Carbon and nitrogen primary productivity in three North Carolina estuaries

Uptake of inorganic carbon and ammonium by the plankton community of three North Carolina estuaries was measured using ¹⁴C and ¹⁵N isotope methods. At 0% light, C appeared to be lost via respiration, and at increasing light levels uptake of inorganic carbon increased linearly, saturated (mean I_k = 358±30 μEin m⁻² s⁻¹), and frequently showed inhibition at the highest light intensities. At 0% light NH₄⁺ uptake was significantly greater than zero and was frequently equivalent to uptake in the light (light independent); at increasing light levels NH₄⁺ uptake saturated (mean I_k = 172±44 μEin m⁻² s⁻¹) and frequently indicated strong inhibition. Light-saturated uptake rates of inorganic carbon and NH₄⁺ were a function of chlorophyll a (r² = 0·7−0·9); average assimilation numbers were 625 nmol CO₂ (μg chl. a)⁻¹ h⁻¹ and 12·9 nmol NH₄⁺ (μg chl. a)⁻¹ h⁻¹ and were positively correlated with temperature (r² = 0·3−0·7). The ratio of dark to light-saturated NH₄⁺ uptake tended to be near 1·0 for large algal populations at low NH₄⁺ concentrations, indicating near light independence of uptake; whereas the ratio was lower for the opposite conditions. These data are interpreted as indicative of nitrogen stress, and it is suggested that uptake of NH₄⁺ deep in the euphotic zone and at night are mechanisms for balancing the C:N of cellular pools. A 24-h study using summed short-term incubations confirmed this; the cumulative C:N of CO₂ and NH₄⁺ uptake during the daylight period was 10–20, whereas over the 24-h period the ratio was 6 due to dark NH₄⁺ uptake. Annual carbon and nitrogen primary productivity were respectively estimated as 24 and 4·0 mol m⁻² year⁻¹ for the South River estuary, 42 and 7·3 mol m⁻² year⁻¹ for the Neuse River estuary, and 9·6 and 1·6 mol m⁻² year⁻¹ for the Newport River estuary.     

Compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 – 0.6 mmol lipid-C m⁻² day⁻¹. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m⁻² day⁻¹ in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 – 0.00003 mmol lipid-C m⁻² day⁻¹. Lipids comprised ≈ 11–23% of C_org in net-plankton, 10–30% in particles exiting the euphotic zone, 2–4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C₁₅ and C₁₇ fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C₃₉ alkenones of marine origin and long-chain C₂₀-C₃₀ fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.     

Non-conservative Nutrient Fluxes from Budgets for the Irish Sea

Budgets for conservative tracers are used to determine the flow through the Irish Sea and combined with available data on nutrient distributions and inputs to estimate non-conservative nutrient fluxes. Steady state salinity and caesium-137 balances yield consistent estimates of the flow through the Irish Sea of Φ≈6×10⁴ m³s⁻¹. Using both tracers together with a mass balance allows the inclusion of separate diffusive flux terms and results in a diffusivity estimate ofK≈450 m²s⁻¹and a reduced flow of Φ≈4×10⁴ m³s⁻¹. These values are, however, sensitive to the gradients of salinity and caesium-137 concentration, which are not well defined by the observations.Following the LOICZ procedures, salinity and mass balances were combined with analogous statements for dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN), in order to assess the non-conservative process rates. With regard to phosphorus it was found that the Irish Sea is close to balance with a slight net uptake of dissolved inorganic phosphorus, but the implied excess of uptake over release is not significant on account of uncertainties in the observations of boundary values and inputs. The DIN budget is subject to comparable uncertainties in the input data but does, however, indicate a significant imbalance with an average rate of denitrification of the order 0·3 mol N m⁻²y⁻¹.The implications of these budget results and their limitations are considered in relation to the application of the budgeting approach to areas with sparse data coverage. While the application of box model disciplines to conservative tracers can lead to satisfactory estimates of advective transport, the extension to non-conservative components requires extensive data to adequately specify the boundary values and input parameters averaged over the seasonal cycle.     

