Sea Stations Research Articles

Effect of short-term hypoxia on marine nematode community structure and vertical distribution pattern in three different sediment types of the North Sea

The responses of nematode communities to short-term hypoxia (1 and 7 days) were investigated in three North Sea stations with different sediment types (coarse silt, fine sand and medium sand). In the field, nematode density, diversity, vertical distribution and community structure differ among the stations. In the laboratory, oxic and hypoxic treatments were established for 1 and 7 days for all sediment types. Comparison between field control and oxic day 1 treatments showed that experimental sediment handling did not affect nematode characteristics. Our results revealed that short-term hypoxia did not affect total density, diversity, community composition, vertical density profiles (except in the fine sand) and densities of five dominant species in all sediment types.

Decadal Variations in Oceanic Properties of the Arabian Sea Water Column since Geosecs

This article reports temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in the environment and climate that have occurred in response to natural or anthropogenic processes. The depth profiles of major parameters such as dissolved oxygen, ΣCO2, major nutrients (silicates, nitrates, and phosphates), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ∼0.2 to 0.3 salinity units in the top 400 m, whereas one station in the equatorial Indian Ocean showed a decrease in salinity by ∼0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The ΣCO2 increased by an average of 8 μM within the top 1200 m of the Arabian Sea. The depth profiles of nitrates and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicates and phosphates relative to the GEOSECS data. The decrease in Δ14C of surface waters is due to the steady decrease in atmospheric 14C concentration since GEOSECS, and the Δ14C increase in subsurface waters is attributed to the downward vertical diffusion of bomb 14C interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.

Dynamics of picoplankton community from coastal waters to the open sea in the Central Adriatic

Flow cytometry was used to describe seasonal cycles of Prochlorococcus (Prochl), Synechococcus (Syn), picoeukaryotes and heterotrophic bacteria in the central Adriatic Sea along the trophic gradient from January to December 2010. All picoplankton parameters decreased from eutrophic to oligotrophic areas, while the biomass ratio of bacterial to autotrophic picoplankton showed an increase along the trophic gradient. Bacterial biomass ranged from 5.28 to 21.20 μg C l-1. Increased values were present during warmer seasons with the domination of low nucleic acid (LNA) group of bacteria. The high nucleic acid (HNA) bacterial group dominated during the winter and the spring. Bacterial production ranged from 0.09 -0.45 × 104 cells ml-1 h-1 .At coastal stations increased production was present during the winter and the spring and was more or less uniform at open sea stations. Biomasses of Syn and Prochl ranged from 0.16 to 11.47 µg C-1 l-1 and from 0.01 to 3.08 µg C l-1, respectively. They were elevated during the summer and the autumn at coastal stations and during the late winter at the open sea. Syn biomass always dominated over Prochl participating with 61.6-97.2% in biomass of cyanobacteria. Biomass of picoeukaryotes ranged from 1.21 to 21.85 µg C l-1 and was the highest during the winter. Their biomass notably prevailed in autotrophic picoplankton (APP) biomass over that of picocyanobacteria during the whole year. Autotrophic components (Prochl, Syn and picoeukaryotes) made greater contribution to the picoplankton biomass in mesotrophic and eutrophic areas, while heterotrophic bacteria became more important under oligotrophic conditions.

