Ross Sea Sector Research Articles

Gross Primary Production of Antarctic Landfast Sea Ice: A Model‐Based Estimate

AbstractMuch of the Antarctic coast is covered by seasonal landfast sea ice (fast ice), which serves as an important habitat for ice algae. Fast‐ice algae provide a key early season food source for pelagic and benthic food webs, and contribute to biogeochemical cycling in Antarctic coastal ecosystems. Summertime fast ice is undergoing a decline, leading to more seasonal fast ice with unknown impacts on interconnected Earth system processes. Our understanding of the spatiotemporal variability of Antarctic fast ice, and its impact on polar ecosystems is currently limited. Evaluating the overall productivity of fast‐ice algae has historically been hampered by limitations in observations and models. By linking new fast‐ice extent maps with a one‐dimensional sea‐ice biogeochemical model, we provide the first estimate of the spatio‐seasonal variability of Antarctic fast‐ice algal gross primary production (GPP) and its annual primary production on a circum‐Antarctic scale. Experiments conducted for the 2005–2006 season provide a mean fast ice‐algal production estimate of 2.8 Tg C/y. This estimate represents about 12% of overall Southern Ocean sea‐ice algae production (estimated in a previous study), with the mean fast‐ice algal production per area being 3.3 times higher than that of pack ice. Our Antarctic fast‐ice GPP estimates are probably underestimated in the Ross Sea and Weddell Sea sectors because the sub‐ice platelet layer habitats and their high biomass are not considered.

Remote Forcing for a Circulation Pattern Favorable to Surface Melt over the Ross Ice Shelf

Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasigeostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño–related sea surface temperature (SST) anomalies in the tropical central–eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to the Ross Sea. The northerly flow toward the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS. Significance Statement During austral summer, surface melt occurs over the Ross Ice Shelf, accelerates ice loss, and poses ice-sheet destabilization risks in a warming world. The northerly wind anomaly over the Ross sector provides strong poleward heat and moisture transport and is favorable for the surface melt. This wind anomaly is influenced by two remote forcings, El Niño and heating anomaly over western Australia, through generating Rossby wave trains from the tropics and subtropical Australia. This study reveals a previously unexplored relationship that atmospheric heating over western Australia influences large-scale circulation, contributing to surface melt.

History of the Antarctic Ice Sheet in the McMurdo Sound region at and since the Last Glacial Maximum: Evidence from Miers Valley

Reconstructions of past Antarctic Ice Sheet (AIS) behavior can afford key information about likely ice-sheet response to future climate change. Here, we examine the history of a marine-based ice mass grounded in McMurdo Sound of the western Ross Embayment during the Last Glacial Maximum and termination. Geomorphological mapping and interpretation of stratigraphic sections, as well as 67 radiocarbon dates of algal mats and 16 234U/230Th ages of carbonate and gypsum in glaciolacustrine sediments, indicate that ice from the broader Ross Embayment entered McMurdo Sound by approximately 24,000 yr BP and blocked the seaward mouth of Miers Valley. Maximum thickness of the McMurdo Sound ice was maintained from ∼19,000 yr BP, with fluctuations, until ∼12,600 yr BP. A lake-ice conveyor operated on a large ice-dammed lake that accompanied this advance until dessication at 10,000–7900 yr BP concurrent with ice recession. In contrast to the expansion of grounded marine-based ice in McMurdo Sound, alpine glaciers at the valley head did not advance at the Last Glacial Maximum. This out-of-phase behavior of the marine-based ice sheet vs. independent terrestrial glaciers is consistent with previous studies suggesting that local glaciers respond primarily to accumulation, which rises during warm periods. The long and late maximum of the McMurdo Sound ice (corresponding largely to Termination I) and delayed recession until after the Antarctic Cold Reversal (∼14,700–12,900 yr BP) lends support to the hypothesis that the AIS in the Ross Sea sector is controlled by the competing effects of marine (sea level, ocean temperatures) and accumulation forcing.

