediments (silt) are dominant in LZ1, indicating a strong hydrodynamic energy conditions affected by tidal currents with low organic matter. Higher sand content during the transition period (LZ2) indicates the strongest hydrodynamic condition and sediment deposition from sea ice. The increasing trend of OM (cyanobacterial benthic mat) beginning at ~ 2101 y BP suggests the isolation of the lake. The highest fine grained sediments (silt-clay) in LZ3 suggests lowered meltwater derived detritus in response to mild austral summer conditions during the Late Holocene.

Revisiting the Australian‐Antarctic Ocean‐Continent Transition Zone Using Petrological and Geophysical Characterization of Exhumed Subcontinental Mantle

AbstractThe final lithospheric breakup of the Australian‐Antarctic rift system remains controversial due to sparse geological constraints on the nature of the basement along the ocean‐continent transition (OCT) zones. We present new interpretations of multichannel seismic reflection transects and new petrological data of dredged mantle rocks along the East Antarctic margin (Seamount B, offshore Terre Adélie). By combining both data sets, we show that a 50–100 km wide domain of cold and fertile subcontinental mantle was exhumed along the magma‐poor Antarctic margin. This study represents only the second locality, along with the Iberia‐Newfoundland margins, where the importance of exhumed mantle domains along OCTs can be clearly identified. The dredged peridotites preserve characteristics similar to mantle xenoliths found in syn‐ to post‐rift volcanism at the eastern end of the Australian margin (Victoria and Tasmania), indicating the exhumation of fertile subcontinental mantle during rifting between Australia and Antarctica. Seamount B represents the initial stages of exhumation of cold subcontinental lithosphere along an OCT during rifting. This thick mantle domain was likely affected by melt impregnation at high pressure (8 kbar), leading to the formation of plagioclase‐pyroxenites. The combination of continental rifted blocks, a wide domain of volcanic‐poor subcontinental mantle and (ultra‐) slow spreading is analogous to OCTs from the Jurassic Western Tethys and Iberia‐Newfoundland rifted margins. Additionally, evidence of melt stagnation at high pressure suggests that magmatism along the Australian‐Antarctic rifted margins was sufficient to form magnetic anomalies that can be used as isochrons despite their formation in lithosphere other than mature, steady‐state ocean crust.

Upper slope processes and seafloor ecosystems on the Sabrina continental slope, East Antarctica

This study applies detailed seafloor bathymetry data and seafloor images to understand upper slope features and how these influence the distribution of seafloor biota on the East Antarctic margin. The East Antarctic slope on the Sabrina margin has been shaped by diverse processes related to repeated glaciation. Differences in the morphology of gullies on the upper slope enable an understanding of the likely processes that have been active on this margin. Gully morphology varies according to changes in slope gradient, which may have driven variations in sedimentation. Areas of lower slope angles may have led to rapid sediment deposition during glacial expansion to the shelf edge, and subsequent sediment failure. Typically, gullies in these areas are U-shaped, initiate well below the shelf break, are relatively straight and long, and have low incision depths, consistent with formation due to mass wastage. Areas of higher slope angles likely experienced enhanced flow of erosive turbidity currents during glaciations associated with the release of sediment-laden basal meltwaters. Sediment-laden subglacial meltwater flows typically create gullies such as those we observe that initiate at, or near, the shelf break; are V-shaped in profile; and have high sinuosity, deep incision depths and a relatively short downslope extent. The short downslope extent reflects a reduced sediment load associated with increased seawater entrainment as the slope becomes more concave in profile. These differences in gully morphology have important habitat implications associated with differences in the composition and beta-diversity of the seafloor communities. This upper slope region also supports seafloor communities that are distinct from those on the adjacent shelf, highlighting the uniqueness of this environment for biodiversity. Conservation strategies therefore need to consider slope and shelf communities as distinct and equally important components of the Antarctic ecosystem.