Gelatinous macroplankton in the Black Sea in the autumn of 2010

In October and November of 2010, the gelatinous macroplankton in the northwestern Black Sea and at the Crimean shelf was represented by the scyphozoan jellyfish Aurelia aurita, three species of ctenophores (Beroe ovata, Mnemiopsis leidyi, and Pleurobrachia pileus), and three species of hydromedusae. A. aurita was more common at the shelf, M. leidyi and P. pileus prevailed at the deeper sea stations, and B. ovata was almost ubiquitous with a biomass from below 1 to 49 g/m2A. aurita, which had an average biomass of 82–224 g/m2, was dominant at all the stations. M. leidyi, which had a biomass from below 1 to 115 g/m2, was recorded in October at only 14 of the 52 stations and in November at 20 of the 46 stations. The highest biomass of M. leidyi in October (105 to 116 g/m2) was recorded in the deep sea areas; in November, it was also the highest in these areas, but it reached at most 100 g/m2. The average daily ration of Aurelia ranged from 19.4 to 27.3 mg/m2 in October and from 7.0 to 17.2 mg/m2 in November; in both cases, it was insufficient to provide for the minimal physiological requirements. The average daily ration of the Mnemiopsis population (2.8–20.5 mg of zooplankton per m2) was invariably more than sufficient to provide for the minimal physiological requirements. Both predatory species together consumed less than 5% of the daily zooplankton production of the sea.

Impact of the inflow of Vistula river waters on the pelagic zone in the Gulf of Gdańsk

The biomass, production, composition of autotrophic phytoplankton and heterotrophic bacteria were studied along with environmental and biological parameters. Samples were taken from Vistula river water (at Kiezmark) and from the river plume to the outer stations in the Gulf of Gdańsk (Baltic Sea) in June 2005. The phytoplankton biomass gradient appeared to be simply the result of dilution of the river water in the sea water, whereas the bacterial abundance and biomass dropped between the river station and the first sea water stations, a decrease that cannot be explained by the dilution effect. The Vistula water stimulated the production mainly of bacterioplankton but also of phytoplankton in the river plume as compared to rates measured in Vistula waters and at the open sea stations. However, this stimulation did not result in a measurable increase in biomasses, probably because of the short retention time of water in the river plume. Phytoplankton production was correlated with phytoplankton biomass (Chl a), while bacterial production was correlated with phytoplankton production and phytoplankton biomass (Chl a).

Caloric content of Chukchi Sea benthic invertebrates: Modeling spatial and environmental variation

The Chukchi Sea shelf off the northern coast of Alaska is rich with infauna and epibenthic macroinvertebrates used by foraging Pacific walrus (Odobenus rosmarus divergens) and other benthic-feeding consumers. Recent seasonal sea-ice retreat on the Chukchi Sea shelf has resulted in walrus hauling out in late summer on beaches of the Chukchi Sea in Russia and Alaska rather than on sea ice. Additional energetic costs may be imposed upon walruses traveling from these haul-outs to more productive foraging areas. Here, we provide an energetic assessment of prey items that could be relevant to the foraging energetics of walruses in haul-out locations. Caloric values for 171 potential walrus prey items (comprising 11 classes of benthic fauna) were obtained over 15 southeastern Chukchi Sea stations in 2010. There were statistically significant relationships between caloric content and increasing latitude (R=0.661) and bottom temperature (R=−0.560). Linear modeling indicated that taxon and latitude were the most important explanatory variables for caloric content in the study area, whereas a second model with taxon dependencies removed returned significant coefficients for the explanatory variables of latitude, depth, bottom water temperature, and sediment total organic carbon and nitrogen. K-means cluster analysis identified 6 clusters based mainly upon environmental variables such as bottom temperature, bottom salinity, and other water-column and sediment parameters that explained 86% of the variation in the data. The finding that caloric content varies strongly with latitude, which is a proxy for both water-mass type and associated water-mass productivity in the study area, may have implications for Pacific walrus, whose historical foraging patterns well offshore on sea ice have been disrupted by sea-ice decline.

