Computing cross-isotherm volume transports from ocean temperature observations and surface heat fluxes,with application to the Barents Sea inflow

A method for determining the cross-isotherm ocean transport from surface heat flux and ocean temperature data is derived. By computing the volume flux through the isotherm that extend from 19°E, 74°N to the eastern part of the Kola Peninsula, the flow through the western entrance of the Barents Sea south of 74°N is estimated. Using three different surface heat flux datasets, the inflow is found to range from 2.9 to 4.5 Sv in winter (October–March) and from 0.4 to 1.4 Sv in summer (April–September; 1 Sv=10⁶ m³ s⁻¹). The seasonal variations are stronger than indicated by results from direct current measurements, probably because the seasonal cycle of the surface heat fluxes is overestimated along the considered isotherm. The annual mean inflow ranges from 1.9 to 2.2 Sv during a cold period (1986–1988), and from 2.4 to 3.0 Sv during a warm period (1990–1992), close to reported observations.     

Intra-seasonal and inter-annual variations in phytoplankton biomass,primary production and bacterial production at North West Cape,Western Australia: Links to the 1997–1998 El Niño event

Phytoplankton biomass, community and size structure, primary production and bacterial production were measured at shelf and continental slope sites near North West Cape, Western Australia (20.5°S–22.5°S) over two summers (October–February 1997–1998 and 1998–1999), and in April 2002. The North West Cape region is characterized by upwelling-favorable, southwesterly winds throughout the summer. Surface outcropping of upwelled water is suppressed by the geostrophic pressure gradients and warm low-density surface waters of the southward flowing Leeuwin Current. Strong El Niño (ENSO) conditions (SOI <0) prevailed through the summer of 1997–1998 which resulted in lower sea levels along the northwestern Australian coast and a weaker Leeuwin Current. La Niña conditions prevailed during the 1998–1999 summer and in April 2002. During the summer of 1997–1998, the North West Cape region was characterized by a shallower thermocline (nutricline), resulting in larger euphotic zone stocks of inorganic nitrogen and silicate over the continental slope. There was evidence for episodic intrusions of upper thermocline waters and the sub-surface chlorophyll maximum onto the outer continental shelf in 1997–1998, but not in 1998–1999. Pronounced differences in phytoplankton biomass, community size structure and productivity were observed between the summers of 1997–1998 and 1998–1999 despite general similarities in irradiance, temperature and wind stress. Phytoplankton primary production and bacterial production were 2- to 4-fold higher during the summer of 1997–1998 than in 1998–1999, while total phytoplankton standing crop increased by<2-fold. Larger phytoplankton (chiefly diatoms in the >10 μm size fraction) made significant contributions to phytoplankton standing crop and primary production during the summer of 1997–1998, but not 1998–1999. Although there were no surface signs of upwelling, primary production rates near North West Cape episodically reached levels (3–8 g C m⁻² day⁻¹) characteristic of eastern boundary Ekman upwelling zones elsewhere in the world. Bacterial production (0.006–1.2 g C m⁻² day⁻¹) ranged between 0.6 and 145 percent (median=19 percent) of concurrent primary production. The observed differences between years and within individual summers suggest that variations in the Leeuwin Current driven by seasonal or ENSO-related changes in the Indonesian throughflow region may have episodic, but significant influences on pelagic productivity along the western margin of Australia.     

Satellite observation of Brazil Current inshore thermal front in the SW South Atlantic: Space/time variability and sea surface temperatures

