Atmospheric impacts of Arctic sea-ice loss, 1979–2009: separating forced change from atmospheric internal variability

The ongoing loss of Arctic sea-ice cover has implications for the wider climate system. The detection and importance of the atmospheric impacts of sea-ice loss depends, in part, on the relative magnitudes of the sea-ice forced change compared to natural atmospheric internal variability (AIV). This study analyses large ensembles of two independent atmospheric general circulation models in order to separate the forced response to historical Arctic sea-ice loss (1979–2009) from AIV, and to quantify signal-to-noise ratios. We also present results from a simulation with the sea-ice forcing roughly doubled in magnitude. In proximity to regions of sea-ice loss, we identify statistically significant near-surface atmospheric warming and precipitation increases, in autumn and winter in both models. In winter, both models exhibit a significant lowering of sea level pressure and geopotential height over the Arctic. All of these responses are broadly similar, but strengthened and/or more geographically extensive, when the sea-ice forcing is doubled in magnitude. Signal-to-noise ratios differ considerably between variables and locations. The temperature and precipitation responses are significantly easier to detect (higher signal-to-noise ratio) than the sea level pressure or geopotential height responses. Equally, the local response (i.e., in the vicinity of sea-ice loss) is easier to detect than the mid-latitude or upper-level responses. Based on our estimates of signal-to-noise, we conjecture that the local near-surface temperature and precipitation responses to past Arctic sea-ice loss exceed AIV and are detectable in observed records, but that the potential atmospheric circulation, upper-level and remote responses may be partially or wholly masked by AIV.     

Speleothems and pine trees as sensitive indicators of environmental pollution – A case study of the effect of uranium-ore mining in Hungary

Four decades of U ore production in Hungary provides an opportunity to study the possible environmental effects of mining. The study reveals significant changes in chemical composition of a stalagmite (cave deposit). The good fit between U content changes in the studied deposit and the U ore production rate support the assumption of the relationship with mining activity. An independent chemoenviromental archive, living pine (Pinus sylvestis) trees were also investigated. Data on pine tree cores collected from the same region show different levels of pollution (Cu, Zn, Mn, U) after the 1950s and 1960s, linked to the opening of mines and subsequent dust fallout around the site. Elevated concentrations of detritally derived elements (Si, Al, Th) coupled with a rise in U concentration and change in δ²³⁴U values of the stalagmite suggest increasing amounts of mine-derived dust from 1 to 3 km distance that settled and washed into the karst system. The combined usage of different proxies not only provides historic records for the anthropogenic impact in the environment, but also allows the timing of U concentration increases within the stalagmite and the identification of elemental behavior from the pollution. This study shows that complementary geochemical archives such as stalagmites and tree rings used together can enhance understanding of past environmental contamination.     

Characterization of bacterial symbioses in Myrtea sp. (Bivalvia: Lucinidae) and Thyasira sp. (Bivalvia: Thyasiridae) from a cold seep in the Eastern Mediterranean

Cold seeps have recently been discovered in the Nile deep‐sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNA‐encoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy‐based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea‐associated bacterium is closely related to lucinid symbionts from both deep‐sea and coastal species, whereas the Thyasira‐associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid‐shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus‐like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives.     

Can salt marsh plants influence levels and distribution of DDTs in estuarine areas?

Sediments are depositories of toxic substances such as organochlorine pesticides and there is a global need for their removal in contaminated environments. Studies that combine contaminated sediments and phytoremediation are relatively recent and their number has been increasing. This work aimed to investigate whether salt marsh plants (sea club-rush Scirpus maritimus, sea rush Juncus maritimus and sea purslane Halimione portulacoides) can favor DDT and metabolites remediation in estuarine environment. For this purpose the levels of DDT, DDE and DDD were compared in vegetated and non-vegetated sediments from an estuary in the North of Portugal (in-situ study) and from another in the South of Portugal (ex-situ study). Results obtained both in the in-situ study, involving S. maritimus and J. maritimus, and in the ex-situ study, involving H. portulacoides, indicated that these plants did not have a significant role in DDTs removal and/or degradation. Therefore, it seems that the tested plants cannot influence levels and distribution of DDTs in estuarine areas.     