Seawater oxygen isotopes as a tool for monitoring future meltwater from the Antarctic ice-sheet

To reduce uncertainties in future sea level projections, it is necessary to closely monitor the evolution of the Antarctic ice-sheet. Here, we show that seawater oxygen isotopes are an effective tool to monitor ice-sheet freshwater discharge and its contributions to sea level rise. Using the isotope-enabled Community Earth System Model with imposed estimates of future meltwater fluxes, we find that the anthropogenic ice-sheet signal in water isotopes emerges above natural variability decades earlier than salinity-based estimates. The superiority of seawater isotopes over salinity in detecting the ice-sheet melting can be attributed to the higher signal-to-noise ratio of the former and the fact that future sea ice changes only contribute little to seawater isotopes but a lot to salinity. We conclude that in particular in the Ross Sea sector, continuous seawater oxygen isotope measurements could serve as an early warning system for rapid anthropogenic Antarctic ice-sheet mass loss.

Distinct Central and Eastern Pacific El Niño Influence on Antarctic Surface Mass Balance

AbstractThe El Niño‐Southern Oscillation causes anomalous atmospheric circulation, temperature and precipitation across southern polar latitudes, but the influence of Central and Eastern Pacific El Niño events on Antarctic surface mass balance and snow accumulation has not yet been assessed. Here, we use reanalysis and reanalysis‐forced regional climate model output and find that Central Pacific El Niño results in significantly increased snow accumulation in the western Ross Sea sector and significantly decreased snow accumulation in the Amundsen Sea sector. Eastern Pacific El Niño is associated with similar but weaker patterns, with some regional exceptions. In some areas, like Dronning Maud Land, or the Wilkes Subglacial Basin, the effect of El Niño on snow accumulation changes from increased to reduced accumulation depending on the type of El Niño. Our results show that projecting El Niño types is important for constraining future changes in Antarctic surface mass balance.

Planktonic, benthic and sympagic copepods collected from the desalination unit of Mario Zucchelli Research Station in Terra Nova Bay (Ross Sea, Antarctica).

Distributional data on planktonic, benthic and sympagic copepods collected in the framework of the XXXIVth Expeditions of the Italian National Antarctic Programme (PNRA) to the Ross Sea sector from 2018-2019 are here provided. These occurrences correspond to specimens collected from the 25 μm filters used in the desalination plant of the Italian research station "Mario Zucchelli" (MZS), located in the Terra Nova Bay area (TNB; Ross Sea, Antarctica). This dataset is a contribution to the Antarctic Biodiversity Portal, the thematic Antarctic node for both the Ocean Biogeographic Information System (AntOBIS) and the Global Biodiversity Information Facility Antarctic Biodiversity Information Facility (ANTABIF). The dataset was uploaded and integrated with the SCAR-AntOBIS database (the geospatial component of SCAR-MarBIN). Please follow the guidelines from the SCAR Data Policy (ISSN 1998-0337) when using the data. If you have any questions regarding this dataset, please contact us via the contact information provided in the metadata or via data-biodiversity-aq@naturalsciences.be. Issues with the dataset can be reported at the biodiversity-aq GitHub project. We describe the diversity of marine copepods Terra Nova Bay sampled by the filters installed in the desalination unit (DU) of the Italian research station "Mario Zucchelli" described in recent work. The opening of the intake pipe of the DU is positioned at a depth of 4 m and allowed a total of 2,116 specimens to be sampled and recognised. In addition, new occurrence records of copepod genera and species are reported in the same zone. We provide an overview of the marine copepod diversity reported for TNB. The total of 2,116 individuals corresponds to 14 genera and 15 species and is represented by 136 occurrence records in this dataset. Around 52% of the total number of species are new records for the TNB area. The publication of this data paper was funded by the Belgian Science Policy Office (BELSPO, contract n°FR/36/AN1/AntaBIS) in the Framework of EU-Lifewatch as a contribution to the SCAR Antarctic biodiversity portal (biodiversity.aq).

