Mawson Station Research Articles

Southern Hemisphere atmospheric history of carbon monoxide over the late Holocene reconstructed from multiple Antarctic ice archives

Abstract. Carbon monoxide (CO) is a naturally occurring atmospheric trace gas, a regulated pollutant, and one of the main components determining the oxidative capacity of the atmosphere. Evaluating climate–chemistry models under different conditions than today and constraining past CO sources requires a reliable record of atmospheric CO mixing ratios ([CO]) that includes data since preindustrial times. Here, we report the first continuous record of atmospheric [CO] for Southern Hemisphere (SH) high latitudes over the past 3 millennia. Our continuous record is a composite of three high-resolution Antarctic ice core gas records and firn air measurements from seven Antarctic locations. The ice core gas [CO] records were measured by continuous flow analysis (CFA), using an optical feedback cavity-enhanced absorption spectrometer (OF-CEAS), achieving excellent external precision (2.8–8.8 ppb; 2σ) and consistently low blanks (ranging from 4.1±1.2 to 7.4±1.4 ppb), thus enabling paleo-atmospheric interpretations. Six new firn air [CO] Antarctic datasets collected between 1993 and 2016 CE at the DE08-2, DSSW19K, DSSW20K, South Pole, Aurora Basin North (ABN), and Lock-In sites (and one previously published firn CO dataset at Berkner) were used to reconstruct the atmospheric history of CO from ∼1897 CE, using inverse modeling that incorporates the influence of gas transport in firn. Excellent consistency was observed between the youngest ice core gas [CO] and the [CO] from the base of the firn and between the recent firn [CO] and atmospheric [CO] measurements at Mawson station (eastern Antarctica), yielding a consistent and contiguous record of CO across these different archives. Our Antarctic [CO] record is relatively stable from −835 to 1500 CE, with mixing ratios within a 30–45 ppb range (2σ). There is a ∼5 ppb decrease in [CO] to a minimum at around 1700 CE during the Little Ice Age. CO mixing ratios then increase over time to reach a maximum of ∼54 ppb by ∼1985 CE. Most of the industrial period [CO] growth occurred between about 1940 to 1985 CE, after which there was an overall [CO] decrease, as observed in Greenland firn air and later at atmospheric monitoring sites and attributed partly to reduced CO emissions from combustion sources. Our Antarctic ice core gas CO observations differ from previously published records in two key aspects. First, our mixing ratios are significantly lower than reported previously, suggesting that previous studies underestimated blank contributions. Second, our new CO record does not show a maximum in the late 1800s. The absence of a [CO] peak around the turn of the century argues against there being a peak in Southern Hemisphere biomass burning at this time, which is in agreement with (i) other paleofire proxies such as ethane or acetylene and (ii) conclusions reached by paleofire modeling. The combined ice core and firn air [CO] history, spanning −835 to 1992 CE, extended to the present by the Mawson atmospheric record, provides a useful benchmark for future atmospheric chemistry modeling studies.

Understanding the Culture and Subcultures of Nakedness in Antarctica

Depictions of nakedness in Antarctica are rare, although there are many sub-cultures and traditions there that involve nakedness – often as an expression of the human body confronting or overcoming the extreme environment. An examination of some of the sub-cultures of nakedness, shows that there are markedly different attitudes to nakedness “off-station” and “on-station”, with official attitudes sanctioning nakedness as not appropriate behaviour “on-station”, but with less rigidity as to what happens “off-station”. There is also a strong sense that naked behaviours, or depictions of nakedness, from earlier eras having a sense of cultural heritage, which can be at odds with contemporary needs of stamping out sexism, as more and more women take up positions on Antarctic stations – often in roles of management. And while no longer condoned in contemporary practice, that such former depictions of nudity can be seen as worth preserving - demonstrated in the reaction to the destruction of the nude pinup pictures on the ceiling of a heritage hut in Australia’s Mawson Station (mainly due to their inherent sexism and objectification of women) shows that views of nakedness can be seen as both heretical or heritage, from different perspectives.

