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  • 301.
    Funquist, Lennart
    et al.
    SMHI, Research Department, Oceanography.
    Ljungemyr, Patrik
    SMHI, Core Services.
    Validation of HIROMB during 1995-961997Report (Other academic)
  • 302. Danielssen, D S
    et al.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Fonselius, Stig
    SMHI, Research Department, Oceanography.
    Hernroth, L
    Ostrowski, M
    Svendsen, E
    Talpsepp, L
    Oceanographic variability in the Skagerrak and Northern Kattegat, May-June, 19901997In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 54, no 5, p. 753-773Article in journal (Refereed)
    Abstract [en]

    The Skagerrak Experiment (SKAGEX), was a large, international, ICES-supported joint venture, carried out in the Skagerrak-Kattegat area on four different surveys in the period 1990-1991. It involved some 20 institutes and, at times, up to 17 research vessels. The main aim of the Experiment was to identify and quantify the different water masses entering and leaving the Skagerrak area and their variation over lime. It also aimed to investigate the mechanisms that drive the circulation and to study their effects on biological processes. The aim was to be attained mostly through extensive synoptic observations. This paper focuses on the variability in physical, chemical and biological parameters during the first part of SKAGEX, 24 May-20 June 1990. During the first half of the period of investigation, the main outflow from the Skagerrak, represented by the Norwegian Coastal Current, was barotropic with daily mean velocities varying from 10-40 cm s(-1). During the second half a clear baroclinic current component developed, giving rise to near surface velocities of up to 100 cm s(-1). A pronounced feature in the Skagerrak during the study was the counter-clockwise circulation of the Norwegian Coastal Current at times of strong northwesterly winds. During such conditions this surface water reached as far as the Danish coast south of 57 degrees N and upwelling along the Norwegian coast was also found. During northerly winds upwelling also occurred along the Swedish coast. The nutrient-rich Jutland Coastal Water, originating from the German Eight, was never found to reach the inner part of the Skagerrak during this first part of SKAGEX. It was partly blocked or diluted by other water-masses. A large ''ridge'' of nutrient-rich Atlantic water was found in the central Skagerrak throughout the investigation. It is shown that this elongated ''ridge'' was associated with the deepest (>500 m) area of the Skagerrak. Within this area, high subsurface chlorophyll concentrations were always found and, due to the persistence of the supply of nutrients, it is concluded that this phenomenon could be one of the main reasons for the high productivity of the Skagerrak. (C) 1997 International Council for the Exploration of the Sea.

  • 303. Aminot, A
    et al.
    Kirkwood, D
    Carlberg, Stig
    SMHI, Research Department, Oceanography.
    The QUASIMEME laboratory performance studies (1993-1995): Overview of the nutrients section1997In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 35, no 1-6, p. 28-41Article in journal (Refereed)
    Abstract [en]

    The QUASIMEME Project (1993-1996) was established to assist European laboratories to improve the data they produce in marine monitoring programmes. Through laboratory performance Studies (with six-monthly reports), workshops and expert visits the programme was fully interactive. There were five rounds of laboratory performance studies. For the nutrient section, in which about 50 laboratories took part, the reference materials distributed to the participants consisted of standard solutions of nutrients and seawater samples stabilized by autoclaving. The material included low and high concentrations typical of those encountered in coastal seawater; at least two samples with different concentrations were distributed in each round. Robust statistics were used to determine the means and standard deviations for each set of results. For inorganic nutrients, the assessment of the data for bias and precision was based mainly on a Z- and P-scoring system in which targets of +/- 6% were allocated to the high concentrations, likewise +/- 12.5% to the low concentrations. This overview discusses overall performance separately for nitrate plus nitrite, nitrite, ammonia, phosphate, total nitrogen and total phosphorus, and classifies the performance of individual laboratories in each round, while maintaining their anonymity. Performance for nitrate plus nitrite and nitrite improved steadily and these determinands are now fully under control; at the end of the programme, standard deviations (SD) for nitrate plus nitrite were 0.2 mu mol l(-1) at low concentration and 0.6 mu mol l(-1) (4%) at high concentration, and for nitrite they were 0.03 mu mol l(-1) and 0.06 mu mol l(-1) (5%) respectively. Phosphate showed a somewhat stable level of performance with SD of 0.06 mu mol l(-1) and 0.10 mu mol l(-1) (10%) at low and high concentrations respectively, but this could be improved. Ammonia proved the most difficult to determine, and in spite of a substantial improvement at the beginning of the exercise, this determinand is not under control in many laboratories. At low concentrations, ammonia shows a positive bias of 0.2 mu mol l(-1) and a SD of 0.3 mu mol l(-1), while at high concentrations SD reaches 0.5 mu mol l(-1) (20%). For total nitrogen (TN) and total phosphorus (TP), the exercises show that only two thirds of the participants produced consistent data for TN, and less than half of them produced consistent data for TP. (C) 1997 Elsevier Science Ltd. All rights reserved.

