ICES Marine Science Symposia, 219: 150-159. 2003

Long-term hydrographic variability patterns off the Norwegian coast and in the Skagerrak

R. Sætre, J. Aure, and D. S. Danielssen

Sætre, R., Aure. J.,and Danielssen, D. S. 2003. Long-term hydrographic variability patterns off the Norwegian coast and in the Skagerrak. - ICES Marine Science Symposia, 219: 150-159.

The Norwegian Coastal Oceanographic Observing System consists of observations of temperature and salinity in the surface layer, carried out at fixed positions from coastal liners, and measurements in the whole water column, carried out by local observers. The observations date back to 1935. Additionally, long-term data from the Institute of Marine Research station in Flødevigen on the Skagerrak coast and some selected data from the Torungen-Hirtshals hydrographic section are included. These data have been used to elucidate the long-term hydrographic variability along the Norwegian coast. Four relatively warm winter periods could be identified in the surface layer, culminating around 1950, 1960, 1975, and in 1990-1992. The long-term temperature and salinity trend 1950-1989 is negative along the whole coast. The 1990s, however, are characterized by having the highest mean decadal temperature for the whole period of observations along the southern coast. The importance of the 1990s in the surface layer is gradually reduced northwards. Along the northernmost coast, other decades, such as the 1950s or the 1960s, show higher decadal mean tem­ perature. Also for the salinity the 1990s show high values along the southern coast, while other high salinity decades dominate further north. The high temperatures and salinities along the southern coast in the 1990s are caused by an increase in the Atlantic inflow in the late 1980s and early 1990s combined with the atmospheric conditions associated with periods of a high level of the North Atlantic Oscillations.

Keywords: long-term hydrographic variability, Norwegian coast, Skagerrak.

R. Saetre and J. Aure: Institute of Marine Research, PO Box 1870, NO-5817 Bergen, Norway. D. S. Danielssen: Institute of Marine Research, Flødevigen Marine Research Station, NO-4817 His, Norway.

Introduction that fluctuations in the hydrographic conditions along the coast might influence the recruitment, Norwegian Coastal Water (NCW) originates prima­ growth, and distribution of fish stocks. This was used rily from the freshwater outflow from the Baltic and as an argument for establishing the Norwegian the freshwater run-off from Norway. This water Coastal Oceanographic Observing System (NCOOS) mixes with North Sea Water (NSW) and Atlantic consisting both of observations from the surface Water (AW) to form the Norwegian Coastal Cur­ layer by ships of opportunity and of fixed hydro- rent, which flows northwards along the coast of graphic station carried out by local observers. The Norway as a wedge-shaped low-salinity current observing system was established in the mid-1930s bordered by the Norwegian North Atlantic Current and is still operational. It represents some of the off the central and northern parts of Norway longest continuous oceanographic time-series in the (Figure 1). A description of the characteristic feature world. Data from this observing system have been of this current system was given by Sætre and Ljøen used in a large number of reports and publications for (1972) and in Sætre and Mork (1981). The current various purposes, including highlighting long-term system and water masses in the Skagerrak area have been described by Gustavsson and Stigebrandt variations (e.g. Ljøen and Sætre, 1978; Blindheim (1996) and by Danielssen et a i (1997). et al., 1981; Danielssen et al., 1996). The Norwegian shelf is the spawning and hatching The aim of this contribution is to elucidate the area for several commercially important fish species. long-term hydrographic variability patterns along Early in the previous century it was acknowledged the Norwegian coast and identify possible regional Long-term hydrographic variability patterns 151