Long-term trends in the population size and breeding success of emperor penguins at the Taylor Glacier colony, Antarctica

The population size of emperor penguins at the land-based Taylor Glacier colony was monitored over 54 years from 1957 to 2010 by intermittent ground counts from 1957 to 1975 and annual photographic counts from 1988 to 2010 of males attending the colony in winter and chicks in early summer. The breeding population in the early years averaged 3,684 ± 492 pairs compared with 2,927 ± 320 pairs from 1988–2010, a reduction of 20.5 %. The exact timing and magnitude of the change is unknown because there was a 13-year gap between the end of the historical counts and start of the contemporary counts. From 1954 to 2010 no real or inferred warming event that may have been linked to the decrease was evident at Australia’s Mawson station, 95 km from Taylor Glacier colony. From 1988 to 2010, variation in breeding population size and breeding success were not related to variation in the distance between the colony and open water. In this period, the number of pairs breeding fluctuated annually and overall showed signs of a gradual decrease. The Taylor Glacier colony is one of only three emperor penguin colonies where populations have been monitored in winter over the long term. Given the threat of climate warming to the future of this ice-dependent species it is imperative that the annual monitoring programme at Taylor Glacier continues well into the future.

Comparison of zooplankton distribution patterns between four seasons in the Indian Ocean sector of the Southern Ocean

We investigated the composition, distribution and abundance of zooplankton in the Indian Ocean sector of the Southern Ocean during the austral summer (December/January) of 2004/05, 2005/06, 2007/08 and 2008/09 using a Continuous Plankton Recorder (CPR). CPR tows were conducted along two transects during voyages south of Cape Town to north of Syowa station and from north of the Mawson station area to south of Fremantle. High zooplankton abundance was recorded on each transect in the Polar Frontal Zone (PFZ) and the northern area of the Antarctic Zone (AZ). Community structure in these zones was dominated by common taxa including the ubiquitous Oithona similis and calanoid copepodites, accounting for >50% of total abundance, and Calanus simillimus, Ctenocalanus citer, Clausocalanus laticeps and Metridia lucens also occurred in high densities. Appendicularians of the genus Fritillaria were the most important component in the Cape Town to Syowa station area in 2008, with 36.9% of total abundance. The average chlorophyll a level at this time of year was the lowest (0.32 mg m −3) among all transects. Appendicularians are suited to oceanic oligotrophic waters; therefore, they are suited to low phytoplankton density. Foraminiferans were numerically dominant throughout the Mawson station area to Fremantle transect in 2005. Unlike Fritillaria spp., foraminiferans prefer high phytoplankton density. The elevated average chlorophyll a biomass in 2005 (0.64 mg m −3) provided favorable conditions for Foraminifera, which were dominant and widespread. CPR surveys provide information on the fine scale structure of the inter-annual distribution changes in micro- and meso- zooplankton assemblages, and the CPR is one of ideal method to monitor organisms that are indicators of environmental change.

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

Abstract. A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms−1 westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms−1, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms−1 weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00.

Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India

Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (≤9.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios.

Mawson and Mirnyy Stations: the spatiality of the Australian Antarctic Territory, 1954–61

This article focuses on the spatiality of the Australian Antarctic Territory in the important 1954–61 period. Attending particularly to three key components of polar spatiality—geopolitics, international territorial law, and the built environment—the article analyses the development of the Territory as a unique Australian space. The 1954–61 period is particularly significant: during this period, the International Geophysical Year brought an unprecedented number of people to Antarctica; the continent's first permanent colonies were constructed; and, despite Cold War tensions, the 1961 Antarctic Treaty established the spatial configurations and rules which continue to govern the continent today. The article focuses particularly on two key stations in the Territory constructed during this period: Australia's Mawson Station and the Soviet Mirnyy Station. Mawson is a legal colony, designed to cement Australia's claim to 42 per cent of the Antarctic continent; Mirnyy, in contrast, is an anti-colony, designed to reject Australia's claim. How the individual spatialities of these two stations articulate to the broader politics of Antarctic territoriality—and particularly Australia's claim to the Australian Antarctic Territory—is the focus of this article.

Number and distribution of Adélie penguin (Pygoscelis adeliae) breeding sites in the Robinson Group of islands, Mac.Robertson Land coast, east Antarctica

ABSTRACTIn November 2005, the first comprehensive survey for Adélie penguin (Pygoscelis adeliae) breeding sites in the Robinson Group of islands, situated 25 to 55 km east of Australia's Mawson station (67.602°S, 62.879°E) was conducted. Breeding Adélie penguins were found on 30 of the 149 islands, with the number of nests on each island ranging from fewer than 10 to several thousand. With the exception of those islands in the southeast, nesting Adélie penguins were found throughout the Robinson Group. In this paper, the spatial coordinates and presence/absence of breeding penguins for all 149 islands are reported so that researchers may interpret the results in relation to possible future survey work. All locations reported in this paper are in decimal degrees.

