Cross-shelf circulation and phytoplankton distribution at the summertime New England shelfbreak front

We investigate aspects of the secondary (cross-shelf) circulation at the Middle Atlantic Bight shelfbreak front using high-resolution data collected on the New England Shelf in August 2002. The alongshore shelfbreak jet coincides with the front at the seaward edge of the cold pool (remnant winter shelf water) and there is a suggestion of a cross-stream convergence centered at the jet core. Despite indications of convergence we found no evidence of a surface subduction on the seaward side of the front. At depth 70 m near the shelfbreak there was a patch of chlorophyll, located within a local temperature–salinity maximum which, though significantly below the euphotic zone, appeared to be photo-acclimated and viable. The chlorophyll feature could be the result of a local subduction by a larger scale eddy circulation seaward of the front.Dye tracer experiments directly observed the convergence at the foot of the shelfbreak front and subsequent upwelling of bottom boundary layer water along the shoreward side of the shelfbreak front. But, we found no evidence that this upwelling influenced productivity at the front. Further, since there was no cross-shelf maximum in subsurface chlorophyll at the front, we conclude that this productivity is in general, sustained by a broadly distributed local vertical nutrient flux from an underlying nutrient reservoir.     

Hydrography and biogeochemistry of the north western Bay of Bengal and the north eastern Arabian Sea during winter monsoon

The north eastern Arabian Sea and the north western Bay of Bengal within the Indian exclusive economic zone were explored for their environmental characteristics during the winter monsoons of 2000 and 2001 respectively. The two regions were found to respond paradoxically to comparable intensities of the atmospheric forcing. There is an asymmetry in the net heat exchange of these two basins with atmosphere because of the varying thickness of barrier layer. During winter, the convective mixing in the Arabian Sea is driven by net heat loss from the ocean, whereas the Bay of Bengal does not contribute to such large heat loss to the atmosphere. It appears that the subduction of high saline Arabian Sea water mass is the mechanism behind the formation of a barrier layer in the northeast Arabian Sea; whereas that in the Bay of Bengal and the southeast Arabian Sea are already established as due to low saline water mass. The weak barrier layer in the Arabian Sea yields to the predominance of convective mixing to bring in nitrate-rich waters from the deeper layers to the surface, thereby supporting enhanced biological production. On the other hand, the river discharge into the Bay of Bengal during this period results in the formation of a thick and stable barrier layer, which insulates vertical mixing and provide oligotrophic condition in the Bay.     

Nitrogenous discharges to the eastern Gulf of Finland, the Baltic Sea: Elemental flows, stable isotope signatures, and their estuarine modification

We studied the nutrient input to the Gulf of Finland via River Neva, the largest river discharging freshwater to the Baltic Sea, and characterised the isotopic signatures (¹⁵N, ¹⁸O, ¹³C) in dissolved and particulate substances (NO₃⁻, PON, POC, DIC) in the River Neva over two seasonal cycles, as well as in samples from St. Petersburg wastewater treatment plants (NO₃⁻, NH₄⁺, PON, POC). These riverine and municipal discharges account for 40% of terrestrial inorganic N loading to the Gulf of Finland, representing annually 7% of the total nitrogen pool in the water mass of the whole Gulf. To describe and evaluate the modification of these isotopic signals along a Gulf of Finland transect towards the Baltic Proper, two cruises were arranged, one in late spring after the annual maximum in River Neva runoff, and one in autumn, in the late phase of the annual growth season.River Neva nitrate signatures of ¹⁵N and ¹⁸O indicated major agricultural fertilizer origin of nitrogen, and the isotopic composition was clearly lighter (δ¹⁵N-NO₃⁻ mean of 2.4‰ air) than previously measured from more southern rivers discharging into the Baltic Sea. Because of the light composition of the River Neva N source, close to the ¹⁵N signatures of the open Gulf, as well as of the efficient depletion of the inorganic load already in the innermost estuary, straightforward end-member tracer analysis of the transport of N in the basin is problematic. St. Petersburg wastewater ammonium showed, however, high δ¹⁵N values (ca. 13‰), which gives a first estimate of 5.8‰ for δ¹⁵N of the easternmost estuarine total inorganic N source. The available sediment data from the basin (δ¹⁵N 6 to 8‰) somewhat exceeds the average source signature. This emphasizes the significance of biological transformation processes, most importantly assimilation of inorganic nitrogen, food web interactions and denitrification, which all involve isotopic fractionation, for the mass balance models describing the dynamics of the sources and sinks of the N cycle of the basin.     