O Loppa OVardø 70°N

• Skrova

'O Hestmannøy

65°N O Folia

Hustadvika Bud O Stad

;0 Sognesjøen

60“N • Utsira ^ FLØDEVIGEN ■ Torungen \ Lista 5 nm i* 30 nm J ® "* ------52 nm

0°E 5°E 10°E 15°E 20°E 25"E 30”E

Figure 1. Selected stations for the present study along with the persistent currents. (1) Surface layer observations from coastal liners. (2) Fixed hydrographic stations. (3) Norwegian Coastal Current. (4) Norwegian North Atlantic Current. differences with special emphasis on the situation Since 1961 the section has on average been worked in the 1990s. It is mainly confined to the winter out 8-12 times a year. Some data from this section situation, as this season is believed better to reflect are presented as seasonal means as a basis for assess­ the long-term climatic signals. ing possible biological effects of the variability in the physical environment. From this section three different positions are selected: one at 10 m depth, 5 Material and methods nmi off Torungen in the Norwegian coastal current (Torungen 5 nmi), one at 300 m depth, 30 nmi from During the period 1935 to 1947 Jens Eggvin at the Torungen in the Atlantic water masses in the central Institute of Marine Research (IMR) established a Skagerrak (Torungen 30 nm), and one at 10 m number of fixed hydrographic stations in Norwe­ depth, 52 nmi from Torungen near the Danish coast gian coastal waters (Eggvin, 1938, 1948). He also in the North Sea water masses (Torungen 52 nmi). initiated a surface layer observation programme Figure 1 shows the location of the stations selected from ships of opportunity. Since 1951, the IMR has for the present study. For the ship of opportunity operated a standard hydrographic section across the programme, regular coastal liners measure the tem­ central part of the Skagerrak between Torungen on perature at predetermined locations at the intake of the Norwegian side to Hirtshals on the Danish side. cooling water to the engine. Simultaneously, a water 152 R. Sielre et al. sample is taken for analysis of the salinity. The depth and in 1990-1992. Up to the end of the 1980s there of observations is approximately 4 m. The frequency was a negative temperature trend along the whole of observations is usually 8-10 times per month. coast (Table 1). The highest normalized temperature At the fixed hydrographic stations the vertical trend for the period 1950-1989 was -0.9 and -1.2 temperature and salinity profiles are measured for Lista in the extreme south and Vardø in the 2-4 times per month by local observers. Aure and extreme north, respectively. Østensen (1993) present both mean values and long­ The last period of warm winters started in 1987 term variations from the fixed stations. Since 1919 and culminated at the beginning of the 1990s temperature and salinity have been measured daily (Figure 2). During this period the highest winter in the pipeline through which seawater is pumped temperatures since 1936 were observed along the from various depths at the IMR's Research Station southern and central parts of the Norwegian coast. in Flødevigen. The salinity has been determined by Daily observations from the Torungen lighthouse means of an aerometer (pycnometer). The quality of back to 1867 strongly indicate that the winter of the salinity observations is uncertain and for that 1990 in southern Norway was the warmest in the reason only the temperature observations have been last 130 years (Anon., 1993). Further north the tem­ used. perature increase in the 1990s was significantly less, The NORWegian ECOlogical Model system and at the stations of Folda, Loppa, and Vardø the (NORWECOM) is a 3-D coupled physical, chemi­ 1960s show higher values. Comparing the mean cal, biological model system (Skogen et al., 1995). In decadal temperature for the 1990s with the mean for the present study, only results from the physical the period 1940-1989 the normalized deviation is module are presented. The physical forcing variables reduced from 1.28 at Flødevigen to 0.17 at Vardø are 6-hourly hindcast atmospheric pressure fields (Table 2, Figure 4A). The numbers of warm winters provided by the Flindcast Archive of the Norwegian in the 1990s reduce from 8 along the Skagerrak Meteorological Institute (Eide et al., 1985, Reistad coast to 1 at Loppa. Consequently, the effect of the and Iden, 1995), 6-hourly windstress derived from warm 1990s was gradually reduced from south to the pressure fields and freshwater run-off. The mean north. oceanic winter inflow (Jan-Mar) to the North In the surface layer there is also a significant Sea across the whole Orkney-Shetland-Norway negative trend in winter salinity along the whole section was calculated from the daily mean current coast up to the end of the 1980s with the strongest component. salinity reduction at the end of this period (Figure 2, The long-term temperature and salinity trends Table 1). The normalized salinity trend (the salinity along the coast have been normalized by taking trend/standard deviation) up to 1989 was highest the ratio between the long-term change and the along the southern and central coasts (Table 1) with a maximum at Stad of about -1.8. From the end of standard deviation for the same period. Similarly, the 1980s there was again an increase in the salinity the deviation in the mean value between two mean of the surface layer (Figure 2). Just as for the tem­ periods has been normalized by using the ratio perature, the salinity increase in the 1990s was between the temperature or salinity deviation for the markedly higher along the southern coast. However, two periods and the standard deviation for the first the negative long-term trend before 1990 resulted in period. The terms “warm winter” or “cold winter” the salinity of the surface layer along most of the mean that the temperature is above or below the coast in the 1990s remaining below the long-term long-term mean ±1 standard deviation. mean for the period 1940-1989. Only in the extreme south were the salinities in the 1990s above the 1940-1989 mean value (Table 2, Figure 4B). Results and discussion Along most of the southern coast there appears to have been a shift in the temperature regime around 1988, and after that the temperatures reached above Surface layer normal. This feature is especially pronounced at 19-m depth at Flødevigen (Figure 2). If we compare Figure 2 shows the mean temperature and salinity the seasonal mean temperature for the period for the first quarter of the year (Jan-Mar) for 1940-1987 with the period 1988-2000 we can see that selected stations along the whole Norwegian coast, during winter and spring there has been a jump of along with the modelled winter inflow to the North more than 1 °C. At the surface layer of the Torungen- Sea during Jan-Mar. The curves have been smo­ Hirtshals section, the station on the Norwegian side othed by 5-year running means. During the period (Torungen 5 nmi, Figure 1) during the same periods 1940-2000 four relatively warm winter periods could shows a difference of 1° to 1.7°Cin winter and spring be identified, culminating around 1950, 1960. 1975. or 0.5-0.7 standard deviations, respectively (Table 4, Long-term hydrographic variability patterns 153

