Djinnridze et al.: Diatoms from Surface Sediments ofthe Saint Anna Trouh
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species (6 genera) were identified. Among the recent diatoms, 30 taxa belong to the class
Centrophyceae and 63 taxa belong to the class Pennatophyceae.
The representatives of phytoplankton are mainly centric species such as: Thalassiosira
gravida and Th. antarctica (16-25%), T. nordenskioldii (IO-16%),T. kryophila (16%), Th.
hyalina (1-8%), Porosira glacialis (20%) and Coscinodiscus oculus-iridis (10-11 %). The
second group, present in lower amounts, is a group of kryopelagic and kryointersticial species,
dwelling on lower and marginal sea ice surfaces: Melosira arctica (2-4%), Fragilariopsis
oceanica (2-12%), F. cylindrus (> 1%), Nitzschia frigida (2%), N. polaris (> I %), Navicula
cancelata var. gregori (2%), Nav. directa (I %), Nav. reinhardtii var. tschuktschorum (4%).
Species of the genera Thalassiosira (9 taxa), Navicula (II taxa), Diploneis (10 taxa) and
Nitzschia (10 taxa) are the most numerous.
All species found in sediments from the St. Anna Trough have been found previously already
in the Kara Sea and are enclosed in the list of Kara Sea diatoms (148 species and varieties)
compiled by Makarevich and Koltsova (1989) from own investigations and literature data
(Zabelina, 1930, 1946; Kiselev, 1935; Usachev, 1938, 1949, 1968). Observations of ice
diatoms the deep Arctic Basin by Horner (1982) showed that the bloom near in the ice margin
mainly consists of pennatic diatoms, whereas the bloom of phytoplankton in ice-free areas is
dominated by centric diatoms. Fragilariopsis oceanica and F. cylindrus are abundant in both
habitats. In spring plankton, the most abundant species are Thalassiosira gravida, T.
nordenskoldii, Fragilariopsis oceanica and Porosira glacialis (Usachev,1968; Grant and
Horner, 1976). All these species are dominant in the assemblage composition in surface
sediments of the St. Anna Trough. They are also typical for diatom compositions found in
sediments under ice packs (Sancetta, 1982; Williams, 1986).
The true marine diatoms in the described assemblages constitute 92-98% (Figure 2).
Brackishwater euryhaline species, dwelling on sea ice are also present (up to 7%). Species of
this group are: Thalassiosira hyperborea var. septentrionalis, Achnanthes taeniata ,A.
hrevipes, Diploneis interrupta, D. stroemii, D. smithii, Nitzschia hvhrida var. kryokonites,
Amphora laevis var. laevissima, Navicula kjellmanii. Freshwater species such as: Aulocoseira
islandica subsp. helvetica, A. granulata, and Amphora ovalis contribute up to 3% of the
sediment assemblage.
The existence of brackishwater species may be explained by a freshening effect of melting sea
ice. The salinity in a thin layer below the sea ice can be strongly variable from 15 to 29%0
(Melnikov, 1989). This fact may allow algae with different salinity tolerances to exist below sea
ice. In 1994 during cruise 9 of RV "Professor Logachev" the surface water salinity at some
stations had decreased to 13-16%0, probably from increased atmospheric precipitation. The
presence of freshwater diatoms in the assemblages allows to suggest that they had lived in sea
ice, which was formed in a proximal freshwater-dominated environment and then drifted to the
open sea. A current transport from the southern Kara Sea to the St. Anna Trough seems rather
unlikely.
In sediments from the majority of stations, the frustules of planktic, mostly neritic species are
prevailing (92-98%; Figure 2). Panthalassic species constitute up to 12% (Coscinodiscus
oculus-iridis, C. curvatulus var. kariana, Actinocyclus curvatulus). In samples from stations
with a water depth of about 100 m, the littoral species constitute up to 30%. This may be
explained by a mechanism of ice flora forming on account of planktic and benthic species
(Melnikov, 1989). In shallow waters the species distribution and quantitative composition of
ice algae is dominated by benthic species, whereas in deep sea regions it is dominated by
planktic species.
