Cold-water Forms Research Articles

Biogeography of Radiolaria Polycystina (Protista) in the World Ocean

Analysis of 307 species of Radiolaria Polycystina in a worldwide dataset of 4774 plankton, sediment trap, and surface sediment samples allows recognizing six major biogeographic Domains. Five of them are circumglobal (Polar North, Polar South, Bi-Subpolar, Transitional and Tropical-Subtropical), and one is restricted to the Eastern Equatorial Pacific. Each Domain is characterized by a particular suite of species, all of which, however, occur widely, albeit sparsely, in one or more other Domains. Of the eight environmental variables evaluated, temperature correlates best with the partitions established. Species distributions in the water column and in the sediments are generally in agreement, but in the sediments cold water forms extend farther towards the equator than do warm water radiolarians towards the poles. In the Recent sedimentary record of planktonic Foraminifera the same phenomenon is magnified by the higher dissolution rates of warm water species, as compared with the cold water ones. Of the three major oceans, the Pacific was the most speciose, but estimates based on data corrected for sample-size show much smaller inter-oceanic differences, with ∼10 radiolarians probably being absent from either basin. The radiolarian biogeographic pattern is generally similar to those based on other planktonic and nektonic open-ocean organisms, but the degree of uniqueness of the Domains, as well as the position of the intervening boundaries, are variable, which reflects methodological differences, as well as taxon-specific traits. Partitions of the World Ocean defined on the basis of species ranges resemble the major divisions (presumably functionally homogeneous units) established on the basis of physical traits and chlorophyll fields, but secondary divisions nested within the latter are not reflected by any of the biogeographic schemes based on species distribution ranges. This conflict raises questions about the importance of several physical mechanisms for structuring pelagic communities, and/or on the coupling of structure and function in the pelagic realm.

Morphological variability of Emiliania huxleyi in the Indian sector of the Southern Ocean during the austral summer of 2010

Abstract We documented scanning electron micrographs of Emiliania huxleyi morphotypes from 9 vertical profile samples collected between 39°S and 65.49°S (57.3°E) during the Fourth Indian Southern Ocean expedition (January–February, 2010). Water samples were obtained from 6 different depths (between 0 and 110 m) to study the distribution and abundance of E. huxleyi morphotypes with respect to associated environmental factors in the oceanic frontal regions of the Southern Indian Ocean. Five E. huxleyi morphotypes were identified, quantified and the preference of each morphotype with regard to physico-chemical parameters assessed by Canonical Correspondence Analysis (CCA). Morphotypes A and B comprised 6.2% and 0.7% of the total E. huxleyi abundance, respectively, and dominated at stations located north of the Southern Subtropical Front (SSTF) associated with warmer, highly saline and nutrient-poor surface waters. Morphotypes C and B/C are cold water forms representing 23.2% and 68.5% of the total E. huxleyi abundance, respectively, and dominated in the Subantarctic (SAF2) and Polar Frontal (PF1) regions of the Southern Indian Ocean. Morphotypes C and B/C dominated in the SAF2 and PF1 regions, which were identified as the most productive areas due to the elevated nutrient concentrations. Salinity, nitrate, phosphate and probably light intensity were the most important parameters for the proliferation of E. huxleyi in these frontal regions. Towards the south, a consistent decrease in the E. huxleyi abundance was observed and their lowest abundance recorded at the southernmost station located in the Antarctic coastal region (65.49°S).

The youngest cambroclaves: Cambroclavus absonus from the Middle Cambrian of the Cantabrian Zone (northwest Spain)

Cambroclayes are Cambrian phosphatized problematica. The group is known from spine-like remains that are locally abundant on a number of Cambrian paleocontinents. Cambroclaves are known through a relatively short time interval (late Early Cambrian-early Middle Cambrian) mostly from tropical, carbonate platform successions on the Siberian Platform, East Gondwana (Australia, China, Kazakhstan), and West Gondwana. The West Gondwana occurrences include Cambroclavus ludwigsdorfensis Elicki, 1994 and Cambroclavus sp. from the late Early Cambrian of eastern Germany (Elicki, 1994, 2005; Elicki and Watte, 2003), and Cambroclavus sp. from the early Middle Cambrian of Sardinia (Elicki and Wotte, 2003;“ Elicki et al., 2003; Elicki, 2005, 2006). Recently, Clausen and Alvaro (2006) reported the zhijinitid form Parazhijinites cf. guizhouensis Qian and Yin, 1984 from the early Middle Cambrian of the Cantabrian zone of northwest Spain. Other than the mentioned tropical occurrences, Landing (1991) published the obviously cool to cold water form Samsanoffoclavus matthewi Landing, 1991 from the middle Early Cambrian of Cape Breton Island (Avalonia).

