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We investigate the seasonal variability in freshwater inputs to the Marguerite Bay region (Western Antarctic Peninsula) using a time series of oxygen isotopes in seawater from samples collected in the upper mixed layer of the ocean during 2002 and 2003. We find that meteoric water, mostly in the form of glacial ice melt, is the dominant freshwater source, accounting for up to 5% of the near-surface ocean during the austral summer. Sea ice melt accounts for a much smaller percentage, even during the summer (maximum around 1%). The seasonality in meteoric water input to the ocean (around 2% of the near-surface ocean) is not dissimilar to that of sea ice melt (around 2% in 2002 and 1% in 2003), contradicting the assumption that sea ice processes dominate the seasonal evolution of the physical ocean environment close to the Antarctic continent. Three full-depth profiles of oxygen isotopes collected in successive Decembers (2001, 2002 and 2003) indicate that around 4 m of meteoric water is present in the water column at this time of year, and around 1 m of sea ice formed from this same water column. The predominance of glacial melt is significant, since it is known to be an important factor in the operation of the ecosystem, for example by providing a source of nutrients and modifying the physical environment to control the spatial extent and magnitude of phytoplankton blooms.The Western Antarctic Peninsula is undergoing a very rapid change in climate, with increasing ocean and air temperatures, retreating glaciers and increases in precipitation associated with changes in atmospheric circulation. As climate change continues, we expect meteoric water inputs to the adjacent ocean to rise further. Sea ice in this sector of the Antarctic has shown a climatic decrease, thus we expect a reduction in oceanic sea ice melt fractions if this change continues. Continued monitoring of the oceanic freshwater budget at the western Peninsula is 2 needed to track these changes as they occur, and to better understand their ecological consequences.

The ocean around South Georgia, in the southwest Atlantic sector of the Southern Ocean, is highly productive, with large stocks of Antarctic krill supporting extensive colonies of marine and land-based predators. The operation of this ecosystem is strongly influenced by physical forcings, and the role of the El Niño/Southern Oscillation (ENSO) phenomenon has been highlighted previously. Here we examine in detail the transmission of ENSO signals to South Georgia, and investigate other sources of interannual variability.ENSO variability generates anomalies in sea surface temperature (SST) across the South Pacific via atmospheric teleconnections. These anomalies are advected toward South Georgia within the Antarctic Circumpolar Current (ACC), and previous studies have focussed on long-period advection (order of 2-3 years) from the southwest Pacific. We observe here, however, that the region close to the Antarctic Peninsula in the southeast Pacific is especially susceptible to ENSO forcing via anomalous meridional winds; this induces SST anomalies that are advected to South Georgia on a much more rapid timescale (order 5-6 months). The phasing of these teleconnections is such that anomalies that reach the southeast Pacific from farther west tend to be reinforced here by air-sea-ice interaction.We also find an important role for the Southern Annular Mode (SAM) in determining SST variability at South Georgia. This is a circumpolar mode of climate variability, and thus can readily influence local SST at South Georgia directly. The SAM is, however, not perfectly zonally symmetric, and (like ENSO) has a particular impact on meridional winds in the southeast 3 Pacific. The average timescale for SAM influence on South Georgia SST is shorter than that of ENSO, since it includes a stronger component of direct local forcing.The South Georgia ecosystem is not self-sustaining, with import of krill from breeding and nursery grounds upstream in the ACC being important. We speculate here that these varying meridional winds close to the Antarctic Peninsula play a direct role in promoting/restricting the injection of shelf waters (and the krill therein) into the ACC, following which anomalies in krill density would be advected toward South Georgia. This offers a dynamical mechanism that might contribute to interannual changes in biological communities at South Georgia, in addition to existing theories.Both SAM and ENSO have shown long-period changes in recent decades, with ENSO exhibiting a higher preponderance of El Niño events compared with La Niña events, and the SAM showing a marked trend toward a higher index state. Such long-period behaviour is likely to induce changes in the South Georgia ecosystem via their impacts on advection and SST, for which an understanding of the physical mechanisms elucidated here will be key to unravelling.