The staggered retreat of grounded ice in the Ross Sea, Antarctica, since the Last Glacial Maximum (LGM)

Abstract. The retreat of the West Antarctic Ice Sheet (WAIS) in the Ross Sea after the Last Glacial Maximum (LGM) was more significant than for any other Antarctic sector. Here we combined the available chronology of retreat with new mapping of seismically resolvable grounding zone wedges (GZWs). Mapping GZWs is important because they record the locations of former stillstands in the extent of grounded ice for individual ice streams during the overall retreat. Our analysis shows that the longest stillstands occurred early in the deglacial period and had millennial durations. Stillstands ended abruptly with retreat distances measured in the tens to hundreds of kilometers creating deep embayments in the extent of grounded ice across the Ross Sea. The location of embayments shifted through time. The available chronological data show that cessation of WAIS and East Antarctic Ice Sheet (EAIS) stillstands was highly asynchronous across at least 5000 years. There was a general shift to shorter stillstands throughout the deglacial period. The asynchronous collapse of individual catchments during the deglacial period suggests that the Ross Sea sector would have contributed to multiple episodes of relatively small-amplitude sea-level rise as the WAIS and EAIS retreated from the region. The high sinuosity of the modern grounding zone in the Ross Sea suggests that this style of retreat persists.

The Influence of Time-Varying Sea Ice Concentration on Antarctic and Southern Ocean Numerical Weather Prediction

Abstract Although operational weather forecasting centers are increasingly using global coupled atmosphere–ocean–ice models to replace atmosphere-only models for short- and medium-range (10 day) weather forecasting, the influence of sea ice on such forecasting has yet to be fully quantified, especially in the Southern Ocean. To address this gap, a polar-specific version of the Weather Research and Forecasting Model is implemented with a circumpolar Antarctic domain to investigate the impact of daily updates of sea ice concentration on short- and medium- range weather forecasting. A statistically significant improvement in near-surface atmospheric temperature and humidity is shown from +24 to +192 h when updating the daily sea ice concentration in the model. The forecast skill improvements for 2-m temperature and dewpoint temperature are enhanced from June to September, which is the period of late sea ice advance. Regionally, model improvement is shown to occur in most sea ice regions, although the improvement is strongest in the Ross Sea and Weddell Sea sectors. The surface heat budget also shows remarkable improvement in outgoing radiative heat fluxes and both sensible and latent heat fluxes. This idealized research demonstrates the nonnegligible effect of including more accurate time-varying sea ice concentration in numerical weather forecasting. Significance Statement The purpose of this study is to understand how a more realistic Antarctic sea ice field may influence the skill of short- and medium-range weather forecasts. Many operational atmospheric numerical weather prediction (NWP) models use a static forecast field through the time frame of the model’s forecast—often 3–10 days. In this study, we updated the sea ice concentration field daily and compared the forecast outcomes with those from model runs using a static sea ice concentration field. We found the forecast skill of near-surface temperature and humidity show the most significant improvements in our idealized experiments. This indicates the importance of incorporating improved dynamic sea ice representation in Antarctic short- to medium-range operational weather forecasting.

Sea ice concentration decline in an important Adélie penguin molt area.

Unlike in many polar regions, the spatial extent and duration of the sea ice season have increased in the Ross Sea sector of the Southern Ocean during the satellite era. Simultaneously, populations of Adélie penguins, a sea ice obligate, have been stable or increasing in the region. Relationships between Adélie penguin population growth and sea ice concentration (SIC) are complex, with sea ice driving different, sometimes contrasting, demographic patterns. Adélie penguins undergo a complete molt annually, replacing all their feathers while fasting shortly after the breeding season. Unlike most penguin species, a majority of Adélies are thought to molt on sea ice, away from the breeding colonies, which makes this period particularly difficult to study. Here, we evaluate the hypothesis that persistent areas of high SIC provide an important molting habitat for Adélie penguins. We analyzed data from geolocating dive recorders deployed year-round on 195 adult penguins at two colonies in the Ross Sea from 2017 to 2019. We identified molt by detecting extended gaps in postbreeding diving activity and used associated locations to define two key molting areas. Remotely sensed data indicated that SIC during molt was anomalously low during the study and has declined in the primary molt area since 1980. Further, annual return rates of penguins to breeding colonies were positively correlated with SIC in the molt areas over 20 y. Together these results suggest that sea ice conditions during Adélie penguin molt may represent a previously underappreciated annual bottleneck for adult survival.

