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1

Water type quantification in the Skagerrak, the Kattegat and off the Jutland west coast

Kristiansen T., Aas E.

Oceanologia

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2015

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No. 57 (2)

177--195

EN

An extensive data series of salinity, nutrients and coloured dissolved organic material (CDOM) was collected in the Skagerrak, the northern part of the Kattegat and off the Jutland west coast in April each year during the period 1996–2000, by the Institute of Marine Research in Norway. In this month, after the spring bloom, German Bight Water differs from its surrounding waters by a higher nitrate content and higher nitrate/phosphate and nitrate/silicate ratios. The spreading of this water type into the Skagerrak is of special interest with regard to toxic algal blooms. The quantification of the spatial distributions of the different water types required the development of a new algorithm for the area containing the Norwegian Coastal Current, while an earlier Danish algorithm was applied for the rest of the area. From the upper 50 m a total of 2227 observations of salinity and CDOM content have been used to calculate the mean concentration of water from the German Bight, the North Sea (Atlantic water), the Baltic Sea and Norwegian rivers. The Atlantic Water was the dominant water type, with a mean concentration of 79%, German Bight Water constituted 11%, Baltic Water 8%, and Norwegian River Water 2%. At the surface the mean percentages of these water types were found to be 68%, 15%, 15%, and 3%, respectively. Within the northern part of the Skagerrak, closer to the Norwegian coast, the surface waters were estimated to consist of 74% Atlantic Water, 20% Baltic Water, and 7% Norwegian River Water. The analysis indicates that the content of German Bight Water in this part is less than 5%.

2

Optical water types of the Nordic Seas and adjacent areas [commun.]

Aas E., Hojerslev N. K., Hokedal J., Sorensen K.

Oceanologia

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2013

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No. 55 (2)

471-482

EN

A new map of Jerlov's optical water types in the Nordic Seas and adjacent waters at 139 locations, as well as a table with statistical and geographical properties of the vertical attenuation coefficient of downward irradiance at 475 nm, are presented. The data analysis is based on 715 recordings at different stations, at latitudes between 54° and 82°N, and longitudes between 31°W and 49°E, obtained by different authors from May 1954 to August 2003. The results show that the Atlantic and Polar waters are typically of oceanic type II-III, although during algal blooms the optical conditions may change to coastal types 1, 3 and 5, which are also the most frequent types found in coastal areas.

3

Spectral light absorption by yellow substance in the Kattegat-Skagerrak area

Hojerslev N. K., Aas E.

Oceanologia

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2001

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No. 43 (1)

39-60

EN

More than 1500 water samples were taken from the Kattegat, the Skagerrak and adjacent waters. The value of the absorption coefficient of yellow substance at 310 nm was found to vary from 0.06 to 7.4 m-1 in the open coastal waters, with a mean value of 1.3 m-1. The corresponding wavelength-averaged value (250-450 nm) of the semilogarithmic spectral slope of the coefficient ranges from 0.008 to 0.042 nm-1, and the mean value is 0.023 nm-1. Closer to river discharges, as in the fjords, the values of the slope seem to be more constant at around 0.0175 š 0.0015 nm-1. In this area the slope must then be known in order to compare absorption at different wavelengths or to model the yellow substance absorption.

4

Attenuation of ultraviolet irradiance in North European coastal waters

Aas E., Hojerslev N. K.

Oceanologia

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2001

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No. 43 (2)

139-168

EN

A total of 439 measurements of downward ultraviolet irradiance in North European coastal waters have been analysed, half of which have been taken from other authors. The depths Z(10%) where the irradiance is reduced to 10% of its surface value vary by one order of magnitude in the open coastal waters, both at wavelengths of 310 nm (0.3–10.4 m) and 380 nm (1.2–13.0 m). In the fjords and estuaries the depth ranges are reduced to 0.08–6.1 m at 310 nm and 0.18–7.7 m at 380 nm. Mixing with saline ocean waters can increase these light penetration depths to more than 10 m, while river water can reduce them to a few centimetres.