Author: admin

Microplankton from the Cape Lamb Member, López de Bertodano Formation (Upper Cretaceous), Cape Lamb, Vega Island

first_imgSamples from the lower Cape Lamb Member, López de Bertodano Formation, Cape Lamb, Vega Island, Antarctic Peninsula have yielded rich and diverse marine palynofloral assemblages. The overall character of the palynofloral assemblages indicate a latest Campanian–earliest Maastrichtian age. Four new dinoflagellate cyst species Canninginopsis ordospinosa sp. nov., Microdinium ? gymnosuturum sp. nov., Phelodinium exilicornutum sp. nov. and Operculodinium radiculatum sp. nov. are described. Certain key dinoflagellate cyst taxa such as Operculodinium radiculatum sp. nov., Manumiella n. sp. 3 and Isabelidinium cretaceum allow a correlation of the lower Cape Lamb Member with the upper palynomorph zone 1/lower zone 2 on nearby Seymour Island.last_img read more

Read More Microplankton from the Cape Lamb Member, López de Bertodano Formation (Upper Cretaceous), Cape Lamb, Vega Island

Antarctic Circumpolar Deep Water; a Quaternary paleoflow record from the northern Scotia Sea, South Atlantic Ocean

first_imgIn the northern Scotia Sea, the main pathway of Circumpolar Deep Water (CPDW) flows north to pass through a deep gap in the North Scotia Ridge before turning east into the Falkland Trough. A sediment drift has developed on the seabed since the early-middle Miocene, coincident with the opening of Drake Passage and the inception of deep-water flow. Seismic and acoustic surveys show that the drift covers an area of 10,500 km 2 and forms a broadly asymmetrical mound up to 800 m thick. There is a zone of sediment thinning along the northwestern margin, the result of accentuated CPDW flow around rough ocean floor topography. Small debris flows originating around the margins of the drift suggest localized instability and high sediment supply. Four cores 3-9 m long have been recovered from the crest and margins of the drift in water depths of 3900-4300 m. Biostratigraphy and chemostratigraphy reveal that the longest core extends down to oxygen isotope stage 10 (approx. 370 ka). The sediments are predominantly fine-grained contourites and diatom-rich hemipelagites, capped by sandy-silty contourites rich in the planktonic foraminifer Neogloboquadrina pachyderma. Grain-size analysis of the fine fraction, finer than 4 phi (63 mm), combined with radiocarbon (AMS) dating and magnetic susceptibility, provide an indication of relative CPDW strength over the last 18 ka. Shortly after the last glacial maximum (LGM), at approximately 17 ka, silt modes fluctuated from 5.5 phi to up to 6.25 phi; this increased current winnowing is indicative of an unstable CPDW, with stormier glacial benthic conditions producing sporadic, high-energy currents across the drift crest and flanks. At approximately 12,280 ka, an increase in sediment sorting is noted, indicative of a strong flow of CPDW over the drift crest, suggesting an unstable and fluctuating deep-water flow. During deglaciation and into the Holocene, at approximately 10 ka, CPDW flow stabilized, becoming less vigorous across the drift crest and flanks with silt modes from 6 phi to 5.5 phi accompanied by increased sorting of the sediments. The gross average sedimentation rate from the crest of the drift is 11.2 cm/ky compared to 2.3 cm/ky on the southeastern flank. The unsteadiness of CPDW during glacials compared to interglacial periods may be the result of stronger wind forcing and a northward shift in the Polar Front. Older CPDW flow records from the cores suggest variable and cyclic bottom-current flow corresponding to glacial-interglacial episodes. Modern CPDW flow across the crest of the drift averages 11.6 cm s (super -1) but with intermittent benthic storm activity resuspending the fines.last_img read more

Read More Antarctic Circumpolar Deep Water; a Quaternary paleoflow record from the northern Scotia Sea, South Atlantic Ocean

Fortuynia (Acari: Oribatida: Ameronothroidea) from the marine littoral of southern Africa

first_imgThree new taxa of the oribatid mite genus Fortuynia van der Hammen, 1960 (Ameronothroidea) were collected from the rocky shores and mangroves of southeastern Africa. These taxa, F. inhambanensis sp. nov., F. rotunda sp. nov. and F. elamellata micromorpha subsp. nov., are described and a key for the genus Fortuynia is presented.last_img

Read More Fortuynia (Acari: Oribatida: Ameronothroidea) from the marine littoral of southern Africa

