Oxygen Isotope Composition of Fjord and River Water in the Sognefjorden Drainage Area, Western Norway. Implications for Paleoclimate Studies

Home , Gat (landform)

Estuarine, Coastal and Shelf Science (2000) 50, 441–448 doi:10.1006/ecss.1999.0581, available online at http://www.idealibrary.com on

G. Mikalsen and H. P. Sejrup

Department of Geology, University of Bergen, Allegt. 41, N-5007 Bergen, Norway

Received 7 June 1999 and accepted in revised form 29 October 1999

During two cruises and one field expedition from 1996 to 1998, 32 water samples from 10 stations in Sognefjorden and tributary fjords and six samples from rivers draining into the fjord were obtained for oxygen isotope measurements. In addition, CTD profiles were obtained from all of the fjord locations. The river samples show a large gradient in the oxygen isotopic composition from the outer fjord region to the rivers at the fjord head. The difference is more than 6‰ with highest values recorded at the fjord mouth decreasing inward along the fjord. The low oxygen isotope values are found in areas with a high altitude from the watershed. The gradient in the river water is explained by distance to the moisture source, topographic effects and temperature of precipitation. The isotopic composition of the fjord waters suggest a mixing line for Sognefjorden of 0·31‰ for a salinity change of 1 which is slightly higher than the North Sea mixing line (Israelson & Buchardt, 1991), and lower than the North Atlantic mixing line (Craig & Gordon, 1965). The river samples are not used in the calculation of the mixing because of the large differences in the isotopic composition of river water along the fjord, and large seasonal differences of precipitation. 2000 Academic Press

Keywords: oxygen isotopes; mixing line; fjords; western Norway

Introduction composition of fjord water is needed for such studies to be quantitative. So far, no such The need for obtaining high resolution climatic proxy studies are published from the western Norwegian records has triggered an increasing interest for fjords. fjord sediments as climate archives. This is also the Oxygen isotope mixing lines have been constructed case for western Norwegian fjords, partly because for North Atlantic waters (Craig & Gordon, 1965) of the probability for obtaining high resolution and the North Sea (Israelson & Buchardt, 1991). paleoceanographic/paleoclimatic records, and partly Craig and Gordon (1965) found for the North because their location close to the Norwegian Atlantic a linear mixing line that gave 0·61‰ Current, that offer possible link between the marine change in isotopic composition for a change in and terrestrial paleoclimate records. salinity of 1. Israelson and Buchardt (1991) Stable oxygen isotope measurements on benthonic proposed a mixing line for the North Sea (0·25‰ foraminifera are a promising method for reconstruct- change in isotopic composition for a change in salinity ing climate change in the fjord environment. From of 1), that is much lower than the North Atlantic such studies it is possible to estimate temperature mixing line. or salinity changes through time (e.g. Sarnthein In this paper a mixing line for Songefjorden (west- et al., 1995). To do this we need to know the ern Norway) is presented, which perhaps is applicable controlling factors of the oxygen isotope composition to other western Norwegian fjords. This is based on of fjord water. As the Holocene (last c. 10 000 years) 32 oxygen isotope measurements at depths between is of particular interest for such studies it can 20 to 638 m at 10 stations in the Sognefjorden fjord be assumed that the global ice volume effect on sea system. Six measurements of fresh water from rivers water 18O is negligible at least since 7–8 ka BP. draining into Sognefjorden will also be discussed in Information on how the mixing of oceanic the light of the location of the samples relative to water and fresh water influences the oxygen isotope topography and distance from the coast, and the

0272–7714/00/040441+08 $35.00/0 2000 Academic Press 442 G. Mikalsen and H. P. Sejrup

40° 30° 20° 10° 0° 10° 20° (a) SVALBARD (b) 76° BEAR ° Is. 70

1000 N 74°

GREENLAND JAN 66° MAYEN Greenland Sea ARCTIC FRONT

1000 70° ea

ICELAND PLATEAU egian S 62° ° orw 66 NORWAY NC CC N Sognefjorden ICELAND FAEROE ° Haugselvi 10 Is. 58 00 ° N. Channel Fortundalselva 62 0 Lista 0 0 1 Skiolden Fjærland North Atlantic NORTH 111-3 SEA 20° 10° 0° 111-4 Årøyelvi Ytredalselva Ygleelvi 111-9 111-8 111-5 118-1 118-5

