Sources and effects of short-term environmental changes in Gullmar Fjord, Sweden, inferred from the composition of sedimentary organic matter

In this study I will assess sources and effects of short-term environmental changes on the sedimentary organic matter in Gullmar Fjord. To achieve this, a high resolution sediment core (sedimentation rate 0.7 cm yr -1) was retrieved from the deepest part in the fjord and analyzed with multiple geochemical methods, targeting bulk organic matter and biomarker composition. The distribution of n-alkanes did not display any major changes for the terrestrial fraction in the investigated time frame from 1954 until 2014. Marine organic matter was found to be the dominant source of sedimentary organic matter in the fjord, though it is most likely produced remotely in the Skagerrak. Sea surface temperature (SST) reconstructions based on long-chain alkenones do not show any general increase during the studied interval, as observed from the hydrographic data set available for Gullmar Fjord. Temperatures of 14.1 to 21.1°C (mean 16.4 ± 1.6) were reconstructed, so the haptophyte blooms producing the long-chain alkenones occurred most likely during summer to early autumn. However, they would also fit to temperatures and blooming seasons reported for the Skagerrak. Even though Gullmar Fjord is considered to be free from industrial pollution, we found indications which could be interpreted as a slight contamination of the sediments by petrogenic hydrocarbons. Lower oxygen minimum concentrations observed in the bottom water since the 1980s are thought to be caused by changes in the North Atlantic Oscillation (NAO) and were related with a possibly ongoing eutrophication in previous studies. Signs for an ongoing eutrophication in the fjord were not visible in our sedimentary organic matter record, suggesting that most marine organic matter is produced in the Skagerrak, or that there is no ongoing eutrophication in the fjord since the 1950s.Den här studien undersöker källor och effekt av kortsiktiga miljöförändringar genom studier av sedimentärt organiskt material (OM) i Gullmarsfjorden. En sedimentsekvens (sedimentationshastighet 0.7 cm år-1) från den djupaste delen av fjorden analyserades i hög upplösning med flera olika geokemiska metoder applicerat på OM med fokus på komposition av biomarkörer. Fördelningen av n-alkener uppvisade inga större förändringar i den terrestra fraktionen under den undersökta tidsperioden mellan 1954 och 2014. Marint OM visade sig vara den dominerande källan av sedimentärt OM i fjorden, dock är det troligt att att produktionen skett längre ut i Skagerrak. Rekonstruktioner av havsytans temperatur baserat på långa kedjor av alkenoner uppvisar ingen generell ökning av temperaturen under den undersökta tidsperioden. Samma slutsats kan dras från hydrografiska data från Gullmarsfjorden. Temperaturer mellan 14.1 till 21.1°C (medel 16.4 ± 1.6) uppmättes vilket tyder på att blomningarna av fästalger (Haptophyta) som producerar långa kedjor av alkenoner troligtvis ägde rum under sommar till tidig höst. Temperaturspannet anstår emellertid också blomningstider och temperaturer rapporterade för Skagerrak. Även om Gullmarsfjorden anses förskonad från industriella föroreningar så fanns indikationer till en ringa förorening av petrogena kolväten. Tidigare studier har föreslagit att de syre-minima som observerats sedan 1980-talet kan vara beroende av den nordatlantiska oscillationen (NAO) vilket även har kopplats till den pågående eutrofieringen av fjorden. I denna studien fanns inga tecken på en pågående eutrofiering i fjorden utifrån det sedimentära organiska materialet, antingen på grund av dominansen av organiskt material från Skagerrak över terrestert alloktont kol alternativt bevis för avsaknaden av en pågående eutrofiering sedan 1950-talet och framåt

Annual report 2006 // Institute of Radiochemistry

[no abstract available

Annual Report 2010 - Institute of Radiochemistry

At the beginning of 2011, the former Forschungszentrum Dresden-Rossendorf (FZD) was fully integrated into the Helmholtz Association, as Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Therefore, the present Annual Report 2010 of the Institute of Radiochemistry (IRC) is published as the first HZDR-Report. The Institute of Radiochemistry is one of the six Research Institutes of this centre. IRC contributes to the research program “Nuclear Safety Research” in the “Research Field of Energy” and performs basic and applied research in radiochemistry and radioecology. Motivation and background of our research are environmental processes relevant for the installation of nuclear waste repositories, for remediation of uranium mining and milling sites, and for radioactive contaminations caused by nuclear accidents and fallout. Because of their high radiotoxicity and long half-life the actinides are of special interest

Biology of a widespread uncultivated archaeon that contributes to carbon fixation in the subsurface

Subsurface microbial life contributes significantly to biogeochemical cycling, yet it remains largely uncharacterized, especially its archaeal members. This 'microbial dark matter' has been explored by recent studies that were, however, mostly based on DNA sequence information only. Here, we use diverse techniques including ultrastuctural analyses to link genomics to biology for the SM1 Euryarchaeon lineage, an uncultivated group of subsurface archaea. Phylogenomic analyses reveal this lineage to belong to a widespread group of archaea that we propose to classify as a new euryarchaeal order ('Candidatus Altiarchaeales'). The representative, double-membraned species 'Candidatus Altiarchaeum hamiconexum' has an autotrophic metabolism that uses a not-yet-reported Factor(420)-free reductive acetyl-CoA pathway, confirmed by stable carbon isotopic measurements of archaeal lipids. Our results indicate that this lineage has evolved specific metabolic and structural features like nano-grappling hooks empowering this widely distributed archaeon to predominate anaerobic groundwater, where it may represent an important carbon dioxide sink

In-situ mechanical weakness of subducting sediments beneath a plate boundary décollement in the Nankai Trough

© 2018, The Author(s). The study investigates the in-situ strength of sediments across a plate boundary décollement using drilling parameters recorded when a 1180-m-deep borehole was established during International Ocean Discovery Program (IODP) Expedition 370, Temperature-Limit of the Deep Biosphere off Muroto (T-Limit). Information of the in-situ strength of the shallow portion in/around a plate boundary fault zone is critical for understanding the development of accretionary prisms and of the décollement itself. Studies using seismic reflection surveys and scientific ocean drillings have recently revealed the existence of high pore pressure zones around frontal accretionary prisms, which may reduce the effective strength of the sediments. A direct measurement of in-situ strength by experiments, however, has not been executed due to the difficulty in estimating in-situ stress conditions. In this study, we derived a depth profile for the in-situ strength of a frontal accretionary prism across a décollement from drilling parameters using the recently established equivalent strength (EST) method. At site C0023, the toe of the accretionary prism area off Cape Muroto, Japan, the EST gradually increases with depth but undergoes a sudden change at ~ 800 mbsf, corresponding to the top of the subducting sediment. At this depth, directly below the décollement zone, the EST decreases from ~ 10 to 2 MPa, with a change in the baseline. This mechanically weak zone in the subducting sediments extends over 250 m (~ 800–1050 mbsf), corresponding to the zone where the fluid influx was discovered, and high-fluid pressure was suggested by previous seismic imaging observations. Although the origin of the fluids or absolute values of the strength remain unclear, our investigations support previous studies suggesting that elevated pore pressure beneath the décollement weakens the subducting sediments. [Figure not available: see fulltext.]

Annual Report 2006 - Institute of Radiochemistry

[no abstract available