High-latitude dust deposition in snow on the glaciers of James Ross Island,Antarctica

High-latitude dust (HLD) depositions on four glaciers of James Ross Island (the Ulu Peninsula) were analysed. The deposition rate on the selected glaciers varies from 11.8 to 64.0 g m⁻², which is one order of magnitude higher compared to the glaciers in Antarctica or elsewhere in the world. A strong negative relationship between the sediment amount and altitude of a sampling site was found. This is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer. General southerly and south-westerly wind directions over the Ulu Peninsula – with exceptions based on local terrain configuration – help to explain the significantly lower level of sediment deposition on San Jose Glacier and the high level on Triangular Glacier. X-ray fluorescence (XRF) spectrophotometry was used to estimate the relative proportions of the main and trace (lithophile) elements in the sediment samples. Both the sediment amount and the XRF results are analysed in a depth profile at each locality and compared among the glaciers, suggesting long-range transport of fine mineral material from outside James Ross Island. The distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the Ulu Peninsula. © 2020 John Wiley & Sons, Ltd.     

Ultrabasic inclusion from the basalts of the Hut Point area,Ross Island,Antarctica

The basaltic rocks of the Hut Point area contain a diverse suite of inclusions. The xenolithic nature of many sedimentary, metamorphic and igneous inclusion types is clearly displayed, but previous studies have left considerable doubt as to whether the ultrabasic inclusions are noncognate xenoliths, and possible relicts from the mantle brought to the surface in a magma originating in this zone; or rather of cognate and/or cumulative origin. Olivine grains in the dunite and enstatite bearing peridotite inclusions commonly display undulose extinction and strain bands (translation laminae), and preferred indicatrix orientations expressed as B γ girdles. Enstatite frequently contains clinopyroxene exsolution laminae, and many grains are deformed and/or disrupted by shear zones. Weak B γ olivine fabrics have also been detected in the titanaugite peridotites and pyroxenites, but no evidence of post-crystallization deformation was detected. Titanaugite also occurs as phenocrysts (xenocrysts?) and in the groundmass of the host basalt chemical and optical data suggest that the titanaugite grains in the basalt and the inclusions are genetically related. These preliminary findings suggest that the titanaugite bearing inclusions may be of cognate origin, and that the dunite and enstatite bearing peridotite fragments are more likely noncognate xenoliths. Field and laboratory studies of this problem are continuing as supported by a grant from the National Science Foundation.     

PCBs and chlorinated pesticides in the atmosphere and aquatic organisms of Ross Island, Antarctica

PCBs, p,p′-DDT, p,p′-DDE and lindane (γ-hexachlorocyclohexane) were monitored in the lower atmosphere of Ross Island, in Antarctica for 2 yr. Geometrical means were 15.2 pg m⁻³ for PCBs, 2.0 pg m⁻³ for p,p′-DDT, 1.0 pg m⁻³ for p,p′-DDE and 25.8 pg m⁻³ for lindane. Atmospheric levels of lindane were positively correlated with temperature, and a significant difference was found between spring-summer and summer-winter concentrations. No season related differences were found for the other chlorinated hydrocarbons, possibly owing to their lower vapour pressure and the cold climate. Periods with increased atmospheric levels of PCBs and DDT compounds were recorded. Lindane, p,p′-DDE and PCBs were present in fish and zooplankton sampled close to Ross Island. Pollutant levels in the zooplankton (on an extractable fat basis) were highest during the Antarctic spring and autumn and were inversely correlated to their fat content.     

Seismicity in the generalized vicinity of large earthquakes

Earthquake catalogs are used to construct a generalized space-time vicinity of large earthquakes and to investigate the seismicity behavior in such areas. We investigate the character of the inverse cascade (seismicity rate increasing toward the time of the main shock) and of the aftershocks, as well as the lower seismicity increase relevant to the larger vicinity of the main shock. It is shown that the inverse and aftershock cascades are accompanied by several anomalies indicating the development of a precursory strength decrease in this space-time volume; this consists in decreased apparent stresses, an increased relative contribution of low frequency oscillations into the earthquake spectrum, and an increased correlation (homogeneity) of stress and strain. We emphasize the special significance of anomalies that also characterize the physical nature of the ongoing process, in addition to the existence of a strength decrease. An example of such an anomaly is provided     

Analysis of the Temporal Occurrence of Seismicity at Deception Island (Antarctica). A Nonlinear Approach

—Deception Island is characterized by small magnitude local events with constant energy flux and very low stress drop. To obtain information about its origin, an interevent time series of 546 events, corresponding to an observational period of two month, has been analyzed. From a statistical point of view, data satisfies a Weibull distribution and presents clustering. A rescaled range analysis reveals that data are not independent, i.e. have memory, and the correlation dimension saturates at 2.2; as a consequence, the system can be modeled as a nonlinear iterative equation with three degrees of freedom that presents chaotic behavior. Taking into account that the average interevent time is of the order of 130 minutes, too short to be only due to tectonic activity, the above results indicate that some other mechanism may coexist with the regional tectonic one. According to several geological and geophysical observations, we suggest that most of the local events may be originated by pressure waves generated by a sudden change of phase, of sea and fresh water infiltrated into the main fractures and faults and also from shallow and confined water-saturated layers.     