Flødevigen 19m North Sea winter inflow ( Utsira -Orkney Islands)

5.0 - 0U 2.0 - H 4.0 - £ 3.5 - ° o

2.5 2.0

1940 1950 1940 1950 1960 1970 1980 1990 2000 1960 1970 1980 1990 2000

Utsira 10m Utsira 10m 33.!

33.4 -

.è* 33.0 - 0u c f- 1 32.6 - 4.5 - 32.2 - 4.0 -

3.0

1940 1950 1960 1970 1980 1990 2000 1940 1950 19701960 1980 1990 2000

Stad 4m 33.6 -i Stad 4m

33.4 - &33.2 - J 33.0 - 0u H 5.0 ^ 32.8 - 32.6 -

4.0 - 32.4 - 32.2

1940 1950 1960 1970 1980 1940 1960 1970 1980 1990 2000

Folda 4m 34.2 Folda 4m

6.0 - 34.0 -

0u H 5.0 33.6 :

33.4 -

4.0 33.2 1940 1950 1960 1970 1980 1990 2000 1950 1960 1970 1980 2000 Loppa 4m Loppa 4m

34.3

p c H 33.9

33.7

2.5 33.5 1940 1950 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000

Vardo 4m Vardø 4m 34.7

34.5 - 0U 3.5 c 34.3 -

2.5

2.0 33.9 1940 1950 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000

Figure 2. Mean temperature and salinity in the surface layer for the first quarter o f the year (Jan Mar) along the coast from north (upper) to south (lower) and the modelled winter inflow to the North Sea (upper right). Five-year running means are indicated. 154 R. Sœtre et al.

