Population dynamics and mortality of reindeer introduced into South Georgia

first_imgReindeer (Rangifer tarandus) were introduced into South Georgia in 1911 and 1925, and now form 3 herds. Each herd was at a different stage of an irruptive oscillation when they were studied during 1972-76. The Barff herd had declined in numbers since about 1958, the Royal Bay herd formed by emigration in 1961-65, and the Busen herd began to decline during the study. Conceptions first occurred at 1½ years of age, and pregnancy rates were 90% in each herd. Adult males lived up to 7-8 years and females up to 11-12 years, which resulted in biased sex ratios. There were significant differences between the mean ages of males and females only in the Barff herd. An adult female annual mortality of about 33% was inferred for the Barff and Busen herds. Perinatal mortality occurred in all herds, and was highest (30%) in the Barff herd. Levels of calf mortality varied with winter severity in the Barff herd, and no mortality differential occurred between sexes. Most adult and yearling females died in late winter and most males died in early winter after the rut. Falls over cliffs were an important cause of death. Overgrazing of tussock grass (Poa flabellata), and the consequent decrease in winter-range carrying capacity, is the most important way by which herd numbers are being controlled. The population responses that most reflected the different irruptive stage of each herd were levels of calf mortality and biased sex ratios.last_img read more

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Compression and rarefaction of F-region plasma caused by an atmospheric gravity wave

first_imgThe Advanced Ionospheric Sounder at Halley (75° 31′S, 26° 59′W) in Antarctica has been used to observe the F-region disturbance caused by an atmospheric gravity wave. Observations at 4.5 MHz were used to examine the variations of group range, obtained from time-of-flight measurements, and of Doppler shift, derived from Fourier analysis of the quadrature components of the signal. A comparison of simultaneous values of group-range and phase-path velocities shows clear evidence of compression and rarefaction of ionization and more complicated changes in the height distribution of ionization in the oscillatory changes associated with the wavelast_img read more

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Cephalopods eaten by wandering albatrosses (Diomedea exulansL.) breeding at six circumpolar localities

first_imgReferences CitationsMetrics Reprints & Permissions PDF Abstract The beaks of 9,994 cephalopods of 61 species, obtained mainly from chick regurgitations of wandering albatrosses (Diomedea exulans L.) at Gough, Auckland, Antipodes, Prince Edward and Macquarie Islands and South Georgia, were used to specify and calculate the biomass of cephalopods consumed. Histioteuthidae were most important by numbers and biomass at Gough Island (in warmest seas), but Onycboteuthidae increasingly superseded them southwards; Kondakovia longimana formed 59 to 75% of biomass eaten at the three localities nearest the Antarctic Polar Front. Other important families were Octopoteuthidae, Cranchiidae, Architeuthidae (juveniles) and Ommastrephidae (South Georgia only). Most frequently eaten were Histioteuthis atlantica 13.7%, Galiteuthis glacialis 12.4%, H. eltaninae 12.0% and Kondakovia longimana 11.6%. Wandering albatrosses rearing chicks can forage at least to 3,000 km in a single foray, and may exploit an important food source about 1200 km from the nest (as in the probable commensalism of South Georgian birds with the Falkland Islands fishery). They feed, sometimes opportunistically, on cephalopods active or moribund at the surface, or discarded or lost by trawlers, cetaceans or seals. Vertically migrating cephalopods, especially bioluminescent species, are disproportionately frequent in their non-commensal diet, suggesting that they often feed at night.last_img read more

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The relationship between water content and cold tolerance in the arctic collembolan Onychiurus arcticus (Collembola: Onychiuridae)

first_imgThe arctic collembolan Onychiurus arcticus is freezing intolerant and experiences temperatures below -25°C during winter periods of low air temperatures and only light snow cover. Summer-collected individuals have a mean (±SE) supercooling point of -6.1 ± 0.1°C. This study was designed to measure the desiccation resistance and subsequent recovery of O. arcticus from partial dehydration and relate these to its cold-hardiness in terms of changes in the supercooling point (SCP) and solute concentration. Drying curves measured with a recording microbalance showed two distinct phases characteristic of the loss of free and chemically bound (osmotically inactive) water. Rates of water loss at 0°C and low relative humidity (< 5%) were similar to those measured for Antarctic Collembola (5% h-1 of the initial total water content). O. arcticus survived losses of 40% of its total body water content and recovered within 36 h but could not survive losses of 50% of its original water content. Differential scanning calorimetry was used to investigate the nature of the body water, i.e. the proportion of freezable to unfreezable water and the nucleation temperature. The melt onset temperature correlated positively with the body water content. But no clear relationship was seen between the water content and the SCP, either because the springtails had low levels of cryoprotectants or because the ice nucleation activity was unaffected. However, long periods (7 months) at -2.5°C reduced the water content from 74 ± 10.1 to 43 ± 7.2% of fresh weight and lowered the SCP from -6.1 ± 2.1 to -15.5 ± 2.3°C. When given access to water these individuals re-gained their body weight within 24 h. During periods of desiccation water losses were attributed to the loss of freezable water with the unfreezable portion remaining almost constant at 16.5 ± 2.0%. It appears that O. arcticus may experience a reduction of body water during winter periods of sub-zero temperatures, which may lower its SCP and enhance its cold tolerance but that it can rapidly return to summer levels given access to free water during the spring melt.last_img read more

