38 255-274 PI. 58-60 FACIES 7Figs. 4Tab. ERLANGEN1998 Ostracods in a Cold-Temperate Coastal Environment, Western Troms, Northern Norway: Sedimentary Aspects and Assemblages Andr6 Freiwald, Bremen and Nasser Mostafawi, Kiel KEYWORDS: OSTRACODS - - COLD-TEMPERATE CARBONATES - - SEDIMENTOLOGY - - MICROPALEONTOLOGY - - COASTAL PLATFORM - - FJORD TROUGH -- TROMS ~ NORWAY SUMMARY This study presents sedimentological and micropal- eontological data on ostracods from a cold-temperate inner shelf setting in the Troms District, northern Nor- way. The coarse fraction analyses carried out on sedi- ment surface samples from coastal platforms and adja- cent outer fjord troughs reveal a considerable contribu- tion from ostracods to the accumulation of skeletal carbonates in distinct depositional settings. Ostracod accumulation is highest along wave-sheltered areas of coastal platforms where fleshy seaweed and coralline algal communities thrive in l0 to 30 m water depth. Current-exposed slopes of outer fjord troughs show a highly mixed ostracod assemblage consisting of im- ported species from the shallow coastal platform which is mixed with the trough assemblage. The hydrodynamic transport of ostracods into deeper areas results from the strong tidal current regime. Because of this mixing process, only the end members, the coastal platform and the fjord trough assemblages can be defined. The former is characterized by Baffinicythere emarginata, Cythere lutea, Finmarchinella angulata, Hemicytherura clathrata, Robertsonites tuberculatus, Sclerochilus rudjakovi, Semicytherura undata and Xestoleberis of. depressa. The outer fjord trough assemblage is characterized by Cluthia cluthae, Cytherella abyssorum, Cytheropteron atatum, Krithe of. adelspergi, Muelterina abyssicola, Cytherella cf. vulgatelIa and Cytheropteron testudo. Members of the northern Norwegian trough assemblage are known to occur in deeper open shelf environments of the NE-Atlantic. INTRODUCTION Knowledge of the distribution ofostracods in modern sediments has been demonstrated to be an useful tool for palaeoecologic and palaeoceanographic studies. Ostra- OFG-$chwerpunkt BIOGENE SEDIMENTATION Addresses: Dr. A. Freiwald, Fachbereich Geowissenschaften, Universitilt Bremen, Postfach 330440, D-28334 Bremen, Germany. Fax: +(0)421/218-7431, e-mail: afreiwald@ mait'sedpal'uni-bremende; Dr. N. Mostafawi, Geologisch-Pakiontologisches lnstitut und Muse- um, Universit~t Kiel, Olshausenstrage 40, D-24118 Kiel, Germany. Fax: +(0)431/880-4376. cods have been described from only a few localities in high latitude shelf areas (BRADY 1866, 1868, 1878; BRADY & NORMAN 1889, 1896: NORMAN 1891;STEPHENSEN 1913, 1938; KLtE 1942; RUI)JA~;OV 1962; SARS 1866 and 1922- 1928). Distribution patterns are known in more detail from the Skagerrak (ELoFSO.~ 1941 ), the northern North Sea (PENr~F~Y 1993a), Newfoundland (BENSON et al. 1983), the North Atlantic (HAZEL 1970), Arctic regions (NEALL" 1972; NEALE & HOWE 1975; JoY & Ct.AR~: 1977: CRONIN 1995; CRONI• et al. 1991, 1995), Greenland (WHATLEY 1982: PENN~Y 1989) and Spitsbergen (HARTMANN, 1992, 1993. 19941. Ostracods are especiaIIy valuable for documenting fluctuations in both environment and climate, and they are increasingly used to estimate palaeoctimate conditions in high latitudinal set- tings (BRoUWERS 1993, 1994: BROUWERS et al. 1991 ; CRONIN I981, 1991; CRONIN& DowsE-rr 1990; CRONtN et al. 1993: IKEYA & CRON~N 1993; PENNE'," 1993b; WHArt.EV & COkeS 1991; WOODet al. 1993). The northern Norwegian waters are affected by an ex- treme seasonality m solar radiation which induces large shifts in physical parameter of both, the atmospheric and marine regime. The study area is located beyond the Polar Circle at 70 ~ northern latitude where generally high Arctic environmental conditions predominate, Despite the Arctic illumination regime, poleward heat transfer of the North Atlantic Current offers relatively ameliorated temperatures in northern Norway. This oceanic heat transfer accounts for the absence of winter sea ice formation along the Norwegian coast up to 71 ~ northern latitude. Therefore, the northern Norwegian shelf is the only area where the cold-temperate marine reahn extends into an otherwise Arctic environment. This study focuses on species assemblages and distribu- tional patterns of ostracods in surface sediments from two
This study presents sedimentological and micropal- eontological data on ostracods from a cold-temperate inner shelf setting in the Troms District, northern Nor- way. The coarse fraction analyses carried out on sedi- ment surface samples from coastal platforms and adja- cent outer fjord troughs reveal a considerable contribu- tion from ostracods to the accumulation of skeletal carbonates in distinct depositional settings. Ostracod accumulation is highest along wave-sheltered areas of coastal platforms where fleshy seaweed and coralline algal communities thrive in l0 to 30 m water depth. Current-exposed slopes of outer fjord troughs show a highly mixed ostracod assemblage consisting of im- ported species from the shallow coastal platform which is mixed with the trough assemblage. The hydrodynamic transport of ostracods into deeper areas results from the strong tidal current regime. Because of this mixing process, only the end members, the coastal platform and the fjord trough assemblages can be defined. The former is characterized by Baffinicythere emarginata, Cythere lutea, Finmarchinella angulata, Hemicytherura clathrata, Robertsonites tuberculatus, Sclerochilus rudjakovi, Semicytherura undata and Xestoleberis of. depressa. The outer fjord trough assemblage is characterized by Cluthia cluthae, Cytherella abyssorum, Cytheropteron atatum, Krithe of. adelspergi, Muelterina abyssicola, Cytherella cf. vulgatelIa and Cytheropteron testudo. Members of the northern Norwegian trough assemblage are known to occur in deeper open shelf environments of the NE-Atlantic.
