Abundance and biomass of planktonic diatom Proboscia alata and associated species, chlorophyll a, organic carbon and nitrogen concentrations in waters over the Bering Sea middle shelf in August 2001

During most of the vegetation season from late May to early September large-sized diatom alga Proboscia alata forms local patches with high abundances and biomasses in different oceanographic domains of the eastern Bering Sea shelf. For 0-25 m layer average abundance and biomass of species in these patches are 700000 cells/l and 5 g/m**3 (wet weight), while corresponding estimates for the layer of maximal species concentrations are 40000000 cells/l and 38 g/m**3 (wet weight) or 1.6 g C/m**3. These levels of abundance and biomass are typical for the spring diatom bloom in the region. Outbursts of P. alata mass development are important for the carbon cycle in the pelagic zone of the shelf area in the summer season. The paradox of P. alata summertime blooms over the middle shelf lies in their occurrences against the background of the sharp seasonal pycnocline and deficiency in nutrients in the upper mixed layer. Duration of the outbursts in P. alata development is about two weeks and size of patches with high abundances can be as large as 200 km across. Degradation of the P. alata summertime outbursts may occur during 4-5 days. Rapid sinking of cells through the seasonal pycnocline results in intense transport of organic matter to bottom sediments. One of possible factors responsible for rapid degradation of the blooms is affect on the population by ectoparasitic flagellates. At terminal stages of the P. alata blooms percentage of infected cells can reach 70-99%.

Dissolved iron measurements from 32 stations in the Central Arctic Ocean and Arctic Shelf Sea during POLARSTERN expedition ARK-XXII/2

Concentrations of dissolved (<0.2 µm) Fe (DFe) in the Arctic shelf seas and in the surface waters of the central Arctic Ocean are presented. In the Barents and Kara seas, near-surface DFe minima indicate depletion of DFe by phytoplankton growth. Below the surface, lower DFe concentrations in the Kara Sea (~0.4-0.6 nM) than in the Barents Sea (~0.6-0.8 nM) likely reflect scavenging removal or biological depletion of DFe. Very high DFe concentrations (>10 nM) in the bottom waters of the Laptev Sea shelf may be attributed to either sediment resuspension, sinking of brine or regeneration of DFe in the lower layers. A significant correlation (R2 = 0.60) between salinity and DFe is observed. Using d18O, salinity, nutrients and total alkalinity data, the main source for the high (>2 nM) DFe concentrations in the Amundsen and Makarov Basins is identified as (Eurasian) river water, transported with the Transpolar Drift (TPD). On the North American side of the TPD, the DFe concentrations are low (<0.8 nM) and variations are determined by the effects of sea-ice meltwater, biological depletion and remineralization and scavenging in halocline waters from the shelf. This distribution pattern of DFe is also supported by the ratio between unfiltered and dissolved Fe (high (>4) above the shelf and low (<4) off the shelf).

(Table 2) 230Th, 230Th xs and 232Th concentrations in dissolved, particulate and total (dissolved+small particles) for all KEOPS stations, Marion Dufresne cruise MD145

In the context of the KErguelen Ocean and Plateau compared Study (KEOPS, 19 January-13 February 2005), particle dynamics were investigated using thorium isotope measurements over and off the Kerguelen plateau. Dissolved and particulate 230Th and 232Th samples were collected at nine stations. Dissolved excess 230Th concentrations (230Thxs) vary from 0.5 to 20.8 fg/kg and particulate 230Thxs concentrations from 0.1 to 10.0 fg/kg. Dissolved and particulate 232Th concentration ranges are 16.8-450.2 pg/kg and 3.8-502.8 pg/kg, respectively. The 230Thxs concentrations increase linearly with depth down to the bottom at most of the plateau stations and down to 1000 m at the off-plateau stations. This linear trend is observed down to the bottom (1550 m) at Kerfix, the open-ocean "upstream" station located west of the Kerguelen plateau. A simple reversible scavenging model applied to these data allowed the estimation of adsorption rate constant (k1~=0.2-0.8 per year), desorption rate constant (k-1~=1-8 per year) and partition coefficients (average K=0.16±0.07). Calculated particle settling velocities S deduced from this simple model are ca. 500 m/year at most of the plateau stations and 800 m/year at all the off-plateau stations. The plateau settling velocities are relatively low for such a productive site, compared to the surrounding HNLC areas. The difference might reflect the fact that lateral advection is neglected in this model. Taking this advection into account allows the reconstruction of the observed 230Thxs linear distributions, but only if faster settling velocities are considered. This implies that the 1D model strongly underestimates the settling velocity of the particles. In the deep layers, the occurrence of intense boundary scavenging along the escarpment due to bottom sediment re-suspension and interaction with a nepheloid layer, yielding a removal of ?50% of the Th stock along the northwestward transect, is suggested.

Abundance of diatoms and foraminifers in the surface sediment layer of the southeastern Laptev Sea shelf

The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by intense interaction between fresh waters of Siberian rivers and basin seawater, Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600-1100 years B.P.) and the Little Ice Age (~100-600 years B.P.) inclusive. In addition, composition and distribution of planktonic foraminifers implies strong influence of Atlantic water during the Holocene optimum ~5100-6200 years B.P.