Delineating Polynya Area Using Active and Passive Microwave Sensors for the Western Ross Sea Sector of Antarctica

A polynya is an area of open water or reduced concentration of sea ice surrounded by either concentrated sea ice or land ice. They are often seen as sites of intense ocean–atmosphere heat exchange and as ice production factories. Given their importance, it is crucial to quantify the accuracy of satellite-derived polynya information. Polynyas in their early evolution phase are generally narrow and occur at scales likely too fine to be detected by widely used passive microwave (PMW) radiometric sensors. We derived 40 m scale polynya information over the western Ross Sea from high-resolution Synthetic Aperture Radar (SAR) Sentinel-1 C-band data and examined discrepancies with larger-scale estimates. We utilized two automated algorithms, supervised (a rule-based approach) and unsupervised (a combination of texture analysis with k-means clustering), to accurately identify the polynya areas. We generated data for validation using Sentinel-1 data at instances where polynyas can be visually delineated. Results from PMW sensors (NSIDC and AMSR2) and SAR-based algorithms (rule-based and texture-based) are compared with manually delineated polynya areas obtained through Sentinel-1. Analysis using PMW sensors revealed that NSIDC overestimates larger polynyas and underestimates smaller polynyas compared to AMSR2. We were more accurately able to identify polynya presence and area using Sentinel-1 SAR observations, especially in clear cases and cases when PMW data miscalculates the polynya’s presence. Of our SAR-based algorithms, the rule-based approach was more accurate than the texture-based approach at identifying clear polynyas when validated against manually delineated regions. Altogether, we emphasize the need for finer spatio-temporal resolution data for polynya studies.

Change at 85 degrees south: Shackleton Glacier region proglacial lakes from 1960 to 2020

Abstract Over the last two decades, anomalous warming events have been observed in coastal Antarctic regions. While these events have been documented in the Ross Sea sector, the Antarctic interior is believed to have been buffered from warming. In this work, we present data from lakes located near Mt. Heekin and Thanksgiving Valley (~85° S) along the Shackleton Glacier, which are believed to be the southern-most Antarctic dry valley lakes. In 2018, the lakes were characterized, repeat satellite images were examined, and lake water chemistry was measured. Our analysis shows that lake areas recently increased, and the water-soluble ion chemistry indicates a flushing of salts from periglacial soils, likely from increased glacial melt as illustrated by water isotope data. Our results show that high southern latitude ice-free areas have likely been affected by warm pulses over the past 60 years and these pulses may be quasi-synchronous throughout the Transantarctic Mountains.

High mid-Holocene accumulation rates over West Antarctica inferred from a pervasive ice-penetrating radar reflector

Abstract. Understanding the past and future evolution of the Antarctic Ice Sheet is challenged by the availability and quality of observed paleo-boundary conditions. Numerical ice-sheet models often rely on these paleo-boundary conditions to guide and evaluate their models' predictions of sea-level rise, with varying levels of confidence due to the sparsity of existing data across the ice sheet. A key data source for large-scale reconstruction of past ice-sheet processes are internal reflecting horizons (IRHs) detected by radio-echo sounding (RES). When IRHs are isochronal and dated at ice cores, they can be used to determine paleo-accumulation rates and patterns on large spatial scales. Using a spatially extensive IRH over the Pine Island Glacier (PIG), Thwaites Glacier (THW), and the Institute and Möller ice streams (IMIS, covering a total of 610 000 km2 or 30 % of the West Antarctic Ice Sheet (WAIS)), and a local layer approximation model, we infer mid-Holocene accumulation rates over the slow-flowing parts of these catchments for the past ∼4700 years. By comparing our results with modern climate reanalysis models (1979–2019) and observational syntheses (1651–2010), we estimate that accumulation rates over the Amundsen–Weddell–Ross Divide were on average 18 % higher during the mid-Holocene than modern rates. However, no significant spatial changes in the accumulation pattern were observed. The higher mid-Holocene accumulation-rate estimates match previous paleo-accumulation estimates from ice-core records and targeted RES surveys over the ice divide, and they also coincide with periods of grounding-line readvance during the Holocene over the Weddell and Ross sea sectors. We find that our spatially extensive, mid-Holocene-to-present accumulation estimates are consistent with a sustained late-Holocene period of higher accumulation rates occurring over millennia reconstructed from the WAIS Divide ice core (WD14), thus indicating that this ice core is spatially representative of the wider West Antarctic region. We conclude that future regional and continental ice-sheet modelling studies should base their climatic forcings on time-varying accumulation rates from the WAIS Divide ice core through the Holocene to generate more realistic predictions of the West Antarctic Ice Sheet's past contribution to sea-level rise.

