Occurrence and turnover of DMSP and DMS in deep waters of the Ross Sea,Antarctica

High concentrations of the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) and its degradation product dimethylsulfide (DMS) are associated with blooms of Phaeocystis antarctica in the Ross Sea, Antarctica. Episodic and rapid vertical export of Phaeocystis biomass to deep water has been reported for the Ross Sea, therefore we examined the distribution and microbial consumption rates of DMSP and DMS throughout the sub-euphotic water column. Total DMSP (dissolved+particulate; DMSPt) was present at 0.5–22 nM at depths between 70 and 690 m during both the early bloom (November) and the late bloom (January). Sub-euphotic peaks of DMSP were sometimes associated with mid-water temperature maxima, and elevated DMSP below 70 m was found mainly in water masses characterized as Modified Circumpolar Deep Water or Antarctic Shelf Water. Overall, 50–94% of the integrated water-column DMSPt was found below the euphotic zone. At one station during the early bloom, local maxima of DMSPt (14 nM) and DMS (20 nM) were observed between 113 and 240 m and these maxima corresponded with high chlorophyll a concentrations, P. antarctica cell numbers, and Fv/Fm (the quantum yield of photosystem II). During the late bloom, a sub-euphotic maximum of DMSPt (15.8 nM) at 250 m cooccurred with peaks of chlorophyll a concentration, DMSP lyase activity, bacterial production and dissolved DMSP consumption rates. DMSP turnover contributed ～12% of the bacterial carbon demand between 200 and 400 m. DMS concentrations peaked at 286 m but the maximum concentration (0.42 nM) was far lower than observed during the early bloom, probably because of relatively rapid biological consumption of DMS (1–3 turnovers per day) which, in turn, contributed to elevated dissolved dimethylsulfoxide (DMSO) concentrations. Relatively stable DMSPt distributions at some sites suggest that rapid sinking of Phaeocystis biomass is probably not the major mechanism responsible for mesopelagic DMSP accumulations. Rather, subduction of near-surface water masses, lateral advective transport or trapping of slowly sinking P. antarctica biomass in intermediate water masses are more likely mechanisms. We found that a culture of P. antarctica maintained cellular integrity during 34 days of darkness, therefore the presence of intact cells (and DMSP) at depth can be explained even under a slow sinking/advection scenario. Whatever the mechanism, the large pools of DMSP and DMS below the euphotic zone suggest that export exerts a control on potential DMS emission from the surface waters of the Ross Sea.     

Dimethylsulphide and dimethylsulphoniopropionate in Antarctic sea ice and their release during sea ice melting

This study presents concentrations of dimethylsulphide (DMS) and its precursor compound dimethylsulphoniopropionate (DMSP) in a variety of sea ice and seawater habitats in the Antarctic Sea Ice Zone (ASIZ) during spring and summer. Sixty-two sea ice cores of pack and fast ice were collected from twenty-seven sites across an area of the eastern ASIZ (64°E to 110°E; and the Antarctic coastline north to 62°S). Concentrations of DMS in 81 sections of sea ice ranged from < 0.3 to 75 nM, with an average of 12 nM. DMSP in 60 whole sea ice cores ranged from 25 to 796 nM and showed a negative relationship with ice thickness (y = 125x^− 0.8). Extremely high DMSP concentrations were found in 2 cores of rafted sea ice (2910 and 1110 nM). The relationship of DMSP with ice thickness (excluding rafted ice) suggests that the release of large amounts of DMSP during sea ice melting may occur in discrete areas defined by ice thickness distribution, and may produce ‘hot spots’ of elevated seawater DMS concentration of the order of 100 nM. During early summer across a 500 km transect through melting pack ice, elevated DMS concentrations (range 21–37 nM, mean 31 nM, n = 15) were found in surface seawater. This band of elevated DMS concentration appeared to have been associated with the release of sea ice DMS and DMSP rather than in situ production by an ice edge algal bloom, as chlorophyll a concentrations were relatively low (0.09–0.42 μg l^− 1). During fast ice melting in the area of Davis station, Prydz Bay, sea ice DMSP was released mostly as extracellular DMSP, since intracellular DMSP was negligible in both hyposaline brine (5 ppt) and in a melt water lens (4–5 ppt), while extracellular DMSP concentrations were as high as 149 and 54 nM, respectively in these habitats. DMS in a melt water lens was relatively high at 11 nM. During the ice-free summer in the coastal Davis area, DMS concentrations in surface seawater were highest immediately following breakout of the fast ice cover in late December (range 5–14 nM), and then remained at relatively low concentrations through to late February (< 0.3–6 nM). These measurements support the view that the melting of Antarctic sea ice produces elevated seawater DMS due to release of sea ice DMS and DMSP.     

