Rapid amino acid cycling in arctic and antarctic soils

Amino acids constitute one of the largest inputs of organic nitrogen (N) to most polar soils and have been hypothesized to be important in regulating vegetational succession and productivity in Arctic ecosystems. Our understanding of amino acid cycling in these soils, however, is poor. The aim of this study was to investigate the size and rate of turnover of the amino acid pool in a range of Arctic and Antarctic soils. Our results indicate that in polar soils with either high or low ornithogenic inputs the amino acid pool is small in comparison to the inorganic N pool (NO^–₃ and NH⁺₄). The free amino acid pool constituted only a small proportion of the total dissolved organic nitrogen (DON) pool in these soils. Here we show that these low concentrations may be due to rapid use by the soil microbial community in both Arctic and Antarctic soils. The turnover of the amino acid pool in soil was extremely rapid, with a half-life ranging from 2 to 24 h, indicating that this N pool can be turned over many hundred times each summer when polar soils are frequently unfrozen. The implications of amino acids in N cycling and plant and microbial nutrition are discussed.     

Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.     

Arctic Tipping Points: Governance in Turbulent Times

Interacting forces of climate change and globalization are transforming the Arctic. Triggered by a non-linear shift in sea ice, this transformation has unleashed mounting interest in opportunities to exploit the region’s natural resources as well as growing concern about environmental, economic, and political issues associated with such efforts. This article addresses the implications of this transformation for governance, identifies limitations of existing arrangements, and explores changes needed to meet new demands. It advocates the development of an Arctic regime complex featuring flexibility across issues and adaptability over time along with an enhanced role for the Arctic Council both in conducting policy-relevant assessments and in promoting synergy in interactions among the elements of the emerging Arctic regime complex. The emphasis throughout is on maximizing the fit between the socioecological features of the Arctic and the character of the governance arrangements needed to steer the Arctic toward a sustainable future.     

Sources and distributions of Cs, Pu, Pu radionuclides in the north-western Barents Sea

Sediment deposits are the ultimate sink for anthropogenic radionuclides entering the marine environment. The major sources of anthropogenic radionuclides to the Barents Sea are fallout from nuclear weapons tests, long range transport from other seas, and river and non-point freshwater supplies. In this study we investigated activity concentrations, ratios, and inventories of the anthropogenic radionuclides, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu in dated sediment cores collected along a north-south transect in the northwestern Barents Sea. The data were used to evaluate the influence of different sources on the derived spatial and temporal patterns of anthropogenic radionuclides in seafloor sediment deposits. Activity concentrations of ¹³⁷Cs ranged from <0.1 Bq/kg to 10.5 Bq/kg while ^239,240Pu ranged from <0.01 Bq/kg to 2.74 Bq/kg and ²³⁸Pu activity concentrations ranged from <0.01 Bq/kg to 0.22 Bq/kg. Total inventories of ¹³⁷Cs ranged from 29.5 ± 1.5 Bq/m² to 152.7 ± 5.6 Bq/m² and for ^239,240Pu inventories (6 sediment layers only) ranged from 9.5 ± 0.3 Bq/m² to 29.7 ± 0.4 Bq/m². Source contributions varied among stations and between the investigated radionuclides. The ²³⁸Pu/^239,240Pu ratios up to 0.18 indicate discharges from nuclear fuel reprocessing plants as a main contributor of plutonium. Based on ²³⁸Pu/^239,240Pu ratio, it was calculated that up to 19-27% of plutonium is supplied from sources other than atmospheric global fallout. Taking into account Atlantic current flow trajectories and that both activity concentrations and inventories of plutonium negatively correlate with latitude, Sellafield is a major source for the Barents Sea. Concentrations and inventories of ¹³⁷Cs correlate positively with latitude and negatively with distance from the Svalbard archipelago. The ¹³⁷Cs concentrations are highest in an area of intensive melting of sea ice formed along the Siberian coast. Thus, sea ice and supplies from Svalbard may be important source of ¹³⁷Cs to the Barents Sea seafloor.     

