Gas hydrate saturation from acoustic impedance and resistivity logs in the Shenhu area, South China Sea

During the China’s first gas hydrate drilling expedition -1 (GMGS-1), gas hydrate was discovered in layers ranging from 10 to 25 m above the base of gas hydrate stability zone in the Shenhu area, South China Sea. Water chemistry, electrical resistivity logs, and acoustic impedance were used to estimate gas hydrate saturations. Gas hydrate saturations estimated from the chloride concentrations range from 0 to 43% of the pore space. The higher gas hydrate saturations were present in the depth from 152 to 177 m at site SH7 and from 190 to 225 m at site SH2, respectively. Gas hydrate saturations estimated from the resistivity using Archie equation have similar trends to those from chloride concentrations. To examine the variability of gas hydrate saturations away from the wells, acoustic impedances calculated from the 3 D seismic data using constrained sparse inversion method were used. Well logs acquired at site SH7 were incorporated into the inversion by establishing a relation between the water-filled porosity, calculated using gas hydrate saturations estimated from the resistivity logs, and the acoustic impedance, calculated from density and velocity logs. Gas hydrate saturations estimated from acoustic impedance of seismic data are ∼10-23% of the pore space and are comparable to those estimated from the well logs. The uncertainties in estimated gas hydrate saturations from seismic acoustic impedances were mainly from uncertainties associated with inverted acoustic impedance, the empirical relation between the water-filled porosities and acoustic impedances, and assumed background resistivity.     

Spatial and temporal variation in surfclam (Spisula solidissima) larval supply and settlement on the New Jersey inner shelf during summer upwelling and downwelling

To examine the relationship between near-bottom larval surfclam concentrations and surfclam settlement at an inner continental shelf site off New Jersey (USA), four consecutive sets of settlement experiments were carried out at three stations at the Long-term Ecosystem Observatory (LEO-15) from 14 to 31 July 1997 during upwelling and downwelling. Two inshore stations were on the landward and seaward sides of Beach Haven Ridge at ∼12 m depth, and a third station was 8 km further offshore at ∼20 m depth. In each experiment, four replicate trays of azoic sand from Beach Haven Ridge were placed flush with the seafloor and exposed for 3–7 days. Larval surfclam concentrations were measured every 4 h at 1 m above the bottom (mab) using Moored, Automated, Serial Zooplankton Pumps at the three stations. At all three stations, larval surfclam concentrations (1 mab) were low during upwelling, and higher during and after downwelling. Pulses of highest larval surfclam concentrations coincided with the initial arrival of downwelled warm water. In addition, larval surfclam concentrations were higher at the two inshore stations than at the offshore station. Larval surfclam settlement in the trays was higher during and following downwelling than during upwelling at one inshore station and at the offshore station. At the other inshore station (landward of Beach Haven Ridge), surfclam settlement did not increase during and following downwelling. Overall, surfclam settlement was higher inshore than offshore. The results indicate that spatial and temporal variation in larval surfclam supply was controlled by upwelling and downwelling circulation and that surfclam settlement was influenced by larval supply. Bottom flows across Beach Haven Ridge during a storm may have reduced larval surfclam settlement on the upcurrent side of the ridge, affecting initial densities on a small (∼1 km) scale.     

Georges bank monitoring program: hydrocarbons in bottom sediments and hydrocarbons and trace metals in tissues

Hydrocarbons in sediments and hydrocarbons and trace metals in tissues from Georges Bank were analyzed to evaluate potential changes to the henthic environment resulting from exploratory drilling operations. Sediment hydrocarbon concentrations varied with grain size: concentrations up to 2·5μg/g dry weight total aromatic equivalents occurred in the fine-grained sediments of Lydonia Canyon and the ‘Mud Patch’ area south of Martha's Vineyard, whereas concentrations were less than I μg/g dry weight in sediments from the shallow areas of Georges Bank, at a regional control site, and at the site of drilling operations. Increases in total aromatic equivalents from approximately 0·1 μg/g dry weight to 0·4 μg/g dry weight were measured in sediments from a site 0.25 km from the drill rig concurrent with drilling operations. Petrogenic hydrocarbons were detected in both drilling fluid extracts and in sediments collected during drilling operations, suggesting short-term deposition of drilling discharges in near-rig sediments. Drilling discharge residues were not observed in the near-rig sediments one month after drilling operations were terminated. Furthermore, hydrocarbon residues from drilling discharges werenot observed in sediments from stations located at distances greater than 6 km from the drill site either during or subsequent to the drilling operations.     