WEDDELL SEAL UNDERWATER CALLING RATES DURING THE WINTER AND SPRING NEAR MAWSON STATION, ANTARCTICA

AbstractUnderwater vocalization monitoring and surveys, both on ice and underwater, were used to determine if Weddell seals (Leptonychotes weddellii) near Mawson Station, Antarctica, remain under the fast ice during winter within close range of breeding sites. Daytime and nighttime underwater calling rates were examined at seven breeding sites during austral winter and spring to identify seasonal and diel patterns. Seals rarely hauled out at any of the sites during winter, although all cohorts (adult males, females, and juveniles) were observed underwater and surfacing at breathing holes throughout winter (June–September) and spring (October–December). Seal vocalizations were recorded during each sampling session throughout the study (n= 102 daytime at seven sites collectively, and n= 5 24‐h samples at each of two sites). Mean daytime calling rate was low in mid‐winter (July) (mean = 18.9 ± 7.1 calls/min) but increased monthly, reaching a peak during the breeding season (November) (mean = 62.6 ± 15.7 calls/min). Mean nighttime calling rate was high throughout the winter and early spring (July–October) with mean nocturnal calling rate in July (mean = 61.8 ± 35.1 calls/min) nearly equal to mean daytime calling rate in November (during 24‐h daylight). Reduced vocal behavior during winter daylight periods may result from animals utilizing the limited daylight hours for nonvocal activities, possibly feeding.

Cold colonies: Antarctic spatialities at Mawson and McMurdo stations

In 1954, a small team of Australian men landed at Horseshoe Harbor and began constructing Mawson Station: the permanent colonization of Antarctica was initiated. Two years later, Americans began the construction of their major Antarctic base, McMurdo. Although Antarctica is routinely represented as an empty wilderness, over the last 50 years tens of thousands of humans have occupied the continent, most of them living in Antarctica's 40 national bases. What kinds of spaces are these Antarctican colonial settlements? How do they function materially, ideologically, legally and spatially? This article explores the anatomy of two of the oldest and most populous of these spaces, Mawson and McMurdo stations. It attends to their physical environments and to the geopolitical epistemologies that shape them. It is thus a study of two distinct Antarctican spatialities. This article is part of a larger endeavour to account for the heterogeneous cultural geographies of the polar south. It works towards a definition of contemporary colonialism in its Antarctican context. In a previously-uninhabited continent governed by scientific internationalism, yet subject to disputed territorial claims and conflicting geopolitical spaces, colonialism takes on specific localized forms. This article attends to the unique colonial spatialities of two key Antarctican settlements.

Australian exploration of Heard Island, 1947–1971

In 1947 knowledge of Heard Island was confined to a rough mapping compiled by nineteenth-century sealers, and the results of four scientific expeditions that had briefly investigated the Atlas Cove area. Exploration continued in two distinct periods between 1947 and 1971. In the first period the Australian National Antarctic Research Expeditions (ANARE) built a scientific station at Atlas Cove in 1947, and occupied it continuously until 1955 as an ‘A Class’ meteorological station, a seismic and magnetic observatory, and a base for other scientific studies and for exploration of the island. In the second period four summer expeditions and one wintering expedition worked on the island between 1963 and 1971. The summer expeditions were an ANARE expedition in 1963, an Australian private expedition (The South Indian Ocean Expedition to Heard Island) in 1965, and ANARE expeditions in 1969 and 1971 associated with United States and French expeditions. A United States expedition wintered in 1969. There were no further expeditions until 1980. The years 1947–1971 saw many achievements. Expedition members recorded seven years of synoptic meteorological observations and four years of seismic and magnetic observations. They developed empirical techniques of work, travel, and survival that shaped the collective character of ANARE and were later applied in Antarctica. Despite difficult terrain and consistently bad weather, and the accidental deaths of two men in 1952, unsupported field parties of two or three men travelling on foot explored and mapped in detail the heavily glaciated island, and documented its topography, geology, glaciology and biology. They made three overland circuits of the island, the first ascent of Big Ben (2745 m), and the first recorded landing on the nearby McDonald Islands. Expedition members bred and trained dog teams for later use in Antarctica. They reported the commencement and subsequent progress of massive glacier retreat caused by regional warming, and of the island's colonisation by king penguins (Aptenodytes patagonicus) and antarctic fur seals (Arctocephalus gazella). They also reported measurements of glacier flow and thickness, the palaeomagnetism of Heard Island rocks, behavioural and population studies of southern giant petrels (Macronectes giganteus) and other birds, studies of southern elephant seals (Mirounga leonina) and leopard seals (Hydrurga leptonyx), and the cold stress and acclimatisation experienced by humans working in the island's wet-cold climate. In addition, Heard Island served as a testing ground for men, equipment, scientific programmes, huskies, general administration, and logistics, without which Mawson station could not have been established as successfully as it was in 1954. The American wintering expedition and the French summer expedition contributed to major international geodetic and geophysical investigations. In sum, the expeditions between 1947 and 1971 added much to our knowledge of Heard Island, and they laid down a solid foundation for the work of later expeditions.