111-1 111-15 Vikja 111-11 Sognesjøen

Sognefjorden drainage area

Glaciers

50 km F 1 (a) A location map showing Sognefjorden and major oceanic surface currents (NC=Norwegian current, CC=Coastal Current) in the North Atlantic and Nordic Seas. =location of Lista (b) Sognefjorden drainage basin with sample locations in the fjords ( ) and from rivers ( ). [=Location of Ygleelvi (Henriksen et al. 1996). isotopic composition of fresh water draining into the summer when snow melts in the mountain areas fjord. surrounding the fjord. Precipitation in western Norway is normally transported with south-westerly winds from the North Sea and North Atlantic. During Physiographical setting times with easterly winds almost all precipitation falls The general physiography of western Norway is char- on the eastern side of the water divide and little is acterized by high mountains that drop oﬀ seawards to contributed to the water in the western Norwegian the strand ﬂat (Nesje & Sulebak, 1994). The western fjords. Norwegian fjords cut far into the country and are deep Sognefjorden is the largest fjord in Norway, (maximum depth of Sognefjorden is c. 1300 m) sur- c. 200 km long and more than 1300 m deep. The fjord rounded by steep slopes high mountains. These are is separated from the shelf areas by three deep sills normally in the inner parts of the fjord between 1300 where the shallowest is more than 160 m deep. The to 1800 m high. The highest total vertical relief in Sognefjorden drainage system covers 12 339 km2 Sognefjorden is up to 2600 m. Rivers enter the fjord at (Nesje & Sulebak, 1994) reaching from the coast to the fjord head or in tributary fjords. Some of the rivers the water divide between the eastern and western part are fed by glaciers and carry older water into the fjord. of Norway (Figure 1). The highest mountains in the The largest freshwater input is during late spring and drainage system reach up to c. 2400 m above sea-level. Oxygen isotope mixing line, western Norway 443

The hydrographical conditions along the western on water samples (Johannessen, pers. comm.). The Norwegian coast is influenced by Atlantic water (>35 samples were measured relative to the VSMOW salinity, Helland-Hansen & Nansen, 1909; Hopkins, standard, and are referenced relative to VSMOW. 1991) flowing northwards into the Nordic Seas (the Norwegian Current). A branch of this current flows Data and calculations southwards in the North Sea (Figure 1). Coastal water flows northwards along the coast (the Coastal Cur- River water 18O rent) (North Sea Task Force, 1993). The coastal current (<35 salinity, Hopkins, 1991) is a mixture of Figures 1 and 3 show that the rivers, from which water Atlantic water, water out-flow from the Baltic Sea, has been sampled, have large differences in size and and precipitation and river runoff from the Norwegian elevation of drainage areas. The results of the oxygen mainland. Within the fjord the hydrological condi- isotope measurements show a decreasing west-east tions are dominated by a low salinity surface water gradient in the fjord (Figure 3). Hence the results (Figure 2) (commonly less than 50 m thick) caused by show a gradient from 9·24‰ in Ytredalselva precipitation and river runoff. Under this (termed the (elva=river) at Vadheim to 14·5‰ in Haugselvi intermediate layer with salinities of less than 35) is a (elvi=river) at Skjolden. mixture of surface water and deep fjord water. This All river samples (except in Ytredalselva at intermediate water can under certain wind conditions Vadheim) have to some extent an input of glacial melt have a connection to the coastal current (Svendsen, water. The glaciers reappeared in western Norway 1981). The deep fjord water has its origin from open c. 5000 years ago (Nesje & Kvamme, 1991). However, ocean water and has salinities close to or above 35 since our river measurements are representing winter (Hermansen, 1974). This water is believed to origi- precipitation (snow melting in the mountains) we nate from cooling of the coastal current water during believe that the isotopic composition has not changed extreme cold winters, or Atlantic water being raised much since. The most likely explanation for the above sill level by favourable wind conditions. The observed gradient is a combination of the continental connection between the basin waters in Sognefjorden effect (distance from source) and temperature of the and the oceanic waters (Atlantic or Coastal waters) is precipitation. As the air is transported, continental believed to be good. All basin water is exchanged on precipitation depletes the clouds of heavy isotopes an average rate between 5 to 10 years (Hermansen, (Dansgaard, 1964). The high inland mountains will 1974). also force the clouds to precipitate at colder temperatures at higher elevations. There is also a continental temperature effect during winter, when the coastal Materials and methods areas are warmer than the inland caused by the coastal Water samples were collected during cruises on Uni- exposure to the Norwegian current which transports versity of Bergen’sRVHans Brattstøm in September warm water northwards. The continental effect and 1996 and February 1998 (cruise HB111-96 and the temperature effects add up to produce a gradient HB118-98). Water from rivers was collected during a from the coast and inland. The low values at the fjord field expedition in June 1998. Salinity was measured head are similar to values as far inland as Pechora in with an accuracy of 0·02 with a CTD SD204 on northern Russia (Rozanski et al., 1993). cruises HB111-96. On cruise HB118-98 a CTD OTS probe was used. The CTDs were run slowly with a 18 Fjord water O maximum speed of 0·5m s 1. Water samples for isotopic measurements was sampled with the CTDs The sampling depth, isotopic measurements and sal- rosette at different depths in the water column. The inity of the fjord water samples are presented in Table river samples were sampled from the surface river 1 and Figure 2. The salinity range (CTD profiles) of water 0·5 to 2 km upsteam from the mouth of the river the fjord waters from 20 m depth and down to the (Figure 1). bottom is between 32·4 to just above 35 for all stations Oxygen isotope ratios were measured at the GMS except the silled tributary fjords (stations 111-8, laboratory at the University of Bergen. Water samples 111-9 and 111-15). The results suggest a mixing line 18 were equilibrated with CO2 at 20 C in an automated of 0·31‰ change in O per unit change in salinity Finnigan preparation line, before automatically trans- [Figure 4(c)]. This indicates an average freshwater fer to a Finnigan DELTA-E mass spectrometer for input of 10·49‰. Equation 1 expresses a mixing isotope analysis. The analytical uncertainty is reported line constructed from water samples within the fjord, to be 0·1‰ for the oxygen isotope measurements x=salinity, R2=0·88. 444 G. Mikalsen and H. P. Sejrup