Variability of sea salt and methanesulfonate in firn cores from northern Victoria Land, Antarctica: Their links to oceanic and atmospheric condition variability in the Ross Sea

The potential ice core proxies of variability in oceanic and atmospheric conditions over the Ross Sea were evaluated. This study examined sea salt sodium (ss–Na+) and biogenic sulfur (methanesulfonate, MS–) records, covering 23 years between 1990 and 2012, from two firn cores drilled on the Styx Glacier plateau (SGP), northern Victoria Land, East Antarctica, to examine the potential links between those records and datasets for various climate variables. The comparison showed that the interannual variability of the ss–Na+ record is closely related to Pacific–South American mode 2 (PSA2) in the Ross Sea sector, exhibiting an increased ss–Na+ flux, owing most likely to more frequent penetration of maritime air masses from the western Ross Sea to the SGP when the winter/spring PSA2 mode becomes more pronounced. The observed MS– record revealed statistically significant positive correlations with the changes in the summertime chlorophyll a concentration in the Ross Sea polynya (RSP) and wind speed in the southern Ross Sea region. This indicates the dominant role of a combination of changes in the summertime primary productivity and wind speed over the RSP in modulating the MS– deposition flux at the SGP. These results highlight the suitability of the ss–Na+ and MS– records from the SGP as proxies for characterizing the dominant patterns of variability in oceanic and atmospheric conditions and their underlying mechanisms on interannual and longer timescales beyond the instrumental limits over the Ross Sea region.

Reconciling persistent sub-zero temperatures in the McMurdo Dry Valleys, Antarctica, with Neogene dynamic marine ice-sheet fluctuations

Abstract In the Ross Sea sector of Antarctica, periodic large-scale marine ice-sheet fluctuations since the mid-Miocene are recorded by drill core and seismic data, revealing a dynamic ice-sheet response to past increases in temperature and atmospheric CO2. In the adjacent, predominantly ice-free McMurdo Dry Valleys (MDVs), preserved terrestrial landscapes reflect persistent cold conditions and have been interpreted as indicators of a stable polar ice sheet, implying that the Antarctic Ice Sheet was largely insensitive during past warm periods. These disparate data-based perspectives highlight a long-standing debate around the past stability of the Antarctic Ice Sheet, with direct implications for the future ice-sheet response to ongoing climate warming. We reconcile marine records of dynamic ice-sheet behavior and episodic open-marine conditions with nearby ancient terrestrial landscapes recording consistent cold-polar conditions. Coupled ice-sheet and regional climate models nested at a high resolution are used to investigate surface temperatures in the MDVs during past warm periods. We find that high-elevation regions of the MDVs remain below freezing even when ice-free conditions prevail in the nearby Ross Sea. We compare observed landscapes with the spatial extent of modeled persistent cold conditions required for preservation of these ancient features, demonstrating that frozen MDVs landscapes could have coexisted with receded or collapsed ice sheets during past warm periods.

Deep ice as a geochemical reactor: insights from iron speciation and mineralogy of dust in the Talos Dome ice core (East Antarctica)

Abstract. Thanks to its insolubility, mineral dust is considered a stable proxy in polar ice cores. With this study we show that the Talos Dome ice core (TALDICE, Ross Sea sector of East Antarctica) displays evident and progressive signs of post-depositional processes affecting the mineral dust record below 1000 m deep. We apply a suite of established and cutting-edge techniques to investigate the properties of dust in TALDICE, ranging from concentration and grain size to elemental composition and Fe mineralogy. Results show that through acidic/oxidative weathering, the conditions of deep ice at Talos Dome promote the dissolution of specific minerals and the englacial formation of others, affecting primitive dust features. The expulsion of acidic atmospheric species from ice grains and their concentration in localized environments is likely the main process responsible for englacial reactions. Deep ice can be seen as a “geochemical reactor” capable of fostering complex reactions which involve both soluble and insoluble impurities. Fe-bearing minerals can efficiently help in exploring such transformations.