Multi-frequency seismic study of gas hydrate-bearing sediments in Lake Baikal,Siberia

In this paper we present and discuss the frequency-dependent behaviour of the acoustic characteristics of methane hydrate-bearing sediments in Lake Baikal, Siberia. Five different types of seismic sources (airgun-array, two types of single airguns, watergun and sparker) are used, encompassing a frequency bandwidth from 10 up to 1000 Hz. On low-frequency airgun-array data, the base of the hydrate stability zone (HSZ) is observed as a high-amplitude bottom-simulating reflection (BSR) with reversed polarity. The amplitude and continuity of the BSR decrease or even disappear on medium- to high-frequency data, a feature explained in terms of vertical and horizontal resolution. The increasing reflection amplitude of the BSR with increasing offset, the calculated reflection coefficient of the BSR and the occurrence of enhanced reflections below the BSR suggest the presence of free gas below the HSZ. The observation of some enhanced reflections extending above the BSR may be interpreted as an indication for free gas co-existing with hydrates within the HSZ. Amplitude blanking above the BSR is highly variable while the BSR itself appears to act as a low-pass frequency filter for medium- to high-frequency data.New single-channel airgun profiles provide the first seismic information across the Baikal Drilling Project (BDP-97) deep drilling site, at which hydrate-bearing sediments were retrieved at about 200 m above the base of the local HSZ. At the drilling site there are no seismic characteristics indicative of the presence of hydrates. Combination of the drilling and seismic information has allowed us to make a rough estimation of the volume of hydrates and carbon stored in the sediments of Lake Baikal, which lead us to conclude that the Lake Baikal gas hydrate reservoirs do not form a prospective energy resource.     

Mussels document loss of bioavailable polycyclic aromatic hydrocarbons and the return to baseline conditions for oiled shorelines in Prince William Sound, Alaska

Polycyclic aromatic hydrocarbons (PAH) were measured in mussels (Mytilus trossulus) collected between 1990 and 2002 from 11 sites on the shores of Prince William Sound (PWS), Alaska, that were heavily oiled by the 1989 Exxon Valdez oil spill (EVOS). This study, utilizing the methods of the NOAA Status and Trends Mussel Watch Program, found that concentrations of PAH released from spill remnants have decreased dramatically with time and by 2002 were at or near the range of total PAH (TPAH) of 3-355 ng/g dry weight obtained for mussels from unoiled reference sites in PWS. Time-series TPAH data indicate a mean TPAH half-life in mussel tissues of 2.4 years with a range from 1.4 to 5.3, yielding an annual mean loss of bioaccumulated TPAH of 25%. The petroleum-derived TPAH fraction in mussel tissues has decreased with time, reflecting the decreasing release of EVOS residues in shoreline sediments. These results show that PAH from EVOS residues that remain buried in shoreline sediments after the early 1990s are in a form and at locations that have a low accessibility to mussels living in the intertidal zone.     

Impact of exploratory offshore drilling on benthic communities in the Minerva gas field, Port Campbell, Australia

Changes to benthic infauna caused by exploratory gas drilling operations in the Minerva field were examined experimentally using a BACI (before, after, control, impact) design. Analysis of 72 x 0.1 m2 Smith-McIntyre grab samples obtained from one pre-drilling and three post-drilling periods yielded a diverse fauna consisting of 196 invertebrate species and 5035 individuals. Changes to benthic community structure were assessed using ANOVA and nonmetric multidimensional scaling (MDS). The abundances of two common species (Apseudes sp. 1 and Prionospio coorilla) decreased significantly at the well-head site immediately after drilling. The size of these reductions in abundance ranged between 71% and 88%, and persisted for less than 4 months after drilling. A third common species (Katlysia sp. 1) increased in abundance 200 m east of the well-head following drilling. Most species occurred at densities too low to be analysed individually and so were pooled at higher taxonomic levels. Changes in the abundance of species aggregated by phylum varied, but significant declines in the most abundant phyla (Crustaceans and Polychaetes) of 45-73% were observed at all sites within a 100 m radius of the well-head following drilling. In most cases these changes became undetectable four months after drilling following species recruitments. MDS ordinations confirm that drilling related changes to benthic community structure are most pronounced at stations located closest to the well-head. Additionally, the ordinations indicate that modified communities persist at the well-head for more than 11 months following exploratory drilling.     