36 33 30 27 24 Salinity HB111-3 21 18 15 0 100 200 300 400

36 36 33 33 30 30 27 27 24 24 21 21 18 Salinity Salinity HB111-4 HB111-9 15 18 12 15 9 12 6 0 100 200 300 400 0 20 40 60 80 100

Inner 36 Inner 36 33 33 30 30 27 27 24 24 21 Salinity Salinity HB111-5 18 HB111-8 21 15 18 12 15 0 200 400 600 800 0 50 100 150 200 250 300

36 36 Tributary fjords Main fjord 34 34 32 32 30 Salinity Salinity HB118-5 HB111-11 30 28 28 26 0 200 400 600 800 1000 0 50 100 150 200

Outer 36 Outer 34

32 32 Salinit Salinity HB118-1 30 HB111-15

28 30 0 200 400 600 800 1000 0 40 80 120 160 Depth in metres 36

32 Outer HB111-1 30 Depth in metres 28 0 100 200 300 400 500 Depth in metres F 2. Salinity proﬁles from the fjord stations. Dark dots indicate salinity and sample depth for the measured samples. For location see Figure 1. All values are listed in Table 1. Oxygen isotope mixing line, western Norway 445

–17 North side –16 2000 –15 Oxygen isotopes (VSMOW)

South side Haugselvi –14 Fortundalselva Jostedalselvi 1500 –13

Ar° –12

ø yelvi 1000 Vikja –11 –10

Ytredalselva –9 Metres above sea level 500 –8 –7 –6 0 25 50 75 100 125 150 175 200 225 250 km from open ocean F 3. An indication of the height of the watershed on the north and south side of the Sognefjorden (height above sea level on left) as a proﬁle from the coast to the inner fjord. The isotopic values from the river samples (thin line) are also plotted (values on right). [=Isotope values of Ygleelvi (Henriksen et al., 1996). =Isotope values for the precipitation along the western Norwegian coast, at Lista (Rozanski et al., 1993; Yurtsever & Gat, 1981).

