Palæomagnetism of some dolerite intrusions from the Theron Mountains and Whichaway Nunataks, Antarctica

first_imgAs a part of the scientific activity of the Commonwealth Trans-Antarctic Expedition a collection of eight oriented samples was made by Stephenson from dolerite sills and dykes in the region of the Theron Mountains, Shackleton Range and Whichaway Nunataks. The seven intrusions which have been sampled bear petrological affinities with the Karroo Dolerites of South Africa and with the dolerite sills of Tasmania, and are thought to be of comparable age. They intrude flat-lying sediments and show no evidence of post-formational tilting.last_img read more

Morphology and adaptation of aquatic mosses in an Antarctic lake

first_imgTwo species of moss growing in Moss Lake on Signy Island, South Orkney Islands, had unusual morphologies with large leaves and long internodes. Both Calliergon sarmentosum and Drepanocladus cf. aduncus differed from their terrestrial counterparts and from each other in the character of their leaves. The two genera differed in the ability of the terrestrial forms to develop a large-leaved growth form. Calliergon, which was represented by the same species in both environments, changed to the aquatic morphology when separated shoots were grown either submerged or under damp conditions. Ught intensity was not an important factor influencing change in morphology. In contrast, terrestrial Drepanocladus uncinatus, the closest taxonomic counterpart of D. cf. aduncus on Signy Island, did not show any adaptation under similar conditions. The aquatic forms also showed a corresponding degree of plasticity in their natural habitat. Calliergon varied from robust shoots to microphyllous or even leafless stems whereas Drepanocladus cf. aduncus only grew in the robust form. These differences were related to the success of the two species at different depths and it is suggested that the very low compensation points of the two mosses (reported in a separate study) resulted from the morphology of the plants.last_img read more

The occurrence of the Upper Jurassic bivalve Malayomaorica malayomaorica (Krumbeck) on the Orville Coast, Antarctica

first_imgMalayomaorica malayomaorica is an important Upper Jurassic bivalve in the southern hemisphere: widely distributed in strata of Early – Middle Kimmeridgian age, it is a zone fossil of considerable potential for regional biostratigraphic correlations. Its common occurrence in the Latady Formation of the Orville Coast, Antarctica, indicates that at least part of this stratigraphic unit has a Kimmeridgian age. Although its precise taxonomic status remains in some doubt, it would appear to be the earliest buchiid-like bivalve so far recorded from the southern hemisphere. Its very wide distribution around the margins of Gondwana is similar to that established for species of the Late Jurassic bivalve genera Retroceramus, Buchia and Anopaealast_img read more

Vertebrate records in polar sediments: Biological responses to past climate change and human activities

first_imgBiological responses to climate and environmental changes in remote polar regions are of increasing interest in global change research. Terrestrial and marine polar ecosystems have suffered from impacts of both rapid climate change and intense human activities, and large fluctuations in the population sizes of seabirds, seals, and Antarctic krill have been observed in the past decades. To understand the mechanisms driving these regime shifts in polar ecosystems, it is important to first distinguish the influences of natural forcing from anthropogenic activities. Therefore, investigations of past changes of polar ecosystems prior to human contact are relevant for placing recent human-induced changes within a long-term historical context. Here we focus our review on the fossil, sub-fossil, archaeological, and biogeochemical remains of marine vertebrates in polar sediments. These remains include well-preserved tissues such as bones, hairs and feathers, and biogeochemical markers and other proxy indicators, including deposits of guano and excrement, which can accumulate in lake and terrestrial sediments over thousands of years. Analyses of these remains have provided insight into both natural and anthropogenic impacts on marine vertebrates over millennia and have helped identify the causal agents for these impacts. Furthermore, land-based seabirds and marine mammals have been shown to play an important role as bio-vectors in polar environments as they transport significant amounts of nutrients and anthropogenic contaminants between ocean and terrestrial ecosystems.last_img read more

Where to find 1.5 million yr old ice for the IPICS “Oldest-Ice” ice core

first_imgThe recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.last_img read more

Observational evidence of the influence of Antarctic stratospheric ozone variability on middle atmosphere dynamics

first_imgModeling results have suggested that the circulation of the stratosphere and mesosphere in spring is strongly affected by the perturbations in heating induced by the Antarctic ozone hole. Here using both mesospheric MF radar wind observations from Rothera Antarctica (67°S, 68°W) as well as stratospheric analysis data, we present observational evidence that the stratospheric and mesospheric wind strengths are highly anti-correlated, and show their largest variability in November. We find that these changes are related to the total amount of ozone loss that occurs during the Antarctic spring ozone hole and particularly with the ozone gradients that develop between 57.5°S and 77.5°S. The results show that with increasing ozone loss during spring, winter conditions in the stratosphere and mesosphere persist longer into the summer. These results are discussed in the light of observations of the onset and duration of the Antarctic polar mesospheric cloud seasonlast_img read more