A data set of 199 sea surface temperature maps derived from the Advanced Very High Resolution Radiometer for the period 2000–2002 was processed to derive the position of the surface inshore thermal front of the Brazil Current (BCIF) in the SE Brazilian coastal and oceanic area. After the derivation of the position of the BC front for each image, the ensemble of digital frontal vectors was processed using the algorithm of frontal density (FD). For each 5′×5′ cell in the domain the calculated FD provided an index expressing the presence and persistence of the front in the area or the probability of finding the front in the region. In the paper we present the results of the FD analysis to get a better view of the space and time variability of the BC front in the region. The highest values of FD were in general observed close to or at the shelf break zone (between 200 and 1000 m isobaths). From 20°S to 23°S there is a tendency of BCIF to be positioned over the outer shelf, inshore of the 200 m isobaths. SE of Cape Sao Tome and S of Cape Frio it was observed a bimodal spatial distribution of highest FD caused by the presence of two semi-permanent frontal eddies. After moving offshore near Cape Frio, the BCIF tends to return to the shelf break zone south of 24°S probably due to a potential vorticity conservation mechanism. The position of the highest FD values calculated for different seasons confirms previous studies in that BCIF is closer to the coast during the summer and furthest offshore in the winter. Statistical analysis of the SST data gave for the BCIF an average SST gradient of 0.31°C km⁻¹ with a standard deviation of 0.15°C km⁻¹. A mean frontal width of 6 km was inferred from the average SST gradient and typical temperatures near the front at both sides, at outer shelf and in the BC itself. A Weibull probability density function can be fitted to describe the BCIF SST gradients with scale factor c=0.3460°C km⁻¹ and shape factor k=2.1737. The BCIF SST gradient showed a seasonal variability with the smallest gradients in summer (~0.24 °C km⁻¹) and the highest in autumn (~0.33 °C km⁻¹). Using a three harmonic Fourier fit for the SST field near the BCIF, at the outer shelf and at interior of BC, it was possible to derive an analytical model for the time variability of the SST gradient of BCIF.     

Levels of Po and Pb in mussel and sediments in Candarlı Gulf and the related dose assessment to the coastal population

²¹⁰Po and ²¹⁰Pb in mussel (Mytilus galloprovincialis) and sediment samples collected at Candarl? Gulf during the period of 2010–2012 are presented and discussed. The activity concentrations of ²¹⁰Po and ²¹⁰Pb were measured by means of alpha spectrometry. Activity concentrations of ²¹⁰Po and ²¹⁰Pb in mussels are in the ranged of 332 ± 17–776 ± 23 Bq kg⁻¹ dw and 14 ± 1–40 ± 5 Bq kg⁻¹ dw, for sediments the ranges for 52 ± 5–109 ± 8 Bq kg⁻¹ dw and 38 ± 5–92 ± 9 Bq kg⁻¹ dw, respectively. The estimated consequent annual effective ingestion dose due to ²¹⁰Po and ²¹⁰Pb from mussel consumption in Candarl? Gulf coastal region were calculated. The highest dose due to ²¹⁰Po and ²¹⁰Po were calculated to be 4232 ± 126 μSv and 126 ± 16 μSv, respectively.     

Mantle plume heterogeneity versus shallow-level interactions: A case study,the São Nicolau Island,Cape Verde archipelago

We present new Sr–Nd–Pb isotopic data, as well as major- and trace-element concentrations, for 19 basaltic samples from São Nicolau Island, Cape Verde archipelago. Fine-scale study of the island argues in favor of mixing between four endmembers to explain isotopic variations of collected samples: 1) a radiogenic endmember (⁸⁷Sr/⁸⁶Sr ~ 0.7034; ¹⁴³Nd/¹⁴⁴Nd ~ 0.51285; ²⁰⁶Pb/²⁰⁴Pb ~ 20.0; ²⁰⁷Pb/²⁰⁴Pb ~ 15.65; ²⁰⁸Pb/²⁰⁴Pb ~ 39.8) representative of the Cape Verde plume deep source; 2) an unradiogenic endmember having isotopic compositions resembling those of Atlantic MORB dredged at the same latitude; 3) a low Sr–high Nd and Pb endmember identified as the Jurassic MORB basement of the archipelago; and 4) São Vicente-like Cape Verde carbonatites. Compositional and isotopic results show that most of the measured variations can be related to mixing of plume-derived melts with shallow-level reservoirs. Therefore the source heterogeneity of the Cape Verde plume is much smaller than the one sampled in basaltic samples. This observation illustrates how caution is required when interpreting global OIB data in terms of mantle topology without filtering from the contribution of shallow-level reservoirs.     

