Estimation of air–sea CO2 fluxes in the Bay of Biscay based on empirical relationships and remotely sensed observations

An empirical algorithm has been developed to compute the sea surface CO₂ fugacity (fCO₂^sw) in the Bay of Biscay from remotely sensed sea surface temperature (SST_RS) and chlorophyll a (chl a_RS) retrieved from AVHRR and SeaWiFS sensors, respectively. Underway fCO₂^sw measurements recorded during 2003 were correlated with SST_RS and chl a_RS data yielding a regression error of 0.1 ± 7.5 µatm (mean ± standard deviation). The spatial and temporal variability of air–sea fCO₂ gradient (ΔfCO₂) and air–sea CO₂ flux (FCO₂) was analyzed using remotely sensed images from September 1997 to December 2004. An average FCO₂ of ? 1.9 ± 0.1 mol m^? 2 yr^? 1 characterized the Bay of Biscay as a CO₂ sink that is suffering a significant long-term decrease of 0.08 ± 0.05 mol m^? 2 yr^? 2 in its capacity to store atmospheric CO₂. The main parameter controlling the long-term variability of the CO₂ uptake from the atmosphere was the air–sea CO₂ transfer velocity (57%), followed by the SST_RS (10%) and the chl a_RS (2%).     

Quantifying erosion rates and stability of bottom sediments at mussel aquaculture sites in Prince Edward Island,Canada

Downward fluxes of organic biodeposits under suspended mussel culture cause benthic impacts such as microbial mat production. Quantifying sediment erosion in these coastal ecosystems is important for understanding how fluxes of organic matter and particulates contribute to benthic–pelagic coupling. Critical shear velocity (u?), erosion rates and particle size distributions of resuspended sediment were measured at two sites; an impacted muddy site with extensive mussel culture (site 1), and a coarser sandier site with less mussel influence (site 2), using a new method for assessing sediment erosion at Tracadie Bay, Prince Edward Island in August 2003. Shear forces were generated by vertically oscillating a perforated disc at controlled frequencies. These forces correspond to shear velocity, using a re-designed and calibrated Particle Erosion Simulator. Undisturbed sediment cores obtained by divers and grab (sub-cored using a Plexiglas? cores) were exposed to shear stress to compare differences between collection methods. Microbial mats were present at site 1 which initially biostabilized sediment against erosion due to ‘armoring’ of the sediment, but onset of erosion was abrupt once these mats failed. Erosion sequences at site 2 (without mat cover) were smoother resulting in less material being eroded. Mean mass of material eroded was 47 and 23 g m^? 2 min^? 1 at sites 1 and 2 respectively. Mat area cover and shear velocity was strongly related. Critical shear velocities varied between 1.70 and 1.77 cm s^? 1, with no obvious differences between location or collection method, so sediments from these two contrasting sites had identical mean critical shear velocities. Significant differences existed in the concentrations of chlorophyll a, colloidal and bulk carbohydrates, between mats and bare sediment from site 1. Particle sizes measured by videography of resuspended sediment at different shear velocities ranged from 100 μm (the minimum diameter capable of being detected by the system), to large mat fragments of 1700 μm for both sites. These results provide evidence of the relevance of using a portable erosion device to indicate how sediment erodability is affected by mussel–microbial relationships.     

Density-dependent effects on seston dynamics and rates of filtering and biodeposition of the suspension-cultured scallop Chlamys farreri in a eutrophic bay (northern China): An experimental study in semi-in situ flow-through systems

