Seabed geodiversity comprises abiotic seabed structures and functions that form valuable natural resources, foundation for benthic habitats and marine ecosystems, and requires knowledge based, sustainable management. Geomorphological mapping involves delineation of surface features based on form, material composition and formative processes. We present an approach that applies methods of scale analysis and geomorphometric classification to characterize seabed morphology and interpretation of geomorphic units in a dynamic and complex marine meander bend. Seabed morphology was delineated using the morphometry as template sup-ported by the DEM and associated surface derivatives. The seabed morphology served as input to an interpre-tation of geomorphic units applying a fluvial classification scheme in channelized marine settings. We demonstrate the potential of using a (semi-) automated morphometric classification scheme to support the characterization of high-resolution seabed morphology based on descriptive definitions and the potential of translating a fluvial classification scheme in channelized marine settings.

Internal hydraulic control, which occurs when stratified water masses are forced through an abrupt constriction, plays an enormous role in nature on both large and regional scales with respect to dynamics, circulation, and water mass formation. Despite a growing literature on this subject surprisingly few direct observations have been made that conclusively show the existence of and the circumstances related to internal hydraulic control in nature. In this study we present observations from the Little Belt, Denmark, one of three narrow straits connecting the Baltic Sea and the North Sea. The observations (comprised primarily of along-strait, detailed transects of salinity and temperature; continuous observations of flow velocity, salinity, and temperature at a permanent station; and numerous vertical profiles of salinity, temperature, fluorescence, and flow velocity in various locations) show that internal hydraulic control is a frequently occurring phenomenon in the Little Belt. The observations, which are limited to south-going flows of approximately twolayered water masses, show that internal hydraulic control may take either of two configurations, i.e. the lower or the upper layer being the active, accelerating one. This is connected to the depth of the pycnocline on the upstream side and the topography, which is both deepening and contracting toward the narrow part of the Little Belt. The existence of two possible flow configurations is known from theoretical and laboratory studies, but we believe that this has never been observed in nature and reported before. The water masses formed by the intense mixing, which is tightly connected with the presence of control, may be found far downstream of the point of control. The observations show that these particular water masses are associated with chlorophyll concentrations that are considerably higher than in adjacent water masses, showing that control has a considerable influence on the primary production and hence the ecosystem in the area.

Previous studies have demonstrated that patches of eel larvae are found in the frontal region of the Subtropical Convergence Zone (STCZ), but to date no clear evidence of why this region might confer advantage to the larvae has been presented. This study demonstrates that there may be localized patches within a frontal region in the STCZ in the Sargasso Sea that experience elevated vertical mixing and an associated vertical flux of nutrients. This localized vertical mixing was suggested by a group of stations within the frontal region that exhibited a greater similarity (Jaccard index) between the diatom communities at 10 m and > 100 m (in the deep chlorophyll maximum, DCM) than in other parts of the frontal region. Thorpe displacements supported the hypothesis of elevated mixing intensities around these stations, as did vertical mixing rates inferred from stratification and vertical current shear calculated from acoustic Doppler current profiler (ADCP) measurements. Combining these mixing estimates with vertical nutrient gradients suggests that nutrient fluxes to the euphotic zone at these mixing sites may be an order of magnitude greater than elsewhere in the frontal region. This mixing may influence the plankton food web, as indicated by elevated values/concentrations of (1) primary production, (2) variable fluorescence (F-v/F-m) and (3) total seston. In addition, the fraction of the total biomass of both copepods and nauplii found closest to the DCM in the frontal region correlated with the stratification (Brunt-V is l frequency), with the greatest fractions found below 75 m at the most weakly stratified stations. While this study cannot directly link these observations to eel larvae ecology, Munk et al. (2010; Proc R Soc B 277: 3593-3599) reported that eel larvae were most abundant at locations where we found evidence for elevated vertical mixing.

4 years long time-series of primary production, Chl-a, salinity, oxygen, and Secchi depth sampled weekly or bi-weekly along a transect in the narrow (similar to 1 km) Little Belt and Little Belt region are analysed. Little Belt (LB) is one of the three Danish straits that connect the Baltic Sea and the North Sea. The time-series were supplemented with Scan Fish transects - a towed CTD, ADCP measurements, and nutrient data. There is a significant maximum in primary production (mg C m(-2) day(-1)) in central LB. which is 30% higher than outside the LB region. Chl-a concentrations are 30% higher in central LB where Secchi depth reaches a minimum. Stratification showed a clear minimum in central LB where extended mixing prevails whereas strong stratification occurred in northern and southern LB. It is shown that mixed conditions in central LB were related to hydraulic control and super-critical flow conditions, as current derived energy for the mixing by comparison was too low. Nutrient (NO2+NO3) concentrations remained high (similar to 5 mu M) in the bottom layer following the spring bloom. It is shown that there is a more or less continuous inflow of nutrient rich bottom water into central LB, which through the strong mixing sustains the high primary production of organic material. The frequency of the hydraulic control governed mixing is presumably high and with a tidal frequency. It was estimated that the 30% higher primary production equalled an annual export out of little Belt of 142 tons Chl-a or about 4261 tons C that might add to the observed oxygen depletion in the area. (C) 2008 Elsevier B.V. All rights reserved.