Spatial variability in organic material sinking export in the Hudson Bay system,Canada, during fall

Spatial variations in the sinking export of organic material were assessed within the Hudson Bay system (i.e., Hudson Bay, Hudson Strait and Foxe Basin) during the second oceanographic expedition of ArcticNet, on board the CCGS Amundsen in early fall 2005. Sinking fluxes of particulate organic material were measured using short-term free-drifting particle interceptor traps deployed at 50, 100 and 150 m for 8–20 h at eight stations. Measurements of chlorophyll a (chl a), pheopigments (pheo), particulate organic carbon (POC), biogenic silica (BioSi), protists, fecal pellets and bacteria were performed on the collected material. In parallel, sea surface salinity and temperature were determined at 121 stations in the Hudson Bay system. Three hydrographic regions presenting different sedimentation patterns were identified based on average surface salinity and temperature. Hudson Strait was characterized by a marine signature, with high salinity (average=32.3) and low temperature (average=2.1 °C). Eastern Hudson Bay was strongly influenced by river runoff and showed the lowest average salinity (26.6) and highest average temperature (7.6 °C) of the three regions. Western Hudson Bay showed intermediate salinity (average=29.4) and temperature (average=4.4 °C). Sinking fluxes of total pigments (chl a+pheo: 3.37 mg m⁻² d⁻¹), diatom-associated carbon (19.8 mg m⁻² d⁻¹) and BioSi (50.2 mg m⁻² d⁻¹) at 50 m were highest in Hudson Strait. Eastern Hudson Bay showed higher sinking fluxes of total pigments (0.52 mg m⁻² d⁻¹), diatom-associated carbon (3.29 mg m⁻² d⁻¹) and BioSi (36.6 mg m⁻² d⁻¹) compared to western Hudson Bay (0.19, 0.05 and 7.76 mg m⁻² d⁻¹, respectively). POC sinking fluxes at 50 m were low and relatively uniform throughout the Hudson Bay system (50.0–76.8 mg C m⁻² d⁻¹), but spatial variations in the composition of the sinking organic material were observed. A large part (37–78%) of the total sinking POC was unidentifiable by microscopic observation and was qualified as amorphous detritus. Considering only the identifiable material, the major contributors to the POC sinking flux were intact protist cells in Hudson Strait (28%), fecal pellets in eastern Hudson Bay (52%) and bacteria in western Hudson Bay (17%). A significant depth-related attenuation of the POC sinking fluxes (average loss between 50 and 150 m=32%) and a significant increase in the BioSi:POC ratio (average increase between 50 and 150 m=76%) were observed in Hudson Strait and eastern Hudson Bay. For all other sinking fluxes and composition ratios, we found no statistically significant difference with depth. These results show that during fall, the sinking export of total POC from the euphotic zone remained fairly constant throughout the Hudson Bay system, whereas other components of the organic sinking material (e.g., chl a, BioSi, fecal pellets, protist cells) showed strong spatial variations.     

Molecular and isotopic characterization of the particulate organic matter from an eutrophic coastal bay in SE Brazil

The present work aimed at studying the origin of particulate organic matter in Guanabara Bay and in some rivers of the Guanabara basin by using elemental composition, isotopic ratios (δ¹³C and δ¹⁵N) and molecular markers (sterols) in samples collected in two periods (winter and summer). Elemental and isotopic compositions were determined by dry combustion and mass spectrometry, respectively, while sterols were investigated by GC–FID and GC–MS. Higher sterol concentrations were present in the north-western part of the bay in winter (5.10–23.5 μg L^–1). The high abundance of algal sterols (26–57% of total sterols), the elemental composition (C/N=6–8) and the isotopic signatures (δ¹³C=−21.3‰ to −15.1‰ and δ¹⁵N=+7.3‰ to +11.1‰) suggested the predominance of autochthonous organic matter, as expected for an eutrophic bay, although seasonal variation in phytoplankton activity was observed. Coprostanol concentration (fecal sterol) was at least one order of magnitude higher in the particulate material from fluvial samples (4.65–55.98 μg L^–1) than in the bay waters (<0.33 μg L^–1). This could be ascribed to a combination of factors including efficient particle removal to sediments in the estuarine transition zone, dilution with bay water and bacterial degradation during particle transport in the water column.     