Table 1. Temperature and salinity trends (T, S trend), stan­ The deeper layer (150-200 ra) dard deviation (stdev), and normalized trend (trend/stdev) at the surface layer stations and in 150-m depth at the fixed There has also been a negative temperature trend in hydrographic stations during winter (Jan- Mar) from 1950 to the deeper layer of the coastal water from about 1989. 1945 to the beginning of the 1980s (Figure 3). The Station T trend T T trend/ s S S trend/ normalized temperature trend 1950-1989 was high­ stdev T stdev trend stdev stdev est at the southern stations (Figure 3, Table 1), with values between -0.3 and -1.0 standard deviation. As Surface layer Vardø -0.68 0.58 -1.17 -0.11 0.18 -0.61 in the surface layer, there was also a significant tem­ Loppa -0.68 0.61 -1.11 -0.10 0.23 -0.43 perature increase after 1987. The winter temperature Skrova -0.48 0.61 -0.79 -0.14 0.38 -0.37 at Utsira, Sognesjøen, and Skrova was the highest -1.08 Folia -0.32 0.59 -0.54 -0.28 0.26 observed since 1936. The normalized temperature Stad -0.40 0.71 -0.56 -0.60 0.33 -1.82 Utsira -0.36 0.87 -0.41 -0.60 0.63 -0.95 deviation in the 1990s compared to the period 1940- Lista -1.08 1.23 -0.88 -1.48 1.14 -1.30 1989 was highest at the stations with highest salin­ 150 depth ity, i.e. those most influenced by the Atlantic Water, Skrova -0.16 0.55 -0.29 -0.12 0.20 -0.60 such as Torungen 30 nmi, Utsira, and Sognesjøen Sognesjøen -0.22 0.29 -0.77 -0.07 0.07 -1.03 (Figures 3, 4C, Table 2). The Torungen 5 nmi, Lista, Utsira -0.21 0.41 -0.52 -0.16 0.11 -1.45 Lista -0.48 0.47 -1.02 -0.12 0.12 -1.02 and Skrova stations are more influenced by the coastal water with lower salinity (Table 2). In the deeper layer there is, in general, also a decrease in salinity from around 1950 to the early Figure 6). There has also been an increase in salinity, 1980s (Figure 3, Table 1). At the Lista, Utsira, and except for the summer (Figure 6). Sognesjøen stations, the reduction was highest Approximately the same feature is seen in the during the period 1970 to the early 1980s, while surface layer on the Danish side (Torungen 52 nmi) further north at Skrova there was a gradual decrease of the section (Table 4, Figure 6), where the North from the mid-1960s to the beginning of the 1990s. Sea water masses enter the area. There has been a At the stations in southern Norway the normalized pronounced increase in temperature, especially in salinity trend during the period 1950-1989 was winter and spring, but not very much during the rest between -1 and -1.4 standard deviations (Table 1). of the year. Here, the spring was also the period The increase in salinity from the mid-1980s and in with the largest increase, 1.44°C, which is about 0.72 the 1990s was highest at the stations with the highest of the standard deviation for the period 1962-1987. salinity, i.e. those mostly influenced by Atlantic There has also been an increase in salinity in all Water, such as in the open Skagerrak (Torungen seasons except the summer. The largest increase 30 nmi) and at Utsira (Figure 4D, Table 2). The has been in the autumn, with 0.61 of the standard relatively cold and low salinity period at the end of deviation of the period 1962-1987 (Table 4, the 1970s to early 1980s, which is most pronounced Figure 6). at Sognesjøen (Figure 3), appears to be associated

Table 2. Mean temperature and salinity (Tm. Sm) during the period from 1940(50) to 1989, mean deviation from this mean in the 1990s (D ev9„s), and normalized deviation (Dev ,0s/stdev 40_89) for the surface stations and in 150 m depth at the fixed hydrographic stations during winter (Jan-Mar).

Stations (surface layer) Tm» 89 DevT,», Dev T„)s/Tstdev 4„_g9 Sm* Dev SWs De vS.,K/Sstdev Sl 89

Vardø 3.10 0.10 0.17 34.41 -0.01 -0.06 Loppa 3.58 0.12 0.20 34.00 -0.10 -0.42 Skrova 3.46 0.24 0.39 33.15 -0.25 -0.66 Folia 5.14 0.29 0.49 33.64 -0.10 -0.38 Stad 5.10 0.40 0.57 32.98 -0.18 -0.55 Utsira 4.89 0.79 0.91 32.95 0.45 0.71 Lista 3.98 1.01 0.84 31.97 0.69 0.61 Flødevigen 3.50 1.53 1.28 30.37 1.34 0.55

Stations (150 m depth) T m50-89 DevT,0 DevT)Ifc/T stdev,® 89 Sm5„ *9 Dev Sikk, Dev S„„/Sstdev ^o_89

