Search

High-resolution ice core records from coastal Antarctica are particularly useful to inform our understanding of environmental changes and their drivers. Here, we present a decadally resolved record of sea-salt sodium (a proxy for open-ocean area) and non-sea salt calcium (a proxy for continental dust) from the well-dated Roosevelt Island Climate Evolution (RICE) core, focusing on the time period between 40–26 ka BP. The RICE dust record exhibits an abrupt shift towards a higher mean dust concentration at 32 ka BP. Investigating existing ice-core records, we find this shift is a prominent feature across Antarctica. We propose that this shift is linked to an equatorward displacement of Southern Hemisphere westerly winds. Subsequent to the wind shift, data suggest a weakening of Southern Ocean upwelling and a decline of atmospheric CO2 to lower glacial values, hence making this shift an important glacial climate event with potentially important insights for future projections. Antarctic ice core records provide insights into past environmental conditions. Here, an abrupt, synchronous increase in dust from ice cores in Antarctica is identified that suggests a sudden equatorward shift of westerly winds and coincides with a reduction in atmospheric CO2. [ABSTRACT FROM AUTHOR]

The timing and magnitude of Holocene glacial oscillations in most currently ice‐free areas of Antarctica remain unknown. This work focuses on the recent deglaciation in the northern sector of the Fildes Peninsula, King George Island, northern Antarctic Peninsula. The ice cap covering ca. 90% of the island has receded since the Last Glacial Maximum and exposed ca. 29 km2 of ice‐free land. We reconstruct its glacial history based on a dataset of 12 36Cl exposure ages obtained through cosmic‐ray exposure (CRE) dating of moraine boulders, polished surfaces and erratic boulders surrounding the peninsula's northern plateau. Results reveal that the deglaciation of the northern Fildes Peninsula took place during the Holocene Thermal Maximum at 7–6 ka, when warm conditions promoted a massive glacial retreat. The present arrangement of ice‐free areas was in place by 6 ka. Small cirque moraines suggest the subsequent occurrence of favourable climate conditions for glacial expansion fed by intense snow deflation at 4.6 and 1 ka at the foot of the northern plateau. The deglaciation pattern of the Fildes Peninsula resulted from the combined shrinkage of different ice masses, rather than of the long‐term retreat of the King George Ice Cap. No evidence of glacier expansion during more recent cold periods (i.e. the Little Ice Age) was found. These results fit well with regional deglacial histories inferred from lacustrine sediments and raised beaches and complement the existing chronological framework to help better understand the peninsula's Holocene geoecological dynamics. [ABSTRACT FROM AUTHOR]

Climate during the last glacial period was marked by abrupt instability on millennial timescales that included large swings of temperature in and around Greenland (Daansgard–Oeschger events) and smaller, more gradual changes in Antarctica (AIM events). Less is known about the existence and nature of similar variability during older glacial periods, especially during the early Pleistocene when glacial cycles were dominantly occurring at 41 kyr intervals compared to the much longer and deeper glaciations of the more recent period. Here, we report a continuous millennially resolved record of stable isotopes of planktic and benthic foraminifera at IODP Site U1385 (the "Shackleton Site") from the southwestern Iberian margin for the last 1.5 million years, which includes the Middle Pleistocene Transition (MPT). Our results demonstrate that millennial climate variability (MCV) was a persistent feature of glacial climate, both before and after the MPT. Prior to 1.2 Ma in the early Pleistocene, the amplitude of MCV was modulated by the 41 kyr obliquity cycle and increased when axial tilt dropped below 23.5 ∘ and benthic δ18O exceeded ∼3.8 ‰ (corrected to Uvigerina), indicating a threshold response to orbital forcing. Afterwards, MCV became focused mainly on the transitions into and out of glacial states (i.e. inceptions and terminations) and during times of intermediate ice volume. After 1.2 Ma, obliquity continued to play a role in modulating the amplitude of MCV, especially during times of glacial inceptions, which are always associated with declining obliquity. A non-linear role for obliquity is also indicated by the appearance of multiples (82, 123 kyr) and combination tones (28 kyr) of the 41 kyr cycle. Near the end of the MPT (∼0.65 Ma), obliquity modulation of MCV amplitude wanes as quasi-periodic 100 kyr and precession power increase, coinciding with the growth of oversized ice sheets on North America and the appearance of Heinrich layers in North Atlantic sediments. Whereas the planktic δ18O of Site U1385 shows a strong resemblance to Greenland temperature and atmospheric methane (i.e. Northern Hemisphere climate), millennial changes in benthic δ18O closely follow the temperature history of Antarctica for the past 800 kyr. The phasing of millennial planktic and benthic δ18O variation is similar to that observed for MIS 3 throughout much of the record, which has been suggested to mimic the signature of the bipolar seesaw – i.e. an interhemispheric asymmetry between the timing of cooling in Antarctica and warming in Greenland. The Iberian margin isotopic record suggests that bipolar asymmetry was a robust feature of interhemispheric glacial climate variations for at least the past 1.5 Ma despite changing glacial boundary conditions. A strong correlation exists between millennial increases in planktic δ18O (cooling) and decreases in benthic δ13C , indicating that millennial variations in North Atlantic surface temperature are mirrored by changes in deep-water circulation and remineralization of carbon in the abyssal ocean. We find strong evidence that climate variability on millennial and orbital scales is coupled across different timescales and interacts in both directions, which may be important for linking internal climate dynamics and external astronomical forcing. [ABSTRACT FROM AUTHOR]

Large volcanic eruptions occurring in the last glacial period can be detected by their accompanying sulfuric acid deposition in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 kyr before 2000 CE (b2k). Over most of the investigated interval the ice cores are synchronized, making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only list Greenland sulfate depositions larger than 20 kgkm-2 and Antarctic sulfate depositions larger than 10 kgkm-2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 737 eruptions in Antarctica within the 51 kyr period – for which the sulfate deposition of 85 eruptions is found at both poles (bipolar eruptions). Based on the ratio of Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. A total of 25 of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years, and 69 eruptions are estimated to have larger sulfur emission strengths than the Tambora, Indonesia, eruption (1815 CE). Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 kab2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. This confirms the suggestion that the isostatic unloading of the Northern Hemisphere (NH) ice sheets may be related to the enhanced NH volcanic activity. Our ice-core-based volcanic sulfate records provide the atmospheric sulfate burden and estimates of climate forcing for further research on climate impact and understanding the mechanism of the Earth system. [ABSTRACT FROM AUTHOR]

In this paper, we present an electric-thermal drill with a novel design of a melting head that was developed within the EnEx-RANGE project. The design combines a short melting head with a large surface area of parabolic shape. It was succesfully tested in the laboratory as well as on Alpine glaciers (Langenferner and Mittelbergferner) and at the Ross Ice Shelf in Antarctica. In all these different environments, a high melting speed per specific power of typically 8.8 cm3 w-1 h-1 is achieved that is close to the ideal maximum bound of ~10.5-11.8 cm³ w-1 h-1 when neglecting all heat losses. It has also been demonstrated that the melting probe can be operated with typical equipment of small-scale field camps including a small power generator. [ABSTRACT FROM AUTHOR]

