Review and revision of measurements of stratospheric N2O5

first_imgMeasurements of N2O5 in the stratosphere and of its spectrum at 1240 cm−1 in the laboratory are reviewed. Errors in previous publications about N2O5 are discussed briefly. The earliest stratospheric measurement is significantly revised in the light of new measurements of band strength. All the measured profiles are tabulated using a standard value for the band strength; they can be linearly scaled if future, more accurate, measurements suggest that a different value should be usedlast_img

Large amplitude magnetic anomalies in the northern sector of the Powell Basin, NE Antarctic Peninsula

first_imgMagnetic profiles obtained during the Hesant 92/93 cruise with the R/V Hesperides show large amplitude anomalies (up to 1000 nT) along a 100 km wide band in the northern margin of the Powell Basin. The anomalies, which are also locally identified in the eastern and western margins, are attributed to the continuation of the two branches of the Antarctic Peninsula Pacific Margin Anomaly (PMA). Interactive modelling of two-dimensional bodies in four profiles oriented NNW-SSE allows us to determine the main features of the magnetic source bodies within the continental crust. These are elongated in a N60/degE trend, and their base is located at a depth exceeding 15 km. Equivalent magnetic susceptibilities mostly between 0.07 and 0.1 (SI) are obtained. These values are consistent with the hypothesis that remanent magnetisation of the magnetic source bodies is sub-parallel to the present geomagnetic field (norÍmally magnetised). The general trends of the bathymetry a nd the geometry of the acoustic basement on multichannel seismic profiles are consistent with the upper surface of magnetic bodies. In order to match the observed anomalies it is also necessary to consider a second tabular shaped body with induced magnetisation in almost all the profiles, which could represent layers 2 and 3 of the oceanic crust of the Powell Basin. Three different geometries of connection between the anomalies in the Powell Basin margins and the PMA branches are discussed. The most plausible one is the occurrence of two branches, although they are closer together than in the Bransfield Strait. The northern branch would continue along the fragments of continental crust of the South Scotia Ridge located at the northern boundary of the Powell Basin, whereas the southern branch would be located only in the eastern and western passive margins of the Powell Basin. The apparent splitting of the southern branch of the anomalous body indicates that it was emplaced before Oligo cene times, when the opening of this basin occurred, and that it was subsequently fragmented during the Cenozoic. A possible time of formation of the PMA body would be during the long Cretaceous normal polarity interval, which also coincides with a peak in magmatic activity along the Antarctic Peninsula.last_img read more

Costs and consequences of evolutionary temperature adaptation

first_imgTemperature affects everything that an organism does. Although we have an increasingly sophisticated understanding of evolutionary adaptation to temperature at the molecular level for some cellular processes, we still know little about evolutionary temperature adaptation in gene expression, cell-cycle control or growth, all of which influence organism performance and fitness. Recent studies have shown that the physiological costs of evolutionary temperature adaptation vary with body temperature. Here, I argue that this macroecological pattern has powerful consequences for life-history theory, and probably also for food-web dynamics, biological diversity and biotic response to climate change. The relationships among evolution, temperature and ecology are multivariate, hierarchical and complex making evolutionary physiology at the macroecological scale an exciting and challenging agenda for the next decade.last_img read more

Community structure and grazing impact of mesozooplankton during late spring/early summer 2004/2005 in the vicinity of the Crozet Islands (Southern Ocean)