Effects of stocking density on seston dynamics and filtering and biodeposition by the suspension-cultured Zhikong scallop Chlamys farreri Jones et Preston in a eutrophic bay (Sishili Bay, northern China), were determined in a 3-month semi-field experiment with continuous flow-through seawater from the bay. Results showed that the presence of the scallops could strongly decrease seston and chlorophyll a concentrations in the water column. Moreover, in a limited water column, increasing scallop density could cause seston depletion due to scallop's filtering and biodeposition process, and impair scallop growth. Both filtration rate and biodeposition rate of C. farreri showed significant negative correlation with their density and positive relationship with seston concentration. Calculation predicts that the daily removal of suspended matter from water column by the scallops in Sishili Bay ecosystem can be as high as 45% of the total suspended matter; and the daily production of biodeposits by the scallops in early summer in farming zone may amount to 7.78 g m^− 2, with daily C, N and P biodeposition rates of 3.06 × 10^− 1, 3.86 × 10^− 2 and 9.80 × 10^− 3 g m^− 2, respectively. The filtering and biodeposition by suspension-cultured scallops could substantially enhance the deposition of total suspended particulate material, suppress accumulation of particulate organic matter in water column, and increase the flux of C, N and P to benthos, strongly enhancing pelagic–benthic coupling. It was suggested that the filtering-biodeposition process by intensively suspension-cultured bivalve filter-feeders could exert strong top-down control on phytoplankton biomass and other suspended particulate material in coastal ecosystems. This study also indicated that commercially suspension-cultured bivalves may simultaneously and potentially aid in mitigating eutrophication pressures on coastal ecosystems subject to anthropogenic N and P loadings, serving as a eutrophic-environment bioremediator. The ecological services (e.g. filtering capacity, top-down control, and benthic–pelagic coupling) functioned by extractive bivalve aquaculture should be emphasized in coastal ecosystems.     

Numerical simulation of flow around a smooth circular cylinder at very high Reynolds numbers

High Reynolds number flows (Re = 1 × 10⁶, 2 × 10⁶ and 3.6 × 10⁶, based on the free stream velocity and cylinder diameter) covering the supercritical to upper-transition flow regimes around a two-dimensional (2D) smooth circular cylinder, have been investigated numerically using 2D Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with a standard high Reynolds number k ? ? turbulence model. The objective of the present study is to evaluate whether the model is applicable for engineering design within these flow regimes. The results are compared with published experimental data and numerical results. Although the k ? ? model is known to yield less accurate predictions of flows with strong anisotropic turbulence, satisfactory results for engineering design purposes are obtained for high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. Re > 10⁶. This is based on the comparison with published experimental data and numerical results.     

Synoptic transects on the distribution of trace elements (Hg,Pb, Cd,Cu, Ni,Zn, Co,Mn, Fe,and Al) in surface waters of the Northern- and Southern East Atlantic

Surface seawater samples were taken in the framework of the GEOTRACES program on “POLARSTERN” expedition ANT XXIII/1 in the Eastern Atlantic in 2005 to study the distribution of the trace elements Hg (mercury), Pb (lead), Cd (cadmium), Cu (copper), Ni (nickel), Zn (zinc), Co (cobalt), Mn (manganese), Fe (iron), and Al (aluminium). With the exception of Hg, results were compared to earlier datasets from 1989 to 1990. The particulate fraction averaged over the transect was calculated to be 49% for Cd, 23% for Mn and 50% for Fe indicating a release of these TEI's (trace elements and their isotopes) from a leachable SPM fraction in the stored and acidified samples.Total Pb concentrations ranged between 5 and 20 pmol kg^? 1 in 2005 with highest values in the ITCZ (intertropical convergence zone). In 1989 Pb concentrations were twice as high in the region of the ITCZ, while by a factor of 10–15 higher values were obtained in the North Atlantic.Total Cd and Co are dominated, by different seasonal upwelling regimes (Equatorial upwelling, Guinea Dome, Angola Dome).Total Cu, Ni, Fe, Mn and Al show nearly identical concentrations in 1990 and 2005. For total manganese and aluminium strong maxima (3–4 nmol kg^? 1 and 55 nmol kg^? 1 respectively) are observed between 23°N and 0°, while the Fe maximum (6–9 nmol kg^? 1) is located at 7°N. Total Hg concentrations ranged between 0.5 and 4.5 pmol kg^? 1.     