I N T R O D U C T I O N
Knowledge of the distribution ofostracods in modern sediments has been demonstrated to be an useful tool for palaeoecologic and palaeoceanographic studies. Ostra-
OFG-$chwerpunkt
BIOGENE SEDIMENTATION
Addresses: Dr. A. Freiwald, Fachbereich Geowissenschaften, Universitilt Bremen, Postfach 330440, D-28334 Bremen, Germany. Fax: +(0)421/218-7431, e-mail: afreiwald@ mait'sedpal'uni-bremende; Dr. N. Mostafawi, Geologisch-Pakiontologisches lnstitut und Muse- um, Universit~t Kiel, Olshausenstrage 40, D-24118 Kiel, Germany. Fax: +(0)431/880-4376.
cods have been described from only a few localities in high latitude shelf areas (BRADY 1866, 1868, 1878; BRADY & NORMAN 1889, 1896: NORMAN 1891;STEPHENSEN 1913, 1938; KLtE 1942; RUI)JA~;OV 1962; SARS 1866 and 1922- 1928). Distribution patterns are known in more detail from the Skagerrak (ELoFSO.~ 1941 ), the northern North Sea (PENr~F~Y 1993a), Newfoundland (BENSON et al. 1983), the North Atlantic (HAZEL 1970), Arctic regions (NEALL" 1972; NEALE & HOWE 1975; JoY & Ct.AR~: 1977: CRONIN 1995; CRONI• et al. 1991, 1995), Greenland (WHATLEY 1982: PENN~Y 1989) and Spitsbergen (HARTMANN, 1992, 1993. 19941. Ostracods are especiaIIy valuable for documenting fluctuations in both environment and climate, and they are increasingly used to estimate palaeoctimate conditions in high latitudinal set- tings (BRoUWERS 1993, 1994: BROUWERS et al. 1991 ; CRONIN I981, 1991; CRONIN & DowsE-rr 1990; CRONtN et al. 1993: IKEYA & CRON~N 1993; PENNE'," 1993b; WHArt.EV & COkeS 1991; WOOD et al. 1993).
The northern Norwegian waters are affected by an ex- treme seasonality m solar radiation which induces large shifts in physical parameter of both, the atmospheric and marine regime. The study area is located beyond the Polar Circle at 70 ~ northern latitude where generally high Arctic environmental conditions predominate, Despite the Arctic illumination regime, poleward heat transfer of the North Atlantic Current offers relatively ameliorated temperatures in northern Norway. This oceanic heat transfer accounts for the absence of winter sea ice formation along the Norwegian coast up to 71 ~ northern latitude. Therefore, the northern Norwegian shelf is the only area where the cold-temperate marine reahn extends into an otherwise Arctic environment. This study focuses on species assemblages and distribu- tional patterns of ostracods in surface sediments from two
2 5 6
cod diversity is highest in the shallow water coastal plat- form environments, benthic foraminifers generally domi- nate in greater water depths such as deeper gulleys and fjord troughs (FRErWALD 1993b) in both diversity and sediment contribution.
Fig. I. Geographic map of the coastal platforms and outer fjord troughs studied in the Troms District, northern Norway (see inlet map).
coastal platform areas and adjacent fjord troughs in the western Troms District, northern Norway (Fig. 1). The coastal platforms studied, the Sve Platform west of KvalCy, and the Sandcyfjord area west of Rebbenescy, are sites of intense biogenic carbonate production and deposition since the Atlanticum (BEt~NKErq 1998; FREIWALD et al., 1991; FREITAG 1997; HZNRICH et al. 1996). In the photic zone, skeletal carbonate production is supported predominantly by macroalgal communities. Along the wave-exposed flanks of the coastal platforms, large kelp forests offer a variety of ecological niches for carbonate-secreting organ- isms such as barnacles, molluscs and echinoderms (FRzrwALo in press). In contrast, the wave-sheltered but tidal-current agitated inner reaches of the platforms are occupied by coralline algal communities which form reefs, rhodolith pavements and maerl bottoms (FREIWALD & HENRICH 1994). Actuopaleontogical studies on living coralline algae dem- onstrate the important role of herbivorous organisms for the ecological success of slow-growing corallines over rapidly growing filamentous algae and sessile inverte- brates (FREIWALD 1993a). The ostracods are obviously involved in grazing processes such as the removal of diatom biofilms. In the sediments studied, ostracods never become a dominant skeletal component but they contrib- ute in places with up to 14 weight % (wt %) to the analysed sand-grade fraction. The benthic foraminifers dominate over ostracods in numbers per weight unit. However the species diversity trends of ostracods v e r s u s foraminifers are inversely related in terms of bathymetry. While ostra-
METHODS
The R/V OTTAR from the University of Tromsr was used for the seabased studies on the Sve- and Storvoll coastal platform, Troms, northern Norway. The sampling of the surface sediments was carried out using a VAt4 VEEN grab. In total, 65 grab samples from water depths between 2 m and 412 m were analyzed (Fig. 2). The sampled sediment surfaces were described, photographed, and stored in plastic bags at 4~ An underwater camera system was used for the mapping of algal vegetation and sediment structures.
About 100 to 300 g of sediment was taken from each sample and dried at 40~ The weighed samples were wet- sieved using deionized water. The grain-size fractions >2000 lam and 63-2000 I.tm were used for component analysis and for carbonate content measurements (see FRErWALD & HZNRICH (1994) for details). The quantitative and qualitative analysis of carbonate particles within the grain-size spectrum 125 - 2000 ~tm was carried out on the surface sediment samples. The subfractions were dry- sieved with an ATM-Sonic-Sifter by using 63 - 125 I.tm, 125 - 250 Ixm, 250 - 500 I.tm, 500 - 1000 I.tm and the 1000
- 2000 I~m sieve-rings. Each fraction was weighed using a precision scale. This method is used to quantify the weight- percentages of every biogenic particle group within the specified grain-size fractions after the method described by SARNTHE~ (1971).
The sedimentological aspects of the ostracod assem- blages (weight %) were studied using the 125 - 250 I.tm and 250 - 500 lam and rarely the 500 - 1000 I.tm grain fraction. For micropaleontological studies 1 ccm dry sediment was subsampled. The evaluation of the diversity of the ostra- cod was carried out on a mixed live and death assemblage from surface sediments. Therefore, the diversity which is expressed by the SHANNoN-WmNE~ index must be regarded as an 'apparent diversity' because seasonal shifts and the admixture of subfossil ostracod valves may bias the com- position. Treatment of 17 % of the sediment surfaces with Rose Bengal dye, however, indicates a high proportion of autochthonous ostracod assemblages at least in the shal- low coastal platform settings. The species list in alphabeti- cal order and references to the plates are quoted in Table 1.
ENVIRONMENTAL SETTING
The coastal areas investigated lie north of the Arctic Circle. Due to the latitude of 70~ the yearly budget of solar irradiation shows a strong gradient. The sun stays below the horizon from the end of November to the mid of January. This period is called the ,,Polar Night" while irradiation is prolonged during the summer period. The
257
Fig. 2. Stationmap with bathymetry of the southern Sandoyfjord (A) and the Sve Platform (B). Stations 68 and 92 to 98 are not indicated.
coastal platfrom, the Storvoll Platform is developed along the southwestern tip of the island (Fig. 2A). The northern part of the Storvoll Platform is 9 to 15 m deep. The southern part consists of a skerry archipelago with small tidal flats in between. The open sea swell is kept away by the Risoy archi- pelago.