Antarctic Cosmic Ray Astronomy

AbstractCosmic ray observations related to Antarctica commenced in the austral summer of 1947-48 from sub-Antarctic Heard and Macquarie Islands and from the HMAS Wyatt Earp. Muon telescope observations from Mawson station, Antarctica, followed from 1955. The International Geophysical Year was the impetus for the installation of a number of neutron monitors around Antarctica, observing the lowest energy cosmic rays accessible by ground based instruments. In 1971 a new observatory was built at Mawson including the only underground muon telescope system at polar latitudes in either hemisphere. Over more than half a century, cosmic ray astronomy has been undertaken from Antarctica and its surrounding regions and these observations have been critical to our growing understanding of the heliosphere.

In-situ U–Pb geochronology and Hf isotope analyses of the Rayner Complex, east Antarctica

In-situ zircon U–Pb and Hf isotopic analysis via laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) of samples from Kemp and MacRobertson Lands, east Antarctica suggests that the Kemp Land terrane evolved separately from the rest of the Rayner Complex prior to the ca. 940 Ma Rayner Structural Episode. Several Archaean metamorphic events in rocks from western Kemp Land can be correlated with events previously reported for the adjacent Napier Complex. Recently reported ca. 1,600 Ma isotopic disturbance in rocks from the Oygarden Group may be correlated with a charnockitic intrusion in the Stillwell Hills before ca. 1,550 Ma. Despite being separated by some 200 km, T Hf DM ages indicate felsic orthogneiss from Rippon Point, the Oygarden Group, Havstein Island and the Stillwell Hills share a ca. 3,660–3,560 Ma source that is indistinguishable from that previously reported for parts of the Napier Complex. More recent additions to this crust include Proterozoic charnockite in the Stillwell Hills and the vicinity of Mawson Station. These plutons have distinct 176Hf/177Hf ratios and formed via the melting of crust generated at ca. 2,150–2,550 Ma and ca. 1,790–1,870 Ma respectively.

Post-fledging and winter migration of Adélie penguins Pygoscelis adeliae in the Mawson region of East Antarctica