The youngest cambroclaves: Cambroclavus absonus from the Middle Cambrian of the Cantabrian Zone (northwest Spain)

Cambroclayes are Cambrian phosphatized problematica. The group is known from spine-like remains that are locally abundant on a number of Cambrian paleocontinents. Cambroclaves are known through a relatively short time interval (late Early Cambrian-early Middle Cambrian) mostly from tropical, carbonate platform successions on the Siberian Platform, East Gondwana (Australia, China, Kazakhstan), and West Gondwana. The West Gondwana occurrences include Cambroclavus ludwigsdorfensis Elicki, 1994 and Cambroclavus sp. from the late Early Cambrian of eastern Germany (Elicki, 1994, 2005; Elicki and Watte, 2003), and Cambroclavus sp. from the early Middle Cambrian of Sardinia (Elicki and Wotte, 2003;“ Elicki et al., 2003; Elicki, 2005, 2006). Recently, Clausen and Alvaro (2006) reported the zhijinitid form Parazhijinites cf. guizhouensis Qian and Yin, 1984 from the early Middle Cambrian of the Cantabrian zone of northwest Spain. Other than the mentioned tropical occurrences, Landing (1991) published the obviously cool to cold water form Samsanoffoclavus matthewi Landing, 1991 from the middle Early Cambrian of Cape Breton Island (Avalonia).

The origin of massive diamicton in Marian and Potter coves, King George Island, West Antarctica

Marine sediment cores were obtained from in front of the tidewater glaciers in Marian and Potter coves in the South Shetland Islands in the austral summer of 1998–1999. Sedimentological and geochemical data from these cores document an advance of ice tongue for the deposition of clast-supported, massive diamicton, interpreted as having been produced by ice rafting in front of glacier margin and/or releasing of clasts from basal debris zones in the sub-ice tongue setting. A C-14 chronology for a core indicates that glacial advance took place ca. 1450–1700 yrs B.P., coincident with warm, humid phase in the study area. During this period, the glacier margin was likely to advance and release diamicton clasts, inferred from a reduction in the total organic carbon content, and an increase in sand and clasts within the diamicton facies. The glacial advance probably caused enhanced ice-edge blooms near the core sites, resulting in increased abundance of sea-ice related diatoms i.e.,Fragilariopsis curta andFragilariopsis cylindrus in the diamicton. The warm and humid conditions between 1450–1700 yrs B.P. might allow the intrusion of warm circumpolar deep water within the fjords, bringing about increased abundance of warm water form, i.e.,Fragilariposis kerguelensis. On the other hands, this warming condition probably prohibited the intrusion of Weddell Ice shelf water from the fjord, as evidenced by lack of cold water form,Thalassiosira antarctica, in the diamicton. Clearly, the response of the outlet glacier system along the periphery of the South Shetland Islands Ice Sheet during the late Holocene warm, humid period (1450–1700 yrs B.P.) was expansion. Thus the process of clast-supported massive diamicton formation is likely to be applicable to a number of areas of the modern and Quaternary Antarctic Peninsula.

Species of Minidiscus (Bacillariophyceae) in the Mexican Pacific Ocean

Minidiscus species are the smallest centric diatoms of the marine phytoplankton (with diameters ranging from 1.9 to 7.5 μm), and they may be easily overlooked in routine analyses. Three species of the genus occurred in samples collected in the Mexican Pacific Ocean: Minidiscus trioculatus, M. comicus and M. chilensis. The identification of these species represents the first documented records for the Mexican Pacific: Minidiscus trioculatus and M. chilensis off the west coast of Baja California, and M. comicus in the Gulf of Tehuantepec. Minidiscus trioculatus is considered a cosmopolitan species, M. comicus has a wide distribution in subtropical-temperate waters, and M. chilensis may be mainly regarded as a temperate to cold-water form.

Lecanid rotifers (Rotifera: Monogononta: Lecanidae) from North-Eastern India

Thirty-five species of the family Lecanidae are examined from Tripura state in North-Eastern India. Of these, Lecane levistyla and L. scutata are interesting cold-water forms; L. batillifer is an Australasian element; L. acanthinula and L. sinuata are Oriental endemics and L. braumi, L. lateralis and L. simonneae are palaeotropical species. The lecanid fauna also includes the pantropical L. thienemanni and L. sola while the remainder are cosmopolitan and tropicopolitan elements.