first_imgNet sampling within the vicinity of the Crozet archipelago, in the Indian Ocean sector of the Southern Ocean, was conducted during late spring/summer (November 2004-January 2005) to describe the composition, distribution and grazing impact of mesozooplankton, and to investigate their relationships with the prevailing oceanographic regime in the area. The mesozooplankton community was intimately linked with the large-scale physical circulation in the region. To the west and north of the Islands, the sub-Antarctic Front (SAF) presented a strong biogeographic boundary between subtropical and sub-Antarctic species. South and east of the SAF, the mesozooplankton community was dominated by Polar Frontal Zone (PFZ) copepod species. Cluster analysis of mesozooplankton abundance data identified two main communities in the PFZ, termed here Island and Oceanic. Island stations, representing the proposed iron-fertilised productive region north of the archipelago, contained an abundance (mean of 2269 ind m(-3)) of the neritic copepod Drepanopus pectinatus, whose presence indicated that the water had interacted with the Crozet Island shelf at some point. D. pectinatus was present in samples north of Crozet up to the SAF, confirming that water passing the Crozet Islands could be transported, throughout the region to the north. The Oceanic stations, south of the Islands and within the SAF, contained similar mesozooplankton abundances and biovolume to the Island stations suggesting little enhanced impact of the iron-fertilised phytoplankton bloom through the mesozooplankton food web. Copepod community grazing pressure, in both Island and Oceanic stations, during November and December was small ( < 7% of chlorophyll-a standing stock per day, < 35% primary production per day). By January, a phytoplankton bloom had developed at some of the Island stations (up to similar to 3000 mg C m(-2) d(-1)) and grazing pressure was < 1% of chlorophyll-a standing stock per day. At the oceanic stations, primary productivity had reduced from similar to 460 to similar to 200 mg C m(-2) d(-1), typical values for high-nutrient low-chlorophyll (HNLC) waters, and the copepod community grazing pressure had increased to similar to 90% of daily primary productivity. This suggests that a combination of grazing and micronutrient availability controls phytoplankton biomass in HNLC waters to the south of Crozet, while grazing had little impact on the "iron- fertilised" bloom north of the Crozet Islands. The intense seasonal phytoplankton bloom around Crozet may therefore be exported to the sea floor rather than fuelling the higher trophic levels. (C) 2007 Elsevier Ltd. All rights reserved.last_img read more

Climate change and the Antarctic marine ecosystem: an essay on management implications

first_imgIn this paper we review evidence for, and anticipated consequences of, climate change in Antarctic marine communities, examining the potential impacts on invertebrates and vertebrates alike and exploring plausible outcomes for species, with examples principally from the Antarctic literature. We suggest that industries with the greatest potential to aggravate climate change impacts on marine communities are marine capture fisheries. In the Southern Ocean, harvesting is governed under the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR). CCAMLR espouses an ecological management framework and so has the capacity to mitigate harvesting impacts such that they do not worsen impacts from climate change. We discuss some of the implications of climate change and advocate that CCAMLR address certain key issues if it is to fulfil its international obligations. It will be essential for CCAMLR to determine relative risks (uncertainties), impacts and timescales, of various processes consequent on climate change. Such risk assessments should be feasible with current knowledge and should provide a focus for future work. We believe it will be important to prioritize issues that reduce impacts and uncertainties by the greatest degree, and propose that future plans should involve shared responsibility (e.g. with SCAR etc.) for each of the risks described.last_img read more

Cellular biomarkers to elucidate global warming effects on Antarctic sea urchin Sterechinus neumayeri

first_imgGlobal warming is a reality and its effects havebeen widely studied. However, the consequences for marineinvertebrates remain poorly understood. Thus, thepresent study proposed to evaluate the effect of elevatedtemperature on the innate immune system of Antarctic seaurchin Sterechinus neumayeri. Sea urchins were collectednearby Brazilian Antarctic Station ‘‘Comandante Ferraz’’and exposed to 0 (control), 2 and 4C for periods of 48 h, 2,7 and 14 days. After the experimental periods, coelomicfluid was collected in order to perform the followinganalyses: coelomocytes differential counting, phagocyticresponse, adhesion and spreading coelomocytes assay,intranuclear iron crystalloid and ultra structural analysis ofcoelomocytes. The red sphere cell was considered a biomarkerfor heat stress, as they increased in acute stress.Besides that, a significant increase in phagocytic indexeswas observed at 2C coinciding with a significant increaseof intranuclear iron crystalloid at the same temperature andsame time period. Furthermore, significant alterations incell adhesion and spreading were observed in elevatedtemperatures. The ultra structural analysis of coelomocytesshowed no significant difference across treatments. Thiswas the first time that innate immune response alterationswere observed in response to elevated temperature in a Polar echinoid.last_img read more

