Ian D. Goodwin

Elevation changes in antarctica mainly determined by accumulation variability

Antarctic Ice Sheet elevation changes, which are used to estimate changes in the mass of the interior regions, are caused by variations in the depth of the firn layer. We quantified the effects of temperature and accumulation variability on firn layer thickness by simulating the 1980–2004 Antarctic firn depth variability. For most of Antarctica, the magnitudes of firn depth changes were comparable to those of observed ice sheet elevation changes. The current satellite observational period (∼15 years) is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes. The amount of surface lowering in the Amundsen Sea Embayment revealed by satellite radar altimetry (1995–2003) was increased by including firn depth fluctuations, while a large area of the East Antarctic Ice Sheet slowly grew as a result of increased accumulation.

Highstand transport of coastal sand to the deep ocean: A case study from Fraser Island, southeast Australia

Deep-water sands form a new frontier for marine geology and petroleum exploration, but how does sand reach the deep sea? Existing geological models predict that deep-water sands are mainly supplied from rivers during times of low sea level, or by incision of canyons into the shelf to tap river or longshore-transport sand sources. Here, we demonstrate that at high sea level, southeast Australian deep-water sands are delivered by a wave-driven coastal transport system, interacting with estuarine ebb tidal flows, that transports sand over the shelf edge at a change in margin orientation. Discovery of this new process results from an investigation that combines multibeam acoustic, microfaunal, zircon and luminescence dating, oceanographic, Landsat, remotely operated vehicle, and sediment property methods. Our longshore transport–driven model is capable of forecasting new locations for deep-water sand deposits in a predictive paleoclimatic and paleotectonic setting.

A 700-Year Record of Atmospheric Circulation Developed from the Law Dome Ice Core, East Antarctica

[1]xa0A 700-year, high-resolution, multivariate ice core record from Dome Summit South (DSS) (66°46′S, 112°48′E; 1370 m), Law Dome, is used to investigate sea level pressure (SLP) variability in the region of East Antarctica. Empirical orthogonal function (EOF) analysis reveals that the first EOF (LDEOF1) of the combined glaciochemical, oxygen isotope ratio, and accumulation rate record from DSS represents most of the variability in sea salt seen in the record. LDEOF1 is positively correlated (at least 95% confidence level) to instrumental June mean SLP across most of East Antarctica. Over the last 700 years, LDEOF1 levels at Law Dome were the highest during the nineteenth century, suggesting an increase in intensification of winter circulation during this period. The Law Dome DSS oxygen isotope ratio series also indicates that the nineteenth century had the coldest winters of any century in the record. In contrast, LDEOF1 levels were the lowest at Law Dome during the eighteenth century, suggesting a significant shift in the patterns and/or intensity of East Antarctic atmospheric circulation between the eighteenth and the nineteenth centuries. The LDEOF1 sea salt record is characterized by significant decadal-scale variability with a strong 25-year periodic structure.

Snow accumulation variability in Wilkes Land, East Antarctica, and the relationship to atmospheric ridging in the 130°–170°E region since 1930

[1]xa0Wilkes Land annual snow accumulation variability is explored together with ice core chemistry data as proxies for circumpolar atmospheric circulation in the 110°E–135°E sector of the circumpolar trough. Four accumulation time series spanning 1930–1985 show a pattern of accumulation related to maritime air mass incursions over the East Antarctic ice sheet slope, which is regionally consistent on interannual and interdecadal timescales. The temporal accumulation pattern in Wilkes Land shows decadal fluctuations of ±10%. Both these fluctuations and the overall trend of increasing accumulation since the middle 1960s are consistent with a poleward shift and intensification of the circumpolar trough. This is consistent with a shift toward the high index state of the southern annular mode. Interannual variability of snow accumulation rate throughout Wilkes Land was found to be dependent upon shifts in the preferred tracks of cyclones along or across the coast and in the location of cyclolysis regions. Significant differences in this temporal accumulation pattern over Wilkes Land can occur as a result of the time-varying location of atmospheric ridging and the circumpolar long-wave structure south of New Zealand and Australia. Snow accumulation at an additional site (GD09) displays a well-defined interdecadal pattern, and the mean annual nitrate (NO3−) concentration of snow is correlated to the winter sea level pressure gradient between East Antarctica and the sub-Antarctic and the upper geopotential height and zonal wind data over East Antarctica. Strong, surface wind drainage during tropospheric ridging in Wilkes Land produces anomalous snow accumulation and annual mean NO3− concentration in firn at GD09.

