Climatic changes in the deep Norwegian coastal waters and Skagerrak 2000-2005 in relation to previous decades

Poste

Fjordbassengene i ytre Oslofjord. Oksygenforbruk, organisk belastning og vannutskifting. (Fjord basins of the Ytre Oslofjord, oxygen consumption, organic load and water exchange)

The major yearly inflow to the Ytre Osloford basins normally occure in the period March - July. In 1995 a stagnation period lastedfrom June until NovemberiDecember and an inflow periodfrom December to May 1996. The mean oxygen consumption rate for the Rauøy-Breidangen and Drøbak basin in the stagnation period were 0.14, 0.15 and 0.16 repectively. n e calculatedflux of particulate organic carbon to the Rauøy basin (6.5 g C m-2 month-l) was about twofold the flux of particulate organic carbon into the Breidangen and Dr~bakb asins (3.1 g Cm-2 month-l). Due to the deep sill leve1 (100-120 meter), and to intensive water exchange above it, the oxygen consumption (and the mean flux of particulate organic carbon) in the basins were most likely related to the in.ow of particulate organic matter from the Skagerrak coast. The main source of organic matter at the 100-120 m leve1 is probably injlowing water from the central and southern North Sea. Observations and calculations show that the mean oxygen minimum concentration in the Rauøy-Breidangen and Drøbak basins were approximately 4.7, 4.1 and 4.0 ml 1-1 respectively. Due to a general 50% increase in the oxygen consumption in sill basins along the Norwegian Skagerrak coast, the lowest mean oxygen concentrations have most likely been reduced by 0.5 ml 1-1 since around 1980. Ifthe mean oxygen consumption (and the mean flux of particulate organic carbon) in the Rauøy basin is increased by a factor of 2.-2.4, and in the Breidangen and Drøbak basin by a factor of 1.5-1.8, the oxygen concentration at the end of a stagnation period will most probably reach the critical oxygen limit of 3.0 ml 1-1. NORSK SAMMENDRAG:Det er vanlig med en årlig hovedinnstrømning av vann fra Skagerrakkysten til terskelbassengene i Ytre Oslofjord i perioden fra mars til juli. Innstrømningen har som oftest en varighet på ca 3 måneder, men kan variere mellom 1 og 6 måneder. Dette betyr at den årlige stagnasjonsperiode i bassengene normalt er ca 9 måneder, og kan variere mellom 6 og 11 måneder. I 1995196 var det en stagnasjonsperiode i de tre terskelbassengene på ca 6 måneder, fra juniljuli til novemberldesember 1995 og en innstrømningsperiode fra novemberldesember til mai 1996. De relativt høye bassengtetthetene våren 1996 vil bidra til å forlenge kommende stagnasjonsperiode i Ytre Oslofjord. I Rauøy - Breidangen - og Drøbakbassenget var midlere oksygenforbruk i stagnasjonsperioden tilnærmet likt, 0.14 - 0.16 ml 1-1 pr måned. Tilførslen av organisk materiale pr flateenhet var imidlertid omlag dobbelt så stor i Rauøybassenget (6.5 gC m-2 måned-1 ) som i Breidangen og Drøbakbassenget (3.0 - 3.1 gC m-2 måned-l). De tre bassengene i Ytre Oslofjord tilføres hovedsakelig organisk materiale fra kystvannet og den lavere organiske belastning i de to indre bassengene kan forklares ved den store avstanden fra kysten (60-80 km), dvs mye av det organiske materiale synker ut i Rauøybassenget før det når de indre terskelbasseng. Den relativt store vertikale transport av organisk materiale (6.0 - 6.5 gC m-2 måned-1 ) mellom 60 og ca 120 m dyp i kystområdet fra Ytre Oslofjord til Arendal skyldes trolig tilførsler av organisk materiale fra sjøområder utenfor Skagerrak og hovedkilden til den økte organiske belastning i disse dyp synes hovedsakelig å være innstrømmende vann fra sentrale og sørlige Nordsjø. Dagens midlere oksygenminimum i Rauøy, Beidangen og Drøbakbassenget er beregnet til henholdsvis ca 4.7, ca 4.1 og ca 4.0 ml 1-1. Midlere oksygenminimum i de tre bassengene er trolig redusert med ca 0.5 ml 1-1 som følge av en generell ca 50% Økning i den organiske belastning i kystvannet langs Skagerrakkysten etter ca 1980. Rauøybassenget har god kapasitet rnhp økt organisk belasting og dagens midlere oksygenforbruk og tilforsel av organisk materiale pr flatenhet i terskelnivå må økes 2.0-2.4 ganger før midlere oksygenkonsentrasjon i slutten av en stagnasjonsperiode kommer under den kritiske grense på 3.0 ml 1-1. I Breidangen og Drøbakbassenget er kapasiteten mindre og tilførslene av organisk materiale pr flateenhet kan bare Økes 1.5-1.8 ganger fØr oksygenkonsentras~onene å slutten av en stagnasjonsperiode blir mindre gode. Den totale omsetning av oksygen og organisk materiale i Rauøybassenget er også ca ti ganger stØrre enn i Breidangen og Drøbakbassenget. Regelmessige langtisdmålinger mangler i Ytre Oslofjord og det er derfor ønskelig at slike målinger iverksettes både for med større saerhet å kunne bestemme "normalsituasjonen" og variasjoner fra &r til år