555
species (6 genera) were identified. Among the recent diatoms, 30 taxa belong to the class
Centrophyceae and 63 taxa belong to the class Pennatophyceae.
The representatives of phytoplankton are mainly centric species such as: Thalassiosira
gravida and Th. antarctica (16-25%), T. nordenskioldii (IO-16%),T. kryophila (16%), Th.
hyalina (1-8%), Porosira glacialis (20%) and Coscinodiscus oculus-iridis (10-11 %). The
second group, present in lower amounts, is a group of kryopelagic and kryointersticial species,
dwelling on lower and marginal sea ice surfaces: Melosira arctica (2-4%), Fragilariopsis
oceanica (2-12%), F. cylindrus (> 1%), Nitzschia frigida (2%), N. polaris (> I %), Navicula
cancelata var. gregori (2%), Nav. directa (I %), Nav. reinhardtii var. tschuktschorum (4%).
Species of the genera Thalassiosira (9 taxa), Navicula (II taxa), Diploneis (10 taxa) and
Nitzschia (10 taxa) are the most numerous.
All species found in sediments from the St. Anna Trough have been found previously already
in the Kara Sea and are enclosed in the list of Kara Sea diatoms (148 species and varieties)
compiled by Makarevich and Koltsova (1989) from own investigations and literature data
(Zabelina, 1930, 1946; Kiselev, 1935; Usachev, 1938, 1949, 1968). Observations of ice
diatoms the deep Arctic Basin by Horner (1982) showed that the bloom near in the ice margin
mainly consists of pennatic diatoms, whereas the bloom of phytoplankton in ice-free areas is
dominated by centric diatoms. Fragilariopsis oceanica and F. cylindrus are abundant in both
habitats. In spring plankton, the most abundant species are Thalassiosira gravida, T.
nordenskoldii, Fragilariopsis oceanica and Porosira glacialis (Usachev,1968; Grant and
Horner, 1976). All these species are dominant in the assemblage composition in surface
sediments of the St. Anna Trough. They are also typical for diatom compositions found in
sediments under ice packs (Sancetta, 1982; Williams, 1986).
The true marine diatoms in the described assemblages constitute 92-98% (Figure 2).
Brackishwater euryhaline species, dwelling on sea ice are also present (up to 7%). Species of
this group are: Thalassiosira hyperborea var. septentrionalis, Achnanthes taeniata ,A.
hrevipes, Diploneis interrupta, D. stroemii, D. smithii, Nitzschia hvhrida var. kryokonites,
Amphora laevis var. laevissima, Navicula kjellmanii. Freshwater species such as: Aulocoseira
islandica subsp. helvetica, A. granulata, and Amphora ovalis contribute up to 3% of the
sediment assemblage.
The existence of brackishwater species may be explained by a freshening effect of melting sea
ice. The salinity in a thin layer below the sea ice can be strongly variable from 15 to 29%0
(Melnikov, 1989). This fact may allow algae with different salinity tolerances to exist below sea
ice. In 1994 during cruise 9 of RV "Professor Logachev" the surface water salinity at some
stations had decreased to 13-16%0, probably from increased atmospheric precipitation. The
presence of freshwater diatoms in the assemblages allows to suggest that they had lived in sea
ice, which was formed in a proximal freshwater-dominated environment and then drifted to the
open sea. A current transport from the southern Kara Sea to the St. Anna Trough seems rather
unlikely.
In sediments from the majority of stations, the frustules of planktic, mostly neritic species are
prevailing (92-98%; Figure 2). Panthalassic species constitute up to 12% (Coscinodiscus
oculus-iridis, C. curvatulus var. kariana, Actinocyclus curvatulus). In samples from stations
with a water depth of about 100 m, the littoral species constitute up to 30%. This may be
explained by a mechanism of ice flora forming on account of planktic and benthic species
(Melnikov, 1989). In shallow waters the species distribution and quantitative composition of
ice algae is dominated by benthic species, whereas in deep sea regions it is dominated by
planktic species.