Sedimentation of PCDD/Fs and PCBs in the Gulf of Finland and the Gulf of Bothnia, the Baltic Sea

Sediment trap material was collected during May–December in the period 1996–2008 in three coastal areas and four open sea stations in the Finnish territory of the Baltic Sea. The highest sedimentation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) with a typical source-related congener profile from chlorophenol production dominated by highly chlorinated dibenzofurans was found close to a historical source in the Kymijoki estuary. This was an order of magnitude higher than in other river estuaries and two orders of magnitude higher than in the open sea stations. The sedimentation of polychlorinated biphenyls (PCBs) was also higher in river estuaries than in other areas. No significant decrease over a 12year period of monitoring was found in concentration or in sedimentation in the Kymijoki estuary. In the western Gulf of Finland, the Archipelago Sea and the Gulf of Bothnia, the dominating congeners, calculated as toxic equivalent (TEQ) in sedimentation were 1, 2, 3, 7, 8-PeCDD and 2, 3, 4, 7, 8-PeCDF, often reported as the main congeners in deposition.

Composition and distribution of diatom assemblages in the surface sediments of the Bering Sea

Diatoms collected from the top 1 cm of the surface sediment layer at seven Bering Sea stations during the Fourth Chinese National Arctic Research Expedition (4th CHINARE-Arctic) in 2010 were studied. In total, 101 taxa belonging to 38 genera were found. The species were divided into four groups: eurythermal species, boreal-temperate species, polar species, and sea-ice species. The diatom assemblages at the stations in the southwestern basin area were primarily composed of boreal-temperate species, such as Neodenticula seminae , Thalassiosira trifulta , Rhizosolenia hebetata f. hiemalis , and Actinocyclus curvatulus . The northeastern shelf stations were dominated by polar species, including Fragilariopsis oceanica , Thalassiosira antarctica spora, Thalassiosira nordenskioeldii , and Thalassiosira hyalina . The overall abundance was highest at the basin stations with 3.7 ×106 cells·g-1 of wet sediment, whereas the eastern shelf stations had the lowest abundance of 0.7×106 cells·g-1 of wet sediment (excluding the resting spores of Chaetoceros spp.). The relationship between the distribution of the surface sediment diatom assemblages and the environment is discussed.

Carbon and nitrogen stable isotope signatures of deep-sea meiofauna follow oceanographical gradients across the Southern Ocean

Carbon (δ13C) and nitrogen (δ15N) stable isotope values of deep-sea benthic copepods, nematodes, and sediments were determined along a latitudinal transect covering bathyal and abyssal depths in the Southern Ocean and the Weddell Sea (49°S–70°S). This is the first time geographical patterns in stable isotope composition including δ15N are reported for deep-sea meiofauna. In agreement with previous findings on isotopic patterns of sea-surface organic matter, the deep-sea meiofauna δ13C values gradually declined with latitude. In the nematodes, δ15N values were depleting southwards and followed the known gradients of increasing nitrate concentrations with decreasing δ15N values available to primary producers in the surface waters. Differences in productivity, water depth, and degradation state of the organic matter at the seafloor along the transect did not influence the southwards declining trend observed in the stable isotope values of the deep-sea meiofauna. The most depleted 13C values were detected in the communities of Maud Rise. The southernmost Lazarev Sea station was an expected exception to this trend: its long-lasting sea-ice cover and a primary production dominated by 13C-enriched ice algae may have lead to the heavier isotopic signatures that were encountered in the organisms and sediments at 70°S. It is suggested that the bulk of benthic meiofauna mainly feeds on degraded organic matter, a food source that is continuously available throughout the year, because only small differences of sediment δ13C and the values for meiofauna were detected. The isotopic composition of consumers such as copepods and nematodes are a combination of geographical conditions and the organisms’ position in the food web. Hence, the comparison of stable isotope values of deep-sea meiofauna over a wide geographical range yields basic information for detailed follow-up studies on Antarctic meiofauna foodwebs.

