Selected aspects of the physical oceanography and particle fluxes in fjords of northern Norway

ELSEVIER

Journal of Marine Systems 8 (1996) 53-71

Selected aspects of the physical oceanography and particle fluxes in fjords of northern Norway P. Wassmann ay*, H. Svendsen b, A. Keck a, M. Reigstad a a Norwegian College of Fishery Science, University of Tromse, N-9037 Trams@, Norway b Geophysical Institute, University of Bergen, Allegt. 44, N-5007 Bergen, Norway

Received 7 March 1995; accepted 14 March 1995

Abstract Results regarding the physical oceanography and the dynamics of particulate fluxes in fiords of northern Norway are presented. The phytoplankton spring bloom takes usually place in April in almost homogeneous water and comes to an end before the estuarine circulation starts in late May/early June when snow and ice melting gives rise to usually one pronounced pulse of freshwater run-off. During late summer and autumn river run-off is usually small and of limited significance for the particulate dynamics. Much of the spring bloom material is apt to sink to the bottom, but overwintering herbivores give rise to decreased vertical losses from the upper layers as well as a tendency towards a decreased seasonal variability compared to more enclosed coastal systems in boreal fjords of southern Norway. While destruction and mineralisation of sedimenting matter is of significance below the euphotic zone, giving rise to a decrease in vertical flux, resuspension is of importance in the lower water column and close to the rivers. Coastal currents strongly influence the north Norwegian fjords and particulate signals from rivers are small and do not penetrate extensively into the fiords. Advection of particulate matter, phytoplankton and zooplankton along with various water masses in and out of the fjords seems to play an important role for the ecology and particulate fluxes in this area. The rapid exchange of water masses between the coastal currents and even the innermost fjords as well as the comparatively small discharge of freshwater gives rise to scenarios where particulate fluxes inside the coastal zone are to a large extent determined by external, oceanic forcing. North Norwegian fjords are, therefore, not independent entities, but in various degrees part of the Norwegian Coastal Current.

1. Introduction Coastal environments in general and at high latitudes in particular are important sinks for the export of organic carbon on a local as well as a global scale (Wollast, 1991; Bienfang and Ziemann, 1992). Fjords and fjord-like embayments

* Corresponding author.

comprise a substantial part of coastal environments at high latitudes (Syvitski et al., 1987). Fjords are often considered as estuaries. Although they have much in common with the majority of estuaries in a number of aspects, they function differently with regard to a suite of characteristics: (a> The freshwater discharge/volume ratio of the recipient is highly variable, but usually low, (b) some tjords have a land-locked character, shallow sills and are topo-

0924-7963/96/$15.00 Q 1996 Elsevier Science B.V. All rights reserved SSDZ 0924-7963(95)00037-2

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graphically complex, (c) many fjords experience intermittent periods of stagnation of bottom water in basins, (d) their depth and length is generally greater than that of non-fjordic estuaries, (e) fjords experience a considerable altitude of their hinterland and (f) some fjords have glaciers in the vicinity of the river mouth or tide-water glaciers extending into the recipient. All these characteristics make fjord ecosystems function differently compared to what is usually thought of when considering estuaries. As a consequence, the dynamics of particulate fluxes in and through estuaries and fjords can be expected to be different. The north Norwegian fjords are high latitude fiords with regard to the light regime, but are characterized by relatively high water temperatures and not significantly influenced by glaciers. The input of turbulent energy by tidal exchange and advection is considerable. Another important characteristic of northern Norwegian fjords is the limited amount of sea-ice coverage during winter

0

A

80

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and spring. Only some remote fjord arms or shallow, innermost parts of fjords (e.g. Porsangen) experience sea-ice during winter. This implies that important characteristics of Arctic environments, for example the dynamics of the marginal ice zone (e.g. Niebauer and Alexander, 1989; Sakshaug and Skjoldal, 1989), ice rafting (Glibert, 19901, suspended sediment transport (Cowan and Powell, 1990) and iceberg sedimentation (Dowdeswell and Murray, 1990) are not relevant. This implies that the particle fluxes in north Norwegian fjords must be different compared to other high latitude fjords influenced by sea-ice and glaciers (Syvitski et al., 1990). While the dynamics regarding particulate fluxes have been evaluated in fjords (e.g. Syvitski et al., 1987; Burrell, 1988) and west Norwegian fjords in particular (e.g. Wassmann, 19911, a thorough evaluation of the particulate fluxes in the subarctic fjords of northern Norway is as yet not available in the literature. The situation is similar with

km

Fig. 1. Overview over the north Norwegian coastal zone from the Lofoten islands to 28” E. (1) Malangen, (2) Balsfjord, (3)

Ullsfiord,(4) Lyngen, (5) Reisafjord, (6) Kvamangen, (7) Altafjord, (8) Porsangen, (9) Lakseljord, (10) Tanafjord, (11) Senja, (12) Andtiya and (12) Lofoten.

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regard to the physical oceanography. Given the importance of the physical environment, investigations of particle floes ought to be supported by best possible knowledge and adjoined by simultaneous investigations of physical oceanography. This contribution attempts to characterise selected aspects of the physical oceanography and particulate dynamics in north Norwegian fiords. It is based on a comparatively small number of publications (e.g. S&en, 1950; Eilertsen et al., 1981; Hopkins et al., 1989; Lutter et al., 1989; Tande, 1991; Noji et al., 1993; Reigstad, 1994) as well as preliminary data derived from ongoing research by the national research project North Norwegian Coastal Ecology (MARE NOR), mainly based on research carried out at the University of Tromso, northern Norway. Despite the preliminary nature of the presented data, it is intended that they will contribute to the general understanding until more in-depth evaluations of the ecology of this area are available.