Modelling the ecosystem dynamics of the Barents Sea including the marginal ice zone: II. Carbon flux and interannual variability

An upgraded and revised physically–biologically coupled, nested 3D model with 4 km grid size is applied to investigate the seasonal carbon flux and its interannual variability. The model is validated using field data from the years for which the carbon flux was modelled, focussing on its precision in space and time, the adequacy of the validation data, suspended biomass and vertical export. The model appears to reproduce the space and time (± 1 week and 10 nautical miles) distribution of suspended biomass well, but it underestimates vertical export of carbon at depth. The modelled primary production ranges from 79 to 118 g C m^− 2 year^− 1 (average 93 g C m^− 2 year^− 1) between 4 different years with higher variability in the ice-covered Arctic (± 26%) than in the Atlantic (± 7%) section. Meteorological forcing has a strong impact on the vertical stratification of the regions dominated by Atlantic water and this results in significant differences in seasonal variability in primary production. The spatially integrated primary production in the Barents Sea is 42–49% greater during warm years than the production during the coolest and most ice-covered year.     

Mass and heat transports in the NE Barents Sea: Observations and models

The strait between Novaya Zemlya and Frans Josef Land, here called the Barents Sea Exit (BSX) is investigated using data obtained from a current-meter array deployed in 1991–1992, and two numerical models (ROMS and NAME). Combining the observations and models the net volume flux towards the Arctic Ocean was estimated to 2.0 ± 0.6 Sv (1 Sv = 10⁶ m³s^? 1). The observations indicate that about half of this transport consists of dense, Cold Bottom Water, which may penetrate to great depths and contribute to the thermohaline circulation. Both models give quite similar net transport, seasonal variations and spatial current structures, and the discrepancies from the observations were related to the coarse representation of the bottom topography in the models. Also the models indicate that actual deployment did not capture the main in- and outflows through the BSX. A snapshot of the hydrographic structure (CTD section) indicates that both models are good at reproducing the salinity. Nevertheless, they react differently to atmospheric cooling, although the same meteorological forcing was applied. This may be due to the different parameterisation of sea ice and that tides were included in only one of the models (ROMS). Proxies for the heat transport are found to be small at the BSX, and it can not be ruled out that the Barents Sea is a heat sink rather than a heat source for the Arctic Ocean.     

CO2 air–sea disequilibrium and preformed alkalinity in the Pacific and Indian oceans calculated from subsurface layer data

This work estimates new regionalized empirical parameterizations for preformed alkalinity (A_T^o) and the CO₂ air–sea disequilibrium (?C_dis). Both are key terms for the computation of anthropogenic CO₂ in the back-calculation methods. Data from the subsurface layer (75–180 m depth range) covering an area from North to South and from 19°E to 67.5°W (Pacific and Indian oceans) were taken from GLODAP (The Global Ocean Data Analysis Project) database. The subsurface layer is proved as a reliable reference for representing the main characteristics of the different water masses of the oceans. Besides, handing data from the two ocean basins altogether makes the new parameterizations of A_T^o and ?C_dis to be more globally consistent. Nevertheless, each ocean basin, at least in some regions, has different oceanographic characteristics based on its proper dynamical processes and water masses formation. In order to maintain each ocean basin ‘identity’ the whole domain was divided in six different regions (two of them sharing waters from Pacific and Indian oceans) and parameterizations in each region for both terms were obtained. Previously, data were transformed into a grid of 4°lat. × 5°lon. and the results obtained from the parameterizations were visualized and compare with pCO₂ climatologies. From the comparisons with previous ?C_dis estimations good results are obtained showing the reliability and robustness of the new regionalized empiric parameterizations.     