We analyzed the single‐grain mineralogical composition of aeolian dust transported to central East Antarctica for provenance purposes. Comparison with data from the last glacial period shows for the first time disappearance of carbonates during the Holocene related to sea level rise and suppressed deflation from the Argentinean continental shelf, exposed during Marine Isotope Stage 2. Zeolites, related to alteration of volcanic glass in the subglacial/periglacial environment of Patagonia, show a similar behavior. The remaining minerals, remarkably similar between the two climatic periods, are compatible with a Pampean and Patagonian provenance, but Holocene data show a more pronounced volcanic and metamorphic imprint and presence of minerals related to warm climate weathering environments compatible with an additional contribution from subtropical latitudes of South America. These results do not imply a major large‐scale reorganization of atmospheric circulation after the last climatic transition. Plain Language Summary: Aeolian mineral dust particles transported through the atmosphere from the austral continents to the Antarctic ice sheet represent a tracer of atmospheric circulation and transport, as well as being a source of information about environmental conditions within dust source regions. Many lines of evidence suggest that central East Antarctic dust is sourced from South America during the last glacial period, whereas there is not a general consensus about dust provenance during the Holocene. A major limitation to this problem is represented by the extremely low dust concentration in Antarctic ice during interglacials. In this study, we analyzed the single‐grain mineralogy of more than 2,300 mineral dust particles transported by winds to Dome C during four different time windows within the Holocene, the current interglacial. Comparing results with those obtained from dust deposited during the last glacial period, we observe that some minerals that are typically associated to glacial climate conditions in Patagonia almost disappear during Holocene, while the remaining minerals are compatible with a South American provenance in both climate periods. Data thus suggest that the dominant atmospheric circulation patterns did not experience a significant change with climate. However, data suggest an additional contribution from subtropical South American latitudes during Holocene. Key Points: The mineralogy of more than 2,300 aeolian dust particles windblown to central East Antarctica (Dome C) during the Holocene was identifiedDisappearance of carbonate dust during the Holocene relates to sea level rise and suppressed deflation from the Argentinean shelfAeolian dust suggests Pampean and Patagonian provenance in the Holocene and a lower latitude contribution, without major circulation changes [ABSTRACT FROM AUTHOR]

The age model of the western Bering Sea core 85 KL was modified through correlation of new and earlier-measured productivity proxies with the Chinese interstadials described by δ18O records of Hulu and Sanbao caves and the relative paleointensity events in the studied core with those in the dated records. Resulted sequence of millennial scale Bering Sea Interstadials recorded by abrupt productivity risings was established during the penultimate glacial consistently with the Chinese interstadials and Antarctica isotope maxima. The pattern of the frequency and amplitude of the millennial productivity/climate variability in the Bering Sea during the penultimate glacial resembles that initially depicted in the δ18O of Chinese cave stalagmites and is quite similar to one of the Dansgaard–Oeschger cycles during last glacial, except for their terminations. Contrary to well-pronounced interstadial A.1 during termination TI, an interstadial B.1 over the TII has lower duration and therefore is weakly observed in Antarctic temperature changes. Our results provide robust evidence that the bipolar seesaw mechanisms of millennial climate changes in the Northern and Southern Hemispheres were similar during the last and penultimate glacials. [ABSTRACT FROM AUTHOR]

The cycling of climate into and out of glacial states in response to orbital forcing illustrates the important role of feedbacks in the Earth system. In this contribution, the Geophysical Fluid Dynamics Laboratory coupled ocean‐atmosphere model is used to qualitatively assess how changes in the Earth's precessional parameters may have impacted Atlantic Meridional Ocean Circulation and Southern Ocean dynamics. The Southern Ocean region responds to precessional forcing similar to that of the Last Glacial Maximum with a slight shift in maximum average annual wind stress, a reduction in austral winter wind stress, and an increase in austral winter sea ice. During austral summer, stratification and wind stress increase, Changes in the temperature and density of the North Atlantic lead to a decrease in Atlantic Meridional Overturning Circulation. Together these changes contribute to aging of the global deep ocean, except around Antarctica where enhanced local convection decreases the age of upwelling waters. These circulation changes may have implications for a precessionally driven feedback that contributes to enhanced storage of CO2 in the deep ocean and a reduction in atmospheric CO2. Plain Language Summary: The Earth has cycled into and out of ice ages over last 2.6 million years. The precise factors that cause these changes in climate are not fully understood. The correspondence between the Earth's climate and the Earth's position in space suggests that there is a connection between the two. In this work we use a fully coupled global climate model to explore whether the season during which Earth is closest to the Sun has an impact on ocean circulation. We use two model runs, one having the Earth in a northern hemisphere winter perihelion (close pass) position and another placing the Earth in a northern hemisphere summer perihelion. We find that the northern hemisphere winter perihelion position is associated with changes in Southern Ocean circulation that include an increase in upwelling and a decrease in the age of the upwelled water. We also find that deep ocean circulation in the Atlantic Ocean decreases and that global ocean deep waters increase in age. The observed changes are consistent with the idea that a Northern Hemisphere winter perihelion position may contribute to glacial interglacial climate change and a drawdown of atmospheric CO2. Key Points: Precessional forcing that places the Earth at a boreal winter perihelion position causes an increase in wind stress and Ekman upwelling during austral summer/fall and a decrease during austral winter/spring in the high‐latitude Southern OceanGlobal deepwater age responds to a boreal winter perihelion position by increasing ~200 yearsAtlantic Meridional Overturning Circulation decreases in response to a boreal winter perihelion position. Southern Ocean ventilation increases [ABSTRACT FROM AUTHOR]

Here we summarize the motivation and issues surrounding the responses of ice sheets and sea level to past climate warming as part of the PALeo constraints on SEA level rise (PALSEA) working group. Papers in this special issue of Quaternary Science Reviews focus on the timescale of glaciations during the late Pliocene, the magnitude of ice-sheet fluctuations and volume leading up to and during the last glacial maximum, the timing and persistence of ice-sheet impacts on deglacial and future relative sea-level change, and relative sea-level change during peak interglacial climate. A more dynamic cryosphere is noted under both late Pliocene and last glacial cycle climate conditions, while relative sea-level changes during the last deglaciation appear to correspond closely with individual ice-sheet deglaciation. Lastly, relative sea-level change during peak interglacial conditions may have fluctuated by as much as a meter, although the sources of such variability (Greenland, Antarctica or elsewhere) remain elusive. [ABSTRACT FROM AUTHOR]

The remains of a small volcanic centre are preserved on a thin bedrock ridge at Harrow Peaks, northern Victoria Land, Antarctica. The outcrop is interpreted as a monogenetic tuff cone relict formed by a hydrovolcanic (phreatomagmatic) eruption of mafic magma at 642 ± 20 ka (by Ar-Ar), corresponding to the peak of the Marine Isotope Stage 16 (MIS16) glacial. Although extensively dissected and strewn with glacial erratics, the outcrop shows no evidence for erosion by ice. From interpretation of the lithofacies and eruptive mechanisms, the weight of the evidence suggests that eruptions took place under a cold-based (frozen-bed) ice sheet. This is the first time that a tuff cone erupted under cold ice has been described. The most distinctive feature of the lithofacies is the dominance of massive lapilli tuff rich in fine ash matrix and abraded lapilli. The lack of stratification is probably due to repeated eruption through a conduit blasted through the ice covering the vent. The ice thickness is uncertain but it might have been as little as 100 m and the preserved tephra accumulated mainly as a crater (or ice conduit) infill. The remainder of the tuff cone edifice was probably deposited supraglacially and underwent destruction by ice advection and, particularly, collapse during a younger interglacial. Dating using Be cosmogenic exposure of granitoid basement erratics indicates that the erratics are unrelated to the eruptive period. The Be ages suggest that the volcanic outcrop was most recently exposed by ice decay at c. 20.8 ± 0.8 ka (MIS2) and the associated ice was thicker than at 642 ka and probably polythermal rather than cold-based, which is normally assumed for the period. [ABSTRACT FROM AUTHOR]

