Weddell Sea Region Research Articles

Correlation of Ice-Rafted Detritus in South Atlantic Sediments with Climate Proxies in Polar Ice over the Last Glacial Period

Previous study identified 6–7 millennial-scale episodes of South Atlantic ice-rafted sediment deposition (SA events) during the glaciation. Questions remain, however, regarding their origin, significance for sea-ice and/or Antarctic ice-sheet dynamics, and relationship to climate. Here I correlate sediment core (TTN057–21) SA events to Greenland and Antarctic ice using two independent methods, stable isotopes and geomagnetic paleointensity, placing SA events in the context of polar climate change in both hemispheres. Marine isotopic stage (MIS) 3 SA events generally coincided with Greenland interstadials and with cooling following Antarctic warm events (A1-A4). This anti-phase behavior is best illustrated when SA0 coincided with both the Antarctic Cold Reversal and Bolling-Allerod warming in Greenland. Moreover, SA events coincide with sea-level rises during the deglaciation (mwp1A) and MIS 3 (30.4, 38.3, 43.7, 51.5 ka), implying unpinning of grounded Weddell Sea region ice masses discharged debris-laden bergs that had a chilling effect on South Atlantic surface temperatures.

Vulnerable ice in the Weddell Sea

Of the West Antarctic ice shelves, those in the Amundsen Sea sector have given the most cause for concern. Ocean modelling of the Weddell Sea region, together with a detailed survey of the ice bed morphology, indicates that this region, too, may change soon.

Late Quaternary glacial–interglacial variations in sediment supply in the southern Drake Passage

Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95m gravity core used in this study records paleoenvironmental changes during the last approximately 600ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases.

Carbonate saturation dynamics during the Paleocene–Eocene thermal maximum: Bathyal constraints from ODP sites 689 and 690 in the Weddell Sea (South Atlantic)

Spatiotemporal patterns of carbonate dissolution provide a critical constraint on carbon input during an ancient (~55.5Ma) global warming event known as the Paleocene–Eocene thermal maximum (PETM), yet the magnitude of lysocline shoaling in the Southern Ocean is poorly constrained due to limited spatial coverage in the circum-Antarctic region. This shortcoming is partially addressed by comparing patterns of carbonate sedimentation at the Site 690 PETM reference section to those herein reconstructed for nearby Site 689. Biochemostratigraphic correlation of the two records reveals that the first ~36ka of the carbon isotope excursion (CIE) signaling PETM conditions is captured by the Site 689 section, while the remainder of the CIE interval and nearly all of the CIE recovery are missing due to a coring gap. A relatively expanded stratigraphy and higher carbonate content at mid-bathyal Site 689 indicate that dissolution was less severe than at Site 690. Thus, the bathymetric transect delimited by these two PETM records indicates that the lysocline shoaled above Site 689 (~1,100m) while the calcite compensation depth remained below Site 690 (~1,900m) in the Weddell Sea region. The ensuing recovery of carbonate sedimentation conforms to a bathymetric trend best explained by gradual lysocline deepening as negative feedback mechanisms neutralized ocean acidification. Further, biochemostratigraphic evidence indicates the tail end of the CIE recovery interval at both sites has been truncated by a hiatus most likely related to vigorous production and advection of intermediate waters.

Distinguishing East and West Antarctic sediment sources using the Pb isotope composition of detrital K-feldspar

New Pb analyses of K feldspars (Kfs) from Archaean–Mesozoic crystalline rocks from across the Weddell Sea region of Antarctica show Pb isotopic compositions that vary geographically. Five distinct basement provinces are defined, each with characteristic Kfs Pb compositions, and indicate that the comparison of the Pb isotopic composition of individual detrital Kfs can be used as a sedimentary provenance tool in this region. This tool is tested on Permian sandstones deposited in a retro-arc foreland basin because the potential source regions for these sandstones, the active Palaeopacific margin arc of West Antarctica and uplifted regions of now ice-covered East Antarctica, comprise rocks with markedly different Pb isotope compositions. Pb compositions of detrital Kfs from sandstone samples collected from Dronning Maud Land suggest that their provenance was entirely from within East Antarctica, while those collected from the Theron Mountains, Coats Land, were wholly derived from the active margin of West Antarctica. Kfs Pb composition of bedrock samples is largely dependent on age and because Kfs tends to only survive a single cycle of erosion, transport, deposition and diagenesis, its provenance when compared with that determined by detrital zircon geochronology, may qualify what proportion of the more robust mineral zircon has been recycled through several sedimentary cycles. Detrital zircon analyses from a Permian sandstone from the Theron Mountains suggest that 45% of its detrital zircon was recycled from pre-existing (meta)sedimentary rocks. The detrital feldspar data also indicate that Archaean and 2.1 Ga crust, with a very different Pb isotope composition to any exposed in the Weddell Sea region, is likely to exist beneath the East Antarctic Ice sheet.