The Sve Platform forms a westward elongation of Kvaloy (Fig. 2B). The 153 m deep Kattfjord Trough borders the Sve Platform to the north and the 420 m deep Malangen Trough to the south. To the west, a deep northeast-southwest striking longitudi- nal trough separates the coastal platform from the outer shelf. The platform itself has numerous islets, such as SommarOy, Hilles~y and EdOy. South of SommarOy, a small skerry archipelago is developed. Topographically dominant elements are extended flat areas with numerous rocky shoals in the shallow subtidal zone down to 30 m water depth on average. These flat but rugged subtidal plains are present around EdOy, Hilles0y, SommarOy and the skerry archipelago. Gulleys connect the shallow subtidal zone with the adjacent fjord troughs and therefore play an important role on the hydrographic regime. The gulleys form conduits which enable rapid water exchange driven by tidal currents and storm wave surge. Ed0y and its surrounding rocky shoals act as wave-break against the open sea swell.
northern Norwegian coastal area differs from other loca- tions at the same latitude because of its Arctic light regime but mild sea temperatures which prevent formation of sea ice. Biogeographically, the study area is at present near the transition between the cold-temperate and subarctic ma- rine provinces (LONING 1985).
Morphology of the coastal area
Morphologically, the northern Norwegian Troms-Dis- trict is characterized by the Caledonian Mountain Range which is deeply dissected by large fjords and sounds (Fig. 1). At many places a pronounced, several hundred to thousand meter wide coastal platform type is present which is known as ,,strandflat" coast (REuscH I894). Numerous islets and skerry archipelagoes form major morphological elements on the coastal platforms, The islets are often separated by deep channels or gulleys. The working areas are the southern Sand~yfjord, southwest of RebbenesCy and the Sve Platform west of Kval~y (Figs. 1- 2).
The 120 m deep Sandoyt]ord is located between RebbenesCy to the east and the Risoy archipelago to the west in the section studied. Off Rebbenescy, a narrow
Oceanography and hydrography
The northern Norwegian shelf is influenced by two northward flowing current systems, the Norwegian Cur- rent (NC) as an elongation of the North Atlantic Current and the Norwegian Coastal Current (NCC). The NCC is less saline (<34 %c,) than the NC (> 34 %0) (S~ZTRE & LJ~EN 1972). The NCC flows over the whole exent of the shelf area and forms a westward thinning wedge upon the more saline watermasses of the NC (EtDE 1978). The surface water temperatures show a seasonal fluctuation with 5~ in winter and 10~ in summer, whereas the nearbottom temperatures show only minor variation from 6~ to 7~ respectively (NORMANN 1993). Following the deep shelf troughs, the more saline water masses of the NC intrude into the fjords (Sur~DBY 1976, EIDE 1978). In the area investigated, intrusion of NC water occurs in the Malangen with its deep-seated sills and water depths of more than 400 m.
The hydrographical regime in the fjords and sounds is controlled by the strong tidal currents which reach up to 168 cm s-1 in the Troms0ysund (EmERTSEN et al. 1981). The average tidal range is 1.78 m and 3 m at spring tides. Due to the late spring and summer meltwater discharge, salinity fluctuates between 30 %0 and 34 %o (No,MANN 1993). In
2 5 8
1992, the surface water temperature measured near the coastal platforms studied was 10~ in August and Septem- ber, but decreased to 4~ in February (NORMANN 1993). Owing to the distinct coupling of the wind regime and water mass circulation in the narrow fjords, the stratifica- tion of the water is weak in the coastal zone (REIGSTAD & WASSMANN 1996).
The sedimentary environment
The inner shelf areas in the Troms District are prime targets for understanding environmental controls on the formation of cool-water carbonate deposits during a gla-
cial-interglacial transition (FREIWALD 1993b; and in press). The carbonate production and accumulation is fostered by restricted terrigenous admixture. Almost all of the river input is deposited in inner fjord deltas (CORNER et al. 1990) or is trapped in the deep fjord basins before they reach the coastal areas (VORREN et al. 1989). On the topographically complex inner shelf environments, the skeletal carbonate facies is highly variable (FREIWALD 1993b). Principally four major facies associations can be related to distinct environmental settings: 1.) wave-sheltered coastal plat- forms with coralline algal buildups and sediments, 2.) wave-exposed coastal platforms with kelp forests and barnacle-mollusc-echinoderm sediments, 3.) gulleys with
P 1 a t e 58 Ostracods from the coastal shelf and outer fjords, Troms District, North Norway
Unless stated otherwise, all specimens from the Station 21, seen in external lateral view, deposited at the Forschungsinstitut Senckenberg (SMF; catalogue-no. Xe 18063-18123).
Fig. 1. Polycope areotata SARS, 1923. Left valve, x 90, Sve Platform, Station 2, 12 m water depth; Xe 18063. Fig. 2. Bairdia inflata (NORMAN, 1862).Right valve, juvenile, x 50, Kattfjord, Station 22, 88 m water depth; Xe
18066. Fig. 3. Cytherella cf. vulgatella AIELLO et al., 1996. Female, right valve, x 50, Malangen, Station 42, 412 m water
depth; Xe 18065. Fig. 4. Cytherella abyssorum SANS, 1866. Female, right valve, x 50, Malangen, Station 42,412 m water depth; Xe
18064. Fig. 5. Cluthia cluthae (BRADY, CROSSKEY & ROBERTSON, 1874).Female, left valve, x 100, Sand0yfjord, Station 75,
74 m water depth; Xe 18068. Fig. 6. Leptocytherepellucida (BAIRD, 1850).Female, left valve, x 60, Sve Platform, Station 2, 12 m water depth;
Xe 18067. Fig. 7. Sarsicytheridea punctillata (BRADY, 1865). Female, left valve, x 50, Kattfjord, Station 21, 88 m water
depth; Xe 18070. Fig. 8. Sarsicytheridea bradii (NORMAN, 1865). Male, left valve, x 50, Sand0yfjord, Station 75, 74 m water depth;
Xe 18069. Fig. 9. Baffinicythere emarginata (SANS, 1865).Female, left valve, x 50, Sve Platform, Station 25, 7 m water depth;
Xe 18077. Fig. 10. FinmarchineUa angulata (SANs, 1866). Female, left valve, x 50, Sve Platform, Station 2, 12 m water depth;
Xe 18076. Fig. 11. Finmarchinellafinmarchica (SANS, 1866). Female, left valve, x 60, Sve Platform, Station 10, 19 m water
depth; Xe 18075. Fig. 12. Laperousecythere yahtsensis BROUWERS, 1993. Female, left valve, x 50, Kattfjord, Station 18, 6 m water
depth; Xe 18078. Fig. 13. Hemicythere viltosa (SANS, 1866). Male, right valve, x 50, Sandoyfjord, Station 70, 6 m water depth; Xe
18080. Fig. 14. Robertsonites tuberculatus (SAns, 1866). Female, left valve, x 50, Sand0yfjord, Station 75, 74 m water
depth; Xe 18071. Fig. 15. Muellerina abyssicola (SANs, 1866). Female, left valve, x 60, Kattfjord, Station 22, 104 m water depth; Xe
18073. Fig. 16. Rabilimis septentrionalis (BRADY, 1866). Female, left valve, x 50, Sandoyfjord, Station 75, 74 m water
depth; Xe 18079. Fig. 17. Cythere lutea O.F. MtJELLEa, 1785. Male, left valve, x 50, Sand0yfjord, Station 81, 9 m water depth; Xe
18090. Fig. 18. Hirschmannia viridis (O.F. MUELLER, 1785). Female, left valve, x 80, Kattfjord, Station 16, 30 m water
depth; Xe 18088. Fig. 19. Palmoconcha laevata (NORMAN, 1865). Female, left valve, x 70, Sve Platform, Station I, 2 m water depth;
Xe 18086. Fig. 20. Loxoconcha sp. Right valve, x 70, Sand0yfjord, Station 75, 74 m water depth; Xe 18087. Fig. 21. Phlyctocytherefragilis (SANs, 1866). Female, left valve, x 90, Sve Platform, Station 39, 10 m water depth;
Xe 18089.