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 248:267-278 (2003) - doi:10.3354/meps248267 Post-fledging and winter migration of Adélie penguins Pygoscelis adeliae in the Mawson region of East Antarctica Judy Clarke1,*, Knowles Kerry1, Charles Fowler2, Ruth Lawless1, Stefan Eberhard1,3, Ray Murphy1,4 1Australian Antarctic Division, Channel Hwy, Kingston, Tasmania 7050, Australia 2Colorado Center for Astrodynamics Research, University of Colorado, Boulder, Colorado 803309-0431, USA *Email: judy.clarke@aad.gov.au ABSTRACT: Seven fledging Adélie penguin Pygoscelis adeliae chicks and 4 post-moult adults were satellite tracked using the Argos system during the winters of 1995-97 and 1998, respectively. Six fledglings departed from Béchervaise Island near Mawson station (67°35¹S, 62°49¹E) during late February of 1996 and 1997 and were tracked for up to 5 mo before transmissions stopped. The 7th fledgling left Magnetic Island near Davis station (68°33¹S, 77°54¹E) in February 1995 and was tracked for 32 d. All fledglings travelled northward initially, then westward along the edge of the fast ice or in the pack-ice. Fledglings had travelled between 536 and 1931 km to the west of their natal colonies by the time transmissions ceased. Adult Adélie penguins were tracked between March and October 1998, following completion of their annual moult at Bechérvaise Island. Instruments were set to transmit for 2 h every 10th day over the first 5 mo and 1 d in 4 thereafter. Adult birds travelled westward until July, after which time they moved north within the expanding pack-ice into known areas of high krill concentration before returning eastward toward their breeding sites. Penguin movements over the winter months were closely related to those of sea ice in the region. Ice motion patterns were in turn influenced by gyral oceanic current systems and wind. We propose that large gyral oceanic systems provide a means for Adélie penguins to reduce costs of transport as they travel into regions of high productivity during winter and return to their breeding colonies in spring. KEY WORDS: Adélie penguin · Winter migration · Satellite tracking · Fledglings · Sea-ice motion · Antarctic divergence · East Antarctica · Oceanic gyres Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 248. Online publication date: February 20, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Variation in the ribosomal ITS-sequence of the lichens Buellia frigida and Xanthoria elegans from the Vestfold Hills, eastern Antarctica

Abstract:Thalli of the lichens Buellia frigida and Xanthoria elegans were collected from five different locations each 5–15km apart in the Vestfold Hills, Princess Elizabeth Land, eastern Antarctica. A further collection was made from Mawson Station, Mac Robertson Land, eastern Antarctica, 660km away. DNA was extracted from whole thalli and the ribosomal ITS region amplified by PCR using fungal specific primers. Resulting products were sequenced to gain an indication of whether or not variation was present within populations of lichen-forming fungi from continental Antarctica, and therefore of the availability of genetic resources to react to pressures such as climate change. Three genotypes ofB. frigida and two of X. elegans were detected in the Vestfold Hill collections. However, these differed by only one nucleotide position suggesting the presence of relatively little genetic variation, if the ITS region is indicative of the overall genome. Buellia frigida collected from Mawson Station had an identical ITS region sequence to the most common Vestfold Hills genotype, indicating that this species may have a low level of genetic variation across much of eastern Antarctica. In contrast, X. elegans collected from Mawson showed considerable genetic variation from the Vestfolds thalli, differing at 14·2% of nucleotide positions and had an identical ITS region sequence to an isolate from maritime Antarctica 4960km away. Samples from the Vestfold Hills formed a distinct cluster in a phylogenetic analysis of ITS sequences from a worldwide collection of X. elegans isolates.

Crevasse fall in the Antarctic: a patient's perspective.

As a veterinarian working on an Adélie penguin research program, I was to spend six months on an island off the coast of Mawson Station in the Australian Antarctic Territory. During a field training exercise on my third day at Mawson, I fell into a crevasse with my four-wheel-drive quad bike and was crushed between the bike and the crevasse wall six metres below the rim. I had hypothermia and abdominal injuries, and underwent two emergency surgical procedures at Mawson Station. Sixteen days after the accident, I was evacuated by helicopter and ship. Here, I describe my experiences.

Effective discrimination of icequakes on seismic records from Mawson station

The telemetered seismic station at Mawson, Antarctica, was one of the primary Australian stations participating in the Group of Scientific Experts Technical Test (GSETT) experiment to test an international seismic monitoring system. Mawson signals are continuously transmitted to the National Data Center (NDC) in Canberra and also forwarded to the International Data Centre (IDC) in Washington, where further event analysis is performed. Numerous seismic signals are recorded on seismograms from the Mawson station, with a likely mechanism of sudden fracturing of ice. The aim of this study was to find a procedure which will effectively discriminate seismic signals from these icequakes and thus speed up the analysis of the other detected events. An automatic algorithm was designed to identify icequakes according to their characteristics: frequency content, duration, azimuth, inclination and magnitude. The program was tested on a few datasets of randomly selected periods and one comprised of records of nuclear explosions detonated in the period of 1995/96. The preliminary results showed that this method was capable of distinguishing icequakes and could substantially improve the production of an automated event list.