Paleohydrographic changes in the Somali Basin (5°N upwelling and equatorial areas) during the last 160 Kyr, based on correspondence analysis of foraminiferal and radiolarian assemblages

This study documents the biological signatures impressed upon the sedimentary record underlying both the 5°N upwelling system of the Somali Current and the equatorial area of the Somali Basin out of the upwelling influence. The evolution of these two distinct hydrographic systems is compared for the last 160 kyr. Correspondence and cluster analyses are performed on combined radiolarian and planktonic foraminiferal quantitative data in order to study the changes of the planktonic assemblages through time and space. The Upwelling Radiolarian Index (URI) is used as a productivity proxy. The water temperature and hydrographic structure of the upper water masses appear to be the major factors controlling the distribution patterns of the fauna. The relative abundances of three groups of foraminifera, cold water form (dextral N. pachyderma), mixed layer dwellers (G. trilobus, G. ruber, G. sacculifer, G. conglobatus, and G. glutinata), and thermocline dwellers (G. menardii, G. tumida, N. dutertrei, G. crassaformis, and P. obliquiloculata), follow distinct evolutionary patterns at the two sites during the last 160 kyr. At the equatorial site (core MD 85668), downcore fluctuations in the relative abundances of the three groups are closely related to the glacial/interglacial cyclicity and provide some insights into the interpretation of hydrographic changes. The dominance of the mixed layer foraminifera at the transition intervals between isotope stages 6/5 and 2/1, combined with weak URI values, is thought to reflect the reorganization of the oceanographic circulation. These short‐term events (with a duration of < 5000 year) could be related to the rapid inflow of oxygen‐depleted water through the Indonesian straits as a result of sea level rise during deglaciation. Underneath the 5°N gyre (core MD 85674), the response to global climatic changes is overprinted by the regional effect of the Somalian upwelling, which has been persistent over the last 160 kyr.

Genetic differentiation among three colony-forming species of Phaeocystis: further evidence for the phylogeny of the Prymnesiophyta

Sequence data from the 18S small subunit ribosomal RNA gene have been used to support the species status of three colony-forming species of Phaeocystis Lagerheim (Prymnesiophyta). Two of these correspond to Phaeocystis globosa Scherffel and Phaeocystis pouchetii (Hariot) Lagerheim. The third species originates from antarctic waters and is referred to Phaeocystis antarctica, described by Karsten at the tum of the century. Morphological and physiological data supporting the separation of the three species is compiled from the literature. Phylogenetic trees generated from the sequence data suggest that the warm-water species, Phaeocystis globosa diverged prior to the separation of the two cold-water forms. Tectonic events and climatic changes during the middle to late Cenozoic provide mechanisms by which speciation events could have occurred as both polar oceans were being formed.

Thermostability differences of allozyme loci in Mytilus edulis, M. galloprovin-cialis and hybrid mussels

A comparison of allozyrne thermostability was made between Mytilus eduljs and M. galloprovincialis populations, and between M. edulis-like and A4. gallopro~.incialis-like mussels of a hybrid population, all from SW Britain. In all 3 populations, alleles at 3 polymorphic allozyme loci (Odh, Pgi and Pgm) of the 8 monoand polymorphic allozyme loci examined were found to exhibit thern~osensitlvlty. For all 3 populations following heat treatment, there was a mean increase of 63 % In the total number of detectable alleles at these locl. Two analyses provided evldence of a significantly greater frequency of heat-sensitive alleles in the M. eduhs genome, whilst one analysis provided evidence of a significantly greater frequency in the M. galloprovincialis genome. However, the majority of allele-by-allele and locus-by-locus comparisons revealed no significant difference In the frequencies of heat-sensitive alleles found in M. eduhs and M. galloprovmcialis. Nei's g e n e t ~ c distance (D) computed from allele frequencies at a locus, and at all 3 loci together, showed similar values before and after heat treatment. Overall the results suggest that there is no difference in the frequency of heatsensitive alleles in M. edulis (a cold-water form) and in M. gallopro.i~jnc~aljs (a warm-water form). Our results contrast w t h previous studies of heat-sensitivity in marine organisms, all of which have reported significant differences in heat-sensitive allele frequencies in intra-specific comparisons between geographically distinct regions with differing temperature regimes.