Spring diel vertical distribution of copepod abundances and diversity in the open Central Tyrrhenian Sea (Western Mediterranean)

Spring vertical distribution of copepod communities was studied every 6h during a 24hcycle, using the BIONESS multinet, to evaluate diel vertical migration (DVM) of the key species in a Central Tyrrhenian Sea station (from 0 to 2000m). Similar abundance trends were detected for the four sampling times. Highest abundances were recorded between 20–40 and 60–80m depth, at midnight and in the morning. In epipelagic layers, highest diversity occurred between 20 and 100m in the morning and at midday, and from 100–200m in the afternoon and 300–400m at midnight, in mesopelagic ones. DVM involved mostly the 60 and 300m depth interval. Epipelagic and mesopelagic copepods co-occurred in this stratum, so diel changes in species composition and diversity induced shifts in the slope of the highest k-dominance curves. The epipelagic Neocalanus gracilis and the intermediate Eucalanus elongatus copepod species showed a bimodal distribution. Only the shallower population of E. elongatus exhibited significant DVM. Few other copepod species showed significant DVM (the epipelagic Scolecithricella dentata and the subsurface Corycaeus furcifer and Pleuromamma gracilis), confirming previous information about the presence of few strong migrants in the Mediterranean Sea. Lucicutia longiserrata, Gaetanus kruppi and Monacilla typica with their copepodites were the only species dominant below 600m depth and they were not affected by DVM.

Habitat partitioning by fish larvae among coastal, offshore and frontal zones in the southern North Sea

This study compared marine and estuarine larval fish assemblages among near- shore, offshore and frontal habitats of the southern North Sea. In late June and early July 2005, parallel cruises collected larvae along offshore transects crossing tidal mixing and river plume frontal zones in the German Bight, and at shallow nearshore stations within the Wadden Sea and associated estuaries of major tributaries. A mixture of larvae from 17 species occurred including the (then) newly re-established 'southern' clupeids (European sardine Sardina pilchardus and anchovy Engraulis encrasicolus) as well as traditional North Sea species such as horse mackerel Trachurus trachurus, solenette Buglossidium luteum and various species of gobies. Multivariate statistics on taxonomic composition indicated that shallow and deep areas were 2 distinct habitats. Wadden Sea stations had a conspicuously different species composition and low species richness compared to all deeper areas. In deeper waters, species composition was similar regardless of frontal strength, and larger larvae occurred most frequently in the cooler areas of the German Bight. Altered species composition observed at some nearshore stations indicated that frontal dynamics and tidal advection may lead to expatriation of larval fish to presumably less favorable areas. Frontal habitats in the German Bight may not necessarily promote higher survival of larval fish than other areas but appear to form important boundaries between species-rich, deeper waters of the German Bight and relatively species-poor, shallower waters of the Wadden Sea.

Isotope constraints on particulate nitrogen source and dynamics in the upper water column of the oligotrophic South China Sea

Particulate nitrogen (PN) dynamics in the oligotrophic northern South China Sea (around the SouthEast Asian Time‐series Study (SEATS) station) was explored by examining the isotopic compositions of suspended PN in the top 200 m over 3 years and sinking PN collected by sediment traps. The PN inventory (IPN) in the upper 100 m is larger than in the lower 100 m, exhibiting stronger seasonality. Both layers reveal significant seasonality in meanδ15NPN, yet, the mean in the upper 100 m (2.0 to 5.3‰) is consistently smaller than that in the lower 100 m, implying the occurrence of vertical biological fractionation and/or an addition of 15N‐depleted N from the atmosphere. Theδ15NPN surges in winter, when the mixed layer is deeper, indicate an intensified nitrate supply from thermocline, during which relatively stronger downward transfer efficiency was inferred by a small IPN gradient. The largest vertical gradient in IPN appeared during intermonsoon periods, corresponding with weak vertical mixing, low δ15NPN, and high N* values. N fixation is likely the cause for the intermonsoon δ15NPN lows. The δ15NPNvalues of trapped material at 374 m and 447 m range from 3.3 to 7.3‰ with a flux‐weighted mean of 5.6‰ resembling theδ15NO3of upwelled sources. By using a mass‐isotope balance model under the assumption of no atmospheric N deposition, we obtained an N fixation input of ∼20 ± 26 mmol N m−2 yr−1. This value accounts for only ∼5–10% of the new production on an annual basis.