Low-ozone events in the southern polar summer as indicated by Met Office ozone analyses

[1] Southern summer low-ozone events (LOEs) are examined using Met Office ozone analyses for 2005–2007. At 31 hPa, tongues of low-ozone air are pulled out of the polar region and extend to lower latitudes. Low tongues are also seen at 100 hPa, but there the low ozone is transported from low to high latitudes. These low tongues are frequently superimposed on one another, meaning that there are often also reductions in total ozone. What is striking is that at high latitudes, summer total ozone is typically lower over the Weddell Sea than at other longitudes. The low-ozone tongues at 31 and 100 hPa are consistent with transport associated with planetary waves. Daily geopotential height fields show a poleward and westward wave tilt with height, indicating the presence of baroclinic waves. The tilt enables the superimposition of the low-ozone tongues at 100 and 31 hPa. Filtered geopotential height anomalies reveal the presence of waves reported in other studies and indicate the connection between tropospheric and stratospheric wave dynamics in driving the LOEs. There is also a high connection between the LOEs and ultraviolet (UV) Index. The Weddell Sea region gets up to 20–30% more UV than the zonal mean, and the tip of South America gets about 10–25% more. There have been numerous studies of the impacts of increased UV on the Antarctic marine ecosystem during the springtime ozone hole, and our results indicate there is a case for these studies being extended to the summer LOEs.

Effects of Hydrographic Variability on the Spatial, Seasonal and Diel Diving Patterns of Southern Elephant Seals in the Eastern Weddell Sea

Weddell Sea hydrography and circulation is driven by influx of Circumpolar Deep Water (CDW) from the Antarctic Circumpolar Current (ACC) at its eastern margin. Entrainment and upwelling of this high-nutrient, oxygen-depleted water mass within the Weddell Gyre also supports the mesopelagic ecosystem within the gyre and the rich benthic community along the Antarctic shelf. We used Conductivity-Temperature-Depth Satellite Relay Data Loggers (CTD-SRDLs) to examine the importance of hydrographic variability, ice cover and season on the movements and diving behavior of southern elephant seals in the eastern Weddell Sea region during their overwinter feeding trips from Bouvetøya. We developed a model describing diving depth as a function of local time of day to account for diel variation in diving behavior. Seals feeding in pelagic ice-free waters during the summer months displayed clear diel variation, with daytime dives reaching 500-1500 m and night-time targeting of the subsurface temperature and salinity maxima characteristic of CDW around 150–300 meters. This pattern was especially clear in the Weddell Cold and Warm Regimes within the gyre, occurred in the ACC, but was absent at the Dronning Maud Land shelf region where seals fed benthically. Diel variation was almost absent in pelagic feeding areas covered by winter sea ice, where seals targeted deep layers around 500–700 meters. Thus, elephant seals appear to switch between feeding strategies when moving between oceanic regimes or in response to seasonal environmental conditions. While they are on the shelf, they exploit the locally-rich benthic ecosystem, while diel patterns in pelagic waters in summer are probably a response to strong vertical migration patterns within the copepod-based pelagic food web. Behavioral flexibility that permits such switching between different feeding strategies may have important consequences regarding the potential for southern elephant seals to adapt to variability or systematic changes in their environment resulting from climate change.