Depositional history of artificial radionuclides in the Ross Ice Shelf,Antarctica

The annual fluxes of artificial radionuclides (²³⁸Pu,^239+240Pu,²⁴¹Am,¹³⁷Cs,⁹⁰Sr and³H) from the atmosphere to the Ross Ice Shelf in Antarctica were determined from measurements in strata dated by²¹⁰Pb. Recognizable sources include the U.S. tests (Mike-Ivy and Castle Hill) in the early 1950s, the U.S.S.R. tests of the early 1960s, the SNAP-9A burnup of 1964 and the French and Chinese tests in the late 1960s and 1970s. There are several problems still awaiting resolution: the differences in atmospheric chemistries of fission products and of transuranics produced in weapons tests and the anomalous fluxes of²³⁸Pu to the ice shelf which do not appear to reflect a one-year stratospheric residence. There is no evidence for a smearing of the fallout record as a consequence of diffusion of these radionuclides in the glacial column.     

Seismicity and stress state in the South China Sea, Indochina and their vicinity

The distribution of earthquakes from 1973 to 1982 in the South China Sea, Indochina and their vicinity was studied using the data from I. S. C. It was found that the earthquakes are mainly concentrated along the boundaries of plates. Beside, some of shallow eartqhuakes are distributed in west part of Burma and the boundary between Burma and China, a few of earthquakes occurred in South China Sea. The features of Benioff zone along the boundaries between India plate, Philippine Sea plate and Eurasia plate were studied. The plate do not coupled well under the Java trench and the Philippine trench. The subducted India plate under Burmese range, Andaman—Nicobar arc moves NNE. The fault plane solutions of earthquakes were studied using the first motions of P wave. The stress state on subduction zones and within the area were deduced from the fault plane solutions and the fault movement. It was found that the direction of principal compression axis of stress is in the NNE in west part of Burma, in S—N in south and middle part of Bruma and Thailand, and in NNE or S—N in the South China Sea. It was also found that the stress state has close relation with the interaction of plates. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 129–137, 1991.     

Seismicity,earthquake mechanisms and tectonics along the Himalayan mountain range and vicinity

The historical as well as recent seismicity data and the focal mechanism solutions for 48 earthquakes determined from the observations of world-wide standardized stations network (WWSSN) records, were used to investigate the tectonics of the Himalayan mountain system and vicinity. Seismicity maps of the region showing large earthquakes (magnitude 7.0 and above, and damaging earthquakes that caused fatalities) from the earliest time through 1976, and instrumentally located earthquakes for the period January 1963–March 1974 are presented. Eleven of these earthquakes are estimated to be of magnitude 8.0 and above. The earthquake epicenters generally follow the trend of the mountains with greatest concentrations of seismic activity occurring along the Hindu Kush and Pamir mountain ranges, and near the Quetta, Kashmir and Assam syntaxes. Throughout Tibet, however, the distribution of epicenters is rather irregular and no clear trends are apparent. Two aseismic lineaments, one west of the Sulaiman Range and the other in the Assam Valley, are identified. Also, seismic activity in the vicinity of the Counter Thrust (Indus-Tsangpo suture zone) is rather small. Based on the identification of these aseismic lineaments and from a consideration of the geometry and kinematics of the continental collision model, a hypothesis for the origin of the Himalayan syntaxes is presented.Focal mechanism solutions confirm northward underthrusting of the Indian Plate along the Main Boundary Thrust and Main Central Thrust system, and eastward underthrusting along the Burmese Arc. Fault-plane solutions indicate left-lateral motion along the Kirthar-Sulaiman Range, right-lateral motion along the Karakoram Fault, left-lateral motion along the eastern extremity of the Himalayan flank of the Assam syntaxis, and right-lateral motion along the northern part of the Naga Hill flank of the syntaxis. These observations are in agreement with the expected sense of lateral (parallel to the collision boundary) mass movement for the continental collision model. Focal mechanism solutions for three earthquakes in east Afghanistan show NW-SE compression. A near-vertical orientation of the axes of tension in the solutions for two earthquakes in the Hindu Kush region is consistent with the sinking of a remnant slab of oceanic lithospere. Normal fault-plane solutions showing NW-SE extension for two events near Gatok, Tibet, and for the recent Kinnaur earthquake are interpreted to indicate a possible subsurface northern continuation of the Aravalli Range of Peninsular India, and its involvement in the tectonic framework of the region. Focal mechanism solutions of three earthquakes near the southern edge of the Shillong Plateau suggest block uplift of the plateau as a horst along the Dauki Fault. The solution for one earthquake near the Yunnan Graben shows NE-SW extension.     