Variability of the subtropical shelf front off eastern South America: Winter 2003 and summer 2004

Hydrographic data collected during surveys carried out in austral winter 2003 and summer 2004 are used to analyze the distributions of temperature (T) and salinity (S) over the continental shelf and slope of eastern South America between 27°S and 39°S. The water mass structure and the characteristics of the transition between subantarctic and subtropical shelf water (STSW), referred to as the subtropical shelf front (STSF), as revealed by the vertical structure of temperature and salinity are discussed. During both surveys, the front intensifies downward and extends southwestward from the near coastal zone at 33°S to the shelf break at 36°S. In austral winter subantarctic shelf water (SASW), derived from the northern Patagonia shelf, forms a vertically coherent cold wedge of low salinity waters that locally separate the outer shelf STSW from the fresher inner shelf Plata Plume Water (PPW) derived from the Río de la Plata. Winter T–S diagrams and cross-shelf T and S distributions indicate that mixtures of PPW and tropical water only occur beyond the northernmost extent of pure SASW, and form STSW and an inverted thermocline characteristic of this region. In summer 2004, dilution of Tropical water (TW) occurs at two distinct levels: a warm near surface layer, associated to PPW–TW mixtures, similar to but significantly warmer than winter STSW, and a colder (T∼16 °C) salinity minimum layer at 40–50 m depth, created by SASW–STSW mixtures across the STSF. In winter, the salinity distribution controls the density structure creating a cross-shore density gradient, which prevents isopycnal mixing across the STSF. Temperature stratification in summer induces a sharp pycnocline providing cross-shelf isopycnal connections across the STSF. Cooling and freshening of the upper layer observed at stations collected along the western edge of the Brazil Current suggest offshore export of shelf waters. Low T and S filaments, evident along the shelf break in the winter data, suggest that submesoscale eddies may enhance the property exchange across the shelf break. These observations suggest that as the subsurface shelf waters converge at the STSF, they flow southward along the front and are expelled offshore, primarily along the front axis.     

Distribution,fluxes and bacterial consumption of total organic carbon in a populated Mediterranean Gulf

Saronikos Gulf (Greece) practically constitutes the sea border of the metropolitan city of Athens and the alongshore outskirts, and it receives the treated wastes of ∼4 million people from a point source that discharges on the sea bottom at ∼65 m water depth. Total organic carbon (TOC) was measured in 477 seawater samples collected in the Saronikos Gulf, during 10 cruises, from August 2001 to May 2004 and analyzed with the High Temperature Catalytic Oxidation method (HTCO). TOC concentrations ranged from 49 to 198 μmol C L⁻¹ in agreement with other Mediterranean coastal waters. The highest TOC concentrations were found in the upper waters (0–75 m), whereas in the deeper parts of the Gulf (between 100 and 400 m) TOC concentrations were kept constantly low (49–70 μmol C L⁻¹). A general pattern towards higher TOC concentrations during summer was also observed. Calculations of non-refractory (labile+semi-labile) organic material based on a one-dimensional (1D) conceptual model showed that it corresponds to 33% of the bulk TOC during summer and to 27% during winter. Bacterial production (BP) was measured at selected stations of ∼70–80 m depth using the [³H] leucine method. Depth integrated BP values varied from 2.8 to 10.9 mmol m⁻² d⁻¹, whereas extraordinary high integrated BP values (126 and 140 mmol m⁻² d⁻¹) were observed at the station over the treated sewage outflow. From the turnover time, τ, of the non-refractory TOC by bacteria it was implied that organic matter in the effluents is extremely labile (2–58 days). Moreover, τ values at the other sites showed that during summer non-refractory organic material resisted bacterial degradation (1–8 months), whereas during early spring it was easily degradable (20–50 days). The balance of TOC fluxes for the Inner Gulf for June and September 2003 showed that the Inner Gulf acts as a net producer of TOC during summer. Our results suggest that the presence of the Athens treated sewage outfall does not contribute to the observed summer accumulation of TOC in the Inner Gulf and other causes such as increased bacteria predation and/or nutrient limitation must be responsible.     

