Living probes into the marine environment – apex predators as oceanographic platforms

first_imgThe primary obstacles to the collection of oceanographic data are the limitations of sampling i n time and in three-dimensional space. Ship-board surveys are well designed for detailed sampling at depth, but are constrained in horizontal space and limited in time by high costs. Satellite monitoring can produce time-series of data over large horizontal spatial scales, but has only limited ability to obtain data concerning parameters at depth, and can also be constrained by the necessity for calibration and ‘ground-truthing’ of data. In contrast, fixed platforms can provide high-resolution data over long time periods, but only within limited three-dimensional space. So what is the answer?last_img read more

Rapid climate change in the ocean west of the Antarctic Peninsula during the second half of the 20th century

first_imgThe climate of the Western Antarctic Peninsula (WAP) is the most rapidly changing in the Southern Hemisphere, with a rise in atmospheric temperature of nearly 3°C since 1951 and associated cryospheric impacts. We demonstrate here, for the first time, that the adjacent ocean showed profound coincident changes, with surface summer temperatures rising more than 1°C and a strong upper-layer salinification. Initially driven by atmospheric warming and reduced rates of sea ice production, these changes constitute positive feedbacks that will contribute significantly to the continued climate change. Marine species in this region have extreme sensitivities to their environment, with population and species removal predicted in response to very small increases in ocean temperature. The WAP region is an important breeding and nursery ground for Antarctic krill, a key species in the Southern Ocean foodweb with a known dependence on the physical environment. The changes observed thus have significant ecological implications.last_img read more

Diurnal variation of ozone depletion during the October–November 2003 solar proton events

first_imgWe have studied the short-term effect of the October–November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES–11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one–dimensional ion and neutral chemistry model. Then we compared the results with ground-based radio propagation measurements, as well as with NO2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to −7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order-of-magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone-depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after-event recovery of ozone is altitude-dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO2 profiles agree well at altitudes 35–60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.last_img read more

The effect of changing Southern Hemisphere winter sea surface temperatures on Southern Annular Mode strength

first_imgWe examine the impact that changes in the winter Southern Hemisphere (SH) meridional sea surface temperature (SST) gradient have on the sign and strength of the SH Annular Mode (SAM). This is undertaken by perturbing either tropical or extra-tropical SSTs in an atmospheric General Circulation Model. Changes in winter tropical SSTs have little direct influence on the SAM but do force a strong wave train in geopotential height across the Southern Ocean. In contrast, changes in winter SSTs in the SH extra-tropics have a profound effect on the SAM: cooler SSTs strengthen the SAM and vice versa. The mechanism involves modifications to the Ferrel cell. As a positive (negative) SAM enhances (reduces) the extra-tropical meridional temperature gradient, these experiments demonstrate a positive feedback mechanism. SAM variability remains unchanged, indicating a shift in the mean, rather than a change in the probability distribution of its positive and negative phaseslast_img read more

Convection-driven melting near the grounding lines of ice shelves and tidewater glaciers

first_imgSubglacial meltwater draining along the bed of fast-flowing, marine-terminating glaciers emerges at thegrounding line, where the ice either goes afloat to form an ice shelf or terminates in a calving face. The input offreshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice–oceaninterface. This process is modeled using the theory of buoyant plumes that has previously been applied to thestudy of the larger-scale circulation beneath ice shelves. The plume grows through entrainment of oceanwaters, and the heat brought into the plume as a result drives melting at the ice–ocean interface. Theequations are nondimensionalized by using scales appropriate for the region where the subglacial drainage,rather than the subsequent addition of meltwater, supplies the majority of the buoyancy forcing. It is foundthat the melt rate within this region can be approximated reasonably well by a function that is linear in oceantemperature, has a cube root dependence on the flux of subglacial meltwater, and has a complex dependencyon the slope of the ice–ocean interface. The model is used to investigate variability in melting induced bychanges in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelvesand tidewater glaciers. The results show how warming ocean waters and increasing subglacial drainage bothgenerate increases in melting near the grounding line.last_img read more

Frontal zones, temperature gradient and depth characterize the foraging habitat of king penguins at South Georgia

first_imgInvestigating the responses of marine predators to oceanographic structures is of key importance for understanding their foraging behaviour and reproductive success. Using Global Positioning System (GPS) and Time-Depth-Temperature-Recorder (TDR) tags, we investigated how king penguins breeding at South Georgia explore their foraging area over the summer season in both the horizontal and vertical dimensions. We determined how horizontal habitat use may relate to different Antarctic Circumpolar Current (ACC) frontal zones and associated thermal structuring of the water column. To study the penguins’ use of the water column, we examined foraging niches defined by temperature, temperature gradient and depth, and explored the importance of these thermal properties for prey pursuit. King penguins foraged within the Polar Front (PF) and its southern edges during incubation, and the Antarctic Zone (AAZ) and Southern ACC Front (SACCF) during brooding. Foraging niches became more distinct with the advancing summer season, defined by strong thermal gradients at shallow depths in the AAZ, and weak gradients at greater depths in the SACCF. These niches indicate foraging in the sub-thermocline Winter Water (WW) in the AAZ, and in deep WW and Circumpolar Deep Water (CDW) at the SACCF. The influence of different ACC frontal zones in the area to the north of South Georgia appears to provide for a horizontally and vertically segregated environment. The presence of optional foraging areas and niches close to the colony clearly play an important role in these king penguins’ foraging success.last_img read more