Solubility of calcite in the ocean

The apparent solubility product K′_sp of calcite in seawater was measured as a function of temperature, salinity, and pressure using potentiometric saturometry techniques. The temperature effect was hardly discernible experimentally. The value of K′_sp at 25°C was 4.59·10⁻⁷ mole²/(kg seawater)² at 35‰S, 5.34·10⁻⁷ at 43‰S, and 3.24·10⁻⁷ at 27‰S. The apparent partial molal volume was found to be −34.4 cm³ at 25°C and −42.3 cm³ at 2°C from a linear fit of log(K′_sp ^P/K′_sp ¹). These results were used in conjunction with field data to calculate the degree of saturation in the oceans and showed undersaturation at shallower depths than previously reported.     

The solubility of CaCO3 in seawater at 2°C based upon in-situ sampled pore water composition

Analyses of the concentration product (Ca²⁺) × (CO₃²⁻) in the pore waters of marine sediments have been used to estimate the apparent solubility products of sedimentary calcite (K′_SPc) and aragonite (K′_SPa) in seawater. Regression of the data gives the relation In K′^P_SPc = 1.94 × 10⁻³ δP − 14.59 The 2°C, 1 atm value of K′_SPc is, then, 4.61 × 10⁻⁷ mol² l⁻². The pressure coefficient yields a at 2°C of −43.8 cm³ atm⁻¹. A single station where aragonite is present in the sediments gives a value of K′_SPa = 9.2 × 10⁻⁷ (4°C, 81 atm). The calcite data are very similar to those determined experimentally by Ingle et al. (1973) for K′_SPc at 2°C and 1 atm. The calculated is also indistinguishable from the experimental results of Ingle (1975) if is assumed to be independent of pressure.     

Settleable and Non-Settleable Suspended Sediments in the Ogeechee River Estuary, Georgia, U.S.A.

Suspended particle dynamics were investigated in the Ogeechee River Estuary during neap tide in July 1996. Samples were operationally separated into ‘ truly suspended ’ (settling velocity <0·006 cm s⁻¹) and ‘ settleable ’ (settling velocity >0·006 cm s⁻¹) fractions over the course of a tidal cycle to determine whether these two fractions were comprised of particles with differing biological and chemical characteristics. Total suspended sediment, organic carbon and nitrogen, chlorophyll a and phaeopigment concentrations were measured in each fraction, as well as rates of bacterial hydrolytic enzyme activity [β-1,4-glucosidase (βGase) and β-xylosidase (βXase)]. The majority of the suspended sediment (by weight) was in the truly suspended fraction; all measured parameters were largely associated with this fraction as well. When compared to the settleable material, the truly suspended material was significantly higher in % POC (5·7±0·6 vs. 3·9±1·8), % chlorophyll (0·07±0·02 vs. 0·03±0·01), % phaeopigment (0·030±0·006 vs. 0·018±0·012), and weight-specific maximal uptake rates (V_maxper mg suspended sediment) of both enzymes (1·8±0·4 vs. 0·7± 0·2 nmol mg⁻¹ h⁻¹βGase and 1·1±0·3vs . 0·3±0·2 nmol mg⁻¹ h⁻¹βXase), providing clear evidence for a qualitative distinction between the two fractions. These results are interpreted to mean that the more organic-rich, biologically active material associated with the suspended fraction is likely to have a different fate in this Estuary, as ‘ truly suspended ’ sediments will be readily transported whereas ‘ settleable ’ sediments will settle and be resuspended with each tide. These types of qualitative differences should be incorporated into models of particle dynamics in estuaries.     

Estimation of the leeway drift of small craft

Small craft (<6·4 m) leeway is determined as a function of the wind speed in the range of 5–20 knots (3·6–10·3 m/sec). Leeway is calculated relative to the surface current by measurement of the separation distance of the small craft from a dyed patch of surface water at sea, using time-sequenced aerial photography. Leeway increases linearly with wind speed for small craft equipped with or without a sea anchor in the wind range studied. Leeway for small craft without sea anchor can be calculated from the equation U_L = 0.07 U_W + 0.04 where U_W is the wind speed at 2 m elevation. Leeway for small craft drifted off the be calculated from the equation U_LD = 0·05 U_W − 0·12. The small craft drifted off the downwind direction in about 80% of the experiments. The drift angle is variable and difficult to predict.     

