Cross-slope zonation of erosion and deposition in the Faeroe-Shetland Channel,North Atlantic Ocean

Boundary currents and internal waves determine cross-slope zonation of erosion and deposition in the Faeroe-Shetland Channel. Currents were measured at 8 and 34–50 m above the bottom at three mooring sites (502, 595 and 708 m depth) for 14 days. The structure of the water column was evaluated from CTD sections, and included nepheloid layers and particulate matter concentrations. Indicators for recent deposition in the sediment (organic carbon, phytopigments, ²¹⁰Pb) were measured at eight stations across the slope. Strong near-bottom currents at the upper slope sustain down-slope particle transport in a benthic nepheloid layer, which is eroded under the influence of critically reflecting M₂ internal tidal waves at 350–550 m, where the major pycnocline meets the sloping bottom. Beam attenuation profiles confirmed the presence of intermediate nepheloid layers intruding into the Channel along the major pycnocline, and elevated concentrations of particulate matter and chlorophyll-a were measured at this depth. Near-bottom currents decreased with depth, thus allowing particle deposition down the slope. Inventories of excess ²¹⁰Pb activity in the sediment deeper than 600 m were higher than what was expected on the basis of atmospheric input of ²¹⁰Pb and production in the water column, thus indicating additional lateral inputs. Simple calculations showed that off-slope input of particles from areas shallower than 600 m may be responsible for the enhanced deposition at greater depths.     

Molecular and isotopic constraints on the sources of suspended particulate organic carbon on the northwestern Atlantic margin

The abundance, carbon isotopic composition (Δ¹⁴C and δ¹³C), and lipid biomarker (alkenones and saturated fatty acids) distributions of suspended particulate organic matter were investigated at three stations centered on the 2000, 3000, and 3500 m isobaths over the New England slope in order to assess particulate carbon sources and dynamics in this highly productive and energetic region. Transmissometry profiles reveal that particle abundances exhibit considerable fine structure, with several distinct layers of elevated suspended particulate matter concentration at intermediate water depths in addition to the presence of a thick bottom nepheloid layer at each station. Excluding surface water samples, the Δ¹⁴C values of particulate organic carbon (POC) indicated the presence of a pre-aged component in the suspended POC pool (Δ¹⁴C<+38‰). The Δ¹⁴C values at the 3000 m station exhibited greater variability and generally were lower than those at the other two stations where the values decreased in a more systematic matter with increasing sampling depth. These lower Δ¹⁴C values were consistent with higher relative abundances of terrigenous long-chain fatty acids at this station than at the other two stations. Two scenarios were considered regarding the potential provenances of laterally transported POC: cross-shelf transport of shelf sediment (Δ¹⁴C=?140‰) and along-slope transport of the slope sediment proximal to the sampling locations (Δ¹⁴C=?260‰). Depending on the scenario, isotopic mass balance calculations indicate allochthonous POC contributions ranging between 15% and 54% in the meso- and bathy-pelagic zone, with the highest proportions at the 3000 m station. Alkenone-derived temperatures recorded on suspended particles from surface waters closely matched in-situ temperatures at each station. However, alkenone-derived temperatures recorded on particles from the subsurface layer down to 250 m were lower than those of overlying surface waters, especially at the 3000 m station, implying supply of phytoplankton organic matter originally produced in cooler surface waters. AVHRR images and temperature profiles indicate that the stations were under the influence of a warm-core ring during the sampling period. The low alkenone-derived temperatures in the subsurface layer coupled with the lower Δ¹⁴C values for the corresponding POC suggests supply of OC on resuspended sediments underlying cooler surface waters distal to the study area, possibly further north or west. Taken together, variations in Δ¹⁴C values, terrigenous fatty acid abundances, and alkenone-derived temperatures among the stations suggest that input of laterally advected OC is a prominent feature of POC dynamics on the NW Atlantic margin, and is spatially heterogeneous on a scale smaller than the distance between the stations (<150 km).     