Post-breeding dispersal of Adélie penguins (Pygoscelis adeliae) nesting at Signy Island, South Orkney Islands

ARGOS satellite telemetry and Global Location Sensors (geolocators) were used to identify the moult locations and the winter foraging dispersal of Adelie penguins after they left their breeding colonies on Signy Island in the South Orkney Islands. Animals were tracked during the period December 2004 to October 2005. All birds displayed a similar pattern of migratory behaviour, remaining away from colonies for approximately 9 months, at distances of up to 2,235 km. Moult locations were within the pack ice. Mean daily travel speeds to the moult locations were significantly faster when moving through open water than through pack ice. Moult occurred during February/March within a narrow latitudinal range (65–71°S), at a mean distance of 126 km from the ice edge; the mean duration of individual moult was c. 18.6 days. After moult, penguins spent the subsequent winter months moving north or north-eastward within the expanding winter pack ice, at a mean distance of 216 km from the ice edge, and in areas with ice cover >80%. The penguins returned to the vicinity of their colony between September 26 and October 22, 2005. This dependence of Adelie penguins on sea ice habitat suggests that any further reductions in sea ice extent in the Weddell Sea region would potentially have important impacts on the population processes of this pagophilic species.

Early Pliocene Weddell Sea seasonality determined from bryozoans

Early Pliocene cheilostome bryozoans are preserved in a glacigenic diamictite at Cascade Cliffs, James Ross Island, northern Antarctic Peninsula. Several different marine bryozoan genera were incorporated into the diamictite during Pliocene ice advance(s). Bryozoan zooid-size Mean Annual Range of Temperature (zs-MART) analysis provides estimates of seasonality which suggest that mean annual marine temperatures for the James Ross Island region varied by at least 4.3°C and possibly by as much as 10.3°C during the Early Pliocene. This represents much greater seasonality for the northern Weddell Sea than seen at the present day (MART ca. 2°C). A cluster of zs-MART values between 6.6°C and 7.7°C from four colonies of the bryozoan Dakariella are considered to represent themost reliable range of seasonality estimates. Although we cannot determine absolute sea temperatures, increased seasonality signals an overall warmer climate for the Weddell Sea region at the time that the bryozoans were living.

Three‐dimensional ionospheric electron density structure of the Weddell Sea Anomaly

This paper provides the first three‐dimensional description of the ionospheric density structure of the Weddell Sea Anomaly (WSA). The WSA is characterized by a nighttime ionospheric density greater than that in daytime in the Weddell Sea region around the Antarctic Peninsula during the southern hemisphere summer. It was first observed by ground‐based ionosondes located in the Antarctica back in the 1950s and was further investigated by two‐dimensional maps over the oceans using TEC measurements collected by the TOPEX/Poseidon recently. Although these TEC maps have provided two‐dimensional views for tracking the time‐evolution and spatial coverage of the WSA, the vertical distribution of this peculiar feature is still unavailable. With the vertical ionospheric density profiles observed by the FORMOSAT‐3/COSMIC, three‐dimensional density structure of the WSA is presented here for the first time. Meanwhile, a similar WSA signature is observed in the northern and eastern hemisphere during June solstice by both the GPS‐TEC and the FORMOSAT‐3/COSMIC electron density observations. From the observed altitudinal structure of the WSA during 1800–2400 LT and the similar feature occurred in the opposite hemisphere suggest that the southward offset of the magnetic equator with respect to the geographic equator plays a major role for the WSA formation.

ENSO and variability of the Antarctic Peninsula pelagic marine ecosystem

AbstractThe West Antarctic Peninsula region is an important source of Antarctic krill (Euphausia superba) in the Southern Ocean. From 1980–2004 abundance and concentration of phytoplankton and zooplankton, krill reproductive and recruitment success and seasonal sea ice extent here were significantly correlated with the atmospheric Southern Oscillation Index and exhibited three- to five-year frequencies characteristic of El Niño–Southern Oscillation (ENSO) variability. This linkage was associated with movements of the Southern Antarctic Circumpolar Current Front and Boundary, a changing influence of Antarctic Circumpolar Current and Weddell Sea waters, and eastward versus westward flow and mixing processes that are consistent with forcing by the Antarctic Dipole high-latitude climate mode. Identification of hydrographic processes underlying ecosystem variability presented here were derived primarily from multi-disciplinary data collected during 1990–2004, a period with relatively stable year-to-year sea ice conditions. These results differ from the overwhelming importance of seasonal sea ice development previously established using 1980–1996 data, a period marked by a major decrease in sea ice from the Antarctic Peninsula region in the late 1980s. These newer results reveal the more subtle consequences of ENSO variability on biological responses. They highlight the necessity of internally consistent long-term multidisciplinary datasets for understanding ecosystem variability and ultimately for establishing well-founded ecosystem management. Furthermore, natural environmental variability associated with interannual- and decadal-scale changes in ENSO forcing must be considered when assessing impacts of climate warming in the Antarctic Peninsula–Weddell Sea region.

