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Bottom type distribution based on wave friction velocity in the Baltic Sea
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
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.

Place, publisher, year, edition, pages
2005. Vol. 25, no 3, 419-435 p.
Keyword [en]
Wave friction velocity; Sediment dynamics; Resuspension; Bottom types; Regional wave modelling; Baltic Sea
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-13420DOI: 10.1016/j.csr.2004.09.011OAI: oai:DiVA.org:liu-13420DiVA: diva2:20695
Available from: 2005-11-09 Created: 2005-11-09
In thesis
1. Model Studies of Surface Waves and Sediment Resuspension in the Baltic Sea
Open this publication in new window or tab >>Model Studies of Surface Waves and Sediment Resuspension in the Baltic Sea
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave heights and periods of surface waves in the Baltic Sea have been modelled for a two-year period (1999-2000) with the wave model Hypas on an 11x11-km grid scale. There is a clear seasonal variation with higher waves during winter and lower during summer. This is mainly a reflection of the wind climate in the area where the winters are windier than the summers. The largest waves are found in the Skagerrak and over the deeper, eastern areas in the Baltic Proper.

In the Baltic Sea, the surface waves influence the bottom sediment by initiating resuspension down to 80 m depths. This process is dependent not only on the waves but also on the varying grain size diameters. Fine and medium sand resuspend more often than other sediment types, and these sediments cover together about 25% of the Baltic Proper area. On average sediment is here resuspended 4-5 times per month with a duration for each event of 22 hours. The highest resuspension frequencies are found on the eastern and southern side of the Baltic Proper.

During resuspension sediment grains are lifted up into the water mass and matters earlier bound in the sediment can be released. This may stimulate both production and degradation of organic matter.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2005. 49 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 332
Keyword
Surface waves, Wave model, Wave friction velocity, Resuspension, Sediment dynamics, Nitrogen fixation, Baltic Sea, Havsvågor, Östersjön, Oceanografi, Sediment
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-4680 (URN)91-85299-94-4 (ISBN)
Public defence
2005-09-23, Elysion, Hus T, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2014-09-22Bibliographically approved
2. The Baltic Sea Wave Field: Impacts on the Sediment and Biogeochemistry
Open this publication in new window or tab >>The Baltic Sea Wave Field: Impacts on the Sediment and Biogeochemistry
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
Hydraulic engineering, HYPAS; Wave modelling; Significant wave height; Wave energy, Vattenteknik
National Category
Water Engineering
Identifiers
urn:nbn:se:liu:diva-5565 (URN)91-7373-249-4 (ISBN)
Presentation
2002-01-21, 00:00 (English)
Available from: 2004-02-16 Created: 2004-02-16 Last updated: 2009-03-02

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Jönsson, AnetteDanielsson, ÅsaRahm, Lars

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