Fine grain sediment transport and deposition in the Patos Lagoon–Cassino beach sedimentary system

Extensive mud deposits superimposed on the predominantly sandy inner continental shelf adjacent to the Patos Lagoon estuary, indicates that the Lagoon is a potential source of fine sediments to the coastal sedimentary system. The lagoon is large and shallow, and the water movement is mainly controlled by wind-driven set-up and set-down. The mean river inflow is around 2000 m³ s⁻¹, although peak flow rates exceeding 20,000 m³ s⁻¹ have been observed during El Niño periods. Though the tidal elevations are small, tidal velocities in the lagoon's inlet can be significant due to the large extension of the backwaters. Moreover, significant exchange flows can be generated between the estuary and coastal area due to barotropic pressure gradients established as a function of wind and freshwater discharge. The predominant net flow is seawards, but opposite near-bed flows due to pronounced vertical salinity stratification can also be observed. The coastal area is characterized by small tidal effects, large scale ocean circulation, wind-induced residual flows and wave-driven currents, where the waves originate from swell or are locally generated.     

Origin and evolution of two contrasting thermal groundwaters (CO2-rich and alkaline) in the Jungwon area,South Korea: Hydrochemical and isotopic evidence

In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20–33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ¹⁸O and δD values (> 1‰ lower in δ¹⁸O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO₂-rich water (P_CO2 = 0.1 to 2 atm) is characterized by lower pH (5.7–6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water (P_CO2 = 10^− 4.1–10^− 4.6 atm) has higher pH (9.1–9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO₂-rich water is influenced by a local supply of deep CO₂ (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca²⁺, Na⁺, Mg²⁺, K⁺, HCO₃⁻ and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water–rock (granite) interaction under the negligible inflow of CO₂. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO₂-rich water resulted from the input of CO₂ in Na–HCO₃ waters and subsequent rock leaching.     

Hydrodynamic accumulation of Karenia off the west coast of Florida

Blooms of the toxic dinoflagellates, Karenia spp. occur nearly annually in the eastern Gulf of Mexico with cell abundances typically >10⁵ cells L⁻¹. Thermal and ocean color satellite imagery shows sea surface temperature patterns indicative of upwelling events and the concentration of chlorophyll at fronts along the west Florida continental shelf. Daily cell counts of Karenia show greater increases in cell concentrations at fronts than can be explained by Karenia's maximum specific growth rate. This is observed in satellite images as up to a 10-fold greater increase in chlorophyll biomass over 1–2 d periods than can be explained by in situ growth. In this study, we propose a model that explains why surface blooms of Karenia may develop even when nutrients on the west Florida shelf are low. In the summer, northward winds produce a net flow east and southeast bringing water and nutrients from the Mississippi River plume onto the west Florida shelf at depths of 20–50 m. This water mass supplies utilizable inorganic and organic forms of nitrogen that promote the growth of Karenia to pre-bloom concentrations in sub-surface waters in the mid-shelf region. In the fall, a change to upwelling favorable winds produces onshore transport. This transport, coupled with the swimming behavior of Karenia, leads to physical accumulation at frontal regions near the coast, resulting in fall blooms. Strong thermal fronts during the winter provide a mechanism for re-intensification of the blooms, if Karenia cells are located north of the fronts. This conceptual model leads to testable hypotheses on bloom development throughout the Gulf of Mexico.     