Total ozone and tropopause zonal asymmetry during the Antarctic spring

Analysis of zonal anomalies in total ozone and thermal tropopause height shows that ozone depletion during austral spring has a strong influence on the height and sharpness of the tropopause over West Antarctica. The seasonal change of tropopause peak height occurs between 9 km (summer and autumn) and 13–14 km (winter and spring) over the Weddell Sea region, and in the range of 9–10 km at opposite longitudes in the Australian sector. Elevation of the tropopause is explained by low stratospheric temperature due to the seasonal temperature minimum in winter and ozone losses in spring. Accordingly, tropopause zonal asymmetry is determined by strong east‐west asymmetry of the surface temperatures in the winter and total ozone asymmetry in spring. Lowering of the elevated tropopause over the boundary of the Antarctic continent is explained by the influence of the cold continental troposphere both in winter and spring. Overall, this work reports some details of relative contribution of radiative (strong cooling of the lower stratosphere and continental troposphere) and dynamical (quasi‐stationary planetary wave 1 in total ozone) processes to the Antarctic tropopause formation. The sloping meridional profile of the tropopause and widening of the transition layer between the troposphere and stratosphere over West Antarctica suggest the possibility of enhanced air mixing not only vertically but also horizontally. This may contribute to the east‐west asymmetry in Antarctic climate change.

ISPOL weather conditions in the context of long-term climate variability in the north-western Weddell Sea

Abstract At the transition from austral spring to summer of 2004/2005, the field experiment Ice Station Polarstern (ISPOL) took place in the north-western Weddell Sea to observe physical and biological atmosphere–sea ice–ocean processes. The objective of this paper is to discuss the meteorological conditions during ISPOL in the context of long-term climate variability mainly in the north-western Weddell Sea region. This is done with a comprehensive climatology focusing on the seasonal and interannual variability of atmospheric and cryospheric data from 1979 to 2005. Key meteorological elements and weather patterns derived from NCEP/DOE Reanalysis 2 results and sea-ice data from passive microwave radiometer satellite observations are analyzed in combination with ISPOL in situ measurements. The monthly mean air temperature and the mean sea-level pressure were above the long-term average. The latter showed a very much extended variability and range associated with more frequent northerly to south-easterly winds.

Discovery of the South African polyplacophoran Stenosemus simplicissimus (Thiele, 1906) (Mollusca, Polyplacophora, Ischnochitonidae) in the Southern Ocean

Recent expeditions to the Atlantic sector of the Southern Ocean have yielded valuable collections of shelf and deep water polyplacophorans. These included several specimens of Stenosemus simplicissimus (Thiele, 1906), a species previously known only by its holotype and type locality at the Cape of Good Hope. The new material enabled a thorough morphological redescription of the species by studying valve, perinotum, and radula characters with SEM. The new records from Shag Rocks and the eastern Weddell Sea enlarge the species' biogeographic distribution from the temperate South African region to the polar South Georgia and Weddell Sea regions. Its bathymetric range is extended from 318 m to 285–1064 m. The limited occurrence of deep-water Antarctic polyplacophorans may be caused by benthic predators that limit the expansion of non-herbivorous chitons in the Antarctic deep sea.