Intrusions of eastern North Atlantic central waters and phytoplankton in the north and northwestern Iberian shelf during spring

The influence of intrusions of eastern North Atlantic central water (ENACW) in the north and northwestern Iberian shelf on phytoplankton composition and abundance and on particle-size distributions of seston was analyzed using data collected on three extensive cruises during spring 1991 and 1992. Water with temperature and salinity values between 12.20 and 13.86 °C and between 35.66 and 35.98 psu, respectively, characteristics of the subtropical type of ENACW (ENACW_t), was detected in the upper 100 m of the water-column in all cruises, but particularly in the western coast in 1992. The highest salinity values of this water were found near the surface (0–100-m depth) and in early spring 1992, while minimum salinity values, and also minimum geographical extension, were found in late spring in both years. Phytoplankton blooms concentrated in frontal areas between different water types, with maximum intensity and extension in early spring.Using temperature and salinity characteristics, samples were classified in four groups corresponding to the major water types found in the region: Bay of Biscay central water (BBCW), two segments of ENACW of different salinity and surface water influenced by continental runoff. This classification was significantly confirmed by three independent discriminant analyses using hydrographic and chemical (dissolved nutrients and chlorophyll) variables, phytoplankton species abundance variables and particle-size concentration of seston variables. Phytoplankton blooms related to the presence of saline waters were characterized by the dominance of either chain-forming diatoms or a mixture of diatoms and phytoflagellates and high concentrations of seston. The diatom species dominating in saline waters were typical of upwelling-induced blooms occurring generally during summer. Blooms occurring in waters influenced by runoff also contained diatoms but in lower numbers than those of saline waters. Nutrients were not exhausted in the region, suggesting that phytoplankton populations were still in active growth. These results are interpreted taking into account the known variability in water-mass formation and in the poleward current driving ENACW_t along the shelf, and indicate that saline intrusions are a major feature affecting the distribution and composition of plankton in the spring in the southern Bay of Biscay, thus enlarging to a wider spatial scale their reported influence on the pelagic ecosystem.     

Comparison of Beach Nourishment along the U.S. Atlantic,Great Lakes,Gulf of Mexico,and New England Shorelines

The U.S. national beach nourishment experience is summarized for the East Coast barrier islands, the Gulf of Mexico, New England, and the Great Lakes. A total of 1,305 nourishment episodes on 382 beaches are recorded at a total estimated cost of approximately $1.4 billion ($2.5 billion in 1996 dollars). In terms of both volume and costs, nourishment has been the most extensive by far on the East Coast barrier islands. Depending on the region, between 65% and 85% of all nourishment projects have a federal funding component. Annual expenditures and sand volumes for beach nourishment are increasing, especially on East Coast barriers. At present, total annual national beach nourishment costs (excluding the Pacific Coast) are on the order of $100 million per year. The cost per cubic yard of nourishment sand as expressed in 1996 dollars has remained more or less constant over time. Additionally, the volumes of sand needed for subsequent nourishment episodes on individual beaches do not decrease, despite contrary assumptions in the shoreface-profile-ofequilibrium concept that subsequent nourishment volumes should diminish. In light of the historical experience of beach nourishment identified in this study, individual state and local coastal communities should reevaluate their plans for future beach nourishment programs. The complete listing of all the data on nourished beaches from this survey is available at www.geo.duke.edu/Research/psds/psds.htm     

Summer distribution of seabirds in the North-East Water polynya, Greenland

The distribution at sea of seabirds was studied in the North-East Water (NEW) polynya, Greenland, during transect counts in the summers of 1991, 1992 and 1993 on board the ice-breaking RVs Polarstern and Polar Sea. Data collected within the polynya ‘box’ (78–82°N; 5–18°W) concern observations of 8000 birds counted during 1350 half-hour counts. Distribution is presented as density (N/km²) and calculated daily food intake. Five bird species were selected for discussion, representing more than 95% of the total numbers encountered: Fulmar (Fulmarus glacialis), Ivory Gull (Pagophila eburnea), Kittiwake (Rissa tridactyla), Glaucous Gull (Larus hyperboreus) and Ross's Gull (Rhodostethia rosea). For these species, densities are comparable in the NE Greenland polynya and in other European Arctic seas. The main difference is the absence in NEW of the species playing the main role in Arctic seas: Brünnich's Guillemot (Uria lomvia) and Little Auk (Alle alle). In the absence of fish-eating birds and of birds consuming zooplankton in the water column, the NEW polynya ecosystem is thus dominated by surface feeders and, closer to the coast, by benthic feeders like eiders, Somateria mollissima and S. spectabilis, and walrus, Odobenus rosmarus. The density and daily food intake for all seabirds are one order of magnitude lower in the polynya than in the Arctic seas. The distribution and abundance of seabirds in the NEW polynya seems to reflect a very low density of pelagic fish and Zooplankton in the water column, while Zooplankton must be present at ‘normal’ concentrations in the upper layer.     