Skrova 6.74 0.28 0.51 34.56 -0.12 -0.60 Sognesjøen 7.72 0.28 0.97 34.93 0.00 0.00 Utsira 7.38 0.35 0.85 34.92 0.06 0.55 Lista 6.87 0.07 0.15 34.81 -0.07 -0.59 Torungen 5 nmi 6.60 0.20 0.33 34.86 -0.07 -0.41 Torungen 30 nmi 6.89 0.51 0.78 35.09 0.05 0.42 Long-term hydrographic variability patterns 155

Lista 150m Lista 150m 35.0 - 7.4 - 34.9 - U o f- 1 34.7 - 34.6 - 6.4 - 6.2 - 34.5 19501940 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000

Utsira 150m Utsira 150m

U 7.6 - H l i ' J on« 34.9 - 7.0 - 34.!

6.4 34.7 1940 1950 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000

Sognesjøen 150m Sognesjøen 150m

o o â H to 34.9 -

7.2 34.1 1940 1950 1960 1970 1980 1990 2000 1940 1950 1960 1970 1980 1990 2000

35.0 -i Skrova 150m Skrova 150m 34.: 7.2 - .3* 34.< u o H 6.4 -

34.2 ■

5.6 34.0 1970 1980195019601940 1990 2000 1940 1950 1960 1970 1980 1990 2000

Figure 3. Mean temperature and salinity at 150-m depth for the first quarter o f the year at the fixed hydrographic stations along the coast. Five-year running means are indicated. with the “Great Salinity Anomaly of the North Discussion Atlantic (Dickson et al., 1988). At 300-m depth in the central Skagerrak the The variable inflow of oceanic water to the Norwe­ normalized seasonal temperature deviation from the gian and North Seas will influence the hydrographic period 1962-1987 to the period 1988-2000 is 1.1 to conditions along the Norwegian coast and in the 1.7 standard deviations, while that of salinity is 0.5 Skagerrak. The modelled winter inflow to the North to 0.9 (Table 4, Figure 6). There was also an increase Sea during January-M arch from 1955 to 2000 in the salinity in all seasons, between 0.5 and 0.9 of appears in Figure 2. As the large-scale wind pattern the standard deviation of the period 1962-1987 is the main driving force, the fluctuation in this (Table 4, Figure 6). There is a very good correlation inflow will most likely also reflect the variability between the temperature and the salinity in the in the inflow to the Norwegian Sea. As seen, there Atlantic water masses of the central Skagerrak, was a significant increase in the inflow in the which is in accordance with the increased inflow of late 1980s and 1990s. During the period 1988-2000 Atlantic Water to the North Sea during the past there were 6 winters with extremely high inflow decade (Figure 2). (> long-term mean +1 standard deviation). The mean 156 R. Sœtre et al.

Temperature 0.97 Temperature 1.28 surface layer 0.85 150 m 078 1.2 0.91 -o c !•'0 0.84 £ .2 0.8 cz c3 0.57 0.49 1 '§ °-61 0.39 0.33 Z "° 0.4 - 0.17 0.20 0.15 0.2 : 0.0 □ ,n 0.0

\

D 0.8 0.71 0.61 0.8 Salinity 0.55 Salinity 0.55 0.6 - Surface layer 0.6 150 m 0.42 ■o 0.4 -o 0.4 .1 0.2 M .1 .1 0.2 0.00 0.0