Matrix bound phosphine in sediments of the yellow sea and its coastal areas

Matrix bound phosphine (MBP), a kind of chemically reduced phosphorus, has received limited attention in prevailing modeling of the phosphorus biogeochemical cycle. MBP has been found to occur in marine sediments. MBP in the sediments of the Yellow Sea and its coastal areas was measured by gas chromatography from 2004 to 2007. MBP levels in surface sediments were 0.19–38.24 ng kg⁻¹ in the shelf of the Yellow Sea, 0.34–17.15 ng kg⁻¹ in the Jiaozhou Bay, 2.11–71.79 ng kg⁻¹ in the Sanggou Bay and 0.28–319.32 ng kg⁻¹ in the rivers around the Jiaozhou Bay. High levels of MBP occurred in the northern and middle areas of the Yellow Sea. Obvious seasonal variation of MBP was observed in surface sediments of the Sanggou Bay, with the highest MBP level occurring in summer and the lowest in winter. MBP in surface sediments of the inner Jiaozhou Bay was higher than those in the outer region. MBP levels increased with depth in the top 5–10 cm sediments of the Jiaozhou Bay and on the intertidal flats. Environmental factors such as type of sediments, temperature, organic matter and human activity were found to affect the concentrations and distribution of MBP in marine sediments.     

Vertical profile,sources, and equivalent toxicity of polycyclic aromatic hydrocarbons in sediment cores from the river mouths of Kaohsiung Harbor,Taiwan

Six sediment cores collected at four contaminated river mouths and two harbor entrances in Kaohsiung Harbor (Taiwan) were analyzed to evaluate the sources and potential toxicity of polycyclic aromatic hydrocarbons (PAHs). PAHs presented the wide variations ranging from 369 ± 656 to 33,772 ± 14,378 ng g⁻¹ at the six sampling sites. The composition of PAHs presented a uniform profile reflecting the importance of atmospheric input from vehicle exhausts or coal combustion in the river mouths. PAHs diagnostic ratios indicated a stronger influence of coal combustion in the Salt River mouth and the prevalence of petroleum combustion and mixed sources in the other rivers and harbor entrances. PAHs toxicity assessment using the mean effect range-median quotient (m-ERM-q: 0.011–1.804), benzo[a]pyrene-toxicity equivalent (TEQ^carc: 22–2819 ng TEQ g⁻¹), and dioxin-toxicity equivalent (TEQ^fish: 37–5129 pg TEQ g⁻¹) identified the Salt River mouth near the industrial area of the harbor as the most affected area.     

Shelf water entrainment by Gulf Stream warm-core rings between 75°W and 50°W during 1978–1999

Previous work concerning Gulf Stream warm-core rings (WCRs) and their associated shelf water entrainments have been based upon single surveys or time series from individual WCRs. To date, estimates of annual shelf water volume entrained into the Slope Sea by WCRs and its interannual variability have not been made. Using a long time series of satellite-derived sea surface temperature (SST) observations of Slope Sea WCRs, we have completed an analysis of 22 years of WCR data (1978–1999) between 75°W and 50°W to understand the interannual variability of WCRs and their role in entraining shelf water. Satellite-derived SST data digitized at Bedford Institute of Oceanography are analyzed using an ellipse-fitting feature model to determine key WCR characteristics including WCR center position, radius and orientation. Key characteristics are then used to compute WCR swirl velocity by finite-differencing WCR orientations (θ) obtained from the feature model time series. Global mean WCR-edge swirl velocity calculated from all observations is 105.72±10.7 km day⁻¹ (122.36±12.4 cm s⁻¹), and global mean WCR radius is 64.8±6.2 km. Primary and derived WCR data are incorporated into a two-dimensional ring entrainment model (RM) using the quasi-geostrophic approximation of the potential vorticity equation. The RM defines ambient water as entrained by a WCR only if the gradient of relative vorticity term (horizontal shear) dominates the potential vorticity. Proximity of a WCR to the position of the shelf-slope front (SSF) is then used to determine whether the ambient water is entrained from the outer continental shelf. WCR-induced shelf entrainment derived from the RM displays considerable spatial variability, with maximum entrainment occurring offshore of Georges Bank, advecting a mean total annual shelf water volume of 7500 km³ year⁻¹ from the region. Estimates of shelf water fluxes display significant interannual variability, which may be in part due to the observed covariance between WCR occurrences and the state of the North Atlantic Oscillation (NAO). Increased (decreased) occurrences of WCRs are evidenced during positive (negative) phases of the NAO. The total mean annual shelf-wide WCR-induced shelf water transport is estimated to be 23,700 km³ year⁻¹ (0.75 Sv), accounting for nearly 25% of the total transport in the Slope Sea region neighboring the outer continental shelf.     

