Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica

first_imgResults are presented from an isopycnic coordinate model of ocean circulation in the Amundsen Sea, focusing on the delivery of Circumpolar Deep Water (CDW) to the inner continental shelf around Pine Island Bay. The warmest waters to reach this region are channeled through a submarine trough, accessed via bathymetric irregularities along the shelf break. Temporal variability in the influx of CDW is related to regional wind forcing. Easterly winds over the shelf edge change to westerlies when the Amundsen Sea Low migrates west and south in winter/spring. This drives seasonal on-shelf flow, while inter-annual changes in the wind forcing lead to inflow variability on a decadal timescale. A modelled period of warming following low CDW influx in the late 1980’s and early 1990’s coincides with a period of observed thinning and acceleration of Pine Island Glacier.last_img read more

Soil trampling in an Antarctic Specially Protected Area: tools to assess levels of human impact

first_imgResearch in extremely delicate environments must be sensitive to the need to minimize impacts caused simply through the presence of research personnel. This study investigates the effectiveness of current advice relating to travel on foot over Antarctic vegetation-free soils. These are based on the concentration of impacts through the creation of properly signed and identified paths. In order to address these impacts, we quantified three factors – resistance to compression, bulk density and free-living terrestrial arthropod abundance – in areas of human activity over five summer field seasons at the Byers Peninsula (Livingston Island, South Shetland Islands). Studies included instances of both experimentally controlled use and natural non-controlled situations. The data demonstrate that a minimum human presence is sufficient to alter both physical and biological characteristics of Byers Peninsula soils, although at the lowest levels of human activity this difference was not significant in comparison with adjacent undisturbed control areas. On the other hand, a limited resilience of physical properties was observed in Antarctic soils, thus it is crucial not to exceed the soil’s natural recovery capability.last_img read more

The reliability of Antarctic tropospheric pressure and temperature in the latest global reanalyses

first_imgIn this study, surface and radiosonde data from staffed Antarctic observation stations are compared tooutput from five reanalyses [Climate Forecast System Reanalysis (CFSR), 40-yr ECMWF Re-Analysis(ERA-40), ECMWF Interim Re-Analysis (ERA-Interim), Japanese 25-year Reanalysis (JRA-25), and Modern Era Retrospective-Analysis for Research and Applications (MERRA)] over three decades spanning 1979–2008. Bias and year-to-year correlation between the reanalyses and observations are assessed for four variables: mean sea level pressure (MSLP), near-surface air temperature (Ts), 500-hPa geopotential height (H500), and 500-hPa temperature (T500).It was found that CFSR andMERRAare of a sufficiently high resolution for the height of the orography tobe accurately reproduced at coastal observation stations. Progressively larger negative Ts biases at thesecoastal stations are apparent for reanalyses in order of decreasing resolution. However, orography height biascannot explain large winter warm biases in CFSR, JRA-25, andMERRA(11.18, 10.28, and 7.98C, respectively)at Amundsen–Scott and Vostok, which have been linked to problems with representing the surface energybalance. Linear trends in the annual-mean T500 andH500 averaged over Antarctica as a whole were found to be mostreliable in CFSR, ERA-Interim, and MERRA, none of which show significant trends over the period 1979–2008. In contrast JRA-25 shows significant negative trends over 1979–2008 and ERA-40 gives significantpositive trends during the 1980s (evident in both T500 andH500). Comparison to observations indicates that thepositive trend in ERA-40 is spurious. At the smaller spatial scale of individual stations all five reanalyses have some spurious trends. However, ERA-Interim was found to be the most reliable for MSLP andH500 trends atstation locations.last_img read more

Subduction-modified oceanic crust mixed with a depleted mantle reservoir in the sources of the Karoo continental flood basalt province

first_imgThe great majority of continental flood basalts (CFBs) have a marked lithospheric geochemical signature, suggesting derivation from the continental lithosphere, or contamination by it. Here we present new Pb and Os isotopic data and review previously published major element, trace element, mineral chemical, and Sr and Nd isotopic data for geochemically unusual mafic and ultramafic dikes located in the Antarctic segment (Ahlmannryggen, western Dronning Maud Land) of the Karoo CFB province. Some of the dikes show evidence of minor contamination with continental crust, but the least contaminated dikes exhibit depleted mantle – like initial εNd (+9) and 187Os/188Os (0.1244–0.1251) at 180 Ma. In contrast, their initial Sr and Pb isotopic compositions (87Sr/86Sr = 0.7035–0.7062, 206Pb/204Pb = 18.2–18.4, 207Pb/204Pb = 15.49–15.52, 208Pb/204Pb = 37.7–37.9 at 180 Ma) are more enriched than expected for depleted mantle, and the major element and mineral chemical evidence indicate contribution from (recycled) pyroxenite sources. Our Sr, Nd, Pb, and Os isotopic and trace element modeling indicate mixed peridotite–pyroxenite sources that contain ∼10–30% of seawater-altered and subduction-modified MORB with a recycling age of less than 1.0 Ga entrained in a depleted Os-rich peridotite matrix. Such a source would explain the unusual combination of elevated initial 87Sr/86Sr and Pb isotopic ratios and relative depletion in LILE, U, Th, Pb and LREE, high initial εNd, and low initial 187Os/188Os. Although the sources of the dikes probably did not play a major part in the generation of the Karoo CFBs in general, different kind of recycled source components (e.g., sediment-influenced) would be more difficult to distinguish from lithospheric CFB geochemical signatures. In addition to underlying continental lithosphere, the involvement of recycled sources in causing the apparent lithospheric geochemical affinity of CFBs should thus be carefully assessed in every case.last_img read more