Recolonization patterns of benthic assemblages after relict sand dredging in the central Tyrrhenian sea

Recolonization patterns of benthic assemblages after relict sand dredging were investigated in an area offshore of Capo d’Anzio (central Tyrrhenian Sea). Surveys were performed before, during, and after dredging in 2007. Sampling stations were located within and outside the dredging site in water depths between 40 and 56 m. Defaunation due to sand extraction was the main impact observed in the inner stations and in stations located in proximity of the dredging site. At the inner stations, 9 months after dredging, a significant increase in species richness and diversity was observed: the sediment removal led to an increase of the sandy sediment fraction, favouring the settlement of sabulicolous species. A decrease in number of individuals and species was also observed in most of the outer stations, probably due to fine sediment redeposition. Recolonization of macrobenthic assemblages was essentially achieved at inner stations both in terms of abundance and species richness, while at outer stations it was still in progress. Results of this study, providing a picture of recovery times and processes in the Tyrrhenian Sea, could be used to develop predictions of the effects of future offshore sand dredging projects in comparable areas. Monitoring programs and research have a key role to provide a more detailed overview of biological recovery processes and times in different regions and with different dredging intensity.     

Diatom biomass and productivity in oceanic and plume-influenced waters of the western tropical Atlantic ocean

Whereas diatoms (class Bacillariophyceae) often dominate phytoplankton taxa in the Amazon estuary and shelf, their contribution to phytoplankton dynamics and impacts on regional biogeochemistry are poorly understood further offshore in the western tropical Atlantic Ocean (WTAO). Thus, relative contribution of diatoms to phytoplankton biomass and primary production rates and associated environmental conditions were quantified during three month-long cruises in January–February 2001, July–August 2001, and April–May 2003. The upper water column was sampled at 6 light depths (100%, 50%, 25%, 10%, 1% and 0.1% of surface irradiance) at 64 stations between 3° and 14°N latitude and 41° and 58°W longitude. Each station was categorized as ‘oceanic’ or ‘plumewater’, based on principal component analysis of eight physical, chemical and biological variables. All stations were within the North Brazil Current, and plumewater stations were characterized by shallower mixed layers with lower surface salinities and higher dissolved silicon (dSi) concentrations than oceanic stations. The major finding was a much greater role of diatoms in phytoplankton biomass and productivity at plumewater stations relative to oceanic stations. Mean depth-integrated bSi concentrations at the plumewater and oceanic stations were 14.2 and 3.7 mmol m⁻², respectively. Mean depth-integrated SiP rates at the plumewater and oceanic stations were 0.17 and 0.02 mmol m⁻² h⁻¹, respectively. Based on ratios of SiP and PP rates, and typical Si:C ratios, diatoms contributed on average 29% of primary productivity at plumewater stations and only 3% of primary productivity at oceanic stations. In contrast, phytoplankton biomass (as chlorophyll a concentrations) and primary production (PP) rates (as ¹⁴C uptake rates) integrated over the euphotic zone were not significantly different at plumewater and oceanic stations. Chlorophyll a concentrations ranged from 8.5 to 42.4 mg m⁻² and 4.0 to 38.0 mg m⁻² and PP rates ranged from 2.2 to 11.2 mmol m⁻² h⁻² and 1.8 to 10.8 mmol m⁻² h⁻² at plumewater and oceanic stations, respectively. A conservative estimate of annual integrated SiP in offshore waters of Amazon plume between April and August is 0.59 Tmol Si, based on mean SiP rates in plumewaters and satellite-derived estimates of the area of the Amazon plume. In conclusion, river plumewaters dramatically alter the silicon dynamics of the WTAO, forming extensive diatom-dominated phytoplankton blooms that may contribute significantly to the global Si budget as well as contributing to energy and matter flow off of the continental shelf.     