Impact of tidal front on the distribution of bacterioplankton in the southern Yellow Sea, China

Three surveys were carried out in anchovy spawning periods in southern Yellow Sea in May and June 2001, and June 2002. Chlorophyll a (Chl-a) concentration, bacterioplankton abundance, biomass and their variations along the zone of tidal fronts were investigated. The results showed that (1) high Synechococcus abundance distributed more often in frontal area and middle-surface layer of a stratified zone; and (2) the maximal abundance of bacteria occurred in stratified and mixed zone.     

Seasonal and interannual variation of physical and biological processes during 1994–2001 in the Sea of Japan/East Sea: A three-dimensional physical–biogeochemical modeling study

A Pacific basin-wide physical–biogeochemical model has been used to investigate the seasonal and interannual variation of physical and biological fields with analyses focusing on the Sea of Japan/East Sea (JES). The physical model is based on the Regional Ocean Model System (ROMS), and the biogeochemical model is based on the Carbon, Si(OH)₄, Nitrogen Ecosystem (CoSiNE) model. The coupled ROMS–CoSiNE model is forced with the daily air–sea fluxes derived from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR) reanalysis for the period of 1994 to 2001, and the model results are used to evaluate climate impact on nutrient transport in Mixed Layer Depth (MLD) and phytoplankton spring bloom dynamics in the JES.The model reproduces several key features of sea surface temperature (SST) and surface currents, which are consistent with the previous modeling and observational results in the JES. The calculated volume transports through the three major straits show that the Korea Strait (KS) dominates the inflow to the JES with 2.46 Sv annually, and the Tsugaru Strait (TS) and the Soya Strait (SS) are major outflows with 1.85 Sv and 0.64 Sv, respectively. Domain-averaged phytoplankton biomass in the JES reaches its spring peak 1.8 mmol N m^− 3 in May and shows a relatively weak autumn increase in November. Strong summer stratification and intense consumption of nitrate by phytoplankton during the spring result in very low nitrate concentration at the upper layer, which limits phytoplankton growth in the JES during the summer. On the other hand, the higher grazer abundance likely contributes to the strong suppression of phytoplankton biomass after the spring bloom in the JES. The model results show strong interannual variability of SST, nutrients, and phytoplankton biomass with sudden changes in 1998, which correspond to large-scale changes of the Pacific Decadal Oscillation (PDO). Regional comparisons of interannual variations in springtime were made for the southern and northern JES. Variations of nutrients and phytoplankton biomass related to the PDO warm/cold phase changes were detected in both the southern and northern JES, and there were regional differences with respect to the mechanisms and timing. During the warm PDO, the nutrients integrated in the MLD increased in the south and decreased in the north in winter. Conversely, during the cold PDO, the nutrients integrated in the MLD decreased in the south and increased in the north. Wind divergence/convergence likely drives the differences in the southern and northern regions when northerly and northwesterly monsoon dominates in winter in the JES. Subjected to the nutrient change, the growth of phytoplankton biomass appears to be limited neither by nutrient nor by light consistently both in the southern and northern regions. Namely, the JES is at the transition zone of the lower trophic-level ecosystem between light-limited and nutrient-limited zones.     

New species of the genus Xanthocalanus (Copepoda, Calanoida, Phaennidae) from the Laptev Sea

Sampling of the near-bottom calanoid copepods was performed on board of the research vessel Polarstern in 1993 in the Laptev Sea (Siberian Arctic). Three new species of Xanthocalanus were identified as such, and are described and figured here: X. spinodenticulatus sp. nov., X. laptevorum sp. nov. and X. polarsternae sp. nov.     

Siliceous plankton dominate primary and new productivity during the onset of El Niño conditions in the Santa Barbara Basin, California