Temporal and spatial hydrographic variability in the Skagerrak

This report addresses the tempora1 and spatial variability in the hydrography of the Skagerrak by means of statistical investigations including frequency analyses and spatial correlations. The analysis is based on the fixed hydrographic section across the Skagerrak between Torungen (Arendal), Norway and Hirtshals, Denmark, close to a full year of temporally highly resolved hydrographic measurements by moored automatic current meters, placed off the coast from Torungen, and modelled output from the coupled physical-chemical-biological model system NORWECOM. NORSK SAMMENDRAG: Rapporten omhandler variabilitet i hydrografien i Skagerrak. Ved hjelp av statistiske metoder analyseres variasjonsmønstre i rom og tid. Metodene brukt omfatter frekvensanalyse og romlig korrelasjonsanalyse. Analysen tar utgangspunkt i det faste hydrografiske snittet som går på tvers av Skagerrak fra Torungen (Arendal) til Hirtshals, nær et år med tidsmessig godt oppløste strømmålinger fra en fast montert automatisk strømmåler plassert utenfor Torungen og modellresultater fra den fysisk-kjemisk-biologiske modellen NORWECOM

Miljøundersøkelser i norske fjorder: Ytre Oslofjord 1937-2011

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”

Hydrografiske undersøkelser og kartlegging av fiskefordeling i Nordsjøen i februar 1972

The present report outlines the results of a survey carried out by R. V. "G. O. Sars" and R. V. "Johan Hjort" in February 1972. The distribution and relative abundance of fish in the North Sea were mapped on the basis of echo integrator readings. Samples obtained by mid water and bottom trawls supported the identification of echo recordings and provided material for biological analyses of dominating fish species. The general features of the hydrography was determined, and the distribution of air and sea temperatures, temperature anomalies, and salinities are presented. Significant differences in echo integrator readings were observed: between day and night, between the two ships and in relation to obtained catch. Bottom trawl catches varied between 45 and 1545 kg per hour. Best catches were taken in the southeastern part of the North Sea. In total, herring, whiting and haddock amounted to 26, 25 and 21 per sent respectively while Norway pout, flatfish and other species each were less than 10 per cent in weight. Distribution, size, age etc. are reported in detail for the dominating species, and the relationship between the distribution and the abiotic environment is discussed, Young herring were found in greatest concentrations in the Bløden area. Sprat were found in the coastal waters, characterized by relatively low salinity, while Norway pout were most numerous in Atlantic water in the northern part on the North Sea plateau. Blue whiting and coalfish were mainly observed along the western slope of the Norwegian trench below the core of the Atlantic water which penetrates into the North Sea

On the migrations of the cod in the Skagerak shown by tagging experiments in the period 1954-1965

1. A total of 1,244 cod was tagged from 1954 to 1965. The recapture percentage from the different tagging years varied between 24.9 aid 35.6 with a mean of 29.5 for the whole period. 2. No cod has been recaptured on the Norwegian Skagerak coast, indicating that there is no connection between the cod populations on the Danish and Norwegian side of the Skagerak. 3. The recaptures in the Kattegat have been very small (15 individuals). The migration into the eastern part of the North Sea somewhat greater (43 individuals), and they were mainly caught in the first part of the year. 4. One cod has been recaptured on the Fyllas Bank on the West Greenland 34 months after the tagging, and one on the Norwegian Helgeland coast after 49 months at sea

Investigations on herring, Clupea harengus L., from the Norwegian Skagerak Coast during the years 1963-64

1) The material was collected on a little part of the Norwegian Skagerak coast in 1963-1964. 2) The following data were sampled: total length and weight, stage and weight of gonads, intestinal fat content, vertebrae number and scales. Otoliths were taken from the last 5 samples. 3) Most of the herring examined appeared to be Skagerak spring spawners with a mean vertebrae number of about 57. Some of the herring with one and two winter rings were autumn spawners, belonging to either the North Sea autumn spawners or the Kattegat autumn spawners. 4) The otoliths of the Skagerak spring spawners had an opaque or a little hyaline nucleus with varying size of the central field. Some of the otoliths in the autumn spawners resemble otoliths previously found in the North Sea. 5) The Skagerak spring spawners had a rapid growth the first three years, and were spawning for the first time at three years age. 6) The maturity and the intestinal fat cycles appeared to be inversed