East Antarctic ice flow dynamic based on subglacial landforms near Dibble Glacier

Paleo ice sheet reconstruction in Antarctica provides key constrains for understanding and predicting future ice sheet behaviour. Along the East Antarctic margin there are still large sections with little or no information about previous extent and dynamics of the paleo-ice sheet. Here we present new multibeam and Chirp subbottom data from the East Antarctic continental margin between the Frost and Dibble Glaciers (128°E and 134°E), acquired during expedition NBP1503 with the icebreaker NB Palmer. The inner continental shelf shows a moderately deep seafloor (200–600 m) with steep and deeply incised channels, most likely created by subglacial meltwater. On the mid shelf we identified a ~1000 m deep basin with drumlin-shaped and linear glacial features. The shelf break is relatively shallow (300–400 m) and incised by numerous gullies that extent onto the continental slope. The presence of these features suggests that grounded, streaming ice has reached the shelf break during the last glaciation. Both, the subglacial channels on the continental shelf and the numerous gullies near the shelf break are indicative of melt water underneath the grounding ice. Our interpretation suggests that compared to toady the ice flow in this area might have been significantly different during glacial times when the paleo ice sheet cover most or all of the continental shelf.

Iceberg Alley, East Antarctic Margin: Continuously laminated diatomaceous sediments from the late Holocene

A 24-meter jumbo piston core (NBP0101 JPC41) collected from an inner shelf basin in Iceberg Alley reveals an approximately 2000-year history of unusually high primary productivity. Iceberg Alley, an ~ 85 km long and 10–20 km wide cross-shelf trough on the Mac.Robertson Shelf, East Antarctica, reaches depths of 850 m and is bounded on either side by shallow banks that are lined with grounded icebergs. The sediments are laminated on a mm- to cm-scale throughout and are highly biosiliceous. Microscopic examination of smear slides, quantitative diatom slides, and sediment thin sections reveals that the sediments are visually dominated by the diatom Corethron pennatum, a large and lightly silicified species notable for its long and narrow shape; the valves, girdle bands and spines are all exceptionally well-preserved, suggesting rapid sedimentation. Other common species include sea ice-related Fragilariopsis, such as F. curta and F. cylindrus, with lesser contribution from other large diatoms, including Rhizosolenia spp. and Chaetoceros Ehrenberg subg. Chaetoceros. Chaetoceros Ehrenberg subg. Hyalochaete Gran resting spores, typically associated with large early-season blooms and common in many laminated sedimentary sections around the Antarctic margin, are surprisingly rare. Laminae with any significant terrigenous component are also very rare. Individual laminations appear to represent blooms, and in some cases sub-seasonal events are likely preserved. We suggest that this productive system is associated with the continuous presence of low-salinity meltwater derived from a combination of sea ice melt and grounded icebergs, which may be a source for a steady supply of micronutrients such as iron to the surface mixed layer.

Bathymetric control of warm ocean water access along the East Antarctic Margin

AbstractObserved thinning of the Totten Glacier in East Antarctica has cast doubt upon the stability of the East Antarctic Ice Sheet. Recent oceanographic observations at the front of the Totten Ice Shelf have confirmed the presence of modified Circumpolar Deep Water (mCDW), which likely promotes enhanced melting. Details of how this water accesses the shelf remain uncertain. Here we present new bathymetry and autumnal oceanographic data from the outer continental shelf, north of the Totten Glacier, that show up to 0.7°C mCDW in a >100 km wide and >500 m deep depression within the shelf break. In other parts of East Antarctica, a shelf break bathymetry shallower than 400 m prevents these warmer waters from entering the shelf environment. Our observations demonstrate that detailed knowledge of the bathymetry is critical to correctly model the across‐shelf exchange of warm water to the various glaciers/ice shelves of Antarctica for future sea level prediction.

Uplift and tilting of the Shackleton Range in East Antarctica driven by glacial erosion and normal faulting