Deep slope currents and suspended particle fluxes in and around the Foix submarine canyon (NW Mediterranean)

Deep slope currents and particulate matter concentrations were studied on the Barcelona continental margin in and around the Foix submarine canyon from May 1993 to April 1994. This year-long moored experiment revealed that near-bottom slope currents are strongly influenced by the bottom topography, being oriented along isobaths and along the canyon axis. The deep slope current fluctuations are controlled by the local inertial motion (18.3 h) and also by low-frequency oscillations at periods of 6–10 days, related to the passage of atmospheric pressure cells. Particulate matter concentrations recorded during the experiment do not show a clear seasonal variability, except outside the canyon, where significant peaks of particulate matter concentrations were recorded only during the winter-fall deployment. In addition, the temporal evolution of suspended particulate matter concentration is not linked to changes in the cross-slope or along-slope current components and did not show a clear relationship with river avenues or wave storm events. This suggests that suspended particulate matter exported from the shelf is dispersed on the slope by advective processes, which attenuate the signal of the shelf-slope sediment transfer. Mean particulate matter concentrations differed among sampling sites, but the magnitude of the mean horizontal suspended particle flux reflects a quite similar value in the whole study area, ranging from 2.53 to 4.05 mg m⁻² s⁻¹. These horizontal suspended particle fluxes are 27 (canyon head) to 360 (open slope) times higher than the settling particle fluxes measured at the same sampling sites, indicating that the suspended particulate transport on the Barcelona continental slope dominates over the settling particle fluxes, even inside the Foix submarine canyon.     

Nepheloid layer distribution in the Benguela upwelling area offshore Namibia

The distribution of nepheloid layers across the outer shelf and upper continental slope off Namibia was studied during a cruise with R.V. Meteor in late austral summer 2003. Optical measurements, carried out with a transmissometer and a backscattering fluorometer, are correlated with suspended particulate matter (SPM) and particulate organic carbon (POC) values from water sample filtration. Conductivity-temperature-depth and oxygen data are used to relate the nepheloid layers to hydrographic structures. The particle content of surface water at the continental slope is controlled primarily by the offshore extension of highly productive upwelling filaments. A pronounced bottom nepheloid layer (BNL) covers the entire area of study with maximum intensity above the outer shelf and at the shelf break—an area where erosional forces dominate. The detachment of this BNL at the shelf break feeds a major intermediate nepheloid layer (INL) at 25.5°S. This INL is positioned at 250–400 m depth, at the lower boundary of an oxygen minimum zone, and is likely connected to the poleward flow of South Atlantic Central Water (SACW) across the shelf break. Together, these strong subsurface nepheloid layers are indicators of intensive lateral particle transport from the outer shelf towards a depocenter of organic matter on the upper continental slope.     

Nepheloid layer dynamics in the northern Portuguese shelf

A general hydrographic and nephelometric survey of the NW Portuguese continental shelf and upper slope was undertaken, under winter and spring conditions. The nepheloid layer dynamics along the shelf during three cruises were controlled, principally by the following factors: (a) the hydrography of the shelf-slope waters, i.e. the nepheloid layers followed isopycnals and water masses; (b) prevalence of upwelling or downwelling circulation over the shelf; (c) dispersion of material by river discharge (mainly the Douro river); (d) resuspension of mid-shelf fine deposits induced by swell; (e) peculiar morphology with the presence of Porto Canyon and outer shelf rock outcrops.The general circulation controls the seaward extension of the nepheloid layers. In winter, under dominant downwelling conditions, an intense bottom nepheloid layer (BNL) was observed on the shelf, due to river borne particle supply and remobilization of mid-shelf muddy sediments (depth ≈100 m). In this period the BNL increased in thickness to the top of the slope, following the isopycnals. Near the shelf-break the BNL detached to form intermediate nepheloid layers (INL). Small INLs appear deeper in some areas of the slope. A surface nepheloid layer (SNL) appears in the surface water over the shelf and slope. In spring, biological particles mainly contribute to the SNL, which is separated from the BNL by a zone of clear water. In winter the SNL is restricted to the inner shelf where there are high inputs of fluvial particles.Downwelling circulation probably induces transport of shelf particles to deeper waters in the BNL. In spring, the predominant circulation was southward (upwelling), the water column was highly stratified, and dispersion of particles in the SNL was offshore.     