y= 10·492‰+0·31x (1) below the surface waters) in the main fjord and above sill level in the tributary fjords (e.g. Gade, 1976). This From Equation 1 and Figure 3 it can be noted that the may influence the low salinity values in the equations. average isotopic composition of the freshwater end member is comparable to outer fjord runoff. Mixing line for Sognefjorden If we combine the results from the water column with the results obtained from rivers [Figure 4(a and Figures 3 and 4(a) show both the variability in the b)], (Equation 2) it can be seen that there is a small oxygen isotope composition of the rivers along the change in the mixing line to 0·37‰ for each salt unit fjord and the decreasing values toward the fjord head. change and the average isotopic composition of The river water samples reflect mostly winter precipi- precipitation/runoff changes to 12·51‰. Equation tation because of snow melting in the mountain areas 2 expresses the mixing line constructed from water reducing sampling. The reason for the decrease inland samples within the fjord and from river samples, has partly to do with the continental effect. The x=salinity, R2=0·96. distance between the sampling locations are only c. 150 km, however the distance where the precipita- y= 12·512‰+0·37x (2) tion fall (drainage areas) is up to c. 200 km. Another factor is topography and its effect on temperature. Clearly the river data changes the average isotopic Since the coastal relief is lower than the relief further composition of the freshwater end member and the inland, the precipitation at the coast will precipitate mixing line. This may be a result of, (a) the fjord water under higher temperatures than in the mountain areas samples in some areas being more strongly influenced at the water divide. by some rivers than others. If the sampling stations are Henriksen et al. (1996) documented oxygen isotope unevenly distributed in the fjord this will affect the values of c. 11·5‰ for the water in the river Ygleelvi isotopic composition of the calculated freshwater in the central part of Sognefjorden (Figures 1 and 3), input. However, in this study we regard the vertical and measurement of the precipitation along the and horizontal sampling as evenly spaced. (b) A Norwegian coast, at Lista (e.g. Rozanski et al., 1993; second explanation may be the sampling strategy of Yurtsever & Gat, 1981) show a annual mean value of the rivers. We do not have control on how much these 6·74‰, with 5·35‰ annual variations. Both rivers (that are sampled) contribute to the mixing these values seem to support the observations of a in the fjord. There are many large rivers in the decreasing gradient inland (Figure 3). Sognefjord drainage system which were not sampled A meteorological station at Fjærland (Figure 1) has (Figure 1). (c) There may be a strong influence from measured the oxygen isotope composition of the pre- the coastal waters, at least in the upper 200 m (but cipitation in 1992–1993 (Henriksen et al., 1996). This 446 G. Mikalsen and H. P. Sejrup

T 1. All river and fjord water samples

Oxygen isotop Sample station Position Water depth Salinity values (VSMOW)

111-1 61.01.35N 04.48.4E 20 32 748 0·33 111-1 61.01.35N 04.48.4E 50 34 475 0·24 111-1 61.01.35N 04.48.4E 200 35 129 0·37 111-1 61.01.35N 04.48.4E 400 35 167 0·53 111-1 61.01.35N 04.48.4E 460 35 165 0·36 111-3 61.26.0N 07.22.6E 20 32 453 0·39 111-3 61.26.0N 07.22.6E 100 34 846 0·36 111-3 61.26.0N 07.22.6E 200 34 941 0·39 111-3 61.26.0N 07.22.6E 325 35 055 0·40 111-4 61.19.5N 07.21.3E 20 32 608 0·38 111-4 61.19.5N 07.21.3E 100 34 944 0·25 111-4 61.19.5N 07.21.3E 300 35 029 0·12 111-4 61.19.5N 07.21.3E 371 35 022 0·39 111-5 61.14.3N 07.22.0E 638 35 030 0·41 111-8 61.12.3N 07.05.9E 20 32 724 0·50 111-8 61.12.3N 07.05.9E 50 33 916 0·06 111-8 61.12.3N 07.05.9E 100 34 109 0·09 111-8 61.12.3N 07.05.9E 200 34 066 0·01 111-9 61.14.65N 07.07.35E 20 32 790 0·44 111-9 61.14.65N 07.07.35E 50 33 064 0·24 111-9 61.14.65N 07.07.35E 80 33 119 0·46 111-11 61.03.7N 06.25.5E 20 32 604 0·27 111-11 61.03.7N 06.25.5E 100 34 899 0·34 111-11 61.03.7N 06.25.5E 190 35 097 0·03 111-15 61.04.5N 05.38.1E 75 33 500 0·21 111-15 61.04.5N 05.38.1E 120 33 554 0·17 118-1 61.08.48N 05.45.69E 40 33 508 0·13 118-1 61.08.48N 05.45.69N 90 34 451 0·11 118-1 61.08.48N 05.45.69E 140 34 846 0·24 118-5 61.09.25N 06.35.90E 40 33 756 0·03 118-5 61.09.25N 06.35.90E 80 34 581 0·16 118-5 61.09.25N 06.35.90E 120 34 752 0·29 Arrøyelvi (Barsnesfjord) 61.16.2N 07.09.5E 0 0 12·35 Jostedalselvi (Gaupne) 61.24.5N 07.16.0E 0 0 13·82 Fortundalselva (Skjolden) 61.29.8N 07.40.0E 0 0 14·04 Haugselvi (Skjolden) 61.30.0N 07.36.2E 0 0 14·50 Ytredalselva (Vadheim) 61.15.5N 05.49.3E 0 0 9·24 Vikja (Vik) 61.04.2N 06.36.5E 0 0 11·17