Profiles of DMSP,algal pigments,nutrients and salinity in pack ice from eastern Antarctica

Concentrations of dimethylsulphoniopropionate (DMSP) were measured in seven pack ice cores from three sites in eastern Antarctica to determine their relation to algal pigments, nutrients (nitrate, silicate and phosphate) and bulk salinity. The algal groups haptophytes, dinoflagellates and diatoms were identified in surface, interior and bottom assemblages in the pack ice cores using the photosynthetic marker pigments 19′-hexanoyloxyfucoxanthin (HEX), peridinin (PER) and fucoxanthin (FUC), respectively. DMSP concentrations were significantly correlated (P<0.01, Pearson) with chlorophyll-a (r=0.58), HEX (r=0.75), PER (r=0.79) and FUC (r=0.63) concentrations. The pool of DMSP within the pack ice (mean 107 nM) was contributed mainly by interior and bottom algal assemblages (mean 94 and 268 nM, respectively), whilst the surface algal assemblages were minor contributors (mean 18 nM). DMSP production and/or accumulation appears to differ between surface, interior and bottom pack ice algal assemblages due to differences in biomass, class composition, and possibly the unique environmental conditions experienced by each assemblage. In pack ice, diatoms appear to be important producers of DMSP, due to their dominance of algal assemblages.     

Seasonal dimethylsulfoniopropionate (DMSP) variability in Dona Paula bay

Data on temporal variations of total dimethylsulfoniopropionate (DMSP_t) and the environmental factors that influence DMSP_t concentrations are important in understanding the biogeochemical cycling of organic sulfur compounds. Annual and diurnal variations of DMSP_t were investigated in relation to environmental variables at a fixed station in Dona Paula bay (west coast of India). DMSP concentrations were high in the day and low at night and ranged from 3.69 to 84 nM with a maximum at 17.00 h. The high concentrations of DMSP_t during daytime closely followed that of Chl a concentrations. The DMSP utilizers averaged 0.8 ± 0.3 × 10³ cells l^?1 during night and 0.4 ± 0.1 × 10³ cells l^?1 during the day. The diel variation of DMSP_t was influenced more by biological variables than hydrographic parameters. In the year-round study, the concentrations ranged from 0.69 to 15.8 nM. It was fourfold higher during the southwest monsoon season (13.4 ± 2 nM) and threefold higher during the post-monsoon season (9.96 ± 5 nM) compared to the pre-monsoon season (3.1 ± 1 nM). DMSP_t concentrations showed temporal variability, both during diurnal and annual studies. Diatoms were identified as producers of DMSP in Dona Paula bay. Dinoflagellates also contributed during the non-monsoon seasons. Another factor involved in the variability of DMSP_t was DMSP utilizing bacteria, which ranged from 1 to 10% of the total heterotrophic count.     

Stock and losses of trace metals from salt marsh plants

Pools of Zn, Cu, Cd and Co in the leaf, stem and root tissues of Sarcocornia fruticosa, Sarcocornia perennis, Halimione portulacoides and Spartina maritima were analysed for a Tagus estuary (Portugal) salt marsh. Pools of Cu and Cd in the salt marsh were higher in spring/summer, indicating a net uptake of these metals during the growing season. Standing stocks of Zn, Cu, Cd and Co in the leaf and stem biomass of S. fruticosa, S. perennis and H. portulacoides showed a strong seasonal variation, with higher values recorded in autumn. The metal-containing leaves and stems that shed in the autumn become metal-containing detritus. The amount of this material washed out from the total marsh area (200 ha) was estimated as 68 kg of Zn, 8.2 kg of Cu, 13 kg of Co and 0.35 kg of Cd. The high tidal amplitude, a branched system of channels and semi-diurnal tidal cycle greatly favour the export of the organic detritus to adjoining marsh areas.     

