Jefferson Cardia Simões

A Review of Antarctic Surface Snow Isotopic Composition: Observations, Atmospheric Circulation, and Isotopic Modeling*

A database of surface Antarctic snow isotopic composition is constructed using available measurements, with an estimate of data quality and local variability. Although more than 1000 locations are documented, the spatial coverage remains uneven with a majority of sites located in specific areas of East Antarctica. The database is used to analyze the spatial variations in snow isotopic composition with respect to geographical characteristics (elevation, distance to the coast) and climatic features (temperature, accumulation) and with a focus on deuterium excess. The capacity of theoretical isotopic, regional, and general circulation atmospheric models (including “isotopic” models) to reproduce the observed features and assess the role of moisture advection in spatial deuterium excess fluctuations is analyzed.

20th-Century doubling in dust archived in an Antarctic Peninsula ice core parallels climate change and desertification in South America

Crustal dust in the atmosphere impacts Earths radiative forcing directly by modifying the radiation budget and affecting cloud nucleation and optical properties, and indirectly through ocean fertilization, which alters carbon sequestration. Increased dust in the atmosphere has been linked to decreased global air temperature in past ice core studies of glacial to interglacial transitions. We present a continuous ice core record of aluminum deposition during recent centuries in the northern Antarctic Peninsula, the most rapidly warming region of the Southern Hemisphere; such a record has not been reported previously. This record shows that aluminosilicate dust deposition more than doubled during the 20th century, coincident with the ≈1°C Southern Hemisphere warming: a pattern in parallel with increasing air temperatures, decreasing relative humidity, and widespread desertification in Patagonia and northern Argentina. These results have far-reaching implications for understanding the forces driving dust generation and impacts of changing dust levels on climate both in the recent past and future.

A new Andean deep ice core from Nevado Illimani (6350 m), Bolivia

Abstract A new ice core record from the Nevado Illimani (16°S), Bolivia, covers approximately the last 18 000 years BP. A comparison with two published ice records, from Sajama (18°S), Bolivia [Thompson et al., Science 282 (1998) 1858–1864] and Huascaran (9°S), Peru [Thompson et al., Science 269 (1996) 46–50], documents a regionally coherent transition from glacial to modern climate conditions in South America north of 20°S. The strong resemblance between the Illimani and Huascaran water isotope records and their differences from the Sajama record, in particular during the period from 9000 years BP to 14 000 years BP, suggest that local water recycling or local circulation changes played a major role for Sajama. We interpret the common Illimani/Huascaran water isotope history in terms of a common change from wetter/cooler conditions during glacial times to drier/warmer conditions in the Early Holocene.

Snow Chemistry Across Antarctica

Abstract An updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http://www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized.

The International Trans-Antarctic Scientific Expedition (ITASE): an overview

Abstract From its original formulation in 1990 the International Trans-Antarctic Scientific Expedition (ITASE) has had as its primary aim the collection and interpretation of a continent-wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations. ITASE offers the ground-based opportunities of traditional-style traverse travel coupled with the modern technology of GPS, crevasse detecting radar, satellite communications and multidisciplinary research. By operating predominantly in the mode of an oversnow traverse, ITASE offers scientists the opportunity to experience the dynamic range of the Antarctic environment. ITASE also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps, without the cost of the former or the lack of mobility of the latter. More importantly, the combination of disciplines represented by ITASE provides a unique, multidimensional (space and time) view of the ice sheet and its history. ITASE has now collected >20 000km of snow radar, recovered more than 240 firn/ice cores (total length 7000 m), remotely penetrated to ~4000m into the ice sheet, and sampled the atmosphere to heights of >20 km.

An improved topographic database for King George Island: compilation, application and outlook

A new topographic database for King George Island, one of the most visited areas in Antarctica, is presented. Data from differential GPS surveys, gained during the summers 1997/98 and 1999/2000, were combined with up to date coastlines from a SPOT satellite image mosaic, and topographic information from maps as well as from the Antarctic Digital Database. A digital terrain model (DTM) was generated using ARC/INFO GIS. From contour lines derived from the DTM and the satellite image mosaic a satellite image map was assembled. Extensive information on data accuracy, the database as well as on the criteria applied to select place names is given in the multilingual map. A lack of accurate topographic information in the eastern part of the island was identified. It was concluded that additional topographic surveying or radar interferometry should be conducted to improve the data quality in this area. In three case studies, the potential applications of the improved topographic database are demonstrated. The first two examples comprise the verification of glacier velocities and the study of glacier retreat from the various input data-sets as well as the use of the DTM for climatological modelling. The last case study focuses on the use of the new digital database as a basic GIS (Geographic Information System) layer for environmental monitoring and management on King George Island.

