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Distribution of Recent Dinocyst Assemblages in the Western Barents Sea 109 NORWEGIAN JOURNAL OF GEOLOGY Distribution of recent dinocyst assemblages in the western Barents Sea 109 Distribution of recent dinocyst assemblages in the western Barents Sea Sandrine Solignac*1,2, Kari Grøsfjeld3, Jacques Giraudeau4, Anne de Vernal2 Sandrine Solignac*, Kari Grøsfjeld, Jacques Giraudeau, Anne de Vernal. Distribution of modern dinocyst assemblages in the western Barents Sea. Norwegian Journal of Geology, Vol. 89, pp. 109-119, Trondheim 2009. ISSN 029-196X. Dinoflagellate cyst (dinocyst) assemblages were analyzed in 43 surface sediment samples from the Barents Sea. They can be divided into five major assemblage types, the distribution of which can clearly be linked to the overlying water masses. Notably, a very clear distinction between sites influ- enced by Atlantic water and Arctic water, respectively, is seen in the change in dominance from O. centrocarpum s.l. to I. minutum and is strongly related to sea-surface temperature. More subtle hydrographical features are also recorded in the assemblages, as can be seen from the spatially cohe- rent distribution of the Atlantic assemblages, which allows discrimination between the Norwegian Coastal Current zone, the Norwegian Atlantic Current zone and two regions of modified Norwegian Atlantic Current waters. Here sea-surface temperature does not seem to be the primary para- meter controlling the distribution of the assemblages. Multivariate analyses suggest that the assemblages are associated with the stratification and productivity annual cycles. Cysts of P. dalei seem to favour stratified environments, while O. centrocarpum s.l. might be more adapted to unstable conditions. Cysts of P. dalei are also associated with early spring stratification and productivity, whereas other species such as S. ramosus are related to late spring/summer productivity and stratification. 1 Department of Earth Sciences, University of Aarhus, Høegh-Guldbergs Gade 2, DK 8000 Aarhus C, Denmark 2 GEOTOP, Université du Québec à Montréal, C.P. 8888, Succursale Centre-ville, Montréal, QC, H3C 3P8, Canada 3 Geological Survey of Norway, N-7021 Trondheim, Norway 4 Environnements et Paléoenvironnements Océaniques, UMR CNRS 5805, Université Bordeaux 1, Avenue des Facultés, 33405 Talence cedex, France * Corresponding author: [email protected] Department of Earth Sciences, University of Aarhus, Høegh-Guldbergs Gade 2, DK 8000 Aar- hus C, Denmark 1. Introduction The strong hydrological gradients of the Barents Sea result in distinct regimes of productivity and different The Barents Sea plays a major role in the oceanic system, phytoplankton communities (e.g., Kögeler & Rey, 1999). as it is one of the main areas of water exchange between The fossil remains of these communities could thus pro- the Atlantic and Arctic oceans. The relative strength of vide useful information on the past variations of the Atlantic and Arctic fluxes can vary considerably on vari- water masses. Notably, among various micropaleonto- ous time scales, having impacts on the global circulation logical tracers, it has been shown in numerous previous through their role in the Arctic Ocean freshwater budget studies that dinoflagellate cysts (or dinocysts) recovered and also on the local hydrography and productivity of from surface sediments are strongly related to the overly- the Barents Sea. An example of these local impacts is the ing water masses (e.g., de Vernal et al., 2005 and refer- fluctuations of the position of the ice edge in the north- ences therein). Moreover, their high resistance to disso- ern Barents Sea, which can shift over several hundreds of lution and their abundance and diversity in harsh condi- kilometres from one year to another (Loeng, 1991; Glo- tions make them useful proxies for the reconstruction of ersen et al., 1992). past high-latitude environments such as the Barents Sea (e.g., de Vernal et al., 2001). The Barents Sea is one of the most productive polar seas (Kögeler & Rey, 1999) and is of major importance for the Our goal here is to assess to what extent dinoflagellate fishery industries of the region (Olsen et al., 2003). Pro- cyst (or dinocyst) assemblages from recent sediments ductivity is intricately linked to physico-chemical oce- reflect the hydrographic conditions and productivity in anic processes such as the volume of inflowing Atlantic overlying water masses of the Barents Sea, and possibly waters, the presence or absence of sea-ice and melt water, to improve our knowledge of the ecological requirements radiation, light, mixed layer depth and nutrient availabil- of the various species. ity (e.g. Engelsen et al., 2002). 