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The Baltic Sea Wave Field: Impacts on the Sediment and Biogeochemistry
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2002 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The wave field in the Baltic Sea has been modelled for a two-year period with the spectral wave model HYPAS. There is a large seasonal variation in the field and a minor annual one, both reflect the wind variation in the area. Since the Baltic Sea is fetch limited, the dominant wind direction is important for the maximum wave heights.

By studying the modelled wave energy density in combination with bottom type maps, the effect of the wave field on the sediment surface is examined. Up to half the bottoms in the Baltic Sea are affected ~25% of the time. A statistical relation between wave energy density and bottom types is found for the Gulf of Riga, but in the rest of the area the sediment maps were to coarse. It is, due to this, not possible to say if the result is valid for the whole area or if it is site specific.

During resuspension events the remineralisation is increased since deposited organic material is reintroduced into the watermass and there exposed to higher levels of oxygen. This process could act as an increased regional source of nitrogen in nutrient budgets and thus influence the conditions for nitrogen fixation and perhaps explain some of the geographical differences in the nitrogen fixation rates.

Place, publisher, year, edition, pages
Tema vatten i natur och samhälle , 2002. , 23 p.
Series
Tema V report (online), ISSN 1652-4268 ; 27
Keyword [en]
Hydraulic engineering, HYPAS; Wave modelling; Significant wave height; Wave energy
Keyword [sv]
Vattenteknik
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:liu:diva-5565ISBN: 91-7373-249-4 (print)OAI: oai:DiVA.org:liu-5565DiVA: diva2:21378
Presentation
2002-01-21, 00:00 (English)
Available from: 2004-02-16 Created: 2004-02-16 Last updated: 2009-03-02
List of papers
1. Variations in the Baltic Sea wave fields
Open this publication in new window or tab >>Variations in the Baltic Sea wave fields
2003 (English)In: Ocean Engineering, ISSN 0029-8018, Vol. 30, no 1, 107-126 p.Article in journal (Refereed) Published
Abstract [en]

The surface waves in the Baltic Sea are hindcast with the spectral wave model HYPAS during a 12-month period. The model results show a strong temporal and spatial variation in the wave field due to the physical dimensions of the different basins and the predominant wind field. The highest waves in the area are found in the outer part of Skagerrak, as well as in the central and southern parts of the Baltic Proper. To get significant waves above 6 m high, strong winds (15–20 m/s) must have been blowing for 6 to 24 h from a favourable direction over a deep area.

Keyword
Wave modelling, HYPAS, Significant wave height, Baltic Sea, Kattegat, Skagerrak
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13765 (URN)10.1016/S0029-8018(01)00103-2 (DOI)
Available from: 2004-02-16 Created: 2004-02-16
2. Bottom type distribution based on wave friction velocity in the Baltic Sea
Open this publication in new window or tab >>Bottom type distribution based on wave friction velocity in the Baltic Sea
2005 (English)In: Continental Shelf Research, ISSN 0278-4343, Vol. 25, no 3, 419-435 p.Article in journal (Refereed) Published
Abstract [en]

Surface waves play an important role for the sediment distribution in the shallow Baltic Sea. This paper presents the large-scale spatio-temporal distribution of wave-induced bottom friction velocity, u*, based on modelled wave data for the years 1999 and 2000. The highest values of u* are found along the eastern coasts of the Baltic Proper and Bothnian Sea—areas characterised by long fetches for the dominant winds. Temporally, the dynamics follow that of the wind climate with higher velocities during winter and lower during summer.

A smooth bottom is assumed for the calculations. To test this assumption, u* is compared to other estimates of u* assuming rough bottoms. The spatio-temporal patterns are similar, although the present approach gives a slight underestimation of u* at areas with coarse grain sizes.

To compare the results, the co-variation between the u* distribution and bottom type distribution from a digitised sediment map is analysed. It shows upon a good agreement. This is also found when comparing critical levels for resuspension found in the literature with the same from modelled u*. In addition, other processes important for bottom stress, such as mesoscale eddies and coastal jets, are discussed.

Keyword
Wave friction velocity; Sediment dynamics; Resuspension; Bottom types; Regional wave modelling; Baltic Sea
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13420 (URN)10.1016/j.csr.2004.09.011 (DOI)
Available from: 2005-11-09 Created: 2005-11-09
3. Nitrogen fixation in the Baltic proper: An empirical study
Open this publication in new window or tab >>Nitrogen fixation in the Baltic proper: An empirical study
2000 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 25, no 3-4, 239-248 p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen as the limiting nutrient for primary production in the eutrophic Baltic proper has been under debate. Based on only a limited number of actual measurements, nitrogen fixation has been assumed to be the only significant internal nitrogen source. It is then assumed that about one fifth of the net nitrogen load to the Baltic proper comes from nitrogen fixation by cyanobacteria. An alternative or additional source is utilisation of dissolved organic nitrogen (DON).

In the present study, we hypothesise that nitrogen fixation is the only internal source for inorganic nitrogen. This was done in order to investigate its potential to maintain net primary production during summer. If inorganic nitrogen is depleted after the spring bloom and if inorganic phosphorus still remains in significant concentrations, then a continuous decrease in phosphorus may be coupled to the net nitrogen fixation rate by cyanobacteria. The estimated phosphorus consumption is adjusted for external and internal inputs. An estimate of the assumed net annual nitrogen fixation based on the proper Redfield ratio in the surface layer down to the seasonal thermocline is calculated for a number of monitoring stations in the Baltic proper. Typical values of nitrogen fixation are in the range 10–130 μmol m−3 day−1. A simple integration over the Baltic proper gives an internal load in the range 30–260×103 ton N year−1. Another result is an east–west gradient in fixation rate that may reflect the nitrogen load.

Keyword
nitrogen fixation, cyanobacteria, Baltic proper, eutrophication
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13423 (URN)10.1016/S0924-7963(00)00018-X (DOI)
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2009-05-29

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Jönsson, Anette

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