Stress response in the Antarctic teleosts (Notothenia neglecta Nybelin and N. rossii Richardson)

first_imgBlood chemistry and haematological parameters have been determined in the Antarctic teleosts, Notothenia neglecta Nybelin and Notothenia rossii Richardson at 2° C. Samples were taken using chronically implanted dorsal aortic cannulae following a minimum of 24–36 h recovery. Broadly similar results were obtained for the two species. In N. neglecta, routinely active specimens had high values of arterial pH (7.81) and PO2 (9.26 kPa), and modest haemoglobin levels (5.6 g dl−1) relative to temperate species. Following 3 min strenuous activity there was a decrease in arterial pH (7.63) and a small rise in lactate from 0.41 to 0.68 mm, but no significant change in the calculated net metabolic acid load (δHm+). PaO2 and PaCO2 varied inversely during exercise, and oxygen content declined by 22%. pHa and most other haematological parameters returned to routine values between 1–3 h post‐exercise. The results suggest that the major effect of strenuous activity in Notothenia spp. is a respiratory, rather than a metabolic acidosis.last_img read more

Taxonomic investigations of palynomorphs from the Byers group (Upper Jurassic‐Lower Cretaceous), Livingston and Snow islands, Antarctic Peninsula

first_imgTwo new palynomorph taxa are described, and several existing taxa are discussed from the Upper Jurassic‐Lower Cretaceous Byers Group of Livingston and Snow islands, South Shetland Islands, Antarctic Peninsula. Oligosphaeridium byersense sp. nov., a dinoflagellate cyst species, is found in the Valanginian interval of the Byers Group. Globorotundata acrita gen. et sp. nov., apalynomorph of unknown affinity, is areliable indicator of dysaerobia‐anaerobia and/or shallow marine paleoceanographic conditions, when present in moderate to high numbers. This paper includes the first description and discussion of focused ion beam milling preparation of palynological material.last_img

Biological sampling

first_imgThe essential aim of biological sampling is to obtainsamples that are representative of the targets underconsideration. Sampling in support of in situ target strength studies should be aimed closely at those targets from which acoustic information is being collected. Other components of the population and contamination of the sample should be avoided if at all possible. Thus if the acoustic measurements are being made on spawning concentrations, it is pointless for the biological sampling to include immaturefish. Similarly, when sampling in a two-layer situation,where the TS data were collected only from the lowerlayer, it is quite possible that incidental catches from theupper layer may contaminate the trawl sample. The idealstudy location would only contain a single species with anarrow unimodal size distribution. The overall programmeof target strength studies and the associated samplingshould, however, be aimed at providing information on alllife history stages of the species relevant to the populationbeing surveyed.It is important to recognise that TS estimation requiresprecise sampling only of the stock component thatcontributes to the TS measurements, whereas acousticabundance surveys require sampling which is aimed atproviding information on the entire target population.last_img read more

Remotely sensed mesoscale oceanography and the distribution of Illex argentinus in the South Atlantic

first_imgIn this study, we consider the influence of mesoscaleoceanographic processes around the Falkland Islands(Islas Malvinas) in the South-west Atlantic, duringthe period in which the commercial squid fishery forIllex argentinus operates. Spatially referenced fisherydata and satellite-derived advanced very high resolutionradiometry (AVHRR) sea surface temperature(SST) data were examined using geographic informationsystem (GIS) techniques. The distribution andrelative abundance of I. argentinus in the FalklandIslands fishery was examined for the period 1989±96.Three consistent areas of high abundance wereobserved to the north-east (shelf-break region) andnorth-west (shelf region) of the islands, and close tothe northern coast of East Falkland. Areas of high seasurface temperature gradients (thermal gradients)extracted from remotely sensed satellite images wereused as an indicator of mesoscale oceanographicactivity and compared with the location of the fishery.I. argentinus were found to be associated with areas ofthermal gradients, commonly seen at the interface ofFalkland Current and Patagonian shelf waters. Thetechniques used in this analysis allow the overlay andanalysis of physical oceanographic and fishery datawith potential applications in fisheries managementand operational fisheries oceanography.last_img read more

On the origin of Antarctic marine benthic community structure

first_imgEnvironmental conditions fostering marine communities around Antarctica differ fundamentally from those in the rest of the world’s oceans, particularly in terms of pronounced climatic fluctuations and extreme cold. Here, we argue that the rarity of pelagic larval stages in Antarctic marine benthic invertebrate species is a consequence of evolutionary temperature adaptation and that this has greatly contributed to the current structure of the Antarctic benthic community. In arguing this position, we challenge the likelihood of previously suggested survival strategies of benthic communities on the Antarctic continental shelf and slope during Cenozoic glacial periods. By integrating evidence from marine geology and geophysics, we suggest that the Antarctic continental shelf and slope were both unfavourable environments for benthic communities during glacial periods and that community survival was only possible in the deep sea or in shelters on the continental shelf as a result of the diachronism in maximum ice extent.last_img read more

An abrupt change of Antarctic moisture origin at the end of Termination II

first_imgThe deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin. New data obtained from the European Project for Ice Coring in Antarctica Dome C East Antarctic ice core provide new insights on the sequence of events involved in Termination II, the transition between the penultimate glacial and interglacial periods. This termination is marked by a north-south seesaw behavior, with first a slow methane concentration rise associated with a strong Antarctic temperature warming and a slow deuterium excess rise. This first step is followed by an abrupt north Atlantic warming, an abrupt resumption of the East Asian summer monsoon, a sharp methane rise, and a CO2 overshoot, which coincide within dating uncertainties with the end of Antarctic optimum. Here, we show that this second phase is marked by a very sharp Dome C centennial deuterium excess rise, revealing abrupt reorganization of atmospheric circulation in the southern Indian Ocean sector.last_img read more