2. Topography and physical oceanography External forcing in subarctic, coastal ecosystems of northern Norway is reflected in a suite of processes of which the most important are (a) local and geostrophic, large-scale wind fields, (b) the seasonality of stratification, ranging from almost homogeneous water in early spring to a sharp, but shallow pycnocline in summer, (c) the topography and (d) insolation. These factors govern freshwater discharge, the dynamics of primary production and hence vertical flux of organic matter. Superimposed on this general pattern is the export and import of water, nutrients, accumulated suspended mass and zooplankton all of which control the particulate dynamics in northern Norwegian fjords. 2.1. Topographic fea cures The part of the Norwegian coast considered here is roughly situated between the Lofoten islands (69” N, 15” E) to the Laksefjord (71” N, 27” E) (Fig. 1). In particular data from the Malan-

Table 1 Length, maximum depth, maximum width and sill depth of some northern Norwegian fjords Fjord

Length &m)

Max. depth Cm>

Max. width (km)

Depth at entrance (sill) Cm)

Malangen Balstjord Altafjord Porsangen

44 46 30 100

450 190 450 230

6 5 14 20

200 35 190 no sill

gen (1) and Balsfjord (2) fjords, close to the city of Tromso, and the Altafjord (7) and Porsangen fjord (8) will be presented. Compared to boreal fjords in southern Norway, one of the characteristics of the present fjords is the considerable depth of sills at the opening to the coastal zone. This makes them open to exchange with water masses from the Norwegian Coastal Current (NC0 and Norwegian Atlantic Current (NAO. The fjords are moderately deep and long, up to 450 m and 100 km, respectively (Table 1). The length varies considerably between larger fjords in the northernmost counties in Norway (Trams and Finnmark) and their depth, width and sill depth vary as well (Table 1). Except for Malangen most fjords in Troms county are narrow and relatively shallow with maximum depths less than 200 m. Some of the fjords communicate with the adjacent coastal waters through narrow inlets (Fig. 1). All fjords in Troms are sill-fjords although the sills may be of considerable depth, for example in Malangen. In the narrow fjords the sill is found in the entrance area (e.g. in Balsfjord) while shallow coastal plateaus act as sills to Malangen. As distinct from the fjords of Troms county, all the main fjords of Finnmark county are broad and except one, the Altafjord, have no sills either in the entrance area or as coastal plateaus. The Altafjord communicates through three narrow inlets, while all the others have unhindered contact with the NCC and the Barents Sea. The large dimensions of these fiords, 80-100 km long and maximum width lo-20 km, give them an appearance of bights.

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2.2. Currents outside the jjords The surface currents of the Norwegian Sea and along the Norwegian coast are strongly influenced by the relatively warm saline water of the NAC whose branches cover large areas of the Norwegian Sea. On the Norwegian coastal shelf, water from the NCC contributes to the northward flow (Saetre and Mork, 1981). The amount of Atlantic water entering the Barents Sea suggests that climatic variation (Adlandsvik and Loeng, 1991) and even salinity anomalies (Dickson et al., 1988) exist. The annual influx of Atlantic water through the Fuglgya-Bjornoya section in the south-western part of the Barents Sea varies between - 0.3 and +0.4 Sv around the average of 2 Sv (Adlandsvik and Loeng, 1991). Extensive variation in ocean climate is considered to influence the plankton dynamics of the north Norwegian coastal zone (Sundby, 1984) and the adjacent Barents Sea (Midttun and Loeng, 1987). Both the NAC and NCC are narrow, deep and strong off the Lofoten islands and follow the bathymetry of the north Norwegian coastal zone. Both water masses enter the trenches which are extensions of the longitudinal axes of the major

of Marine Systems 8 (1996) 53-71

fjords. These trenches separate relatively shallow coastal banks, and here clockwise circulation patterns are found (Sundby, 1984). Before both currents come to the entrance of the Barents Sea they follow the shelf break. The NAC branches into the West Spitsbergen Current and the remaining water turns into the southern Barents Sea as the North Cape Current. The NCC continues, but eventually looses its identity through mixing with the Atlantic water. The NCC is broad and shallow in May to September (50-100 m), but weaker and deeper during autumn and winter (< 200 m). The seasonal lateral oscillation of the coastal water has been attributed to upwelling events forced by north-westerly winds (Sztre et al., 1988). These variations give rise to differences in water exchange with the fjord basins as fjords with deep sills are able to experience inflow of dense Atlantic water during the productive part of the year, for example in Malangen fjord (see Fig. 4 and below). The strong currents along the shelf break, on the banks and into the deeper parts of the fjords create a complex scenario for the dynamics of particulate matter in this region. Even narrow fjords with shallow sills and situated in

5OOr

‘1 JAN 1 FES 1 MAR 1 APR 1 MAY 1 JUN 1 JUL 1 AUG 1 SEP 1 OCT 1 NOV 1 DEC

Fig. 2. Freshwater discharge from the M&elva river into Malangen from March to October in 1991. Also shown is the decadal, monthly average freshwater discharge (according to Aure, 1983).

P. Wassmann et al. /Journal of Marine System 8 (1996) 53-71 \JJind

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Fig. 3. Wind observations at 07.00, 13.00 and 19.00 at Hekkingen lighthouse outside fjord Malangen from March to October, 1991.

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the innermost part of the coast have to be regarded as part of the Norwegian coastal zone, closely interacting with water masses outside. 2.3. Hydrology All the north Norwegian fjords have rivers as their main freshwater sources. The discharge has a seasonal variation pattern with a maximum during snow melt. Maximum freshwater discharge takes place in early summer (Fig. 2) while a minimum is usually found in February, but this can vary as a function of weather conditions during winter. A second maximum may appear during periods of heavy rain in autumn, usually during September-November. The largest rivers running into the fjords up to the Porsangen fiord are the MHlselva (Malangen) and Altaelva (Altafjord). They have maximum discharges above 400 m3se1 in June (Fig. 2). The discharge to all fjords in northern Norway is on average less than 30 m3s-r between November and April. The contribution of the rivers from the counties Troms and Finnmark to the coastal zone and the Barents Sea (Paris Convention, 1991) is comparatively low (about 24 km3yr-‘). For comparison, this is only about 0.5% of the annual discharge of the Lena river to the Laptev Sea (Cauwet and Sidorov, 1996). The average total discharges of nitrate and phosphate by rivers to the Barents Sea region is low, about 584 and 24 t yr - ‘, respectively. This is only 4 and 9% of the Norwegian discharge to the Skagerrak region (Paris Convention, 19911, indicating that sewage and agricultural run-off are of little significance for the nutrient dynamics in this region. The rivers and fjords can therefor be assumed to be pristine with regard to nutrients.