Photochemical processing of aldrin and dieldrin in frozen aqueous solutions under arctic field conditions

Organochlorine (OC) contaminants are transported to the Polar Regions, where they have the potential to bioaccumulate, presenting a threat to the health of wildlife and indigenous communities. They deposit onto snowpack during winter, and accumulate until spring, when they experience prolonged solar irradiation until snowmelt occurs. Photochemical degradation rates for aldrin and dieldrin, in frozen aqueous solution made from MilliQ water, 500 μM hydrogen peroxide solution or locally-collected melted snow were measured in a field campaign near Barrow, AK, during spring-summer 2008. Significant photoprocessing of both pesticides occurs; the reactions depend on temperature, depth within the snowpack and whether the predominant phase is ice or liquid water. The effect of species present in natural snowpack is comparable to 500 μM hydrogen peroxide, pointing to the potential significance of snowpack-mediated reactions. Aldrin samples frozen at near 0 °C were more reactive than comparable liquid samples, implying that the microenvironments experienced on frozen ice surfaces are an important consideration.     

Photoinduced reduction of divalent mercury in ice by organic matter

Reduction of divalent mercury and subsequent emission to the atmosphere has been identified as loss process from surface snow, but its mechanism and importance are still unclear. The amount of mercury that stays in the snow pack until spring is of significance, because during snow melt it may be released to the aquatic environment and enter the food web. Better knowledge of its fate in snow might further assist the interpretation of ice core data as paleo-archive. Experiments were performed under well-controlled laboratory conditions in a coated wall flow tube at atmospheric pressure and irradiated with light between 300 nm and 420 nm. Our results show that the presence of benzophenone and of oxalic acid significantly enhances the release of mercury from the ice film during irradiation, whereas humic acid is less potent to promote the reduction. Further it was found that oxygen or chloride, and acidic conditions lowered the photolytically induced mercury release in the presence of benzophenone, while the release got larger with increasing temperatures.     

中国第二次北极科学考察沿线气溶胶可溶性离子分布特征和来源

对2003年7月15～9月28日间中国第二次北极科学考察沿线所采集的气溶胶样品进行分析,获得了Na 、NH4 、K 、Mg2 、Ca2 、Cl-、MSA、SO2-4、NO3-、C2O2-4和CH3COO-11种离子的浓度.离子组成表明,气溶胶主要以海盐颗粒为主,其中(Na Cl-)的贡献平均为60.2%;其次为硫酸盐.根据因子分析,11种离子归为4个因子,解释方差为83.7%.因子1包括Na 、nss-Mg2 、nss-Ca2 、Cl-和nss-SO2-4,代表陆地和海洋混合源,解释方差为41.2%;因子2包括NH 4、nss-K 和NO3-,来源于化石燃料燃烧和生物质燃烧所释放的二次污染物,解释方差为18.9%;因子3只有MSA,来源于海洋表层浮游植物排放的二甲基硫(DMS)的氧化,解释方差为11.9%;因子4包括CH3COO-和C2O2-4,主要来源于高纬度的北温带北部森林大火,解释方差为11.6%.     

北极沉积物中硫酸盐还原菌与生物地球化学要素的相关分析

对北极楚科奇海、白令海测区34个沉积物样品的硫酸盐还原菌(SRB)含量与CaCO3、Si、S、P、Cd、Fe、Ti、Pb、Hg等地球化学要素作了相关分析．同时分析了SRB与其所在沉积物粒度与底层水温间的关系．结果表明：SRB与Si、砂及底层水温为正相关；SRB与CaCO3、Fe、Ti、P、Pb、Hg、粉砂、粘土为负相关；而SRB与Cd、S的相关性因海区不同而不同．既有负相关．也有正相关．分析了这些相关状况及其原因．