Trace element concentrations in Coastal Hawaiian waters

The objective of this work is to characterize the concentrations of selected trace elements (V, Mn, Ni, Fe, Co, Cu, Zn, Se, As, Mo, Cd, Pb, U) in diverse nearshore (50 m), coastal (1.5 km) and seawater well environments within the Hawaiian Archipelago using robust analytical methods that are appropriate for metals analyses in seawater. The sampling sites include locations having varying type, quality and quantity of freshwater input. In most coastal and nearshore cases, the trace element concentrations approximate values characteristic of offshore waters. Concentrations of trace elements in coastal waters that were enriched through either urban or agricultural inputs declined sharply within a short distance from shore; this is taken to indicate the predominant importance of physical mixing/advective processes along with particle scavenging in these dynamic areas. Trace element levels in seawater wells did not evidence any concentration trends consistent with island age suggesting little or no impact of island weathering on metal concentrations; concentration differences among wells appeared to be more dependent on well depth, redox conditions, and/or salinity. Sampling also targeted nearshore locales where ciguatera fish poisoning is prominent because of suggested linkages between trace element concentrations and aberrant dinoflagellate growth. Nearshore stations where ciguatera is prevalent failed to show clearly different trace element levels except for two prominent locales which showed elevated Mn and Fe concentrations.     

Spatial organization of a sedimentary macrobenthic community located on the West African Equatorial margin

Multiscale variability of a macrobenthic community inhabiting fine sediments on the West African Equatorial margin was assessed during three cruises as part of the BIOZAIRE research program. Spatial scales ranged from 15 to 550 m (within station) and from 1000 to 7000 m (between stations). Principal Coordinates of Neighbour Matrices (PCNM) allowed the detection of multiscale patterns of variability within a location, while a binary coding of the sampling stations was used at broad spatial scales. Significant patterns were observed at 170 and >4000 m. The two spatial scales displayed similar biotic responses, with the Scaphopoda and Bivalvia having patterns that were opposite to the Pholoidae. A spatio-temporal patchwork of environmental variables might explain the observed patterns. Practically, these results emphasis the need to develop balanced and crossed designs among the sources of variation (geography, time, depths).     

Physical control of sediment carbon content in an estuarine tidal flat system (Nanakita River, Japan): A mechanistic case study

Temporal variations in sediment carbon content were tracked by sampling every 2 weeks for 6 to 33 months at 6 tidal flat stations with different carbon content levels (0.05–1.64%) in a single estuary. Three temporal series of current velocity at 5 cm above the sediment were also obtained. Non-cohesive and cohesive sediment stations differed in patterns of temporal variation in sediment carbon content, suggesting the difference in processes controlling sediment carbon content. In the stations of non-cohesive sandy sediment with relatively low carbon content (0.05–0.15%), sediment carbon content fluctuated within ranges specific to each station. In these stations, current velocity data suggested that frequency of sand resuspension washing out sediment carbon controls sediment carbon content level. In the stations of cohesive sediment with relatively high carbon content (0.77–1.64%), sediment carbon contents showed some unusual upward and downward peaks, recovered to usual levels specific to the stations, and was always kept higher than that in the non-cohesive sediment stations. We speculate that in the cohesive sediment stations, sand inputs may significantly control processes establishing the consolidated sediments with various carbon content levels. Spatial transitions from non-cohesive to cohesive sediments and from low to high sediment carbon contents likely occur as sand resuspension at spring tides become more irregular and less frequent. Based on these results, conceptual models describing physical processes controlling sediment carbon content at the studied stations were proposed.     

Phytoplankton driven distribution of dissolved and particulate lipids in a semi-enclosed temperate sea (Mediterranean): Spring to summer situation

The relationship between changes in lipid classes and phytoplankton composition and abundance in the northern Adriatic was studied during spring and summer 2008 at two stations with different nutrient levels, i.e. at the western mesotrophic and eastern oligotrophic areas. Changes in the phytoplankton community depended on temporal surface nutrient depletion and bottom accumulation; that is, microphytoplankton, mainly diatoms Pseudo-nitzschia sp., developed at nutrient richer surface layers of the mesotrophic area in spring and at deeper layers of the oligotrophic site in late summer. In other periods nanophytoplankton dominated. Dissolved organic carbon (DOC) and lipid content were comparable for the two stations, while particulate organic carbon (POC) was richer at the mesotrophic side. Total lipid concentrations varied in the range from 8.0 to 92.2 μg l⁻¹ and from 16.9 to 76.9 μg l⁻¹ in the dissolved and particulate fractions, respectively. DOC and POC contents were in the ranges from 0.77 to 1.58 mg l⁻¹ and from 0.06 to 0.56 mg l⁻¹, respectively. Lipid and organic carbon distribution did not follow phytoplankton progression, indicating decoupling between organic matter production and decomposition throughout the investigation period. The main sources of lipids were marine phytoplankton and bacteria. Low nutrient conditions caused increased biosynthesis of lipids. Also, increasing oligotrophy led to an increasing number of phytoplankton taxa. The synthesis and accumulation of glycolipids by the developed taxa were enhanced during nutrient exhaustion, contributing in late summer, on average, 20.2 and 22.0% at the mesotrophic and oligotrophic stations, respectively, in the particulate fraction. The distribution of bacterial lipids and lipid breakdown products implies that bacterial lipid degradation was significant in spring, while very probably lipid abiotic degradation took place during summer.     