Areal distribution of the oxygen-isotope ratio in Antarctica: comparison of results based on field and remotely sensed data

An updated compilation of oxygen-isotope ratio data for 562 sites in Antarctica shows a significant increase in the number of sites and a n improvement in the representation of the coasta l zone over previous versions. The data base consists of ratio values (0 0 ; multi-year mean 18 0 / 6 0 relative to Standard Mean O cean Vater, in % 0 ) . compiled as the dependent vari able, together with data for the so-called independent variabl es: latitude, surface elevation, mean annual surface temperature and mean annual shortest distance to open ocean denoted by the 20% sea-ice concentration boundary. The problem of covariation between so-called independent variables is minimized using stepwise regression analyses. A general model is described using all the fi eld data, a nd the regional variation at drainage-sys tem scale is assessed by contrasting models for two physiographically distinct regions. In addition, entity-specific models are determined using data subsets for the conterminous grounded-ice and ice-shelf areas. Inversions of the specific models a re applied to a 100 km grid data base to produce two contoured distributions of the ratio, one based on fi eld data, and the other on remotely sensed da ta. The difference between these produces residuals that, relative to the summation of standard errors of the models, are small in most of the interior area of the ice sheet, and large in several areas of mountain and coasta l regions, where interpolation and extrapolation of field data are particula rly unreliable. Remotely sensed data generally produce ratio values which are isotopically cooler. INTRODUCTION In the fo llowing sections we discuss aspects of: 7Time series of surface air temperature for particular sites are among the most important data bases used to assess global change (e.g. Jones, 1994; Parker and others, 1995). Oxygen-isotope ratio values obtained from polar firn and ice samples are determined by complex phenomena that include the condensation history of air masses, but in practice are taken to indicate the temperature of condensation in the lower troposphere at the time of precipitation, and are used as proxy data for surface temperature (e.g. Dansgaard and others, 1973; Lorius and Merlivat, 1977). Applying diverse dating criteria, time series of oxygen-isotope ratio values obtained from deep ice cores yield complete temperature records of varying time resolutions covering millennia (e.g. H echt, 1989; Jouzel and others, 1993). Values of 0 0 (in this study, multi-year mean value of 18 0 / 0 relative to Standard Mean Ocean Water, in %0 ) (SMOW; repositories at the U.S. National Bureau of Standards, Washington, DC, and at the International Atomic Energy Agency, Vienna) need to be adjusted for ice flow, normally using modeling procedures that incorporate an assumed surface distribution of either 00 or multi-year mean temperature values upstream of the sampling site (e.g. Robin, 1976; Budd and Young, 1983). The present study provides a benchmark distribution for any such modeling in studies of deep ice cores from Antarctica. (a ) the sample-site dataset and 100 km grid data subse ts. (b) the genera l model derived using the whole sample-site dataset, and the possibly maximum regional differences at drainage-system scale within the general model. (c) entity-specific models that result from splitting the sample-site data to represent locations exclusively on the conterminous grounded-ice area, and on ice-shelf a reas (including islands and ice rises). (d ) two areal dist ributions of 0 180 that result from the inversion of entity-specific models applied to 100 km grid data subsets, one based largely on data obtained from surface observations, and the other based la rgely on remotely sensed data. (e) a comparison between the areal distribution of 0180 produced using the fi eld and remotely sensed data subsets showing the distribution of residuals. The principal differences between the present study and a preceding study (Giovinetto and Zwally, 1997) are the compilation of a significa ntly larger a nd overall more representative sampling-site dataset, an assessment of regional departures from the general model, the introduction of a remotely sensed grid data subset and the production of a contoured di stribution based on it, as well as a di scussion of

