The geochemistry of iron and manganese in the waters and sediments of Bolstadfjord,S.W. Norway

The distributions of dissolved and solid phase Fe and Mn have been variously determined in vertical profiles through the water column and sediments at three stations in Bolstadfjord, S.W. Norway. Elevated concentrations of dissolved and suspended particulate Fe and Mn are associated with restricted deep waters as a result of redox reactions and with river discharge. The basin sediments are anoxic throughout but because of the greatly restricted circulation, remobilized Fe and Mn appear to remain predominantly trapped within the fjord. Differentiation of Fe and Mn occurs to the extent that Fe sulphide precipitation is ubiquitous in the sediments whereas the entrapment of Mn, probably through Mn carbonate precipitation, is found only in the sediments of the more seaward basin (maximum Mn content of 1·5% by weight).     

Tidally averaged circulation in Puget Sound sub-basins: Comparison of historical data,analytical model,and numerical model

Through extensive field data collection and analysis efforts conducted since the 1950s, researchers have established an understanding of the characteristic features of circulation in Puget Sound. The pattern ranges from the classic fjordal behavior in some basins, with shallow brackish outflow and compensating inflow immediately below, to the typical two-layer flow observed in many partially mixed estuaries with saline inflow at depth. An attempt at reproducing this behavior by fitting an analytical formulation to past data is presented, followed by the application of a three-dimensional circulation and transport numerical model. The analytical treatment helped identify key physical processes and parameters, but quickly reconfirmed that response is complex and would require site-specific parameterization to include effects of sills and interconnected basins. The numerical model of Puget Sound, developed using unstructured-grid finite volume method, allowed resolution of the sub-basin geometric features, including presence of major islands, and site-specific strong advective vertical mixing created by bathymetry and multiple sills. The model was calibrated using available recent short-term oceanographic time series data sets from different parts of the Puget Sound basin. The results are compared against 1) recent velocity and salinity data collected in Puget Sound from 2006 and 2) a composite data set from previously analyzed historical records, mostly from the 1970s. The results highlight the ability of the model to reproduce velocity and salinity profile characteristics, their variations among Puget Sound sub-basins, and tidally averaged circulation. Sensitivity of residual circulation to variations in freshwater inflow and resulting salinity gradient in fjordal sub-basins of Puget Sound is examined.     

Fluxes of organic carbon in a fjord on the west coast of Ireland

The supply of particulate organic carbon (POC) via freshwater influx, and its exchange with the open sea, were estimated for a fjord-like coastal inlet (Killary Harbour, Ireland) during 1981. Biological production and destruction of organic matter within the inlet were also studied. POC levels in rivers feeding the system were correlated with rainfall. C : N ratios suggested an increased proportion of POC of terrestrial origin at stations influenced by freshwater inflow, and throughout the fjord in the non-productive season.A tentative annual carbon budget is presented.     

Temporal variations in the concentration and settling flux of carbon and phytoplankton pigments in a deep fjordlike estuary

The weekly mass flux of C and phytoplankton pigments at five depths in the main basin of Puget Sound, a deep (200 m) fjordlike estuary, was sampled for a year with moored sequentially-sampling sediment traps. Flux measurements were compared with weekly samples of suspended pigments in the euphotic zone and bi-monthly samples of total suspended matter and particulate C throughout the water column at the mooring site.Seasonal changes in the total mass flux at all depths were small; instead, physical (river runoff, bottom resuspension) and biological (phytoplankton blooms) events caused occasional sharp increases on a weekly scale. The dry weight concentration of pigments in the trap samples mirrored the concentration of pigments in the euphotic zone suspended matter, increasing from 0·01% in winter to a maximum of 0·65% in late summer. Bloom-induced changes in the pigment concentration were observed almost simultaneously in the euphotic zone and in the traps to a depth of 160 m, indicating a rapid vertical transfer of surface-originating particles by organic aggregates. In contrast to the strong seasonal signal in the pigment concentration, C concentration varied by only a factor of three during the year.The seasonal trend of C/pigment ratios in the C flux arises from at least two sources: (1) a balance between terrestrial sources of C during the high-runoff winter season and in-situ primary production in spring and summer, and (2) cycling of C through the zooplankton population. Budget calculations suggest that the loss of primary-produced C and pigment from the euphotic zone by settling is 5% regardless of season. On an annual basis, this C flux (16 g m⁻²) is sufficient to support previously measured values of benthic aerobic respiration at the mooring site. To account for other C sinks such as burial, predation and chemical oxidation, however, terrestrial C sources and alternate transport pathways, such as vertical advection and sediment movement down the steep basin walls, are necessary.     