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India (Arabian Sea) observed in May 2005 is reported. Around 4802 filaments of T. erythraeum ml⁻¹ seawater was observed and a colony consisted of 3.6 × 10⁵ cells. The bloom was predominant off Suratkal (12° 59′N and 74° 31′E) with a depth of about 47 m, covering an area of 7 km in length and 2 km width. The concentrations of Zinc, Cadmium, Lead, Copper, Nickel and Cobalt were determined in samples collected from the bloom and non-bloom sites using stripping voltammetry. The observed hydrographical and meteorological parameters were found to be favorable for the bloom. The concentrations of Zinc, Cadmium and Nickel were found to be higher at bloom stations, while the concentrations of Lead, Copper and Cobalt were found to be very low at bloom stations. Elevated concentrations of Cadmium and Cobalt were observed at Valappad mainly due to the decomposition of detrital material produced in the bloom. Statistically significant differences (P > 0.01) in metal concentrations between the bloom and non-bloom stations were not observed except for Copper. Metals such as Lead, Copper and Cobalt were removed from the seawater at all places where bloom was observed. Cadmium was found to be slowly released during the decaying process of the bloom.     

Meiofaunal distributions on the Peru margin:: relationship to oxygen and organic matter availability

A quantitative study of metazoan meiofauna was carried out on bathyal sediments (305, 562, 830 and 1210 m) along a transect within and beneath the oxygen minimum zone (OMZ) in the southeastern Pacific off Callao, Peru (12°S). Meiobenthos densities ranged from 1517 (upper slope, middle of OMZ) to 440–548 ind. 10 cm⁻² (lower slope stations, beneath the OMZ). Nematodes were the numerically dominant meiofaunal taxon at every station, followed by copepods and nauplii. Increasing bottom-water oxygen concentration and decreasing organic matter availability downslope were correlated with observed changes in meiofaunal abundance. The 300-m site, located in the middle of the OMZ, differed significantly in meiofaunal abundance, dominance, and in vertical distribution pattern from the deeper sites. At 305 m, nematodes amounted to over 99% of total meiofauna; about 70% of nematodes were found in the 2–5 cm interval. At the deeper sites, about 50% were restricted to the top 1 cm. The importance of copepods and nauplii increased consistently with depth, reaching ∼12% of the total meiofauna at the deepest site. The observation of high nematode abundances at oxygen concentrations <0.02 ml l⁻¹ supports the hypothesis that densities are enhanced by an indirect positive effect of low oxygen involving (a) reduction of predators and competitors and (b) preservation of organic matter leading to high food availability and quality. Food input and quality, represented here by chloroplastic pigment equivalents (CPE) and sedimentary labile organic compounds (protein, carbohydrates and lipids), were strongly, positively correlated with nematode abundance. By way of contrast, oxygen exhibited a strong negative correlation, overriding food availability, with abundance of other meiofauna such as copepods and nauplii. These taxa were absent at the 300-m site. The high correlation of labile organic matter (C-LOM, sum of carbon contents in lipids, proteins and carbohydrates) with CPE (Pearson's r=0.99, p<0.01) suggests that most of the sedimentary organic material sampled was of phytodetrital origin. The fraction of sediment organic carbon potentially available to benthic heterotrophs, measured as C-LOM/Total organic carbon, was on average 17% at all stations. Thus, a residual, refractory fraction, constitutes the major portion of organic matter at the studied bathyal sites.     