P l a t e 58 259
2 6 0
barnacle-foraminifer-bryozoan sediments, and 4.) outer fjord troughs with foraminifer-bryozoan-bivalve sediments (Fig. 3). Each of the facies associations show two or more sedimentary lithologies which are described in detail in FREIWALD (1993b and in press).
RESULTS Ostracods as sediment constituents
The equivalent weight percentages of ostracod valves in the cold-temperate coastal platform and outer fjord trough environments ranges from 0 to 14 % of the total sand fraction. The highest mean values of ostracod amounts are in the shallow fjord troughs and on the coralline algal dominated zones of the coastal platforms, with 4.43 wt % and 4.13 wt %. Lowest mean values exist in the wave-
exposed coastal platform areas with 0.05 wt % and in tidal current-agitated channels and narrow sounds in the central areas of the coastal platforms (Tab. 2). The sand grade fractions which yield ostracod valves span the spectrum from 63 to 1000 p-m. On average, the highest amounts of ostracods exist in the 125 - 250 ~m fraction.
Ostracod distribution in the facies associations
Wave-sheltered coastal platforms The inner areas of the coastal platforms are swell-
protected but are tidal current-swept. The tidal channels from 6 to 25 m generally are covered by coralline algal reefs or rhodolith pavements (FREIWALD & HENRICH ! 994). Owing to the funneling effect of narrow sounds, this environment creates predominantly gravelly coralline al-
P l a t e
Fig. 1.
Fig. 2.
Fig, 3.
Fig. 4.
Fig. 5.
Fig. 6.
Fig. 7.
Fig. 8.
Fig. 9.
Fig. 10.
Fig. 11.
Fig. 12. Fig. 13.
Fig. 14. Fig. 15.
Fig. 16.
Fig. 17.
Fig. 18.
Fig. 19. Fig. 20.
Fig. 21.
59 Ostracods from the coastal shelf and outer fjords, Troms District, North Norway
Acanthocythereis dunelmensis (NORMAr~, 1865). Male, left valve, x 50, Kattfjord, Station 75, 74 m water depth; Xe 18072. Pterygocythereis mucronata (SARS, 1866). Female, left valve, x 50, Sve Platform, Station 41, 89 m water depth; Xe 18074. Elofsonella concinna (JONES, 1857). Female, left valve, x 50, Kattt]ord, Station 2 I, 88 m water depth; Xe 18082. Palmenella limicola (NORMAN, 1865). Female, right valve, x 60, Kattt:jord, Station 21,88 m water depth; Xe 18081. Cytheropteron nodosoalatum NEALE & HOWE, 1973. Female, right valve, x60, Sve Platform, Station 39, 10m water depth; Xe 18092. Cytheropteron pyramidale BRADY, 1868. Female, right valve, x60, Sve Platform, Station 39, 10m water depth; Xe 18091. Cytheropteron alatum SARS, 1866. Female, right valve, x 60, Malangen, Station 42, 412 m water depth; Xe 18093. Cytheropteron latissimum (NORMAN, 1865). Female, left valve, x 60, Sve Platform, Station 41,89 m water depth; Xe 18095. Cytheropteron testudo SARS, 1866. Female, right valve, x 60, Malangen, Station 42,412 m water depth; Xe 18094. Semicytherura similis (SARs, 1866). Female, left valve, x 100, Sandcyfjord, Station 72, 36 m water depth; Xe 18109. Semicytherura acuticostata (SARs, 1866). Female, right valve, x 100, Kattfjord, Station 17, 16 m water depth; Xe 18106. Semicytherura sp. 2. Female, left valve, x 100, Kattfjord, Station 22, 102 m water depth; Xe 18111. Cytheropteron nodosoalatum NEALE & HOWE, 1973. Female, right valve, x 60, Sve Platform, dorsal view; Xe 18092. Cytheropteron pyramidale BRADY, 1868. Female, right valve, x 60, Sve Platform, dorsal view; Xe 18091. Semicytherura sella (SARS, 1866). Female, right valve, x 100, Kattfjord, Station 22, 102 m water depth; Xe 18107. Semicytherura undata (SARs, 1866). Female, right valve, x t00, Sve Platform, Station 37, 7m water depth; Xe 18104. Semicytherura nigrescens (BAIRD, 1838). Female, right valve, x 100, Sand0yfjord, Station 81, 9 m water depth; Xe 18108. Semicytherura angulata (BRADY, 1868). Female, right valve, x 100, Kattfjord, Station 17, 16 m water depth; XE 18103. Semicytherura sp. 1. Female, right valve, x 100, Sand0yfjord, Station 71, 14 m water depth; Xe 18110. Semicytherura striata (SARs, 1866). Female, right valve, x 100, Kattfjord, Station 22, 102 m water depth; Xe 18102. Semicytherura affinis (SARs, 1866). Female, left valve, x I00, Sve Platform, Station 2, 12 m water depth; Xe 18105.
P l a t e 59 261
262
gal deposits under the influence of the tides (Fig. 3). This sediment type is comparable to the maerl from other cold- temperate coastal areas along the Northeast Atlantic shelves (BosEr~CE 1983). The prominent phaeophytic algae which lives on the tidal current-agitated gravel bottoms is the long-bladed Chorda filum. The maerl sediments show high carbonate contents, with 92 to 98 % respectively. Owing to the vigorous current regime and the lack of suitable habitats, ostracods are rarely found within the maerl with less than 0.5 wt %. The dominant species found in the maerl are Cythere lutea(P1.58/17), Finmarchinella angulata (PI. 58/10), Baffinicythere emarginata (PI. 58/ 9)and Xestoleberis cf. depressa (P1.60/7).
The coralline frameworks and the multilayered rhodolith pavements, however, are rich in sheltered microhahitats
which allow sandy bioclastic particles to settle. Algal gravel sand is developed in 6 to 25 m depth. In addition, bioeroded coralline algal fragments, heteranomiid and modiolid bivalves, echinoid plates and spines, small gas- tropods, and ophiuroid ossicles form major skeletal com- ponents. On the Sve Platform, ostracod contents in the algal gravel sand range from 0.28 to 2.93 wt % while in the Sand~yfjord area, ostracods are more important in the corresponding facies with 3.68 to 13.99 wt % respectively. The carbonate content of the algal gravel sand varies from 78 to 96 %. Major ostracod species are Cythere lutea, Cytheropteron nodosoalatum (P1.59/5,13), Finmarchinella an gulata, Baffinicythere emarginata, Palmoconcha laevata (PI. 58/19), Phlyctocytherefragilis (PI. 58/21)), Robertsonites tuberculatus (PI. 58/14), Semicytherura nigrescens (PI.