of Marine Systems 8 (19%)

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amount of precipitation in the innermost parts of fjords is usually greater compared to the outer parts and on the coast. Wind in a fjord arises by differences in local physical processes (heating and cooling) and by large-scale geostrophic wind-fields passing the fjord region. The wind direction related to local processes and geostrophical wind-fields is mainly up- or down-fjord. An air current crossing a narrow fjord is forced to follow the longitudinal direction of the fjord due to topographical influences (Svendsen, 1977). Fjords in the same region, but with different orientation of the longitudinal axis, may therefore have different wind directions at the same time. Although strong cross-fjord wind components may occur in broad fjords, the prevailing wind directions in these fjords are also along the longitudinal direction. Along the coast the mean wind conditions have a geostrophic character and are characterized by prevailing southward and northward wind during spring and summer, and autumn and winter, respectively. Except for a few short periods the wind direction off Malangen has a prevailing northward component (Fig. 3). The longest period of wind, although weak, with a southward component appears in June to August. As Malangen is oriented northwest-southeast it is expected that winds with a dominating northward component results in down-fiord wind and vice versa. From this it is concluded that a prevailing down-fjord mean wind appears in Malangen during March to May and September to October and a prevailing mean up-fjord wind occurs in the summer months. However, the short-term variability of local wind forcing is considerable (Fig. 3). 2.5. Water masses and tide

2.4. Meteorology As the fjords extend far inland from the coast climatic differences exist which at times entail large gradients along the fjords in meteorological parameters such as air temperature, wind and precipitation. On the average temperature increases down-fjord in autumn and winter, and the opposite occurs during spring and summer. The

A pronounced seasonal variation pattern in temperature and salinity appear in the fjords and coastal waters (Fig. 4). Stratification is usually minimum in early spring followed by an increase from the beginning of the snow melt in May-June to September. Stratification decreases in late fall and during winter. Since the discharge of freshwater is situated in the inner part in most of

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northern fjords, stratification in the upper layers show an increasing tendency up-fjord. In broad fjords the distribution of salinity and temperature may show pronounced cross-fjord differences (Fig. 5B) which is related to the rotation of the earth (Coriolis effect). Dense Atlantic water enters these fjords during late spring and summer. In Malangen this was observed during early June and early August (Fig. 4). The tide appears along the coast of Norway as a progressive wave (period of 12.41 h) with a phase speed proportional to the square root of the bottom depth over which the wave passes. The varying depth of the coast and other topo-

0” 0

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a 7 6 5 4 i

33 36.0

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32.0

I April

I

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May

June

I

July

I

I

I

Aug.

Sept.

Oct.

Fig. 4. Variations of temperature (A) and salinity at six depths (B) at a station in the middle of Malangen, March to October, 1991. Note the general increase in temperature, the weak stratification in spring and the influx of saline water in June and August.

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graphic features, like islands and sounds, causes the time for maximum tide to vary considerably in the north Norwegian coastal zone. Phase differences (f30 min) even over relatively short distances of some few kilometres are observed. This, together with the complicated topography of many fjord systems, complicates the circulation related to the tide, especially in junction areas between fjord arms. Tidal exchange is noted to influence the flux of particulate matter in coastal areas (Lewis and Thomas, 1986; Griffin and LeBond, 1990). 2.6. Circulation and water mass exchange The weak stratification (Fig. 4) and the prevailing down-fjord wind in the winter months suggests that the mean circulation above the sill level in narrow fjords ( < 3 km in width) is dominated by a down-fjord current in the upper layer and a compensating up-fiord current below. As stratification increases during spring and summer, this circulation pattern is limited to the upper layers in periods of down-fjord wind and coastal wind towards the north. Northerly wind causes an Ekman transport out from the coast in the surface layer and a compensating inshore flow below, controlling the prevailing circulation (Svendsen, 1981). In periods when the wind at the coast and in the fjords interact in an antagonistic pattern (southerly winds at the coast and down-fiord wind) onshore Ekman transport forces water masses into the fjords below the surface layer, compensated by an outflow at depth. A three-layer circulation takes place. For example, in periods with up-fjord wind and in transition periods when the wind at the coast changes, a multi-layer structure appears in the circulation pattern. In narrow fjords, for example the Balsfjord, surface water properties will gradually change along the fjord axis (Fig. 5A). In broad fjords the circulation is different from that described for the narrow fjords. With prevailing down-fiord winds and weak stratification, a down-fjord current appears along the fjord side to the right of the current with a compensating inward directed current boarding the down-fjord current. As stratification increases it is most likely

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that the circulation will take a two-layer structure in parts of the fjord: a down-fjord surface current with a compensating up-fjord current below. The compensating current may be surfacing and a frontal zone appears along the fjord axis. Salinity data from the Altafjord reflect the marked crosssectional differences which can be expected in broad fjords (Fig. 5B). The above considerations are based on investigations in the broad fjord Porsangen and Altafjord (Svendsen, 1991) and on an analytical study (Cushman-Roisin et al., 1994). Studies indicate that Coriolis effect is considerable in broad fjords (Figs. 5B and Fig. 6). The distance from the shore sides where the frontal zone appears varies and depends on the strength of the wind, stratification and freshwater supply. It is most likely that the described current pattern is present in fjords most of the time that the water masses are stratified. As stratification varies, the zero-current level

I 35’

of Marine Systems 8 (1994) 53-71

varies and is situated at shallower depths in months of marked stratification, i.e., from late spring to late autumn. The basin water in these fiords is renewed in spring and summer as reflected by an increase in salinity. The renewal is a consequence of periods of wind towards the south along the coast. This causes upwelling of water at the coast with a density higher than that in the resident basin water (Fig. 4). Superimposed on the circulation patterns described above is the tide. In stratified water the internal tide (baroclinic mode) may cause excursion of several kilometres during an half tidal period. Although the net excursion is negligible, the supply of mixing energy by this excursion may be considerable. Especially in junction areas of fjord arms and narrow sounds, strong tidal mixing takes place, e.g. around the area of Tromso and the Altafjord (Fig. 1).

N

30’ 10’

7o” .69’ 15’

30’ E

30’ E

23O

Fig. 5. Distribution of surface salinity in (A) Balstjord, June 6,1992 and (B) Ahfjord,

June 13,1992.