The potential for carbon export and the role of siliceous plankton in the cycling of C and N was assessed in natural plankton assemblages in the Santa Barbara Basin, California, by examining uptake rates of inorganic carbon, nitrate and silicic acid. In April–August 1997, the concentrations of chlorophyll a, particulate organic carbon, particulate organic nitrogen and biogenic silica were measured twice monthly, and results revealed the occurrence of at least three blooms, the largest in June. Particulate elemental ratios of C, N and Si were similar to ratios of nutrient-replete diatoms, suggesting that they dominated this bloom. Mean integrated rates of carbon, nitrate and silicon uptake during the 4-month study period are similar to other productive coastal and upwelling regions (103, 8.3 and 13 mmol m⁻² day⁻¹, respectively). New production rates were twice as high as previously reported in this region and indicate that high rates of new production along eastern boundary currents are not confined to the major coastal upwelling regions. C/NO₃⁻, Si/NO₃⁻ and Si/C uptake ratios varied widely, and mean integrated ratios were 14±5.4, 1.6±1.0 and 0.12±0.07 (S.D.), respectively. That mean C/NO₃⁻ uptake ratio corresponds to an f-ratio of about 0.5 indicating a large potential for particulate export. Based on the average Si/NO₃⁻ and Si/C uptake ratios, diatoms could perform all of the primary production and nitrate uptake that occurred during the study; these rates also suggest that export is controlled by diatoms in this system. The mean Si/C biomass ratio was lower than the mean Si/C uptake ratio, consistent with the preferential export of Si relative to C observed in sediment traps in the basin. The study took place during a period of surface-water warming, with nitrate and silicic acid concentrations decreasing throughout the onset of the 1997–1998 El Niño conditions. Although diatoms contributed less to particulate biomass during the low nutrient conditions, high f-ratios (0.33–0.66) were maintained.     

艰苦创业元勋，走向世界先导——追忆新中国第一任船舶工业局局长程望

程望同志（1916～1991）是新中国船舶工业的创业奠基人之一，是建国后第一任船舶工业局局长。生前在军工、船舶、航运等部门担负领导工作。他成功地贯彻实施了中央对船舶工业发展的战略步骤，使船舶工业为海军建设、航运、船舶出口和国家重大工程建设作出卓有成效的贡献，他在全国海事界享有很高的声誉。他诚信待人，知人善任，尤为海事界人士爱戴。从1952年起连任了六届（第二至七届）上海市造船工程学会理事长，并长期担任中国造船工程学会副理事长。程望同志为新中国造船事业呕心沥血无私奉献是一座不朽丰碑。     

Hydrography, currents and distribution of suspended matter during a dumping experiment in the western Baltic Sea at a site near Warnemünde

During a dumping experiment on 20/21 June 2001, an extensive data record was collected to understand the dynamical processes in the water column of the investigation area and to validate model results. Weak westerly winds with strongly changing cloud coverage characterized the meteorological situation. During the second day the wind calmed down and moved shortly to easterly directions. The water column was characterized by a strong vertical stratification with discontinuity layers in temperature and salinity in 12 and 16 m. The current regime was dominated by outflow at the water surface and inflow along the German coast, with strong current shearing in the dumping area. The suspended matter clouds could be identified by optical methods and ADCP (Acoustic Doppler Current Profiler) scattering intensity. During the experiment the suspended matter plumes were only visible at the surface up to 1 h after the dumping. The aerial photographs document that the particle clouds at the surface drifted to the west and, after approximately 40 min, they were only weakly visible. The fine material was concentrated in the discontinuity layer leading to substantially higher values of optical parameters and suspended matter concentration than measured in the surface clouds. Due to the vertical current shears the material was transported in the water column in different directions. At the first day the maximum of the suspended matter in the discontinuity layer was in the north-western corner and in the bottom layer in the northeast corner of the dumping area. Strong wind conditions after the dumping led to periodical resuspension processes.     

Response of benthic infauna and epifauna to ocean disposal of red clay dredged material in the New York Bight: A study using sediment-profile imaging, surface imaging and traditional methods

In 1997, approximately 1 million cubic yards of consolidated red clay was dredged from Newark Bay in New Jersey and deposited on the seafloor at an open-water dredged material disposal site located on the inner continental shelf of the New York Bight. To address concerns about the ability of benthic organisms to colonize the seafloor deposits of this compact, organic-poor red clay, monitoring surveys were conducted in 1998 (1 year after disposal) and 2002 (5 years after disposal). The surveys used a combination of sediment imaging and traditional grab sampling methods to characterize physical and biological conditions over the surface of the red clay deposits in comparison to nearby reference areas consisting of either naturally-occurring, sandy surface sediments or deposits of unconsolidated, muddy dredged material. Sediment-surface and sediment-profile images (SPI) collected in summer 2002 indicated that the surface of the red clay deposits had become much smoother and more heterogeneous in texture compared to images collected in 1998. The images also indicated that these deposits had become colonized to a much greater degree by relatively abundant and diverse infaunal and epifaunal communities compared to 1998. Taxonomic analysis of benthic grab samples confirmed the imaging results and indicated relatively high infaunal organism abundance and diversity over the red clay deposits in 2002 compared to the reference areas. However, the structure of the benthic community inhabiting the red clay was fundamentally different from the communities in the reference areas, due to the differences in sediment texture and composition. The combination of imaging and traditional taxonomic approaches used in this study provided much greater insight on the red clay colonization process than either approach by itself.