show large differences in the oxygen isotope compos- water along the fjord (>6‰) and the large differences ition related to season (from max 1·17‰ to min related to seasonal variations in the precipitation 17·4‰, mean value 8·58) with low values (more than 15‰), make us believe that the water recorded during winter and highest values during measurements within the fjord waters are the most summer. The meteorological station (Norsk Meteor- suitable for calculating an oxygen isotope mixing line ologisk Institutt, 1992, 1993) shows that most of the for this fjord. We suggest an oxygen isotope mixing precipitation is received during the months (winter line of 0·31‰ for each salt unit for Sognefjorden time) with low oxygen isotope values. including tributary fjords, and assume this to be a The oxygen isotope mixing line calculation based linear correlation. This fjord mixing line differs from on the rivers and fjord samples gives a mixing line of other calculations (by 0·06‰) for the North Sea 0·37‰ for each salt unit change (Figure 4). If only the (Israelson & Buchardt, 1991). We have demonstrated fjord water samples are considered, a lower line of that the approach of using endmembers (highest to 0·31‰ per salt unit is obtained (Figure 4). The lowest salinity) for calculations of mixing lines is variability in oxygen isotope composition in the river not satisfactory for the fjord environment. In this Oxygen isotope mixing line, western Norway 447

runoﬀ along the fjord, and mixing of Atlantic and 0 (a) Coastal waters. Y = 0.37x – 12.51 R2 = 0.97 –4 Implications for paeloclimate/oceanographic studies The oxygen isotope composition of calcareous organ- –8 isms such as foraminiferas, molluscs, ostracods etc. (VSMOW)

Oxygen isotope that calcify these tests in isotopic equilibrium with the adjacent water masses or with a known isotopic vital –12 eﬀect is a promising paleoclimate proxy. To be able to quantify temperature and salinity variations in the adjacent water masses a detailed mixing line is re- 0 6121824 3036 quired. The mixing line present here is probably not Salinity valid in the surface water masses, because no samples 1 above 20 m water depth have been obtained and (b) due to local isotopic variations in freshwater input. We believe the mixing line is valid for intermediate and basin waters in western Norwegian fjords and hence should be applied in future studies of western Norwegian fjords. 0 The low gradient mixing line (0·31‰ for each salt unit) shows that salinity changes are harder to detect (VSMOW) in the fjords than in the North Atlantic. Hermansen Oxygen isotope (1974) showed that there has been a parallel trend between temperature and salinity in the deeper parts of Sognefjorden from 1930 to 1970 and that larger –1 amplitudes are recorded in temperature (c.0·5 C) 32 34 36 and smaller amplitude changes in salinity (c. 0·08). Salinity This gives an oxygen isotopic variation of 1‰ for temperature and 0·0248 for salinity. Also in the outer 1 part of Sognefjorden (Sognesjøen, Figure 1) oceano- (c) graphic measurements has been performed since the Y = 0.31x – 10.68 1930s (Aure & Østensen, 1993), and show the same 2 R = 0.89 relationship between temperature and salinity as the deep fjord. However, the amplitude of the signals are 0 larger of more frequent water exchange, and show 2·5 C(0·575‰ of stable oxygen isotopes) and 0·3in