Calcification of Encrusting Aragonitic Algae (Peyssonneliaceae): Implications for the Origin of Late Paleozoic Reefs and Cements

ABSTRACT Encrusting aragonitic calcareous algae of the family Peyssonneliaceae are the largest group of calcified red algae outside the well-known Mg calcite Corallinaceae. They are distributed worldwide, are most heavily calcified in temperate and tropical waters, and grow as prone but arched sheets on soft mud substrates, on hard rock surfaces, as extensive bridge-like networks between corals in reefs, and as concentric layers in nodules. Calcification is entirely aragonitic, species-specific, and both intracellular and extracellular below the thallus as a hypobasal layer. The hypobasal layer develops outside the tissue as an encrustation of small aragonite botryoids attached to the lower surface between rhyzoids, and on living plants it may exceed the thickness of the thallus. Calcification ranges from nonexistent in some cold-water forms, to thallus calcification only, to both thallus and hypobasal calcification, to species in which the thallus is noncalcified but there is a hypobasal layer of aragonite botryoids. Although the confirmed fossil range of this family extends only to the Early Cretaceous, striking similarities between these aragonitic forms and some late Paleozoic phylloid algae suggest that they may be closely related. Their ability to grow on soft mud substrates and form structures composed of irregular arched sheets with extensive pore space, as well as their brittle nature, so susceptible to fragmentation, are all characteristics of mound-forming fossil phylloid algae. The hypobasal layer of botryoidal aragonite, developed while the plant is still growing, could easily act as a nucleation site for further epitaxial submarine precipitation, thus explaining the common association of Paleozoic phylloid algae and extensive fossil-reef cements that resemble botryoidal aragonite. The presence of hypobasal botryoidal aragonite on plants with a noncalcified thallus raises the possibility that some fossil-reef cements may be related to now-vanished algae.

Polycystine radiolaria of the California Current region: Seasonal and geographic patterns

Analysis of the 155 radiolarian taxa recorded in 48 plankton samples collected by means of 0–100 m tows between January and November 1972 in the California Current region revealed three faunal zones. The northernmost of these was dominated by Subarctic-transitional species; the central, which was comprised of three closely related subgroups, by intermediate-transitional taxa; and the southernmost by warm-transitional radiolarians. Of the taxa present in >5 samples, 47 — distributed among 12 species groups — plus 7 isolated species, showed significantly ( p<0.05) higher abundances in either one of the areas defined. Four additional groups and several species were considerably more abundant and frequent in some areas than in others, but the corresponding differences were statistically non-significant. Some species (i.e., Acrosphaera murrayana, Spongocore cylindrica, Pseudocubus obeliscus, Trisulcus triacanthus, Botryostrobus auritus/australis, Spirocyrtis scalaris/cornutella, and Botryopyle dictyocephalus) were found to be associated with the coldest of the areas defined, rather than with the waters with highest tropical-equatorial influence, as would have been expected on the basis of previous studies. Comparison of our results with similar studies based on sedimentary materials showed some conspicuous differences, suggesting that sediments yield radiolarian assemblages with higher proportions of cold-water forms, presumably advected via subsurface currents. The cold-transitional assemblage had the lowest specific diversity and the highest dominance of a few abundant species over the rest; the intermediate-transitional showed highest diversities; and the warm-transitional lowest dominance. Indirect evidences suggest that the assemblages recorded are representative of normal, non-El Nin˜o conditions.

Differences in species diversity of Monogenea between the Pacific and Atlantic Oceans

Data from five extensive surveys each in the Pacific and Atlantic Oceans show that relative species diversity (number of parasite species per host species) of gill Monogenea of coastal marine fishes is greater in the northern and southwestern Pacific than in the northeastern and central- and southwestern Atlantic. Relative species diversity is markedly lower in the cold northeastern Atlantic than in the warmer parts of the Atlantic examined, and in the northern Pacific than in the warm southwestern Pacific. The difference between the northern Pacific and Atlantic is entirely or almost entirely due to a much greater number of species of Gyrodactylidae in the northern Pacific. A species-area relationship cannot explain the difference, because the area of the northern Pacific is not larger than that of the northern Atlantic and because Gyrodactylidae are cold-water forms which cannot have immigrated from warmer seas. The difference is tentatively explained by an evolutionary time hypothesis: more species of Gyrodactylidae have accumulated in the much older Pacific than in the Atlantic Ocean. Alternatively, an ecological time hypothesis may explain the difference: ice sheets during the last glaciation covered much more of the continental shelf in the northern Atlantic than in the northern Pacific, possibly extinguishing more Monogenea in the former than in the latter Ocean.