AbstractUnravelling the long‐term evolution of the subglacial landscape of Antarctica is vital for understanding past ice sheet dynamics and stability, particularly in marine‐based sectors of the ice sheet. Here we model the evolution of the bedrock topography beneath the Recovery catchment, a sector of the East Antarctic Ice Sheet characterized by fast‐flowing ice streams that occupy overdeepened subglacial troughs. We use 3‐D flexural models to quantify the effect of erosional unloading and mechanical unloading associated with motion on border faults in driving isostatic bedrock uplift of the Shackleton Range and Theron Mountains, which are flanked by the Recovery, Slessor, and Bailey ice streams. Inverse spectral (free‐air admittance) and forward modeling of topography and gravity anomaly data allow us to constrain the effective elastic thickness of the lithosphere (Te) in the Shackleton Range region to ~20 km. Our models indicate that glacial erosion, and the associated isostatic rebound, has driven 40–50% of total peak uplift in the Shackleton Range and Theron Mountains. A further 40–50% can be attributed to motion on normal fault systems of inferred Jurassic and Cretaceous age. Our results indicate that the flexural effects of glacial erosion play a key role in mountain uplift along the East Antarctic margin, augmenting previous findings in the Transantarctic Mountains. The results suggest that at 34 Ma, the mountains were lower and the bounding valley floors were close to sea level, which implies that the early ice sheet in this region may have been relatively stable.

Robustness of fossil fish teeth for seawater neodymium isotope reconstructions under variable redox conditions in an ancient shallow marine setting

AbstractFossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous‐dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid‐REE‐enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth, and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources.

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 …

Environmental and climate changes in Antarctica in the Geological Past

In the Cretaceous time, Antarctica was characterized by subtropical and tropical climate. The Early Eocene was warmest in the Antarctic history but this Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica at about 34 Ma ago. There is indirect evidence that small ice caps developed within central Antarctica in the Late Eocene (42−34 Ma). From the Early Oligocene to the Middle Miocene (34−13 Ma) ice sheet was wet-based and fluctuated considerably in volume, but about 14 m.y. ago it became dry-based and more stable. Seismic data collected on the East Antarctic margin give valuable information on dynamics of the past ice sheets. These data shows that the sedimentary cover of the western Wilkes Land margin includes a giant (c. 200 000 km 2 ) deep-water fan which formed between c. 43 and 34 Ma ago. The average rate of sedimentation in the central part of fan was 230–250 m/m.y. Active input of terrigenous sediments into deep-water denotes high-energy fluvial system within the Wilkes Land. Emergence of this fluvial system evidences earliest glaciation in the Antarctic interior which fed full-flowing rivers. The thickness of strata deposited during post-Early Oligocene glaciations on the Antarctic margin generally reflects the averaged energy of depositional environments. The thickest sediments (up to 2.0 km, i.e. almost twice more than in other parts of East Antarctic margin) and inferred highest energy are seen in the central Cooperation Sea, on the central Wilkes Land margin and in the D'Urville Sea. The areas with the thickest post-Early Oligocene strata correlate with places where present-day ice discharge is highest, such as via the Lambert, Totten and Mertz/Ninnis Glaciers. The correlation points to high ice (and sediment) flux in the same areas since the Early Oligocene.

Antarctica and supercontinental evolution: clues and puzzles

ABSTRACTAntarctica has been known as the “keypiece” of the Gondwana supercontinent since publication of Du Toit's 1937 classic bookOur Wandering Continents. It is also important to reconstruction of the early Neoproterozoic supercontinent Rodinia. Laurentia, with its circumferential late Precambrian rifted margins, can be regarded as the ‘keypiece’ of Rodinia. TheSouthwest US–EastAntarctica (SWEAT) hypothesis suggested former juxtaposition of the Pacific margins of Laurentia and East Antarctica. Several new lines of evidence support this hypothesis in a revised form, but must be reconciled with opening of the Pacific Ocean basin predating amalgamation, not only of Gondwana, but even of today's East Antarctic craton. The sequence of events is envisaged to have been: (1) formation prior to 1·6 Ga of a craton, including Laurentia and the Mawson craton, that extended from South Australia along the present Transantarctic margin to the Shackleton Range; (2) suturing of southernmost Laurentia to the Kalahari craton along the Grenville, Namaqua–Natal–Maud orogenic belt ca. 1·0 Ga; (3) rifting of the East Antarctic margin (Mawson craton) from western Laurentia ca. 0·7 Ga; (4) pan-African suturing of the Mawson craton to southernmost Laurentia as Gondwana amalgamated, forming the ephemeral Pannotia supercontinent; and (5) end-Precambrian separation of Laurentia as Iapetus opened.