Clade perseverance from mesozoic to present: a multidisciplinary approach to interpretation of pattern and process

first_imgTwo clades of marine bryozoans, cyclostomes and cheilostomes, exemplify the benefits of applying a multidisciplinary approach to the interpretation of long-term evolutionary patterns. The cyclostome bryozoans were dominant in the Mesozoic; since that era, they have decreased in absolute terms and the cheilostomes have come to exceed them in both abundance and diversity. Many studies of living assemblages of the encrusting members of these two clades indicate that cheilostomes are superior space competitors, but paleontological studies suggest that competition between the two taxa has not been escalating over geological time. Both clades occur throughout the world’s oceans and seas, and recent work in the geographical extremes has shown that the relative success of the clades varies markedly from place to place. In this study, the importance of differential patterns of recruitment and cumulative space occupation in the two clades was evaluated over four years and in two environments, one temperate and one polar. In both of these environments, peaks of recruitment and space occupation by the two clades were out of phase. The different strategies and outcomes of spatial competition are examined, largely using data from the literature. Only recently has it been realized that tied outcomes of competition are stable alternative results and not simply transitory phases. Many competitive encounters involving cyclostomes result in ties, implying that their strategy is based on persistence rather than dominance. When different indices and models are used to analyze competition data from the two clades, the interpretation varies markedly with methodology. The differences in patterns of recruitment, space occupation, and spatial competition have influenced both our understanding of how the two clades have persisted alongside each other and our perception of cheilostome superiority. Analysis of fluid dynamics has shown that small differences in the mechanical structure of typical members of each clade lead to fundamental differences in water movement. For animals that rely on water motion for transport of nutritional and excretory elements (suspension feeders), small changes in current velocity and direction can have a major impact. Preliminary chemical analysis of the excurrent stream leaving cheilostome colonies has shown it to be laden with excretory products, which can interfere and mix with a neighbor’s feeding currents. Clearly, spatial competition involves more than a simple mechanical “showdown.”.last_img read more

Read More Clade perseverance from mesozoic to present: a multidisciplinary approach to interpretation of pattern and process

Scotia Arc kinematics from GPS geodesy

first_imgGPS crustal velocity data from the Scotia and South Sandwich plates, transform azimuths, spreading data, and an updated earthquake slip vector catalog provide the first Scotia and South Sandwich plate Euler vector estimates not dependent on closure as the GPS data tie them to the global plate circuit. Neither the GPS data, which sample limited portions of the plates, nor the geologic data, which are not tied to the global spreading circuit, are sufficient individually to define the Euler vectors. As Scotia plate GPS measurements do not sample the stable plate interior, plate boundary deformation field modeling is necessary for Euler vector estimation. Our South America- Antarctic and Scotia- South Sandwich Euler pole estimates agree with previous estimates from either GPS or geologic data. Our South America- Scotia Euler vector, however, is significantly different and near the South America- Antarctic Euler vector producing an approximately coaxial motion of Scotia between South America and Antarctica.last_img read more

Read More Scotia Arc kinematics from GPS geodesy

Channelized ice melting in the ocean boundary layer beneath Pine Island Glacier, Antarctica

first_imgIce shelves play a key role in the mass balance of the Antarctic ice sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the ice shelf of the remote Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier shelf.last_img read more

Read More Channelized ice melting in the ocean boundary layer beneath Pine Island Glacier, Antarctica

The influence of the Amundsen–Bellingshausen Seas low on the climate of West Antarctica and its representation in coupled climate model simulations

first_imgIn contrast to earlier studies, the authors describe the climatological deep low pressure system that exists over the South Pacific sector of the Southern Ocean, referred to as the Amundsen–Bellingshausen Seas low (ABSL), in terms of its relative (rather than actual) central pressure by removing the background area-averaged mean sea level pressure (MSLP). Doing so removes much of the influence of large-scale variability across the ABSL sector region (e.g., due to the southern annular mode), allowing a clearer understanding of ABSL variability and its effect on the regional climate of West Antarctica. Using ECMWF Interim Re-Analysis (ERA-Interim) fields, the annual cycle of the relative central pressure of the ABSL for the period from 1979 to 2011 shows a minimum (maximum) during winter (summer), differing considerably from the earlier studies based on actual central pressure, which suggests a semiannual oscillation. The annual cycle of the longitudinal position of the ABSL is insensitive to the background pressure, and shows it shifting westward from 250° to 220°E between summer and winter, in agreement with earlier studies. The authors demonstrate that ABSL variability, and in particular its longitudinal position, play an important role in controlling the surface climate of West Antarctica and the surrounding ocean by quantifying its influence on key meteorological parameters. Examination of the ABSL annual cycle in 17 CMIP5 climate models run with historical forcing shows that the majority of them have definite biases, especially in terms of longitudinal position, and a correspondingly poor representation of West Antarctic climate.last_img read more

Read More The influence of the Amundsen–Bellingshausen Seas low on the climate of West Antarctica and its representation in coupled climate model simulations