P l a t e 60
Fig. 1.
Fig. 2.
Fig. 3. Fig. 4.
Fig. 5.
Fig. 6.
Fig. 7.
Fig. 8.
Fig. 9.
Fig. 10.
Fig. 1 I. Fig. 12.
Fig. 13.
Fig. 14.
Fig. 15.
Fig. 16.
Fig. 17.
Fig. 18.
Fig. 19. Fig. 20. Fig. 21.
Fig. 22. Fig. 23.
Ostracods from the coastal shelf and outer fjords, Troms District, North Norway
Hemicytherura clathrata (SARs, 1866). Female, right valve, x 100, Kattfjord, Station 21, 88 m water depth; Xe 18113. Hemicytherura cellulosa (NORMAN, 1865). Female, right valve, x 100, Sve Platform, Station 23, 19m water depth; Xe 18114. Cytherura atra SARS, 1866. Male, right valve, x 100, Kattfjord, Station 12, 52 m water depth; Xe 18112. Kangarina septentrionalis NEALE, 1972. Female, right valve, x 100, Malangen, Station 42, 412 m water depth; Xe 18096. Pseudocythere caudata SARS, 1866. Female, right valve, x 60, Kattfjord, Station 22, 102 m water depth;
�9 Xe 18084. Jonsia acuminata (Saas, 1866). Female, right valve, x 500, Kattfjord, Station 22, 102 m water depth; Xe 18085. Xestoleberis cf. depressa SARS, 1866. Female, left valve, x 60, Sand~yfjord, Station 80, 12 m water depth; Xe 18097. Propontocypris trigonetla SARS, 1866. Left valve, x 60, Sve Platform, Station 6, 9 m water depth; Xe 18099. Pontocypris mytiloides (NORMAN, 1862). Left valve, x 60, Kattfjord, Station 22, 102 m water depth; Xe 18098. Eucythere declivis (NORMAN, 1865). Female, right valve, x 60, Sand0yfjord, Station 78, 13 m water depth; Xe 18083. Argilloecia conoidea SARS, 1923. Left valve, x 70, Malangen, Station 42, 412 m water depth; Xe 18100. Krithe cf. adelspergi B ROUWERS 1990. Female, right valve, x 60, Malangen, Station 42, 412 m water depth; Xe 18101. Paradoxostoma normani BRADY, 1868. Left valve, x 60, Sve Platform, Station 6, 9 m water depth; Xe 18118. Paradoxostoma abbreviatum SARS, 1866. Left valve, x 60, Kattfjord, Station 22, 102 m water depth; Xe 18119. Paradoxostoma cf. prolockensis HOaNE & WHITTAKER, 1985. Right valve, x 100, Malangen, Station 42, 412 m water depth; Xe 18120. Paradoxostoma variabile (BAreD, 1835). Right valve, x 60, Kattt]ord, Station 22, 412 m water depth; Xe 18117. Paradoxostoma obliquum SARS, 1866. Right valve, x 60, Kattfjord, Station 22, 102 m water depth; Xe 18116. Sclerochilus rudjakovi ATHERStJCH & HORNE, 1987. Left valve, x 60, Kattfjord, Station 22, 102 m water depth; Xe 18121. Sclerochilus sp. 1. Left valve, x 60, Kattt]ord, Station 21, 88 m water depth; Xe 18122. Sclerochilus sp. 2. Left valve, x 60, Sve Platform, Station 2, 12 m water depth; Xe 18123. Cytherella cf. lata BRADY, 1880. Female, left valve, x 50, Malangen, Station 42, 412 m water depth; Xe 18065. Finmarchinella angulata (SARs, 1866). Female carapace, dorsal view, x 50; Xe 18076. Laperousecythere yahtsensis BROUWERS, 1993. Female carapace, dorsal view, x 50; Xe 18078.
P l a t e 60 263
2 6 4
Fig. 3. Distribution of major facies associations with variations in the lithologies on the Sandcyfjord (A) and the Sve Platform (B).
59/17), S. undata and Xestoleberis cf. depressa. Bivalve - coralline algal gravel mud is developed only
south of SommarCy in l0 to 20 m water depth. The carbonate content varies between 95 % and 98 %. In this
location large amounts of kelp-rafted rhodoliths are stranded. Because of the high input of fleshy algae, oxygen is depleted a few centimeters below the seafloor. Ostracods contribute with 0.5 to 4 wt % to the sediment supply. The
265
Fig. 4. Plot of the total number of ostracod specimens per ccm dry sediment on the Sandcyfjord (A) and the Sve Platform (B).
most abundant ostracods are Cythere Iutea, Finmarchinella angulata, Baffinicythere emarginata, F. finmarchica (PI. 58ll 1), Semicytherura undata and Xestoleberis cf. depressa.
Echinoderm - bivalve - foraminifer sand is distributed south of SommarOy and east of Hillesoy. On the Storvoll Platform, this sediment often lie in an intermittent position between the maerl and the outer fjord trough facies (see below). The depth interval of the echinoderm-bivalve- foraminifera sand is 7 to 30 m. The carbonate content of the sediments are the lowest found within the coralline algal association, with 60 to 80 % respectively. The constituent sediment particles such as echinoid fragments are almost allochthonous. The living community found in the echino- derm - bivalve - fo~'aminifer sand is diverse; opbiuroids (Ophiopholis aeuleata), onuphid polychaetes, Chlamys islandica and Aporrhais pespelecani. Major contributors to the sediment supply are benthic foraminifers, trans- ported coralline algal branches and ophiuroid ossicles. Adjacent to outcropping rocks and boulder fields, plates of verrucid barnacles (Verruca stroemia) are common. Large shells and boulders are colonized by dense fleshy algal stocks. The ostracod content is high with 2 - 9 wt % respectively. The most abundant ostracod species are Cythere lutea, FinmarchineUa angulata, Baffinicythere emarginata,
Hemicytherura clathrata (PI. 60/1), Robertsonites tuberculatus, Semicytherura nigrescens, S. undata and Xestoleberis cf. depressa. East of Hilles~y Acanthocythereis dunelmensis (P1.59/1) was found in large quantities in one sample of the echinoderm - bivalve - foraminifer sand in 19 m water depth.