Mesoscale decrease of surface phosphate and associated phytoplankton dynamics in the vicinity of the subtropical South Pacific islands

Surface distributions of nutrients and phytoplankton were investigated in the vicinity of the subtropical South Pacific islands by using a continuous underway system with a highly sensitive nutrient analysis. A total of 17 transects, whose lengths ranged between 42 and 271 km, were sampled for continuous nutrient measurements. The study area was characterized by an overall depletion of nitrate+nitrite (<15 nM), but phosphate varied from 7 to 192 nM. The transects were grouped into 4 patterns according to distribution of phosphate concentrations. In 7 transects, a mesoscale decrease in phosphate occurred, coinciding with an elevation of in vivo chlorophyll fluorescence, which was accompanied by an increase in phytoplankton abundance as revealed by microscopy, flow cytometry, and accessory pigments. This mirror–image relationship between the phosphate concentration and phytoplankton abundance was most apparent on both a 99-km transect east of Tonga, where the phosphate concentration ranged from 17 to 125 nM, and on a 98-km transect west of Fiji, where the phosphate concentration ranged from 23 to 136 nM. Both these transects contained distinct blooms of Trichodesmium in areas with the lowest concentrations of phosphate. In other 2 transects, fluctuations in phosphate concentrations showed no distinct relationship with chlorophyll fluorescence. Other patterns that emerged included consistently high concentrations, ranging from 109 to 192 nM, in 5 transects and consistently low phosphate concentrations, ranging from 7 to 50 nM, in 3 transects. Abundance of Trichodesmium, Prochlorococcus, Synechococcus, and all accessory pigments examined tended to be higher in the low phosphate transects than in the high phosphate ones. In particular, Trichodesmium occurred in low phosphate water (<25 nM). There was no significant relationship between phosphate concentrations and nanoplanktonic unicellular cyanobacteria. Our observations suggest that surface phosphate decreases are associated with phytoplankton utilization of phosphate, and that nitrogen supply from Trichodesmium may contributes to this utilization.     

Vertical distributions of dissolved organic carbon and nitrogen in the Southern Ocean

Detailed vertical profiles of dissolved organic carbon (DOC), nitrogen (DON) and DOC/DON ratios in the Australian sector of the Southern Ocean (56°–65°S around 140°W transect) were obtained by a high-temperature catalytic oxidation method with a modified Shimadzu TOC-5000 unit. The simultaneous analyses of DOC and total dissolved nitrogen (TDN) gave high precision results (±0.7 μMC and ±0.3 μMN). In surface layers, DOC concentrations were lower (45–55 μM) than those generally obtained from other oceanic environments (60–90 μM). The surface concentrations of DON varied from 4 to 9 μM, but within the range generally reported for other ocean regions. Surface excesses of DOC and DON were calculated against nearly constant subsurface concentrations. A consistent contribution of low C/N ratio (2.7–5.0) was found in the mid-surface layer (30–75 m), suggesting more extensive degradation of carbon-enriched materials and/or enhanced supply of nitrogen-enriched ones.     

Atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary

Measurements of nitrate and ammonium in precipitation and associated with aerosols were conducted at Rutgers University Marine Field Station in Tuckerton, New Jersey from March 2004 to March 2005 to characterize atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary. The arithmetic means of nitrate and ammonium concentrations for precipitation samples were 2.3 mg L⁻¹ and 0.42 mg L⁻¹, respectively. Nitrate and ammonium concentrations in aerosol samples averaged 3.7 μg m⁻³ and 1.6 μg m⁻³, respectively. Wet deposition rates appeared to vary with season; the highest rate of inorganic nitrogen deposition (nitrate + ammonium) occurred in the spring with an average value of 1.33 kg-N ha⁻² month⁻¹. On an annual basis, the total (wet and dry) direct atmospheric deposition fluxes into the Mullica River-Great Bay Estuary were 7.08 kg-N ha⁻² year⁻¹ for nitrate and 4.44 kg-N ha⁻² year⁻¹ for ammonium. The total atmospheric inorganic nitrogen directly deposited to the Mullica River-Great Bay Estuary was estimated to be 4.79 × 10⁴ kg-N year⁻¹, and the total atmospheric inorganic nitrogen deposited to the Mullica River watershed was estimated to be 1.69 × 10⁶ kg-N year⁻¹. Only a fraction of the nitrogen deposited on the watershed will actually reach the estuary; most of the nitrogen will be retained in the watershed due to utilization and denitrification during transport. The amount of N reaching the Mullica River-Great Bay Estuary indirectly is estimated to be 5.07 × 10⁴ kg-N year⁻¹, approximately 97% is retained within the watershed. This atmospheric nitrogen deposition may stimulate phytoplankton productivity in the Mullica River-Great Bay ecosystem.     

Isotopic and elemental indicators of nutrient sources and status of coastal habitats in the Caribbean Sea,Yucatan Peninsula,Mexico

Nutrient inputs associated with coastal population growth threaten the integrity of coastal ecosystems around the globe. In order to assess the threat posed by rapid growth in tourism, we analyzed the nutrient concentrations as well as the δ¹⁵N of NO₃⁻ and macrophytes to detect wastewater nitrogen (N) at 6 locations along a groundwater-dominated coastal seagrass bed on the Caribbean coast of Mexico. We predicted that locations with greater coastal development would have higher concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (P), as well as δ¹⁵N of NO₃⁻, reflecting wastewater sources of N. However, concentrations of NO₃⁻ were not significantly different between developed (3.3 ± 5.3 μM NO₃⁻) and undeveloped (1.1 ± 0.7 μM) marine embayments. The most important control on DIN concentration appeared to be mixing of fresh and salt water, with DIN concentrations negatively correlated with salinity. The δ¹⁵N of NO₃⁻ was elevated at an inland pond (7.0 ± 0.42‰) and a hydrologically-connected tide pool (7.6 ± 0.57‰) approximately 1 km downstream of the pond. The elevated δ¹⁵N of NO₃⁻ at the pond was paralleled by high δ¹⁵N values of Cladophora sp., a ubiquitous green alga (10 ± 1‰). We hypothesize that inputs of nitrogen rich (NO₃⁻ > 30 μM) groundwater, characterized by ¹⁵N enriched signatures, flow through localized submarine groundwater discharges (SGD) and contribute to the elevated δ¹⁵N signatures observed in many benthic macrophytes. However, changes in nitrogen concentrations and isotope values over the salinity gradient suggest that other processes (e.g. denitrification) could also be contributing to the ¹⁵N enrichments observed in primary producers. More measurements are needed to determine the relative importance of nitrogen transformation processes as a source of ¹⁵N to groundwaters; however, it is clear that continued inputs of anthropogenic N via SGD have the potential to severely impact ecologically and economically valuable seagrass meadows and coral reefs along the Caribbean coast of Mexico.     

Nitrogen assimilation and the f-ratio in the northwestern Indian Ocean during an intermonsoon period