The Young Sound/Tyrolerfjord system is a 90 km long and 2–7 km wide sill fjord in northeast Greenland, with a mean depth of 100 m. Observations of the bottom topography are presented from different sections of the fjord system, which has a total volume of 40 km3 and a surface area of 390 km2. Hydrographic observations from the summer period show the large influence from the freshwater discharge on the mixed layer depth in the fjord, which, during summer, is less than 5 m, with surface salinity increasing from values below 10 in the inner part of Young Sound to about 30 above the sill in the outer part of the fjord. The deep and intermediate water in the fjord is characterized by a temperature of -1.7 °C and a salinity of 33.1, corresponding to σt < 26.5. The maximum tidal amplitude is 0.8 m and 0.4 m during flood and neap tide, respectively, and is dominated by the lunar semi-diurnal M2 tidal constituent. New model simulations show the evolution of the mixed layer during the summer season. A sensitivity study based on this model is presented, showing that the mixed layer thickness will decrease by about 20% if the runoff is increased by a factor of two, and the implications for the hydrographic conditions in relation to a global warming scenario are discussed.

Inputs of dissolved carbon, nitrogen, and phosphorus were assessed for an estuary and its catchment (Horsens, Denmark). Seasonal patterns in the concentrations of DOM in the freshwater supply to the estuary differed depending on the soil and drainage characteristics of the area. In streams draining more natural areas the, patterns observed were largely driven by seasonal temperature fluctuations. The material exported from agricultural areas was more variable and largely controlled by precipitation events. Positive exponential relationships were found between the nitrogen and phosphorus loading, and the percentage of catchment area used for agriculture. Colored DOM (CDOM) loading measurements were found to be a good predictor of dissolved organic carbon (DOC) loading across the different subcatchments, offering a rapid and inexpensive alternative of operationally monitoring DOC export. For all the dissolved nutrient inputs to the estuary, dissolved inorganic nitrogen (DIN) and dissolved organic phosphorus dominated the loadings. Although 81% of the nitrogen annually supplied to the estuary was DIN, 83% of the nitrogen exported from the estuary was dissolved organic nitrogen (DON). Results show that increasing the area of the catchment covered by forest and natural pastures would have a positive effect on the trophic status of the estuary, leading to a considerable decrease in the phosphorus loading and a shift in the nitrogen loading from DIN to DON. Such a change in land use would also increase the export of DOC and CDOM to the estuary having the potential to increase oxygen consumption and reduce the photic depth.

Bottom-mounted acoustic Doppler current profiler measurements indicate that the net transport of water (844 m(3) s(-1)) in the Little Belt makes up only 6% of the total transport between the Baltic Sea and the North Sea. This is a smaller percentage than the 9% commonly found in the literature. Owing to barotropic and tidal currents the gross transport is 5 times larger. The net transport is directed towards the North Sea mainly in the top 32 m of the water column but towards the Baltic Sea it occurs in the lower 5 m of the water column. The resulting transport of phosphorus is strongly affected by vertical mixing in an area of hydraulic control in the narrow part of the Little Belt. Comparisons of phosphorus profiles in stratified waters and in the mixing area indicate a yearly entrainment of 15 tonnes P from the bottom water to the surface layer. This vertical transport of P forms part of an internal loop in the general transport between the Baltic Sea and the North Sea. Compared to the transport observed 15-16 years ago, the present net phosphorus transport of 163 tonnes yr(-1) from the Baltic Sea through the Little Belt is substantially lower.

A combined inflow and intrusion event was studied in the Little Belt region in the southwest Kattegat during autumn 1999. A persistent period of outflow from the Baltic Sea towards the North Sea was replaced by a strong southward flow in the opposite direction. This reverse of flow direction was related to a change in dominant wind direction and prevailed for about 14 days as demonstrated by current measurements. The study is based on CTD-casts at seven stations, ADCP current data, water sampling for nutrient analyses ((NH3+NH4), (NO2+NO3), PO4 and SiO2), and phytoplankton species composition. The reversal caused a considerable increase in bottom water salinity reaching up to 10 at several stations. The inflow water reached into a region of strong mixing where surface and bottom water became nearly fully mixed in the Little Belt constriction where high current speeds prevail. An intrusion of mixed water developed when current again turned into a flow out of the Little Belt and the intrusion was clearly recognised as a band of high fluorescence. The increase in fluorescence was related to a strong bloom of the potential toxic diatom Pseudo-nitzschia pseudodelicatissima. Cell concentrations in the intrusion reached up to 3249 cells ml−1. Nutrient concentrations were consistently higher in the inflow bottom water as compared to surface concentrations. The bloom was supposedly fuelled by the mixing of nutrient rich bottom water into the photic zone. The occurrence and frequency of these intrusion events are discussed in relation to general hydrographical conditions in the region, as well as the intrusions contribution to the primary production. A conceptual model for the development of the intrusion is proposed.