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tion is usually rather low for the rest of the year. Autumn blooms are not regular and probably dependent on the incident light regime and in conjunction with increased wind mixing in early autumn. However, significant differences in the quantity and the timing of primary productivity and suspended biomass between fjords have been reported (E. Hegseth, pers. commun.). For example, the spring bloom apparently develops much later in Porsangen compared to the open coast, Altafjord, Malangen and Balsfjord. During mild winters continuous freshwater run-off gives rise to some stratification of surface waters which, in

3. Particle fluxes 3.1. Primary production and suspended biomass Few annual primary production measurements are available. In general, the spring bloom in the coastal zone of northern Norway occurs in late March to April (Fig. 7) and develops in cold, weakly stratified to non-stratified surface water (Eilertsen and Taasen, 1984; Reigstad, 1994). Additional increases in primary production are recorded in May-June, probably due to freshwater run-off and entrainment. Primary produc-

N

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TEMPERATURE

(“C)

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16-17

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1990

’ 0

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1990

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2’6O Fig. 6. Contour plot of sea-surface

AUGUST

distribution

2’6O

in Porsangen during June and August, 1990.

E

62

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turn, causes more rapid spring bloom development. The factors regulating the onset and development of the spring bloom in the region are not at present well-known; however, light penetration, wind-driven vertical mixing and sporadic freshwater run-off are probably the most important factors. The extent of the euphotic zone during the pre-bloom period varies between 30-40 m. During the spring bloom and periods of freshwater discharge, the depth of the euphotic zone can be reduced to about lo-15 m (E. Hegseth, pers. commun.). The weak stratification of the euphotic zone during spring can easily be broken down by strong winds of short duration (mostly down-fjord) which are frequently observed during spring, particularly in the innermost fjords (Fig. 3). It is widely accepted that the seasonal development of a pycnocline in combination with increasing solar radiation in spring, is a prerequisite for vernal spring blooms (Sverdrup, 1953; Smetacek and Passow, 1990). However, the spring bloom in north Norwegian fjords takes place in nearly

of Marine Systems 8 (1996) 53-71

non-stratified waters (Eilertsen, 1993) where growing cells can easily be mixed to depths below the euphotic zone. This has also been observed in boreal shelf and open ocean environments off Main (Townsend et al., 1992) and suggests that the phenomena is wide-spread and more the rule than the exception in many boreal and polar environments characterized by low spring freshwater supply. Deep penetration of light and the absence of wind-driven vertical mixing appear to support cell growth that overcome the vertical excursion rates of phytoplankton in the neutrally stable water column, thus giving rise to a bloom (Townsend et al., 1992). The importance of the climatic forcing of phytoplankton cell growth and the magnitude primary production in spring creates a scenario where the timing and the development of the vernal bloom is probably subjected to considerable interannual variability in north Norwegian fiords. However, the few annual cycles of primary production hitherto investigated indicate that the interannual variability in the Balsfjord is limited (Fig. 7). Fig. 8 shows the development of the sus-

‘\

lAlSlOlNlD Time (months) Fig. 7. Primaly production in Balsfjord 1976-1978 (redrawn from Eilertsen and Taasen, 1984).

P. Wassmann et al. /Journal of Marine Systems 8 (1996) 53-71

63

fleet several moderate phytoplankton blooms throughout the course of the year. There are indications of a first spring bloom in April at stations O-III. Increases in phytoplankton biomass

pended phytoplankton biomass from river Milselva (0) in the innermost reaches in Malangen to Hekkingen light house (V) on the coast in 1991. The suspended biomass data seem to re-

SUSPENDEDBIOMASS: 8. _

Chlorophyll

a

[ms m-* I

Malangen 199 1

60-

-

c4 ‘E

P

100 r

60-

m = 2 :

60-

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60 8

60

I

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J

I

J

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0

1

Time [months]

Fig. 8. Suspended chlorophyll a (mg rnm2) in the upper 30 m of the water column in Malangen from March to October, 1991 at 6 stations stretching from the mouth of the M8lselva river (0) and Hekkingen lighthouse (VI.

P. Wassmann et al. /Journal of Marine Systems 8 (1996) 53-71

64

Particulate

organic

carbon

sedimentation 30m

600

N :

6oo

III I

.E

jJ-j-jj!)

c E z “E 200 a 3 4000 : .o 0 E! 60° 600

1

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V

400 -200 -

‘I

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’

A

’

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’ J Time (months)

’

A

’

S

’

0

’

Fig. 9. Sedimentation of particulate organic carbon (POC) at 30 m depth in Malangen from March to October, 1991 at 5 stations from the inner part (I) to the outer part of the fjord close to Hekkingen lighthouse (V) (mg C m-‘d-‘1. ND: no data.

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are also obvious during the early stages of increased freshwater run-off and the concomitant development of a shallow pycnocline in late May throughout the fjord. A third bloom in July is indicated. For the rest of the year suspended biomass as reflected by chlorophyll does not indicate additional blooms. Except for the period March-April, the differences in suspended phytoplankton biomass are small throughout the fjord, indicating that phytoplankton dynamics along the longitudinal axis of Malangen are similar. The annual variation in suspended biomass in the euphotic zone is smaller than that in moderately exposed, boreal fjords of western Norway (Wassmann, 1991). Generally speaking, advection plays an increasing role for the seasonal flux of particles along gradients stretching from land-locked fjords and fjords to the shelf (e.g. Farmer and Freeland, 1983; Aure and Stigebrandt, 1989). Its significance increases at higher latitudes in Norway due to increasing tidal elevation and generally increasing sill depth. Evidence for advection of phytoplankton over long distances within the coastal zone and between inner parts and offshore has been provided from fjord environments in southern Norway (e.g. Braarud, 1975; Erga and Heimdal, 1984). Advection may terminate existing blooms and transport remnant shelf communities and new nutrients into the area. This is supported by observations from Balsfjord and Malangen during spring and early summer 1992 when water masses and different phytoplankton assemblages were exchanged at least three times during April-May (Reigstad, 1994; Riebesell et al., 1995). The fate of phytoplankton spring blooms in coastal waters has been discussed by several authors with regard to where it is transported and oxidised (e.g. Falkowski et al., 1988; Jickels et al., 1991). The general drift pattern of suspended particles in the north Norwegian waters suggests that the phytoplankton exported from the fjords is transported along the shelf and the shelf break. Cross-shelf transport probably takes place only through channels between coastal banks and in the benthic nepheloid layer. To which extent fjords are net importers or exporters of organic