Wave-exposed coastal platforms Dense stocks of kelp forests of Laminaria
hyperborea are found along wave-exposed areas of the coastal platforms. These kelp forests provide shelter for a diverse community. Sedimentologi- cally, a gravelly and more distally, a well-sorted barnacle - bivalve - echinoderm sand is transported from this high energy environment onto adjacent shoals (Fig. 3). The sediment particles are polished which indicate the considerable degree of transporta- tion. Ostracods are rarely preserved in these highly mobile sands (< 0.05 wt %). The few valves present belong to Cythere lutea, BaffiniQ'there emarginata, Semicytherura undata and Xestoleberis cf. depressa:
Rocks in the intertidal and down to the shallow subtidal zones are intensely colonized by the Fucus - Ascophyllum belt. In contrast to the deeper kelp forests, gastropods (Patella valgata, Littorina spp., Gibbufa cinereus) and bivalves ( Mytihts edulis) gain importance. This phaeophytic zone is replaced by the Balamts balanoides belt in the intertidal to supratidal
zone. Permanently water-filled rock pools support thickets of Corallbza officinalis. During the storm season, the calcareous skeletons are washed onshore where a gravelly to sandy barnacle - gastropod - Corallina deposit forms centimeter- to meter-thick veneers in depressions between the coastal rocks. Although this seaweed zone is known to serve as a major habitat for ostracods (HAGERMAN t968), almost none are preserved in the swash zone of the beach. HAC;ERMAN (1968) recognized Elofsonella concinna (Pl. 59/3), Semicytherura nigrescens, Xestoleberis depressa and Paradoxostoma pulchellum as permanent inhabitors of the shallow-water Corallina officmalis zone.
Coastal platform gulleys A completely different facies association exists in the
coastal platform gulleys below the zone of dense macroalgal stocks (Fig. 3). In the tidal current-washed ramp-like gulleys of the Sve Platform a bryozoan - barnacle sand accumulates between 40 and 80 m water depth. The gulleys are rich in byssate bivalves (Modiolus modiolus, Chlamys islandica ), brachiopods ( Hemithyris psittacea, Macandrevia cranium) and serpulids. The carbonate content of the deposits is high and ranges from 77 to 90 %. Ostracods are present with l - 4 wt % and are dominated by Cythere lutea,
Tab. 1. List of the determined species and plate references of ostracods from the area studied.
Baffinicythere emarginata, Semicytherura undata and Xestoleberis cf. depressa.
At the upper entrances of some gulleys a barnacle - foraminifer sand is developed between 40 and 50 m water depth. According to video-tape analysis, winnowed and concave-up shells of Cyprina islandica, Mya truncata, Astarte borealis, Chlamys islandica and conchs of Neptunea sp. serve as substrates for a diverse fouling community dominated by Verruca stroemia, Balanus balanus, Serpula vermicularis, Hemithyris psittacea, Terebratulina retusa, hydroids and porifera. The winnowed shells are heavily infested by endolithic borers (SCHMIDT & FREIWALD 1993). Ostracods contribute with 1 - 2 wt % to the sediment supply and the most abundant ostracod valves belong to Cythere
Outer fjord troughs Calcareous sediments of the outer fjord trough facies
primarily consist of foraminifers, bryozoans and bivalves (Fig. 3). Planktonic foraminifers only exist in deep fjord troughs which show deep-water exchange with the North Atlantic Current such as the Malangen. However, the content of planktonic foraminifers rarely exceeds 1 wt %.
The foraminifer - bryozoan sand is distributed in the southern Sandcyfjord Trough from 40 to 120 m water depth and in the outer Kattfjord Trough beween 30 and 100 m water depth. Both troughs lie in a hydrodynamically
Tab. 2. Ostracod contents of the sand grade fraction of cold-tem- perate coastal platform, gulley and fjord trough deposits, Troms Dis- trict, northern Norway.
267
exposed position which is reflected by the sand-grade texture extending to considerable water depths and by the large contribution of bryozoan fragments to this environ- ment. The bryozoans are imported from the surrounding shallow coastal platforms and form the dominant particle type in the 125 - 250 gm fraction. This transfer of skeletal carbonate particles from the photic zone into the fjord troughs is also shown by large amounts of minute coralline algal fragments which are present in the upper parts of the trough slopes. Thick carpets of decaying kelp and other phaeophytes form a distinct sediment that is rich in organic carbon (up to 5 % TOC) and skeletal particles such as shallow-water gastropods (FRHTAG, 1997; BEaNKEN 1998). The carbonate content of this facies varies from 40 to 70 %, while the ostracod content is from 2.5 to 10 wt % in the more turbulent outer fjord trough settings. The foraminifer - bryozoan sand spans a wide bathymetric range. In the shallower range of this facies, from 30 to 50 m water depth, Cythere lutea, Baffinicythere emarginata, Robertsonites tuberculatus, Semicytherura undata and Xestoleberis cf. depressa are the dominating species while in the deeper range from 50 to 120 m depth, Aeanthocythereis dunelmensis, Cytheretla abyssorum (PI. 58/4), Hemicytherura clathrata, Paradoxostoma variabile (PI. 60/16), Pterygocythereis mucronata (P1. 59/2)and Sarsicytheridea bradii (Pl. 58/ 8)are common.
The sediments of the foraminifer - bivalve sand and clay is located in deep fjord troughs and are distributed in the Malangen, the inner Kattfjord and in the central Sand~yfjord Trough, all in greater than 100 m water depth. Owing to the high amount of quartz and mica grains, the carbonate content with 22 to 32 % is comparatively low. The ostracods are present with 1 - 5 wt % in the deep fiord trough deposits and are characterized by Acanthocythereis dunelmensis, Baffinicythere emarginata, Cytherella abyssorum, Finmarchinella angulata, F. finnlarchica. Hemicytherura clathrata, Pterygocythereis mucronata, Robertsonites tuberculatus, Sarsicytheridea bradii and Xestoleberis cf. depressa. The deep Malangen Trough is the only fjord with deep-water inflow from the Norwegian Sea in the area studied. The dominating ostracods there are Argilloecia conoidea (PI. 60/19), Cytherella abyssorum and Krithe cf. adelspergi (PI. 6012).
Ostracod assemblages
Quantity of specimens and apparent diversity The 65 grab samples analyzed contain 61 ostracod
species belonging to 39 genera (Tab. 1). A comparison between live and dead assemblages carried out on Rose Bengal-stained aliquots of some representative grab sta- tions reveals a complete correlation which indicates a large number of autocbthonous ostracod communities. In certain species, such as Semicytherura nigrescens, living specimens are readily distinguishable by their externally visible appendages. More difficult to discern are many Paradoxostoma species. They commonly show postmor- tem closure of the valves without leaving any appendages
1200
E 1000
E ~ ~ 400
Q. O~
200
"= =l I �9 ~ .
A
1,6
:Z 1.4 O ~ $ ~,,,2
~ . 0,8 �9 g ua
;~ 0,4
0,2
0 50
f 100 150 200 250 300 350 400
I Water depth [m]
B
I
�9 |
l
..I
!-I"
J,'." I 0 50 100 150 200 250 300 350 400
Water depth [m]
Fig. 5. Plot of the 'apparent diversity' index (Shannon-Wiener) against bathymetry (A) and total number of ostracod specimens per ccm dry sediment (B).
external. In this case, the carapace has to be opened to see whether or not it contains soft parts.