Long-range detection of hydroacoustic signals from large icebergs in the Ross Sea, Antarctica

Hydroacoustic signals detected in late 2000 by seismic stations in Polynesia are shown to originate from huge icebergs which at the time were drifting in the Ross Sea after calving off the Ross Ice Shelf. The signals present a broad variety of spectral characteristics, most of them featuring prominent eigenfrequencies in the 4-7 Hz range, often complemented by overtones. Most epicenters, obtained by combining observations of distant hydroacoustic and regional seismic records, follow the spatio-temporal evolution of the drift of iceberg B-15B. Most of the signals are generated during a 36-day time window when it is speculated that B-15B collided with smaller icebergs or was scraping the ocean floor on the shallow continental shelf. We speculate on the possible physical nature of the resonator generating the signals, which could correspond to an elastic mode of the iceberg, or to the oscillation of fluid-filled cracks in the ice.     

Seismicity in the vicinity of the India-Burma border: Evidence for a sinking lithosphere

The vicinity of the India-Burma border region is among a few intracontinental regions in the world where intermediate-focus earthquakes occur. The recent installation of new seismic stations has improved the detection and location capabilities for earthquakes in this region. Three seismic stations belonging to this new array are located over the zone of intermediate-focus earthquakes. Analysis of recently acquired seismic data reveals a well-defined near-vertical zone of earthquake foci extending to 200 km beneath the Arakan-Yoma fold belt. On the basis of seismic, gravity and other geological data, it is suggested that this zone of earthquakes is associated with remnants of the already subducted, but not totally assimilated, Tethys oceanic lithosphere below the Burmese plate.     

岛弧构造的垂直形变场与水平位移场及其构造运动和地震活动特征

本文根据水平构造应力作用，推导了弧形构造的理论垂直形变场、水平位移场和应力场，进而对全球性的岛弧构造带在构造运动、地震活动和震源机制等方面的特征给出了新的解释；提出岛弧等弧形构造主要是在弧形构造位移场、应力场作用下逐渐形成的，而大洋板块的俯冲作用是次要的。     

Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea,Antarctica, to the atmospheric forcing

Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of atmospheric forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different atmospheric forcing sets. A first forcing (DFS3) is based on ERA40 atmospheric surface variables and satellite products. A second forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two forcing sets shows that the MAR forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR forcing and the properties of HSSW are notably improved as compared to the DFS3 forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s⁻¹).     

The Vertical Deformation and Horizontal Displacement Fields,Movement, and Seismicity of the Island Arc Tectonics

In this work,the vertical deformation,horizontal displacement,and stress fields of arcuate tectonics are theoretically derived from the horizontal tectonic stress; then the characteristics of tectonic movement,seismicity,and focal mechanism of arcuate tectonics of the entire world are explained.It is pointed out that the island arc and other arcuate tectonics are gradually developed under the displacement and stress fields of the arcuate tectonics and that the under-thrusting action of the ocean plate is secondary.The distance formulas between the volcanic arc and the trench are suggested and also that theoretical results are consistent with actual data.     

The P-wave velocity structure of Deception Island,Antarctica, from two-dimensional seismic tomography

Deception Island is a volcanic island with a flooded caldera that has a complex geological setting in Bransfield Strait, Antarctica. We use P-wave arrivals recorded on land and seafloor seismometers from airgun shots within the caldera and around the island to invert for the P-wave velocity structure along two orthogonal profiles. The results show that there is a sharp increase in velocity to the north of the caldera which coincides with a regional normal fault that defines the northwestern boundary of the Bransfield Strait backarc basin. There is a low-velocity region beneath the caldera extending from the seafloor to > 4 km depth with a maximum negative anomaly of 1 km/s. Refracted arrivals are consistent with a 1.2-km-thick layer of low-velocity sediments and pyroclastites infilling the caldera. Synthetic inversions show that this layer accounts for only a small portion of the velocity anomaly, implying that there is a significant region of low velocities at greater depths. Further synthetic inversions and melt fraction calculations are consistent with, but do not require, the presence of an extensive magma chamber beneath the caldera that extends downwards from ≤ 2 km depth.     