This paper presents data on physical conditions and carbon transport in a typical northeast Greenland fjord along with predictions of expected changes in the area due to climate change. The fjord has an average depth of 100 m; the maximum depth is 360 m, and a sill at a depth of 45 m is found at its entrance. Sea ice covers the fjord from early October to late July. The freshwater input to the fjord, occurring from June to September, is 1063x10(6) m(3) from the catchment area (3109 km(2)) and 440x10(6) m(3) from melting of sea ice. During the ice-free period this buoyancy input and mixing by wind and tides results in an estuarine circulation in which lighter low-salinity water is moved seaward above denser water from the Greenland Sea. The tidal amplitude is 0.8 to 1.5 m, and the transport of tides from the outer parts of the fjord to the inner parts is delayed less than 15 min due to low friction in the fjord system. During the ice-free period, a net carbon input of 15-50 t C d(-1) occurs in the outer region of the fjord due to transport from land and the adjacent Greenland Sea. A regional atmosphere-ocean model predicts a temperature increase of 6-8degreesC at the end of this century (2071-2100) that will lead to increase in freshwater runoff, thinning of the sea ice, and an increase in ice-free conditions from 2.5 mo to 4.7-5.3 mo in Young Sound. The increased freshwater input will greatly enhance the estuarine circulation and nutrient input to the fjord and is expected to increase biological productivity.

Upwelling of cold. saline, and nutrient rich water was observed in late September 1999 along an east-west transect in the SW Kattegat. The Kattegat forms part of the transitional zone between the high saline North Sea and the low saline Baltic Sea. The upwelling occurred after an extended period of northward flow and eastern winds in the Kattegat, that changed into a southward flow as wind ceased. The upwelling was the result of a combination of high current speeds and bottom topography whereby the high-speed inflow water was forced towards the surface at the slope. Nutrient data show that the upwelling brought nutrient rich bottom water to the light exposed surface and a related strong (1943.5 ml(-1)) bloom of Pseudo-nitzschia pseudodelicatissima was observed. Surface (1.0 m) chlorophyll-a values increased from 3.7 to 10.0 mug l(-1) during upwelling. A frontal structure developed during the upwelling with raised fluorescence values at the front related to convergence. The present upwelling front was only indirectly related to the wind conditions and the front propagated off shore as compared to other upwelling fronts. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/CNRS/IRD. All rights reserved.

Geografisk Tidsskrift, Danish Journal of Geography 97: 1–10, 1997. The nutrient transport through southwestern Kattegat was predicted for a 4 year period using the numerical, hydrodynamic model “MIKE12”. Model results were validated through direct measurements of nutrient concentrations in the study area, and through measurements of total-P and total-N deposition and resuspension rates. The local terrestrial supply of nutrients makes up only 2–5% of the total transport through the area, which was dominated by fluxes over Little Belt and Great Belt boundaries to the study area. A mass balance for 1990 showed that ∼30% of the external N load and ∼100% of the external P load was deposited in the sediment. This is in reasonable agreement with field measurements of yearly net deposition rates in the study area. Resuspension rates in the area were however much higher (on average 17 times) than net deposition rates. Two scenarios were simulated for 1990, one with the actual local load of external nutrients and one with a local load reduction according to the national “Action Plan for the Aquatic Environment”. A comparison between the two scenarios showed that after reduction, nutrient concentrations dropped significantly (same magnitude as load reduction) in the inner parts of fiords close to the nutrient sources. In the open water parts of the study area the resulting decrease in nutrient concentrations (15% for N and 2–5% for P) was mostly manifested in the spring after high fresh water discharges.

Sixty three percent of the nitrogen (total transported 2041 × 103 kg y−1) and 17% of the phosphorus (total 159 × 103 kg y−1) supplied from terrestrial sources to Vejle Fjord during the period September 1988 to October 1989 is exported to the Kattegat. The sediment nutrient concentrations in the estuary are mainly governed by hydrography and resuspension. The general wind-induced circulation consists of outgoing currents along the southern side and ingoing currents along the northern side of the estuary. The sediments in shallow water on the southern side had higher concentrations of nutrients.