In total, more than 25,000 ostracods have been counted (Tab. 2 and 3). Richest ostracod specimens with 800 to 1000 valves per ccm dry sediment have been sampled along the eastern shallow subtidal zone off the Risky skerries, while the high energy settings show lowest num- bers (Fig. 4). In the slope and fjord trough settings the number of specimens varies between 50 and 750 spec./ccm dr?' sediment (Fig. 5A). Highest diversity was detected in two samples from the outer Kattt]ord Trough in 88 m and 102 m depth with 37 and 41 different taxa. These samples were peculiar in that they have a decaying phaeophytic mat on the sediment surface. These disloged algae were im- ported from the photic zone and were trapped in the numerous sub-basins of the outer Kattfjord Trough. How- ever, the SHANNoN-WIENER index which is used to express the 'apparent diversity' of the thanatocoenoses yield low diversity indices (< 2). The highest indices with 1.66 and 1.39 are calculated for those areas which already show highest numbers of specimens. These sites are located in the shallow subtidal zone east of Risky and at the Storvoll Platform, southern tip of Rebbenes0y, and in the calm water channel south of Sommar0y (Fig. 6). Plotting the SH,',NNoN-Wm~ER indices against bathymetry reveals a nuTnber of trends (Fig. 5B). On the coastal platform (0 - 35 in depth) a wide range of indices from 0 to 1.66 indicate the presence of high-energy and low-energy depositional set- tings at the same depth range. The ostracod record along the wave-exposed flanks, however, is very poor. In con- trast, the apparent diversity range found in the upper slope
268
Tab. 3. Total (live and dead) population of ostracod species per ccm dry sediment
settings (35 - 100 m water depth) is narrower, with values of 0.6 - 1.2 respectively. The deep fjord trough sample (412 m water depth) shows an diversity index of 0.81.
Coastal platform vs. fjord trough assemblages Despite the large bathymetric range from 2 to 412 m
water depth, eight species, Cythere lutea (P1. 58/17), Finmarchinella angulata (PI. 58/10), Baffinicythere emarginata (PI. 58/9), Hernicytherura clathrata (PI. 60/1), Robertsonites tuberculatus (PI. 58/14), Sclerochilus rudjakovi, Semicytherura undata and Xestoleberis cf. depressa (PI. 60/7 )show a presence in 90 - 100 % of the samples analyzed (Tab. 3). These species show a domi- nance in water depths between 10 and 50 m which is consistent with the coastal platform and upper slope envi- ronment (Fig. 7). The fjord trough notations of these species result from transported valves. Xestoleberis cf. depressa and Cythere lutea and Baffinicythere emarginata reveal the highest abundancies with 20.45, 19.68 and 12.91% respectively. With the exception of Finmarchinella angulata (4.46 %), Robertsonites tuberculatus (5.59 %), Semicytherura angulata (3.02 %), S. undata (6. I0 %) and
Hemicytherura cellulosa (2.12 %), ~ill other species have abundancy values of less than 2 % (Tab. 3). The following 18 species are restricted to the coastal platforms down to 100 m or attain their maximum development in these depths: Acanthocythereis dunelmensis (PI. 59/1), Bairdia inflata (PI. 58/2), Cytheropteron latissimum (PI. 59/8), Cytherura atra (P1.60/2), Hemicythere villosa (PI. 58/13), Elofsonella concinna (P1.59/3), Hirschmannia viridis (Pi. 58/18), Laperousecythere yahtsensis (P1. 58/12), Leptocythere pellucida (P1. 58/6), Palmenella limicola (PI. 59/4), Palmoconcha laevata (PI. 58/19), Phlyctocythere fragilis, Polycope areolata (PI. 58/1), Propontocypris trigonella (PI. 60/8), Robertsonites tuberculatus (PI. 58/ 14), Sarsicytheridea bradii (PI. 58/8), Semicytherura sella (PI. 59/15) and Semicytherura similis (PI. 59/10). A few empty valves of these taxa were found at depths of 412 m, but most of them are immature. Among these species, there are some algal feeders, such as Paradoxostoma variabile (P1.60/16) and Sclerochilus species (Pl. 60/19-20) which usually do not exceed the littoral zone. Obviously, they have been transported from the littoral zone into the fjord troughs.
0.81 232J0.1 0 . 4 1 0 ~ 0 ~ i ] o e - ' ~ T e ' 1 0 1 1 0 ~ i ' r ~ ' ~ s ' t 3 o ? t I ~ O ~ ' 0 8 " ~ : ' B ' O ~ S 04 s s - o ' a 2 1 r 1 6 2 a t Q44 " " '
Tab. 3. continued
The fjord trough assemblages are characterized by Cluthia cluthae (PI. 58/5), Cytherella abyssorum (P1.58/ 4), Cytheropteron alatum (PI. 59/7), Krithe cf. adelspergi (P1. 60/12) , Muellerina abyssicola (P1. 58/15) and Pterygocythereis mucronata (PI. 59/12). Some members of the fjord trough assemblage also occur in the deeper coastal platform stations with low numbers. Sediments of these stations yield considerable amounts of relict macrofauna which correspond to a higher sea level during the Late Weichsel ian and Early Holocene in that part icular area. In addit ion to the fjord trough assemblage already men- tioned, the deepest station with 412 m from the outer M a l a n g e n Trough is character ized by occurrence of Cy- therella cf. vulgatella (P1. 5813, 60/21) and Cytheropteron testudo (PI. 59/9).
D I S C U S S I O N
O s t r a c o d s a s s e d i m e n t c o n t r i b u t o r s
Detai led coarse fraction analysis of predominantly biogenic sediments after the method of SARNTHEm (1971) have been rarely carried out on cool-water carbonate sedimentary environments. The component analysis con-
ducted on coastal platform and outer fjord trough settings from northern Norway underlines the importance of ostra- cod valves to the sediment supply. Among the variety of environmental niches and sedimentary l i thologies which generally exist along topographical ly complex inner shelf and coastal zones, four settings yield large amounts of ostracods (> 5 wt %) in the sediments. These are the coralline algal gravel sand (< 14 wt %), the echinoderm - bivalve - foraminifer sand (-< 9 wt %), the foraminifer - bryozoan sand (_< 10 wt %) and the foraminifer - bivalve clay (<_ 5 wt ct). The corall ine algal sand and echinoderm - bivalve -foraminifer sand both exist on the wave-shel- tered areas of the coastal platforms but with different dominances in the benthic algal vegetation. While the corall ine algal sand form in protected niches between rhodolith pavements and reefal frameworks, the echino- derm - bivalve - foraminifer sand predominant ly is inhab- ited by fleshy seaweeds. The foraminifer - bryozoan sand shows a wide depth occurrence from 36 to 100 m water depth along the slopes bordering the coastal platforms. The deeper slopes are void of living benthic algal vegeta- tion with the exception of encrusting corall ines which colonize outcropping rocks and boulders. The analysis of
270
they rarely contribute with more than 1 wt % to the sediment supply. The tidal currents rework ostra- cods from their biocoenoses into adjacent deposi- tional settings where ostracods form up to 3 wt % of the sediment content.
