Metabolism and feeding in the Antarctic brachiopod Liothyrella uva: A low energy lifestyle species with restricted metabolic scope

first_imgThe effect of feeding on metabolism (specific dynamic action; SDA) was assessed in the articulate brachiopod Liothyrella uva (Broderip, 1833) at Signy Island, Antarctica. The response was low and on a much longer timescale than previously reported SDA responses. Oxygen consumption rose post-prandially to a peak which was 1.64 $times $ higher than the prefeeding basal metabolic rate. The response peaked on the 5$^{text{th}}$ day and returned to basal levels on the 18$^{text{th}}$ day after feeding. Maximum metabolic scope was therefore restricted, and was 0.41 $mu $molO$_{2}$ h$^{-1}$ (24.5 microwatts) for a 290 mg ash-free dry mass individual. Unusually ammonia excretion was little affected by feeding, except for a short sharp peak on the 4$^{text{th}}$ post-prandial day. Metabolic O:N ratios were very low, ranging from 2.9 to 6.6 and indicated an almost sole use of protein to fuel metabolism throughout. Urea excretion showed no pattern in relation to feeding, and accounted for around 7% of nitrogen excreted. It is suggested that metabolic scope is limited in L. uva for two reasons: because it has evolved to live at low temperatures and because of phylogenetic limitations related to articulate brachiopod lifestyles.last_img read more

Heart rates and abdominal temperatures of free-ranging South Georgian shags, Phalacrocorax georgianus

first_imgThe South Georgian shag (Phalacrocorax georgianus) shows a remarkable diving ability comparable to that of penguins, yet nothing is known of the physiology of these birds. In this study, heart rates and abdominal temperatures were recorded continuously in four free-ranging South Georgian shags using an implanted data-logger. A time­depth recorder was also attached to the back of the implanted birds to record their diving behaviour. The diving behaviour of the birds was essentially similar to that reported in other studies, with maximum dive durations for individual birds ranging between 140 and 287 s, and maximum depths between 35 and 101 m. The birds, while at the nest, had a heart rate of 104.0±13.1 beats min-1 (mean ± s.e.m.) and an abdominal temperature of 39.1±0.2 °C. During flights of 221±29 s, heart rate and abdominal temperature rose to 309.5±18.0 beats min-1 and 40.1±0.3 °C, respectively. The mean heart rate during diving, at 103.7±13.7 beats min-1, was not significantly different from the resting values, but the minimum heart rate during a dive was significantly lower at 64.8±5.8 beats min-1. The minimum heart rate during a dive was negatively correlated with both dive duration and dive depth. Abdominal temperature fell progressively during a diving bout, with a mean temperature at the end of a bout of 35.1±1.7 °C. The minimum heart rate during diving is at a sub-resting level, which suggests that the South Georgian shag responds to submersion with the ‘classic’ dive response of bradycardia and the associated peripheral vasoconstriction and utilisation of anaerobic metabolism. However, the reduction in abdominal temperature may reflect a reduction in the overall metabolic rate of the animal such that the bird can remain aerobic while submerged.last_img read more

A Lower Cretaceous clastic slope succession, Livingston Island, Antarctica: sand-body characteristics, depositional processes and implications for slope apron depositional models

first_imgThe early Cretaceous fill of the forearc/intra-arc Byers Basin includes a 600- to 900-m-thick interval of marine slope apron deposits, the President Beaches Formation. This is a predominantly argillaceous succession within which coarser-grained deposits are largely confined to lenticular packages of low width–thickness ratios. The entire formation was deposited in mid- to late-Berriasian times, coincident with a pulse of regional arc expansion, at minimum mean accumulation rates of 120–225 mm 1000 years–1. The mudstones are finely laminated, with a restricted benthic macrofauna and minimal bioturbation, indicating relatively inhospitable sea-floor environments. Sand-rich packages occur as 7- to 30-m-thick channel-fill units composed chiefly of classical medium-grained turbidites, in some cases associated with complex high-concentration turbidity current deposits and minor mud-rich debrites. These sand-bodies are apparently elongate along (normal to) the NW-facing palaeoslope implied by slump-fold axes (and the strike of the volcanic arc). Similarly, palaeocurrent indices show a consistent arc-parallel, NE-directed trend, suggesting that transport processes were strongly influenced by the structural ‘grain’ of the irregular slope morphology. Slope instability is recorded by widespread slump and soft-sediment collapse features promoted by a combination of steep sea-floor gradients and relatively high rates of sedimentation. A lack of systematic vertical facies trends indicates that this was not a progradational or well-organized system, despite high rates of sediment supply. However, the strong systematic relationship between palaeocurrents and palaeoslope suggests a promising basis for evaluating organization in otherwise poorly ordered slope apron depositional systems.last_img read more