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carbon is not known, but largely dependent on the frequency and duration of advective episodes during the productive season. 3.2. Patterns of particulate organic carbon sedimentation The classical pattern of spring bloom sedimentation followed by reduced loss rates thereafter has been recorded in boreal regions such as fjord embayments and entire fjords (e.g. Hargrave et al., 1985; Laws et al., 1988; Wassmann, 1991). It is also encountered in the NCC (Peinert, 1986) and in shelf seas like the Barents Sea (Wassmann et al., 1990). Shelf and fjords systems in the North Atlantic of similar latitude and hydrodynamic energy input should, therefore, be generally comparable with respect to their flux patterns (Wassmann et al., 1991). Sedimentation measurements are only available from two northern Norwegian fjords, Balsfjord and Malangen (Lutter et al., 1989; Reigstad, 1994; P. Wassmann and A. Keck, unpubl. res.). The data base is thus too small to give an indepth evaluation of the vertical flux in northern fjords. Rather some selected results will be presented which may shed light over the patterns, dynamics and order of magnitudes of vertical flux in this area. Fig. 9 shows the sedimentation of particulate organic carbon (POC) at 30 m depth in Malangen from station I close to river Mglselva to station V at Hekkingen light house in the outermost part of the fjord. The majority of seasonal POC sedimentation rates ranges between about 100 to 800 mg C me2d-‘. Three periods of increased POC sedimentation were recorded close to the river (I): April-May, June-July and September. These maxima concur with the spring bloom, the start of freshwater run-off (estuarine circulation) and a second increase in freshwater discharge in early autumn. Station II, situated less than 7 km away from the river mouth, also indicates seasonality in POC sedimentation, but a maximum in autumn was not recorded. At station III in the middle of the fjord the seasonality with regard to POC sedimentation was even more reduced, but average rates were rather high, about 500 mg C

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of Marine Systems 8 (1996) 53-71

to interpret the autumn signals with regard to sedimentation of POC. During the onset of winter suspended biomass and sedimentation rates were still quite substantial (about 120 pg C 1-l and 80 mg C m-*d-l, respectively) in Balsfjord (Noji et al., 19931, indicating that export of carbon to the sediment surface and the benthos is of significance also in winter. From the data presented in Fig. 9 some preliminary conclusions can be drawn. (1) River Milselva does not give rise to significant increases in POC sedimentation rates since they

m-*d-l. In the outer part of the fjord (stations IV and V) increased sedimentation of POC during spring, summer and autumn was observed. Of particular significance were maxima in September, coinciding with large amounts of pteropods in the sediment traps. Although well known to be of significance for the vertical flux of carbon in the Norwegian Sea (e.g. Bathmann et al., 1991) and an important plankton group in Malangen, our understanding of pteropod population and feeding dynamics in north Norwegian coastal waters is rather limited. It is presently not possible

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P. Wassmann et al. /Journal

were higher in the outer part of the fjord and highest before the increase of freshwater discharge in May-June. (2) POC sedimentation in a subarctic fiord like Malangen is in the same range with regard to annual POC sedimentation rates as well as annual variation compared to boreal fjords in western Norway (Wassmann, 1991). (3) The differences with regard to POC sedimentation between the inner and outer part of Malangen are small, indicating that processes governing the vertical flux of POC do not change significantly along a longitudinal axis with a length of 45 km. A comparison of two adjacent fjords, Balsfjorden and Malangen (see Fig. 1) with regard to POC sedimentation is shown in Fig. 10. Both stations were in the centre of the fjords. Despite obvious differences in topography, freshwater discharge and physical oceanography, both fjords had similar patterns of POC sedimentation during 1992. Also, the POC sedimentation rates were of the same order. The main difference between the fjords with regard to POC sedimentation were the higher rates at 30 m depth in Balsfjord. Investigations by Lutter et al. (1989) and Riebesell et al. (1995) have indicated significant dissolution of sedimenting particulate organic matter in the upper part of the water column in Balsfjord. Despite the difference with regard to POC sedimentation at 30 m depth, the similarities between the fjords are striking (Reigstad, 1994). This suggests that the plankton ecology in both fjords as reflected by POC sedimentation, is governed by similar processes, for example external forcing of NCC water through large-scale wind fields along the coast, nutrients and light. Water circulation and water exchange may play a similar role in various parts of the north Norwegian coastal zone, especially as concerns plankton dynamics and POC sedimentation. The vertical flux of organic matter is strongly influenced by the timing between phytoplankton and zooplankton production (Peinert et al., 1989). Along with the extensive advection of deep and surface water over the deep sills of northern fiords, variable phyto- and zooplankton populations follow one another, influencing the phytoand zooplankton composition encountered inside

of Marine Systems 8 (l!ZXi) 53-71

67

the fjords. The basins of the fjords also can host over-wintering meso-zooplankton populations such as copepods and krill (Hopkins et al., 1985; Tande and Slagstad, 1992). The spring bloom can therefore readily be grazed upon by pre-adult and adult meso-zooplankton. Compared to some western Norwegian fjords where over-wintering plays a minor role (Wassmann, 1991) increased grazing is reflected in decreased amplitude in suspended biomass and the presence of faecal pellets in the traps, in particular during spring (Riebesell et al., 1995). The flux of organic matter due to zooplankton faecal pellets is thus a significant component of export from the euphotic zone in north Norwegian fjords. 3.3. Patterns of total particulate matter sedimentation Fig. 11 shows the average sedimentation of total particulate matter (TPM) as a function of depth at 5 stations from the inner part (I) to the outer part (close to Hekkingen, V> of Malangen. TPM sedimentation in the upper 100 m close to river M%lselva (I) is obviously much higher compared to the more remote stations. The distance between station I and II is only about 5 km, indicating that the supply of particulate matter from river MHlselva and possibly resuspension along its alluvial fan is limited to the innermost reaches of Malangen. The limited impact of river MHlselva on the sedimentation of particulate matter in Malangen can also be illustrated through some rough calculations. The average annual content of suspended particulate matter in Milselva and the average freshwater discharge to Malangen are 1 mg 1-i and 93 m3s-i, respectively (Paris Convention, 1991). Assuming a surface area of Malangen of about 100 km* and that the suspended particles are evenly distributed over the fjord surface, the annual supply of suspended matter would be about 30 g m-*yr-‘. This is less then 4% of the TPM sedimentation rates in the upper layers in the fjord (about 700-1000 g m-*yr-l). Fig. 12 shows the depth variation along the longitudinal axis of Malangen and isopleths of average annual TPM sedimentation. The impact