Museum archives of the 19 years long time-series sediment trap samples collected at central subarctic Pacific Station SA and Bering Sea Station AB during 1990-2010

PARLUX type sediment traps were moored at 600 m above the sea-floor at Station SA (water depth: 5,406m) in the central subarctic Pacific and at Station AB (water depth: 3,788m) in the Aleutian Basin of the Bering Sea. The time-series flux samples were obtained during 1990-2010 for nineteen years. This allowed us to characterize primary fluxes of biogenic particles primarily produced near the surface layers of the deep water columns as well as to decipher the environmental variations associated with climate changes. Based on the samples various studies were conducted thus far, including the followings types: quantitative plankton taxon-numerical studies on diatoms, silicoflagellates, radiolarians, coccolithophores and planktic foraminfers; and geochemical aspects of chemical compounds such as biogenic opal, calcium carbonate and hexosamine as well as elements such as rare earth elements. Such studies published thus far are cited in this paper. The sediment trap samples are archived at the Kyushu University Museum for permanent preservation. The grand total of the currently archived samples, including membrane filters and microslides for the two stations, is 3,552. The details of the samples are described herein and spreadsheet tables of the archives will also be electronically published by the Museum. This makes it possible for future scientists and students, who need to examine the relevant sediment trap samples, to access them properly.

Fifteen year time-series of radiolarian fluxes and environmental conditions in the Bering Sea and the central subarctic Pacific, 1990–2005

In order to examine radiolarian fluxes and evaluate their relationships to environmental conditions, a fifteen year long time-series observation on radiolarian fluxes was conducted using sediment trap materials collected at the Bering Sea Station AB (53.5°N, 177°W) and the central subarctic Pacific Station SA (49°N, 174°W) during 1990–2005. Encountered radiolarian assemblages include 124 taxa at Station AB and 110 taxa at Station SA. In general, total radiolarian fluxes of the coarse fraction (63μm−1mm) at Station AB (mean: 8.7×103shellsm−2d−1) were greater than those observed at Station SA (mean: 6.5×103shellsm−2d−1), mainly due to the differences in physico-chemical conditions (i.e., mixed layer depth, surface circulation, nutrient concentrations, etc.). Out of >110 taxa, thirty-eight abundant radiolarian taxa were chosen for enumeration and further statistical treatment, including the taxa with >1% annual mean occurrence. As abundant radiolarian species display variable flux patterns during the study period, an R-mode cluster analysis was used to identify eight clusters at Station AB, and eleven clusters at Station SA. Marked changes in the relative contribution of each of the clusters to the total radiolarian assemblages are apparent. Notably high flux maxima of total radiolarians were observed around 1990, 1995, 2000, 2003 and 2004. The observed inter-annual variations in the faunal assemblages in the Bering Sea and the central subarctic Pacific were related to large scale climatic shift such as the Arctic Oscillation (AO). The negative correlation between the radiolarian assemblages including surface to subsurface dwellers and the AO Index may suggest a significant influence by the intensity of surface water mixing and water mass exchanges.

Comparison of Larval Fish Density Between Seagrass Beds and Outside Seagrass Beds of the Southwestern Johor, Peninsular Malaysia