Kinetics of microbially mediated reactions: dissimilatory sulfate reduction in saltmarsh sediments (Sapelo Island, Georgia, USA)

A sediment disk reactor was tested in once flow-through mode to retrieve kinetic parameters for the Monod rate law that describes sulfate reduction. The experimental method was compared with a previously described procedure by the authors where a sediment plug-flow reactor was operated in a recirculation mode. In recirculation mode, accumulation of metabolic byproducts in certain cases may result in negative feedback, thus preventing accurate determination of kinetic information. The method described in this article provides an alternative to the recirculation sediment plug-flow-through reactor technique for retrieving kinetic parameters of microbially mediated reactions in aquatic sediments.For sulfate reduction in a saltmarsh site, a maximum estimate of the half-saturation concentration, K_s, of 204±26 μM and a maximum reaction rate, R_m, of 2846±129 nmol cm_{(wetsediment)}³ d⁻¹ was determined. The K_s value obtained was consistent with the one estimated previously (K_s=240±20 μM) from a different site within the same saltmarsh mud flat using a recirculating reactor. From the R_m value and reduction rates determined using ³⁵SO₄²⁻ incubation experiments, we infer that sulfate reduction is limited in the field. Substrate availability is not the main contributor for the limitation, however. Competition from other microbes, such as iron reducers affects the activity of sulfate reducers in the suboxic to anoxic zones, whereas aerobes compete in the oxic zone. High sulfide concentration in the pore water may also have acted as a toxin to the sulfate reducers in the field.     

Inverse-estuarine Features of the Upper Gulf of California

The Upper Gulf of California is the shallow (depth <30 m), tidal area at the head of the Gulf of California. It is an inverse estuary, due to the high evaporation rate (E1·1 m year⁻¹) and almost nil freshwater input from rainfall and the Colorado River. Historical and recent hydrographic data show that the area is almost vertically well-mixed throughout the year, that the horizontal distribution of properties follows the bathymetry, and that the hydrography has a strong annual modulation. As in other negative estuaries, the year-round salinity increase toward the head causes the density to do likewise, despite the seasonally reversing temperature gradient. The pressure gradient thus formed leads to water-mass formation and gravity currents (speed 0·1 ms⁻¹), both in winter and in summer. In winter, the high salinity water sinks beyond 200 m, while in summer it only reaches a depth of 20–30 m. The gravity currents appear to be modulated by the fortnightly tidal cycle, with events in neap tides. This phenomenon causes the presence, at least during neap tides, of slight stratification (Δσ_t≈−0·2).     

Benzo[a]pyrene-dione-stimulated oxyradical production by microsomes of digestive gland of the common mussel, Mytilus edulis L

The potential of benzo[ a]pyrene (BaP) quinones (diones) to stimulate NAD(P)H-dependent hydroxyl radical (·OH) production (2-keto-4-methiolbutyric acid (KMBA) oxidation) by digestive gland microsomes of M. edulis was studied using iron/EDTA as a promotor of the Haber-Weiss reaction (O₂⁻ + H₂O₂ = ·OH + OH⁻ + O₂). Stimulation of basal rates of KMBA oxidation was observed for all three diones. Stimulation was similar for the 1,6- and 3,6-diones, but much less for the 6,12-dione, and greater for the NADH than the NADPH-dependent reaction, viz. % increases of 78 to 333 (NADH) compared to 0 to 78 (NADPH). Maximal KMBA oxidation was obtained at dione concentrations of 12.5 to 50 μm. Inhibition of KMBA oxidation by Superoxide dismutase and catalase indicated the involvement of respectively Superoxide anion radical (O₂⁻) and hydrogen peroxide (H₂O₂) in 1,6-dione stimulated NADPH-dependent · OH formation. The apparent K_m values of xenobiotic-stimulated KMBA oxidation were lower for BaP-diones than for the model redox cycling quinone menadione (2-methyl-1,4-naphthoquinone), viz. in μm, 0.6 to 14.6 (NADH) and 4.4 to 28.5 (NADPH) compared to 315 to 457 (NADH) and 72 to 103 (NADPH). The results are consistent with metabolism of BaP to diones and resultant enhanced generation of oxyradicals being a potential mechanism of pollutant-mediated toxicity in molluscs.     