The pattern of cross-slope depositional fluxes

A simple model with horizontal and vertical diffusivities and settling velocity is used to calculate expected distributions of suspended particulate matter in a section across the continental shelf and slope. Dependencies on the shelf and slope profile, diffusivities, settling velocity, cross-slope advection and boundary sources/sinks are explored. It is found that the strongest factors are relative values of diffusivities and settling velocity, and the distribution of sources and sinks – including bottom deposition or resuspension. The latter is the principal means whereby an increased concentration near the bottom is likely, and is suggested as the usual reason for increased deposition recorded by sediment traps nearer the bottom. Observed thin, near-horizontal intermediate nepheloid layers put bounds on the vertical diffusivity and settling velocity, e.g. O(10^-4 m² s^-1, 10^-5 m s^-1) over Goban Spur in OMEX.     

Particle flux across the mid-European continental margin

Results are presented from particle flux studies using sediment trap and current meter moorings along a transect at the European continental margin at 49°N within the EU-funded Ocean Margin Exchange (OMEX) project. Two moorings were placed, at the mid- and outer slope in water depths of 1500 and 3660 m, with traps at 600 and 1050 m and at 580, 1440 and 3220 m, respectively. Residual currents at the mid-slope follow the slope contour, whereas seasonal off-slope flow was registered at the outer slope. At 600 m on the slope fluxes are similar to those in the abyssal North Atlantic. The flux of all components (bulk dry weight, particulate organic and inorganic carbon, lithogenic matter and opal) increased with water depth. Highest fluxes were recorded at 1440 m at the outer slope, where off-slope residual currents mediate particle export. The injection of biogenic and lithogenic particles below the depth of winter mixing results in the export of particles from shallower waters. Calculated lateral fluxes of particulate organic carbon exceed the primary flux by over a factor of 2 at 1440 m on the outer slope. Estimated lateral fluxes of suspended particulate matter in the water column and intermediate nepheloid layers at the outer slope are potentially large compared to sinking fluxes measured by sediment traps. A comparison is made of particle flux at three continental margin sites and two sites in the adjacent open North Atlantic, from which it is seen that bulk and organic matter flux increases exponentially with proximity to the shelf break. The percentage contribution of particulate organic carbon to biogenic fluxes increases from a mean of 5.7% in the abyssal N. Atlantic to 13.9% at the continental margins.     

The importance of subsurface nepheloid layers in transport and delivery of sediments to the eastern Cariaco Basin,Venezuela

Optical transmissometer measurements were coupled with particulate organic matter (POM) observations to understand suspended sediment composition and distribution in the eastern Cariaco Basin during the rainy seasons of September 2003 and 2006. Our results suggest that nepheloid layers originating at the mouth of small mountainous rivers discharging into the eastern Basin are a major delivery mechanism of terrigenous sediments to the Basin interior. Intermediate nepheloid layers (INL) were observed near the shelf break (～100 m) and appear to effectively transport terrigenous material laterally from the shelf to deep waters, thereby providing a plausible supply mechanism of the terrestrial material observed in sediment traps. These findings highlight the importance of small, local rivers in the Cariaco Basin as sources of terrestrial material. In contrast, these nepheloid layers contained only limited POM. When this information is combined with published sediment trap POM data, it suggests that nepheloid layers may not be a primary mechanism for delivering terrigenous POM to the deeper waters of the basin during the rainy season. Rather, BNL may redistribute marine-derived POM from shallow waters to the Basin's interior by providing ballast materials, particularly during episodic events driven by wind and precipitation. Though we have determined that nepheloid layers play an important role in the seaward transport of particulate material in the Cariaco Basin, their composition and temporal variability have not been fully characterized. This is critical to understand lateral particle transport, since nepheloid layers constitute a significant source of sediment to the deep Cariaco Basin.     

