The possibility of a global warming induced by increasing levels of atmospheric carbon dioxide has led to increased interest in monitoring global temperatures. Polar regions are of particular interest because temperature changes may be amplified in these regions by the complex feedback mechanisms which operate in the atmosphere-ice-ocean system1. Monthly mean station surface air-temperature data have been objectively analysed to produce time series of temperature anomalies for the Northern Hemisphere (1881-1980)2,3, the Arctic (1881-1980)4 and the Antarctic (1957-82)5. A comparison of recent changes in these three regions is made here. Previously published series have been updated to 1982. Changes in Arctic temperatures since about 1966 and in Antarctic temperatures since 1960 show significant warming trends. For the period from 1975 to 1982 there is a high positive correlation between temperature variations in the Arctic and Antarctic.
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On the relationship between the magnetic and VLF signatures of the substorm expansion phase
We firmly establish a certain class of post-midnight ELF/VLF wave events as a signature of the substorm expansion phase. These substorm chorus events (SCEs) have been observed near L = 4 at Halley, Antarctica (76°S, 27°W), by the VELOX instrument. By examining 4 years (1992–1995) of nearly continuous Halley VELOX data, we identified 973 SCEs. From this database a subset of 258 events was selected, occurring within ±1 hour of local magnetic midnight at Halley, that is, between 0200 and 0400 UT. The epochs of these events were used to perform a superposed epoch analysis on the three components of the Halley fluxgate magnetometer data. A significant negative bay in the magnetic H component was observed to start at the SCE epoch, as expected for a ground station near the westward electrojet of the substorm current wedge. Positive and negative bays, respectively, were seen in the D and Z components. We interpret the detailed features of the composite magnetograms and conclude that the SCE is an unambiguous signature of substorm expansion phase onset. Given this association of the SCE with the substorm expansion phase based on the qualitative features of the superposed epoch ground magnetic signature, this paper also provides the most complete quantitative description to date of both the VLF and magnetic substorm signatures observed at a near-auroral zone ground station.
A search for ENSO teleconnections in the west Antarctic Peninsula climate in austral winter
Evidence is sought for El Niño–Southern Oscillation (ENSO) teleconnections in the South Pacific extratropical atmospheric circulation and in seasonal temperatures in the west Antarctic Peninsula (WAP) during austral winter. Emphasis is placed on winter sea surface temperature (SST) changes in the tropical central Pacific to infer the seasonal evolution of ENSO events. SST changes are statistically independent of absolute SSTs and are also rarely the same in warm events. Variations in winter tropical SST changes are also found to be strongly mirrored in South Pacific extratropical circulation adjustments that are consistent with Rossby wave modulation. They include changes in the westerlies in the central Pacific (40°S–55°S) and in Antarctic Peninsula meridional flows. ENSO teleconnections are found to indirectly reach WAP winter temperatures via alterations in the local ice extent that is sensitive to the local, ENSO teleconnected, meridional circulation variations. Winter temperatures are also very closely coupled to the winter ‘baseline’ ice extent. It is shown that above-normal pre-winter ice extent is a necessary condition for cold winters but that wintertime ice extent changes owing to ENSO-related meridional flow variations must also be taken into account. The study results are supported by a regression modelling analysis that captures most cold winters in the study period. From these findings and those of previous ENSO teleconnection studies for the South Pacific, it is surmised that ENSO plays a major role in driving interannual temperature variability in this part of Antarctica in the austral winter.
Variation in maternal provisioning by lactating Antarctic fur seals (Arctocephalus gazella): response to experimental manipulation in pup demand
An experiment involving the supplementary feeding of pups was conducted on Antarctic fur seals to investigate the factors influencing maternal foraging-attendance cycles and the differential use of nutritional resources for growth, maintenance and storage by pups. For 40% of the lactation period, male pups were given a supplement mimicking the chemical composition of Antarctic fur seal milk at a dose equivalent to 35% of the normal mass-specific milk energy intake for the species. Milk consumption, body composition and growth rates were monitored during and after the supplementary feeding period and maternal foraging-attendance cycles were monitored throughout lactation. During the supplementary feeding period, treatment pups (n=8) grew 32% faster and deposited greater adipose tissue stores than controls (n=8) but consumed the same amount of maternal-delivered milk. When supplementary feeding was stopped (timed to coincide with peak maternal milk yield in this species), treatment pups lost mass whereas control group pups continued to grow. Treatment pups weaned at a younger age (109 days) than control pups (116 days) but at the same mass (13 kg). Maternal attendance durations did not differ between the treatment and control groups throughout lactation. However, mothers of treatment pups had significantly shorter foraging trip durations (3.74 days) than mothers of control pups (4.74 days) during the period of supplementary feeding (there were no significant differences throughout the rest of lactation). These findings are in accordance with predictions of a marginal-value model of fur seal lactation behaviour.
A high-resolution simulation of convective roll clouds during a cold-air outbreak
A ubiquitous feature of the high latitude ocean is the occurrence of convective clouds that are organized into two-dimensional structures known as roll clouds or cloud streets. In this paper, we present a simulation of these structures that was performed in a domain large enough to simulate numerous roll clouds and their downstream evolution at a resolution sufficient to resolve the individual convective clouds. The simulations were initialized and validated using observations of roll clouds over the Labrador Sea. The model results indicate that the secondary flow associated with the roll clouds results in significant differences in the temperature, humidity and momentum fields between the updrafts and downdrafts. The model was also able to reproduce the observed downstream evolution of the clouds as the organization of the convection changed from two-dimensional rolls to three-dimensional closed cells.