Direct measurements of diapycnal mixing in a fjord reach—Puget Sound's Main Basin

In the spring of 1988, time series of microstructure and ADCP current profiles were collected at four locations in the North Main Basin of Puget Sound, Washington. Depth and time averages of diapycnal diffusivity at the four stations (1.8−67.0×10⁻⁴ m² s⁻¹) were one to three decades above typical open-ocean thermocline levels. The buoyancy frequency-squared N² was near open-ocean levels, but unlike the open-ocean where N²S², finescale shear-squared S² was three to six times N² over significant portions of the water column at two of the stations. The time and space mean of all measurements ( ) is close to inferred vertical eddy diffusivity from a primitive equation model for Puget Sound (K_z=3×10⁻³ m² s⁻¹) (J. Geophys. Res. 96 (1991) 16779). Large time and space variability of K_ρ was found, with differences of inter-station, depth–time means over one decade. A simple scaling argument using the observed K_ρ suggests significant exchange of mass between the layers of the subtidal flow over the basin's residence time. Additionally, measurements show that local mixing may be comparable to volume-weighted sill mixing in modifying the Main Basin's stratification. Both are contrary to the “advective reach” simplification of fjord dynamics. The mixing levels were dominated by the passage of a mid-depth, southward-flowing density intrusion and what we interpret as a strongly advected, non-linear internal tide. These mechanisms elevated profile-averaged K_ρ by more than 10 times background levels, with sustained patches of K_ρ≥1×10⁻² m² s⁻¹. Critical 8-m gradient Richardson numbers (Ri₈<0.25) matching regions of overturns (>20 m) and strong turbulence suggest that shear instabilities dominated the turbulence production, though there was support for double-diffusive convection in the warm core of the density intrusion.     

Circulation and mixing of Mediterranean water west of the Iberian Peninsula

The spreading of water of Mediterranean origin west of the Iberian Peninsula was studied with hydrographic data from several recent cruises and current measurements from the BORD-EST programme. The vertical breakdown of the “Mediterranean salt” content reveals the dominant contribution of the so-called lower core of the outflow (60%), and the significant fraction (22%) brought downward to levels below 1500 m by diffusion. Intense salinity maxima in the upper core (18%) are only encountered south of 38°N in the vein flowing northward along the continental slope, and at a few stations in the deep ocean. Apart from the coastally trapped vein, other preferred paths of the water mass are revealed by the horizontal distributions of salinity maximum and Mediterranean Water percentage. One is southward, west of the Gorringe Bank, and two northwestward ones lie around 40°N and west of the Galicia Bank. Year-long velocity measurements in the Tagus Basin show westward mean values of 7 × 10⁻² m s⁻¹ at 1000 m associated with a very intense mesoscale variability. This variability is related to the pronounced dynamical signature of the outflow which favours instability in any branch having detached from the slope current. From a mixing point of view, the strong interleaving activity occurring near Cape St-Vincent is illustrated, but its contribution to the downstream salinity decrease in the coastally trapped vein is weak. Current and meddy detachment play the dominant role, with a scaling estimate of their associated lateral diffusivity of order 500 m² s⁻¹. The statistical distribution of the density ratio parameter, which governs double-diffusion at the base of the Mediterranean Water, was found to be very tight around R_π = 1.3 in the temperature range of 5°C< φ < 8°C. North of 40°N, the presence of a fraction of Labrador Sea Water in the underlying water is shown to decrease that parameter and should favour the formation of salt fingers.     

The distribution and population dynamics of O-group plaice (Pleuronectes platessa L.) on nursery grounds in the Firth of Forth

Midsummer (1 August) population estimates of about 2 million O-group plaice (Pleuronectes platessa L.) were derived for sandy bays around the Firth of Forth in 1979–1980. This is an order of magnitude less than similar estimates made for the Clyde Sea Area in 1973–1974. Autumn population estimates of 0·4–1·0 million fish were comparable to estimates by the Ministry of Agriculture, Fisheries and Food for the area between the Scottish border and Flamborough Head (2·3 million for 1970 and 1973) which represented 4·8% (1973) to 5·3% (1970) of the total number of O-group fish on the English east coast.Largo Bay was the most important nursery area holding 25% of the total population. It is particularly well situated to receive newly metamorphosed plaice carried in water currents along the north side of the Forth from the spawning ground off Fife Ness. Plaice in the Forth are mainly distributed on fine to medium sandy beaches (186–480 μm), the mean number per haul in midsummer (D) being correlated with the median diameter (m.d. in μm) of the low water sediments by the equation: D=−45·7666+0·2327 m.d. (n=11,r=0·68,P<0·02 but>0·01).The shallow inshore water in sandy bays in the outer Firth was well mixed and more marine than estuarine (27·7–35·0‰). The correlation coefficient between fish density and water temperature was low, while that with salinity (S‰) was: D=6·1618+0·2238S (n=23,r=0·62,P<0·005).Regression analysis demonstrated that the relationship between the instantaneous mortality rate (Z) and the initial population density (D_p) was: Z×100=0·7480+0·0546d_p (n=12,r=0·87,P<0·001).The mean mortality rate for the O-group plaice in the Forth nursery areas was 53% month⁻¹.     