Estimation of ice shelf melt rate in the presence of a thermohaline staircase

first_imgDiffusive convection–favorable thermohaline staircases are observed directly beneath George VI Ice Shelf, Antarctica. A thermohaline staircase is one of the most pronounced manifestations of double-diffusive convection. Cooling and freshening of the ocean by melting ice produces cool, freshwater above the warmer, saltier water, the water mass distribution favorable to a type of double-diffusive convection known as diffusive convection. While the vertical distribution of water masses can be susceptible to diffusive convection, none of the observations beneath ice shelves so far have shown signals of this process and its effect on melting ice shelves is uncertain. The melt rate of ice shelves is commonly estimated using a parameterization based on a three-equation model, which assumes a fully developed, unstratified turbulent flow over hydraulically smooth surfaces. These prerequisites are clearly not met in the presence of a thermohaline staircase. The basal melt rate is estimated by applying an existing heat flux parameterization for diffusive convection in conjunction with the measurements of oceanic conditions at one site beneath George VI Ice Shelf. These estimates yield a possible range of melt rates between 0.1 and 1.3 m yr−1, where the observed melt rate of this site is ~1.4 m yr−1. Limitations of the formulation and implications of diffusive convection beneath ice shelves are discussed.last_img read more

Assessing the design and power of capture-recapture studies to estimate demographic parameters for the Endangered Oceania humpback whale population

first_imgCapture-recapture studies offer a powerful tool to assess abundance, survival and population rate of change (λ). A previous capture-recapture study, based on DNA profiles, estimated that the IUCN-listed Endangered Oceania population of humpback whales had a superpopulation size of 4329 whales (95% confidence limits, CL: 3345, 5315) and λ = 1.03 (95% CL: 0.90-1.18) for the period 1999-2005. This low estimate of λ contrasts with the high estimated λ for the neighbouring east Australia population (1.11; 95% CL: 1.105-1.113). A future assessment of Oceania humpbacks through capture-recapture methodology has been proposed to meet 3 objectives: (1) estimate population size with a coefficient of variation of <20%, and detect if λ is significantly different from (2) 1.00 or (3) λ of east Australia. The proposed survey design involves using DNA profiles to identify whales on principal breeding grounds within Oceania in proportion to the abundance of whales on these grounds over the 10 to 12 wk wintering period, to minimise capture heterogeneity between individuals and to maximise capture probabilities. Simulations of the idealised survey design incorporating data from the previous surveys (1999-2005) with 3 new survey years were conducted under a range of scenarios for the ‘true’ demographic status of the population. Simulations of the entire Oceania region showed that the proposed design will give sufficient power to meet objectives (1) under all scenarios, (2) if the true λ ≥ 1.05 and (3) if the true λ ≤ 1.05. Region-specific simulations suggested there was scope to test for differences in recovery between principal breeding sites within Oceania.last_img read more

Annotated zoogeography of non-marine Tardigrada. Part IV: Africa

first_imgThis paper is the fourth monograph in a series that describes the global records of limno-terrestrial water bears (Tardigrada). Here, we provide a comprehensive list of non-marine tardigrades recorded from Africa, providing an updated and revised taxonomy accompanied by geographic co-ordinates, habitat, and biogeographic comments. It is hoped this work will serve as a reference point and background for further zoogeographical and taxonomical studieslast_img

Scientific challenges and present capabilities in underwater robotic vehicle design and navigation for oceanographic exploration under-ice.

first_imgThis paper reviews the scientific motivation and challenges, development, and use of underwater robotic vehicles designed for use in ice-covered waters, with special attention paid to the navigation systems employed for under-ice deployments. Scientific needs for routine access under fixed and moving ice by underwater robotic vehicles are reviewed in the contexts of geology and geophysics, biology, sea ice and climate, ice shelves, and seafloor mapping. The challenges of under-ice vehicle design and navigation are summarized. The paper reviews all known under-ice robotic vehicles and their associated navigation systems, categorizing them by vehicle type (tethered, untethered, hybrid, and glider) and by the type of ice they were designed for (fixed glacial or sea ice and moving sea ice). © 2020 by the authors.last_img read more

Ventilation of the abyss in the Atlantic sector of the Southern Ocean

first_imgThe Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses—ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4–9.7 Sv) yielding larger rates than tracer-based estimates (3.7–4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m−3 γn is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.last_img read more

Utah State’s Jordan Love Named America First Credit Union Student-Athlete of the Week

first_img Written by September 4, 2018 /Sports News – Local Utah State’s Jordan Love Named America First Credit Union Student-Athlete of the Week Brad James Tags: America First Credit Union USU Student Athlete of the Week/Izzie Hinton-Belnap/Jordan Love/Marli Niederhauser/Michigan State/Shannon Maloney FacebookTwitterLinkedInEmailLOGAN, Utah-Monday, Utah State quarterback Jordan Love was named the America First Credit Union USU Student-Athlete of the week. This award is voted on by a statewide media panel.This is the second time the 6-4 225-pound star sophomore out of Bakersfield, Calif. has received this award in his collegiate career for the Aggies.Love was stellar in the Aggies’ 38-31 loss at #11 Michigan State at East Lansing, Mich. August 31 as he went 29-44 for a career-high 319 yards. His 29 completions are also a career high for the rising star.Other nominees among Aggie athletes include women’s soccer freshman forward Marli Niederhauser of Mendon, Utah, women’s volleyball junior right side Izzie Hinton-Belnap of Fort Worth, Texas and women’s cross country senior Shannon Maloney of Durango, Colo.last_img read more