Rates of nitrogen assimilation by phytoplankton were measured at 13 stations along a transect in the northwestern Indian Ocean, from the Gulf of Oman, southwards to approximately 8°N, during November and December 1994. Nitrate (NO₃), ammonium (NH₄) and urea assimilation were measured using simulated in situ ¹⁵N incubation techniques. These measurements were supported by simultaneous rate measurements of primary production using ¹⁴C incubation techniques and detailed vertical distributions of temperature and chlorophyll concentrations. Euphotic zone integrated nitrogen assimilation rates varied between 1.1 and 23.6 mmol N m^-2 day^-1, with generally higher rates occurring at the northern and southern ends of the transect. At the majority of stations ammonium was the preferred nitrogen substrate assimilated; the average integrated assimilation rate of ammonium being 3.7 mmol N m^-2 day^-1 compared to 1.6 and 1.8 mmol N m^-2 day^-1 for urea and nitrate respectively. This general preference is reflected in the low f-ratios, which were ⩽0.52 for all stations and in the relative preference indices (RPI) values which were consistently >1 for ammonium and <1 for nitrate. A further examination of the data has lead to an apparent partitioning of the northwestern Indian Ocean into 2 regions; a region north of 17°30′N and a region south of this, to about 8°N. This division is based on: (i) the relationship between the f-ratio and ambient nitrate levels; (ii) nitrogen assimilation and primary production and (iii) the biomass distribution. It is suggested that this partitioning should be investigated further with the development of biogeochemical provinces in mind and the estimation of f-ratios on much larger, horizontal scales.     

Iron fertilization of Trichodesmium off the west coast of Barbados: A one-dimensional numerical model

A one-dimensional quasi-Eulerian model, describing the biological and chemical interactions of autotrophic and heterotrophic plankton populations within the upper 100 m of the water column, was used to explain the relative impact of iron fertilization from Saharan dust on phosphorus cycling by the cyanobacterium, Trichodesmium spp. We examined the Caribbean surface waters off the west coast of Barbados using seasonal cases of dust delivery (summer peak) in relation to periods of elevated phosphorus stocks found in episodic pulses of Amazon River water advected past Barbados by the Guiana Current. The additional iron and phosphorus supplied by fluvial sources, available after biological depletion of nitrogen, could alleviate the growth limitation of Trichodesmium far downstream of the river plumes. The model results were compared with measurements made of Trichodesmium stocks 8 km off the west coast of Barbados. Modeled concentrations within the low-salinity Amazon plumes reached ∼7.4 mg chl m⁻², as seen at Barbados. In the absence of the low-salinity signal, the Trichodesmium biomass shifted to phosphorus limitation with little response to iron fertilization. This indicates that Trichodesmium stocks may indeed be mainly a function of phosphorus availability within the upper water column. Therefore, the supply of phosphorus from subtropical/tropical rivers, such as the Amazon and Orinoco, limits the potential cyanophyte response, despite adequate atmospheric iron delivery. This alters our view not only of the western North Atlantic nitrogen budget, but potentially several regions downstream of low N:P river systems.     

The relative contributions of unicellular and filamentous diazotrophs to N2 fixation in the South China Sea and the upstream Kuroshio

We studied the seasonal, diel, and vertical distribution of phytoplankton N₂ fixation to understand the relative contributions of unicellular and filamentous nitrogen fixers (diazotrophs) to N₂ fixation and nitrogen recycling in the northern South China Sea (SCS) and the neighboring upstream Kuroshio. N₂-fixation rates were measured by the ¹⁵N₂ tracer technique (addition by bubble) on unicellular (<10 or 20 µm) and the filamentous diazotrophs (>10 or 20 µm, mostly Trichodesmium and Richelia) fractionated by 10- or 20-µm mesh sizes. The mean depth-integrated total (unicellular+filamentous) N₂-fixation rates in the SCS (51.7±6.2 µmol N m⁻² d⁻¹) averaged 1/3 of that in the Kuroshio (142.7±29.6 µmol N m⁻² d⁻¹), with higher rates in the winter than in other seasons in the SCS and the opposite seasonal pattern in the Kuroshio. Unicellular diazotrophs contributed 65% of the total N₂ fixation in the SCS, which were negatively correlated with surface temperature and, as for total N₂ fixation, were higher in the winter when Trichodesmium spp. were scarce. In comparison, the unicellular diazotrophs contributed 50% of total N₂ fixation in the Kuroshio, and their contributions were not significantly correlated with surface temperature. In both the SCS and the Kuroshio, the unicellular N₂ fixation was more important during the night than during the day, and in the deep euphotic layer than in the surface layer, even in the daytime. Our results show that the unicellular diazotrophs were important N₂ fixers and contributed significantly to N₂ fixation in the tropical marginal seas, more so in the SCS than the Kuroshio.     