- 0.2 -0.06 - 0.2 -0.4 -0.4 -0.38 LJ - 0.6 0.42 -0.41 -0.55 - 0.6 - - 0.8 - 0.66 -0.8 ^ -0.60 •0.59

& ■0V V & <3 , < y «T

Figure 4. The normalized temperature and salinity deviation (temperature difference-salinity difference/standard deviation) between the decadal mean during the 1990s and the period 1940-1989 (temperature) and 1950-1989 (salinity). inflow in the 1990s was 1.75 Svor 1.6standard devia­ 0 .6 -i tions above the long-term mean for 1955-1989. This Q1 vs temperature 0.50 0.46 inflow was highly correlated with the North Atlantic 0.5 - surface laver 0.40 Oscillation (NAO) winter index (Hurrell, 1995) with 0.36 0.4 r2 approaching 0.5. A high NAO index is associated 0.27 with mild winters and an increase in the westerly "ai 0.3 -I winds and the winter precipitation over Scandinavia. 0.2 0.15 The wedge-shaped Norwegian Coastal Current is 0.1 0.00 0.00 deep and narrow during winter and wide and shal­ 0 low during summer. The driving mechanism for this seasonal lateral oscillation of the current is most likely an effect of the monsoon-like wind pattern V ^ V along the Norwegian coast (Sætre et al., 1988). High Figure 5. The correlation coefficient (r2) between the winter NAO levels mean increased southwesterly winds, inflow to the North Sea (Jan-Mar) and the temperature in the and this will deepen the Norwegian Coastal Current upper layer for the period 1989-2000. off most of the coast and could result in colder and less saline coastal water. Consequently, a high NAO winter index is not necessarily synonymous with southern coast the correlation is reasonably good higher temperature and salinity in coastal waters. (Table 3), but is markedly reduced further north. The increased temperatures and salinities during The variability pattern in the Atlantic inflow to the winter in Norwegian coastal water in the 1990s are Norwegian Sea will most likely be similar to that of clearly related to a significant increase of the inflow the N orth Sea. The Stad station is believed to reflect of relatively warm and saline Atlantic Water during the fluctuations in this northern branch of the the same period and especially in the deeper layers Atlantic inflow towards the Norwegian coast. The which are more directly influenced by the Atlantic correlation between the winter temperatures at Stad Water. Figure 5 shows the relationship between the versus those of the other coastal stations (Table 3) winter inflow to the North Sea and the temperature indicates low Atlantic influence off the coast of in the upper layer for the period 1989-2000. Off the northern Norway. Long-term hydrographic variability patterns 157

