Biogeochemical measurements at the Antarctic Peninsula

Size-fractionated chlorophyll a and photosynthetic carbon incorporation, microbial oxygen production and respiration and particulate vertical flux were measured in January 1996 at three regions, characterized by distinct hydrographic fields and planktonic communities, of the Antarctic Peninsula: (1) a diatom-Phaeocystis sp., dominated community associated with the relatively stratified waters of the Gerlache Strait, (2) a nanoplankton-Cryptomonas sp. dominated assemblage at the Gerlache-Bransfield confluence; and (3) a nano- and picoplankton community in mixed waters of the Bransfield Strait. Despite the marked differences in both community structure and total phytoplankton biomass and primary production, and against predictions from models about trophic control of C export, the lowest respiration rates were measured at Bransfield (pico- and nanoplankton), and no difference was observed between the Gerlache (large diatoms) and Bransfield stations in relative vertical particle flux (6.4 vs. 5.1 % of suspended C; 14.9 vs. 10.4 % of net community production, respectively). Growth and loss rates of the phytoplankton population studied for each community indicate that microbial populations can be explained by in situ growth, but spatial (diatom-Phaeocystis sp., bloom) and temporal (diatom-Phaeocystis sp. bloom and nanoplankton communities) scales of study were shown to be insufficient for addressing the coupling between primary production and biogenic carbon export, especially after the appreciation of the accumulation of dissolved organic carbon in the water column. This would explain the unexpected results and highlights the necessity of including the mechanisms controlling accumulation and consumption of dissolved organic matter into conceptual models about the trophic control of C export.

Characteristics and stomach contents of Greenland sharks (Somniosus microcephalus) caught in Svalbard during June 2008-2009

Harbour seals in Svalbard have short longevity, despite being protected from human hunting and having limited terrestrial predation at their haulout sites, low contaminant burdens and no fishery by-catch issues. This led us to explore the diet of Greenland sharks (Somniosus microcephalus) in this region as a potential seal predator. We examined gastrointestinal tracts (GITs) from 45 Greenland sharks in this study. These sharks ranged from 229 to 381 cm in fork length and 136-700 kg in body mass; all were sexually immature. Seal and whale tissues were found in 36.4 and 18.2%, respectively, of the GITs that had contents (n = 33). Based on genetic analyses, the dominant seal prey species was the ringed seal (Pusa hispida); bearded seal (Erignathus barbatus) and hooded seal (Cystophora cristata) tissues were each found in a single shark. The sharks had eaten ringed seal pups and adults based on the presence of lanugo-covered prey (pups) and age determinations based on growth rings on claws (<1 year and adults). All of the whale tissue was from minke whale (Balenoptera acutorostrata) offal, from animals that had been harvested in the whale fishery near Svalbard. Fish dominated the sharks' diet, with Atlantic cod (Gadus morhua), Atlantic wolffish (Anarhichas lupus) and haddock (Melanogrammus aeglefinus) being the most important fish species. Circumstantial evidence suggests that these sharks actively prey on seals and fishes, in addition to eating carrion such as the whale tissue. Our study suggests that Greenland sharks may play a significant predatory role in Arctic food webs.

Biological, physical and chemical characteristics of water and sediment samples from the Volga River delta, northern Caspian

Based on the data of synchronous observations of hydrophysical and biogeochemical parameters in the near-mouth and shallow-water areas of the northern Caspian in 2000-2001, the scale of spatiotemporal variability in the following characteristics of the water-bottom system was estimated (1) flow velocity and direction within vortex structures formed by the combined effect of wind, discharge current, and the presence of higher aquatic plants; (2) dependence of the spatial distribution of the content and composition of suspended particulate matter on the hydrodynamic regime of waters and development of phytoplankton; (3) variations in the grain-size, petrographic, mineralogical, and chemical compositions of the upper layer of bottom sediments at several sites in the northern Caspian related to the particular local combination of dominant natural processes; and (4) limits of variability in the group composition of humus compounds in bottom sediments. The acquired data are helpful in estimating the geochemical consequences of a sea level rise and during the planning of preventive environmental protection measures in view of future oil and gas recovery in this region.

Abundance of zooplankton based on a long-term study at the Galata transect and covers the spring-summer periods from 1967 till 2005

The dataset is based on a long-term study (38 years) at the Galata transect and covers the spring-summer periods from 1967 till 2005. The whole dataset is composed of 360 data of total zooplankton biomass and abundance . Samples were collected in discrete layers 0-10m, 10-20m, 10-25m, 25-50m, 50-70m, 50-100m, 100-150. Mesozooplankton abundance: the collected material was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber for taxomomic identification and count. Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Fishery Resource by Prof. Asen Konsulov and Institute of Oceanology by Prof. Asen Konsulov, Lyudmila Kamburska and Kremena Stefanova using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972). Taxon-specific mesozooplankton abundance: The collected material was analysed using the method of Domov (1959). Samples were brought to volume of 25-30 ml depending upon zooplankton density and mixed intensively until all organisms were distributed randomly in the sample volume. After that 5 ml of sample was taken and poured in the counting chamber for taxomomic identification and count. Copepods and Cladoceras were identified and enumerated; the other mesozooplankters were identified and enumerated at higher taxonomic level (commonly named as mesozooplankton groups). Large (> 1 mm body length) and not abundant species were calculated in whole sample. Counting and measuring of organisms were made in the Dimov chamber under the stereomicroscope to the lowest taxon possible. Taxonomic identification was done at the Institute of Fishery Resource by prof. Asen Konsulov and Institute of Oceanology by Prof. Asen Konsulov, Lyudmila Kamburska and Kremena Stefanova using the relevant taxonomic literature (Mordukhay-Boltovskoy, F.D. (Ed.). 1968, 1969,1972).