Radium isotopes in coastal and open ocean surface waters of the Western North Pacific

Using manganese-impregnated fiber extraction and high-efficiency gamma counting techniques, we measured the distribution of ²²⁸Ra and ²²⁶Ra in surface waters near the coast of Japan and in the western North Pacific. There is no evidence in our data that any significant amount of ²²⁸Ra is added to open ocean surface waters from the coastal waters around Tokyo Bay. High ²²⁸Ra concentrations (> 10 dpm/10³ kg), were observed along the Kuroshio Current as compared to < 2.5 dpm/10³ kg between 10° and 30°N of the central gyre, and hence the major source of ²²⁸Ra in the surface water is likely to be the East Asian continental shelf zones. A simple one-dimensional eddy diffusion and advection model is used to explain the observed decrease of ²²⁸Ra from coast to the open ocean. The model results indicate two mixing regimes across the Kuroshio Current System with apparent eddy diffusion coefficients of K_y = 4 × 10⁵ cm² s⁻¹ at distance y < 200 km from the coast, and K_y = 4 × 10⁷ cm² s⁻¹ at y > 200 km. Along 40°N where an eastward flow of the ‘Kuroshio Extension’ prevails, an advective flow of > 0.1 knot is consistent with the observation of nearly constant ²²⁸Ra along the track.The geographical distribution pattern of ²²⁸Ra is clearly different from that of atmospherically derived ²¹⁰Pb. Thus the ²²⁸Ra in surface water serves as a useful tracer that accompanies fluvially and coastally derived elements during their subsequent lateral transport toward the central gyre.     

Elemental mercury concentrations and formation rates in the Scheldt estuary and the North Sea

Concentrations of Hg⁰ in surface waters and atmosphere of the Scheldt estuary and the North Sea are presented and their relationship with biological processes is discussed. Hg⁰ concentrations in the Scheldt estuary range from 0.1 to 0.38 pmol·l⁻¹ in the winter and from 0.24 to 0.65 pmol·l⁻¹ in the summer and show a positive relationship with phytoplankton pigments. In the North Sea Hg⁰ concentrations range from 0.06 to 0.8 pmol·l⁻¹ and are higher in coastal stations. Transfer velocities across the air–sea interface were calculated using a classical shear turbulence model. Volatilization fluxes of Hg⁰ were calculated for the Scheldt estuary and the North Sea. For the Scheldt estuary the fluxes range from 226–284 pmol·m⁻²·d⁻¹ in winter and 500–701 pmol·m⁻²·d⁻¹ in summer and for the North Sea the fluxes range from 59–1110 pmol·m⁻²·d⁻¹ for an average windspeed of 8.1 m·s⁻¹. These fluxes are comparable to the wet and dry depositional fluxes to the North Sea. Hg⁰ formation rates necessary to balance the volatilization fluxes vary from 0.2 to 4% d⁻¹.     

Relationships between macroalgal biomass and nutrient concentrations in a hypertrophic area of the Venice Lagoon

Macroalgae biomass and concentrations of nitrogen, phosphorus and chlorophyll a were determined weekly or biweekly in water and sediments, during the spring-summer of 1985 in a hypertrophic area of the lagoon of Venice. Remarkable biomass production (up to 286 g m⁻² day⁻¹, wet weight), was interrupted during three periods of anoxia, when macroalgal decomposition (rate: up to 1000 g m⁻² day⁻¹) released extraordinary amounts of nutrients. Depending on the macroalgae distribution in the water column, the nutrients released in water varied from 3·3 to 19·1 μg-at litre⁻¹ for total inorganic nitrogen and from 1·8 to 2·7 μg-at litre⁻¹ for reactive phosphorus. Most nutrients, however, accumulated in the surficial sediment (up to 0·640 and to 3·06 mg g⁻¹ for P and N respectively) redoubling the amounts already stored under aerobic conditions, Phytoplankton, systematically below 5 mg m⁻³ as Chl. a, sharply increased up to 100 mg m⁻³ only after the release of nutrients in water by anaerobic macroalgal decomposition. During the algal growth periods, the N:P atomic ratio in water decreased to 0·7, suggesting that nitrogen is a growth-limiting factor. This ratio for surficial sediment was between 6·6 and 13·1, similar to that of macroalgae (8·6–12·0).     

