Mass balance measurements on King George Island ice cap in 2007 and 2008

The Antarctic Peninsula has been identified as a region of rapid on-going climate change with impacts on the cryosphere. The knowledge of glacial changes and freshwater budgets resulting from intensified glacier melt is an important boundary condition for many biological and integrated earth system science approaches. We provide a case study on glacier and mass balance changes for the ice cap of King George Island. The area loss between 2000 and 2008 amounted to about 20 km**2 (about 1.6% of the island area) and compares to glacier retreat rates observed in previous years. Measured net accumulation rates for two years (2007 and 2008) show a strong interannual variability with maximum net accumulation rates of 4950 mm w.e./a and 3184 mm w.e./a, respectively. These net accumulation rates are at least 4 times higher than reported mean values (1926-95) from an ice core. An elevation dependent precipitation rate of 343 mm w.e./a (2007) and 432 mm w.e./a (2008) per 100 m elevation increase was observed. Despite these rather high net accumulation rates on the main ice cap, consistent surface lowering was observed at elevations below 270 m above ellipsoid over an 11-year period. These DGPS records reveal a linear dependence of surface lowering with altitude with a maximum annual surface lowering rate of 1.44 m/a at 40 m and -0.20 m/a at 270 m above ellipsoid. These results fit well to observations by other authors and surface lowering rates derived from the ICESat laser altimeter. Assuming that climate conditions of the past 11 years continue, the small ice cap of Bellingshausen Dome will disappear in about 285 years.

Acid-base balance and changes in haemolymph properties of the South African rock lobsters, Jasus lalandii, a palinurid decapod, during chronic hypercapnia

Few studies exist reporting on long-term exposure of crustaceans to hypercapnia. We exposed juvenile South African rock lobsters, Jasus lalandii, to hypercapnic conditions of pH 7.3 for 28 weeks and subsequently analysed changes in the extracellular fluid (haemolymph). Results revealed, for the first time, adjustments in the haemolymph of a palinurid crustacean during chronic hypercapnic exposure: 1) acid-base balance was adjusted and sustained by increased bicarbonate and 2) quantity and oxygen binding properties of haemocyanin changed. Compared with lobsters kept under normocapnic conditions (pH 8.0), during prolonged hypercapnia, juvenile lobsters increased bicarbonate buffering of haemolymph. This is necessary to provide optimum pH conditions for oxygen binding of haemocyanin and functioning of respiration in the presence of a strong Bohr Effect. Furthermore, modification of the intrinsic structure of the haemocyanin molecule, and not the presence of molecular modulators, seems to improve oxygen affinity under conditions of elevated pCO2.

Lipid composition of particulate matter measured on water bottle samples during POLARSTERN cruise ARK-XI/1

The lipid composition of particulate matter in oceanic environments can provide informations on the nature and origin of the organic matter as well as on their transformation processes. Molecular characteristics for lipids in the Arctic environment have been used as indicators of the sources and transformation of organic particulate matter (Smith et al., 1997; Fahl and Stein, 1997, 1999). However, the features of the lipid composition of particulate matter in the Arctic with its high seasonality of ice Cover and primary productivity has been studied insufficiently. Lipids are one of the most important compounds of organic matter. On the one hand, the composition of lipids is a result of the variability of biological sources (phyto- and zooplankton, higher plants, bacteria etc.). On the other hand, the lipid composition of particulate matter is undergone significant alteration during vertical transport. The organic matter balance in the Arctic marginal seas, such as the Kara and Laptev seas, is characterized by the significant supply of dissolved and particulate material by the major Eurasian rivers - Ob, Yenisei and Lena (Cauwet and Sidorov, 1996; Gordeev et al., 1996, Martin et al., 1993). In relation to the world's ocean the primary productivity values are lower in the Arctic seas due to the ice-cover. However local increased values of primary productivity can be connected with the melting processes inducing increased phytoplankton growth near ice-edge (Nelson et al., 1989; Fahl and Stein, 1997) and enhanced river supply of nutrients, These features can influence the proportion of allochtonous and autochtonous components of the organic matter in the Arctic marginal seas (Fahl and Stein, 1997; Stein and Fahl, 1999). Furthermore, increased lipid contents in aquatic environments were found near density discontinuities (Parish et al., 1988). Although being less informative than lipid studies on the molecular level the character of lipid composition analysis on the group could also be used for studying of particulate organic matter and its transformation in sedimentation processes in the Arctic. In this paper the investigation of the characteristics of lipid composition performed by Alexandrova and Shevchenko (1997) in Arctic seas was continued.

Corrected ICESat altimetry data, surface mass balance, and firn elevation change on Antarctic ice shelves

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Floating ice shelves buttress the flow of grounded tributary glaciers and their thickness and extent are particularly susceptible to changes in both climate and ocean forcing. Recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. However, the extent and magnitude of ice-shelf thickness change, its causes and its link to glacier flow rate are so poorly understood that its influence on the future of the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal for the first time the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary driver of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet that has led to accelerated glacier flow. The highest thinning rates (~7 m/a) occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen Seas and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic Ice Sheet mass balance, and hence global sea-level, on annual to decadal timescales.