Ice core records as sea ice proxies: An evaluation from the Weddell Sea region of Antarctica

Ice core records of methanesulfonic acid (MSA) from three sites around the Weddell Sea are investigated for their potential as sea ice proxies. It is found that the amount of MSA reaching the ice core sites decreases following years of increased winter sea ice in the Weddell Sea; opposite to the expected relationship if MSA is to be used as a sea ice proxy. It is also shown that this negative MSA‐sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the Weddell Sea has on MSA production area and transport distance. A historical record of sea ice from the northern Weddell Sea shows that the negative relationship between MSA and winter sea ice exists over interannual (∼7‐year period) and multidecadal (∼20‐year period) timescales. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the Weddell Sea, which act to synergistically increase sea ice extent (SIE) while decreasing MSA delivery to the ice core sites. Hence our findings show that in some locations atmospheric transport strength, rather than sea ice conditions, is the dominant factor that determines the MSA signal preserved in near‐coastal ice cores. A cautious approach is thus required in using ice core MSA for reconstructing past sea ice conditions, including the need for networks of ice core records and multiproxy studies to assess the significance of past MSA changes at different locations around Antarctica.

The effect of diapycnal mixing on the ventilation and CFC-11 uptake in the Southern Ocean

The Miami Isopycnic Coordinate Ocean Model (MICOM) is used to investigate the effect of diapycnal mixing on the oceanic uptake of CFC-11 and the ventilation of the surface waters in the Southern Ocean (south of 45°S). Three model experiments are performed: one with a diapycnal mixing coefficientK d (m2 s−1) of 2 × 10−7/N (Expt. 1), one withK d = 0 (Expt. 2), and one withK d = 5 × 10−8/N (Expt. 3),N (s−1) is the Brunt-Väisälä frequency. The model simulations indicate that the observed vertical distribution of CFC-11 along 88°W (prime meridian at 0°E) in the Southern Ocean is caused by local ventilation of the surface waters and westward-directed (eastward-directed) isopycnic transport and mixing from deeply ventilated waters in the Weddell Sea region. It is found that at the end of 1997, the simulated net ocean uptake of CFC-11 in Expt. 2 is 25% below that of Expt. 1. The decreased uptake of CFC-11 in the Southern Ocean accounts for 80% of this difference. Furthermore, Expts. 2 and 3 yield far more realistic vertical distributions of the ventilated CFC-waters than Expt. 1. The experiments clearly highlight the sensitivity of the Southern Ocean surface water ventilation to the distribution and thickness of the simulated mixed layer. It is argued that inclusion of CFCs in coupled climate models could be used as a test-bed for evaluating the decadal-scale ocean uptake of heat and CO2.

A year‐long record of size‐segregated aerosol composition at Halley, Antarctica

Size‐segregated aerosol samples were collected with a cascade impactor at 2 week intervals for a year at the research station Halley, situated near the coast in the Weddell Sea region of Antarctica. Sea salt is a major component of aerosol throughout the year, and we estimate that at least 60% of the total sea salt arriving at Halley is from brine and frost flowers on the sea ice surface rather than open water. Chloride in sea‐salt particles is depleted relative to sodium in summer, consistent with loss of HCl as sea‐salt particles react with gaseous acidic species, but is enhanced in large particles in winter because of fractionation occurring during the production of new sea ice. Non‐sea‐salt sulphate peaks in the summer, with the majority being in small particles indicative of a gas phase origin. The distribution of methane sulphonic acid closely follows that of non‐sea‐salt sulphate. In the winter, non‐sea‐salt sulphate is frequently negative, especially on stages collecting large particle sizes, consistent with the source of sea salt during the winter being predominantly the sea ice surface rather than open water. Nitrate peaks in the spring and summer and shows some association with sea‐salt particles.

Recent, Large-Scale Changes in the Extratropical Southern Hemisphere Atmospheric Circulation

The zonal anomalies in the 500-hPa geopotential height field of the Southern Hemisphere are examined using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalyses, 1958–96. The zonal anomalies were constructed by removing the zonal mean from each grid point, and principal components analysis was performed on the resulting spatial anomalies. The principal components of the leading EOF of the seasons March–April–May (MAM) to September–October–November (SON) indicate that a change has occurred in the extratropical, large-scale, atmospheric circulation of the Southern Hemisphere. It is estimated to have begun after 1975 and is limited to the southern late fall, winter, and early spring. The elements of this change are a deeper Pacific trough and higher Indian Ocean ridge at subtropical latitudes. At higher latitudes the ridge over the Pacific strengthened and shifted east while troughing occurred in the southwest Atlantic–Weddell Sea region. Consistent with the changes in the zonal anomalies, zonal wave 1 experienced a large increase in amplitude in the late winter–early spring. On the other hand, zonal wave 3 reached its maximum one month earlier, shrank more quickly, and reached lower-than-average amplitudes in spring after 1975.