Holocene break-up and reestablishment of the Petermann Ice Tongue, Northwest Greenland

first_imgOver the last decade, two major calving events of the Petermann Ice Tongue in Northwest Greenland have led to speculation on its future stability and contribution to further Greenland Ice Sheet mass loss. However, it has been unclear if these events are anomalous or typical within the context of limited historical observations. We extend the historical record of the floating ice tongue using the stratigraphy of Petermann Fjord sediments to provide a longer-term perspective. Computed tomography (CT) scans, X-Ray Fluorescence (XRF) scans, Ice-Rafted Debris (IRD) counts, and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites, allowing for reconstructions of past behavior of the Petermann Ice Tongue. Radiocarbon dating of foraminifera, 210Pb, and paleomagnetic secular variation (PSV) provide age control and help to address uncertainties in radiocarbon reservoir ages. A floating ice tongue in Petermann Fjord formed in late glacial time as Petermann Glacier retreated from an advanced grounded position. This paleo-ice tongue broke-up during the early Holocene when high northern latitude summer insolation was higher than present. After gradual regrowth of the ice tongue associated with regional cooling, the ice tongue reached its historical extent only within the last millennium. Little or no ice tongue was present for nearly 5000 years during the middle Holocene, when decadal mean regional temperatures are estimated to be 0.8e2.9 °C higher than preindustrial (1750 CE) and seasonal sea-ice in the Lincoln Sea was reduced. This pre-historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break-up by the mid- 21st Century.last_img read more

Gene network analyses support subfunctionalization hypothesis for duplicated hsp70 genes in the Antarctic clam

first_imgA computationally predicted gene regulatory network (GRN), generated from mantle-specific gene expression profiles in the Antarctic clam Laternula elliptica, was interrogated to test the regulation and interaction of duplicated inducible hsp70 paralogues. hsp70A and hsp70B were identified in the GRN with each paralogue falling into unique submodules that were linked together by a single shared second neighbour. Annotations associated with the clusters in each submodule suggested that hsp70A primarily shares regulatory relationships with genes encoding ribosomal proteins, where it may have a role in protecting the ribosome under stress. hsp70B, on the other hand, interacted with a suite of genes involved in signalling pathways, including four transcription factors, cellular response to stress and the cytoskeleton. Given the contrasting submodules and associated annotations of the two hsp70 paralogues, the GRN analysis suggests that each gene is carrying out additional separate functions, as well as being involved in the traditional chaperone heat stress response, and therefore supports the hypothesis that subfunctionalization has occurred after gene duplication. The GRN was specifically produced from experiments investigating biomineralization; however, this study shows the utility of such data for investigating multiple questions concerning gene duplications, interactions and putative functions in a non-model species.last_img read more

Can DEB models infer metabolic differences between intertidal and subtidal morphotypes of the Antarctic limpet Nacella concinna (Strebel, 1908)?

first_imgStudying the influence of changing environmental conditions on Antarctic marine benthic invertebrates is strongly constrained by limited access to the region, which poses difficulties to performing long-term experimental studies. Ecological modelling has been increasingly used as a potential alternative to assess the impact of such changes on species distribution or physiological performance.last_img

Variation in zoobenthic blue carbon in the Arctic’s Barents Sea Shelf Sediments

first_imgThe flow of carbon from atmosphere to sediment fauna and sediments reduces atmospheric CO2, which in turn reduces warming. Here, during the Changing Arctic Ocean Seafloor programme, we use comparable methods to those used in the Antarctic (vertical, calibrated camera drops and trawl-collected specimens) to calculate the standing stock of zoobenthic carbon throughout the Barents Sea. The highest numbers of morphotypes, functional groups and individuals were found in the northernmost sites (80–81.3° N, 29–30° E). Ordination (non-metric multidimensional scaling) suggested a cline of faunal transition from south to north. The functional group dominance differed across all six sites, despite all being apparently similar muds. Of the environmental variables we measured, only water current speed could significantly explain any of our spatial carbon differences. We found no obvious relationship with sea ice loss and thus no evidence of Arctic blue carbon–climate feedback. Blue carbon in the Barents Sea can be comparable with the highest levels in Antarctic shelf sediments. This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning’.last_img read more