68

R Wasmann et al. /Journal of Marine Systems 8 (1996) 53-71 AverageTPM sedimentalban (g rn.’ d”) 0 0,

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of the M&elva river on the vertical flux of particulate matter in the inner reaches of Malangen is obvious with sedimentation rates > 7.5 g mF2d-‘. While TPM sedimentation was < 3 g mm2d-’ in the upper 100 m (comparable to equivalent sedimentation rates in west Norwegian fiords, Wassmann (1991)) a band of increased TPM sedimentation is found above the bottom along the longitudinal axis throughout the fjord. Similar increases in TPM sedimentation were also found in Balsfjord (Lutter et al., 1989; Reigstad, 1994). The increase in TPM sedimentation with increasing depth reflects the dynamics of the benthic turbidity zone (resuspension and particulate discharge down the slope of the MHlselva alluvial fan) and sediment focusing from the steep fjord walls. Also in the outer part of the fjord resuspension obviously plays an important role for the particle dynamics below 100 m depth (Fig. 12). Malangen with its steep walls and excellent connection to the shelf waters has to be considered as a channel with a high turbulent energy supply in its deeper waters which greatly influence nepheloid particle dynamics. Transport of settling and sedimented particles from littoral areas and surrounding slopes by wind induced, tidal and/or subsurface currents (Gardner et al., 1985; Floderus and HAhanson, 1989) are an important source of particles for the deeper parts of these

[g me2 dv’)

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Fig. 12. Average annual sedimentation of total particulate matter (TPM) as a function of depth along the axis of Malangen in 1991. Note the high sedimentation rates close to the bottom (resuspension) in the outer part and along the deposition fan of the M&elva river (resuspension, small turbidities and plume of dense, river-derived particles).

P. Wassmannet al./Journal of Marine Systems8 (1996) 53-71

fjords giving rise to sediment basins (Hilton, 1985).

focusing in their

4. Concluding remarks As long as the horizontal circulation pattern in fjords and adjacent coastal waters in northern Norway remain virtually unknown, it will be difficult to interpret differences in primary production, suspended biomass and species composition along cross and longitudinal sections within and between fjords. Seasonal and annual differences in species composition, succession, suspended mass and vertical flux could be the result of variations in advective transport along the coast and between the open coastal zone and fjord environments. The variability of pulses of sedimenting particulate matter (caused for example by advection, spring bloom, estuarine circulation and river discharge) results in northern fjords being characterized as multi-pulse systems. The number of pulses in vertical flux and their biochemical composition can differ from year to year, reflecting a particular and interannuallyvariable “blend” of physical events and biological processes. Great care must be taken to interpret data of suspended biomass and species composition as long as the timing and interannual variability of advective transport inside fjords is unknown, in particular when the sampling frequency of suspended mass is more or less sporadic. At least weekly sampling would be necessary to address differences in development between fjords or along longitudinal sections of fjords. Rivers, even the largest ones (e.g. Malselva) seem to play a minor role in controlling the particle dynamics matter of northern Norwegian fjords. The adjacent coastal zone is therefore a part of the Arctic region where estuarine processes are of limited significance. The zone comprises areas where full strength sea water penetrates more or less unhindered into the innermost reaches. Shelf as well as local processes cause sporadic exchange of fjord bottom, intermediate and surface water. In general, two boundaries can be distinguished in these areas: (a) the outer

69

oceanic boundary of the continental margin (exchange with the open ocean) and (b) the inner boundary (exchange with fiords, fluvial systems and littoral zones). Due to the small extension, the topographic complexity of the continental shelf, the variability in volume and speed of the NCC and the NAC as well as advection and upwelling, these two boundaries are never permanently physically separated, but are periodically in close contact. Therefore, northern Norwegian fjords, even the innermost ones far away from the open coast, are in various degrees part of the Norwegian continental margin. This finding implies that the Norwegian coastal zone is significantly different with respect to the biogeochemical dynamics compared to the adjacent Barents Sea as well as the vast Siberian shelf. To study the coastal ocean off northern Norway and adjacent fjords as a system subjected to exogenous input conditions is undoubtedly an important goal for the future. Although some of the physical processes in the coastal zones are reasonably well known, quantitative predictions of the biogeochemical cycles are for the time being out of reach. For example, we know neither how primary production is controlled in the north Norwegian coastal zone nor can we predict it from physical variables. The overwhelming importance of physical forcing on the rates and forms of biological activity, pelagic-benthic coupling as well as retention and recycling of organic matter calls for holistic ecological and comparative approaches which focus on well-integrated, combined physical and biological, multi-year and synoptic investigations in fjordic systems as well as adjacent shelf regions outside. Acknowledgements Comments to a previous version of the manuscript by B. v. Bodungen, S. Fowler, E. Hegseth and K. Tande are gratefully acknowledged. This investigation was supported by the Roald Amundsen Center for Arctic Research, University of Tromso, the Norwegian Fisheries Research Council (NFFR) and is a contribution from the research programme North Norwegian Coastal Ecology (MARE NOR).