Results from field observations and in situ 13C feeding experiments in the Nazaré Canyon conducted during RRS James Cook 10 cruise Leg 2

Submarine canyon systems provide a heterogeneous habitat for deep-sea benthos in terms of topography, hydrography, and the quality and quantity of organic matter present. Enhanced meiofauna densities as found in organically enriched canyon sediments suggest that nematodes, as the dominant metazoan meiobenthic taxon, may play an important role in the benthic food web of these sediments. Very little is known about the natural diets and trophic biology of deep-sea nematodes, but enrichment experiments can shed light on nematode feeding selectivity and trophic position. An in-situ pulse-chase experiment (Feedex) was performed in the Nazaré Canyon on the Portuguese margin in summer 2007 to study nematode feeding behaviour. 13C-labelled diatoms and bacteria were added to sediment cores which were then sampled over a 14-day period. There was differential uptake by the nematode community of the food sources provided, indicating selective feeding processes. 13C isotope results revealed that selective feeding was less pronounced at the surface, compared to the sediment subsurface. This was supported by a higher trophic diversity in surface sediments compared to the subsurface, implying that more food items may be used by the nematode community at the sediment surface. Predatory and scavenging nematodes contributed relatively more to biomass than other feeding types and can be seen as key contributors to the nematode food web at the canyon site. Non-selective deposit feeding nematodes were the dominant trophic group in terms of abundance and contributed substantially to total nematode biomass. The high levels of 'fresh' (bioavailable) organic matter input and moderate hydrodynamic disturbance of the canyon environment lead to a more complex trophic structure in canyon nematode communities than that found on the open continental slope, and favours predator/scavengers and non-selective deposit feeders.

Relative abundance of prokaryotic picoplankton populations in the Atlantic Ocean

Members of the prokaryotic picoplankton are the main drivers of the biogeochemical cycles over large areas of the world's oceans. In order to ascertain changes in picoplankton composition in the euphotic and twilight zones at an ocean basin scale we determined the distribution of 11 marine bacterial and archaeal phyla in three different water layers along a transect across the Atlantic Ocean from South Africa (32.9°S) to the UK (46.4°N) during boreal spring. Depth profiles down to 500 m at 65 stations were analysed by catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) and automated epifluorescence microscopy. There was no obvious overall difference in microbial community composition between the surface water layer and the deep chlorophyll maximum (DCM) layer. There were, however, significant differences between the two photic water layers and the mesopelagic zone. SAR11 (35 ± 9%) and Prochlorococcus (12 ± 8%) together dominated the surface waters, whereas SAR11 and Crenarchaeota of the marine group I formed equal proportions of the picoplankton community below the DCM (both ~15%). However, due to their small cell sizes Crenarchaeota contributed distinctly less to total microbial biomass than SAR11 in this mesopelagic water layer. Bacteria from the uncultured Chloroflexi-related clade SAR202 occurred preferentially below the DCM (4-6%). Distinct latitudinal distribution patterns were found both in the photic zone and in the mesopelagic waters: in the photic zone, SAR11 was more abundant in the Northern Atlantic Ocean (up to 45%) than in the Southern Atlantic gyre (~25%), the biomass of Prochlorococcus peaked in the tropical Atlantic Ocean, and Bacteroidetes and Gammaproteobacteria bloomed in the nutrient-rich northern temperate waters and in the Benguela upwelling. In mesopelagic waters, higher proportions of SAR202 were present in both central gyre regions, whereas Crenarchaeota were clearly more abundant in the upwelling regions and in higher latitudes. Other phylogenetic groups such as the Planctomycetes, marine group II Euryarchaeota and the uncultured clades SAR406, SAR324 and SAR86 rarely exceeded more than 5% of relative abundance.

Nematode abundance in cold seep sediments of the Darwin mud volcano

During the JC-10 cruise (2007), we sampled the Darwin mud volcano (MV) for meiofaunal community and trophic structure in relation of pore-water geochemistry along a 10 m transect from a seep site on the rim of the crater towards the MV slope. Sediment samples were retrieved by the ROV Isis using push cores. On board and after the pore water extraction, the top 10 cm of the cores were sliced into 1 cm sections and fixed them in 4% formaldehyde for meiofaunal community analysis. In the home laboratory, the formaldehyde-fixed samples were washed over a 32 µm mesh sieve and extracted the meiofauna from the sediment by Ludox centrifugation (Heip et al. 1985). Meiofauna was then sorted, enumerated and identified at coarse taxonomic level. From each slice, ca. 100 nematodes were identified to genus level. Afterwards, abundance of Nematoda were depth integrated over the top 5 cm to gain individual abundances per 10 cm**2. Overall, total nematode biomass in the top 5 cm of the seep sediment core was ~10x higher than that in the core taken 1100 m away. Nematode genus composition varied little among cores and was mainly dominated by Sabatieria.