IMF-driven change to the Antarctic tropospheric temperature due to the global atmospheric electric circuit

first_imgWe use National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data to investigate the Antarctic mean tropospheric temperature anomaly associated with changes in the dawn-dusk component By of the interplanetary magnetic field (IMF). We find that the mean tropospheric temperature anomaly for geographical latitudes ≤ −70° peaks at about 0.7 K and is statistically significant at the 5% level between air pressures of 1 000 and 500 hPa (∼0.1–5.6 km altitude above sea level) and for time lags with respect to the IMF of up to 7 days. The peak values of the air temperature anomaly occur at a greater time lag at 500 hPa (∼5.6 km) than at 1 000 – 600 hPa (∼0.1–4.2 km), which may indicate that the signature propagates vertically. The characteristics of prompt response and possible vertical propagation within the troposphere have previously been seen in the correlation between the IMF and high-latitude air pressure anomalies, known as the Mansurov effect, at higher statistical significances (1%). For time lags between the IMF and the troposphere of 0–6 days and altitudes between 1 000 and 700 hPa (∼0.1–3 km), the relationship between highly statistically significant (1% level) geopotential height anomaly values and the corresponding air temperature anomaly values is consistent with the standard lapse rate in atmospheric temperature. We conclude that we have identified the temperature signature of the Mansurov effect in the Antarctic troposphere. Since these tropospheric anomalies have been associated with By-driven anomalies in the electric potential of the ionosphere, we further conclude that they are caused by IMF-induced changes to the global atmospheric electric circuit (GEC). Our results support the view that variations in the ionospheric potential act on the troposphere, possibly via the action of consequent variations in the downwards current of the GEC on tropospheric clouds.last_img read more

Read More IMF-driven change to the Antarctic tropospheric temperature due to the global atmospheric electric circuit

Ground‐based observations of VLF waves as a proxy for satellite observations: Development of models including the influence of solar illumination and geomagnetic disturbance levels

first_imgGround VLF observations have often been used to infer VLF activity in the magnetosphere, however, they are not an unbiased measure of activity at satellite altitudes due to transionospheric absorption and subionospheric attenuation. We propose several empirical models that control for these effects. VLF power spectral density (PSD) from the VLF/ELF Logger Experiment (VELOX, L=4.6, Halley, Antarctica) is used to predict DEMETER low Earth orbit VLF PSD. Validation correlations of these models are as high as 0.764, thus ground VLF receivers spaced around the Earth could provide complete coverage of outer radiation belt lower band chorus over the latitudinal limits of this model (±45‐75°). Correlations of four frequency bands (centered at 0.5 kHz, 1.0 kHz, 2.0 kHz, and 4.25 kHz) are compared. The simple linear correlation between ground and satellite VLF PSD in the 1.0 kHz channel was 0.606 (at dawn). A cubic model resulted in higher correlation (0.638). VLF penetration to the ground is reduced by ionospheric absorption during solar illumination and by disruption of ducting field lines during disturbed conditions. Subionospheric attenuation also reduces VLF observations from distant field lines. Addition of these covariates improved predictions. Both solar illumination and disturbed conditions reduced ground observation of VLF PSD, with higher power waves penetrating to the ground proportionately less than lower power waves. The effect of illumination in reducing wave penetration was more pronounced at higher frequency (4.25 kHz), with the effect at a mid‐range frequency (2.0 kHz) falling between these two extremes.last_img read more

Read More Ground‐based observations of VLF waves as a proxy for satellite observations: Development of models including the influence of solar illumination and geomagnetic disturbance levels

Antarctic Futures: An Assessment of Climate-Driven Changes in Ecosystem Structure, Function, and Service Provisioning in the Southern Ocean

first_imgIn this article, we analyze the impacts of climate change on Antarctic marine ecosystems. Observations demonstrate large-scale changes in the physical variables and circulation of the Southern Ocean driven by warming, stratospheric ozone depletion, and a positive Southern Annular Mode. Alterations in the physical environment are driving change through all levels of Antarctic marine food webs, which differ regionally. The distributions of key species, such as Antarctic krill, are also changing. Differential responses among predators reflect differences in species ecology. The impacts of climate change on Antarctic biodiversity will likely vary for different communities and depend on species range. Coastal communities and those of sub-Antarctic islands, especially range-restricted endemic communities, will likely suffer the greatest negative consequences of climate change. Simultaneously, ecosystem services in the Southern Ocean will likely increase. Such decoupling of ecosystem services and endemic species will require consideration in the management of human activities such as fishing in Antarctic marine ecosystems.last_img read more

Read More Antarctic Futures: An Assessment of Climate-Driven Changes in Ecosystem Structure, Function, and Service Provisioning in the Southern Ocean