Did Holocene climate changes drive West Antarctic grounding line retreat and readvance?

Abstract. Knowledge of past ice sheet configurations is useful for informing projections of future ice sheet dynamics and for calibrating ice sheet models. The topology of grounding line retreat in the Ross Sea sector of Antarctica has been much debated, but it has generally been assumed that the modern ice sheet is as small as it has been for more than 100 000 years (Conway et al., 1999; Lee et al., 2017; Lowry et al., 2019; McKay et al., 2016; Scherer et al., 1998). Recent findings suggest that the West Antarctic Ice Sheet (WAIS) grounding line retreated beyond its current location earlier in the Holocene and subsequently readvanced to reach its modern position (Bradley et al., 2015; Kingslake et al., 2018). Here, we further constrain the post-LGM (Last Glacial Maximum) grounding line retreat and readvance in the Ross Sea sector using a two-phase model of radiocarbon input and decay in subglacial sediments from six sub-ice sampling locations. In addition, we reinterpret high basal temperature gradients, measured previously at three sites in this region (Engelhardt, 2004), which we explain as resulting from recent ice shelf re-grounding accompanying grounding line readvance. At one location – Whillans Subglacial Lake (SLW) – for which a sediment porewater chemistry profile is known, we estimate the grounding line readvance by simulating ionic diffusion. Collectively, our analyses indicate that the grounding line retreated over SLW 4300-2500+1500 years ago, and over sites on Whillans Ice Stream (WIS), Kamb Ice Stream (KIS), and Bindschadler Ice Stream (BIS) 4700-2300+1500, 1800-700+2700, and 1700-600+2800 years ago, respectively. The grounding line only recently readvanced back over those sites 1100-100+200, 1500-200+500, 1000-300+200, and 800±100 years ago for SLW, WIS, KIS, and BIS, respectively. The timing of grounding line retreat coincided with a warm period in the mid-Holocene to late Holocene. Conversely, grounding line readvance is coincident with cooling climate in the last 1000–2000 years. Our estimates for the timing of grounding line retreat and readvance are also consistent with relatively low carbon-to-nitrogen ratios measured in our subglacial sediment samples (suggesting a marine source of organic matter) and with the lack of grounding zone wedges in front of modern grounding lines. Based on these results, we propose that the Siple Coast grounding line motions in the mid-Holocene to late Holocene were primarily driven by relatively modest changes in regional climate, rather than by ice sheet dynamics and glacioisostatic rebound, as hypothesized previously (Kingslake et al., 2018).

Quantifying the causes and consequences of variation in satellite‐derived population indices: a case study of emperor penguins

AbstractVery high‐resolution satellite (VHR) imagery is a promising tool for estimating the abundance of wildlife populations, especially in remote regions where traditional surveys are limited by logistical challenges. Emperor penguins Aptenodytes forsteri were the first species to have a circumpolar population estimate derived via VHR imagery. Here we address an untested assumption from Fretwell et al. (2012) that a single image of an emperor penguin colony is a reasonable representation of the colony for the year the image was taken. We evaluated satellite‐related and environmental variables that might influence the calculated area of penguin pixels to reduce uncertainties in satellite‐based estimates of emperor penguin populations in the future. We focused our analysis on multiple VHR images from three representative colonies: Atka Bay, Stancomb‐Wills (Weddell Sea sector) and Coulman Island (Ross Sea sector) between September and December during 2011. We replicated methods in Fretwell et al. (2012), which included using supervised classification tools in ArcGIS 10.7 software to calculate area occupied by penguins (hereafter referred to as ‘population indices’) in each image. We found that population indices varied from 2 to nearly 6‐fold, suggesting that penguin pixel areas calculated from a single image may not provide a complete understanding of colony size for that year. Thus, we further highlight the important roles of: (i) sun azimuth and elevation through image resolution and (ii) penguin patchiness (aggregated vs. distributed) on the calculated areas. We found an effect of wind and temperature on penguin patchiness. Despite intra‐seasonal variability in population indices, simulations indicate that reliable, robust population trends are possible by including satellite‐related and environmental covariates and aggregating indices across time and space. Our work provides additional parameters that should be included in future models of population size for emperor penguins.