Oxygen-isotope (δ18O) evidence of Holocene hydrological changes at Signy Island, maritime Antarctica

A record of Holocene hydrological changes has been produced from variations in oxygen-isotope composition (δ18O) preserved in freshwater lake sediments from maritime Antarctica. Small amounts (<5%) of authigenic carbonate have been extracted from a non-marl sediment core from Sombre Lake, Signy Island (60°43'S, 45°38'W). Oxygen-isotope and particle-size analysis provide a sensitive record of hydrological events in the lake arising from local and regional climate phenomena. The climate affects δ18O through snowpack volume and glacier activity in the catchment, lakewater temperatures, the input versus evaporation balance and the duration of seasonal lake ice cover. The most depleted (negative) δ18O values are associated with influxes of meltwater at times of glacier advance or retreat. Enriched (positive) δ18O values occur during more arid, warmer conditions with longer periods of open water in summer. This isotope record can be used to determine century-scale to decadal variability in air circulation and moisture origin. Strong similarities with other Holo cene proxy records from the Weddell Sea and Antarctic Peninsula Region are apparent, including the mid-Holocene climate optimum followed by the Neoglacial and, most recently, late twentieth-century climatic warming. The oxygen-isotope record from Sombre Lake illustrates the importance of remote islands in contribu ting to our understanding of teleconnections in atmospheric and oceanographic circulation, sea-ice extent, air temperatures and precipitation in the Southern Ocean.

Perturbations of the Earth's rotation and their implications for the present-day mass balance of both polar ice caps

The present-day perturbations of the Earth's rotation are sensitive to the glacial isostatic adjustment (GIA) arising from the Late Pleistocene glacial cycles and also to the recent mass balance of polar ice caps. In this study, we evaluate the polar wander and the change of degree-two harmonic of the Earth's geopotential , proportional to the rotation rate, for four Late Pleistocene ice models. We examine these perturbations as a function of lower- and upper-mantle viscosities and lithospheric thickness and rheology (elastic or viscoelastic), in which a compressible Earth model with elasticity and density given by the seismological model PREM is used. By considering the observations and predictions including the GIA process arising from the Late Pleistocene ice and recent mass balance of polar ice caps, we discuss the recent mass balance of the Antarctic and Greenland ice sheets. We also examine the effects of internal processes and the melting of mountain glaciers, although this work is only preliminary. The results shown below seem to be supported even if these effects are included. Two solutions are obtained for source areas of the recent Antarctic melting. We denote an equivalent sea level (ESL) rise (mm yr−1)) from the Greenland and Antarctic ice sheets as and , respectively, being positive for melting and negative for growth. One, solution s1, is a solution satisfying the relationship , and the other, solution s2, generally satisfies the relationship and . In most cases, the magnitude of for solution s2 is larger than that for solution s1. The melting area of the Antarctic ice sheet for solution s1 roughly corresponds to the Weddell Sea region, approximately located on the symmetric part of Greenland to the Equator. The area for solution s2 is located on the symmetric part of Greenland to the centre of the Earth. In both solutions, therefore, the polar wander direction caused by the mass imbalance of each ice sheet is in an opposite direction. The reason for this is that the observed polar wander direction is nearly identical to the prediction from the GIA process for the Late Pleistocene ice models. However, it is difficult to independently examine which solution is better. If we consider a recent ESL rise of ∼0.6 mm yr−1 from the Greenland ice sheet, then a similar ESL rise of 0.5–1.0 mm yr−1 is also suggested for the Antarctic ice sheet around the Weddell Sea region. This solution also suggests the lower-mantle viscosity to be ∼1022 Pa s.