Temperature, water level and bathymetry of thermokarst lakes in the continuous permafrost zone of northern Siberia - Lena River Delta, Siberia

Thermokarst lakes are typical features of the northern permafrost ecosystems, and play an important role in the thermal exchange between atmosphere and subsurface. The objective of this study is to describe the main thermal processes of the lakes and to quantify the heat exchange with the underlying sediments. The thermal regimes of five lakes located within the continuous permafrost zone of northern Siberia (Lena River Delta) were investigated using hourly water temperature and water level records covering a 3-year period (2009-2012), together with bathymetric survey data. The lakes included thermokarst lakes located on Holocene river terraces that may be connected to Lena River water during spring flooding, and a thermokarst lake located on deposits of the Pleistocene Ice Complex. Lakes were covered by ice up to 2 m thick that persisted for more than 7 months of the year, from October until about mid-June. Lake-bottom temperatures increased at the start of the ice-covered period due to upward-directed heat flux from the underlying thawed sediment. Prior to ice break-up, solar radiation effectively warmed the water beneath the ice cover and induced convective mixing. Ice break-up started at the beginning of June and lasted until the middle or end of June. Mixing occurred within the entire water column from the start of ice break-up and continued during the ice-free periods, as confirmed by the Wedderburn numbers, a quantitative measure of the balance between wind mixing and stratification that is important for describing the biogeochemical cycles of lakes. The lake thermal regime was modeled numerically using the FLake model. The model demonstrated good agreement with observations with regard to the mean lake temperature, with a good reproduction of the summer stratification during the ice-free period, but poor agreement during the ice-covered period. Modeled sensitivity to lake depth demonstrated that lakes in this climatic zone with mean depths > 5 m develop continuous stratification in summer for at least 1 month. The modeled vertical heat flux across the bottom sediment tends towards an annual mean of zero, with maximum downward fluxes of about 5 W/m**2 in summer and with heat released back into the water column at a rate of less than 1 W/m**2 during the ice-covered period. The lakes are shown to be efficient heat absorbers and effectively distribute the heat through mixing. Monthly bottom water temperatures during the ice-free period range up to 15 °C and are therefore higher than the associated monthly air or ground temperatures in the surrounding frozen permafrost landscape. The investigated lakes remain unfrozen at depth, with mean annual lake-bottom temperatures of between 2.7 and 4 °C.

Phosphate d18O pore-water profiles of sediment core GeoB11807-2 and GeoB11804-4

Phosphorus cycling in the ocean is influenced by biological and geochemical processes that are reflected in the oxygen isotope signature of dissolved inorganic phosphate (Pi). Extending the Pi oxygen isotope record from the water column into the seabed is difficult due to low Pi concentrations and small amounts of marine porewaters available for analysis. We obtained porewater profiles of Pi oxygen isotopes using a refined protocol based on the original micro-extraction designed by Colman (2002). This refined and customized method allows the conversion of ultra-low quantities (0.5 - 1 µmol) of porewater Pi to silver phosphate (Ag3PO4) for routine analysis by mass spectrometry. A combination of magnesium hydroxide co-precipitation with ion exchange resin treatment steps is used to remove dissolved organic matter, anions, and cations from the sample before precipitating Ag3PO4. Samples as low as 200 µg were analyzed in a continuous flow isotope ratio mass spectrometer setup. Tests with external and laboratory internal standards validated the preservation of the original phosphate oxygen isotope signature (d18OP) during micro extraction. Porewater data on d18OP has been obtained from two sediment cores of the Moroccan margin. The d18OP values are in a range of +19.49 to +27.30 per mill. We apply a simple isotope mass balance model to disentangle processes contributing to benthic P cycling and find evidence for Pi regeneration outbalancing microbial demand in the upper sediment layers. This highlights the great potential of using d18OP to study microbial processes in the subseafloor and at the sediment water interface.

Table 1: Basic mass-balance, Peyto Glacier, 1967/1974

The eight-year record of mass balance of Peyto Glacier is correlated to meteorological data measured near the glacier and at Lake Louise 30 km to the south. The period investigated includes the llighest and lowest accumulations for the past 40 years. The primar'y controls of net annual balance are seen to be the depth of the 'winter sno,y pack and the temperature record during the summer. Extensive summer snowfalls in the ablation area can slow down melt rates very considerably and affect the net annual balance positively. The variable nature of winter accumulation and its influence on snowline retreat and ice melt is illustrated by three years' data.

Differential response of two Mediterranean cold-water coral species to ocean acidification

Cold-water coral (CWC) reefs constitute one of the most complex deep-sea habitats harboring a vast diversity of associated species. Like other tropical or temperate framework builders, these systems are facing an uncertain future due to several threats, such as global warming and ocean acidification. In the case of Mediterranean CWC communities, the effect may be exacerbated due to the greater capacity of these waters to absorb atmospheric CO2 compared to the global ocean. Calcification in these organisms is an energy-demanding process, and it is expected that energy requirements will be greater as seawater pH and the availability of carbonate ions decrease. Therefore, studies assessing the effect of a pH decrease in skeletal growth, and metabolic balance are critical to fully understand the potential responses of these organisms under a changing scenario. In this context, the present work aims to investigate the medium- to long-term effect of a low pH scenario on calcification and the biochemical composition of two CWCs from the Mediterranean, Dendrophyllia cornigera and Desmophyllum dianthus. After 314 d of exposure to acidified conditions, a significant decrease of 70 % was observed in Desmophyllum dianthus skeletal growth rate, while Dendrophyllia cornigera showed no differences between treatments. Instead, only subtle differences between treatments were observed in the organic matter amount, lipid content, skeletal microdensity, or porosity in both species, although due to the high variability of the results, these differences were not statistically significant. Our results also confirmed a heterogeneous effect of low pH on the skeletal growth rate of the organisms depending on their initial weight, suggesting that those specimens with high calcification rates may be the most susceptible to the negative effects of acidification.