Optimal estimation of changes in the mass of ice sheets

first_imgWe describe a new approach for estimating changes in ice sheet mass. Two methods are in common use: the ice budget and geodetic methods. The first makes use of separate estimates of the mass fluxes into and out of a domain, differencing them to obtain the local mass balance. The second estimates mass balance directly, using measurements of the change in surface elevation, often from aircraft or satellites. Here we combine ice budget and geodetic approaches to obtain an optimal estimate of mass balance. We seek maximum likelihood solutions for three terms: (1) the rate of change of surface elevation, (2) the rate of snow accumulation, and (3) the local divergence of the ice flux. These estimates are constrained to obey the continuity equation. We allow the location and temporal averaging interval of the estimates to be chosen arbitrarily. This approach can use all relevant measurements. The fidelity of any measurement is lowered by measurement error, and by fluctuations in each of the three terms driven by random year-to-year snowfall variations. We take full account of both error sources, weighting the data so as to minimize the confounding effect of these influences. Realistic covariance between randomly forced fluctuations are provided by a linearized model of ice sheet flow. We test the approach by applying the algorithm to synthetically generated measurements. The method performs better than either ice budget or geodetic methods applied in isolation, and has the important advantage that good estimates may still be derived when measurements appropriate to either technique are lacking or inaccurate.last_img read more

The large-scale dynamics of the mesosphere-lower thermosphere during the Southern Hemisphere stratospheric warming of 2002

first_imgAn unprecedented major stratospheric warming occurred in the Antarctic winter of 2002. We present measurements of winds in the mesosphere-lower thermosphere (MLT) made with MF radars located at Davis (69degreesS, 78degreesE), Syowa (69degreesS, 40degreesE) and Rothera (68degreesS, 68degreesW). The mesospheric wind field in 2002 was found to be considerably different to other years due to increased planetary wave activity throughout the winter. Zonal winds were weaker than usual during the 2002 winter and also during the transition to the summer circulation. The MLT zonal winds showed a reversal about one week earlier than the stratospheric reversal associated with the warming. Meridional winds showed oscillations consistent with the presence of traveling wave-1 planetary waves with periods similar to14 days. The results are compared with similar mesospheric observations made during northern hemisphere stratospheric warmings. Some similarities between hemispheres were found, notably that the reversal in the mesospheric winds precedes the warming events.last_img read more

Meteor radar observations at middle and Arctic latitudes. Part 1: Mean temperatures

first_imgObservations with a Meteor radar operating at 32.55 MHz have been used to derive daily atmospheric temperature data for an altitude of 90 km at mid-latitudes during November 1999 until August 2001, and at high latitudes during September 2001 until December 2002. The neutral air temperatures are derived from determination of the ambipolar diffusion coefficient variation as a function of height, and are then corrected by application of a temperature-gradient model. The seasonal variations at both latitudes are characterized by high temperatures in winter and markedly smaller ones during summer. Whereas the winter temperatures at high latitudes are slightly warmer than at mid-latitudes by about 10 K, during summer the temperatures at high latitudes are colder by up to about 40 K. The majority of the variation in temperatures measured by this technique is due to variations in the ambipolar diffusion coefficient, but the accuracy of the temperature gradient model is important for second-order corrections. The meteor technique is valuable toot to study the short time temperature variability. The temperature data derived in this manner are in reasonable agreement with independent experimental results from different rocket, satellite and ground-based measurements, as well as with theoretical results obtained from calculations with the global circulation model COMMA-IAP.last_img read more