  • 304.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Meuller, Lars
    SMHI.
    Nyberg, Leif
    SMHI.
    Interannual, seasonal and regional variations of precipitation and evaporation over the Baltic Sea1997In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 26, no 8, p. 484-492Article in journal (Refereed)
    Abstract [en]

    Precipitation and evaporation rates over the Baltic Sea during the period 1981-1994 have been analyzed. The precipitation rate was based upon available meteorological weather, which were interpolated to grid paints using a two-dimensional objective analysis scheme, The evaporation rate was calculated using an ocean model, in which the Baltic Sea was treated as 13 sub-basins with high vertical resolution. Sea-surface temperatures as well as sea ice were calculated and verified extensively against temperature and ice-chart information, In the model, the latent heat flux was calculated according to a bulk formula parameterization. The evaporation rate was then calculated from the latent heat calculations and reduced by sea ice concentration, assuming that evaporation from sea ice is negligible. The long-term difference between precipitation and evaporation rates (the atmospheric fresh water inflow) is positive, which implies that the atmosphere adds fresh water to the Baltic Sea. For the period 1981 - 1994, the total mean atmospheric freshwater inflow was calculated to be 1986 m(3) s(-1). This is less than the total river runoff, but almost as large as the contribution from the River Neva, and thus an important source in the freshwater balance of the Baltic Sea. For the long time mean, the inclusion of sea ice increased (by reducing evaporation with 8%) the atmospheric freshwater inflow by 26% for the studied period, compared to an artificial case without ice in the Baltic Sea. The precipitation and evaporation over the Baltic Sea show, however, large interannual, seasonal and regional differences.

  • 305. Enoksson, V
    et al.
    Fogelqvist, E
    Fonselius, Stig
    SMHI, Research Department, Oceanography.
    Nitrogen speciation and nitrification potential in the Skagerrak area during the SKAGEX IV experiment1996In: Deep Sea Research Part I: Oceanographic Research Papers, ISSN 0967-0637, E-ISSN 1879-0119, Vol. 43, no 7, p. 1029-1044Article in journal (Refereed)
    Abstract [en]

    Nitrification was studied in relation to the inorganic nitrogen species in the Skagerrak in May 1991 during the SKAGEX IV expedition. The distribution of density, ammonium, nitrite and nitrate are shown for the four north-south sections and, for two of these, the distribution of nitrification potential (NP, i.e. nitrification with excess ammonium during incubation) and oxygen saturation values are also presented. Highly saline and ammonium rich Atlantic/North Sea water was sinking into the Skagerrak along the Danish slope, where it gradually mixed with the ''old'' and relatively stagnant Skagerrak water with high nitrate concentrations but very low ammonium concentrations. The zone of mixing was characterised by high concentrations of nitrite, an intermediate product during the,bacterial oxidation of ammonium to nitrate. The NP rates were in the range 0-60 nmoll(-1) day(-1). Water masses with undetectable or low NP included the upper water layers and water flowing in at depth. Maximum NP rates were found in or near the zone with high nitrite concentrations just below the upper layers and at the border between inflowing water and ''old'' Skagerrak water at depth. It is postulated that nitrification was stimulated in the mixture of inflowing, ammonium rich water and ''old'' Skagerrak water. Copyright (C) 1996 Elsevier Science Ltd.