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Ocean biogeochemical response to phytoplankton-light feedback in a global model

first_imgOceanic phytoplankton, absorbing solar radiation, can influence the bio-optical properties of seawater and hence upper ocean physics. We include this process in a global ocean general circulation model (OGCM) coupled to a dynamic green ocean model (DGOM) based on multiple plankton functional types (PFT). We not only study the impact of this process on ocean physics but we also explore the biogeochemical response due to this biophysical feedback. The phytoplankton-light feedback (PLF) impacts the dynamics of the upper tropical and subtropical oceans. The change in circulation enhances both the vertical supply in the tropics and the lateral supply of nutrients from the tropics to the subtropics boosting the subtropical productivity by up to 60 gC m(-2) a(-1). Physical changes, due to the PLF, impact on light and nutrient availability causing shifts in the ocean ecosystems. In the extratropics, increased stratification favors calcifiers (by up to similar to 8%) at the expense of mixed phytoplankton. In the Southern Ocean, silicifiers increase their biomass (by up to similar to 10%) because of the combined alleviation of iron and light limitation. The PLF has a small effect globally on air-sea fluxes of carbon dioxide (CO2, 72 TmolC a(-1) outgassing) and oxygen (O-2, 46 TmolO(2) a(-1) ingassing) because changes in biogeochemical processes (primary production, biogenic calcification, and export production) highly vary regionally and can also oppose each other. From our study it emerges that the main impact of the PLF is an amplification of the seasonal cycle of physical and biogeochemical properties of the high-latitude oceans mostly driven by the amplification of the SST seasonal cycle.last_img read more

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The Tectonothermal evolution and provenance of the Tyrone Central Inlier, Ireland: Grampian imbrication of an outboard Laurentian microcontinent?

first_imgThe Tyrone Central Inlier is a metamorphic terrane of uncertain affinity situated outboard of themain Dalradian outcrop (south of the Fair Head–Clew Bay Line) and could represent sub-arc basement topart of the enigmatic Midland Valley Terrane. Using a combination of isotopic, structural and petrographicevidence, the tectonothermal evolution of the Tyrone Central Inlier was investigated. Sillimanite-bearingmetamorphic assemblages (c. 670 degreesC, 6.8 kbar) and leucosomes in paragneisses are cut by granite pegmatites,which post-date two deformation fabrics. The leucosomes yield a weighted average 207Pb/206Pb zircon ageof 467 +/- 12 Ma whereas the main fabric yields a 40Ar–39Ar biotite cooling age of 468 +/- 1.4 Ma. Thepegmatites yield 457 +/- 7 Ma and 458 +/- 7 Ma Rb–Sr muscovite–feldspar ages and 40Ar–39Ar step-heatingplateaux of 466 +/- 1 Ma and 468 +/- 1 Ma, respectively. The metasedimentary rocks yield PalaeoproterozoicSm–Nd model ages and laser ablation inductively coupled plasma mass spectrometry detrital zircon U–Pbanalyses from a psammitic gneiss yield age populations at 1.05–1.2, 1.5, 1.8, 2.7 and 3.1 Ga. Combined,these data permit correlation of the Tyrone Central Inlier with either the Argyll or the Southern HighlandGroup of the Dalradian Supergroup. The inlier was thus part of Laurentia onto which the Tyrone ophiolitewas obducted.last_img read more

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Surface Ocean CO2 Atlas (SOCAT) gridded data products

first_imgAs a response to public demand for a well-documented, quality controlled, publically available, global surface ocean carbon dioxide (CO2) data set, the international marine carbon science community developed the Surface Ocean CO2 Atlas (SOCAT). The first SOCAT product is a collection of 6.3 million quality controlled surface CO2 data from the global oceans and coastal seas, spanning four decades (1968–2007). The SOCAT gridded data presented here is the second data product to come from the SOCAT project. Recognizing that some groups may have trouble working with millions of measurements, the SOCAT gridded product was generated to provide a robust, regularly spaced CO2 fugacity (fCO2) product with minimal spatial and temporal interpolation, which should be easier to work with for many applications. Gridded SOCAT is rich with information that has not been fully explored yet (e.g., regional differences in the seasonal cycles), but also contains biases and limitations that the user needs to recognize and address (e.g., local influences on values in some coastal regions).last_img read more