Temporal variation of fish larval density and composition between seagrass and outside seagrass beds of the southwestern Johor, Malaysia were investigated between October 2007 and September 2008. Fish larvae were sampled monthly by using a bongo net with 500 μm mesh size and 30 min sub-surface tow. In situ environmental variables were also recorded during the sampling works. The fish larval assemblage comprised of 20 families from the seagrass beds and 16 families recorded from the outside seagrass beds station. In total, 3738 larvae (2,801 from seagrass and 937 from non-seagrass area) were collected. Total larva density was at 79 individuals per 100 m3 and 34 individuals per 100 m3 for seagrass beds and outside seagrass station respectively. Larval abundance varied significantly within monsoon and inter-monsoon seasons, with peaks in February-March and May-July. Top five families were Blenniidae, Clupeidae, Gobiidae, Sillaginidae and Terapontidae and they occurred consistently throughout the year. Larvae belonging to family Clupeidae (47.94% in seagrass and 42.03% in outside seagrass) and Terapontidae (17% in seagrass and 24% in outside seagrass) were the most abundant family in the study areas. The highest density of total larval fishes was recorded at the seagrass ecosystem. The spatial variations in larval density were not significantly (p>0.05) different between the seagrass beds and open sea station.

Relationships between suspended mineral concentrations and red-waveband reflectances in moderately turbid shelf seas

This paper considers the uncertainties that arise in estimating the concentration of suspended minerals by optical remote sensing in waters which contain unknown concentrations of other optically significant constituents. Relationships between suspended mineral concentrations and remote sensing reflectance were calculated by radiative transfer modelling using representative specific inherent optical properties ( SIOPs) for phytoplankton ( CHL), suspended mineral particles of terrigenous origin ( MSS ter ) and coloured dissolved organic matter ( CDOM) that were derived from measurements at 173 stations in UK shelf seas. When only suspended minerals were present, remote sensing reflectance ( R rs ) was related to MSS ter by a family of saturation curves whose shape depended strongly on wavelength. However the addition of CHL and CDOM made this relationship considerably more complex. Polynomial expressions were therefore derived for the maximum and minimum values of MMS ter consistent with a given R rs 667 in the presence of independently varying concentrations of CHL and CDOM. For CHL ranging from 0 to 10 mg m −3 and CDOM from 0 to 1 m −1, for example, an R rs 667 observation 0.01 sr −1 could corresponded to MSS ter values between 7 and 12 g m −3. The presence of biogenic minerals in the form of diatom frustules, MSS dia had little influence on the accuracy of MSS ter retrieval. The degree of variability in the relationship between MSS ter and Rrs667 predicted by the model was confirmed by measurements of radiometric profiles and mineral concentrations at 110 Irish Sea stations. Uncertainties in the remote sensing of MSS ter in coastal waters are more appropriately indicated by upper and lower limits set according to the likely ranges of other optically significant constituents than by percentage errors. Moreover, the influence of these constituents should be eliminated before variations in the relationship between MSS ter and Rrs are attributed to qualitative changes in mineral particle characteristics.

Combined model state and parameter estimation with an ensemble Kalman filter in a North Sea station 1-D numerical model

The combined estimation of model state and parameters is investigated by using an ensemble Kalman filter in a 1-D numerical study of the temperature profile at a North Sea station located at 55°30’ North and 0°55’ East. This simplified model implementation allows to test many configurations for the sampling of the model error for the model state as well as for the parameters. Temperature profiles from thermistor data are assimilated. The influence of a vertically or non-vertically correlated model error is examined through the computation of correlation coefficients, root mean square errors, and model bias. As the CS station is located in the North Sea region stratified in summer, vertically non-correlated model error terms have a slight positive impact on the assimilative runs. The benefit of the combined estimation of the model state and parameters is examined by comparison of a simulation where the model parameters are not adjusted to simulations with the combined estimation of the model state either with one parameter or with a set of parameters related to the surface heat exchange. The optical attenuation coefficient, the sensible, and latent heat exchange coefficients are considered. The best results are obtained when a set of parameters are simultaneously adjusted.

