Radiogenic Isotope Geology

This report presents the latest version of the Rossby Centre regional atmospheric model, RCA3, with focus on model improvements since the earlier version, RCA2. The main changes in RCA3 relate to t ...

A 140-year simulation of European climate with the new version of the Rossby Centre regional atmospheric climate model (RCA3)

By means of a numerical model of an idealized flat-bottom estuary, the paper studies the hydrodynamic control of the turbidity zone by the combined effect of the salt wedge and tidal movements. The model is of two- dimensional (x, z) finite-difference type with high resolution in time and space. It computes momentum, surface elevation, salinity, suspended particulate matter (SPM), turbulent kinetic energy, and dissipation rate as prognostic state variables. At the seaward boundary a tidal forcing is applied. At the landward boundary a weir is situated where a constant freshwater discharge is prescribed. The initial SPM concentration is horizontally homogeneous. After simulating a few tidal periods the model results exhibit the evolution of a stable SPM peak (the estuarine turbidity maximum or ETM) at the tip of the salt wedge. An inspection of the tidal mean velocity profiles around the ETM shows that this trapping of SPM is due to a residual near-bottom upstream current in the region of the salt...

The Formation of Estuarine Turbidity Maxima Due to Density Effects in the Salt Wedge. A Hydrodynamic Process Study

We tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized-additive model (GAM) analys ...

CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering.

On the dynamics of oxygen, phosphorus and cyanobacteria in the Baltic Sea; A model study

We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km 2 ) in northern Sweden with a detailed analysis of the rivers Lulealven and Kalixalven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing pro- portion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.

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Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land- sea fluxes

. The Swedish Coastal zone Model (SCM) was used at a test site, the Stockholm archipelago, located in the northern part of the central Baltic Sea, to study the retention capacity of the coastal filter on nitrogen (N) and phosphorus (P) loads from land and atmosphere. The efficiency of the coastal filter to permanently retain nutrients determines how much of the local nutrient loads actually reach the open sea. The SCM system is a nutrient–phytoplankton–zooplankton–detritus-type model coupled to a horizontally integrated, physical model in particular suitable for estuaries. In this study the Stockholm Archipelago, consisting of 86 sub-basins, was divided into three sub-areas: the inner, the intermediate and the outer archipelago. An evaluation of model results showed that the modelled freshwater supply agrees well with observations. The nutrient, salinity and temperature dynamics simulated by the SCM are also found to be in good or acceptable agreement with observations. The analysis showed that the Stockholm Archipelago works as a filter for nutrients that enter the coastal zone from land, but the filter efficiency is not effective enough to retain all the supplied nutrients. However, at least 65 and 72 % of the P and N, respectively, are retained during the studied period (1990–2012). A major part of the retention is permanent, which for P means burial. For N, almost 92 % of the permanent retention is represented by benthic denitrification, less than 8 % by burial, while pelagic denitrification is below 1 %. Highest total amounts of P and N are retained in the outer archipelago, where the surface area is largest. The area-specific retention of P and N, however, is highest in the smaller inner archipelago and decreases towards the open sea. A reduction scenario of the land loads of N and P showed that the filter efficiencies of N and P increase and the export of N from the archipelago decreases. About 15 years after the reduction, the export of P changes into an import of P from the open sea to the archipelago.

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Modelling nutrient retention in the coastal zone of an eutrophic sea

Vertical temperature profiles are analysed for the case of cooling of brackish sea water around the temperature of maximum density. Field measurements in the Bay of Bothnia cover a period of 52 days, during which the surface water was cooled from 6°C to 1.5°C. A mathematical model, which is based on the conservation equations for momentum, heat and salt in their one-dimensional forms, is presented. The equation of state is linear with respect to salinity and quadratic with respect to temperature. Turbulent exchange coefficients are calculated with a two-equation model of turbulence. The measured temperature profiles clearly demonstrate the importance of both temperature and salinity gradients in the mixed-layer dynamics. The mathematical model describes these and the general development of the temperature profile in a most satisfactory way. DOI: 10.1111/j.1600-0870.1983.tb00200.x

Measured and numerically-simulated autumn cooling in the Bay of Bothnia

The Swedish Coastal and Ocean Biogeochemical model (SCOBI) is used for the assessment of eutrophication status in the Skagerrak and the Kattegat, and of the following long-term effects on the ecosy ...

/pdf/model-assessment-of-the-predicted-environmental-consequences-3zoeig4liq.pdf

Model assessment of the predicted environmental consequences for OSPAR problem areas following nutrient reductions

Ett gemensamt svensk-finskt havsisexperiment genomfordes under mars 1977. Matningar i atmosfaren, isen och havet utfordes under sex dagar ombord pa det finska forskningsfartyget Aranda som var plac ...

Jörgen Sahlberg

Papers

Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land- sea fluxes

Modelling nutrient retention in the coastal zone of an eutrophic sea

Measured and numerically-simulated autumn cooling in the Bay of Bothnia

Model assessment of the predicted environmental consequences for OSPAR problem areas following nutrient reductions

Some results from a joint Swedish-Finnish sea ice experiment, March, 1977