Mercury in the ecosystem of Admiralty Bay,King George Island,Antarctica: Occurrence and trophic distribution

Mercury (Hg) can reach the environment through natural and human-related sources, threatening ecosystems all over the planet due to its well known deleterious effects. Therefore, Antarctic trophic webs, despite being relatively isolated, are not exempt of its influence. To evaluate Hg concentrations in an Antarctic ecosystem, different tissues from 2 species of invertebrates, 2 of fish, 8 of birds, 4 of pinnipeds and at least 5 of vegetation were investigated (n = 176). For animals, values ranged from 0.018 to 48.7 μg g^? 1 dw (whole Antarctic krill and Antarctic Fur Seal liver). They were generally correlated to trophic position (assessed by δ¹⁵N and δ¹³C) but also to cephalopods and myctophids consumption. For vegetation, values ranged from 0.014 to 0.227 μg g^? 1 dw (Colobanthus quitensis and an unidentified lichen), with lichens presenting significantly higher values than mosses, likely due to year-round exposure and absorption of animal derived organic matter, as hypothesized by literature.     

Seasonal copula models for the analysis of glacier discharge at King George Island,Antarctica

Modelling glacier discharge is an important issue in hydrology and climate research. Glaciers represent a fundamental water resource when melting of ice and snow contributes to runoff. Glaciers are also studied as natural global warming sensors. GLACKMA association has implemented one of their Pilot Experimental Catchment areas at the King George Island in the Antarctica which records values of the liquid discharge from Collins glacier. In this paper, we propose the use of time-varying copula models for analyzing the relationship between air temperature and glacier discharge, which is clearly non constant and non linear through time. A seasonal copula model is defined where both the marginal and copula parameters vary periodically along time following a seasonal dynamic. Full Bayesian inference is performed such that the marginal and copula parameters are estimated in a one single step, in contrast with the usual two-step approach. Bayesian prediction and model selection is also carried out for the proposed model such that Bayesian credible intervals can be obtained for the conditional glacier discharge given a value of the temperature at any given time point. The proposed methodology is illustrated using the GLACKMA real data where there is, in addition, a hydrological year of missing discharge data which were not possible to measure accurately due to problems in the sounding.     

Sources and transport of As,Cu, Cd and Pb in the environmental compartments of Deception Island,Antarctica

Sources and transport processes of As, Cu, Cd and Pb were studied in different environmental compartments of Deception Island, an active volcano in the South Shetland Islands, Antarctica. Element concentrations in fresh water samples are consistent with the lowest values reported elsewhere in Antarctica. Interestingly, higher concentration values of As were found in samples collected in or near spring water courses and its transport may be related with processes of lixiviation in underground waters. While in saline waters Cu and Pb had important punctual sources, concentration values for Cd were consistently high pointing to the existence of a natural and diffuse source possibly related with the hydrothermal activity. The high Si/Al ratio, low carbon content, and a non-significant anthropogenic heavy metal input may explain the surprisingly homogeneous heavy metal content found in sediment samples.     

Persistent organic pollutants and stable isotopes in pinnipeds from King George Island,Antarctica

In the present work, fat, skin, liver and muscle samples from Leptonychotes weddellii (Weddell seal, n = 2 individuals), Lobodon carcinophagus (crabeater seal, n = 2), Arctocephalus gazella (Antarctic fur seal, n = 3) and Mirounga leonina (southern elephant seal, n = 1) were collected from King George Island, Antarctica, and analysed for POPs (PCBs, organochlorine pesticides and PBDEs) and stable isotopes (δ¹³C and δ¹⁵N in all tissues but fat). PBDEs could be found in only one sample (L. weddellii fat). Generally, PCBs (from 74 to 523 ng g⁻¹ lw), DDTs (from 14 to 168 ng g⁻¹ lw) and chlordanes (from 9 to 78 ng g⁻¹ lw) were the prevailing compounds. Results showed a clear stratification in accordance with ecological data. Nonetheless, stable isotope analyses provide a deeper insight into fluctuations due to migrations and nutritional stress. Correlation between δ¹⁵N and pollutants suggests, to some degree, a considerable ability to metabolize and/or excrete the majority of them.     

Arsenic and trace metal contents in sediment profiles from the Admiralty Bay, King George Island, Antarctica

Admiralty Bay (Antarctica) hosts three scientific stations (Ferraz, Arctowski and Macchu Picchu), which require the use of fossil fuel as an energy source. Fossil fuels are also considered the main source of pollution in the area, representing important inputs of major pollutants (organic compounds) and trace metals and metalloids of environmental interest. Accordingly, this work presents the results of As, Cd, Cr, Cu, Ni, Pb and Zn in sediment profiles from Admiralty Bay. The sediment results from Ferraz station were slightly higher than the other sampling sites. The highest contents were observed for Cu and Zn (from 44 to 89 mg kg⁻¹). Otherwise, by using enrichment factors and geochronology analysis, the most relevant enrichment was observed for As in the samples collected close to the Ferraz station, indicating that increasing As content may be associated with the activities associated with this site.