Calcification of Encrusting Aragonitic Algae: Implications for Origin of Late Paleozoic Reefs and Cements: ABSTRACT

Encrusting aragonitic calcareous algae of the family Peyssonneliacae are the largest group of calcified red algae except for the well-known Mg-calcite coralline algae. They are distributed worldwide, are most heavily calcified in temperate and tropical waters, and grow as prone but arched sheets on soft mud substrates, on hard rock surfaces, as extensive bridgelike networks between corals in reefs, and as concentric layers in nodules. Calcification is entirely aragonite, species specific, and both intracellular and extracellular below the thallus as a hypobasal layer. The hypobasal layer develops outside the tissue as an encrustation of small aragonite botryoids attached to the lower surface between rhyzoids, and on living plants it may exceed the thickness of the thallus Calcification ranges from nonexistent in some cold-water forms to thallus calcification only, to both thallus and hypobasal calcification, to species in which the thallus is noncalcified but there is a hypobasal layer of aragonite botryoids. Although the confirmed fossil range of this family extends only to the Early Cretaceous, striking similarities between these aragonitic forms and some late Paleozoic phylloid algae suggest that they may be closely related. Their ability to grow on soft mud substrates and form structures composed of irregular arched sheets with extensive pore space, as well as their brittle nature so susceptible to fragmentation, are all characteristics of mound-forming fossil phylloid algae. The hypobasal layer of botryoidal aragonite, developed while the plant is still growing, could easily act as a nucleation site for further epitaxial submarine precipitation, thus explaining the common association of Paleozoic phylloid algae and extensive fossil reef cements that resemble botryoidal aragonite. The resence of hypobasal botryoidal aragonite on plants with a noncalcified thallus raises the possibility that some fossil reef cements may be related to now-vanished algae. End_of_Article - Last_Page 491------------

Stratigraphic and Environmental Interpretation of Miocene Radiolarian Assemblages of Maria Madre and Maria Cleofas Islands and Baja California, Mexico: ABSTRACT

Miocene radiolarian assemblages were collected from Maria Madre and Maria Cleofas islands and five localities along Baja California (Tortugas, Bahia de Asuncion, Cien, Cabo San Lucas-La Paz, and San Felipe). Most of these sequences are composed of diatomaceous and/or diatomaceous shales or very fine sands. Stratigraphic correlation with previous work on the Monterey Formation, Experimental Mohole, and DSDP Legs 5, 7, 18, 32, and 66 indicate that the radiolarian zones Diartus petterssoni, Didymocyrtis antepenultima, Didymocyrtis penultima, and Stichocorys peregrina are present in these newly worked sections. The oldest dates obtained were from the Tortugas Formation (middle Miocene); the youngest was uppermost Miocene from the section at San Felipe. Paleoenvironmental interpretations were based on quantitative analyses on warm, cold, deep, and intermediate water forms, as well as abundances of diatoms and silicoflagellates. The Tortugas Formation (middle to upper Miocene) represents a slope biofacies characterized by relatively high percentages of cold and intermediate water forms, and the absence of deepwater radiolarians. Diatomaceous layers increase upsection and show an increase in radiolarian abundance and diversity (especially of cold water forms and silicoflagellates). These conditions reflect an enhancement of upwelling areas and low oxygen depositional facies. Previous radiolarian and diatom studies in Maria Madre and Bahia de Asuncion as well as Maria Cleofas, indicate that these environments of deposition are analogous to the Monterey Formation. Radiolarian faunas from these three sections are correlated to the Didymocyrtis antepenultima Zone and reflect an intensification of upwelling, perhaps as a result of the buildup of the Antarctic ice cap. The El Cien section and the section collected between La Paz and Cabo San Lucas are representative of the Didymocyrtis penultima Zone. The El Cien sequence is underlain by pillow basalts that may represent the contact between the East Pacific Rise and North America. Radiolarian faunas in both sections represent a mixture of warm and cold water forms with considerable dilution by terrigeneous sediments. San Felipe, the only section located on the gulf side, contains a unique radiolarian/fauna. This unique fauna may have been the result of basin isolation during the opening of the Gulf of California. End_of_Article - Last_Page 531------------

Population dynamics and production of Daphnia carinata (King) and Simocephalus exspinosus (Koch) in waste stabilization ponds