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References Adlandsvik, B. and Loeng, H., 1991. A study of the climatic system in the Barents Sea. In: E. Sakshaug, C.C.E. Hopkins and N.A. Oritsland (Editors), Proc. Pro Mare Symp. Polar Marine Ecology. Trondheim, 12-16 May 1990. Polar Res., 10: 45-49. Aure, J., 1983. Akvakultur i Troms. Kartlegging av hovelige lokaliteter for fiskeoppdrett. Fisken Havet, Bl: l-89. Aure, J. and Stigebrandt, A., 1989. On the influence of topographic factors upon the oxygen consumption rate in sill basins of fjords. Estuarine Coast. Shelf Sci., 28: 59-69. Bathmann, U., Noji, T. and Bodungen, B. v., 1991. Sedimentation of pteropods in the Norwegian Sea in autumn. Deep-Sea Res., 38: 1341-1360. Bienfang, P. and Ziemann, D., 1992. The role of coastal high latitude ecosystems in global export production. In: PG. Falkowski and A.D. Woodhead (Editors), Primary Productivity and Biogeochemical Cycles in the Sea. Plenum Press, New York, pp. 285-297. Braarud, T., 1975. The natural history of the Hardangerfiord. 12. The late summer water exchange and phosphate distribution, and the introduction of an offshore population into the fjord in June, 1956. Sarsia, 58: 9-30. Burrell, DC., 1988. Carbon flow in fjords. Oceanogr. Mar. Biol. Rev., 26: 143-226. Cauwet, G. and Sidorov, I., 1996. The biogeochemistry of Lena river. Mar. Chem., in press. Cowan, E.A. and Powell, R.D., 1990. Suspended sediment transport and deposition of cyclical interlaminated sediment in a temperate fjord, Alaska, U.S.A. In: J.A. Dowdeswell and J.D. Scourse (Editors), Glacimarine Environments: Processes and Sediments. Geol. Sot. Spec. Publ., 53: 75-90. Cushman-Roisin, B., Asplin, J. and Svendsen, H., 1994. Upwelling in a broad fiord. Cont. Shelf Res., 14/15: 17011721. Dickson, R.R., Meinke, J., Malmberg, S.-A. and Lee, A.J., 1988. The “great salinity anomaly” in the northern North Atlantic 1968-1982. Prog. Oceanogr., 22: 103-151. Dowdeswell, J.A. and Murray, T., 1990. Modelling rates of sedimentation from icebergs. In: J.A. Dowdeswell and J.D. Scourse (Editors), Glacimarine Environments: Processes and Sediments. Geol. Sot. Spec. Publ., 53: 121-138. Eilertsen, H.C., 1993. Spring blooms and stratification. Nature, 363: 24. Eilertsen, H.C., Schei, B. and Taasen, J., 1981. Investigations on the plankton community of Balsfiorden, northern Norway. Sarsia, 66: 129-141. Eilertsen, H.C. and Taasen, J.P., 1984. Investigations on the plankton community of Balsfiorden, northern Norway. The phytoplankton 1976-1978. Environmental factors, dynamics of growth and primary production. Sarsia, 69: 1-15. Erga, S.R. and Heimdal, B.R., 1984. Ecological studies of the phytoplankton of Korstjorden, western Norway. The dynamic of a spring bloom seen in relation to hydrographic conditions and light regime. J. Plankton Res., 6: 67-90.

of Marine Systems 8 (1996) 53-71

Falkowski, P.G., Flagg, C.N., Rowe, G.T., Smith, S.L., Whitledge, T.E. and Wirick, C.D., 1988. The fate of a spring phytoplankton bloom: export or oxidation? Cont. Shelf Res., 8: 457-484. Farmer, D.M. and Freeland, H.J., 1983. The physical oceanography of ljords. Prog. Oceanogr., 12: 159-219. Floderus, S. and Hiikanson, L., 1989. Resuspension, ephemeral mud blankets and nitrogen cycling in Laholmsbukten, south east Kattegat. Hydrobiologia, 176/177: 61-75. Gardner, W.D., Southard, J.B. and Hollister, C.D., 1985. Sedimentation and resuspension in the northwest Atlantic. Mar. Geol., 65: 199-242. Glibert, R., 1990. Rafting in glacimarine environments. In: J.A. Dowdeswell and J.D. Scourse (Editors), Glacimarine Environments: Processes and Sediments. Geol. Sot. Spec. Publ., 53: 105-120. Griffin, D.A. and LeBond, P.H., 1990. Estuary/ocean exchange controlled by spring-neap tidal exchange. Estuarine Coastal Shelf Sci., 30: 275-297. Hargrave, B.T., Harding, G.C., Drinkwater, K.F., Lambert, T.C. and Harrison, W.G., 1985. Dynamics of the pelagic food web in St. Georges Bay, southern Gulf of St. Lawrence. Mar. Ecol. Prog. Ser., 20: 221-240. Hilton, J., 1985. A conceptual framework for predicting the occurrence of sediment focusing and sediment redistribution in small lakes. Lhnnol. Oceanogr., 30: 1131-1143. Hopkins, C.C.E., Tande, KS., Gronvik, S., Sargent, J.R. and Schweder, T., 1985. Ecological investigations of the zooplankton community of Balstjorden, Northern Norway: Growth, and quantification of condition, in relation to over-wintering and food supply in Metrkiia longa, Calanus finmurchicus, Thysanoessa inermis and Thysanoessa raschi. In: J.S. Gray and M.E. Christensen (Editors), Marine Biology of Polar Regions and Effect of Stress on Marine Organisms. Wiley, New York, pp. 83-102. Hopkins, C.C.E., Grotnes, P.E. and Eliassen, J.-E., 1989. Organization of a fiord community at 70” north: The pelagic food web in Balstjord, northern Norway. Rapp. P.-V. R&m. Cons. Int. Explor. Mer, 188: 146-153. Jickels, T.D. et al., 1991. Group report: What determines the fate of materials within the ocean margins? In: R.F.C. Mantoura, J.-M. Martin and R. Wollast (Editors), Ocean Margin Processes in Global Change. Wiley, New York, pp. 211-234. Laws, E.A., Bienfang, P.K, Ziemann, A.D. and Conquest, L.D., 1988. Phytoplankton population dynamics and the fate of production during the spring bloom in Auke Bay, Alaska. Limnol. Oceanogr., 33: 57-65. Lewis, A.G. and Thomas, AC., 1986. Tidal transport of planktonic copepods across the sill of a British Columbia fjord. J. Plankton Res., 8: 1079-1089. Lutter, S., Taasen, J.P., Hopkins, C.C.E. and Smetacek, V., 1989. Phytoplankton dynamics and sedimentation processes during spring and summer in Balstjord, Northern Norway. Polar Biol., 10: 113-124. Midttun, L. and Loeng, H., 1987. Climatic variations in the Barents Sea. In: H. Loeng (Editor), The Effect of Oceano-