110 S. Solignac et al. NORWEGIAN JOURNAL OF GEOLOGY Zemlya as the Persey Current. The East Spitsbergen Cur- 2. Oceanographic setting rent flows south along the coast of Svalbard, where it becomes the South Cape Current, and eventually flows The Barents Sea is a continental shelf with an area of as a northward coastal current along the western coast of 1.4 × 106 km2 (Strass & Nöthig, 1996) and an average Svalbard. The major part of the Persey Current follows depth of 230 m (Loeng, 1991). The oceanic circulation is the eastern slope of the Spitsbergenbanken and becomes mainly characterized by northward/northeastward-flow- the Bjørnøya Current (Loeng, 1991). Arctic and Atlan- ing warm and saline Atlantic water and cold, fresh water tic waters meet along the continental slope and form the coming from the Arctic Ocean. Polar Front, which roughly follows the 250 m isobath (Fig. 1; Gawarkiewicz & Plueddemann, 1995). Atlantic waters, which are defined by salinity higher than 35.0, are carried by the Norwegian Atlantic Cur- The Norwegian Coastal Current is another major current rent. Part of it flows north towards the west coast of in the region. It flows along the western and northern Svalbard and becomes the West Spitsbergen Current, coast of Norway and continues along the Russian coast while the remainder enters the southern Barents Sea as the Murman Coastal Current (Loeng, 1991). It carries through Bjørnøyrenna and becomes the North Cape waters that are slightly cooler and significantly fresher Current. It then divides into two branches, one flowing (<34.7) than Atlantic Water (Loeng, 1991). In winter, this eastward towards Novaya Zemlya and the other turning current is deep and narrow and closer to the Norwegian north towards Hopen. Part of this northern branch sinks coast. In summer, the dominant winds change direction, under the lighter Arctic waters between Hopen and Stor- causing the coastal water to spread up to 100-150 km banken and between Storbanken and Sentralbanken, and away from the shore and to form a wedge overlying the becomes an intermediate current (Fig. 1, Loeng, 1991). more saline Atlantic waters (Fig. 1; Loeng, 1991; Olsen et al., 2003). Arctic waters, identified by their low temperature (< 0ºC), flow at the surface into the Barents Sea between The distribution of the water masses has a direct impact Svalbard and Frans Josef Land as the East Spitsbergen on the formation of sea-ice. Sea-ice develops in the Current, and between Frans Josef Land and Novaya northern Barents Sea, with the ice edge generally follow- Figure 1. Location of the 2000 FRANS JOSEF 1000 LAND major surface currents 200 80°N . of the Barents Sea (in C 200 blue, polar currents, in n e SVALBARD g W r red, Atlantic currents, in e 200 e sb s it Current green, coastal current; t p ersey S S P p t Loeng, 1991), along with i s 78°N ts a Stor- b E the sampling sites. The e r banken g e solid black line repre- n C sents the mean position . Hopen of the Polar Front (Loeng, 32 33 3031 . 76°N 29 C t 1991). 28 n 27 a e 26 y r 25 r 24 ø Spitsbergen- n u r C Sentral- 23 22 21 20 banken jø e B p a 200 banken C th or N 74°N 3000 500 NOVAYA t 11 12 13 14 15 16 17 18 19 n ZEMLYA e Bjørnøy- r r 9 8 6 5 4 3 2 1 renna u N 72°N C o 35 r c 34 th i t 2000 1000 36 37 C n 38 orwegi a a 39 N an p l C t 40 o e A 41 a C s u 200 n 42 t 3000 a rr a 43 l e i n g 44 C t 45 e . w 70°N r o N NORWAY 5°E 10°E 15°E 20°E 25°E 30°E 35°E 40°E 45°E 50°E 55°E NORWEGIAN JOURNAL OF GEOLOGY Distribution of recent dinocyst assemblages in the western Barents Sea 111 ing the Polar Front. The exact position of the ice edge, trast, in Atlantic waters, which evolve slowly from deeply however, can vary by hundreds of kilometres interannu- mixed in winter to stratified in spring, the spring bloom ally and also on longer, multidecadal timescales (Glo- starts later (late May-early June) than in the ice marginal ersen et al., 1992; Divine & Dick, 2006), due to variable zone, and develops during the summer, with the weaker inflows of Atlantic waters and/or atmospheric processes and deeper mixed layer allowing the exchange of nutri- such as the North Atlantic Oscillation (NAO; Loeng, ents with deeper water masses (Kögeler & Rey, 1999). 1991; Vinje, 2001). On average, in the northern Barents Sea, freezing starts in September, and the maximum sea- ice cover (concentrations of 70%) is reached in April. Melting starts in May and the entire Barents Sea is ice 3. Material and methods free from about July to September (Kögeler & Rey, 1999). The southern Barents Sea is usually devoid of sea-ice all The study region is located between northern Norway year long due to the presence of Atlantic Water, but in and Svalbard, at the western limit of the Barents Sea.
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