Seasonal patterns in the fish and epibenthic crustaceans community of an intertidal zone with particular reference to the population dynamics of plaice and brown shrimp

The intertidal zone of a sandy beach located on the French coast of the Eastern Channel, was sampled during spring and summer 2000 to analyse the community structure of fish and epibenthic crustaceans. The presence of many juvenile fish (mainly O-group) and crustaceans indicated the important role played by the intertidal zone as a nursery ground. The brown shrimp, Crangon crangon and O-group plaice, Pleuronectes platessa are the two most abundant species of the intertidal ecosystem.Plaice settlement period extended from mid-March to early June. Over the survey period, densities increased to maximum numbers of about 27 ind. 10 m⁻² in mid-April. In the following week, density rapidly decreased due to mortality and migration into deeper waters. The mortality was attributed mainly to predation by brown shrimp (C. crangon) and to a lesser extent by the shore crab (Carcinus maenas). The mean size of 0-group plaice increased from 19 mm in mid-April to 58 mm in July. Growth of juvenile 0-group plaice is described by an exponential equation: total length (TL, mm) = 12.602 e^{0.022 (post-settlement age)}. Post-settlement growth rates, estimated by otolith microstructure analysis, were 0.38 mm d⁻¹ for plaice ≤30 mm and 0.61 mm d⁻¹ for plaice >30 mm. Settlement of juvenile brown shrimp started in mid-April, peaked in early June (93 ind. 10 m⁻²) and continued with fluctuating intensity throughout the summer. Growth rate of juvenile C. crangon, estimated after the settlement peak, was 0.163 mm d⁻¹. Growth conditions of juvenile plaice and C. crangon were analysed by comparing estimated growth in the field with predicted maximum growth according to temperature-growth rate models from experimental studies of growth with unlimited food supply. For plaice, the estimated growth rate was lower (plaice ≤30 mm) but similar (plaice >30 mm) to the predicted maximum growth suggesting a food limitation only for newly settled individual. The observed increase in mean length of juvenile C. crangon was lower than the maximum possible growth. The function of the intertidal zone in the early juvenile stages of marine species is discussed.     

Dissolved and particulate organic carbon and nitrogen in the Northwestern Mediterranean

The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.     

Seasonal and spatial patterns of sedimentary denitrification rates in the Chukchi sea

Recent constructions of the global nitrogen budget estimate that at least half of the ocean's fixed nitrogen is lost by sedimentary denitrification, the majority of which occurs in continental shelves. The Arctic contains approximately 20% of the world's continental shelf, suggesting it is a substantial contributor to the global sedimentary denitrification rate. During two cruises in the summer and spring of 2002 and 2004, respectively, denitrification rates were calculated from the downward diffusive flux of nitrate in the shelf and slope sediments of the Chukchi Sea in the western Arctic. Additionally, in the spring of 2004, denitrification rates were determined by whole-core incubations in which the flux of nitrogen gas out of the sediments was measured. Measurements were made along three transects crossing the shelf and slope (50–3000 m), each transect having different overlying water characteristics. Denitrification rates generally decreased with increasing water depth: rates varied from about 1.6 mmol N m⁻² d⁻¹ for the shallow-water sediments to undetectable in deep-water sediments. Rates showed little variation between the two seasons. However, rates were found to correspond with differences in annual overlying primary productivities and particulate organic carbon export fluxes. An extrapolation to the whole Arctic yielded an average Arctic sedimentary denitrification rate of 13 Tg N yr⁻¹. Taken in the context of the global nitrogen budget, it is about 4–13% of the total sink of fixed nitrogen in the ocean.     