Metal concentrations in sediments from tourist beaches of Miri City,Sarawak, Malaysia (Borneo Island)

Forty-three sediment samples were collected from the beaches of Miri City, Sarawak, Malaysia to identify the enrichment of partially leached trace metals (PLTMs) from six different tourist beaches. The samples were analyzed for PLTMs Fe, Mn, Cr, Co, Cu, Ni, Pb, Sr and Zn. The concentration pattern suggest that the southern side of the study area is enriched with Fe (1821–6097 μg g⁻¹), Mn (11.57–90.22 μg g⁻¹), Cr (51.50–311 μg g⁻¹), Ni (18–51 μg g⁻¹), Pb (8.81–84.05 μg g⁻¹), Sr (25.95–140.49 μg g⁻¹) and Zn (12.46–35.04 μg g⁻¹). Compared to the eco-toxicological values, Cr > Effects range low (ERL), Lowest effect level (LEL), Severe effect level (SEL); Cu > Unpolluted sediments, ERL, LEL; Pb > Unpolluted sediments and Ni > ERL and LEL. Comparative results with other regions indicate that Co, Cr, Cu, Ni and Zn are higher, indicating an external input rather than natural process.     

Spatial and temporal variability of seawater properties,current velocity and SPM concentration off Cassino Beach-Rio Grande-Southern Brazil

Water column profiles and near-bed time series of pressure, current velocity, suspended-particulate matter (SPM) concentration and seawater temperature and salinity were collected during three short cruises carried out in May 2005 in the shoreface and inner shelf area adjacent to Cassino Beach, southern Brazil. The measurements were part of the Cassino Experiment, a project conducted at an open, sandy coastal area known for the occurrence of patches of fairly large amounts of muddy sediments that are sporadically fluidized, transported onshore and eventually stranded on the beach. The study area is close to the Patos Lagoon mouth, being influenced by its water and suspended-sediment discharge. The presence of the Patos Lagoon outflow on the inner shelf was detected in one of the cruises (May 13) through measurements of near-surface salinity: while close to shore salinity was 29.4, a minimum value of 13.8 was measured at ∼10 km from the coast. Four days later, no trace of the plume was detected in the area. Regarding seawater temperature, no large temporal or spatial variability was documented with measured values ranging from 19.3 to 20 °C. Water column currents were prominently to N and NE, except at the outermost station, located ∼42 km from the coast, where NW-directed flows were observed at surface and mid-depth. Maximum near-bed current velocity oscillated between 18 and 42 cm s⁻¹ in the east–west direction and between 14 and 42 cm s⁻¹ in the north–south direction. Near-surface concentration of SPM oscillated between 11 and 99 mg L⁻¹, in general one order of magnitude lower than near-bed values. However, near-bed concentration of SPM showed large spatial variability: the highest value (2200 mg L⁻¹) was yielded by a water sample collected at ∼8 m water depth, at a station located ∼2 km away from the shoreline; two water samples collected 500 m, apart from this station, yielded SPM concentrations of 148 and 205 mg L⁻¹, one order of magnitude lower. Spectral analyses of near-bed current speed and SPM concentration indicate the relevance of oscillations in the low-frequency (<0.05 Hz) range. Detailed sampling of bottom sediment indicated that in May 2005 the mud patch was centered at ∼8.5 m water depth.     