Geochemistry of recent sediments of the East African continental margin, Arabian Sea

Chemical analyses have been carried out on 40 samples from the sediment surface and 210 samples from cores that were taken from the edge of the African continental block at the Arabian Sea (coasts of Somalia and Kenya, from Cape Guardafui to Mombasa) on the occasion of the Indian Ocean Expedition of the German research vessel "Meteor" during the years 1964/65. The carbonate content shows its maximum on the northern part of the continental shelf of Africa, where fossil reef debris furnish the detritic portion of carbonate. In the southern part of the continental shelf of Africa the portion of carbonate is low, as it is heavily diluted by the non-carbonatic detritus. It is also in the deep-sea that a lower carbonate content is encountered below the calcite compensation depth. Trace elements in the carbonates: On the shelf and in its vicinity Sr and Mg are enriched. The enrichment has been brought about by the portion of reef debris, as this latter contains aragonite (enrichment of Sr) as well as high-magnesium calcite. The greatest part of the slope contains carbonates that are poor in trace elements and mainly made up of foraminifera (and of coccoliths). Below the carbonate compensation depth another enrichment of Mg takes place in the carbonates, which is probably due to a selective dissolution of calcite in comparison to dolomite. The iron and manganese contents of the carbonates are high (iron higher in coast proximity, manganese higher in the depth), but not genuine, as they come about in the course of the extraction of the carbonates as a result of the dissolution of authigenic Mn-Fe-minerals. Non-carbonatic portion of the sediments: In coast proximity an enrichment of quartz comes about. Within the quartz-rich zone it is the elements V, Cr, Fe, Ti, and B that have been enriched in the non-carbonatic components. This enrichment must be attributed to an elevated content of heavy minerals. In the case of Ti and Fe the preliminary enrichment brought about by processes of lateritisation on the continent plays a certain role. Toward the deep-sea an enrichment of the elements Mn Ni, Cu, and Zn takes place; these enrichments must be explained by authigenic Mn-Fe-minerals. Within the Mn-rich zone a belt running parallel to the coast stands out that shows an increased Mn-enrichment. However, this increase in enrichment does not apply to the elements Ni, Cu, and Zn. It is probable that this latter increased enrichment comes about as a result of the migration of manganese to the sediment surface. (Within the sediments there prevail reductive conditions, in the presence of which Mn is capable of migration, whereas at the sediment surface its precipitation comes about under oxidizing conditions). The quantity of organic matter mainly is dependent on grain size and on the rate of sedimentation. On the shelf an impoverishment of organic matter is to be encountered, as the sediments are coarse-grained. In the depth the impoverishment must be explained on the strength of a small rate of sedimentation. Between those two ranges organic substance is enriched. P and N show an enrichment in comparison to Corg with this applying all the more the smaller the absolute quantity of Corg is. In this particular case one has to do with an enrichment coming about during the diagenetic processes of organic matter. A comparison with the sediments from the Indian and Pakistani continental border in Arabian Sea shows as follows: on the African continental border the coarse detrital material has been transported farther out to deep-sea, which has something to do with the greater inclination of the surface of sedimentation. Carbonate is found in greater abundance on the African side. Its chemical composition is influenced by reef-debris which is missing by Indian-Pakistani side. The content of organic matter is lower on the African side. Contrary to that, the enrichments of N and P compared to organic matter are of an equal order of magnitude on both sides of the Arabian Sea.

Grain properties of rock fragments from shelf bottom sediments of the Sea of Okhotsk

Grain size, shape and roundness of rock fragments, texture, composition of bottom sediments from the Sea of Okhotsk are under study. These data are compared with parameters of modern lithodynamic conditions of the sea and genetic types of deposits are identified. These criteria are used for partition of Holocene and Upper Pleistocene sediment series and for identifying conditions of their formation. Dependence of structure of different genetic types of deposits on intensity of hydrodynamic processes, of terrigenous contribution, and on direction consedimentational tectonic movements is under consideration.

Phytoplankton responses and associated carbon cycling during shipboard carbonate chemistry manipulation experiments conducted around Northwest European shelf seas

The ongoing oceanic uptake of anthropogenic carbon dioxide (CO2) is significantly altering the carbonate chemistry of seawater, a phenomenon referred to as ocean acidification. Experimental manipulations have been increasingly used to gauge how continued ocean acidification will potentially impact marine ecosystems and their associated biogeochemical cycles in the future; however, results amongst studies, particularly when performed on natural communities, are highly variable, which may reflect community/environment-specific responses or inconsistencies in experimental approach. To investigate the potential for identification of more generic responses and greater experimentally reproducibility, we devised and implemented a series (n = 8) of short-term (2-4 days) multi-level (>=4 conditions) carbonate chemistry/nutrient manipulation experiments on a range of natural microbial communities sampled in Northwest European shelf seas. Carbonate chemistry manipulations and resulting biological responses were found to be highly reproducible within individual experiments and to a lesser extent between geographically separated experiments. Statistically robust reproducible physiological responses of phytoplankton to increasing pCO2, characterised by a suppression of net growth for small-sized cells (<10 µm), were observed in the majority of the experiments, irrespective of natural or manipulated nutrient status. Remaining between-experiment variability was potentially linked to initial community structure and/or other site-specific environmental factors. Analysis of carbon cycling within the experiments revealed the expected increased sensitivity of carbonate chemistry to biological processes at higher pCO2 and hence lower buffer capacity. The results thus emphasise how biogeochemical feedbacks may be altered in the future ocean.