Seasonal and interannual variability of the air–sea CO2 flux in the Atlantic sector of the Barents Sea

The seasonal and interannual variability of the air–sea CO₂ flux (F) in the Atlantic sector of the Barents Sea have been investigated. Data for seawater fugacity of CO₂ (fCO₂^sw) acquired during five cruises in the region were used to identify and validate an empirical procedure to compute fCO₂^sw from phosphate (PO₄), seawater temperature (T), and salinity (S). This procedure was then applied to time series data of T, S, and PO₄ collected in the Barents Sea Opening during the period 1990–1999, and the resulting fCO₂^sw estimates were combined with data for the atmospheric mole fraction of CO₂, sea level pressure, and wind speed to evaluate F.The results show that the Atlantic sector of the Barents Sea is an annual sink of atmospheric CO₂. The monthly mean uptake increases nearly monotonically from 0.101 mol C m^− 2 in midwinter to 0.656 mol C m^− 2 in midfall before it gradually decreases to the winter value. Interannual variability in the monthly mean flux was evaluated for the winter, summer, and fall seasons and was found to be ± 0.071 mol C m^− 2 month^− 1. The variability is controlled mainly through combined variation of fCO₂^sw and wind speed. The annual mean uptake of atmospheric CO₂ in the region was estimated to 4.27 ± 0.68 mol C m^− 2.     

Short-term variability of fCO2 in seawater and air–sea CO2 fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

Coastal upwelling systems are regions with highly variable physical processes and very high rates of primary production and very little is known about the effect of these factors on the short-term variations of CO₂ fugacity in seawater (fCO₂^w). This paper presents the effect of short-term variability (<1 week) of upwelling–downwelling events on CO₂ fugacity in seawater (fCO₂^w), oxygen, temperature and salinity fields in the Ría de Vigo (a coastal upwelling ecosystem). The magnitude of fCO₂^w values is physically and biologically modulated and ranges from 285 μatm in July to 615 μatm in October. There is a sharp gradient in fCO₂^w between the inner and the outer zone of the Ría during almost all the sampling dates, with a landward increase in fCO₂^w.CO₂ fluxes calculated from local wind speed and air–sea fCO₂ differences indicate that the inner zone is a sink for atmospheric CO₂ in December only (−0.30 mmol m⁻² day⁻¹). The middle zone absorbs CO₂ in December and July (−0.05 and −0.27 mmol·m⁻² day⁻¹, respectively). The oceanic zone only emits CO₂ in October (0.36 mmol·m⁻² day⁻¹) and absorbs at the highest rate in December (−1.53 mmol·m⁻² day⁻¹).     

Benthic microalgal biomass in sediments of Onslow Bay, North Carolina

Sediment samples were collected at stations along cross-shelf transects in Onslow Bay, North Carolina, during two cruises in 1984 and 1985. Station depths ranged from 11 to 285 m. Sediment chlorophyll a concentrations ranged from 0·06 to 1·87 μg g⁻¹ sediment (mean, 0·55), or 2·6–62·0 mg m². Areal sediment chlorophyll a exceeded water column chlorophyll a a at 16 of 17 stations, especially at inshore and mid-shelf stations. Sediment ATP concentrations ranged from 0 to 0·67 μg g⁻¹ sediment (mean, 0·28). Values for both biomass indicators were lowest in the depth range including the shelf break (50–99 m). Organic carbon contents of the sediments were uniformly low across the shelf, averaging 0·159% by weight. Photography of the sediments revealed extensive patches of microalgae on the sediment surface.Our data suggest that viable benthic microalgae occur across the North Carolina continental shelf. The distribution of benthic macroflora on the North Carolina shelf indicates that sufficient light and nutrients are available to support primary production out to the shelf break. Frequent storm-induced perturbations do not favour settling of phytoplankton, an alternative explanation for the presence of microalgal pigments in the sediments. Therefore, we propose that a distinct, productive benthic microflora exists across the North Carolina continental shelf.