Nonbreeding distribution of flesh-footed shearwaters and the potential for overlap with north Pacific fisheries

first_imgPopulations of flesh-footed shearwaters on Lord Howe Island, Tasman Sea, have declined recently, with mortality in longline fisheries likely to be one of the major causes. It is therefore imperative to increase our understanding of their distribution at sea, especially during winter. Although they are known to migrate to the north Pacific Ocean, until this study there was very little information available on timing of movements, distribution and habitat use of individuals. Ten to 16 flesh-footed shearwaters (37 in total) were tracked from Lord Howe Island in each of three winter seasons (2005, 2007 and 2008). All birds migrated to the north-west Pacific Ocean, with approximately 70% wintering to the east of Japan in the Kurashio and Oyashio currents, around the Bonin Islands in the north Philippine Sea, or in the eastern Sea of Japan. Others spent a varying amount of time in the Yellow and East China seas, or in the western Sea of Japan. These waters already support intensive fisheries and demand for seafood is likely to rise in tandem with the increasing human populations of East Asia. Consequently, results presented here show that members of the largest population of flesh-footed shearwaters winter exclusively in the north-west Pacific Ocean around Japan and East Asia, in areas they are likely to overlap extensively with a number of fisheries; it is therefore imperative to obtain more information on current and projected levels of bird bycatch and effort in these fisheries in order to developing management strategies for the conservation of the east Australian and New Zealand populations of the flesh-footed shearwater.last_img read more

The Antarctic ozone hole during 2013

first_imgWe review the 2013 Antarctic ozone hole, making use of various ground-based, in-situ and remotely-sensed ozone measurements, ground-based measurements of ultraviolet radiation and meteorological reanalyses. Based on analysis of 34 years of satellite records spanning 1979-2013 (which excludes 1995), we find that in terms of maximum area, minimum ozone level and total ozone deficit, the ozone hole in 2013 was typical of other years of moderate ozone loss. The estimated integrated ozone mass effectively depleted within the ozone hole of 2013 was approximately 1037 Mt, which was the 17th largest deficit on record and 41% of the peak deficit observed in 2006. Anomalously cold winter temper-atures in the lower stratosphere over Antarctica and concurrent strong and stable vortex conditions favoured the potential for strong ozone depletion in 2013. However, anomalous warming of the polar vortex that occurred from late Au-gust limited the overall severity of ozone depletion during spring, and resulted in the relatively early breakup of the ozone hole in mid-November.last_img read more

Evidence of sub-MeV EMIC-driven electron precipitation

first_imgElectromagnetic ion cyclotron (EMIC) waves are potentially important drivers of the loss of energetic electrons from the radiation belts. Numerous theoretical calculations exist with conflicting predictions of one of the key parameters: the minimum resonance energy of electrons precipitated into the atmosphere by EMIC waves. In this study we initially analyze an EMIC electron precipitation event using data from two different spacecraft instruments to investigate the energies involved. Combining observations from these satellites, we find that the electron precipitation has a peak flux at ∼250 keV. Extending the analysis technique to a previously published database of similar scattering events, we find that the peak electron precipitation flux occurs predominantly around 300 keV, with only ∼11% of events peaking in the 1–4 MeV range. Such a significant population of low-energy EMIC-driven electron precipitation events highlights the possibility for EMIC waves to be significant drivers of radiation belt electron losses.last_img read more

Inhomogeneity of the surface air temperature record from Halley, Antarctica

first_imgCommencing in 1956, observations made at Halley Research Station, Antarctica provide one of the longest continuous series of near-surface temperature observations from the Antarctic continent. Since few other records of comparable length are available, the Halley record has been used extensively in studies of long-term Antarctic climate variability and change. The record does not, however, come from a single location but is a composite of observations from a sequence of seven stations, all situated on the Brunt Ice Shelf, that range from around 10 km to 50 km distance from the coast. Until now, it has generally been assumed that temperature data from all of these stations could be combined into a single composite record with no adjustment. Here, we examine this assumption of homogeneity. Application of a statistical change point algorithm to the composite record detects a sudden cooling associated with the move from Halley IV to Halley V station in 1992. We show that this temperature step is consistent with local temperature gradients measured by a network of automatic weather stations and with those simulated by a high-resolution atmospheric model. These temperature gradients are strongest in the coastal region and result from the onshore advection of maritime air. The detected inhomogeneity could account for the weak cooling trend seen in the uncorrected composite record. In future, studies that make use of the Halley record will need to account for its inhomogeneity.last_img read more