Normal forms for reduced stochastic climate models

first_imgThe systematic development of reduced low-dimensional stochastic climate models from observations or comprehensive highdimensional climate models is an important topic for atmospheric low-frequency variability, climate sensitivity, and improved extended range forecasting. Here techniques from applied mathematics are utilized to systematically derive normal forms for reduced stochastic climate models for low-frequency variables. The use of a few Empirical Orthogonal Functions (EOFs) (also known as Principal Component Analysis, Karhunen–Loéve and Proper Orthogonal Decomposition) depending on observational data to span the low-frequency subspace requires the assessment of dyad interactions besides the more familiar triads in the interaction between the low- and high-frequency subspaces of the dynamics. It is shown below that the dyad and multiplicative triad interactions combine with the climatological linear operator interactions to simultaneously produce both strong nonlinear dissipation and Correlated Additive and Multiplicative (CAM) stochastic noise. For a single low-frequency variable the dyad interactions and climatological linear operator alone produce a normal form with CAM noise from advection of the large scales by the small scales and simultaneously strong cubic damping. These normal forms should prove useful for developing systematic strategies for the estimation of stochastic models from climate data. As an illustrative example the one-dimensional normal form is applied below to lowfrequency patterns such as the North Atlantic Oscillation (NAO) in a climate model. The results here also illustrate the short comings of a recent linear scalar CAM noise model proposed elsewhere for low-frequency variability.last_img read more

Environmental signals in a highly resolved ice core from James Ross Island, Antarctica

first_imgThe accumulation, isotopic and chemical signals of an ice core from James Ross Island, Antarctica, are investigated for the interval from 1967 to 2008. Over this interval, comparison with station, satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice. Accumulation at James Ross Island is enhanced during years when the circumpolar westerlies are weak, allowing more precipitation events to reach the northeastern Antarctic Peninsula. The stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope‐temperature gradient across Antarctica, and preserves information about both summer and winter temperature variability in the region. Sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of James Ross Island and transported to the site by strengthened northerly and westerly winds in the winter. A strong covariance with temperature means that the sea salt record may be able to be utilized, in conjunction with the isotope signal, as an indicator of winter temperature. Marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of James Ross Island. This source region may have become significant only in recent decades, when the collapse of nearby ice shelves established new sites of open water with high summer productivity. These findings provide a foundation for interpreting the environmental signals in the James Ross Island ice core, which extends though the whole Holocene and represents the oldest ice core that has been recovered from the Antarctic Peninsula region.last_img read more

West Antarctic Peninsula: An ice-dependent coastal marine ecosystem in transition

first_imgThe extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms’ life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.last_img read more

Transcriptomic SNP discovery for custom genotyping arrays: impacts of sequence data, SNP calling method and genotyping technology on the probability of validation success

first_imgBackground Single nucleotide polymorphism (SNP) discovery is an important goal of many studies. However, the number of ‘putative’ SNPs discovered from a sequence resource may not provide a reliable indication of the number that will successfully validate with a given genotyping technology. For this it may be necessary to account for factors such as the method used for SNP discovery and the type of sequence data from which it originates, suitability of the SNP flanking sequences for probe design, and genomic context. To explore the relative importance of these and other factors, we used Illumina sequencing to augment an existing Roche 454 transcriptome assembly for the Antarctic fur seal (Arctocephalus gazella). We then mapped the raw Illumina reads to the new hybrid transcriptome using BWA and BOWTIE2 before calling SNPs with GATK. The resulting markers were pooled with two existing sets of SNPs called from the original 454 assembly using NEWBLER and SWAP454. Finally, we explored the extent to which SNPs discovered using these four methods overlapped and predicted the corresponding validation outcomes for both Illumina Infinium iSelect HD and Affymetrix Axiom arrays. Results Collating markers across all discovery methods resulted in a global list of 34,718 SNPs. However, concordance between the methods was surprisingly poor, with only 51.0 % of SNPs being discovered by more than one method and 13.5 % being called from both the 454 and Illumina datasets. Using a predictive modeling approach, we could also show that SNPs called from the Illumina data were on average more likely to successfully validate, as were SNPs called by more than one method. Above and beyond this pattern, predicted validation outcomes were also consistently better for Affymetrix Axiom arrays. Conclusions Our results suggest that focusing on SNPs called by more than one method could potentially improve validation outcomes. They also highlight possible differences between alternative genotyping technologies that could be explored in future studies of non-model organisms.last_img read more