Copper in the resurrection fjord, Alaska

Copper concentrations have been measured in more than 200 samples collected from an Alaskan fjord and continental shelf and slope regions in the northwestern Gulf of Alaska. Concentrations were lowest (2·1 nmol kg⁻¹) at depths of 400–1000 m in the continental slope waters of the Gulf of Alaska. Copper increased systematically with decreasing salinities shoreward to concentrations >30 nmol kg⁻¹ in fjord surface waters during summer months of high freshwater runoff. Copper concentrations increased with depth at an inner fjord station where deep basin waters have restricted circulation, and these data together with surface (<5 cm) pore water copper concentrations (mean=122 nmol kg⁻¹) about an order of magnitude higher than bottom water copper concentrations are indicative of a flux of copper across the sediment-seawater interface. This latter was estimated at 32±12 nmol cm⁻² annually, and represented less than 20% of the annual input to fjord surface water (228–411 nmol cm⁻²) added during summer months. Mass balances in bottom waters indicate a vigorous recycling of copper with a residence time estimated at 21±11 days. Most copper that is remobilized in surface sediments is returned to bottom waters and little (3%) is removed by subsequent diagenetic reaction in the buried sediments. However, an estimate of copper accumulating in anoxic fjord sediments was comparable with copper added to fjord surface waters suggesting that input-removal reactions rather than internal cycling controls copper geochemistry in this estuary.     

Seasonal and spatial changes in the zooplankton community of Kongsfjorden, Svalbard

Seasonal changes in the zooplankton composition of the glacially influenced Kongsfjorden, Svalbard (79°N, 12°E), and its adjacent shelf were studied in 2002. Samples were collected in the spring, summer and autumn in stratified hauls (according to hydrographic characteristics), by means of a 0.180-mm Multi Plankton Sampler. A strong front between the open sea and the fjord waters was observed during the spring, preventing water mass exchange, but was not observed later in the season. The considerable seasonal changes in zooplankton abundance were related to the seasonal variation in hydrographical regime. The total zooplankton abundance during the spring (40–2010 individuals m⁻³) was much lower than in the summer and autumn (410–10 560 individuals m⁻³). The main factors shaping the zooplankton community in the fjord include: the presence of a local front, advection, the flow pattern and the decreasing depth of the basin in the inner fjord. Presumably these factors regulate the gross pattern of zooplankton density and distribution, and override the importance of biological processes. This study increased our understanding of seasonal processes in fjords, particularly with regard to the strong seasonal variability in the Arctic.     

Stratification patterns in Taconite Inlet, Ellesmere Island, N.W.T.

The middle arm of Taconite Inlet shows many features in common with high-Arctic fjords and coastal meromictic lakes. The surface mixed layer is fresh, and a relatively constant 5.5 m deep, indicating a layer of ice of approximately the same thickness blocks communication with the Arctic Ocean. Below the primary halocline to a depth of 85 m, at least partial communication with the Arctic Ocean exists as indicated by the oxygen, salinity and thermal structures. A sill is probably found between 40 and 85 m depth, reducing circulation below it and contributing to the oxycline. For a long but undetermined period prior to the separation of lakes C1, and C2 from the middle arm of Taconite Inlet, the surface water of the inlet was probably strongly brackish to marine suggesting that the entrance to Taconite Inlet was not blocked by an ice shelf at the time of separation. The deep water of these future lakes probably became isolated from the general estuarine circulation and began to develop some of their present limnological features prior to actual separation of the surface waters of the lakes from the inlet.This is the seventh in a series papers published in this issue on the Tactonite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

Hydrocarbons in the sediments of Port Valdez,Alaska: Consequences of five years' permitted discharge

Hydrocarbons have been investigated in the sediments of Port Valdez, Alaska after three to five years of oil terminal operation with a routine daily discharge of 170 kg of petroleum residue in an otherwise undeveloped area. Surficial benthic sediments (0–5 cm) and core segments down to 30 cm have been analyzed. Information about total hydrocarbons, unresolved complex mixture, normal alkanes, pristane, phytane, hopanes and polycyclic aromatic hydrocarbons indicates that petroleum, biogenic hydrocarbons, and combustion-derived aromatic hydrocarbons are present in sediments around the terminal at concentrations up to 218 μg g^?1 dry sediment. The vertical, horizontal and temporal distributions of anthropogenic hydrocarbons indicate that most of the sedimentary hydrocarbon accumulation has occurred within 1 km of the terminal. A simple calculation suggests that less than 3% of the total oil discharged during routine operations of the terminal has entered the sediments of Port Valdez. For comparison sediment hydrocarbon accumulation associated with a nearby small boat harbor was also examined.     

Some features of the dynamic structure of a deep estuary

A boundary layer formulation for the dynamic structure of a deep estuary is developed. Cross-stream averages are used, but the boundary layer structure is shown to depend on the cross-stream geostrophic constraint. A similarity transformation and a weighted residual method are used to derive an approximate solution for the velocity and salinity structure of the upper layer. This solution indicates that, in the central regime of the estuary, outflow extends through the entire halocline. Inflow takes place in a much less stratified lower layer, and mass exchange between the layers is by upwelling. This structure is modified in the outer regime of the estuary, where mixing between the layers develops, and in the inner regime, where a sharp halocline develops and where the dynamics are dominated by river runoff. The implications of the dynamics for the flushing process and for pollutant movement and dispersion are discussed.