Trace element distribution in uraninite from Mesoarchaean Witwatersrand conglomerates (South Africa) supports placer model and magmatogenic source

The first systematic analyses of the trace and rare earth element (REE) distribution in uraninite from various gold-bearing conglomerates of the Mesoarchaean Central Rand Group in South Africa’s Witwatersrand Basin by in situ laser ablation-inductively coupled plasma-mass spectrometry confirms a placer origin for the uraninite and a magmatogenic provenance thereof. The chemistry of commonly rounded to sub-rounded uraninite is highly variable from grain to grain but generally marked by elevated Th, W, Bi, Mo, Ta, Y, REE contents and unusually high Au concentrations. Especially, the high Th contents and the chondrite-normalised REE patterns are incompatible with post-sedimentary hydrothermal genetic models for the U mineralisation and point to derivation of the detrital uraninite from a high-temperature, magmatogenic, presumably granitic to pegmatitic source. The elevated Au concentrations (of as much as 67 ppm) in this uraninite are unique to the Witwatersrand and hint at a granitic hinterland that was enriched in both U and Au, thus presenting a potential source domain for some of the detrital gold in the Witwatersrand conglomerates. Minute fracture fills of brannerite in close proximity to the larger, rounded uraninite grains are devoid of detectable Bi, Mo, REE and Au and have only very low concentrations of Th, W, Ta and Y. This is explicable by crystallisation from a low-temperature hydrothermal fluid. Thus, Witwatersrand U phases show, analogous to many other ore constituents, such as pyrite and gold, clear evidence of partial, short-range mobilisation of originally detrital particles by post-sedimentary fluids.     

Modelling Microbial Degradation Coupled to Reactive Transport in Groundwater: A Benchmark Analysis

Microbes are ubiquitous in groundwater systems, and they play an important role in the redox state of groundwater and especially on the fate of organic contaminants. In this context, numerical simulations that couple microbial processes to reactive transport models are becoming more popular. In the present work, we revisit the mathematical ground of microbial redox reactions and perform a benchmark analysis of the simulation of aerobic benzene degradation in a shallow and oxidizing aquifer. Numerical results indicate that the two codes tested (one using the finite elements approach and the other using the finite differences approach) lead to very similar results. In addition, the coupling of heterogeneous geochemical reactions to the benchmarked example problem provides a solid basis for the understanding of the redox reactions and the changes on the carbon system triggered by the aerobic degradation of benzene.     

Global warming and South Indian monsoon rainfall—lessons from the Mid-Miocene

Precipitation over India is driven by the Indian monsoon. Although changes in this atmospheric circulation are caused by the differential seasonal diabatic heating of Asia and the Indo-Pacific Ocean, it is so far unknown how global warming influences the monsoon rainfalls regionally. Herein, we present a Miocene pollen flora as the first direct proxy for monsoon over southern India during the Middle Miocene Climate Optimum. To identify climatic key parameters, such as mean annual temperature, warmest month temperature, coldest month temperature, mean annual precipitation, mean precipitation during the driest month, mean precipitation during the wettest month and mean precipitation during the warmest month the Coexistence Approach is applied. Irrespective of a ~ 3–4 °C higher global temperature during the Middle Miocene Climate Optimum, the results indicate a modern-like monsoonal precipitation pattern contrasting marine proxies which point to a strong decline of Indian monsoon in the Himalaya at this time. Therefore, the strength of monsoon rainfall in tropical India appears neither to be related to global warming nor to be linked with the atmospheric conditions over the Tibetan Plateau. For the future it implies that increased global warming does not necessarily entail changes in the South Indian monsoon rainfall.     

Sediment macrobenthos off eastern Waiheke Island,Hauraki Gulf,New Zealand

Aspects of sea-bed structure and benthic-macroinvertebrate species composition, distribution, richness and diversity in coastal waters off eastern Waiheke Island, Hauraki Gulf, are reported. In contrast to the sole historical account of sea-bed community structure from this same region, no widely distributed assemblages of species are recognised throughout it; no two sites share the exact same complement of species; and almost all sites are less than 80% similar in their taxonomic composition, most considerably so. Species richness and diversity are reported to vary with substratum type and depth, and spatially; species occurring within muds are the least diverse and species rich, followed by those of muddy gravels, and then gravels; many taxa prove common to the three substratum types; and dominance of taxa is recognised to decrease with an increase in substratum complexity, from muds to gravels, and species richness. With the exception of invasive marine species, apparent changes in the composition of assemblages throughout this region over the eight-decade period that data span are considered artefacts of the way in which such assemblages were historically defined. We recommend historical accounts of sea-bed community distributions throughout Hauraki Gulf be interpreted with caution, especially when attempting to use such schematic depictions to determine whether changes have occurred in assemblage composition.