Particulate organic carbon budget in the open Algero-Balearic Basin (Western Mediterranean): Assessment from a one-year sediment trap experiment

With the aim of improving the knowledge of the open ocean carbon cycle, we present a budget of particulate organic carbon (POC) fluxes carried out in the deep central part of the Algero-Balearic Basin (ABB) at 2850 m water depth based on a single mooring equipped with five automated sediment traps deployed from April 2001 to May 2002 at depths of 250, 845, 1440, 2145 and 2820 m. Suspended particulate matter (SPM) and superficial sediments were also used as indicators of hydrodynamics and carbon burial, respectively. The data reveal that the fraction of primary production buried in the sediment, which finally leads to the sequestration of carbon dioxide from the atmosphere, is 0.16%, lower than the values found in the nearby continental margin regions such as the Alboran Sea (0.48–0.89%) but of the same order as recorded at other Mediterranean sites at similar depths, such as the Ionian Sea (0.11%). As they sink through the water column, the particles exhibit decreases in flux that are similar to those observed elsewhere, but also show variations that appear to correlate with hydrological features of the water masses present in the basin, as revealed by SPM concentrations and compositions. The input of the tyrrhenian deep water (TDW) into the ABB at 800–1500 m of water depth exhibits low suspended POC concentrations and low sinking POC fluxes were also observed in this depth range. Gulf of Lions water mass formation appears to also contribute to elevated suspended POC concentrations and perhaps POC accumulation in the traps and sediments by spreading of dense cold water along the whole ABB that supplied POC at depths higher than 2000 m.     

Scavenging,cycling and removal fluxes of 210Po and 210Pb at the Bermuda time-series study site

Quantifying relative affinities of Po and Pb in different populations of marine particulate matter is of great importance in utilizing ²¹⁰Po as a tracer for carbon cycling. We collected and analyzed water samples for the concentrations of dissolved and total ²¹⁰Po and ²¹⁰Pb from the upper 600 m of the water column at Bermuda Time-series Study site (September 1999–September 2000) to investigate their seasonality of concentrations and their activity ratio (²¹⁰Po/²¹⁰Pb activity ratio, AR). Sinking particles collected in sediment traps at depths of 500 m, 1500 m, and 3200 m from the Oceanic Flux Program (OFP) time-series sediment traps were analyzed over a period of 12 months (May 1999–May 2000). The objective was to compare the deficiencies of ²¹⁰Po with respect to ²¹⁰Pb in the water column to that measured in the sediment traps and to assess the relative affinities of Po and Pb with different particle pools.Inventories of ²¹⁰Po in the upper 500 m water column varied by a factor of 2, indicating seasonal variations of particulate flux dominated the removal of ²¹⁰Po. The ²¹⁰Po/²¹⁰Pb ARs in the dissolved phase were generally less than the secular equilibrium value (1.0) in the upper 600 m, while were generally greater than 1.0 in the particulate phase, indicating higher removal rates of ²¹⁰Po relative to ²¹⁰Pb by particulate matter. The measured fluxes of ²¹⁰Po and ²¹⁰Pb in the 500 m, 1500 m, and 3200 m traps increased with depth, while the ²¹⁰Po/²¹⁰Pb ARs decreased with depth except from May–August 1999. From the measured fluxes of ²¹⁰Po and ²¹⁰Pb at these three traps and the concentrations of ²¹⁰Po and ²¹⁰Pb in the water column, this region appears to be a sink for ²¹⁰Pb which is likely brought-in by lateral advection.     