Assimilating Along-Track Altimetric Observations through Local Hydrostatic Adjustment in a Global Ocean Variational Assimilation System

Abstract A global ocean three-dimensional variational data assimilation system was developed with the aim of assimilating along-track sea level anomaly observations, along with in situ observations from bathythermographs and conventional sea stations. All the available altimetric data within the period October 1992–January 2006 were used in this study. The sea level corrections were covariated with vertical profiles of temperature and salinity according to the bivariate definition of the background-error vertical covariances. Sea level anomaly observational error variance was carefully defined as a sum of instrumental, representativeness, observation operator, and mean dynamic topography error variances. The mean dynamic topography was computed from the model long-term mean sea surface height and adjusted through an optimal interpolation scheme to account for observation minus first-guess biases. Results show that the assimilation of sea level anomaly observations improves the model sea surface height skill scores as well as the subsurface temperature and salinity fields. Furthermore, the estimate of the tropical and subtropical surface circulation is clearly improved after assimilating altimetric data. Nonnegligible impacts of the mean dynamic topography used have also been found: compared to a gravimeter-based mean dynamic topography the use of the mean dynamic topography discussed in this paper improves both the consistency with sea level anomaly observations and the verification skill scores of temperature and salinity in the tropical regions. Furthermore, the use of a mean dynamic topography computed from the model long-term sea surface height mean without observation adjustments results in worsened verification skill scores and highlights the benefits of the current approach for deriving the mean dynamic topography.

ESTIMATING ACCURACY OF WIND DATA OVER THE SETO INLAND SEA BASED ON SDP OVERLAND WIND DATA AND MESOSCALE METEOROLOGICAL MODEL MM5

Accuracy of two kinds of wind data during 15 typhoons calculated at 9 sea stations of the Seto Inland Sea is estimated by comparing with wind data measured at those stations. One set of data is extracted from a 45-year wind data set for the concerned area which was made by Yamaguchi et al.(2009) using SDP overland wind data acquired by the Japan Meteorological Agency. The other is the wind data set made by Lee et al.(2009) applying a mesoscale meteorological model MM5. The degree of agreement between the time series of calculated and measured winds during a typhoon is evaluated by 7 error indices. Almost all mean values and standard deviations of the error indices suggest that the SDP data-based wind data shows a higher degree of accuracy than the MM5-based wind data.

Seasonal to interannual variability and geographic distribution of the silicoflagellate fluxes in the Western Mediterranean

A total of 337 samples collected from five sediment traps located in the Gulf of Lions, Catalan margin and the Alboran Sea have been analyzed in order to study the seasonal, interannual and geographical distributions of silicoflagellate fluxes in the Western Mediterranean. As a general trend, maximum fluxes of silicoflagellate skeletons always occurred during the spring bloom; i.e. during the winter–spring transition, while minimum fluxes were recorded during summer, characterised by a strong stratification and oligotrophic conditions. However, the sediment trap record of the Catalan margin did not exhibit any clear seasonal signal, probably owing to the fertilizing effect of the rivers Llobregat and Besos. Regarding interannual variability, no clear relationship between the NAO (North Atlantic Oscillation) and the silicoflagellate fluxes was found. In contrast, the silicoflagellate assemblages from the Alboran Sea and the Gulf of Lions responded with low fluxes and a delay in their annual maximum to the anomalous conditions elicited by the 1997–98 El Niño Event. Furthermore, the 2003 summer heat wave over the Western Mediterranean had similar repercussions on the silicoflagellate spring maximum 2004 in the Gulf of Lions. Three silicoflagellate species were identified in the samples, following the taxonomic concepts of Throndsen (1997): Dictyocha fibula (Ehrenberg), Dictyocha speculum (Ehrenberg) and Octactis octonaria (Ehrenberg) Hovasse 1946. D. fibula was cosmopolitan and the dominant species at all sites, always accounting for more than 80%. Moreover, its maximum fluxes were recorded in those sampling sites which were under the influence of high nutrient concentrations caused by the river input. D. speculum was only recorded in the northern locations, which suggests an affinity for colder water masses. In contrast, O. octonaria was restricted to the Alboran Sea stations, where temperatures reached the highest values and nutrients were scarcer.