Nutrient and phytoplankton dynamics off the west coast of Vancouver Island during the 1997/98 ENSO event

Six research cruises were conducted off the west coast of Vancouver Island between April and October of 1997 and 1998 as part of the Canadian GLOBEC project to compare nutrient and phytoplankton dynamics between ENSO (1997) and non-ENSO (1998) years. Limited sampling also was conducted during three cruises in 1999. During the 1997 ENSO period, there was a shallow thermocline (∼10 m) that resulted in a shallower mixed layer, lower salinity and density, and stronger summer stratification. In general on the shelf, the 1997 growing season was characterized by higher nitrate (7.5 μM) and silicic acid (17 μM) concentrations, lower total chlorophyll (∼76 mg m⁻²), lower phytoplankton carbon biomass (0.2 mg C L⁻¹), and lower diatom abundance and biomass than in 1998. Phytoplankton assemblages were dominated by nanoplankton in 1997 and by diatoms in 1998. These results suggest that the 1997 ENSO was responsible for a reduction in the growth and biomass of larger phytoplankton cells. In mid-1998, the hydrographic characteristics off the west coast of Vancouver Island changed suddenly. The 1997 poleward transport of warm water reversed to an equatorward transport of coastal water in July 1998, which was accompanied by normal summer upwelling. During 1998, a large diatom bloom (mainly dominated by Chaetoceros debilis, Leptocylindrus danicus and to a lesser extent by Skeletomema and Pseudo-nitzschia sp.) was observed in July over the continental shelf. This large bloom resulted in chlorophyll concentrations of up to 400 mg m⁻², primary productivity of up to 11 g C m⁻² d⁻¹, and near undetectable dissolved nitrogen concentrations at some of the shelf stations in 1998. In contrast, during 1997, the sub-tropical waters that were advected over the slope, resulted in low chlorophyll a and primary productivity (generally <1 g C m⁻² d⁻¹). Therefore, there was a sharp contrast between the very high primary productivity on the shelf in July 1998, due to normal nutrient replenishment from summer upwelling and outflow from the Strait of Juan de Fuca, and the lower primary productivity during the 1997 ENSO year. During 1998, non-ENSO conditions resulted in phytoplankton biomass that was twice as high on the shelf as that measured in regions beyond the continental shelf of the west coast of Vancouver Island.     

Study on the total water pollutant load allocation in the Changjiang (Yangtze River) Estuary and adjacent seawater area

With the rapid economic development, the water quality is worsening and red tide takes place frequently in the Changjiang Estuary and adjacent seawaters. To improve the marine water quality, the total inland pollutant load should be controlled effectively. With efficiency and fairness in consideration, the total maximum allowable loads of COD_Mn, NH₃–N, inorganic nitrogen and active phosphate to the seawaters were calculated and allocated by the linear programming method based on the water quality response fields of the pollution sources. The maximum allowable loads are 2008 × 10³ tons, 169 × 10³ tons, 226 × 10³ tons and 18 × 10³ tons for COD_Mn, NH₃–N, inorganic nitrogen and active phosphate when the water quality targets are requested to be achieved in the whole studied region, and 346 × 10³ tons and 32 × 10³ tons for inorganic nitrogen and active phosphate when the water quality targets to be achieved only in the red tide sensitive area. The cut task of COD_Mn and NH₃–N is relatively easy and can be finished by the watershed environmental plan; while the cut task of inorganic nitrogen and active phosphate is tremendous. The coastal provinces should install more denitrification and dephosphorization facilities in the existing waste water treatment plants or build new ones to control the red tides in the concerned seawaters.     

Fish settlement in the ocean vs. estuary: Comparison of pelagic larval and settled juvenile composition and abundance from southern New Jersey,U.S.A.