An extension of the TALDICE ice core age scale reaching back to MIS 10.1

TALDICE (TALos Dome Ice CorE) is a 1620 m deep ice core drilled at Talos Dome, an ice dome located at the edge of the East Antarctic Plateau in the Ross Sea Sector. The Antarctic Ice Core Common Chronology (AICC2012) extended the age scale of the core until ∼150 ka (1438 m depth) (Bazin et al., 2013), while no age scale was available below 1438 m depth.In this work we present the new TALDICE-deep1 chronology using the new measurements of δ18Oatm, δD and 81Kr as well as the inverse model IceChrono1.The TALDICE-deep1 chronology stops at 1548 m, as the portion below this depth is probably affected by mixing processes. The new age scale extends the climate record for the Ross Sea Sector of the East Antarctic Ice Sheet back to MIS 10.1–343 ka (1548 m depth) and identifies both MIS 7 and 9 warm stages, which show specificities in the δD signal. However, it is not possible to recover the isotopic record beyond stage 10.1 as the signal shows a quasi-flat shape. Thereby, the new chronology TADICE-deep1 doubles the extension of the previous age scale as it covers the three past glacial/interglacial cycles.

Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation

The West Antarctic climate has witnessed large changes during the second half of the twentieth century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determination of whether they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and $$\delta ^{{18}}\hbox{O}$$ ) and tree-ring width records situated in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data assimilation method. This ultimately provides a complete spatial reconstruction over the West Antarctic region. Our reconstruction reproduces well the main characteristics of the observed changes over the instrumental period. We show that the observed sea-ice reduction in the Bellingshausen-Amundsen Sea sector over the satellite era is part of a long-term trend, starting at around 1850 CE, while the sea-ice expansion in the Ross Sea sector has only started around 1950 CE. Furthermore, according to our reconstruction, the Amundsen Sea Low pressure (ASL) displays no significant linear trend in its strength or position over 1850–1950 CE but becomes stronger and shifts eastward afterwards. The year-to-year sea-ice variations in the Ross Sea sector are strongly related to the ASL variability over the past two centuries, including the recent trends. By contrast, the link between ASL and sea-ice in the Bellingshausen-Amundsen Sea sector changes with time, being stronger in recent decades than before. Our reconstruction also suggests that the continental response to the variability of the ASL may not be stationary over time, being significantly affected by modification of the mean atmospheric circulation. Finally, we show that the widespread warming since 1958 CE in West Antarctica is unusual in the context of past 200 years and is explained by both the deeper ASL and the positive phase of the Southern Annular Mode.

Physical properties of shallow ice cores from Antarctic and sub-Antarctic islands

Abstract. The sub-Antarctic is one of the most data-sparse regions on earth. A number of glaciated Antarctic and sub-Antarctic islands have the potential to provide unique ice core records of past climate, atmospheric circulation, and sea ice. However, very little is known about the glaciology of these remote islands or their vulnerability to warming atmospheric temperature. Here we present melt histories and density profiles from shallow ice (firn) cores (14 to 24 m) drilled on three sub-Antarctic islands and two Antarctic coastal domes. Additionally, complementary ground-penetrating radar (GPR) data were collected to further characterize each site and assess the spatial distribution of the observed melt layers. This study includes the first ever firn cores from Bouvet Island (54∘25′19′′ S, 03∘23′27′′ E) in the South Atlantic, from Peter I Island (68∘51′05′′ S, 90∘30′35′′ W) in the Bellingshausen Sea, and from Young Island (66∘31′44′′ S, 162∘33′21′′ E) in the Ross Sea sector's Balleny island chain. Despite their sub-Antarctic location, surface melt is low at most sites (melt layers account for ∼ 10 % of total core), with undisturbed ice layers in the upper ∼ 40 m, suggesting minimal impact of meltwater percolation. The exception is Young Island, where melt layers account for 47 % of the firn core. Surface snow densities range from 0.47 to 0.52 kg m−3, with close-off depths ranging from 21 to 51 m. Based on the measured density, we estimate that the bottom ages of a 100 m ice core drilled on Peter 1 Island would reach ∼ 1856 CE and ∼ 1874 CE at Young Island.