The Amundsen Sea Embayment of West Antarctica hosts one of the most rapidly changing sectors of the West Antarctic Ice Sheet. With the fastest-flowing ice streams in Antarctica, the region around Pine Island Bay is characterized by rapid ice-sheet thinning and grounding-line retreat. Published surface-exposure data are limited to a few isolated nunataks making it difficult to assess the long-term deglacial history of the area. To address this, we correlate existing records of lateral ice-stream retreat from marine sediment cores with onshore glacial thinning in two key areas of eastern Marie Byrd Land: the Kohler Range and Pine Island Bay. Our 10Be surface-exposure ages are the first from the isolated Kohler Range and show that the nunataks there became ice-free between 8.6 and 12.6 ka. This implies a minimum long-term average thinning rate of 3.3 ± 0.3 cm/yr, which is one order of magnitude lower than recent rates based on satellite data. We also present pre- to early Holocene 10Be surface-exposure ages from two islands located approximately 80 km downstream of the Pine Island Glacier ice-shelf front to constrain the lateral deglacial history in the Pine Island Bay area. This study provides insight into the significance of local ice sheet variations and suggests that the post-LGM history in the Amundsen Sea sector was characterized by glacial thinning as well as lateral retreat in pre- to early Holocene times. [ABSTRACT FROM AUTHOR]

In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur. [ABSTRACT FROM AUTHOR]

The IceCube Neutrino Observatory and its prototype, AMANDA, were built in South Pole ice, using powerful hot-water drills to cleanly bore >100 holes to depths up to 2500 m. The construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques. We made high-resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010. The South Pole laser logs are among the most clearly resolved measurements of Antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail. Here we use manual and algorithmic matching to synthesize our South Pole measurements with ice-core and logging data from Dome C, East Antarctica. We derive impurity concentration, precision chronology, annual-layer thickness, local spatial variability, and identify several widespread volcanic ash depositions useful for dating. We also examine the interval around ∼74 ka recently isolated with radiometric dating to bracket the Toba (Sumatra) supereruption [ABSTRACT FROM AUTHOR]

The article presents a study which characterizes the glacial conditions at Halvfarryggen ice dome in Dronning Maud Land, Antarctica. It explores the potential drill site for the International Partnerships in Ice Core Sciences with specific atmospheric conditions, surface topography, and ice stratigraphy from radar data. It details the comprehensive approach in field data, remote sensing, and anisotropic ice-flow model in characterization of glacial conditions. The study suggests drilling into the apices of the deep anticlines for record length and temporal resolution.

The article reports on a study which discovered the active glaciological bodies sharing similar basal conditions for surface lakes. It refers to the unrelated subglacial lakes under the ice streams of Antartica and the supraglacial lakes observed in Iceland ice sheet. The Antarctic ice streams derive water from energy dissipation due to basal friction, while the Gleenland ice sheet derive water from atmospherically driven surface melting. It implies that glacial bodies can share common basal conditions and basal lakes can exist in tandem.

Abstract: A long-standing debate concerning Neogene Antarctic climate in the McMurdo Dry Valleys relies largely on evidence from landscape evolution, glacial modeling and stratigraphy. We provide new evidence from meteoric 10Be for the onset of frozen, hyper-arid conditions on a high elevation (1840m) interfluve at Table Mountain. A simple decay model for the co-occurrence of meteoric 10Be and illuviated clay in cores of ice-cemented glacial sediments indicates that the clays were actively migrating down from the surface in a warm climate until the system froze between 6 and 9Ma. Although this age range may be sensitive to possible interference by in situ produced 10Be, the implied minimum age of 6Ma for the Sirius Group indicates that the Dry Valleys were permanently frozen down to this elevation at this time. The model also suggests denudation rates of 1–6cmMyr−1 since freezing. These data provide an independent test of glacial-stratigraphic evidence used to determine Antarctic paleoclimate. [Copyright &y& Elsevier]

The article presents a study which investigates on the use of radar diagnosis to determine the subglacial condition in Dronning Maud Land in East Antarctica. The study was performed to three ground-based and pulse-modulated radar sounders, wherein two radar sounders have a centre frequency of 179MHz. The study shows that returned power decreases in the area as ice becomes thicker.

Abstract: Understanding of Neogene climate in Antarctica has been an intractable problem for over 20 years. Competing models of the effect of Pliocene climatic warmth have not yet been reconciled. New sedimentological and paleontological data from Dry Valley Drilling Project core (DVDP-10) demonstrate a dynamic climate regime for the early and mid-Pliocene record preserved in the floor of Taylor Valley. This succession of interbedded mudrocks, sandstones, conglomerates and diamictites includes evidence for times when the coastal plain landscape of Taylor Valley may have been vegetated by higher land plants. Biostratigraphic data from DVDP-10 are utilized to correlate to the more detailed and finely resolved record in the AND-1B core in southern McMurdo Sound. Accordingly, the interval in DVDP-10 that records dynamic environmental fluctuations with a possible vegetated coastal plain land system is bracketed at 4.92–4.25Ma. These data suggest that low altitude terrains of the Dry Valleys during the Early Pliocene were subjected to glacial-interglacial cycles in which some interglacials were largely ice-free. [Copyright &y& Elsevier]

Abstract: The climate of the last glacial Marine Isotopic Stage 3 (MIS3) period is characterized by strong millennial-scale variability with a succession of Dansgaard–Oeschger events first identified in Greenland ice cores and associated with variations of the Atlantic Meridional Overturning Circulation (AMOC). These abrupt events have a smooth and lagged counterpart in water stable isotopes from Antarctic ice cores. In this study we aim at depicting and understanding the circum-Antarctic expression of this millennial-scale variability. To illustrate the mechanisms potentially at work in the response of the southern high latitudes to an abrupt decrease of the AMOC, we first present results from experiments performed with the IPSL-CM4 atmosphere-ocean coupled model under glacial boundary conditions. When the AMOC is perturbed by imposing an additional freshwater flux in the North Atlantic, our model produces the classical bipolar seesaw mechanism generally invoked to explain the warming of the Southern Ocean/Antarctic region. However, this mechanism can be locally offset by faster atmospheric teleconnections originating from the tropics, even though the precise location of this fast response is not coherent among different climate models. Our model results are confronted with a synthesis of Antarctic records of ice core stable isotope and sea-salt sodium, including new data obtained on the TALDICE ice core. The IPSL-CM4 produces a dipole-like pattern around Antarctica, with warming in the Atlantic/Indian sectors contrasting with an unexpected cooling in the East-Pacific sector. The latter signal is not detected in our data synthesis. Both ice core data and simulations are consistent in depicting a more rapid response of the Atlantic sector compared to the Indian sector. This feature can be explained by the gradual impact of ocean transport on which faster atmospheric teleconnections are superimposed. Detailed investigations of the sequence of events between different proxies are conducted in three ice cores. Earlier shifts in deuterium excess and significant changes in sea-salt sodium fluxes in the most coastal sites (TALDICE and EDML) compared to EDC suggest reorganizations in local moisture sources, possibly linked with sea-ice cover. This study demonstrates the added value of circum-Antarctic ice core records to characterize the patterns and mechanisms of glacial climate variability. [Copyright &y& Elsevier]

The article presents the first seasonal variations of 17O-excess and d-excess to offer an analogy with glacial climatic conditions in Vostok Station, Antarctica on an event basis over one year. It mentions that the 17O-excess and d-excess variations can be explained through the influence of low temperatures' kinetic fractionation. It states that the comparison with simple isotopic models affirms the explanation, but cannot explain the association between temperature, 17O-excess and d-excess without a particular relationship between surface temperature and condensation.

