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A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ13CPOC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ13CPOC in the coastal western Antarctic Peninsula (WAP) sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/2006 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10‰ negative isotopic shift in δ13CPOC that cannot be explained by a con10 current change in concentration or isotopic signature of CO2. We hypothesise that the δ13CPOC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms in different diatom species. These short-lived yet pronounced negative δ13CPOC excursions drive a 4‰ decrease in the seasonal average δ13CPOC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ13CPOC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary δ13CPOC. We also find significantly higher δ13CPOC in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and production of exopolymeric substances (EPS). This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ13CPOC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ13CPOC in the sedimentary record. A high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (δ13CPOC) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting δ13CPOC in the coastal western Antarctic Peninsula (WAP) sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/2006 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10‰ negative isotopic shift in δ13CPOC that cannot be explained by a con10 current change in concentration or isotopic signature of CO2. We hypothesise that the δ13CPOC shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms in different diatom species. These short-lived yet pronounced negative δ13CPOC excursions drive a 4‰ decrease in the seasonal average δ13CPOC signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4‰ difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean δ13CPOC variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary δ13CPOC. We also find significantly higher δ13CPOC in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and production of exopolymeric substances (EPS). This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for δ13CPOC in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based δ13CPOC in the sedimentary record. [ABSTRACT FROM AUTHOR]

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'., (© 2018 The Authors.)

This paper describes the application of a simple chromium reduction furnace which can be interfaced with a dual inlet isotope-ratio mass spectrometer thus providing the capacity for cheap, fast, accurate and precise measurement of deltaD(V-SMOW) by dynamic mass spectrometry. Measurements are precise to the order of < or =0.5 per thousand. Mean 95% confidence intervals for the Vienna Standard Mean Ocean Water (V-SMOW) to Standard Light Antarctic Precipitation (SLAP) range are in the order of 2.5 per thousand and the system is linear over the range -428 to 23,000 per thousand. Memory effects do exist, but are small for natural abundance samples and can be minimised by careful planning of the analytical load., (Copyright 2001 John Wiley & Sons, Ltd.)