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ATAT 1.1, the Automated Timing Accordance Tool for comparing ice-sheet model output with geochronological data

first_imgEarth’s extant ice sheets are of great societal importance given their ongoing and potential future contributions to sea-level rise. Numerical models of ice sheets are designed to simulate ice-sheet behaviour in response to climate changes but to be improved require validation against observations. The direct observational record of extant ice sheets is limited to a few recent decades, but there is a large and growing body of geochronological evidence spanning millennia constraining the behaviour of palaeo-ice sheets. Hindcasts can be used to improve model formulations and study interactions between ice sheets, the climate system and landscape. However, ice-sheet modelling results have inherent quantitative errors stemming from parameter uncertainty and their internal dynamics, leading many modellers to perform ensemble simulations, while uncertainty in geochronological evidence necessitates expert interpretation. Quantitative tools are essential to examine which members of an ice-sheet model ensemble best fit the constraints provided by geochronological data. We present the Automated Timing Accordance Tool (ATAT version 1.1) used to quantify differences between model results and geochronological data on the timing of ice-sheet advance and/or retreat. To demonstrate its utility, we perform three simplified ice-sheet modelling experiments of the former British–Irish ice sheet. These illustrate how ATAT can be used to quantify model performance, either by using the discrete locations where the data originated together with dating constraints or by comparing model outputs with empirically derived reconstructions that have used these data along with wider expert knowledge. The ATAT code is made available and can be used by ice-sheet modellers to quantify the goodness of fit of hindcasts. ATAT may also be useful for highlighting data inconsistent with glaciological principles or reconstructions that cannot be replicated by an ice-sheet model.last_img read more

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Energy and mass balance dynamics of the seasonal snowpack at two high-altitude sites in the Himalaya

first_imgSnow dynamics play a crucial role in the hydrology of alpine catchments in the Himalaya. However, studies based on in-situ observations that elucidate the energy and mass balance of the snowpack at high altitude in this region are scarce. In this study, we use meteorological and snow observations at two high-altitude sites in the Nepalese Himalaya to quantify the mass and energy balance of the seasonal snowpack. Using a data driven experimental set-up we aim to understand the main meteorological drivers of snowmelt, illustrate the importance of accounting for the cold content dynamics of the snowpack, and gain insight into the role that snow meltwater refreezing plays in the energy and mass balance of the snowpack. Our results show an intricate relation between the sensitivity of melt and refreezing on the albedo, the importance of meltwater refreezing, and the amount of positive net energy used to overcome the cold content of the snowpack. The net energy available at both sites is primarily driven by the net shortwave radiation, and is therefore extremely sensitive to snow albedo measurements. We conclude that, based on observed snowpack temperatures, 21% of the net positive energy is used to overcome the cold content build up during the night. We also show that at least 32–34% of the snow meltwater refreezes again for both sites. Even when the cold content and refreezing are accounted for, excess energy is available beyond what is needed to melt the snowpack. We hypothesize that this excess energy may be explained by uncertainties in the measurement of shortwave radiation, an underestimation of refreezing due to a basal ice layer, a cold content increase due to fresh snowfall and the ground heat flux. Our study shows that in order to accurately simulate the mass balance of seasonal snowpacks in Himalayan catchments, simple temperature index models do not suffice and refreezing and the cold content needs to be accounted for.last_img read more

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Local and remote influences on the heat content ofSouthern Ocean mode water formation regions

first_imgThe Southern Ocean (SO) is a crucial region for the global ocean uptake of heat and carbon. There are large uncertainties in the observations of fluxes of heat and carbon between the atmosphere and the ocean mixed layer, which lead to large uncertainties in the amount entering into the global overturning circulation. In order to better understand where and when fluxes of heat and momentum have the largest impact on near‐surface heat content, we use an adjoint model to calculate the linear sensitivities of heat content in SO mode water formation regions to surface fluxes. We find that the heat content of these regions is, in all three basins, most sensitive to same‐winter, local heat fluxes, and to local and remote wind one to eight years (the maximum lead‐time of our simulations) previously. This is supported by sensitivities to potential temperature changes, which reveal the sources of the mode water formation regions as well as dynamic links with boundary current regions and the Antarctic Circumpolar Current. We use the adjoint sensitivity fields to design a set of targeted perturbation experiments, allowing us to examine the linear and non‐linear responses of the heat content to changes in surface forcing. In these targeted experiments, the heat content is sensitive to both temperature changes and mixed layer volume changes in roughly equal magnitude.last_img read more

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