Mineral dust aerosols represent an active component of the Earth's climate system, by interacting with radiation directly, and by modifying clouds and biogeochemistry. Mineral dust from polar ice cores over the last million years can be used as paleoclimate proxy, and provide unique information about climate variability, as changes in dust deposition at the core sites can be due to changes in sources, transport and/or deposition locally. Here we present results from a study based on climate model simulations using the Community Climate System Model. The focus of this work is to analyze simulated differences in the dust concentration, size distribution and sources in current climate conditions and during the Last Glacial Maximum at specific ice core locations in Antarctica, and compare with available paleodata. Model results suggest that South America is the most important source for dust deposited in Antarctica in current climate, but Australia is also a major contributor and there is spatial variability in the relative importance of the major dust sources. During the Last Glacial Maximum the dominant source in the model was South America, because of the increased activity of glaciogenic dust sources in Southern Patagonia-Tierra del Fuego and the Southernmost Pampas regions, as well as an increase in transport efficiency southward. Dust emitted from the Southern Hemisphere dust source areas usually follow zonal patterns, but southward flow towards Antarctica is located in specific areas characterized by southward displacement of air masses. Observations and model results consistently suggest a spatially variable shift in dust particle sizes. This is due to a combination of relatively reduced en route wet removal favouring a generalized shift towards smaller particles, and on the other hand to an enhanced relative contribution of dry coarse particle deposition in the Last Glacial Maximum. [ABSTRACT FROM AUTHOR]

Abstract: Marine Isotope Stage 31 (MIS-31) is one of the major interglacials of the early Pleistocene ~1.08 to 1.06Ma. Data from proximal sediment cores around several sectors of Antarctica indicate strong sea surface warming and ice shelf and sea ice retreat. Benthic deep-sea-core δ18O values at this time are some of the lowest of the Pleistocene, indicating both deep sea warming and reduced global ice volume. A coeval alignment of orbital parameters produces one of the strongest high-latitude summer insolation anomalies of the last several million years. Here we use a 3-D ice sheet-shelf model to simulate the evolution of Antarctic ice sheets through the event, and a global climate model to simulate temperatures and sea ice during peak Antarctic warmth. The ice model predicts nearly complete collapse and subsequent recovery of marine ice in West Antarctica, and the ice and climate model results agree well with proximal sediment core data in the Ross Embayment recovered by the ANDRILL and Cape Roberts drilling projects. The dominant forcing is found to be variations in sub-ice-shelf oceanic melting, with insignificant surface melting of terrestrial ice flanks even during peak warmth. Implications are noted in light of other observations and theories of Pliocene–Pleistocene Antarctic ice sheet variability that do involve surface melt. [Copyright &y& Elsevier]

Abstract: Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream''s dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73°S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only ∼80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric “bottle neck”. [Copyright &y& Elsevier]

Central East Antarctic ice cores preserve stratigraphic records of mineral dust originating from remote sources in the Southern Hemisphere, and represent useful indicators of climatic variations on glacial-interglacial time scales. The peripheries of the East Antarctic Ice Sheet, where ice-free areas with the potential to emit dust exist, have been less explored from this point of view. Here, we present a new profile of dust deposition flux and grain size distributions from an ice core drilled at Talos Dome (TALDICE, Northern Victoria Land, East Antarctica), where there is a significant input of dust from proximal Antarctic ice-free areas. We analyze dust and stable water isotopes variations from the Last Glacial Maximum to the Late Holocene, and compare them to the EPICA Dome C profiles from central East Antarctica. The smaller glacial-interglacial variations at Talos Dome compared to Dome C and a distinctive decreasing trend during the Holocene characterize the TALDICE dust profile. By deciphering the composite dust signal from both remote and local sources, we show the potential of this combined proxy of source activity and atmospheric transport to give information on both regional and larger spatial scales. In particular, we show how a regional signal, which we relate to the deglaciation history of the Ross Sea embayment, can be superimposed to the broader scale glacial-interglacial variability that characterizes other Antarctic sites. [ABSTRACT FROM AUTHOR]

During glacial periods, atmospheric CO2 concentration increases and decreases by around 15 ppm. At the same time, the climate changes gradually in Antarctica. Such climate changes can be simulated in models when the AMOC (Atlantic Meridional Oceanic Circulation) is weakened by adding fresh water to the North Atlantic. The impact on the carbon cycle is less straightforward, and previous studies give opposite results. Because the models and the fresh water fluxes were different in these studies, it prevents any direct comparison and hinders finding whether the discrepancies arise from using different models or different fresh water fluxes. In this study we use the CLIMBER-2 coupled climate carbon model to explore the impact of different fresh water fluxes. In both preindustrial and glacial states, the addition of fresh water and the resulting slow-down of the AMOC lead to an uptake of carbon by the ocean and a release by the terrestrial biosphere. The duration, shape and amplitude of the fresh water flux all have an impact on the change of atmospheric CO2 because they modulate the change of the AMOC. The maximum CO2 change linearly depends on the time integral of the AMOC change. The different duration, amplitude, and shape of the fresh water flux cannot explain the opposite evolution of ocean and vegetation carbon inventory in different models. The different CO2 evolution thus depends on the AMOC response to the addition of fresh water and the resulting climatic change, which are both model dependent. In CLIMBER-2, the rise of CO2 recorded in ice cores during abrupt events can be simulated under glacial conditions, especially when the sinking of brines in the Southern Ocean is taken into account. The addition of fresh water in the Southern Hemisphere leads to a decline of CO2, contrary to the addition of fresh water in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Abstract: Cores acquired by the ANDRILL McMurdo Ice Shelf Project (AND-1B) provide the basis for a new sedimentation model for glacimarine depositional sequences that reflect cyclic glacial–interglacial fluctuations of a marine-based ice sheet in the western Ross Embayment over the past 2.0 Ma. Notwithstanding periodic erosion during advances of the ice sheet, uncertainties inherent to the sedimentological interpretation, and a limited number of chronological datums, it is clear that subglacial to grounding-zone sedimentation was dominant at the AND-1B site during the Late Pleistocene with interglacials being represented only by thin intervals of ice-shelf sediment. Each sequence is characterised by subglacial, massive diamictite that pass upwards into glacimarine diamictites and mudstones. This provides the first direct evidence that the marine-based Antarctic Ice Sheet has oscillated between a grounded and floating state at least 7 times in the Ross Embayment over the last 780ka, implying a Milankovitch orbital influence. An unconformity in AND-1B, that spans most (∼200 kyr) of the Mid-Pleistocene Transition is inferred to represent widespread expansion of a marine-based ice sheet in the Ross Embayment at 0.8 Ma. Prior to 1.0 Ma, interglacial periods are characterised by open-water conditions at the drill site with high abundances of volcanoclastic deposits and occasional diatomaceous sediments. These may have responded to precession (∼20-kyr) or obliquity (∼40-kyr) orbital control. The occurrence of 6.7 m of phonolitic glass reworked from Mt Erebus in interglacial deposits beneath Last Glacial Maximum till requires open ocean or ice shelf conditions in the western Ross Sea around the drill site within the past 250 ka and implies a Ross Ice Shelf similar to or less extensive than today during Marine Isotope Stage 7 or 5. [Copyright &y& Elsevier]