A study of particle exchange at the sediment–water interface in the Benguela upwelling area based on 234Th/238U disequilibrium

The natural isotope ²³⁴Th is used in a small-scale survey of particle transport and exchange processes at the sediment–water interface in the Benguela upwelling area. Results from water and suspended particulate matter (SPM) samples from the uppermost and lowermost water column as well as the underlying sediment of three stations are compared. The stations are situated in different sedimentological environments at 1200–1350 m water depth at the continental slope off Namibia. Highly differing extent and particle content of the bottom nepheloid layer (BNL) are determined from transmissometer data. Three models are presented, all explaining the ²³⁴Th depletion of the BNL and ²³⁴Th excess of the surface sediment that were observed. While the first model is based solely on local resuspension of surface sediment particles, the second evaluates the influence of vertical particle settling from the surface waters on the ²³⁴Th budget in the BNL. The third model explains ²³⁴Th depletion in the BNL by sedimentation of particles that were suspended in the BNL during long-range transport. Particle inventory of the BNL is highest at a depocenter of organic matter at 25.5°S, where strong deposition is presently taking place and lateral particle transport is suggested to predominate sediment accumulation. This is supported by the high settling flux of particles out of the BNL into the sediments of the depocenter, exceeding the vertical particle flux into sediment traps at intermediate depth in the same area by up to an order of magnitude. High particle residence/removal times in the BNL above the depocenter in the range of 5–9 weeks support this interpretation. Comparison with carbon mineralization rates that are known from the area reveals that, notwithstanding the large fraction of advected particles, organic carbon flux into the surface sediment is remineralized to a large extent. The deployment of a bottom water sampler served as an in situ resuspension experiment and provided the first data of ²³⁴Th activity on in situ resuspended particles. We found a mean specific activity of 86 disintegrations per minute (dpm) g⁻¹ (39–339 dpm g⁻¹), intermediate between the high values for suspended particles (in situ pump: 580–760 dpm g⁻¹; CTD rosette: 870–1560 dpm g⁻¹) and the low values measured at the sediment surface (26–37 dpm g⁻¹). This represents essential information for the modeling of ²³⁴Th exchange processes at the sediment–water interface.     

Spatial and temporal variability of POC in the northeast Subarctic Pacific

Particulate organic carbon (POC) concentrations from 0 to 1000 m were quantified in size-fractionated particulate matter samples obtained by the multiple unit large volume in situ filtration system (MULVFS) in 1996 and 1997 along the 1600 km long “line P” transect from continental slope waters near southern Vancouver Island to Ocean Station PAPA (OSP, 50°N, 145°W). Regression of in situ POC vs. beam attenuation coefficient, c, from a simultaneously deployed 1-m pathlength SeaTech transmissometer gave slope, intercept and r² values of 6.15±0.19×10⁻⁵ m⁻¹ (nmol C l⁻¹)⁻¹, 0.363±0.003 m⁻¹, and 0.951 (n=145), respectively. This result agreed within several percent of calibrations obtained from two 2600-km-long transects of the equatorial Pacific in 1992 (Bishop, 1999). Data from other, more frequently deployed transmissometers were standardized against the 1-m instrument, and the combined optical data set was used to document POC variability at finer spatial and temporal scales than could be sampled directly using either conventional water bottle casts or MULVFS. Published bottle POC vs. c relationships show much more variability and remain problematic. Along the line P transect in the salinity-stratified upper 100 m, POC isolines shoaled from winter to summer in concert with seasonal stratification. At the same time, POC was progressively enriched in subeuphotic zone waters to depths greater than 500 m. Near-surface POC fields sampled in the winter time showed strong temporal POC variability over time scales of days as well as between years. POC concentrations at OSP in February 1996 were higher than those found at any other time of year. Less variability was found along line P in other seasons. In May 1996, kilometer-scale spatial variability of POC at OSP was small; dawn vs. dusk variations of c were used to calculate 0–100 m POC turnover times shorter than 6 d. Calculations also suggest that 25–50% of primary productivity was expressed as dissolved organic carbon at OSP in May 1996.     

