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1

Formation and species composition of stormcast beach wrack in the Gulf of Riga, Baltic Sea

Suursaar Ű., Torn K., Martin G., Herkül K., Kullas T.

Oceanologia

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2014

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No. 56 (4)

673--695

EN

The aim of the study was to investigate hydrodynamic effects on the formation of beach wrack at three locations in the northern Baltic Sea and to quantify the differences between the composition of species found in the beach wrack and in the neighbouring sea. Hydrodynamic measurements and modelling indicated that the beach wrack was mostly of local origin and that it was formed during high sea level and wave events. Comparison of the methods of beach wrack sampling and seabed sampling (diver, underwater video) demonstrated that beach wrack sampling can be considered an alternative tool for describing the species composition of macrovegetation in near-coastal sea areas. Although the hydrodynamic variability is greater in autumn and more biological material is cast ashore, the similarity between the two sampling methods was higher in spring and summer.

2

Currents and waves in the northern Gulf of Riga: measurement and long-term hindcast

Suursaar Ű., Kullas T., Aps R.

Oceanologia

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2012

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No. 54 (3)

421-447

EN

Based on measurements of waves and currents obtained for a period of 302 days with a bottom-mounted RDCP (Recording Doppler Current Profiler) at two differently exposed locations, a model for significant wave height was calibrated separately for those locations; in addition, the Gulf of Riga-Väinameri 2D model was validated, and the hydrodynamic conditions were studied. Using wind forcing data from the Kihnu meteorological station, a set of current, water exchange and wave hindcasts were obtained for the period 1966-2011. Current patterns in the Gulf and in the straits were wind-dependent with characteristic wind switch directions. The Matsi coast was prone to upwelling in persistent northerly wind conditions. During the hindcast period, currents increased along the Ko~iguste coast and in the Suur Strait, waves decreased noticeably off Ko~iguste but fluctuated without a clear linear trend near Matsi. The spatially contrasting results for differently exposed coasts were related to the corresponding variations in local wind conditions and to changes in atmospheric circulation patterns over northern Europe.

3

Decadal variations in wave heights off Cape Kelba, Saaremaa Island, and their relationships with changes in wind climate

Suursaar Ű., Kullas T.

Oceanologia

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2009

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No. 51 (1)

39-61

EN

Based on wind data from the Vilsandi meteorological station and a 5-month calibration measurement with a bottom-mounted Recording Doppler Current Profiler (RDCP), a semi-empirical hindcast of wave parameters near the quickly developing accumulative Kelba Spit is presented for the period 1966-2006. The significant wave heights with a gross mean value of 0.56 m exhibited some quasiperiodic cycles, with the last high stage in 1980-95 and a decreasing overall trend of -0.001 m per year. At the same time, both the frequency and intensity of high wave events showed rising trends, and the mean wave heights during winter (December to February) increased as well. As the study area has the longest fetches in westerly directions, the discussed tendencies in wave conditions are sensitive to regional changes in the wind climate and can be related to a decrease in the local average wind speed on the one hand, but an intensification of westerly winds, storm events and the wintertime NAO index on the other. The roughest wave storms on record were associated with prominent W-storms on 2 November 1969 and 9 January 2005; a few other extreme wind events (e.g. in 1967, 1999, 2001), however, did not yield equally prominent waves.

4

Influence of wind climate changes on the mean sea level and current regime in the coastal waters of west Estonia, Baltic Sea

Suursaar Ű., Kullas T.

Oceanologia

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2006

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No. 48 (3)

361-383

EN

The response of semi-realistic wind speed increase scenarios to the mean sea level and current regime of semi-enclosed sub-basins in the Baltic Sea is studied with a 2D hydrodynamic model. According to the model output of spatial mean sea levels, an increase in the westerly wind component by 2 m s-1 leads, for example, to a mean sea level rise of up to 3 cm in windward locations in the study area. The sea level change patterns depend on the wind scenario and coastline configuration. The increases in wind speed considered here also lead to enhanced water exchange through the straits, strengthening of the basin-scale circulation, enhancement of up- and downwelling, and increased bottom stresses near coasts.