Abstract: We present a new reconstruction of the Antarctic Ice Sheets between 20 ka BP and the present day. Our reconstruction is derived using a numerical model to generate a physically-consistent ice surface across the whole of the continent. We define the extent of the ice sheet at five time slices; 20, 15, 10, 5 and 0 ka BP, assuming an equilibrium state for the 20 ka BP time slice, and a transient state for the deglacial time slices. The evolution of the ice sheet within the numerical model is driven by variations in temperature, accumulation rate, and relative sea level. In order to reconstruct the concave profile of the ice sheet in marine-grounded regions, such as the Ross and Weddell Seas, we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams. We find a strong dependence upon the basal sliding parameters, and also the position of the grounding line. We use an extensive data base of geological and glaciological data to constrain our ice-sheet reconstruction. Grounding-line extent is prescribed from marine geological data and we test ice-sheet thickness against onshore geological data at 62 sites. Of the five time slices considered, our 20 ka BP reconstruction is the best constrained by data and has an RMS misfit of 147.6 m when compared to observations of ice thickness change between 20 ka BP and the present day. Across all time slices there are large regions of the ice-sheet which are poorly constrained, especially after 20 ka BP. We estimate the spatial distribution of uncertainty in our ice-sheet reconstruction, and note that the solutions are least reliable in regions of complex topography. We predict that the Antarctic Ice Sheets contributed 9 ± 1.5 m of eustatic sea level to the global ocean between 20 ka BP and the present, and our reconstruction with minimum misfit contributes ∼8 m eustatic sea level during this period. These values, which we argue are an upper bound, are lower than many previous estimates. The reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models. [Copyright &y& Elsevier]

Abstract: The Antarctic Peninsula is one of the most rapidly warming regions on Earth, as evidenced by a recent increase in the intensity and duration of summer melting, the recession of glaciers and the retreat and collapse of ice shelves. Despite this, only a limited number of well-dated near shore marine and lake sediment based palaeoenvironmental records exist from this region; so our understanding of the longer-term context of this rapid climate change is limited. Here we provide new well-dated constraints on the deglaciation history, and changes in sea ice and climate based on analyses of sedimentological proxies, diatoms and fossil pigments in a sediment core collected from an isolation basin on Beak Island in Prince Gustav Channel, NE Antarctic Peninsula (63°36′S, 57°20′W). Twenty two radiocarbon dates provided a chronology for the core including a minimum modelled age for deglaciation of 10,602 cal yr BP, following the onset of marine sedimentation. Conditions remained cold and perennial sea ice persisted in this part of Prince Gustav Channel until c. 9372 cal yr BP. This was followed by a seasonally open marine environment until at least 6988 cal yr BP, corresponding with the early retreat and disintegration of the ice shelf in southern Prince Gustav Channel. Following isolation of the basin from 6988 cal yr BP a relatively cold climate persisted until 3169 cal yr BP. A Mid-late Holocene climate optimum occurred between 3169 and 2120 cal yr BP, inferred from multiple indicators of increased biological production. This postdates the onset of the Mid-late Holocene climate optimum in the South Shetland Islands (4380 cal yr BP) and the South Orkney Islands (3800 cal yr BP) suggesting that cooler climate systems of the Weddell Sea Gyre to the east of the Peninsula may have buffered the onset of warming. Climate deterioration is inferred from c. 2120 cal yr BP until 543 cal yr BP. This was followed by warming. Superimposed on this warming trend, the instrumental record of recent warming at nearby Hope Bay is mirrored by a recent increase in the lake’s primary production and a shift in the diatom communities in the uppermost 3 cm of sediments, suggesting that this is amongst the first records to show an ecological response to recent rapid temperature increase. These new constraints on glaciological and climate events in Prince Gustav Channel are reviewed in the context of wider changes in the Antarctic region. [Copyright &y& Elsevier]

Abstract: New diatom-biostratigraphic age data derived from piston core were used to constrain the chronology for a seismic-based interpretation of West Antarctic Ice Sheet (WAIS) advance and retreat from the North Basin outer shelf in western Ross Sea. The data demonstrates that grounded ice occupied the outer shelf on at least ten occasions during the last 2.0Ma of the Pleistocene. Although the biostratigraphic resolution is low, the constraints permit correlations to coeval section recently drilled in South McMurdo Sound at the AND-1B drill site. Our interpretation of regional-scale correlations suggests that the Pleistocene dynamics of the WAIS involved grounding-line translations in excess of 600km. However, the data also suggests that only two major advances of grounded ice occurred since ~0.71Ma. In other words, several of the late Pleistocene sediment cycles at AND-1B must represent only minor advance and retreat of grounded ice to and from South McMurdo Sound. The results prove false the long-standing tacit assumption that the WAIS experienced major advances in association with peak glacials and eustatic lowstands during the last 700ka of the Pleistocene. These results show that piston cores can be used to constrain the timing of pre-Holocene grounding events. These data also highlight the need for regional-scale correlations to distinguish between major versus minor grounding-line translations of grounded ice in the marine setting. [Copyright &y& Elsevier]

Abstract: The Antarctic Peninsula has been identified as a region of rapid on-going climate change with impacts on the cryosphere. The knowledge of glacial changes and freshwater budgets resulting from intensified glacier melt is an important boundary condition for many biological and integrated earth system science approaches. We provide a case study on glacier and mass balance changes for the ice cap of King George Island. The area loss between 2000 and 2008 amounted to about 20km2 (about 1.6% of the island area) and compares to glacier retreat rates observed in previous years. Measured net accumulation rates for two years (2007 and 2008) show a strong interannual variability with maximum net accumulation rates of 4950mm w.e. a−1 and 3184mm w.e. a−1, respectively. These net accumulation rates are at least 4 times higher than reported mean values (1926–95) from an ice core. An elevation dependent precipitation rate of 343mm w.e. a−1 (2007) and 432mm w.e. a−1 (2008) per 100m elevation increase was observed. Despite these rather high net accumulation rates on the main ice cap, consistent surface lowering was observed at elevations below 270m above ellipsoid over an 11-year period. These DGPS records reveal a linear dependence of surface lowering with altitude with a maximum annual surface lowering rate of 1.44ma−1 at 40m and −0.20ma−1 at 270m above ellipsoid. These results fit well to observations by other authors and surface lowering rates derived from the ICESat laser altimeter. Assuming that climate conditions of the past 11years continue, the small ice cap of Bellingshausen Dome will disappear in about 285years. [Copyright &y& Elsevier]

Abstract: The question of whether Pliocene climate was warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of Antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations. Here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from Early Pliocene diamictites and underlying late Cretaceous sediments collected from James Ross Island, northern Antarctic Peninsula. The diamictites are dated using a combination of 40Ar/39Ar and 87Sr/86Sr isotope ages on interbedded lavas and pristine bivalves. Well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph-bearing sediments were probably deposited during warmer Pliocene interglacials and later amalgamated into a diamictite formed by a major ice advance during cold glacial cycle. The palynological analyses presented herein do not identify any in-situ pollen and spores which indicate the presence of a substantial vegetation cover. Our study suggests a local (i.e. James Ross Island) provenance for most of the diamictites, whilst sediments from the western coast might have been delivered by ice sheets from the Antarctic Peninsula. Whilst the acritarch Leiosphaeridia might imply the presence of sea-ice and near-modern climate conditions during the Late Neogene, the presence of the dinoflagellate cyst Bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials. The absence of in-situ pollen and spores in the James Ross Island diamictites cannot be taken as proof of non-existence of vegetation. However, the combined palynological and geological evidence presented in this paper makes the presence of a substantial Pliocene vegetation cover on James Ross Island unlikely and supports previous reconstructions of a permanent ice sheet on the Antarctic Peninsula throughout the Late Neogene. [Copyright &y& Elsevier]