Phytoplankton dynamics related to water mass properties in the Gulf of Gabes: Ecological implications

The spatial distribution of chlorophylls and carotenoids was recorded throughout the Gulf of Gabes (South Ionian Sea) in March 2007, and was related to patterns of the physical structure and the nutrient concentrations.Two distinct water masses were identified based on the temperature and salinity (T–S) analysis: a cool and less salty Modified Atlantic Water (MAW) and a saltier Mediterranean Mixed Water (MMW). There was no significant difference in the mean nitrogen and phosphate concentrations between MMW and MAW, although the silica values were significantly higher in MAW. The Integrated chlorophyll a mean value was about 4 mg m^? 2, with a maximum of 13 mg m^? 2 at MAW stations.Higher Chlorophyll a records in typical MAW stations were mainly due to chlorophytes, which contributed up to 58% of the pigments concentrations in the MAW and about 46% in the MMW. The contribution of chlorophytes to total Chlorophyll a was found to be relatively stable throughout the water column. The contribution of diatoms, which were twofold higher in the MMW than in the MAW, did not exceed 17% of chlorophyll a and was mainly due to subsurface maxima. The chlorophytes, pelagophytes, prymnesiophytes and cryptophytes all together accounted for more than 77% of total chlorophyll a in the MAW and about 67% in the MMW.There were statistically significant differences between MMW and MAW in the pigment contribution of cyanobacteria and pelagophytes. These two taxa accounted for 13% and 24% of chlorophyll a respectively in the MAW and MMW indicating that these differences concerned phytoplankton classes at relatively low contributions to total chlorophyll a.     

Development and lipid storage in Calanus euxinus from the Black and Marmara seas: Variabilities due to habitat conditions

Oil sac volume, gonad size and moulting patterns were investigated in the copepod Calanus euxinus inhabiting deep and shallow zones of the Black Sea and penetrating into the Marmara Sea. In summer the C. euxinus population in deep layers of the Black Sea was dominated by pre-diapause and diapausing postmoult copepodite stage V (CV) with small sexually undifferentiated gonads and mean lipid content of 14.1 ± 6.0% of body volume. The lipid content of deep-living females was 7.2 ± 4.2% of body volume. At the same time, intermoult and premoult CV with enlarged gonads and low lipid content (7.7 ± 5.1% of body volume) and females with oil sac volume of 1.4 ± 1.0% were found at shallow stations. Premoult CV with oil volume of 0.6 ± 0.8% and mature females with little visual evidence of substantial lipid storage dominated in the Marmara Sea. The differences in moulting patterns and oil sac volumes of C. euxinus from deep zones and shallow regions suggest that vertical migrations to the oxygen minimum zone (OMZ) are necessary for formation of large lipid reserves providing high reproductive potential of this species. On the basis of an energy balance model it was shown that under low phytoplankton concentration of about 30 μg C l^− 1 preadults and adults migrating to the OMZ could accumulate lipids (up to 5% of body energy content daily), in contrast to copepods constrained to shallow oxic water columns of the Black Sea and from the Marmara Sea.     

Predicting the chloride penetration of fly ash concrete in seawater

In this study, a model for predicting chloride penetration in fly ash concrete under long-term exposure in a marine environment is developed. The empirical model was based on 2-, 3-, 4-, and 5-year investigation of concretes in a marine site. Regression analysis of the data was carried out by applying Fick's second law of diffusion to generate an empirical formula for predicting chloride concentration in concrete. The model uses the water to binder (W/B) ratio, fly ash content, distance from the concrete surface, and exposure time. Model validation revealed that the predicted chloride concentration levels were within a ±25% error margin (R² = 0.91 ? 0.99) in the samples used to develop the model. The model was also verified using data from previous laboratory and field studies. Most predicted chloride concentration levels were within a ±30% margin of error from field samples. The model also predicted the strong effect of fly ash and W/B ratio on reducing chloride diffusion in concrete. Results clearly indicated that a high volume fly ash replacement (up to 50% by weight of binder) and a low W/B ratio will yield good chloride resistance in concrete under long-term exposure in a marine environment.     