Effects of oilfield brine effluent on sediments and benthic organisms in trinity bay,Texas

Field studies have established the concentrations of naphthalenes in bay sediments and water in the vicinity of an oil separator platform and their effects on the benthic fauna. Fifteen stations were occupied monthly, from July, 1974 to December, 1975, along three transects extending from the separator platform outfall outwards for a distance of 4·0 to 5·6 km. A lesser number of stations were occupied from April, 1974 to June, 1974. Bottom sediments at each station were analysed for total naphthalenes content and for number of species and individuals. All stations were located in 2 to 3 m of water. The outfall was located 1 m off the bay bottom.There was a definite correlation between sediment naphthalenes concentration and number of species and individuals. As expected, the first station, located 15 m from the outfall, had the highest concentration of naphthalenes of all stations sampled. The naphthalenes levels dropped sharply from the outfall to the stations located 75 m from the platform where levels were about 20–50% of those found 15 m from the outfall. Naphthalenes concentrations then decreased gradually to near background levels at stations farther out. Hydrocarbon concentrations in bottom water 15 m from the outfall were three orders of magnitude lower than those in the full strength effluent, but sediments 15 m from the outfall had hydrocarbon concentrations four times as great as in the full strength effluent. There were approximately four orders of magnitude more hydrocarbons in the sediment than in the overlying water.The bay bottom was almost completely devoid of organisms within 15 m of the effluent outfall. Stations located 150 m from the outfall had severely depressed benthic faunas but not to the extent of stations nearer the outfall. Stations located 455 m from the platform were unaffected. Both numbers of species and individuals increased with distance from the platform and reached a peak at the first station medial to the control on each transect (685 to 1675 m from the platform) and then dropped at the control station. Physical environmental factors such as temperature, salinity, water depth and sediment type were essentially the same at all stations.The temporary use of a second outfall located 275 m from the main platform outfall resulted in a rapid build up of naphthalenes in surrounding sediments which persisted for at least six months following the termination of use of the second outfall. The benthic fauna was also severely depressed in the vicinity of the second outfall. The use of multiple outfalls, located some distance apart, appears to be more harmful than the use of a single outfall.Trinity Bay, Texas, the site of this investigation, has a mean depth of 2·5 m. The bay water is highly turbid due to the presence of a high concentration of clay-sized particulate material. The brine outfall was located approximately 1 m above the bay bottom. These special conditions undoubtedly contributed significantly to the observed impact of the brine. Therefore, extrapolations from the results of this study to offshore oil production and brine disposal should be made with extreme caution.     

Monsoonal influence on the distribution of phytoplankton pigments in the Arabian Sea

Variations in the distribution of chemotaxonomic pigments were monitored in the Arabian Sea and the Gulf of Oman at the end of the SW monsoon in September 1994 and during the inter-monsoon period in November/December 1994 to determine the seasonal changes in phytoplankton composition. The Gulf of Oman was characterized by sub-surface chlorophyll maxima at 20-40 m during both seasons, and low levels of divinyl chlorophyll a indicated that prochlorophytes did not contribute significantly to the total chlorophyll a. Prymnesiophytes (19′-hexanoyloxyfucoxanthin), diatoms (fucoxanthin) and chlorophyll b containing organisms accounted for most of the phytoplankton biomass in September, while prymnesiophytes dominated in November/December. In the Arabian Sea in September, high total chlorophyll a concentrations up to 1742 ng l^-1 were measured in the coastal upwelling region and a progressive decline was monitored along the 1670 km offshore transect to oligotrophic waters at 8°N. Divinyl chlorophyll a was not detected along this transect except at the two most southerly stations where prochlorophytes were estimated to contribute 25–30% to the total chlorophyll a. Inshore, the dominance of fucoxanthin and/or hexanoyloxyfucoxanthin indicated that diatoms and prymnesiophytes generally dominated the patchy phytoplankton community, with zeaxanthin-containing Synechococcus also being important, especially in surface waters. At the southern oligotrophic localities, Synechococcus and prochlorophytes dominated the upper 40 m and prymnesiophytes were the most prominent at the deep chlorophyll maximum. During the inter-monsoon season, total chlorophyll a concentrations were generally half those measured in September and highest levels were found on the shelf (1170 ng l^-1). Divinyl chlorophyll a was detected at all stations along the Arabian Sea transect, and we estimated that prochlorophytes contributed between 3 and 28% to the total chlorophyll a, while at the two oligotrophic stations this proportion increased to 51–52%. While procaryotes were more important in November/December than September, eucaryotes still accounted for >50% of the total chlorophyll a. Pigment/total chlorophyll a ratios indicated that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were the dominant group, although procaryotes accounted for 65% at the two southerly oligotrophic stations.     