Remote sensing of temporal and spatial patterns of suspended particle size in the Irish Sea in relation to the Kolmogorov microscale

Suspended sediments form an integral part of shelf sea systems, determining light penetration for primary production through turbidity and dispersion of pollutants by adsorption and settling of particles. The settling speed of suspended particles depends on their size and on turbulence. Here a method of determining particle size via remote sensing measurements of ocean colour and brightness has been applied to a set of monthly satellite images of the Irish Sea covering a full year (2006). The suspended sediment concentration was calculated from the ratio between green (555 nm) and red (665 nm) wavelengths in MODIS imagery. Empirical formulae were employed to convert suspended sediment concentrations and irradiance reflectance in the red part of the spectrum into specific scattering by mineral particles and floc size. A geographical pattern was evident in all images with shallow areas with fast currents having high year-average suspended sediment concentrations (7.6 mg l⁻¹), high specific scattering (0.225 m² g⁻¹) and thus small particle sizes (143 μm). The reverse is true for deeper areas with slower currents, e.g. the Gyre southwest of the Isle of Man where turbidity levels are lower (3.3 mg l⁻¹), specific scattering is lower (0.081 m² g⁻¹) and thus particle sizes are larger (595 μm) on average over a year. Temporal signals are also seen over the year in these parameters with minimum seasonal amplitudes (a factor 3.5) in the Turbidity Maximum and maximum seasonal amplitudes twice as large (a factor 7) in the Gyre. In the Gyre heating overcomes mixing in summer and stratification occurs allowing suspended sediments to settle out and flocs to grow large. The size of aggregated flocs is theoretically proportional to the Kolmogorov scale. This scale was calculated using depth, current, and wind speed data and compared to the size of flocculated particles. The proportionality changes through the year, indicating the influence of biological processes in summer in promoting larger flocs.     

Entrainment of fine-grained surface deposits into new ice in the southwestern Kara Sea,Siberian Arctic

The entrainment of bottom deposits (silt and clay) into newly formed ice was investigated in the Amderma/Vaygach flaw lead in the southwestern Kara Sea, Siberian Arctic. Fine-grained bottom deposits and sea ice sediments (SIS) were analyzed by granulometry, scanning electron microscopy and X-ray diffractometry. On average, SIS contain by a factor of four times more silt than the shelf deposits (66.7% vs. 16.3%), and the SIS clay percentage is more than three-fold of the bottom value (31.2% vs. 9.1%). Sand-sized particles are significantly less abundant in SIS compared to bottom sediment (2.1% vs. 74.6%). The preferred entrainment of silt into ice is underpinned by the enhanced silt-to-clay-ratio in SIS compared to bottom deposits. Though silt is preferably entrained into SIS, no evidence was found for preferential ice-entrainment of any silt sub-fraction (coarse, medium or fine). However, sub-angular- and angular-discoidal silt particles are favorably entrained into local sea ice. Clay mineral assemblages in SIS and shelf surface sediments match very well revealing that no individual clay mineral is preferably enriched in SIS or reduced at the bottom. The general textural, compositional and statistical match of fine-grained shelf surface deposits and SIS proves that bottom sediment is the principle source for ice-entrained material in the study area. We propose e.g. wave action and thermohaline convection to take sediment particles upward from the bottom nepheloid layer into the well-mixed 10–40 m deep water column of the Amderma/Vaygach flaw lead, and the turbulent process of suspension freezing to bring sediment particles and frazil crystals into contact, finally leading to the formation of sediment-laden ice. The role of SIS entrainment and export for local/regional shelf erosion and coastal retreat is of minor importance in the SW Kara Sea compared to other circum-Arctic shelf seas. However, the characteristic clay mineral assemblage of local SIS and bottom deposits can help identify the origin of SIS both on regional and Arctic-wide scales.