Sediment community biomass and respiration in the Northeast water polynya, Greenland: a numerical simulation of benthic lander and spade core data

Sediment community metabolism (oxygen demand) was measured in the Northeast Water (NEW) polynya off Greenland employing two methods: in situ benthic chambers deployed with a benthic (GOMEX) lander and shipboard laboratory Batch Micro-Incubation Chambers (BMICs) utilizing ‘cores’ recovered from USNEL box cores. The mean benthic respiration rate measured with the lander was 0.057 mM O₂ m⁻² h⁻¹ (n = 5); whereas the mean measured with the BMICs was 0.11 mM O₂ m⁻² h⁻¹ (n = 21; p < 0.01 that the means were the same). In terms of carbon fluxes (14 and 27 mg C m⁻² d⁻¹), these respiration rates represent ca. 5–15% of the average net primary production measured in the euphotic zone in 1992. The biomass of the bacteria, meiofauna and macrofauna were measured at each location to quantify the relationship between total community respiration and total community biomass (mean 1.42 g C m⁻²). Average carbon residence time in the biota, calculated by dividing the biomass by the respiration, was on the order of 50–100 days, which is comparable to relatively oligotrophic continental margins at temperate latitudes.The biomass and respiration data for the aerobic heterotrophic bacteria, the infaunal invertebrates (meiofauna and macrofauna), and the epifaunal megabenthos (two species of brittle stars) are summarized in a ‘steady-state’ solution of a sediment food chain model, in terms of carbon. This carbon budget illustrates the relative importance of the sediment-dwelling invertebrates in the benthic subsystem, compared to the bacteria and the epibenthos, during the summer open-water period in mud-lined troughs at depths of about 300 m. The input needed to drive heterotrophic respiratory processes was within the range of the input of organic matter recorded in moored, time-sequencing sediment traps.A time-dependent numerical simulation of the model was run to investigate the potential responses of the three size groups of benthos to abrupt seasonal pulses of particulate organic matter. The model suggests that there is a time lag in the increase in bottom community biomass and respiration following the POC pulse, and provides hypothetical estimates for the potential carbon storage in the summer (open water), followed by catabolic losses during each ensuing winter (ice covered).This sequence of storage and respiration may contribute to the process of seasonal CO₂ ‘rectification’ (sensu Yager et al., 1995) in some Arctic ecosystems.     

Rigid moorings in shallow water: A wave power application. Part I: Experimental verification of methods

Experimental work carried out at 1:60 scale in a wave flume assessed the pitch motion and anchor loading of 3 articulated tower installations in 50 m water depth while being exposed to north Atlantic storms with H_s of 15.2 m and T_p of 18.4 s. The three installations differ only in that their mass and buoyancy characteristics provide a natural period in pitch at equilibrium of 13 s, 20 s and 34 s respectively. It is verified that the dominant behaviour can be simulated by a relatively simple mathematical model, allowing the critical parameters of peak anchor loads and pitch angles to be calculated and extrapolated to full scale. It is demonstrated from the experimental and simulation results that the mass characteristics of a non surface piercing tower can be used to offset some of the challenges of moving to shallow water. If done correctly, it is possible to keep horizontal anchor loads under control and reduce vortex-induced transverse loading at the expense of increased pitch motions. Overall, the use of articulated tower installations in water depths of 50 m would appear to be technically feasible, even in exposed areas. The limitations on the size of such structures and the consequences of the resulting pitch accelerations and induced anchor loads are the subject of further study. It is proposed that the model verified herein can be used to further assess their potential at delivering viable wave power position mooring systems.     

Primary productivity and export fluxes on the Canadian shelf of the Beaufort Sea: A modelling study

We present a coupled sea ice–ocean-biological (including ice algae) model in the Arctic Ocean. The 1D model was developed and implemented on the Canadian Beaufort Sea shelf to examine the importance of different physical processes in controlling the timing and magnitude of primary production and biogenic particle export over an annual cycle (1987). Our results show that the snow and sea ice cover melt and/or break-up controls the timing of the phytoplankton bloom but primary producers (ice algae and phytoplankton) on the outer shelf are essentially nutrient limited. The total annual primary production (22.7 to 27.7 g-C m^? 2) is thus controlled by nutrient “pre-conditioning” in the previous fall and winter and by the depth of wind mixing that is controlled in part by the supply of fresh water at the end of spring (ice melt or runoff). The spring bloom represents about 40% of the total annual primary production and occurs in a period of the year when sampling is often lacking. Time interpolation of observed values to obtain total annual primary production, as done in many studies, was shown to lead to an underestimation of the actual production. Our simulated ratios of export to primary production vary between 0.42 and 0.44.     