To describe the larval and juvenile fish fauna and to evaluate the relative contribution of the ocean and the estuary as settlement areas for benthic species, we compared the composition and abundance of larval fish supply to that of recently settled juvenile fishes in both ocean and an adjacent estuary habitats in southern New Jersey. The study was conducted from May to November 1992 in the Great Bay–Little Egg Harbor estuary (<1–8 m sampling depth) and on the adjacent inner continental shelf in the vicinity of Beach Haven Ridge (8–16 m). During the study more larvae nearing settlement (postflexion) were captured in the estuary than in the ocean. Settlement occurred earlier in the estuary than in the ocean perhaps under the influence of earlier, seasonal warming of estuarine waters. There appeared to be two spatial patterns of settlement in the study area based on the dominant species (n = 17) represented by a sufficient number of individuals (n ≥ 25 individuals). There were species that primarily settle in the estuary, as represented by both estuarine residents (n = 3) and transients (n = 4), and those that settle in both the estuary and the ocean (n = 10). However, there were no species whose larvae were present in the estuary yet settle in the ocean. The fact that many of the species settle in both the estuary and the ocean indicates an overlap between these habitats because, at least for some species, these habitats may function in the same way. Further resolution of fish settlement patterns, and its influence on recruitment will need to rely on synoptic comparisons between estuaries and the ocean over multiple years.     

The copepod Tigriopus japonicus genomic DNA information (574 Mb) and molecular anatomy

The intertidal copepod, Tigriopus japonicus, has been recognized as a promising model species for marine environmental genomics. To obtain extensive genomic DNA sequences from this species, we sequenced genomic DNA from adult copepods using genomic sequencers GS-FLX and GS-FLX-Titanium and attained 1,914,995 reads (average read length 299.8 bp) including 574.2 Mb of genomic DNA information. After subjecting them to assembly, we acquired 193,642 contigs (total contigs length 129.7 Mb), and finally were able to obtain 10,894 unigenes (E-value > 0.1; length > 200 bp) containing 33,081,455 bp after a nonredundant (NR) blast search. In this paper, we summarize the genomic DNA sequences of T. japonicus and discuss its potential use in environmental genomics and ecotoxicological studies for uncovering mechanisms of environmental stresses and chemical toxicities to marine crustaceans.     

Biogeochemical cycling of N and Si during the mesoscale iron-enrichment experiment in the western subarctic Pacific (SEEDS-II)

Biogeochemical cycles of N and Si were examined in the surface mixed layer during the mesoscale iron-enrichment (IE) experiment in the high-nutrient low-chlorophyll (HNLC) western subarctic Pacific (SEEDS-II). Although the IEs increased nitrate uptake, silicic acid utilization was not stimulated. The nitrate drawdown in the iron-patch (IN-patch, 140.3 mmol m⁻² in the surface mixed layer, 0–30 m) was only 25% of the initial inventory, which was 1/3–2/5 of the previous IE experiments in the subarctic Pacific. This relatively weak response of nutrient drawdown to IEs was due to the high biomass of mesozooplankton (MZ) dominated by copepod Neocalanus plumchrus. Feeding of MZ (247.2 mmol m⁻² during Day 0–21 from the first IE) in the IN-patch was higher than the nitrate drawdown and prevented further development of the phytoplankton bloom. In the later period of the experiment (Day 14–21), the increase in the feeding activity and resultant decrease in phytoplankton biomass induced the accumulation of dissolved organic nitrogen (DON) and ammonium. Among total growth of MZ (81.6 mmol N m⁻²), 89% (72.8 mmol N m⁻²) was transported to the depth by the ontogenetic downward migration of N. plumchrus. Although silicic acid drawdown was not increased by the IEs, Si export flux increased by 2.7 times. The increase in Si export was also due to the increase in MZ, which egested faecal pellets with higher Si:N ratio and faster sinking speed than diatoms. The export efficiency (78% of new production) and total amount of export flux (143.8 mmol N m⁻², 1392 mmol C m⁻²) were highest records within the IE experiments despite weak responses of nutrient drawdown to the IE. During SEEDS-II, the high biomass of MZ reduced the phytoplankton response and nutrient drawdown to the IEs but via grazing and ontogenetic vertical migration accelerated the export flux as well as accumulations of dissolved forms of N. Results of the present and previous IE experiments indicate that the ecosystem and biogeochemical responses to IEs in the HNLC region are quite sensitive to the ecosystem components, especially for grazers of diatoms such as copepods and heterotrophic dinoflagellates. More attention needs to be paid to the ecosystem components and their biogeochemical functions as well as physical and chemical properties of the ecosystems in order to hindcast or forecast the impacts of changes in atmospheric iron deposition.