Secchi Disk Data Collection for the North Sea and
Baltic Sea
This data collection is the result of a Secchi depth
data mining study for the North Sea – Baltic Sea region carried out by Thorkild
Aarup (t.aarup@unesco.org). It covers the period from 1902 to 1999. The study
was completed in 2002.
40,829 measurements of Secchi depth were compiled from
the area as a result of this study. 4.3% of the observations were found in the
international data centers [ICES Oceanographic Data Centre and the World Ocean Data Center A (WDC–A) in
the USA], while 95.7% of the data were provided by individuals and ocean
research institutions from the surrounding North Sea and Baltic Sea countries.
Inquiries made at the World Ocean Data Center B (WDC–B) in Russia suggested that
there could be significant additional holdings in that archive but,
unfortunately, no data could be made available.
The earliest Secchi depth measurement retrieved in
this study dates back to 1902 for the Baltic Sea, while the bulk of the
measurements were gathered after 1970. The spatial distribution of Secchi depth
measurements in the North Sea is very uneven with surprisingly large sampling
gaps in the Western North Sea. Quarterly and annual Secchi depth maps with a
0.5.×0.5. spatial
resolution are provided for the transition area between the North Sea and the
Baltic Sea (4.E–16.E, 53.N–60.N).
Downloads available from this site are:
Data set description - Reprint of article “Transparency of the
North Sea and Baltic Sea – a Secchi
Depth data mining study” by Thorkild Aarup (Oceanologia 44(3) 2002).