Miljøundersøkelser i norske fjorder: Ytre Oslofjord 1937-2011

Abstract

In the surface layer in Outer Oslofjord autumn temperatures were 2 - 4 °C above normal between 1996 and 2011 and summer temperatures (august) in 1995, 1997, 2002, 2004 and 2006 (19-21°C) were unormal high (19-21°C). In contrast summer temperatures in 2002 and 2003 were unormal low. In the basin water (300 m), influenced by Atlantic water, temperature increased with about 0.8°C after 1990 in accordance with the general temperature increase in Atlantic water along the Norwegian coast. About 0.5°C of the temperture increase seems to be connected to global warming and 0.3 °C to natural variations. The local input of antrohropogenic nutrients increased winter values of nitrate and summer values of chlorophyll - a in the upper layer of the Outer Oslofjord. The environmental conditions related to nitrate and chlorophyll-a were” less good” in the inner part of the fjord and “good” in the central part and in the coastal water. The oxygen conditions in the main basins in Outer Oslofjord, dominated by conditions in inflowing Atlantic water, were “very good”.