  • 306. Kirkwood, D S
    et al.
    Aminot, A
    Carlberg, Stig
    SMHI, Research Department, Oceanography.
    The 1994 QUASIMEME laboratory performance study: Nutrients in seawater and standard solutions1996In: Marine Pollution Bulletin, ISSN 0025-326X, E-ISSN 1879-3363, Vol. 32, no 8-9, p. 640-645Article in journal (Refereed)
    Abstract [en]

    The 1994 QUASIMEME (nutrients) Laboratory-Performance Study (LPS) is presented, The year's programme consisted of two periods, December-May and June-November, (These are referred to as Round 2 and Round 3, respectively, the previous 1993 LPS being Round 1.) In each period, participating laboratories were sent two types of sample material, that is seawater samples and a standard solution containing a mixture of nutrient salts, The standard solution required dilution (by participants) and multiple analyses over several weeks in order to assess long-term repeatability, In Round 2, a few laboratories, identified as poor performers in Round 1 (1993), undertook a 'learning programme' in which they received, unknowingly, samples identical to those analysed in Round 1, The other laboratories received samples different from those used in Round 1, In Round 3, all laboratories received the same package of samples, different from those used in Round 1 and Round 2, The results clearly indicate that general all-round improvements in data quality have been achieved. Crown copyright (C) 1996 Published by Elsevier Science Ltd

  • 307.
    Fonselius, Stig
    SMHI, Research Department, Oceanography.
    The upwelling of nutrients in the central Skagerrak1996In: Deep-sea research. Part II, Topical studies in oceanography, ISSN 0967-0645, E-ISSN 1879-0100, Vol. 43, no 1, p. 57-71Article in journal (Refereed)
    Abstract [en]

    Measurements of inorganic nutrients during four expeditions to the Skagerrak, within the SKAGEX programme in 1990 and 1991, form the basis for estimation of the magnitude of potential new primary production caused by upwelling of nutrients in the central part of Skagerrak. Calculations have been made using available transport and upwelling data given in the literature together with the concentrations of nitrogenous nutrients (nitrite, nitrate and ammonia), phosphate and silicate in the lower part of the pycnocline in the upwelling area. The potential new production of organic matter due to upwelling is estimated at 6.15 x 10(6) t C year(-1) based on a vegetative period of 8 months. This corresponds to 190 gC m(-2) year(-1) if distributed over the entire Skagerrak area. A possible contribution to diatom production from the upwelling of silicate is estimated to be 2.09 x 10(6) t C year(-1), which corresponds to 64 gC m(-2) year(-1).

  • 308.
    Mattsson, Johan
    SMHI, Research Department, Oceanography.
    Analysis of the exchange of salt between the Baltic and the Kattegat through the Oresund using a three-layer model1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no C7, p. 16571-16584Article in journal (Refereed)
    Abstract [en]

    The shallowness of the Oresund prevents a continuous inflow of saline Kattegat water to the Baltic. Instead, the salt is exchanged largely by fluctuating barotropic transports. Buffer effects and temporal storage of low-salinity Baltic surface water complicate the exchange. The analysis of salt exchange through the Oresund requires use of a model of the stratification and baroclinically modified exchange processes. In this paper a three-layer model of the Oresund, forced by the exchange with the Kattegat and the Baltic, is formulated and calibrated. Frontal dynamics, necessary to explain the retreat of the uppermost layer, are included. The model is calibrated using genetic algorithms, which provide an efficient and robust optimization method for this kind of model. An analysis of the exchange in view of the model results is presented. The paper also gives estimates of typical mean quantities. For the analyzed period of 11 years (1977-1987) the mean salt outflow rate from the Baltic during outflows is 311,000 kg s(-1) and the mean salt inflow rate to the Baltic during inflows is 500,000 kg s(-1). The net salt outflow from the Baltic is estimated to 19,000 kg s(-1). The mean frontal speed is estimated at 0.25 m s(-1) and the typical required length of an inflow event for high-salinity Kattegat water to reach the Baltic is estimated at 4 days. Further results are also given. In addition, the baroclinic dynamics of the Oresund are discussed.