Abstract: The Little Ice Age (LIA) is one of the most prominent climate shifts in the past 5000yrs. It has been suggested that the LIA might be the most recent of the Dansgaard–Oeschger events, which are better known as abrupt, large scale climate oscillations during the last glacial period. If the case, then according to Broecker (2000a, 2000b) Antarctica should have warmed during the LIA, when the Northern Hemisphere was cold. Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~2°C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. Whilst we find there was large spatial and temporal variability, overall Antarctica was cooler and stormier during the LIA. Although temperatures have warmed since the termination of the LIA, atmospheric circulation strength has remained at the same, elevated level. We conclude, that the LIA was either caused by alternative forcings, or that the sea-saw mechanism operates differently during warm periods. [Copyright &y& Elsevier]

Abstract: Understanding climate during the last interglacial is critical for understanding how modern climate change differs from purely naturally forced climate change. Here we present the first high-resolution ice core record of the last interglacial and transition to the subsequent glacial period from Antarctica and the first glaciochemical record for this period from West Antarctica. Samples were collected from a horizontal ice trench in the Mt. Moulton Blue Ice Area (BIA) in West Antarctica and analyzed for their soluble major anions (Cl−, NO3 −, SO4 2-), major and trace elements (Na, Mg, Ca, Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Al, S, Ti, V, Cr, Mn, Fe, Co, Cu, Zn) and water hydrogen isotopes (δD). The last interglacial is characterized by warmer temperatures (δD), weakened atmospheric circulation (dust elements, seasalts aerosols), decreased sea ice extent (Na, nssSO4 2-) and decreased oceanic productivity (nssSO4 2-). A combined examination of Mt. Moulton seasalts, dust, nssSO4 2- and δD records indicates that the last interglacial was extremely stable compared to glacial age climate events and it ended through a long period of gradual cooling unlike that projected for future Holocene climate. [Copyright &y& Elsevier]

Abstract: Present understanding of Antarctic climate change during the Early to Mid-Miocene, including major cycles of glacial expansion and contraction, relies in large part on stable isotope proxies from deep sea core drilling. Here, we summarize the lithostratigraphy of the ANDRILL Southern McMurdo Sound Project drillcore AND-2A. This core offers a hitherto unavailable ice-proximal stratigraphic archive from a high-accommodation continental margin setting, and provides clear evidence of repeated fluctuations in climate, ice expansion/contraction and attendant sea-level change over the period c. 20.2–14.2Ma, with a more fragmentary record of Late Miocene and Pliocene time. The core is divided into seventy-four high-frequency (fourth- or fifth-order) glacimarine sequences recording repeated advances and retreats of glaciers into and out of the Victoria Land Basin. The section can be resolved into thirteen longer-term, composite (third-order) sequences, which comprise packages of higher frequency sequences that show a consistent stratigraphic stacking pattern (Stratigraphic Motif). The distribution of the six recognized motifs indicates intervals of less and more ice-proximal, and temperate to subpolar/polar climate, through the Miocene period. The core demonstrates a dynamic climate regime throughout the Early to Mid-Miocene that may be correlated to some previously-recognized events such as the Mid-Miocene Climatic Optimum, and provides a detailed reference point from which to evaluate stable isotope proxy records from the deep-sea. [Copyright &y& Elsevier]

The article focuses on the deep ice core drilling in Lake Vostok, Antarctica. It states that the drilling started in the 1970s using thermal drill system hanged on a cable. It cites that the Vostok ice core provided a detailed paleoclimate record during the past four glacial-interglacial cycles that occurs every 100,000 years. It also mentions that studies of sub-glacial water properties are important parts for the drilling project in Lake Vostok.

During the last glacial/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A was accompanied by a rapid sea level rise of about 20m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate. In-situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10±1 ppmv in 230 yr at the same time. Allowing for the modelled age distribution of CO2 in firn, we show that atmospheric CO2 could have jumped by 20-35 ppmv in less than 200 yr, which is a factor of 2-3.5 greater than the CO2 signal recorded in-situ in EDC. This rate of change in atmospheric CO2 corresponds to 29-50% of the anthropogenic signal during the last 50 yr and is connected with a radiative forcing of 0.59-0.75 W m-2. Using a model-based airborne fraction of 0.17 of atmospheric CO2, we infer that 125 Pg of carbon need to be released into the atmosphere to produce such a peak. If the abrupt rise in CO2 at the onset of the B/A is unique with respect to other Dansgaard/Oeschger (D/O) events of the last 60 kyr (which seems plausible if not unequivocal based on current observations), then the mechanism responsible for it may also have been unique. Available δ13CO2 data are neutral, whether the source of the carbon is of marine or terrestrial origin. We therefore hypothesise that most of the carbon might have been activated as a consequence of continental shelf flooding during MWP-1A. This potential impact of rapid sea level rise on atmospheric CO2 might define the point of no return during the last deglaciation. [ABSTRACT FROM AUTHOR]

Abstract: We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5–9ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere''s Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today. [Copyright &y& Elsevier]

Antarctica has a complex and multifaceted geologic and oceanographic history that has influenced and shaped patterns of marine invertebrate diversity. This evolutionary history consists of major events on a wide range of time scales such as the formation of the Antarctic Polar Front (25–41 million years ago) to repeated glacial cycles during the past million years. These factors variably influenced genetic connectivity of fauna to produce a highly unique, but incredibly diverse marine community. Use of molecular phylogeographic methods is creating the need to revise our understanding of Antarctic patterns of biodiversity. In particular, almost every phylogeographic study carried out to date, suggests that the biodiversity of Antarctic marine shelf fauna is considerably underestimated. In discovering this diversity, some lineages (i.e., cryptic lineages) show no diagnostic morphological differences whereas others (i.e., unrecognized species) show differences that were unknown to science. The sea star genus Odontaster is among the best-studied of Antarctic invertebrate groups. Nonetheless, two unrecognized lineages were recently discovered along the Antarctic Peninsula, which is one of the best-studied regions in Antarctica. Herein, we elucidate the molecular and morphological uniqueness of these species and name them O. roseus and O. pearsei. The latter is in honor of John Pearse, an Antarctic biologist, as well as past President and long-time member of the Society of Integrative and Comparative Biology. [ABSTRACT FROM AUTHOR]