Persistence of oiling in mussel beds after the Exxon Valdez oil spill

Persistence and weathering of Exxon Valdez oil in intertidal mussel (Mytilus trossulus) beds in Prince William Sound (PWS) and along the Gulf of Alaska was monitored from 1992 to 1995. Beds with significant contamination included most previously oiled areas in PWS, particularly within the Knight Island group and the Kenai Peninsula. In sediments, yearly mean concentrations of total petroleum hydrocarbons ranged from < 60 micrograms/g in reference beds to 62,258 micrograms/g wet wt., or approximately 0 to 523 micrograms/g dry wt. total polynuclear aromatic hydrocarbons (TPAHs). In mussels, mean TPAH concentrations ranged up to 8.1 micrograms/g dry wt. Hydrocarbon concentrations declined significantly with time in some, but not all mussels and sediments, and should reach background levels within three decades of the spill in most beds. In 1995, mean hydrocarbon concentration was greater than twice background concentration in sediments from 27 of 34 sites, and in mussels from 18 of 31 sites.     

Bathymetric variations in vertical distribution patterns of meiofauna in the surface sediments of the deep Arctic ocean (HAUSGARTEN,Fram strait)

Deep-sea benthic communities and their structural and functional characteristics are regulated by surface water processes. Our study focused on the impact of changes in water depth and food supplies on small-sized metazoan bottom-fauna (meiobenthos) along a bathymetric transect (1200–5500 m) in the western Fram Strait. The samples were collected every summer season from 2005 to 2009 within the scope of the HAUSGARTEN monitoring program. In comparison to other polar regions, the large inflow of organic matter to the sea floor translates into relatively high meiofaunal densities in this region. Densities along the bathymetric gradient range from approximately 2400 ind. 10 cm^-2 at 1200 m to approximately 300 ind. 10 cm^-2 at 4000 m. Differences in meiofaunal distribution among sediment layers (i.e., vertical profile) were stronger than among stations (i.e., bathymetric gradient). At all the stations meiofaunal densities and number of taxa were the highest in the surface sediment layer (0–1 cm), and these decreased with increasing sediment depth (down to 4–5 cm). However, the shape of the decreasing pattern differed significantly among stations. Meiofaunal densities and taxonomic richness decreased gradually with increasing sediment depth at the shallower stations with higher food availability. At deeper stations, where the availability of organic matter is generally lower, meiofaunal densities decreased sharply to minor proportions at sediment depths already at 2–3 cm. Nematodes were the most abundant organisms (60–98%) in all the sediment layers. The environmental factors best correlated to the vertical patterns of the meiofaunal community were sediment-bound chloroplastic pigments that indicate phytodetrital matter.     

Zooplankton distribution across Fram Strait in autumn: Are small copepods and protozooplankton important?

We investigated zooplankton distribution in September 2006/2007 at eight stations across Fram Strait in contrasting water masses ranging from cold Polar water to warm Atlantic water. Our main objectives were: (1) to describe the plankton community in the upper 200 m during autumn, and (2) to investigate the importance of small-sized copepods and protozooplankton in an arctic ecosystem when the majority of the large Calanus species had entered diapause. We sampled both with a WP-2 net and Go-Flo bottle and show that small copepods <1 mm are significantly undersampled using a WP-2 net with 90 μm mesh.Small copepods and protozooplankton made a significant contribution both in terms of abundance and total zooplankton biomass at all stations in September, when the large calanoid copepods had left the upper 200 m. The dominating group in the upper 60 m at all stations was Oithona spp. nauplii and their daily estimated grazing potential on the <10 μm phytoplankton ranged from 0.1% to 82% of the standing stock. Both Oithona copepodites and nauplii biomass showed a significantly positive relation with temperature, but not with potential food. Heterotrophic protozooplankton, on the other hand, were most likely bottom-up regulated by the availability of phytoplankton <10 μm. We hypothesise that Oithona nauplii and protozooplankton compete for food and conclude that there was a strong link between the zooplankton community and the microbial food web in Fram Strait.