Origin and variability of downward biogeochemical fluxes on the Rhone continental margin (NW mediterranean)

A one year study of downward particle fluxes conducted in the northwestern Mediterranean Sea is presented. Two mooring lines equipped with sediment traps and current meters were deployed at around 1000 m depth on the northeastern continental slope of the Gulf of Lions, one inside the Grand-Rhône canyon and the other outside on the adjacent open slope. Mean total mass fluxes increased slightly with trap depth inside the canyon, a feature quite typical of fluxes in continental margin environments. The near-bottom trap inside the canyon collected more material than its counterpart deployed at equivalent depth on the open slope, indicating a preferential transport of material within the canyon. Major biogeochemical constituents (organic and inorganic carbon, opal, and siliciclastic residue) revealed a marked difference in particle composition between the sub-surface (80 m) and deeper traps, suggesting the existence of at least two sources of material. The two shallower traps showed a clear biological signal: flux peaks were related to periods of surface biological production, especially perceptible in summer and autumn. The particulate matter trapped at deeper levels in the canyon and on the open slope was characterized by a more stable composition with a major lithogenic contribution, originating from sedimentary material most probably resuspended on the upper- or mid-slope. The seasonal variability was dominated by the summer/winter alternation; the latter period was characterized by a weak stratification of the water column and an enhanced current variability favoring vertical exchanges. The present results are compared with those obtained previously in the Lacaze-Duthiers canyon on the southwestern side of the Gulf of Lions. The comparison shows strong differences between the NE entrance and the SW exit of the gulf, with respect to the general along-slope circulation of water masses, both in terms of intensity of particulate fluxes and transport processes.     

Spatial and seasonal evolution of dissolved oxygen and nutrients in the Southern Levantine Basin (Eastern Mediterranean Sea): chemical characterization of the water masses and inferences on the N : P ratios

The spatial and seasonal variability of nutrients and dissolved oxygen concentrations as well as the chemical characterization of the different water masses of the Southern Levantine Basin were determined in detail. In summer, the upper 150 m of the water body was stratified and the cross basin distribution of dissolved oxygen and nutrients was fairly constant. Surficial waters were saturated with dissolved oxygen, and a shallow oxygen maximum (oversaturated) was present at about 80 m depth. Oversaturation was attributed mainly to the physical process of rapid capping and trapping of oxygen in the Atlantic water (AW) mass, with only 28% of the excess oxygen originating from biological production. Nutrient concentrations were very low and showed an increase in the intermediate levels, coupled with a decrease in oxygen. The winter cross-section distribution showed an upper mixed layer of 100 m, with dissolved oxygen and nutrient concentrations fairly constant across the basin. The concentration of nitrate was higher than in summer, while phosphate was slightly lower and silicic acid similar. In winter, the influence of the physical features (gyres) could be detected up to the surface, and in summer they were detected by the chemical properties in the 150–600 m layer. In the transition layer between the Levantine intermediate water (LIW) and the deep water (DW) (400–700 m) there was a gradual decrease in dissolved oxygen and an increase in nutrient concentrations eastwards. The DW showed no seasonal variation, only spatial variability: dissolved oxygen decreased and silicic acid increased eastwards. No differences were found in nitrate and phosphate concentrations between the DW in the western and eastern provinces, indicating the oxidation of organic matter poor in N and P.N : P ratios in the upper water masses were seasonally dependent. The largest variation was found in the Levantine surface water (LSW), from an average of 52 in winter to 5 in summer. It is hypothesized that the gradual decrease from winter to summer values was due mainly to preferential atmospheric input of N in winter and P in summer, together with biological consumption and differential regeneration of N and P. In the DW, the N : P ratios were constant throughout the year (25.2±2.7, n=567), and higher than Redfield's ratio. It was speculated that the high N : P ratio in the DW was a result of oxidation of particulate organic matter deficient in P.The winter wet atmospheric input of N provided 12% of new N to the LSW. Average new production for the Southern Levantine Basin was estimated from the new N as 4.75 g C m⁻² yr⁻¹. The dry atmospheric contribution of P was estimated to significantly increase the P pool in the LSW. Dry deposition is not evenly distributed and occurs in episodic and localized events, which may have a large effect on productivity in the short periods when deposition occurs.There have been recently reported changes in the deep thermohaline circulation of the Eastern Mediterranean, with main contribution of the Aegean Sea as a source of DW. The data presented here can serve as a reference for assessing future changes in the chemical composition of the water masses in the Southern Levantine.     