  • 309.
    Karlson, Bengt
    et al.
    SMHI, Research Department, Oceanography.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Graneli, W
    Sahlsten, Elisabeth
    SMHI, Research Department, Oceanography.
    Kuylenstierna, M
    Subsurface chlorophyll maxima in the Skagerrak - Processes and plankton community structure1996In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 35, no 1-3, p. 139-158Article in journal (Refereed)
    Abstract [en]

    Subsurface chlorophyll maxima are common phenomena in both the coastal and open ocean. The main objective of this study was to clarify possible differences in the structure and function of the plankton community in subsurface chlorophyll maxima and at the surface. Sampling was performed at seven stations in the Skagerrak, northeast Atlantic, during five cruises in May and August 1992 and April, May and August 1993. Subsurface chlorophyll fluorescence maxima (FM) occurred on 25 out of 32 sampling occasions. The FMs were usually situated below the pycnocline and associated with the nutricline. The ratio of chlorophyll a to particulate carbon and the light-saturated primary production were higher for plankton at the FM than at the surface, although assimilation numbers (primary production rate:chlorophyll a) were not different from surface plankton. The light protective pigment diadinoxanthin occurred in higher concentrations relative to chlorophyll a in surface plankton than in FM plankton. Respiration was higher in the FM than at the surface. This was not related to abundance of bacteria or bacterial production since no differences between surface and FM values were detected for these parameters. FM plankton was characterized by high nutrient uptake rates, but in this study there were no significant differences compared to surface plankton. 'New' production was on average 25%, but up to about 50% in the western Skagerrak in spring. The average nitrogen uptake rates were dominated by the regenerated nutrients ammonium and urea, accounting for about 50 and 25%, respectively. The <3 mu m size fraction contributed significantly to concentrations of total chlorophyll a, particulate carbon, and nitrogen as well as to nitrogen uptake. Its contribution was highest when total values were low. Microscopical investigations and analysis of pigments specific to algal groups showed that diatoms dominated in the FMs in spring and that peridinin-containing dinoflagellates dominated in FMs in August. Autotrophic nanoplankton was dominated by the Prymnesiophyceae contributing about 50% of total cell numbers. Colonies of Phaeocystis sp. were abundant along the NW Danish coast in April and May 1993, Autotrophic eukaryotic picoplankton occurred in cell numbers up to about 30 x 10(6) cells . dm(-3) along the Swedish coast. The highest cell numbers of cyanobacteria of the Synechococcus-type, about 100 x 10(6) cells . dm(-3), were found in the central Skagerrak in August and the abundance of Synechococcus was correlated with nitrogen uptake in the <3 mu m size fraction.

  • 310. Sanden, P
    et al.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Long-term trends in Secchi depth in the Baltic Sea1996In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 41, no 2, p. 346-351Article in journal (Refereed)
    Abstract [en]

    Nutrient loads to the Baltic Sea have increased during the last century, and primary production has probably also risen. However, the evidence of such a rise is circumstantial, and most of the available findings concerning primary production cover only brief time periods. A more appropriate type of data in this area is Secchi disk measurements. We present the results of trend tests applied to Secchi depth values recorded during two discrete time periods: 1919-1939 and 1969-1991. We performed a step trend test to compare the data from the two periods and applied a monotonic trend test to the later series. Both tests showed that Secchi depth decreased by similar to 0.05 m yr(-1) during both periods. Calculations of changes in chlorophyll concentrations suggest a yearly increase of similar to 1%. Extending the calculations to represent primary production indicates an increase of slightly <1% yr(-1). These calculations, however, are unreliable due to substantial uncertainty regarding the relationships between Secchi depth and chlorophyll concentration and chlorophyll and primary production.

  • 311.
    Håkansson, Bertil
    et al.
    SMHI, Research Department, Oceanography.
    Alenius, P
    Brydsten, L
    Physical environment in the Gulf of Bothnia1996In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, p. 5-12Article in journal (Refereed)
    Abstract [en]

    The Gulf of Bothnia contains about 29% of the whole water volume of the Baltic Sea. The water exchange between the Baltic proper and the Gulf is good, which results in a water renewal time of about 4 to 5 yrs. The dynamics and thermodynamics of the Gulf of Bothnia are guided by hydrological, meteorological and, partly, topographical factors, such as freshwater supply, wind over sea, sun radiation, sea ice and sill depth between the sub-basins, The water mass is vertically divided into two layers with a halocline at 50 to 60 m depth. The deep water, below 60 m, mainly originates from the upper layer of the Baltic proper and has a salinity of 6-7 psu. In the surface layer, a thermocline develops each summer. This upper well-mixed layer is, on average, 15 m deep. The north to south water transport mainly occurs in this surface layer along the coasts, with a tendency to cyclonic circulation. It is, however, strongly wind-dependent and thus intermittent in time, On a long time scale, pulse-like wind events produce on average an eastbound current drift in the open sea. The river runoff causes a slow southbound current drift of diluted freshwater along the western region of the Bothnian Sea. Distribution and deposition of dissolved and particulate matter occurs with several types of transport mechanisms. Our measurements during 1991 show that in the surface water, substances can be distributed right across the Bothnian Sea in about one to two weeks, but perhaps more normally in about one month, The geographical extension of the accumulation bottoms is most often limited to areas deeper than 40 m. Transport of particulate matter can however also occur below this critical depth especially during periods of strong winds, forcing wind waves of sufficient wave length and amplitude to erode bottom particulate matter.