Geometry and thermal regime of the King George Island ice cap, Antarctica, from GPR and GPS

Abstract King George Island is the largest of the South Shetland Islands, close to the tip of the Antarctic Peninsula. The annual mean temperature on the island has increased by 1°C during the past three decades, and the ice cap that covers the majority of the island is sensitive to climatic change. We present data from two field campaigns (1997 and 2007): 700 km of global positioning system (GPS) and ground-penetrating radar (GPR) profiles were collected on Arctowski Icefield and on the adjacent central part. The data were analysed to determine the surface and bed topography and the thermal regime of the ice. Average ice thickness is 250 m and maximum thickness is 420 m. The GPR profiles show isochrones throughout the ice cap which depict the uparching of Raymond bumps beneath or close to the ice divides. A water table from percolation of meltwater in the snowpack shows the firn-ice boundary at ∼ 3 5 m depth. The firn layer may be temperate due to the release of latent heat. In the area below 400ma.s.l., backscatter by water inclusions is abundant for ice depths below the water table. We interpret this as evidence for temperate ice. Scatter decreases significantly above 400 m. Ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations.

Evidence of glacial flour in the deepest 89 m of the Vostok ice core

The 3623 m long Vostok ice core is divided into two main parts: (1) from the surface to a depth of 3310 m, the ice layers are undisturbed and may be used to reconstruct the climatic record over the past 420 kyr; (2) from 3538 m to the bottom, the core is made up of accreted ice formed by freezing of the lake. In between, the glacier ice is disturbed by ice dynamics, as shown, for example, by inclined volcanic-ash layers. Microparticle concentrations and distributions as well as ionic and isotopic content were used to subdivide this third section. The identification of layers with bedrock material provides clues as to the entrainment processes at sub-freezing temperatures. Dust concentration and size distribution as well as ionic content are comparable with values found in ice of glacial and interglacial periods. Below 3450 m depth, however, the mode of the volume size distribution clearly shifts from 2.1 μm to 3.4 μm in diameter. Particles as large as 30 μm in diameter are observed and cannot have an aeolian origin. From microscopic observations, we suggest that they originate from the bedrock and represent glacial flour entrained in a shear layer up to 89 m from the glacier sole. This process most likely occurred when the ice sheet was grounded before flowing over the lake.

Transport of crustal microparticles from Chilean Patagonia to the Antarctic Peninsula by SEM-EDS analysis

The individual elemental composition of insoluble airborne particulates found in King George Island (KGI), Antarctic Peninsula (atmosphere, snow, firn and ice deposits) and in the atmosphere of Chilean Patagonia by SEM-EDS analysis identify probable sources and transport mechanisms for the atmospheric aerosols observed in these regions. Insoluble airborne particulates found in the snow, firn and ice in a core from Lange Glacier (KGI) call for significant crustal influence, mainly associated with aluminium potassium, aluminium calcium and magnesium iron silicates together with other aluminium silicates of calcium and magnesium, among rare others containing Ti, Ni and Cr. Our study suggests that 95% of the bulk mode insoluble particulates deposited in Lange Glacier can be explained by atmospheric transport from Chilean Patagonia. Cyclonic systems passing between southernmost South America and the Antarctic Peninsula are the most probable atmospheric transport mechanism, tracked by measurements of 222Rn and Si.

Distinct composition signatures of archaeal and bacterial phylotypes in the Wanda Glacier forefield, Antarctic Peninsula.

Several studies have shown that microbial communities in Antarctic environments are highly diverse. However, considering that the Antarctic Peninsula is among the regions with the fastest warming rates, and that regional climate change has been linked to an increase in the mean rate of glacier retreat, the microbial diversity in Antarctic soil is still poorly understood. In this study, we analysed more than 40 000 sequences of the V5-V6 hypervariable region of the 16S rRNA gene obtained by 454 pyrosequencing from four soil samples from the Wanda Glacier forefield, King George Island, Antarctic Peninsula. Phylotype diversity and richness were surprisingly high, and taxonomic assignment of sequences revealed that communities are dominated by Proteobacteria, Bacteroidetes and Euryarchaeota, with a high frequency of archaeal and bacterial phylotypes unclassified at the genus level and without cultured representative strains, representing a distinct microbial community signature. Several phylotypes were related to marine microorganisms, indicating the importance of the marine environment as a source of colonizers for this recently deglaciated environment. Finally, dominant phylotypes were related to different microorganisms possessing a large array of metabolic strategies, indicating that early successional communities in Antarctic glacier forefield can be also functionally diverse.