Middle to late Holocene coastal evolution along the south coast of Upolu Island, Samoa

Abstract Stratigraphic surveys and sedimentological analyses of coastal sediments and reef cores along the south coast of Upolu Island, Samoa, reveal that during the middle Holocene this coast was characterised by barrier spits, open lagoons, and estuaries. These estuarine systems matured during the late Holocene, with progressive sedimentation and inlet closure, leading to the dominance of mangrove swamps in the past 1000 years. Contemporaneous with the transition of open estuaries to mangrove swamps was the aggradation and progradation of coastal plains. The coastal progradation since 700–1000 years BP is best explained by increased sediment availability and reduced incident wave energy at the shore resulting from the shallowing and subsequent cessation of reef crest accretion following the mid-Holocene sea-level highstand ca. ∼4500 yr BP. A small relative sea-level (RSL) lowering since 700–1000 years may have contributed to the positive sediment budget. This study highlights the need for island-wide coastal surveys to assess the relative roles of RSL, sediment budgets, and hydrodynamics on coastal evolution and stability. Differences in coastal evolution around Upolu Island may also be influenced by differential tectonic movements associated with late Holocene volcanism, coseismicity, and/or submarine landslides.

Glacio-lacustrine aragonite deposition, meltwater evolution and glacial history during isotope stage 3 at Radok Lake, Amery Oasis, northern Prince Charles Mountains, East Antarctica

Abstract The late Quaternary glacial history of the Amery Oasis, and Prince Charles Mountains is of significant interest because about 10% of the total modern Antarctic ice outflow is discharged via the adjacent Lambert Glacier system. A glacial thrust moraine sequence deposited along the northern shoreline of Radok Lake between 20–10 ka bp, overlies a layer of thin, aragonite crusts which provide important constraints on the glacial history of the Amery Oasis. The modern Radok Lake is fed by the terminal meltwaters of the alpine Battye Glacier. The aragonite crusts were deposited in shallow water of ancestral Radok Lake 53 ka bp, during the A3 warm event in Isotope Stage 3. Oxygen isotope (δ18O) analysis of the last glacial-age aragonite crusts indicates that they precipitated from freshwater with a δ18OSMOW composition of -36%, which is 8% more depleted than the present water (-28%) in Radok Lake. A regional oxygen isotope (δ18O) and elevation relationship for snow is used to determine the source of meltwater and glacial ice in Radok Lake during the A3 warm event. This relationship indicates that Radok Lake received meltwater from the confluence of both Battye Glacier ice and an expansion of grounded western Lambert Glacier ice in the Amery embayment.

Research targets 2000 years of climate‐induced sea level fluctuations

Sea level rise as a consequence of “greenhouse-induced” global warming has been a major focus of global change science for the last 2 decades. The principle approach has been to test climate-forced sea level models by comparing model results with regional or global averages of sea level rise based on multidecadal, and in a few cases, centennial tidegauge records, corrected for local crustal movements that in turn are based on millennialscale records of relative sea level change. The majority of the multi-decadal instrumental records are inherently noisy (±0.3 m) due to sub-decadal and decadal variability in ocean temperature, salinity fields,and circulation, any of which can affect density and hence local sea level. This variability is induced by atmospheric and oceanographic phenomena such as ENSO.

Effort explores 130 Million years of Antarctic paleoenvironment

Antarctic climate history has been dominated by events and turning points with causes that are poorly understood. To fill the gaps in our knowledges new effort is underway in the international geologic community to acquire and coordinate the circum-Antarctic geologic data needed to derive and model paleoenvironments of the past 130 m.y. The effort, which focuses principally on using shallow (<100 m) stratigraphic drilling and coring to acquire the geologic data, is being led by the Antarctic Offshore Stratigraphy Project (ANTOSTRAT), a group that works under the aegis of the Scientific Committee on Antarctic Research (SCAR). n nAbout 40 scientists from 12 countries met this past summer in Wellington, New Zealand, at an ANTOSTRAT meeting to discuss strategies for implementing the desired paleoenvironmental field and modeling studies. The meeting was held in conjunction with the 8th International Symposium on Antarctic Earth Sciences.