The population dynamics and production of D. carinata and S. exspinosus were investigated in two adjacent maturation-type waste stabilization ponds in South Australia. Population parameters (b', r', and d') for both species were determined from population density, brood size, and egg-development time. Length-weight relationships were determined for both species. Growth of D. carinata was investigated experimentally. Net production of both species was determined using Edmondson's population turnover- time model. Production of D. carinata was also determined using Winberg's biomass turnover model. D. carinata, the numerically dominant species, was a cold water form; high water temperatures increased mortality and reduced growth rate. Both species were food-limited at high population densities. Total annual net production of D. carinata in pond 1 during 1977 (345 g dry wt m-2): calculated using the population turnover-time model, was the highest yet recorded for any planktonic cladoceran. Annual net production of D. carinata determined using the population turnover-time model exceeded annual production determined using the biomass turnover model by 100%. Overestimation of daily production rate was highest during periods of high egg mortality. Total annual net production of D. carinata and S. exspinosus (biomass turnover model) represented a nutrient store equivalent to less than 6% of total PO4-P and total nitrogen retained in the ponds annually.

Interoceanic differences in vulnerability of shelled prey to crab predation

SHELLED gastropods living on intertidal open rocky surfaces exhibit various shell features which can be interpreted as adaptations against such shell-breaking predators as fishes, spiny lobsters, and crabs. These anti-predatory devices include strong external shell sculpture, elongate or dentate apertures and low spires1. Not only are these characteristics more common among tropical species compared with ecologically similar cold-water forms, but within the tropics they are more prevalent and better developed in the Pacific and Indian Oceans than in the Atlantic1,2. Any or all of three conditions must obtain in areas with a high incidence and strong development of anti-predatory armour compared with areas where such armour is reduced: the prey are stronger, that is, the criteria needed by the prey to avoid being crushed are more stringent; the predators are stronger; and shell-breaking predators account for relatively greater mortality. Here I report data confirming the first two of these possibilities.

PROTEIN POLYMORPHISM OF THE HYBRIDIZING SEASTARSASTERIAS FORBESIANDASTERIAS VULGARISAND IMPLICATIONS FOR THEIR EVOLUTION

The seastars Asterias forbesi and A. vulgaris share 67% of their genes in common (based on 27 loci). These species are normally easily characterized by 7 prominent phenotypic differences but naturally occurring hybrids are found in localities with typical adults of the two species.A. forebesi and A. vulgaris are thought to have evolved during the mid to late Pleistocene as a result of a restriction in the range of a more widely distributed Miocene or early Pleistocene form due to lowering of sea level and the coincident emergence of a disrupting land barrier (Cape Cod-Georges Bank). At least one local population of the ancestral species evolved into the present cold water form (A. vulgaris) during selection in an arctic-fed Gulf of Maine. Coincidently, at least one other local population of the ancestral species evolved with selection in warmer, southern waters into the present shallow water, temperate form (A. forbesi).If A. forbesi and A. vulgaris have been derived from a late Tertiary wide-ranging species which underwent geographic partitioning during the late Pleistocene, then both their present distribution and their lack of total reproductive isolation are understandable.

Vertical and horizontal distribution of biocoenoses in the upper zones of the Japan and Okhotsk seas and their dependence on the hydrological system

Abstract The composition of bottom biocoenoses, their distribution and biogeographical structure in the upper zones of Possjet Bay and Tartar Strait (Sea of Japan) and of Aniva and Terpenia Bays (Okhotsk Sea) were studied by means of a quantitative diving method. The vertical distribution of biocoenoses and their biogeographical composition were correlated with the position of the layers of different water masses and depended primarily on temperature conditions. In Possjet Bay at least 4 vertical zones, which coincided with the position of the layers of the surface water mass during various seasons, could be distinguished. In Asiatic waters and off the coast of Norway the horizontal distribution of organisms is different. In low-boreal Pacific waters the most thermophilous species live in lagoons and bays isolated from the open sea while in European waters the warm-water members of the fauna and flora live off the open coasts and are replaced by cold-water forms in fjords where there is greater isolation ...

Diatoms as indicators of Pleistocene climatic fluctuations in the Pacific sector of the Southern Ocean

Present diatom species distribution in both the water masses and the surface sediment of the Pacific sector of the Southern Ocean is temperature dependent, with different species complexes existing north and south of the Antarctic Polar Front (Convergence). Ten long cores have been examined and three different diatom assemblages found. Zone ω− ψ contains cold water forms and extends from the Recent through the upper part of the Pleistocene. Zone χ contains a warm water flora and is lower Pleistocene in age. Zone φ is characterized by warm water Tertiary (probably Pliocene) diatoms. This sequence of zones suggests a gradual cooling of the Pacific sector of the Southern Ocean during Pleistocene time.