(VSMOW) salinity (0·093‰ in oxygen isotopes). This, and the Oxygen isotope parallel trend between temperature and salinity indicates that oxygen isotope records retrieved for paleoclimatic/paleoceanographic reconstructions from –1 Sognefjorden (western Norwegian fjords) are most 32 34 36 likely reflecting a minimum temperature signal. Salinity  18 F 4. (a) Salinity vs Owater for all samples (Fjord and rivers). (b) An enlargement of Figure 4(a) in the range 18 Acknowledgements between 32 to 36 salinity. (c) Salinity vs Owater from the fjord samples. We would like to thank the crew of RV Hans Bratstrøm for their help, Odd Hansen for laboratory assistance; study it is assumed that the mixing of oceanic and Dorthe Klitgaard-Kristensen, Eystein Jansen and fresh waters has a linear relationship for the oxygen reviewer Denise Smythe Wright for comments on the isotope signal. This is not necessarily true in a fjord manuscript; and Jane Karin Ellingsen and Else environment because of the 18O variations in river Hansteen Lier for the help with the map. The project 448 G. Mikalsen and H. P. Sejrup has been funded through the Norwegian Research Israelson, C. & Buchardt, B. 1991 The isotopic composition of Consul and the EU (funded ENAM2 project. oxygen and carbon in some fossil and recent bivalve shells from East Greenland. LUNDQUA Report 33, 117–123. Nesje, A. & Kvamme, M. 1991 Holocene glacier and climate variations in western Norway: Evidence for early Holocene gla- References cier demise and multiple Neoglacial event. Geology 19, 610–612. Nesje, A. & Sulebak, J. R. 1994 Quantification of late Cenozoic Aure, J. & Østensen, Ø. 1993 Sognesjøen. St nr: 67, 1935–92, erosion and denudation in the Sognefjord drainage basin, western 6104N0450.4E. Hydrografiske normaler og langtidsvarias- Norway. Norsk Geografisk Tidsskrift 48, 85–92. joner i Norske kyst farvann. Fisken og Havet 6, 36–43. Craig, H. & Gordon, L. I. 1965 Deuterium and oxygen 18 Norsk Meteorologisk Institutt. 1992 Daglige nedbørhøyder for 1992, variations in the oceans and the marine atmosphere. In Stable Skarestad, Fjærland. Isotopes in Oceanographic Studies and Paleotemperatures, Spoleto, Norsk Meteorologisk Institutt. 1993 Daglige nedbørhøyder for 1993, July, 23th–26th. Consigilo Nazionale Delle Richerche, Labora- Skarestad, Fjærland. torio di Geologia Nucleare, Pisa, pp. 9–130. North Sea Task Force. 1993 North Sea Subregion 1. Assessment Dansgaard, W. 1964 Stable isotopes in precipitation. Tellus 16, Report, 44 pp. 436–469. Rozanski, K., Aragua´s-Aragua´s, L. & Gonfiantini, R. 1993 Isotopic Gade, H. 1976 Transport mechanisms in fjords. In Freshwater on the patterns in modern global precipitation. Geophysical Monograph Sea (Skreslet, S., Leinebø, R., Matthews, J. B. L. & Sakshaug, E., 78, 1–36. eds), The Association of Norwegian Oceanographers, pp. 51–56. Sarnthein, M., Jansen, E., Weinelt, M., Arnold, M., Duplessy, Helland-Hansen, B. & Nansen, F. 1909 The Norwegian Sea. Its J. C., Erlenkeuser, H., Flatøy, A., Johannessen, G., Johannessen, physical oceanography. Based upon the Norwegian researches T., Jung, S., Koc, N., Laberie, L., Marslin, M., Pflaumann, U. & 1900–1904. The Norwegian Report on Norwegian Fisheries and Schulz, H. 1995 Variations in Atlantic surface ocean paleocea- Marine Investigations 2, 1–359. nography, 50–80N: A time-slice record of the last 30 000 years. Henriksen, H., Rye, N. & Soldal, O. 1996 Groundwater transit Paleoceanography 10, 1063–1094. times in a small coastal aquifer at Esebotn, Sogn of Fjordane, Svendsen, H. 1981 Wind-induced variations of circulation and western Norway. Nores Geologiske Undersøkelser, Bull 431, 5–17. water level in coupled fjord-coast system. In (Sætre, R. & Mork, Hermansen, H. O. 1974 Sognefjordens hydrografi og van- M., eds), University of Bergen, Bergen, pp. 229–262. nutveksling. Candidate’s Science Thesis, Geophysical Ins, University Yurtsever, Y. & Gat, J. R. 1981 Atmospheric waters. In Stable of Bergen. 56 pp. Isotope Hydrology—Denterium and Oxygen in the Water Cycle (Gat, Hopkins, T. S. 1991 The GIN Sea—A synthesis of its physical J. R. & Gonfiaritini, R., eds), IAEA Technical Reports Series oceanography and literature review 1972–1985. Earth and no. 210 Wien, pp. 103–142. Planetary Letters 30, 175–318.