The annual cycle of vertical mixing and restratification in the Northern Gulf of Eilat/Aqaba (Red Sea) based on high temporal and vertical resolution observations

The stratification in the Northern Gulf of Eilat/Aqaba follows a well-known annual cycle of well-mixed conditions in winter, surface warming in spring and summer, maximum vertical temperature gradient in late summer, and erosion of stratification in fall. The strength and structure of the stratification influences the diverse coral reef ecosystem and also affects the strength of the semi-diurnal tidal currents. Long-term (13 months) moored thermistor data, combined with high temporal and vertical resolution density profiles in deep water, show that transitions from summer to fall and winter to spring/summer occur in unpredictable, pulses and are not slow and gradual, as previously deduced from monthly hydrographic measurements and numerical simulations forced by monthly climatologies. The cooling and deepening of the surface layer in fall is marked by a transition to large amplitude, semi-diurnal isotherm displacements in the stratified intermediate layer. Stratification is rebuilt in spring and summer by intermittent pulses of warm, buoyant water that can increase the upper 100–150 m by 2 °C that force surface waters down 100–150 m over a matter of days. The stratification also varies in response to short-lived eddies and diurnal motions during winter. Thus, the variability in the stratification exhibits strong depth and seasonal dependence and occurs over range of timescales: from tidal to seasonal. We show that monthly or weekly single-cast hydrographic data under-samples the variability of the stratification in the Gulf and we estimate the error associated with single-cast assessments of the stratification.     

Particle sedimentation patterns in the eastern Fram Strait during 2000–2005: Results from the Arctic long-term observatory HAUSGARTEN

Since 2000 long-term measurements of vertical particle flux have been performed with moored sediment traps at the long-term observatory HAUSGARTEN in the eastern Fram Strait (79°N/4°E). The study area, which is seasonally covered with ice, is located in the confluence zone of the northward flowing warm saline Atlantic water with cold, low salinity water masses of Arctic origin. Current projections suggest that this area is particularly vulnerable to global warming. Total matter fluxes and components thereof (carbonate, particulate organic carbon and nitrogen, biogenic silica, biomarkers) revealed a bimodal seasonal pattern showing elevated sedimentation rates during May/June and August/September. Annual total matter flux (dry weight, DW) at ～300 m depth varied between 13 and 32 g m^?2 a^?1 during 2000 and 2005. Of this total flux 6–13% was due to CaCO₃, 4–21% to refractory particulate organic carbon (POC), and 3–8% to biogenic particulate silica (bPSi). The annual flux of all biogenic components together was almost constant during the period studied (8.5–8.8 g m^?2 a^?1), although this varied from 27% to 67% of the total annual flux. The fraction was lowest in a year characterized by the longest duration of ice coverage (91 and 70 days for the calendar year and summer season, May–September, respectively). Biomarker analyses revealed that organic matter originating from marine sources was present in excess of terrigenious material in the sedimented matter throughout most of the study period. Fluxes of recognizable phyto- and protozooplankton cells amounted up to 60×10⁶ m^?2 d^?1. Diatoms and coccolithophorids were the most abundant organisms. Diatoms, mainly pennate species, dominated during the first years of the investigation. A shift in the composition occurred during the last year when numbers of diatoms declined considerably, leading to a dominance of coccolithoporids. This was also reflected in a decrease in the sedimentation of bPSi. The sedimentation of biogenic matter, however, did not differ from the amount observed during the previous years. Among the larger organisms, pteropods at times contributed significantly to both the total matter and CaCO₃, fluxes.     

Hydrological properties,suspended matter,and particulate fluxes in the water column of the Bear Island Trough

The CTD and nephelometric sounding data are considered along with the parameters of the nearbottom currents and particulate fluxes measured by a subsurface mooring station in the northern part of the Bear Island Trough. It is shown that the near-bottom current is characterized by highly variable parameters, while the distribution of suspended particulate matter demonstrates surface and bottom maximums. The horizontal and vertical fluxes of sedimentary matter in the nepheloid layer are studied.     

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.