Fig. 6. Spatial distribution of 'apparent diversity' for the ostracod species expressed by the SHANNOr~-WmNER index on the Sandcyfjord (A) and the Sve Platform (B).
the macrofauna reveals strong evidence for intense downslope transport of particles from the coastal zone into the fjord troughs. This is indicated by layers of partly decayed seaweed still associated with its gastropod fauna (FREITAG 1997; BEHNKEN 1998). The same observation holds for ostracods which form a mixed assemblage consisting of imported coastal platform species and autochthonous fjord troug h species. Thus the separation between coastal plat- form and fjord trough ostracod assemblage is difficult to define because of the reworking. In addition, the intense bias due to transportation is indicated by the impoverished preservation of ostracods in the wave-exposed kelp forest and seaweed belts as well as in tidal channels. These macroalgal habitats are known to provide the ecologic frame for many ostracods. The impact of a vigorous tidal current regime on the deposition of ostracods was shown by WEHRMANN (1994) from the macrotidally-controlled Baie de Modaix, northern Brittany coast, France. This coastal platform is located near the southern boundary of the cold-temperate bioprovince. Although ostracods were commonly found alive in the benthic algal communities,
Biogeographic aspects
Some species found in the investigated area, such as Leptocythere pellucida (P1. 58/6), are liv- ing at the northern limit of their biogeographic distribution. Others, which prefer cooler waters, live near their southern biogeographical limits. These species include Cytheropteron nodosoalatum (PI. 59/3), Cytheropteron pyramidale (PI. 59/6), Hemicytherura clathrata (PI. 60/1) and Rabilimis septentrionalis (P1.58/16). Cytheropteron testudo (PI. 59/9) is widespread in upper Pliocene and Pleistocene deposits of the Mediterranean area (BONADOCE & SPROVIERI 1985). Along the Norwe- gian coast it lives in clayey sediments at the depths of 80 to 240 m (ELoFSON 1941). However, in the Bay of Biscay and in the Eurasian Basin of the Arctic Cytheropteron testudo lives in greater depths at 700 to 2000 m (CRONIN 1995; YASSIm 1969). Cytherella vulgatella (PI. 58/3)occurs in the Medi- terranean Sea from the Tortonian and lives at present in the Adriatic and Tyrrhenian Sea at depths of 15 - 180 m (AIELLO et al. 1996). Cluthia cluthae (P1. 58/5) and Muellerina abyssicola (P1. 58/15)are amphiatlantic and predominantly Arctic in distri- bution (ELoFSON 1941; HAZEL 1970; NEALE & HOWE 1975; ATtmRSUCH et al., 1989). MueUerina abyssicola, however, is associated with sub-frigid and cold- temperate marine climates (HAZEL, 1970) and oc- curs in shallower depths near the northern limit of its occurrence. South of Nova Scotia, Muellerina
abyssicola submerges to mid- and lower bathyal depths (-1600 m) below warm waters of the North Atlantic Current (HAZEL 1970). Krithe adelspergi (P1. 60/12) is only known from Arctic regions. BROUWERS (1990) erected this species from the Pleistocene of Alaska. Other occur- rences of this species are mostly registered as Krithe sp. (e.g. MALZ 1989, MOSTAFAWI 1990) or as Krithe producta BRADY, 1880 (e.g. KLIE 1942, HARTMANN 1992, 1993). Cytheropteron alatum seems to be restricted to moderately deep water in the boreal region off northwestern Europe (WHATLEY ~,~ MASSON 1980). This species lives in the Mediterranean Sea at the depths of 150 to 2250 m (PURl et al. 1969) and in the Bay of Biscay .at 200 to 400 m (GUILLAUME et al. 1985).
CONCLUSIONS
Ostracods play a considerable role in cold-temperate inner shelf sediments in northern Norway. The highest ostracod contents exist in current-reduced environments which are the wave-sheltered coastal platforms and outer
271
Iz 3 0 0
~ . . . ,.._ e -
2oo. .
t D W
0 �9
ca
300"
200
100
0
uE 300 T
0
300
200
I O0
E 300 T
8. E zoo
E = 100
0 o SO ~00 ISO ZOO ZSO
Water depth [m] 300 350 400
300
200
I O0
0
Fig. 7. Plot of dominant coastal platform ostracod species against depth.
50 100 150 200 250 300 350 400 Water depth [m]
fjord troughs. Tidal currents induce the strong removal of ostracods from the shallow-water habitats into the adja- cent troughs. Key species of the coastal platform ostracod assemblage are Cythere lutea, Finmarchinella angulata, Baffinicythere ernarginata, Hemicytherura clathrata, Robertsonites tuberculatus, Sclerochilus rudjakovi, Semicytherura undata and Xestoleberis cf. depressa. The outer fjord trough assemblage is characterized by Cluthia cluthae, Cytherella abyssorum, Cytheropteron alatum (PI. 5917), Krithe cf. adelspergi, Muellerina abyssicola, Ptery- gocythereis mucronata, CythereUa cf. vulgatella and Cy- theropteron testudo. However, large numbers of ostracods belonging to the coastal platform assemblages and the algal vegetation zones are transported downslope and mixed with the deeper trough assemblage. This high de- gree of ostracod export into the deeper depositional set- tings is enhanced by the steep bathymetric gradient be- tween the narrow coastal platforms and the steep-flanked fjord troughs and also by the tidal current regime.
A c k n o w l e d g e m e n t s
This contribution is part of the German Science Foun- dation (DFG) project He 1671/1 ,,Controls in formation of
cold-water carbonates" which is part of a major research program ,,Global and regional controls in biogenic sedi- mentation". We thank T. O. VORREN, M. HALD and B. GULLmSEN from the University of Tromsr for their invalu- able logistic help and for their invitation to work on R/V Onar. This research vessel was skillfully operated by Captain K. BENDIKSEN. S. RASMUSSEN and A.-E. RORNES provided invaluable help on R/V Ottar. A. MUr~NECKE, H. ANDRULErr, and S. SCHAUER aided in the sample prepara- tion. Special thanks are due to R. HENRICH and P. SCHAFE~ for discussing the data. We also are grateful to U. SCHOLDT and C. SAMTLEBEN who are responsible for the SEM- Laboratory of the Geologisch-Pal~iontologisches Institut, Kiel University, for their considerable support in taking the micrographs. The manuscript benefited from construc- tive comments and linguistic assistance by J. B. WILSON, Royal Holloway University of London. The reviews by T. M. CRONIN and anonymous were greatly appreciated.
R e f e r e n c e s
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- Synopsis of the British Fauna (new Series), 4, 343 pp. BEHNKEN, A. (1998): Sedimentologische Charakterisierung yon
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BONADUCE) G. (~ SFROVIERI, R. (1985): The appearence of Cytheropteron testudo Sars (Crustacea, Ostracoda) is a Pliocene event. Evidences from a Sicilian sequence in Italy, - Bollettino della Societa Paleontologica Italiana, 23, 13 I- 136
BOS~.NCE, D,W.J. (1983): Coralline algal reef frameworks--. Journal of the Geological Society of London, 140:365-376
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-- (1878): Note on the Ostracoda. - In: NARES, G.S. (ed.): Narrative of avoyage to the Polar Sea during the years 1875- 1876 in H.M.Ships ,,Alert" and ,,Discovery", 2, 253-256, London
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