P. Wassmann et al. /Journal

graphic Conditions on Distribution and Population Dynamics of Commercial Fish Stocks in the Barents Sea. Proc. 3rd Soviet-Norwegian Symp., Inst. Mar. Res., Bergen, pp. 13-27. Niebauer, H.J. and Alexander, V., 1989. Current perspectives on the role of ice margins and polynyas in high latitude ecosystems. In: L. Rey and V. Alexander (Editors), Proc. sixth Conf. Comitt Arctique International. Brill, Leiden, pp. 121-144. Noji, T.T., Noji, CL-M. and Barthel, K.-G., 1993. Pelagic-benthic coupling during the onset of winter in a northern Norwegian fjord. Carbon flow and fate of suspended particulate matter. Mar. Ecol. Prog. Ser., 93: 89-99. Paris Convention, 1991. Annual Report on Direct and Riverine Input to Norwegian Coastal Waters during the Year 1990. NIVA-Rep., 2577, Oslo, 103 pp. Peinert, R., 1986. Production, grazing and sedimentation in the Norwegian Coastal Current. In: S. Skreslet (Editor), The Role of Freshwater Outflow in Coastal Marine Ecosystems. Springer, Berlin, pp. 361-374. Peinert, R., von Bodungen, B. and Smetacek, V., 1989. Food web structure and loss rates. In: W. Berger, V. Smetacek and G. Wefer (Editors), Productivity of the Ocean: Present and Past. Wiley, New York, pp. 34-48. Reigstad, M., 1994. V&roppblomstringsdynamikk og Sedimentering i to Nordnorske Fjorder, Balstjorden og Malangen, i 1992. Unpubl. cand. scient. Thesis, Univ. Tromsg, 79 PP. Riebesell, U., Reigstad, M., Wassmann, P., Passow, U. and Noji, T., 1995. On the trophic fate of Phaeocystis pouchetii (Hariot): V. Bloom and sedimentation of P. pouchetii in Balstjord, northern Norway. Neth. J. Sea Res., 33: 193-203. Saelen, O.H., 1950. The hydrography of some fiords in northem Norway: Balstjord, Ullsfjordd Grotsund, Vengsfjord and Malangen. Troms Museums Arshefter, 70: l-102. Saetre, R. and Mork, M., 1981. The Norwegian Coastal Current. Univ. Bergen, 795 pp. Saetre, R., Aure, J. and Lj@en, R., 1988. Wind effects on the lateral extension of the Norwegian Coastal Water. Continental Shelf Res., 8: 239-253. Sakshaug, E. and Skjoldal, H.R., 1989. Life at the ice edge. Ambio, 18: 60-67. Smetacek, V. and Passow, U., 1990. Spring bloom initiation and Sverdrup’s critical depth model. Limnol. Oceanogr., 35: 228-234. Sundby, S., 1984. Influence of bottom topography on the circulation at the continental shelf of northern Norway. Fisk. Dir. Skr. Ser. Havunders.. 17: 501-519.

of Marine Systems 8 (1996) 53-71

71

Svendsen, H. , 1977. A study of the circulation in a sill fiord on the west coast of Norway. Mar. Sci. Comm., 3: 151-209. Svendsen, H., 1981. Wind-induced variations of circulation and water level in coupled fjord-coast systems. In: R. Saetre and M. Mork (Editors), The Norwegian Coastal Current. Univ. Bergen, pp. 229-262. Svendsen, H., 1991. Preliminary Results from a Hydrographical Investigation of Porsangenfjord, Alta!jord and Adjacent Coastal Waters, June-August 1990. Rep. Geophys. Inst., Univ. Bergen. Sverdrup, H.U., 1953. On conditions for the vernal blooming of phytoplankton. J. Cons. Int. Explor., 18: 287-295. Syvitski, J.P.M., Burrell, DC. and Skei, J.M., 1987. Fjords: Processes and Products. Springer, New York, pp. 615-624. Syvitski, J., LeBlanc, K.W.G., Cranston and R.E., 1990. The flux and presemation of organic carbon in Baffin Island fjords. In: J.A. Dowdeswell and J.D. Scourse (Editors), Glacimarine Environments: Processes and Sediments. Geol. Sot. Spec. Publ., 53: 177-200. Tande, KS., 1991. Calanus in high latitude environments. In: E. Sakshaug, C.C.E. Hopkins and N.A. Oritsland (Editors), Proc. Pro Mare Symp. Polar Marine Ecology. Trondheim, 12-16 May 1990. Polar Res., 10: 389-407. Tande, K. and Slagstad, D., 1992. Regional and interannual variations in biomass and productivity of the marine copepod, Calanus fknarchicus, in subarctic environments. Oceanol. Acta, 15: 309-321. Townsend, D.W., Keller, M.D., Sieracki, M.E. and Ackelson, S.G., 1992. Spring phytoplankton blooms in the absence of vertical water column stratification. Nature, 360: 59-62. Wassmann, P., 1991. Dynamics of primary production and sedimentation in shallow fjords and polls of western Norway. Oceanogr. Mar. Biol. At-mu. Rev., 29: 87-154. Wassmann, P., Vemet, M., Mitchell, G. & Rey, F., 1990. Mass sedimentation of Phaeocystis pouchetii in the Barents Sea. Mar. Ecol. Prog. Ser., 66: 186-195. Wassmann, P., Peinert, R. and Smetacek, V., 1991. Patterns of production and sedimentation in the boreal and polar northeast Atlantic. In: E. Sakshaug, C.C.E. Hopkins and N.A. (dritsland (Editors), Proc. Pro Mare Symp. Polar Marine Ecology. Trondheim, 12-16 May 1990. Polar Res., lo: 209-228. Wollast, R., 1991. The coastal organic carbon cycle: fluxes, sources and sinks. In: R.F.C. Mantoura, J.-M. Martin and R. Wollast (Editors), Ocean Margin Processes in Global Change. Wiley, New York, pp. 265-381.