Optical measurements in the North Sea-Baltic Sea transition zone. I. On the origin of the deep water in the Kattegat

Højerslev, Niels K.; Holt, N.; Aarup, Thorkild

doi:10.1016/0278-4343(95)00075-5

Cited by 72 publications

(43 citation statements)

References 14 publications

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“…A very thorough analysis of the Secchi depths in the North Sea-Baltic Sea region has been made by Aarup (2002). Surface salinities in the northeastern part of the Skagerrak are in the range 25-32, and below the surface layer the waters become more Atlantic, with salinities up to 35 (Højerslev et al, 1996;Aarup et al 1996a).…”

Section: E Aas Et Al: Secchi Depth In the Oslofjord-skagerrak Areamentioning

confidence: 99%

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Secchi depth in the Oslofjord–Skagerrak area: theory, experiments and relationships to other quantities

2014

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Abstract. The Secchi depth and its relationships to other properties of the sea water in the Oslofjord-Skagerrak area have been investigated. White and black disks of different sizes have been applied, and the Secchi depth has been observed with the naked eye, through colour filters and with a water telescope. Spectral luminances and illuminances have been calculated from recordings of radiance and irradiance, and attenuation coefficients have been determined. A theoretical expression for the Secchi depth based on luminances has been tested against field observations, and it is found that the field results for the product of Secchi depth and attenuation coefficients are on average only 4 % less than the predicted value for the white disk. For the Secchi depths observed through colour filters or for the black disk, the average field results are more than 30 % smaller than the theoretical estimates. The reduction in the disk diameter from 30 to 10 cm should theoretically reduce the Secchi depths by 13-22 %, while the field observations show an average reduction of 10-20 %. Similarly we find from theory that the removal of sun glitter should increase the Secchi depth by 12 %, while the observed increase is 14 % on average for the white disk. Our overall conclusion is that the theoretical expression works well for the white disk, but less so for the colour filter observations and the black disk.Statistical relationships between Secchi depths and attenuation coefficients have been determined, and it is found that the root-mean-square errors relative to the mean value are smaller for the beam attenuation coefficients (12-24 %, white disk) than for the vertical attenuation coefficients (16-65 %, white disk). The depth of the 1 % level of surface quanta irradiance (PAR) can be estimated with a relative root-mean-square error of 23 % from observations of the white Secchi depth. Similar estimates of chlorophyll a and total suspended material will have rms errors in the range 40-90 %. Our conclusion becomes that the Secchi depth observation is a very useful tool for checking the value and order of magnitude of other related quantities in the OslofjordSkagerrak area.

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Section: E Aas Et Al: Secchi Depth In the Oslofjord-skagerrak Areamentioning

confidence: 99%

“…References: a Gade (1963Gade ( , 1967; Aure et al (1996); Staalstrøm et al (2012); b Aarup et al (1996a);Højerslev et al (1996); c Norwegian Meteorological Institute (personal communication, 2014); d Andresen (1993); e Aarup (2002).…”

Section: Areamentioning

confidence: 99%

Secchi depth in the Oslofjord–Skagerrak area: theory, experiments and relationships to other quantities

2014

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“…Pure water is a weak absorber of blue and green wavelengths (450 to 550 nm), while absorption generally increases for particulate organic and dissolved compounds (yellow substance) as wavelength decreases into the blue and ultraviolet (< 550 nm, Kirk 1994). Yellow substance is considered a quasi-conservative parameter, because it decomposes slowly and does not precipitate in waters with salinities > 6 (Højerslev et al 1996). Several studies have found a negative relation between yellow substance and salinity, and have used these relationships for water mass identification (Højerslev et al 1996 and references therein).…”

Section: Discussionmentioning

confidence: 99%

“…Yellow substance is considered a quasi-conservative parameter, because it decomposes slowly and does not precipitate in waters with salinities > 6 (Højerslev et al 1996). Several studies have found a negative relation between yellow substance and salinity, and have used these relationships for water mass identification (Højerslev et al 1996 and references therein). Baltic sea water is characterised by low salinities and an intermediate to high content of yellow substance.…”

Section: Discussionmentioning

confidence: 99%

Concurrent temporal patterns in light absorbance and fish abundance

Sørnes

Aksnes²

2006

Mar. Ecol. Prog. Ser.

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The abundance of midwater fishes in fjord basins, as well as the abundance and size of mesozooplankton, have previously been related to optical properties of the basin water. Herein, we report on concurrent temporal changes in light absorbance and fish abundance for Masfjorden and modest changes in both variables for Lurefjorden and Sognefjorden, western Norway. The inverse relationship between fish abundance and absorbance in the temporal data, spanning 9 yr, is consistent with the relationship previously described for spatial data representing different fjords. The combination of salinity and oxygen accounted for 94% of the observed variance in absorbance of the 3 fjords, and we suggest that these variables serve as proxies for regional and local determinants of absorbance in fjord basins, respectively. While salinity indicates basin water origin and its optical properties, oxygen is a measure of turnover time and local degradation of organic matter, presumably affecting absorbance.

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“…Mechanistic inter pretation of the age and source of CDOM from the spectral slope is difficult due to the complexity of the degradation process, which is described by at least two rate con stants that span days to weeks (Twardowski and Donaghay, 2002). Despite these uncer tainties, CDOM slope has been effectively associated with specific water masses in the Baltic Sea (Højerslev et al, 1996), Gulf of Mexico (Carder et al, 1989), Caribbean (Blough et al, 1993), Mid-Atlantic Bight (Vodacek et al, 1997), and Sargasso Sea (Nelson et al, 1998). Developing methods to characterize CDOM composition from space does not exist, but as the spectral resolu tion of satellite systems increases, the ocean optics community will undoubtedly explore the potential for new algorithms.…”

Section: Oceanography June 2004mentioning

confidence: 99%