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We present observations of zooplankton diel vertical migration (DVM) over a period of 2 yr in an ice‐free and a seasonally ice‐covered Arctic fjord. The contrasting environments permitted assessment of the influences of physical and biological factors on temporal variability in DVM patterns and a test of the hypothesis that a reduction in summer sea ice extent and thickness following climatic warming will lead to changes in DVM via the loss of a shading effect on the pelagic marine environment. Acoustic backscatter and vertical velocity data from moored 300‐kHz acoustic Doppler current profilers were used to derive DVM patterns, while measurements of sea ice and snow thickness enabled assessment of the underwater light environment and consideration of its potential to influence DVM. Pronounced differences in DVM between the sites emerged during summertime when intermittent synchronized DVM was observed at the ice‐free site, whereas the ice‐covered site was characterized by asynchronous behavior, thereby highlighting the influence of sea ice. Notably, the 0.8‐m‐thick sea ice cover was deemed important for its influence on water column properties such as food, turbidity, and zooplankton species composition, as indicated by biological samples from moored sediment traps, rather than a simple shading of the ocean and direct modification of zooplankton DVM. Loss of Arctic sea ice is likely to have an indirect but substantial effect on zooplankton DVM via modification of hydrography and composition of the pelagic community.

Primary production export flux in Marguerite Bay (Antarctic Peninsula): Linking upper water-column production to sediment trap flux., Deep-Sea Research I, http://dx.doi.org/10.1016/j.dsr.2013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A study was carried out to assess primary production and associated export flux in the coastal waters of the western Antarctic Peninsula at an oceanographic time-series site.New, i.e. exportable, primary production in the upper water-column was estimated in two ways; by nutrient deficit measurements, and by primary production rate measurements using separate 14 C-labelled radioisotope and 15 N-labelled stable isotope uptake incubations. The resulting average annual exportable primary production estimates at the time-series site from nutrient deficit and primary production rates were 13 and 16 mol C m -2 respectively. Regenerated primary production was measured using 15 N-labelled ammonium and urea uptake, and was low throughout the sampling period.The exportable primary production measurements were compared with sediment trap flux measurements from 2 locations; the time-series site and at a site 40 km away in deeper water. Results showed ~1% of the upper mixed layer exportable primary production was exported to traps at 200m depth at the time-series site (total water column depth 520m). The maximum particle flux rate to sediment traps at the deeper offshore site (total water column depth 820m) was lower than the flux at the coastal time-series site.Flux of particulate organic carbon was similar throughout the spring-summer high flux period for both sites. Remineralisation of particulate organic matter predominantly 3 occurred in the upper water-column (<200m depth), with minimal remineralisation below 200m, at both sites. This highly productive region on the Western Antarctic Peninsula is therefore best characterised as 'high recycling, low export'.

We present observations of zooplankton diel vertical migration (DVM) over a period of 2 yr in an ice-free and a seasonally ice-covered Arctic fjord. The contrasting environments permitted assessment of the influences of physical and biological factors on temporal variability in DVM patterns and a test of the hypothesis that a reduction in summer sea ice extent and thickness following climatic warming will lead to changes in DVM via the loss of a shading effect on the pelagic marine environment. Acoustic backscatter and vertical velocity data from moored 300-kHz acoustic Doppler current profilers were used to derive DVM patterns, while measurements of sea ice and snow thickness enabled assessment of the underwater light environment and consideration of its potential to influence DVM. Pronounced differences in DVM between the sites emerged during summertime when intermittent synchronized DVM was observed at the ice-free site, whereas the ice-covered site was characterized by asynchronous behavior, thereby highlighting the influence of sea ice. Notably, the 0.8-m-thick sea ice cover was deemed important for its influence on water column properties such as food, turbidity, and zooplankton species composition, as indicated by biological samples from moored sediment traps, rather than a simple shading of the ocean and direct modification of zooplankton DVM. Loss of Arctic sea ice is likely to have an indirect but substantial effect on zooplankton DVM via modification of hydrography and composition of the pelagic community.