Abstract: A major trough (“Belgica Trough”) eroded by a palaeo-ice stream crosses the continental shelf of the southern Bellingshausen Sea (West Antarctica) and is associated with a trough mouth fan (“Belgica TMF”) on the adjacent continental slope. Previous marine geophysical and geological studies investigated the bathymetry and geomorphology of Belgica Trough and Belgica TMF, erosional and depositional processes associated with bedform formation, and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments. Here, we present multi-proxy data from sediment cores recovered from the shelf and uppermost slope in the southern Bellingshausen Sea and reconstruct the ice-sheet history since the last glacial maximum (LGM) in this poorly studied area of West Antarctica. We combined new data (physical properties, sedimentary structures, geochemical and grain-size data) with published data (shear strength, clay mineral assemblages) to refine a previous facies classification for the sediments. The multi-proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings: 1) subglacial, 2) proximal grounding-line, 3) distal sub-ice shelf/sub-sea ice, and 4) seasonal open-marine. In the seasonal open-marine facies we found evidence for episodic current-induced winnowing of near-seabed sediments on the middle to outer shelf and at the uppermost slope during the late Holocene. In addition, we obtained data on excess 210Pb activity at three core sites and 44 AMS 14C dates from the acid-insoluble fraction of organic matter (AIO) and calcareous (micro-) fossils, respectively, at 12 sites. These chronological data enabled us to reconstruct, for the first time, the timing of the last advance and retreat of the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS) in the southern Bellingshausen Sea. We used the down-core variability in sediment provenance inferred from clay mineral changes to identify the most reliable AIO 14C ages for ice-sheet retreat. The palaeo-ice stream advanced through Belgica Trough after ∼36.0 corrected 14C ka before present (B.P.). It retreated from the outer shelf at ∼25.5kaB.P., the middle shelf at ∼19.8kaB.P., the inner shelf in Eltanin Bay at ∼12.3kaB.P., and the inner shelf in Ronne Entrance at ∼6.3kaB.P. The retreat of the WAIS and APIS occurred slowly and stepwise, and may still be in progress. This dynamical ice-sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass-balance changes in the study area. The glacial history of the southern Bellingshausen Sea is unique when compared to other regions in West Antarctica, but some open questions regarding its chronology need to be addressed by future work. [Copyright &y& Elsevier]

Abstract: Recent studies show that oxygen three isotope measurement (16O, 17O, and 18O) of water provides additional information for investigating the hydrological cycle and paleoclimate. For determining the 18O/16O value of water, a conventional CO2–water equilibration method involves measurement of the ratios of CO2 isotopologues which were equilibrated with water. However, this long-established technique was not intended to measure the 17O/16O ratio, primarily because the historic ion correction scheme does not allow for possible deviations from a fixed (and mass-dependent) relationship between 17O/16O and 18O/16O isotope ratios. Here, we propose an improved method for obtaining the 17O/16O isotope ratio of fresh water by the equilibration method and measurement of the 45/44 CO2 ion abundance ratio. Equations which we formulated for 17O/16O measurement have two features: first, instead of absolute isotope ratio (R), all equations are formulated in δ values, measured by isotope ratio mass spectrometry. Second, we include two “assigned”δ values of water standards in the equations, because the δ 18O are commonly measured against two working standards to normalize the span of the δ scale. This approach clarifies that the contribution from 17O (12C16O17O+) to the molecular ion current at mass-to-charge ratio m/z 45 signal depends not on the absolute 13C/12C ratio, but on the relative δ 13C differences between the working standards and the sample. The pH value of water affects δ 17O estimation because δ 13C of CO2 was changed in the water–CO2 system. We reevaluated this effect using a set of equations, which explicitly includes CO2 partial pressure effect on pH value. Our new estimation of pH effect is significantly smaller than previously reported value, but it does not alter the main conclusions in the previous study. The method was verified by δ 17O measurements of an international standard reference water (GISP) provided by the IAEA. We applied the method to investigate 17O-excess of the ice core drilled at the Dome Fuji station, Antarctica. A total of 1320 samples from a 130m section around Marine Isotope Stage 9.3 (∼330,000 years before present) were measured. The error of a measurement for δ 17O is 0.175‰ and that of 17O-excess is 184per meg. Although these analytical uncertainties hampered accurate estimation of the changes in 17O-excess, the averaged data indicate that 17O-excess around MIS 9.3 was higher than during the subsequent glacial period. This approach can be applied only to fresh water samples, and additional improvements will be needed to measure samples which contains significant amount of carbonate minerals. [Copyright &y& Elsevier]

Abstract: We present new isobases constraining the Holocene isostatic uplift of the South Shetland Islands, northern Antarctic Peninsula, based on evidence from raised shorelines. Holocene shorelines were described and surveyed at fifteen sites to determine the spatial variability of relative sea level (RSL) change across the South Shetland Islands, and provide new spatial RSL change corrections for the region. Results show that the highest shoreline is a transgressive feature, correlated by geomorphological evidence on most exposed coastlines of the archipelago. Its surveyed height was corrected for local variability in wave energy by subtracting the measured altitude of the present day shoreline. These corrected surveyed heights of the highest raised beach were modelled using quadratic polynomial trend surface analysis to constrain differing rates of regional isostatic uplift. We present two isobase models of isostatic uplift since formation of the highest Holocene raised beach circa 7360–7000 years ago. These models suggests a maximum uplift of ca 20 m was centred on an area north of Greenwich Island, with isobases implying an elongate zone of uplift orientated east-southeast to west-northwest along the spine of the island chain. This corresponds well with previously published geomorphologically based estimates of palaeo ice-extent and the deglaciation history of the South Shetland Islands and gives new context to the palaeo ice-extent and glacial history of the region. [Copyright &y& Elsevier]

Abstract: Subglacial conditions of large polar ice sheets remain poorly understood, despite recent advances in satellite observation. Major uncertainties related to basal conditions, such as the temperature field, are due to an insufficient knowledge of geothermal heat flow. Here, a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique. Additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots, as well as the distribution of subglacial lakes. In this way, geothermal heat-flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available. Results of the sensitivity experiments show that 55% of the grounded part of the Antarctic ice sheet is at pressure melting point. Calculated basal melt rates are approximately 65Gtyear−1, which is 3% of the total surface accumulation. Although these sensitivity experiments exhibit small variations in basal melt rates, the impact on the ice age of basal layers is quite important. In areas that are characterized by relatively low melt rates, this may lead to standard deviations up to 50% (in a model run over a period of 106 years). Subglacial water flow is concentrated underneath the large outlet glaciers of Antarctica. The larger subglacial lakes are perched at the head of these subglacial water systems. An exception, however, is the lake system of the Recovery Ice Stream Catchment, that receives a substantial amount of subglacial melt water from the upstream catchment. [Copyright &y& Elsevier]

Rapid warming and consequent ice-shelf collapse have focused attention on the glacial record of the Antarctic Peninsula. Here, we present the fi rst record of terrestrial organic material exposed by recently retreating ice that bears on past glacier extent and climate in this sensitive region. Radiocarbon dates show that ice on Anvers Island was at or behind its present position at 700-970 cal. yr B.P., coincident with ice reduction elsewhere in the Southern Hemisphere. Moreover, the data indicate that present reduced ice extent on the western Antarctic Peninsula is not unprecedented and is similar to that experienced during at least three periods in the last 5600 yr. [ABSTRACT FROM AUTHOR]

Abstract: Antarctic and Greenland ice-core records reveal large fluctuations of dust input on both orbital and millennial time-scales with potential global climate implications. At least during glacial periods, the Antarctic dust fluctuations appear to be largely controlled by environmental changes in southern South America. We compare dust flux records from two Antarctic ice-cores to variations in the composition of the terrigenous supply at ODP Site 1233 located off southern Chile and known to record fluctuations in the extent of the northern part of the Patagonian ice-sheet (NPIS) during the last glacial period (Marine Isotope Stage, MIS, 4 to 2). Within age uncertainties, millennial-scale glacial advances (retreats) of the NPIS correlate to Antarctic dust maxima (minima). In turn, NPIS fluctuations were closely related to offshore sea surface temperature (SST) changes. This pattern suggests a causal link involving changes in temperature, in rock flour availability, in latitudinal extensions of the westerly winds and in foehn winds in the southern Pampas and Patagonia. We further suggest that the long-term trend of dust accumulation is partly linked to the sea-level related changes in the size if the Patagonian source area due to the particular morphology of the Argentine shelf. We suggest that sea-level drops at the beginning of MIS 4 and MIS 2 were important for long-term dust increases, while changes in the Patagonian dust source regions primarily control the early dust decrease during the MIS 4/3 transition and Termination 1. [Copyright &y& Elsevier]

The causes of the ∼8O ppmv increase of atmospheric carbon dioxide (CO2) during the last glacial-interglacial climatic transition remain debated. We analyzed the parallel evolution of CO2 and its stable carbon isotopic ratio (δ13CO2) in the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core to bring additional constraints. Agreeing well but largely improving the Taylor Dome ice core record of lower resolution, our δ13CO2 record is characterized by a W shape, with two negative ö13CO2 excursions of 0.5%엯 during Heinrich 1 and Younger Dryas events, bracketing a positive ö13CO peak during the B&3x00F8;lling/Aller&3x00F8;d warm period. The comparison with marine records and the outputs of two C cycle box models suggest that changes in Southern Ocean ventilation drove most of the CO2 increase, with additional contributions from marine productivity changes on the initial CO2 rise and ö13CO2 decline and from rapid vegetation buildup during the CO2 plateau of the B&3x00F8;lling/Aller&3x00F8;d. [ABSTRACT FROM AUTHOR]

The retreat history of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum is important for understanding the process of rapid deglaciation, constraining models that seek to predict the future trajectory of the ice sheet, and for estimating rates of sea-level change. Here we report new glacial geologic data from the southwestern Weddell Sea embayment that demonstrate that this part of the WAIS was thinner than previously suggested, and that there was progressive thinning of the ice sheet by 230-480 m since ca. 15 ka. We use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the Weddell Sea at the Last Glacial Maximum. The volume of this ice would have added between 1.4 and 2.0 m to postglacial sea-level rise and would not have been suffi cient to contribute signifi cantly to meltwater pulse 1A, a rapid rise in sea level ∼14,200 yr ago. [ABSTRACT FROM AUTHOR]

Abstract: The aim is to investigate the evolution of the subglacial landscape of Antarctica using an ice sheet and erosion model. We identify different stages of continental glaciation and model the erosion processes associated with each stage. The model links erosion to the basal thermal regime and indicates that much of the Antarctic interior may have been subject to less than 200m of erosion. The depth of erosion reflects the presence or absence of warm-based ice and the consistency of ice flow direction. This information, linked with knowledge about landscapes of glaciation in the northern hemisphere and some simple but robust assumptions about initial topography, is used to generate a map of the subglacial Antarctic landscape in which much of the lowland interior resembles the landscapes of areal scouring typical of the Laurentian and Scandinavian shields. Near the continental margins selective linear erosion has overdeepened pre-existing river valleys by as much as 2.8km. High elevation plateaus adjacent to such drainage systems have survived largely unmodified under cold-based ice. High erosion rates result from steep thermal gradients in basal ice. Mountain regions such as the Gamburtsev Mountains, uplands in Dronning Maud Land and massifs in West Antarctica are likely to bear features of local alpine glaciation. Such landscapes may have been protected under cold-based ice for the last 34Myrs or possibly longer. [Copyright &y& Elsevier]

Abstract: The preferential altitude of transport of continental tracers towards Antarctica under present and Last Glacial Maximum (21kyr BP) conditions is analysed using an atmospheric general circulation model with idealized tracers which are emitted at the surface of Australia and South America. It is shown that the difference between the preferential transport altitude of Australian and South American tracers is similar in glacial and interglacial climates. Australian tracers arriving in Antarctica are consistently transported at higher altitudes than tracers emitted in South America. The frequency of low-level transport is stronger at the LGM than at present, reflecting a more vigorous atmospheric circulation at the LGM as a consequence of increased baroclinicity. While the spatial patterns of the total tracer concentrations at the Antarctic surface differ for Australian and South American tracers, with the regions of maximum surface concentration being located to the south-east of the respective tracer sources, the spatial distribution of the part advected via upper atmospheric levels is very similar for the Australian and South American tracers, with a maximum over Queen Maud Land. The simulated changes in transport characteristics cannot explain observed glacial to interglacial variations of dust size spectra which have been interpreted as indicators of the relative intensity of upper and lower level atmospheric dust transport to Antarctica. [Copyright &y& Elsevier]

Abstract: Sulfate (SO4 2−) and ammonium (NH4 +) flux records over the last 150,000years from both Antarctic EPICA ice cores (European Project for Ice Coring in Antarctica) are presented. The ice core record from Dome C is influenced by the Indian sector of the Southern Ocean (SO), whereas Dronning Maud Land is facing the Atlantic sector. Generally, they reflect the past atmospheric aerosol load and, thus, potentially reveal the fingerprint of marine biogenic sources from the SO. The most important feature of both, the nssSO4 2− as well as NH4 + flux records, is the absence of any significant glacial cycles, in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150,000years. This finding challenges the iron fertilization hypothesis on long time scales, as the significant changes in dust, e.g. from the last glacial maximum toward the Holocene have neither an impact on nssSO4 2− nor on NH4 + fluxes found in interior Antarctica. The inter-site correlation of both species is weak, r 2 =0.42 for the nssSO4 2− flux and r 2 =0.12 for the NH4 + flux respectively, emphasizing the local source characteristics of biogenic aerosol from the SO. Millennial variability in NH4 + and nssSO4 2− is within the uncertainty of our flux estimates. Correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssSO4 2− flux for the Atlantic sector of the Southern Ocean, but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at EDML. [Copyright &y& Elsevier]

Abstract: Diatom assemblages in marine cores and sea salt deposition fluxes in ice cores have been used as sea ice proxies in the southern hemisphere. Here, a marine and an ice core proxy record for the Indian Ocean covering the last two glacial cycles are compared in order to illustrate their potential and limitations. The marine core was extracted in a location completely ice free under present-day conditions, and therefore was unable to record changes to the recent sea ice extent. Similarly, no sea ice was recorded at that location during the previous interglacial period. During the last glacial period, however, the site was seasonally covered by sea ice, and the diatom assemblages allowed an estimation of average seasonal sea ice presence. The ice core data originated from the East Antarctic plateau. The marine sodium present in the ice core was used as a proxy of the sea-ice coverage and, on average, a larger sea ice surface led to an increased sea-salt aerosol flux, seen e.g. at the last glacial inception. However, the response of the sea salt flux to increasing sea ice extent diminished during peak glacial conditions when only minimal variability was recorded in the ice core record. A first-order approximation is used to take this non-linear response of the ice core sea ice proxy into account. Based on the ice core proxy record, sea ice extent was reduced considerably during the warm episodes of the previous two interglacial periods compared to modern sea ice extent, in particular during the peak warmth of the Last Interglacial. The ice core proxy also showed a very strong precessional variability (pronounced spectral peak at 23ka period) over the past 240ka. The advantage of combining the two proxy records lies in the complementary nature of their response. While the ice core proxy showed limited sensitivity during full glacial conditions, the marine proxy recorded the seasonal sea-ice coverage. Once the sea ice retreated south of the location of the marine core, the ice core proxy responded to changes in sea ice extent. A composite of marine and ice core records may thus provide a data basis for a more detailed reconstruction of sea ice around Antarctica over the last few glacial–interglacial cycles. [Copyright &y& Elsevier]