Geochemistry of pockmark sediments from the inner Oslofjord

Pockmarks are geological features that are found on the bottom of lakes and oceans all over the globe. Some are active, seeping oil or methane, while others are inactive. Active pockmarks are well studied since they harbor specialized microbial communities that proliferate on the seeping compounds. Such communities are not found in inactive pockmarks. Interestingly, inactive pockmarks are known to have different macrofaunal communities compared to the surrounding sediments. It is undetermined what the microbial composition of inactive pockmarks is and if it shows a similar pattern as the macrofauna. The Norwegian Oslo Fjord contains many inactive pockmarks and they are well suited to study the influence of these geological features on the microbial community in the sediment. Here we present a detailed analysis of the microbial communities found in three inactive pockmarks and two control samples at two core depth intervals. The communities were analyzed using high-throughput amplicon sequencing of the 16S rRNA V3 region. Microbial communities of surface pockmark sediments were indistinguishable from communities found in the surrounding seabed. In contrast, pockmark communities at 40 cm sediment depth had a significantly different community structure from normal sediments at the same depth. Statistical analysis of chemical variables indicated significant differences in the concentrations of total carbon and non-particulate organic carbon between 40 cm pockmark and reference sample sediments. We discuss these results in comparison with the taxonomic classification of the OTUs identified in our samples. Our results indicate that microbial surface sediment communities are affect by the water column, while the 40 cm communities are affect by local conditions within the sediment.

Migration forms of hydrocarbons in waters and bottom sediments of the Gulf of Riga

It is found that hydrocarbons are constantly accumulated on the main geochemical barriers: water-atmosphere, river-sea, water-suspended matter, and water-bottom sediment interfaces. Degree of hydrocarbon accumulation reaches 13.5-17.6 in the surface microlayer and exceeds 1000 in bottom sediments. Hydrocarbon composition changes in this process. Local pollutant loads result in accumulation of polycyclic aromatic hydrocarbons by bottom sediments and benzo(a)pyrene concentration sometimes exceeds MPC. Content of hydrocarbon migratory forms is calculated.

Sources and seasonality of polycyclic aromatic hydrocarbons transported to Alert, Canadian Arctic

A probabilistic function (integrated source contribution function, ISCF) based on backward air mass trajectory calculation was developed to track sources and atmospheric pathways of polycyclic aromatic hydrocarbons (PAHs) to the Canadian High Arctic station of Alert. In addition to the movement of air masses, the emission intensities at the sources and the major processes of partition, indirect photolysis, and deposition occurring on the way to the Arctic were incorporated into the ISCF. The predicted temporal trend of PAHs at Alert was validated by measured PAH concentrations throughout 2004. The PAH levels in the summer are orders of magnitude lower than those in the winter and spring when long-range atmospheric transport events occur more frequently. PAHs observed at Alert are mostly from East Asia (including Russia Far East), North Europe (including European Russia), and North America. These sources account for 25, 45, and 27% of PAHs atmospheric level at Alert, respectively. Source regions and transport pathways contributing to the PAHs contamination in the Canadian High Arctic vary seasonally. In the winter, Russia and Europe are the major sources. PAHs from these sources travel eastward and turn to the north at approximately 120°E before reaching Alert, in conjunction with the well- known Arctic haze events. In the spring, PAHs from Russia and Europe first migrate to the west and then turn to the north at 60°W toward Alert. The majority of PAHs in the summer are from northern Canada where they are carried to Alert via low- level transport pathways. In the fall, 70% of PAHs arriving at Alert are delivered from North American sources.

Polyaromatic hydrocarbons in sediments from the Barents and White Seas

Polycyclic aromatic hydrocarbons (PAHs) are common environmental contaminants which can be derived from anthropogenic sources, such as combustion and discharges from extraction and transport, and natural processes, including leakage and erosion of fossil carbon. Natural PAH sources contribute, along with biological activities and terrestrial run-off, to the organic carbon content in sediments.The Barents Sea region is far from many anthropogenic sources of PAH, but production and trans-shipment of hydrocarbons is increasing. We present data for polycyclic aromatic hydrocarbon (PAH) concentrations in bottom sediments from 510 stations in the Barents and White Seas, and along the northern coast of Norway.