Continuous moulting by Antarctic krill drives major pulses of carbon export in the north Scotia Sea, Southern Ocean

Antarctic krill play an important role in biogeochemical cycles and can potentially generate high-particulate organic carbon (POC) fluxes to the deep ocean. They also have an unusual trait of moulting continuously throughout their life-cycle. We determine the krill seasonal contribution to POC flux in terms of faecal pellets (FP), exuviae and carcasses from sediment trap samples collected in the Southern Ocean. We found that krill moulting generated an exuviae flux of similar order to that of FP, together accounting for 87% of an annual POC flux (22.8 g m−2 y−1). Using an inverse modelling approach, we determined the krill population size necessary to generate this flux peaked at 261 g m−2. This study shows the important role of krill exuviae as a vector for POC flux. Since krill moulting cycle depends on temperature, our results highlight the sensitivity of POC flux to rapid regional environmental change

Recruitment of Antarctic krill Euphausia superba in the South Georgia region: adult fecundity and the fate of larvae

The high concentration of adult Antarctic krill Euphausia superba Dana around South Georgia, Antarctica, is a product of immigration and not local recruitment. We investigated whether reproduction and early larval development are the cause of local recruitment failure. It was found that the majority of adult females were reproductively active in summer and that there was a comparatively high investment in the ovary, reaching up to 46% of the total wet weight of the krill. The corresponding egg batches were amongst the largest ever reported for E. superba. A semi-empirical model predicted that 11% of females completed just 1 spawning episode per year, 60% completed 2, and 29% completed 3 or more. On average, a South Georgian krill released 12 343 eggs yr–1. The eggs were unable to complete the descent–ascent developmental cycle on-shelf because the bathymetry was too shallow but, off-shelf, they were predicted to sink to between 490 and 520 m and return to the surface either as a metanauplius or 1st calyptopis stage with plenty of energy reserves remaining. Feeding conditions were adequate for the development of later larval stages once these reserves were exhausted. Although net surveys found calyptopis and early stage furcilia in the vicinity of South Georgia, numbers were mostly lower than predicted. Overall, reproduction or early stage development are successful in this region, leaving predation on larvae and advective export during winter as the main potential causes of local recruitment failure

Synchroton energy dispersive powder diffraction A report on trial experiments conducted on station 9.7 at the Daresbury Synchroton Radiation Facility

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Comparison of the structure and function of Southern Ocean regional ecosystems: The Antarctic Peninsula and South Georgia

The ocean ecosystems around the west Antarctic Peninsula and South Georgia are two of the best described regional ecosystems of the Southern Ocean. They therefore provide a useful basis for developing comparative analyses of ocean ecosystems around the Antarctic. There are clear and expected differences in seasonality and species composition between the two ecosystems, but these mask an underlying similarity in ecosystem structure and function. This similarity results from the two ecosystems being part of a continuum, from more ice covered regions in the south to open water regions in the north. Within this continuum the major factors affecting ecosystem structure and function are the sea ice, the biogeochemical conditions and the connectivity generated by the flow of the Antarctic Circumpolar Current. Antarctic krill are central to the food web in both ecosystems, but the other species of plankton and predators present are different. These different species provide alternative pathways of energy transfer from primary production to the highest trophic levels. The relative dominance of these species can provide indicators of change in ecosystem structure and function. Both ecosystems are changing as a result of physically and biologically driven processes, and the ecological responses being observed are complex and variable across different species and within the two regions. Species in parts of the northern Antarctic Peninsula are being replaced by species that currently dominate farther north in more oceanic areas such as at South Georgia. The similarity of structure and strong connectivity, mean that projections of future change will require generic models of these ecosystems that can encompass changes in structure and function within a connected continuum from ice covered to open water in winter

Spatial and Temporal Operation of the Scotia Sea Ecosystem

Analysis of the operation of ocean ecosystems requires an understanding of how the structure of the ecosystem is determined by interactions between physical, chemical and biological processes. Such analysis needs to consider the interactions across a wide range of spatial (approx. 10 m–10,000 km) and temporal (minutes to centuries) scales and trophic levels (primary producers to top predators) (Angel, 1994; Murphy et al., 1988;Werner et al., 2003). There are, however, few areas of the global ocean where there is sufficient knowledge to achieve such an integrated analysis (deYoung et al., 2004). Circulation patterns of the major ocean gyres, such as the North Atlantic and Pacific Oceans, involve movement of water masses through very different climatic regimes which favour distinctly different groups of organisms (Longhurst, 1998). Generating comprehensive views of the operation of oceanic ecosystems is complicated as a result of such heterogeneity in species distribution and ecosystem structure (Levin, 1990; Longhurst, 1998; Murphy et al., 1988). In contrast to othe

Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño–Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts