BS5 background information

BS 5 Visibility depth

Visibility depth or secchi depth is measured..

A) Visibility depth in Gulf of Finland (metres)

Year
1905	8.0		1931	7.3		1957	6.2		1983	6.0
1906	8.0		1932	7.2		1958	6.2		1984	6.0
1907	7.9		1933	7.2		1959	6.1		1985	5.9
1908	7.9		1934	7.2		1960	6.1		1986	5.8
1909	7.9		1935	7.1		1961	6.1		1987	5.8
1910	7.9		1936	7.1		1962	6.1		1988	5.7
1911	7.8		1937	7.0		1963	6.1		1989	5.7
1912	7.8		1938	7.0		1964	6.1		1990	5.6
1913	7.8		1939	6.9		1965	6.1		1991	5.5
1914	7.8		1940	6.9		1966	6.1		1992	5.4
1915	7.7		1941	6.9		1967	6.1		1993	5.3
1916	7.7		1942	6.8		1968	6.1		1994	5.2
1917	7.7		1943	6.8		1969	6.1		1995	5.2
1918	7.7		1944	6.7		1970	6.1		1996	5.0
1919	7.6		1945	6.7		1971	6.1		1997	4.9
1920	7.6		1946	6.6		1972	6.2		1998	4.8
1921	7.6		1947	6.6		1973	6.2		1999	4.7
1922	7.6		1948	6.5		1974	6.2		2000	4.6
1923	7.5		1949	6.5		1975	6.2		2001	4.5
1924	7.5		1950	6.4		1976	6.2		2002	4.5
1925	7.5		1951	6.4		1977	6.2		2003	4.4
1926	7.4		1952	6.4		1978	6.2		2004	4.4
1927	7.4		1953	6.3		1979	6.1		2005	4.3
1928	7.4		1954	6.3		1980	6.1		2006	4.3
1929	7.4		1955	6.3		1981	6.1		2007	4.3
1930	7.3		1956	6.2		1982	6.0		2008	4.4

B) Visibility depth in Bothnian Sea (metres)

Year
1905	8.9		1931	9.5		1957	7.5		1983	6.6
1906	8.9		1932	9.5		1958	7.4		1984	6.6
1907	9.0		1933	9.4		1959	7.3		1985	6.5
1908	9.0		1934	9.4		1960	7.2		1986	6.5
1909	9.1		1935	9.3		1961	7.2		1987	6.4
1910	9.1		1936	9.3		1962	7.1		1988	6.4
1911	9.2		1937	9.2		1963	7.0		1989	6.3
1912	9.2		1938	9.1		1964	7.0		1990	6.3
1913	9.3		1939	9.1		1965	6.9		1991	6.2
1914	9.3		1940	9.0		1966	6.9		1992	6.1
1915	9.3		1941	8.9		1967	6.9		1993	6.1
1916	9.4		1942	8.8		1968	6.8		1994	6.0
1917	9.4		1943	8.7		1969	6.8		1995	6.0
1918	9.4		1944	8.6		1970	6.8		1996	5.9
1919	9.5		1945	8.6		1971	6.8		1997	5.9
1920	9.5		1946	8.5		1972	6.8		1998	5.8
1921	9.5		1947	8.4		1973	6.8		1999	5.7
1922	9.5		1948	8.3		1974	6.8		2000	5.7
1923	9.6		1949	8.2		1975	6.8		2001	5.6
1924	9.6		1950	8.1		1976	6.8		2002	5.6
1925	9.6		1951	8.0		1977	6.8		2003	5.5
1926	9.6		1952	7.9		1978	6.8		2004	5.5
1927	9.6		1953	7.8		1979	6.7		2005	5.4
1928	9.6		1954	7.7		1980	6.7		2006	5.3
1929	9.6		1955	7.6		1981	6.7		2007	5.3
1930	9.5		1956	7.6		1982	6.6		2008	5.2

C) Visibility depth in Bay of Bothnia (metres)

Year
1905	9.3		1931	7.9		1957	6.4		1983	6.0
1906	9.2		1932	7.9		1958	6.3		1984	6.0
1907	9.2		1933	7.8		1959	6.3		1985	6.0
1908	9.1		1934	7.8		1960	6.2		1986	5.9
1909	9.1		1935	7.7		1961	6.2		1987	5.9
1910	9.0		1936	7.7		1962	6.2		1988	5.8
1911	9.0		1937	7.6		1963	6.1		1989	5.8
1912	8.9		1938	7.5		1964	6.1		1990	5.7
1913	8.9		1939	7.5		1965	6.1		1991	5.7
1914	8.8		1940	7.4		1966	6.0		1992	5.6
1915	8.8		1941	7.3		1967	6.0		1993	5.5
1916	8.7		1942	7.3		1968	6.0		1994	5.5
1917	8.7		1943	7.2		1969	6.0		1995	5.4
1918	8.6		1944	7.1		1970	6.0		1996	5.3
1919	8.6		1945	7.1		1971	6.0		1997	5.2
1920	8.5		1946	7.0		1972	6.0		1998	5.1
1921	8.5		1947	6.9		1973	6.0		1999	5.1
1922	8.4		1948	6.9		1974	6.0		2000	5.0
1923	8.4		1949	6.8		1975	6.1		2001	4.9
1924	8.3		1950	6.8		1976	6.1		2002	4.8
1925	8.3		1951	6.7		1977	6.1		2003	4.7
1926	8.2		1952	6.6		1978	6.1		2004	4.6
1927	8.2		1953	6.6		1979	6.1		2005	4.5
1928	8.1		1954	6.5		1980	6.1		2006	4.3
1929	8.1		1955	6.5		1981	6.1		2007	4.2
1930	8.0		1956	6.4		1982	6.0		2008	4.1

Download data on a spreadsheet from here

Links:

Water transparency in the Baltic Sea between 1903 and 2007 (Helsinki Comission)

References:

HELCOM 2009. Eutrophication in the Baltic Sea - An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region: Executive summary. Baltic Sea Environment Proceedings No. 115A.