Table 3. The correlation coefficient (r) between the winter 1990s mostly influenced the hydrographic con­ inflow of Atlantic Water to the North Sea (Q, ) and surface ditions in the upper layer along the southern and layer temperature in Jan-M ar at the coastal stations and central Norwegian coasts. There is a rather strong between winter temperature at the station Stad versus the other coastal stations during the period 1989 2000. positive correlation between the temperature and salinity variations (r2 around 0.5) along the southern Station r ( Q l) r(Stad) coast, while further north the two parameters appear to be uncorrelated. This supports the above Vardø 0 0.28 statement. Loppa 0 0.10 Skrova 0.15 0.14 The long-term decreasing salinity trend in the Folda 0.27 0.90 surface layer along the Norwegian coast is probably Stad 0.36 * Utsira 0.50 0.70 mainly caused by the increased precipitation and Lista 0.46 0.68 thereby the substantial increase in freshwater Flødevigen 0.40 0.75 run-off. Førland et al. (2000) demonstrated that the winter precipitation in western Norway is more than 25% higher during 1980-1999 than for the normal period 1961-1990. It is likely that this precipitation Table 4. Mean seasonal temperature and salinity in the periods 1962-1987 and 1988-2000, the difference in means pattern reflects that of northwestern Europe, so in between the two periods, the standard deviation for the the 1990s the Norwegian Coastal Current has been period 1962-1987 and the normalized deviation (Diff/stdev) supplied with more freshwater from the Baltic and between the two periods at the stations Toningen 30 nmi from the North Sea. One of the effects of the regula­ (300 m). Torungen 5 nmi (10 m) and Torungen 52 nmi (10 m) tion of the freshwater run-off due to construction (Torungen- Hirtshals section). of hydroelectric power plants is increased winter discharge and this may also be an important S 62-87 S 88-00 DilTS StdeV S 62-87 Diff S/stdev explanatory factor. Asvall (1976) shows that in the 30 nmi 300 m S-Season southeastern region of Norway the mean natural Winter 35.12 35.15 0.03 0.07 0.47 winter freshwater discharge during the period Spring 35.08 35.14 0.06 0.07 0.86 Summer 35.11 35.17 0.06 0.07 0.82 1969-1973 increased by up to 170% due to flow Autumn 35.13 35.18 0.05 0.06 0.87 regulation. Along the southern and central Norwegian coasts 30 nmi 300 m T-Season Winter 6.27 6.91 0.63 0.56 1.1 the winters of the 1990s are characterized by the Spring 5.72 6.61 0.88 0.62 1.4 highest decadal mean temperatures both in the sur­ Summer 5.68 6.57 0.89 0.51 1.7 face and in deeper layers for the whole period of Autumn 6.02 6.78 0.76 0.5 1.5 observations. In the upper layer this tendency is 5 nmi 10 m S-Season most pronounced in the southern parts. Along the 32.13 0.97 2.08 0.47 Winter 31.15 northern coast, however, other decades, such as Spring 29.08 29.74 0.65 2.87 0.23 Summer 30.01 30.35 0.34 1.67 0.20 the 1950s and the 1970s, show higher decadal mean Autumn 31.33 30.97 -0.36 2.02 -0.18 temperatures. 5 nmi 10 m T-Season Along the northern Norwegian coast bordering Winter 4.63 5.68 1.06 2.27 0.46 the Barents Sea, variability patterns seem to follow Spring 4.36 6.09 1.72 2.63 0.65 that observed in the open Barents Sea (Ingvaldsen Summer 14.34 14.32 -0.02 2.63 -0.01 Autumn 12.14 13.06 0.92 2.30 0.40 et al., 2003), where the 1950s were notably colder than the 1990s. Although the NAO has a significant 52 nmi 10 m S-Season effect on the climatic variability of the area, local Winter 33.78 34.14 0.36 0.95 0.38 Spring 33.40 33.67 0.28 1.31 0.21 wind and atmospheric pressure forces seem to be Summer 32.39 32.25 -0.14 1.14 -0.12 major factors determining the degree of Atlantic Autumn 32.94 33.48 0.55 0.90 0.61 inflow to, as well as the circulation and water mass 52 nmi 10 m T-Season distribution within, the Barents Sea (Ingvaldsen Winter 5.69 6.51 0.82 1.68 0.49 et al., 2003). 6.58 1.44 1.99 0.72 Spring 5.14 The observations of long-term temperature and Summer 13.89 14.29 0.40 2.50 0.16 Autumn 12.40 12.54 0.14 2.34 0.06 salinity variability in Norwegian Coastal waters sug­ gest that the fluctuations may be due either to direct changes in the heat transfer of the region or be This, combined with the reduced normalized tem­ advective in nature (Blindheim et al., 1981). How­ perature and salinity deviation from south to north ever, this is most likely not a case of “either/or”. The during the 1990s (Table 2, Figure 4A, B), indicates two types of climatic signals probably interact in a that the increased inflow of Atlantic Water in the rather complicated way. 158 R. Sœtre et al.

Torungen 5nm Torungen 5nm 0.9 - 10m 0.9 - 10m

0.7 - 0.7 o -a - ir. 0.5 - 0.5 - H fc: "O 0.3 - 0.3 - i— i—i—i o ö 0.1 J -0.1 J Winter Spring Summer Autumn Winter Spring Summer Autumn

1.0 - Torungen 52nm Torungen 52 nm 10m 0.9 0.8 - 10m

0.7 1 0.6 -

1 0.5 fc 0.4 - Cf) 1 0.3 0.2 -

1— 1 0.1 0.0 -

Winter Spring Summer Autumn Winter Spring Summer Autumn

2 0 n Torungen 30 nm .0 -| Torungen 30nm IS- \ 6 : 300m 300mi-----1 0.8 - L4 : 1.2 - I 0.6 - 1.0 - C / 3 0.8 - fe 0.4 0.6 - 0.4 - 0.2 -I 0.2 : 0.0 - 0.0 LQI Winter Spring Summer Autumn Winter Spring Summer Autumn

Figure 6. The normalized seasonal deviation (deviation/standard deviation) in temperature and salinity between the periods 1962-1987 and 1988-2000 for 3 stations on the Torungen-Hirtshals section.

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