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Model Studies of Surface Waves and Sediment Resuspension in the Baltic Sea
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
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 [en]
Surface waves, Wave model, Wave friction velocity, Resuspension, Sediment dynamics, Nitrogen fixation, Baltic Sea
Keyword [sv]
Havsvågor, Östersjön, Oceanografi, Sediment
National Category
Oceanography, Hydrology, Water Resources
Identifiers
URN: urn:nbn:se:liu:diva-4680ISBN: 91-85299-94-4 (print)OAI: oai:DiVA.org:liu-4680DiVA: diva2:20699
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
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. Resuspension patterns in the Baltic proper
Open this publication in new window or tab >>Resuspension patterns in the Baltic proper
2007 (English)In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 57, no 4, 257-269 p.Article in journal (Refereed) Published
Abstract [en]

Waves induce resuspension of surface sediments and contribute to the long-term mobilisation of particulate matter from erosion to accumulation bottoms. This has a major impact on the nutrient cycle in shallow seas by enhancing degradation, microbial production and recycling. The Baltic Sea represents such an area. The aim of this work is to analyse the spatial and temporal resuspension patterns in the Baltic Sea. To estimate the bottom friction velocity, modelled wave data are used in combination with data on grain size. This new data set is compared to a resuspension threshold of friction velocity to estimate the events of resuspension.

The variation in bottom friction velocity, resuspension frequency and duration are related to wind climate, fetch, water depth and sediment type. Substantial resuspension can be found down to 40–60 m, with durations from one day to as much as two weeks. The highest winds in the area are highly anisotropic with a dominance of S-SW-W winds and the highest resuspension frequencies are found along the shallow eastern coasts. A seasonal pattern is observed with relatively high friction velocities and high resuspension frequencies during winter. There is also a variation depending on grain size, where sediments with fine and medium sand have a considerably higher percentage of resuspension events than bottoms with other dominant grain sizes. Five sub-areas are identified, characterised by different sediment types, resuspension and wind characteristics. If, in the future, wind speed increases as predicted, resuspension of sediments will also increase with effects on the nutrient cycle.

Keyword
Resuspension, Wave friction velocity, Wind patterns, Sediment distribution, Fluffy layer, Baltic Sea
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13421 (URN)10.1016/j.seares.2006.07.005 (DOI)
Note

On the day of the defence date the title of this article was Resuspension patterns in the Baltic proper, the Baltic Sea.

Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-13
4. A model study of suspended sand due to surface waves during a storm in the Baltic Proper
Open this publication in new window or tab >>A model study of suspended sand due to surface waves during a storm in the Baltic Proper
2006 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 63, no 3-4, 91-104 p.Article in journal (Refereed) Published
Abstract [en]

During 28 November–5 December 1999 three storms passed the Baltic Sea area. The modelled surface waves in the Baltic Proper during this period have been used to calculate the amount of suspended sand in the water mass. Different parameterisations depending on the flow regimes (rippled bed flow or sheet flow) have been used for the suspended sediment calculations.

The study shows that the shallow areas along the eastern and southern sides of the Baltic Proper were most exposed to the wave induced resuspension during this period. The resuspension events lasted for about 6–12 h, thereafter the sediment settled again within an hour. During each low passage, about 2.5 Mton sand were suspended, releasing about 0.5·106 m3 earlier trapped interstitial water. This might have a large effect on the nutrient concentrations in the water mass above these bottoms.

Keyword
Storm events; Surface waves; Resuspension; Suspended sediment; Scandinavia; Baltic Sea; Baltic Proper; 54° N–59° N 16° E–25° E
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13422 (URN)10.1016/j.jmarsys.2006.05.005 (DOI)
Note

On the day of the defence date the title of this article was A model study of suspended sand due to surface waves during a winter storm in the Baltic Proper.

Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2014-09-22
5. 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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