The measurement of food and energy intake in man—an evaluation of some techniques

first_imgA dietary survey was carried out on an Antarctic base over a period of 6 to 12 months on twelve individuals. Three methods of determining individual food and energy intake were used—weighing and recording of food as eaten in combination with food tables, dietary recall, and bomb calorimetry of duplicate meals. Use of weighed food intakes and food composition tables underestimated energy intake by 7% when compared to analysis of duplicate meals by bomb calorimetry. One week was found to be the most practical period over which intake should be measured to determine “habitual” food intake.last_img read more

Weddell Sea abyssal sediments a record of Antarctic Bottom Water Flow

first_imgDeep circulation in the Weddell Sea is a clockwise gyre, with bottom water formed by mixing along the southern and western margins. Most Antarctic Bottom Water originates here, leaving the Weddell Sea to the east (depths > 4500 m) or to the north (depths 16 m/Ma. Sediments from the deep Weddell Basin are hemipelagic muds with ash laminae and (mainly in the centre of the gyre) distal turbidites derived from the southwest. Thin debris flows occur near seamounts. The hemipelagic muds become coarser from the centre to the edge of the gyre. Winnowing by strong bottom currents is localised along the northern margin of the basin. The absence of diatoms from the Weddell Basin sediments may result from dissolution as well as low productivity. Sediments from Jane Basin consist of alternating diatomaceous and barren hemipelagic muds, considered to represent interglacial and glacial conditions respectively. The diatomaceous sediments contain more silt, suggesting that bottom water flow increases during interglacial periods.last_img read more

A general method for the linear stability analysis of stratified shear flows

first_imgA general method for testing the stability of a stratified, parallel shear flow is presented. The technique allows the routine determination of unstable modes from any high resolution radiosonde data and is a development of the procedure described by Lalas and Einaudi. Stability analyses of several idealized velocity profiles have been performed in order to validate the method. A particularly important feature is the ability to predict marginally unstable modes with more than one critical level; several examples are presented. An example using real radiosonde data is given.last_img read more

Petrography and provenance of the Marambio Group, Vega Island, Antarctica

first_imgLate Cretaceous sedimentary rocks assigned to the Santa Marta (Herbert Sound Member) and López de Bertodano (Cape Lamb and Sandwich Bluff members) formations of the Marambio Group, crop out on Cape Lamb, Vega Island. Although previous studies have recognized that these sedimentary rocks were derived from the northern Antarctic Peninsula region, the work presented here allows the provenance and palaeogeographical evolution of the region to be described in detail. On the basis of both sandstone petrography and clay mineralogy, the Herbert Sound and Cape Lamb members reflect sediment input from a low relief source area, with sand grade sediment sourced from low grade metasediments, and clay grade sediment ultimately derived from the weathering of an andesitic source area. In contrast, the Sandwich Bluff Member reflects a switch to a predominantly andesitic volcaniclastic source. However, this sediment was largely derived from older volcanic suites due to renewed source area uplift, with only a minor component from coeval volcanism. Regional uplift of both the arc terrane and the western margin of the James Ross Basin was likely during the Maastrichtian.last_img read more

Influence of environmental variability on breeding effort in a long-lived seabird, the yellow-nosed albatross

first_imgThe provisioning parameters, breeding success, adult mass, and survival of yellow-nosed albatrosses were studied over 7 successive years at Amsterdam Island, southern Indian Ocean. We examined the ability of this long-lived seabird to adjust its breeding effort under different environmental conditions and the fitness consequences in terms of survival and quality of offspring produced. Provisioning rate and adult mass varied extensively between years, and the lowest and highest values were associated with sea surface temperature anomalies. When waters around the island were colder, adults were in good condition and brought large meals at short intervals, whereas warmer waters resulted in lower provisioning rates, lower adult mass, and lighter chicks at fledging. Adult survival and fledging success were not affected by sea surface temperature anomalies. Yellow-nosed albatrossesappear to be unable to adjust their breeding effort every season, and their differential breeding investment probably primarily reflects different levels of food availability. Yellow-nosed albatrosses are able to regulate their provisioning behavior according to the nutritional status of their chick only when conditions are favorable. Birds appear to invest primarily in their own future maintenance rather than in provisioning. They have a wide safety margin in body mass that limits mortality risks during goodyears as well as during poor years. However, during unfavorable seasons adults continue to provision chicks that have a poor prospect of survival to breeding, without additional survival costs for the parents. Favorable seasons therefore have a high value in terms of fitness because of the high quality of the chick produced. We suggest that understanding how long-lived animalsoptimize their provisioning behavior and lifetime reproduction can only be achieved through studies encompassing several contrasted seasons.last_img read more

Sea ice is a mushy layer

first_imgSea ice is a two-phase, two-component, reactive porous medium: an example of what is known in other contexts as a mushy layer. The fundamental conservation laws underlying the mathematical description of mushy layers provide a robust foundation for the prediction of sea-ice evolution. Here we show that the general equations describing mushy layers reduce to the model of Maykut and Untersteiner (1971) under the same approximations employed therein.last_img