Eradication of the non-native Poa pratensis colony at Cierva Point, Antarctica: A case study of international cooperation and practical management in an area under multi-party governance

first_imgThe on-going introduction of non-native species to Antarctica due to expanding human activity presents an increasing threat to biodiversity. Under the Protocol on Environmental Protection to the Antarctic Treaty, all introduced non-native species should be removed from the Antarctic Treaty area. The non-native grass Poa pratensis was first introduced to Cierva Point (Danco Coast, Antarctic Peninsula), along with substantial quantities of non-Antarctic soil, in the mid-1950s. Consistent with the Protocol, in January 2015 an internationally coordinated team undertook the eradication of the grass. Immediately prior to removal of P. pratensis, factors affecting its establishment, persistence and impacts upon local indigenous species was examined within the international management framework of the Antarctic Treaty System. The underlying soil had a high organic content of 15.5%, which may have contributed to the successful establishment of P. pratensis and restricted, at least initially, its vegetative growth to the enriched area. Examination of P. pratensis expansion from the original introduction sites showed that the plant colony intricate root system facilitated little or no coexistence of other native plants within its extent. The non-native plant colony also constituted a novel habitat for soil fauna within Antarctic terrestrial environments. The P. pratensis plant colony provided an unfavorable habitat for two of the locally endemic soil invertebrates, Cryptopygus antarcticus and Belgica antarctica. These observations led to the selection of an appropriate eradication approach, where the plants were targeted for physical extraction along with all underlying soil. During the eradication, c. 500 kg of soil and plant material from the P. pratensis colony was removed from the site. Monitoring one year later showed no evidence of re-establishment. Consistent with the Committee for Environmental Protection ‘Non-native Species Manual’, we recommend development and implementation of rapid response protocols following the discovery of a non-native plant colony to limit future impacts on indigenous species and local habitats.last_img read more

Subglacial sediment pathways and deglacial chronology of the northern Barents Sea Ice Sheet

first_imgNew information is presented on the configuration of the northern Barents Sea Ice Sheet (BSIS) during the last glacial and deglaciation (21–11.5 ka). The glacial dynamics of the BSIS that we discuss are based on clay-mineral compositions of subglacial tills and a distinct kaolinite source in the central Barents Sea where previous workers have placed a large, single ice dome for the last glacial BSIS. Our results, which appear to show that subglacial sediments were sourced locally, suggest that the BSIS consisted at least temporarily of multiple domes and may have been more dynamic than previously thought. New radiocarbon dates are presented along with new ice-extent reconstructions for 16.5–15, 14, 13.5 and 11.5 ka. Our reconstructions add information to previous regional and continental-scale efforts in areas east of Svalbard. Ice retreat in the northern Barents Sea progressed as follows. (i) 19–16.5 ka. Major calving led to dynamic thinning in shelf troughs and was accompanied by significant ice-sheet thinning inland as a result of ice drawdown. (ii) 16.5–15 ka. Rapid ice-margin retreat of between 75–100 km occurred, via lift-off and iceberg calving, in Hinlopen and Kvitøya troughs, as well as major retreat (>300 km) in Franz Victoria Trough (FVT) further east. (iii) 15–13.5 ka. Retreat progressed westwards from the FVT towards Svalbard with troughs east of Svalbard (Kvitøya, Olga, and Erik Eriksen) mostly ice-free by 13.5 ka. (iv) 13.5–11.5 ka. Ice retreated gradually towards residual ice masses on Svalbard, Kong Karls Land and possibly Storbanken. Our data require a modification of earlier views of the BSIS because they point toward a more dynamic ice sheet and decay that, once initiated at the shelf break, was dominated by the withdrawal of ice from the FVT that progressed westwards towards the Svalbard archipelago.last_img read more

Changing measurements or changing movements? Sampling scale and movement model identifiability across generations of biologging technology

first_imgAnimal movement patterns contribute to our understanding of variation in breeding success and survival of individuals, and the implications for population dynamics. Over time, sensor technology for measuring movement patterns has improved. Although older technologies may be rendered obsolete, the existing data are still valuable, especially if new and old data can be compared to test whether a behavior has changed over time. We used simulated data to assess the ability to quantify and correctly identify patterns of seabird flight lengths under observational regimes used in successive generations of wet/dry logging technology. Care must be taken when comparing data collected at differing timescales, even when using inference procedures that incorporate the observational process, as model selection and parameter estimation may be biased. In practice, comparisons may only be valid when degrading all data to match the lowest resolution in a set. Changes in tracking technology, such as the wet/dry loggers explored here, that lead to aggregation of measurements at different temporal scales make comparisons challenging. We therefore urge ecologists to use synthetic data to assess whether accurate parameter estimation is possible for models comparing disparate data sets before planning experiments and conducting analyses such as responses to environmental changes or the assessment of management actions.last_img read more

Microplastics in marine sediments near Rothera Research Station, Antarctica

first_imgAntarctica and surrounding waters are often considered pristine, but may be subject to local pollution from tourism, fishing and governmental research programme activities. In particular, the quantification of microplastic pollution within the Antarctic Treaty area (south of latitude 60°S) has received little attention. We examined microplastic particle concentrations in sediment samples from 20 locations up to 7 km from Rothera Research Station. The highest concentrations of microplastic (<5 particles 10 ml−1) were recorded in sediment collected near the station sewage treatment plant outfall. The concentrations were similar to levels recorded in shallow and deep sea marine sediments outside Antarctica. The detected microplastics had characteristics similar to those commonly produced by clothes washing. We recommend further research on microplastics around Antarctic stations to inform policy discussions and the development of appropriate management responses.last_img read more