  • 312.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Nyberg, Leif
    SMHI, Research Department.
    Response of Baltic Sea ice to seasonal, interannual forcing and climate change1996In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, no 5, p. 644-662Article in journal (Refereed)
    Abstract [en]

    The objectives of the present paper are to formulate and explore a coupled sea ice-ocean model and to examine the sensitivity of ice in the Baltic Sea to climate change. The model treats the Baltic Sea as 13 sub-basins with vertical resolution, horizontally coupled by estuarine circulation and vertically coupled to a sea ice model which includes both dynamic and thermodynamic processes. The reducing effect on the barotropic exchange due to sea ice in the entrance area is also added. The model was first verified with data from 3 test periods representing one mild, one normal and one severe ice winter. The maximum seasonal ice extent was then examined on the basis of simulated and observed data for the period 1980-1993. After that, some climate scenarios (both warm and cold) were examined. The seasonal, regional and interannual variations of sea ice were well described by the model, and the thermal response in the Baltic Sea can be realistically simulated applying forcing data from rather few stations. The Baltic Sea system is highly sensitive to climate change, particularly during the winter season, Warming may drastically decrease the number of winters classified as severe, forcing the climate towards more oceanic conditions. On the other hand, cooling will increase the number of severe winters, forcing the climate towards more sub-arctic conditions.

  • 313.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Special issue with papers presented at ''first study conference on BALTEX'' in Visby, Sweden, 28 August 1 September 1995 - Preface1996In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, no 5, p. 607-607Article in journal (Other academic)
  • 314.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Nyberg, Leif
    SMHI, Research Department.
    Lepparanta, M
    On the ice-ocean response to wind forcing1996In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, no 4, p. 593-606Article in journal (Refereed)
    Abstract [en]

    The ice-ocean response to variable winds is analysed based upon two types of models. An analytical ice-ocean model with linear stress laws and forced by periodic winds is first derived. Secondly a numerical, vertically resolved ice-ocean model is introduced. In the numerical model, the ice-water stress law is calculated from a turbulence model and the wind stress is calculated on the basis of a square law formation. By comparing the ice-ocean stress law formulations, it is illustrated that the numerical model predicts an ice-ocean stress law that has a power slightly less than 2 compared to 1 for the analytical model. The numerical prediction is in good accordance with field observations and the slight deviation from 2 is due to wall effects close to the ice-water interface. It is then demonstrated that the ice-ocean response to variable winds could be well simulated by both models, but the analytical model did not capture the wind dependency properly (because of the linear approach). The ice and current factors are amplified at wind frequencies close to inertial (omega = -f) and damped at high positive and negative frequencies. The maximum ice and current factors at a wind frequency equal to the inertial oscillation are shown to be dependent only on the friction coefficients. With the constants applied in the present study, the maximum ice drift and current speed are equal to 7.8% and 5.5% of the wind speed, respectively. These steady state values are however quite unrealistic as they would require a uniformly changing wind direction for many inertial periods.

  • 315.
    Ljungemyr, Patrik
    et al.
    SMHI, Core Services.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Parameterization of lake thermodynamics in a high-resolution weather forecasting model1996In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 48, no 5, p. 608-621Article in journal (Refereed)
    Abstract [en]