Testing Munk’s hypothesis for submesoscale eddy generation using observations in the North Atlantic

first_imgA high-resolution satellite image that reveals a train of coherent, submesoscale (6 km) vortices along the edge of an ocean front is examined in concert with hydrographic measurements in an effort to understand formation mechanisms of the submesoscale eddies. The infrared satellite image consists of ocean surface temperatures at inline image m resolution over the midlatitude North Atlantic (48.69°N, 16.19°W). Concomitant altimetric observations coupled with regular spacing of the eddies suggest the eddies result from mesoscale stirring, filamentation, and subsequent frontal instability. While horizontal shear or barotropic instability (BTI) is one mechanism for generating such eddies (Munk’s hypothesis), we conclude from linear theory coupled with the in situ data that mixed layer or submesoscale baroclinic instability (BCI) is a more plausible explanation for the observed submesoscale vortices. Here we assume that the frontal disturbance remains in its linear growth stage and is accurately described by linear dynamics. This result likely has greater applicability to the open ocean, i.e., regions where the gradient Rossby number is reduced relative to its value along coasts and within strong current systems. Given that such waters comprise an appreciable percentage of the ocean surface and that energy and buoyancy fluxes differ under BTI and BCI, this result has wider implications for open-ocean energy/buoyancy budgets and parameterizations within ocean general circulation models. In summary, this work provides rare observational evidence of submesoscale eddy generation by BCI in the open ocean.last_img read more

The South Sandwich Islands – a community of meta-populations across all trophic levels

first_imgThe South Sandwich Islands are a relatively pristine volcanic archipelago in the Southern Ocean that experience high levels of natural disturbance. The archipelago spans the biological transition between the sub-Antarctic and maritime Antarctic. They host the southern boundary for some sub-Antarctic communities and the northern boundary for some maritime Antarctic communities. Vertebrate communities are dominated by Chinstrap and Macaroni penguins in the north and Adélie penguins in the south. Terrestrial plant and animal communities are less well differentiated; their distribution more influenced by the distribution of geothermally-warmed ground. We review current biodiversity knowledge, the influence of contemporary change on the archipelago, and their regional importance to Southern Ocean species. We pose questions on how to manage the islands in the contexts of climate change, fishing and human visitation. Climate change and fisheries will likely impact on the islands’ biota, but we conclude that introduced species pose the largest threat to biodiversity. Given the ephemeral nature of populations across all trophic levels, we suggest that the islands be managed as one unit rather than individually and we recommend practical changes to permitting and to increase the no-take zone in the existing Marine Protected Area to protect penguin foraging areas.last_img read more

UK Global Ocean GO6 and GO7: a traceable hierarchy of model resolutions

first_imgVersions 6 and 7 of the UK Global Ocean configuration (known as GO6 and GO7) will form the ocean components of the Met Office GC3.1 coupled model and UKESM1 earth system model to be used in CMIP61 simulations. The label “GO6” refers to a traceable hierarchy of three model configurations at nominal 1, 1∕4 and 1∕12° resolutions. The GO6 configurations are described in detail with particular focus on aspects which have been updated since the previous version (GO5). Results of 30-year forced ocean-ice integrations with the 1∕4° model are presented, in which GO6 is coupled to the GSI8.1 sea ice configuration and forced with CORE22 fluxes. GO6-GSI8.1 shows an overall improved simulation compared to GO5-GSI5.0, especially in the Southern Ocean where there are more realistic summertime mixed layer depths, a reduced near-surface warm and saline biases, and an improved simulation of sea ice. The main drivers of the improvements in the Southern Ocean simulation are tuning of the vertical and isopycnal mixing parameters. Selected results from the full hierarchy of three resolutions are shown. Although the same forcing is applied, the three models show large-scale differences in the near-surface circulation and in the short-term adjustment of the overturning circulation. The GO7 configuration is identical to the GO6 1∕4° configuration except that the cavities under the ice shelves are opened. Opening the ice shelf cavities has a local impact on temperature and salinity biases on the Antarctic shelf with some improvement in the biases in the Weddell Sea.last_img read more

Diving behaviour of albatrosses: implications for foraging ecology and bycatch susceptibility.

first_imgDiving is an ecologically important behaviour that provides air-breathing predators with opportunities to capture prey, but that also increases their exposure to incidental mortality (bycatch) in commercial fisheries. In this study, we characterised the diving behaviour of 26 individuals of three species, the black-browed albatross Thalassarche melanophris, grey-headed albatross T. chrysostoma and light-mantled albatross Phoebetria palpebrata, breeding at Bird Island, South Georgia. Individuals were tracked using Global Location Sensor (GLS)-immersion loggers and time-depth recorders (TDRs) and, for two species, Global Positioning System (GPS) loggers. Although the TDRs recorded 589 dives (defined in this paper as submersion > 1 m), average dive depths and durations were just 1.30–1.49 m and 2.5–3.3 s, respectively, for the three species. In addition, many individuals (22% of black-browed, 20% of grey-headed, and 57% of light-mantled albatrosses; total n = 9, 10 and 7 individuals, respectively) did not dive at all. Most dives occurred at the distal end of foraging trips and were rare during the commuting phase. No dives took place in darkness, despite long periods spent on water at night. The limited and shallow dive activity contrasts with impressions from a previous study using capillary-tube depth gauges (which are less accurate than TDRs) and has implications for the susceptibility of albatrosses to bycatch on longlines. This study provides further support for regulations requiring night setting and increased sink rates of baited hooks to help mitigate albatross bycatch.last_img read more