The effects of temperature on peripheral neuronal function in eurythermal and stenothermal crustaceans

first_imgTo determine whether neuronal function in Antarctic crustaceans is adapted to the low and narrow range of temperatures at which these animals live, we have compared conduction velocities in the peripheral nervous systems of two temperate species, the decapod Carcinus maenas and the isopod Ligia oceanica, and two Antarctic species, the isopod Glyptonotus antarcticus and the amphipod Paraceradocus gibber. Neuronal conduction velocity differs among the species in the order C. maenas > G. antarcticus > P. gibber > L. oceanica. When measured at the normal environmental temperatures characteristic of each species, conduction velocity of the Antarctic peracarid P. gibber is greater than that of its similar sized temperate relativeL. oceanica, demonstrating complete thermal compensation. The temperate decapod C. maenas has a higher thermal dependence of neuronal conduction velocity than either of the Antarctic species, G. antarcticus and P. gibber, but the temperate L. oceanica does not. These data, when collated with published values, indicate that peracarid crustaceans (L. oceanica, G. antarcticus and P. gibber) have lower neuronal conduction velocities and a lower thermal dependence of neuronal conduction velocity than do other arthropods, irrespective of habitat. There is a linear dependence of conduction velocity on temperature down to –1.8°C in all three species. Our data extend by more than 10° the lower range of temperatures at which conduction velocities have been tested systematically in previous studies. The upper thermal block of neuronal conduction is similar in C. maenas, G. antarcticus, P. gibber and L. oceanica at 24.5, 19.5, 21.5 and 19.5°C, respectively. This suggests that failure to conduct action potentials is not what determines the mortality of Antarctic invertebrates at approximately 10°C. The excitability of axons in the leg nerve of G. antarcticus is not affected by temperatures ranging from –1.8 to +18°C. The responses of sensory neurones activated by movements of spines on the leg, however, are strongly modulated by temperature, with maximal responses at 5–10°C; well above the normal environmental temperature range for the species. The responses fail at 20–22°C. The number of large diameter axons (which produce the fast action potentials recorded in this study) is the same in L. oceanica and G. antarcticus, but the median axon diameter is greater in L. oceanica than G. antarcticus. In G. antarcticus, however, there are glial wrappings around some large (>5 µm diameter) axons that may increase their conduction velocity. Such wrappings are not found in L. oceanica.last_img read more

Marine cold-air outbreaks in the North Atlantic: temporal distribution and associations with large-scale atmospheric circulation

first_imgThe spatial and temporal distributions of marine cold air outbreaks (MCAOs) over the northern North Atlantic have been investigated using re-analysis data for the period from 1958 to 2007. MCAOs are large-scale outbreaks of cold air over a relatively warm ocean surface. Such conditions are known to increase the severity of particular types of hazardous mesoscale weather phenomena. We used a simple index for identifying MCAOs: the vertical potential temperature gradient between the sea surface and 700 hPa. It was found that atmospheric temperature variability is considerably more important than the sea surface temperature variability in governing both the seasonal and the inter-annual variability of MCAOs. Furthermore, a composite analysis revealed that a few well-defined and robust synoptic patterns are evident during MCAOs in winter. Over the Labrador and Irminger Seas the MCAO index was found to have a correlation of 0.70 with the North Atlantic Oscillation index, while over the Barents Sea a negative correlation of 0.42 was found.last_img read more

Ecosystem impacts of feral rabbits on World Heritage sub-Antarctic Macquarie Island: a palaeoecological perspective

first_imgThe introduction and establishment of non-indigenous species through human activities often poses a major threat to natural biodiversity. In many parts of the world management efforts are therefore focused on their eradication. The environment of World Heritage sub-Antarctic Macquarie Island has been severely damaged by non-indigenous species including rabbits, rats and mice, introduced from the late AD 1800s. An extensive eradication programme is now underway which aims to remove all rabbits and rodents. To provide a long-term context for assessing the Island’s pre-invasion state, invasion impacts, and to provide a baseline for monitoring its recovery, we undertook a palaeoecological study using proxies in a lake sediment core. Sedimentological and diatom analyses revealed an unproductive catchment and lake environment persisted for ca. 7100 years prior to the introduction of the invasive species. After ca. AD 1898, unprecedented and statistically significant environmental changes occurred. Lake sediment accumulation rates increased >100 times due to enhanced catchment inputs and within-lake production. Total carbon and total nitrogen contents of the sediments increased by a factor of four. The diatom flora became dominated by two previously rare species. The results strongly suggest a causal link between the anthropogenic introduction of rabbits and the changes identified in the lake sediments. This study provides an example of how palaeoecology may be used to determine baseline conditions prior to the introduction of non-indigenous species, quantify the timing and extent of changes, and help monitor the recovery of the ecosystem and natural biodiversity following successful non-indigenous species eradication programmes.last_img read more

Experimental influence of pH on the early life-stages of sea urchins II: increasing parental exposure times gives rise to different responses

first_imgMany studies into the responses of early life-stages to ocean acidification utilise offspring obtained from parents reared under present-day conditions. Their offspring are directly introduced to altered-pH conditions. This study determined whether this approach is suitable by pre-exposing parent sea urchins (Psammechinus miliaris) to altered seawater pH (~1000 μatm) for several durations, spawning them and rearing their offspring to settlement. Parents acclimated when exposed to low seawater pH for extended periods (>42 d). Longer adult pre-exposures reduced larval survival and less competent offspring were removed from populations earlier than in controls. Control offspring were larger during earlier development stages (2–7 d), but smaller during later development stages (14 + d) than offspring reared under low pH conditions. Juvenile settlement levels were similar across all treatments. After 17 d, offspring sourced from parents pre-exposed to low pH for 42 and 70 d were larger than those pre-exposed for 28 d and ambient sourced offspring directly transferred to low pH. These different responses show that the use of ambient derived offspring utilised in many studies is likely not an ideal approach when assessing larval development responses via morphometric measurements and survivorship prior to settlement. This study also suggests that calcifying organisms have capacities to acclimate and possibly adapt towards conditions beyond natural rates of ocean acidification.last_img read more