    A model for the parameterization of lake temperatures and lake ice thicknesses in atmospheric models is presented. The model is verified independently, and it is also tested within the framework of the High Resolution Limited Area Model(HIRLAM), applied operationally for short range weather forecasting at the Swedish Meteorological and Hydrological Institute (SMHI). The lake model is a slab model based upon energy conservation and treats the lakes as well mixed boxes with depths represented by the mean depths. The model is forced by near surface fluxes calculated from total cloudiness, air temperature, air humidity and low-level winds. A data base, describing 92000 Swedish lakes. provides the model with lake mean depths, areal sizes and locations. When the model is used for parameterization of lake effects in the atmospheric model, all the smaller lakes and the fractions of larger lakes within each horizontal grid square of the atmospheric model are parameterized by four model lakes, representing the lake size distribution. The verification of the lake model is done by comparing it with a more advanced, vertically resolved model, including parameterization of turbulent mixing processes, as well as by comparison with observations. A sensitivity test shows great interannual variations of the ice-covered season, which implies that lake models should be used instead of climate data. The results from an experiment with two-way coupling of the lake model to the atmospheric model are verified by comparing forecasted weather parameters with routine meteorological observations. These results show that the impact of lake effects can reach several degrees C in air temperatures close to the surface.

  • 316.
    Köuts, Tarmo
    et al.
    Estonian Met. And Hyd. Inst. Marine Res..
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Observations of water exchange, currents, sea levels and nutrients in the Gulf of Riga1995Report (Other academic)
  • 317.
    Funquist, Lennart
    et al.
    SMHI, Research Department, Oceanography.
    Kleine, Eckhard
    SMHI.
    Application of the BSH model to Kattegat and Skagerrak1995Report (Other academic)
  • 318.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Nyberg, Leif
    SMHI.
    A coupled ice-ocean model supporting winter navigation in the Baltic Sea: Part 2. Thermodynamics and meteorological coupling1995Report (Other academic)
  • 319. KAHRU, M
    et al.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    RUD, O
    DISTRIBUTIONS OF THE SEA-SURFACE TEMPERATURE FRONTS IN THE BALTIC SEA AS DERIVED FROM SATELLITE IMAGERY1995In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 15, no 6, p. 663-679Article in journal (Refereed)
    Abstract [en]

    A 9-month time series of satellite infrared imagery was used to examine the sea surface temperature (SST) variability in the northern and central Baltic Sea. Objective multi-level edge detection techniques were applied to find sharp SST gradient areas known as fronts. The spatial distribution of frontal frequency was calculated over time periods from a few days to 9 months covering different thermal and wind conditions. The 9-month average frequency that a front is detected in a pixel of 1.1 x 1.1 km is up to 10% in certain areas whereas the median is around 2%. Large scale fronts are aligned to the coast and isobaths, and occur predominantly in areas of straight and uniformly sloping bottom topography. The major frontal areas are along the eastern coast of the Bothnian Sea and along the north-western coast of the Gulf of Finland. Low large-scale frontal frequency is characteristic to areas with highly structured bottom topography. The major mechanism of front generation is coastal upwelling, being complemented by coastal jets, eddies, differential heating and cooling, and water exchange between basins with different water characteristics. Filaments (''squirts'') originating from upwelling areas are shown to be an important mechanism for transporting water and substances over long distances.

  • 320.
    Rahm, Lars
    et al.
    SMHI, Research Department, Oceanography.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    LARSSON, P
    FOGELQVIST, E
    BREMLE, G
    Valderaama, Jorge
    SMHI.
    NUTRIENT AND PERSISTENT POLLUTANT DEPOSITION ON THE BOTHNIAN BAY ICE AND SNOW FIELDS1995In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 84, no 1-2, p. 187-201Article in journal (Refereed)
    Abstract [en]

    A study of atmospheric deposited nutrients and some persistent pollutants has been carried out on the ice and snow fields of the subarctic Bothnian Bay, the northernmost basin of the Baltic Sea. Total amounts of 600, 500 and 400 tons NO3-N, NH4-N and N-org-N, respectively are deposited in the snow while the corresponding amounts for P-tot-P is 40 tons. The corresponding amount for PCB and lindane are 1.0 and 0.2 kg, respectively. The measurements were carried out on the snow-covered ice four to six weeks old. A part of the deposited snow has been incorporated into the snow-ice and an attempt to estimate its mean thickness and its amount of nutrients has been made. The total amounts now reach 1700, 1300 and 1100 tons of NO3-N and NH4-N and N-org-N, respectively in the snow and ice together. The results obtained support the use of land-based stations in estimates of seasonal atmospheric nutrient deposition to the Bothnian Bay. The observed concentrations of chloroorganic compounds correspond to those land-based observations reported from the same latitude in the northern hemisphere and reported in literature.

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