Importance of particle-associated bacterial heterotrophy in a coastal Arctic ecosystem

The large quantities of particles delivered by the Mackenzie River to the coastal Beaufort Sea (Arctic Ocean) have implications for the spatial distribution, composition and productivity of its bacterial communities. Our objectives in this study were: (1) to assess the contribution of particle-associated bacteria (fraction ≥ 3 µm) to total bacterial production and their relationships with changing environmental conditions along a surface water transect; (2) to examine how particle-based heterotrophy changes over the annual cycle (Nov 2003–Aug 2004); and (3) to determine whether particle-associated bacterial assemblages differ in composition from the free-living communities (fraction < 3 µm). Our transect results showed that particle-associated bacteria contributed a variable percentage of leucine-based (BP-Leu) and thymidine-based (BP-TdR) bacterial production, with values up to 98% at the inshore, low salinity stations. The relative contribution of particle-associated bacteria to total BP-Leu was positively correlated with temperature and particulate organic material (POM) concentration. The annual dataset showed low activities of particle-associated bacteria during late fall and most of the winter, and a period of high particle-associated activity in spring and summer, likely related to the seasonal inputs of riverine POM. Results from catalyzed reporter deposition for fluorescence in situ hybridization (CARD-FISH) confirmed the dominance of Bacteria and presence of Archaea (43–84% and 0.2–5.5% of DAPI counts, respectively), which were evenly distributed throughout the Mackenzie Shelf, and not significantly related to environmental variables. Denaturing gradient gel electrophoresis (DGGE) revealed changes in the bacterial community structure among riverine, estuarine and marine stations, with separation according to temperature and salinity. There was evidence of differences between the particle-associated and free-living bacterial assemblages at the estuarine stations with highest POM content. Particle-associated bacteria are an important functional component of this Arctic ecosystem. Under a warmer climate, they are likely to play an increasing role in coastal biogeochemistry and carbon fluxes as a result of permafrost melting and increased particle transport from the tundra to coastal waters.     

The biogeochemical cycling of methane in Ria de Vigo, NW Spain: Sediment processing and sea–air exchange

Methane (CH₄) concentrations were measured in the water column, in sediment porewaters, and in atmospheric air, in the Ría de Vigo, NW Spain, during both the onset (April 2003) and at the end of (September 2004) seasonal upwelling. In addition, CH₄ concentration and stable isotopic signatures (δ¹³CH₄) were measured in porewaters, and sediment methanogenesis and aerobic oxidation of CH₄ were determined in sediment incubations. Surface water column CH₄ (2 m depth) was in the range 3–180 nmol l^− 1 (110–8500% saturation) and followed a generally landward increase but with localised maxima in both the inner and middle Ría. These maxima were consistent with CH₄ inputs from underlying porewaters in which CH₄ concentrations were up to 3 orders of magnitude higher (maximum 350 μmol l^− 1). Surface water CH₄ concentrations were approximately three times higher in September than in April, consistent with a significant benthic CH₄ flux driven by enhanced sediment methanogenesis following the summer productivity maximum. CH₄ and δ¹³CH₄ in sediment porewaters and in incubated sediment slurries (20 °C) revealed significant sediment CH₄ oxidation, with an apparent isotopic fractionation factor (r_c) of  1.004. Using turbulent diffusion models of air–sea exchange we estimate an annual emission of atmospheric CH₄ from the Ría de Vigo of 18–44 × 10⁶ g (1.1–2.7 × 10⁶ mol). This estimate is approximately 1–2 orders of magnitude lower than a previous estimate based on a bubble transport model.     