Flight morphology and foraging behaviour of male and female Cory’s shearwaters
In some seabirds sexually dimorphic in size, males and females segregate at sea or diverge in other aspects of foraging behavior. We examined factors influencing foraging strategies of Cory’s Shearwater and compared the sexes’ flight morphology and activity patterns. Trip duration, incubation-shift length, total mass gain, and rate of mass gain at sea of birds from our two study colonies differed. The colonies are situated in regions of contrasting oceanographic conditions: Selvagem Grande, a remote subtropical oceanic island, and Berlengas, an island on the Portuguese continental shelf. Although the wing loading and wing span of males and females breeding at Selvagem Grande differed significantly, sex did not consistently influence activity patterns of Cory’s Shearwaters foraging at sea during the incubation period. Moreover, both sexes breeding at Selvagem Grande foraged in areas with similar sea-surface temperatures. Our study suggests that sexual differences in size and shape may be poor predictors of differentiation in the ways male and female pelagic seabirds use the marine environment.
Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 1. Evaluation for electrostatic electron cyclotron harmonic waves
Using statistical wave power spectral profiles obtained from CRRES and the latitudinal distributions of wave propagation modeled by the HOTRAY code, a quantitative analysis has been performed on the scattering of plasma sheet electrons into the diffuse auroral zone by multiband electrostatic electron cyclotron harmonic (ECH) emissions near L = 6 within the 0000–0600 MLT sector. The results show that ECH wave scattering of plasma sheet electrons varies from near the strong diffusion rate (timescale of an hour or less) during active times with peak wave amplitudes of an order of 1 mV/m to very weak scattering (on the timescale of >1 day) during quiet conditions with typical wave amplitudes of tenths of mV/m. However, for the low-energy (∼100 eV to below 2 keV) electron population mainly associated with the diffuse auroral emission, ECH waves are only responsible for rapid pitch angle diffusion (occasionally near the limit of strong diffusion) for a small portion of the electron population with pitch angles αeq 70°. Computations of the bounce-averaged coefficients of momentum diffusion and (pitch angle, momentum) mixed diffusion indicate that both mixed diffusion and energy diffusion of plasma sheet electrons due to ECH waves are very small compared to pitch angle diffusion and that ECH waves have little effect on local electron acceleration. Consequently, the multiple harmonic ECH emissions cannot play a dominant role in the occurrence of diffuse auroral precipitation near L = 6, and other wave-particle interaction mechanisms, such as whistler mode chorus-driven resonant scattering, are required to explain the global distribution of diffuse auroral precipitation and the formation of the pancake distribution in the inner magnetosphere.
A leg-band for mounting geolocator tags on penguins
We present a design for a simple, inexpensive leg band for mounting GLS tags on penguins. It causes a low level of injury and can be madefrom materials and tools that are readily available. We provide information on captive and field trials and outline deployment strategies thatimprove recovery rates. This device should facilitate further studies of penguin winter movements using geolocation.
nrDNA:mtDNA copy number ratios as a comparative metric for evolutionary and conservation genetics
Identifying genetic cues of functional relevance is key to understanding the drivers of evolution and increasingly important for the conservation of biodiversity. This study introduces nuclear ribosomal DNA (nrDNA) to mitochondrial DNA (mtDNA) copy number ratios as a metric with which to screen for this functional genetic variation prior to more extensive omics analyses. To illustrate the metric, quantitative PCR was used to estimate nrDNA (18S) to mtDNA (16S) copy number ratios in muscle tissue from samples of two zooplankton species: Salpa thompsoni caught near Elephant Island (Southern Ocean) and S. fusiformis sampled off Gough Island (South Atlantic). Average 18S:16S ratios in these samples were 9:1 and 3:1, respectively. nrDNA 45S arrays and mitochondrial genomes were then deep sequenced to uncover the sources of intra-individual genetic variation underlying these 18S:16S copy number differences. The deep sequencing profiles obtained were consistent with genetic changes resulting from adaptive processes, including an expansion of nrDNA and damage to mtDNA in S. thompsoni, potentially in response to the polar environment. Beyond this example from zooplankton, nrDNA:mtDNA copy number ratios offer a promising metric to help identify genetic variation of functional relevance in animals more broadly.
Genomics detects population structure within and between ocean basins in a circumpolar seabird: the white‐chinned petrel
The Southern Ocean represents a continuous stretch of circumpolar marine habitat, but the potential physical and ecological drivers of evolutionary genetic differentiation across this vast ecosystem remain unclear. We tested for genetic structure across the full circumpolar range of the white‐chinned petrel (Procellaria aequinoctialis) to unravel the potential drivers of population differentiation and test alternative population differentiation hypotheses. Following range‐wide comprehensive sampling, we applied genomic (genotyping‐by‐sequencing or GBS; 60,709 loci) and standard mitochondrial‐marker approaches (cytochrome b and 1st domain of control region) to quantify genetic diversity within and among island populations, test for isolation by distance, and quantify the number of genetic clusters using neutral and outlier (non‐neutral) loci. Our results supported the multi‐region hypothesis, with a range of analyses showing clear three‐region genetic population structure, split by ocean basin, within two evolutionary units. The most significant differentiation between these regions confirmed previous work distinguishing New Zealand and nominate subspecies. Although there was little evidence of structure within the island groups of the Indian or Atlantic oceans, a small set of highly‐discriminatory outlier loci could assign petrels to ocean basin and potentially to island group, though the latter needs further verification. Genomic data hold the key to revealing substantial regional genetic structure within wide‐ranging circumpolar species previously assumed to be panmictic.