Compilation of shipborne magnetic and gravity data images crustal structure of Prydz Bay (East Antarctica)

A magnetic anomaly map and a free air anomaly map of Prydz Bay, of the adjacent slope and over the continental rise area (63°S-69.5°S, 69°E-81°E) were compiled using Russian, Australian, Japanese and other available data (more than 20 000 km in total length). Adjustment of different data sets was performed before gridding and making contour maps. Crossover differences of the magnetic data were significantly reduced by removing data segments with short-period time variations, by applying time variation corrections of Mawson Station to Australian and Japanese data, and by giving a constant bias to each trackline. Crossover differences of the gravity data were also substantially reduced by applying a constant bias to each cruise/leg. According to the compiled gravity data, in the western part of Prydz Bay the continent ocean boundary is inferred to be situated around the shelf edge at the seaward end of Prydz Channel, while it is in the continental rise in the eastern part. The gravity data also suggest the presence of sediments in the Prydz Bay basin reaching a thickness of about 8 km and overlying a "granitic" layer; the Moho beneath the basin is located at a depth of about 22 km. According to the magnetic data, highly-magnetized rocks occur at shallow depths northwest of the Prydz Bay basin and other parts of Prydz Bay.

Further observations of the thermospheric vertical wind at the auroral oval/polar cap boundary

Abstract We present further observations of thermospheric winds and temperatures, derived from observations of the λ630 nm oxygen auroral/airglow emission (from ∼240 km altitude), obtained with a Fabry-Perot spectrometer (FPS) at Mawson station, Antarctica (L = 9). We report further instances of large upward zenith winds, with velocities up to ∼80ms−1, often associated with increases in temperature of up to 200 K. These upward winds are mostly seen around 21 Z, which is when Mawson station passes under the poleward edge of the (discrete) auroral oval during intervals of low to moderate geomagnetic activity, and are yet further examples of the type of event presented in an earlier paper (Innis et al., 1996). We also find intervals, up to several hours in length, when the temperatures measured South and East of the station can be several hundred degrees higher than those measured in the North and West directions, which we ascribe to the expansion of the hot polar cap into the South and East viewing directions. We have observed examples of seemingly anomalous wind measurements in the South and East directions during these times, which appear to be related to the presence of an upward wind in the observing volume of the FPS. Our observations suggest, however, that the upward wind would cause only a small perturbation (relative to the horizontal component) of the high-latitude thermospheric neutral wind field. The size of the zenith wind events (up to ∼120 m s−1) seen in our observations at Mawson are comparable with the amplitude of oscillations seen in gravity waves propagating at ∼300 km altitude over the polar cap from the nightside to the dayside, detected by Johnson et al. (1995) from Dynamics Explorer 2 observations. This similarity and the fact that we see the upward winds at the night-time auroral oval/polar cap boundary suggest that the origin of the upward winds may be intrinsically linked to the processes that generate these gravity waves.

Diet composition of Emperor Penguin chicks Aptenodytes forsten‘ at two Mawson Coast colonies, Antarctica

The diet composition of Emperor Penguin Aptenodytes forsteri chicks was examined at Auster and Taylor Glacier colonies, near Australia's Mawson station, Antarctica, between hatching in mid‐winter and fledging in mid‐summer by “water‐offloading” adults. Chicks at both colonies were fed a similar suite of prey species. Crustaceans occurred in 82% of stomach samples at Auster and 87% of stomachs at Taylor Glacier and were heavily digested: their contribution to food mass could not be quantified. Fish, primarily bentho‐pelagic species, accounted for 52% by number and 55% by mass of chick diet at Auster, and squid formed the remainder. At Taylor Glacier the corresponding values were 27% by number and 31% by mass of fish and 73% by number and 69% by mass of squid. Of the 33 species or taxa identified, the fish Trematomus eulepidotus and the squid Psychroteuthis glacialis and Allu‐roteuthis antarcticus accounted for 64% and 74% of the diets by mass at Auster and Taylor Glacier, respectively. The sizes of fish varied temporally but not in a linear manner from winter to summer. Adult penguins captured fish ranging in length from 60 mm (Pfeura‐gramma antarcticum) to 250 mm (T. eulepidotus) and squid (P. glacialis) from 19 to 280 mm in mantle length. The length‐frequency distribution of P. glacialis showed seasonal variation, with the size of squid increasing from winter to summer. The energy density of chick diet mix increased significantly prior to “fledging”.