Residual stress distributions in ship hull specimens

This paper provides an in-depth study of residual stress distributions found in stiffened steel plate structures, such as those typically used in ship hulls. The effect of stiffener spacing on the distribution of residual stress components was studied. The welding heat input was also varied between high and moderate to study the effect of heat input level on residual stress distributions. Four specimens, resembling typical stiffened steel plate structures used in ship hulls were built and tested. Steel plates of 9.5 mm thickness were stiffened by welding L127 × 76 × 9.5 steel angles. The test was completed using the neutron diffraction method. The three normal components of residual stress were obtained in this study. It was found that a lower heat input results in higher tensile residual stress and that there exists a critical stiffener spacing somewhere beyond 250 mm that creates a maximum tensile residual stress value near the welded connection.     

An analysis of the characteristics of chlorophyll in the Sulu Sea

The seasonal and spatial variations of chlorophyll concentrations, Sea Surface Temperature (SST), wind fields and wind-induced Ekman pumping in the Sulu Sea are investigated using a set of new remote sensing measurements from October 1997 to December 2004. The results show the seasonality of chlorophyll, wind fields and SST and reveal the phytoplankton blooming events in the Sulu Sea basin during the northeast monsoon season. In summer, chlorophyll concentrations were relatively low (< 0.2 mg/m³) and distributed uniformly throughout the basin with a narrow belt of high chlorophyll concentrations along the coastal waters, particularly the coasts of Borneo and of the Sulu Archipelago. In winter, chlorophyll concentrations increased (> 0.2 mg/m³) throughout the entire basin, and phytoplankton bloomed southward to the central basin, while chlorophyll concentrations reached high levels (1 mg/m³) in the center of the blooms. One peak was observed during the northeast monsoon season each year. SSTs have significant negative correlations with chlorophyll concentrations; i.e., high and uniformly distributed in summer but lower with an obvious tongue of cold waters southward to the central basin in winter. The seasonal variation of chlorophyll concentrations and SST distribution were associated with the seasonally reversing monsoon. The winter phytoplankton blooming and the tongue of the cold waters were correlated to the vertical upwelling cold and nutrient-rich waters drawn by the northeast wind, with the center of the blooms and the location of cold tongues coinciding with the maximum of the wind speeds and the Ekman pumping velocities.     

Sediment profile imaging (SPI) and micro-electrode technologies in impact assessment studies: Example from two fjords in Southern Chile used for fish farming

Two state-of-the-art techniques were used to assess the impact of organic loading from fish farming in two fjords of Southern Chile, Pillan and Reñihue Fjords. A sediment profile imaging (SPI) camera was deployed and sediment microprofiles (oxygen, H₂S, redox and pH) were measured in undisturbed sediment cores collected using a HAPS corer. Four out of seven stations in Pillan Fjord were found to be severely disturbed: SPI images showed azoic conditions (no apparent Redox Potential Discontinuity layer, no evidence of aerobic life form, presence of an uneaten fish food layer, negative OSI scores). These findings were corroborated by very high oxygen consumption rates (700–1200 mmol m^− 2 day^− 1), H₂S concentrations increasing quickly within the sediment column and redox potential decreasing towards negative values within a few mm down core. Results for Reñihue Fjord were not so straightforward. SPI images indicated that most of the stations (R3 to R7) presented well-mixed conditions (high apparent RPD layers, presence of infauna, burrows, etc.), but oxygen profiles yielded consumption rates of 230 to 490 mmol m^− 2 day^− 1 and organic carbon mineralization of 2.16 to 4.53 g C m^− 2 day^− 1. These latter values were close to the limit of aerobic degradation of organic matter although no visible changes were recorded within the sediment column. In view of our findings, the importance of integrating multidisciplinary methodologies in impact assessment studies was discussed.