Arctic Diatom Research Articles

Taxonomic composition, paleoecology and biostratigraphy of Late Cretaceous diatoms from Devon Island, Nunavut, Canadian High Arctic

Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm.

Numerical analysis of small Arctic diatoms (Bacillariophyceae) representing the Staurosira and Staurosirella species complexes

T.M. Paull, P.B. Hamilton, K. Gajewski and M. LeBlanc. 2008. Numerical analysis of small Arctic diatoms (Bacillariophyceae) representing the Staurosira and Staurosirella species complexes. Phycologia 47: 213–224. DOI:10.2216/07-17.1Small benthic fragilarioid diatoms (Bacillariophyceae) are dominant taxa in circumpolar Arctic lakes and ponds. These small forms are difficult to identify under light microscope (LM) because of valve size, the limited number of visible characters, and considerable morphological variability within populations. For this reason, ultrastructural characters visible only under a scanning electron microscope (SEM) such as areolae and spine structure are usually recommended for species- and even genus-level identification. This is, however, often impractical. In this study we show that selected characters of Staurosirella pinnata (Ehrenberg) Williams & Round and Staurosira venter (Ehrenberg) Cleve & Möller measurable under LM correlate with diagnostic characters that can only be evaluated under SEM. We measured 32 morphological characters from SEM observations of 510 valves representing Staurosirella pinnata sensu Hustedt, Staurosira venter sensu Hustedt, and two morphologically distinct forms of S. venter sensu lato from lakes in Canada, Fennoscandia, and Siberia. Specimens from the circumpolar Arctic region identified as Staurosirella pinnata can be distinguished from Staurosira venter sensu lato using valve width and areola length (at margin), both visible under LM. Specimens with areolae lengths (at margin) larger than 0.4 µm are Staurosirella pinnata. For specimens with areolae lengths (at margin) smaller than 0.4 µm, those with valves wider than 2.9 µm are Staurosira venter sensu lato, whereas those with valves smaller than 2.9 µm are Staurosirella pinnata. Application of these numerical criteria allows for correct identification of 94% of specimens to either Staurosira venter (including morphotypes) or Staurosirella pinnata.

Ultraviolet radiation negatively affects growth but not food quality of arctic diatoms

We studied the short‐term effects of ultraviolet radiation (UV radiation, 280–400 nm) on the fatty acid composition and cellular stoichiometry of three dominant arctic diatom species (Thalassiosira antarctica var. borealis, Chaetoceros socialis, Bacterosira bathyomphala) in laboratory experiments. Photosynthetic efficiency during UV irradiation was inhibited 90%, which led to a substantial reduction in biomass. In contrast to results of previous studies, the percentage of total polyunsaturated fatty acids (PUFAs) did not decrease during UV exposure. Instead, the two major PUFAs, 16:4(n‐1) and 20:5(n‐3), of B. bathyomphala increased, and the PUFA content of T. antarctica and C. socialis did not change significantly. However, the monounsaturated fatty acid 16:1(n‐7) content in all three species substantially decreased during UV radiation. Since high concentrations of 16:1(n‐7) are usually associated with exponential growth under favorable conditions, UV radiation probably did not affect a specific type of fatty acid directly; the fatty acid profile rather reflected a general deterioration in the algal physiological state. The nutritional quality of the fatty acids did not decrease during UV exposure; the C: P and N: P ratios decreased by 50% in all species, whereas the C:N ratios increased slightly in two species. Our results indicate that UV radiation has strong negative effects on photosynthesis and biomass production, but not on food quality with regard to PUFAs and stoichiometry.

Effects of changes in ambient PAR and UV radiation on the nutritional quality of an Arctic diatom ( Thalassiosira antarctica var. borealis)

Polyunsaturated fatty acids (PUFAs) are essential macromolecules that are synthesized by phytoplankton during spring bloom, and they play a key role in the Arctic food web. They are, however, considered to be sensitive to oxidation by UV radiation (280–400 nm). Changes in the food quality of primary producers may affect the transport of biomass and energy in the whole ecosystem. Using a common Arctic diatom, we looked at the effect of ambient and increased UV radiation on its nutritional quality, specifically, the fatty acid composition and elemental ratios. In May 2004, in the archipelago of Svalbard (79° N), a unialgal culture of Thalassiosira antarctica var . borealis was subjected to a 17-day experiment in outdoor aquaria. The diatoms were kept in semi-continuous culture (40 1) and exposed to three treatments with different levels of UV radiation: none (UV-shielded), ambient, and enhanced. Fatty acid composition, C:N:P ratios, photosynthetic pigment composition, optimum quantum yield of PSII, and cell numbers were analysed over the experimental period. An initial increase in PAR (photosynthetically active radiation, 400–700 nm) intensities profoundly affected the fatty acid composition and substantially inhibited the synthesis of PUFAs, but the relative amounts of PUFAs were not reduced by UV radiation. Enhanced UV radiation did, however, cause a significant reduction in optimum quantum yield of PSII and affected some fatty acids, mainly 18:0 and 16:1 n-7, during the first week of the experiment. Both ambient and enhanced UV radiation caused significantly lower C:P and N:P ratios. At the same time, these treatments elicited a higher relative content of the photoprotective pigments diadinoxanthin and diatoxanthin. After acclimation to the new light levels these effects faded off. Thus, brief periods with high light exposure may cause significant changes in photosynthetic activity and food quality, but the capacity for photo-acclimation seems high. The impact of UV radiation seems to be less important for food quality than that of PAR during a sudden rise in total light intensity.

PERIPHYTIC DIATOM ASSEMBLAGES FROM BATHURST ISLAND, NUNAVUT, CANADIAN HIGH ARCTIC: AN EXAMINATION OF COMMUNITY RELATIONSHIPS AND HABITAT PREFERENCES

Diatoms are potentially the most important biomonitors of environmental change in high arctic lakes and ponds, but to date few autecological data are available. Because of the shallow nature of many of these water bodies, a large proportion of taxa are periphytic and planktonic diatoms are absent for the most part. By determining the microhabitat and substrate preferences of these benthic diatom taxa, the potential exists to infer past changes in available habitats from fossil diatom assemblages collected from sediment cores and ultimately to reconstruct past environmental and climatic changes responsible for these shifts in habitat availability. To refine our understanding of high arctic diatom habitat preference, the common diatom taxa found on submerged moss (bryophyte), sediment, and rock substrates from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic were examined. The relationships among key limnological variables and the common taxa from each habitat were examined. Many diatom taxa exhibited varying degrees of microhabitat preference, with moss representing the more unique habitat. In addition, the following limnological variables significantly (P≤ 0.05) explained the species variance for each of the three substrates: Na+ and total nitrogen for moss; total phosphorus (filtered) and pH for rock; and Fe3+, total phosphorus (unfiltered), total nitrogen, temperature, and pH for sediment. These data can be used to help interpret monitoring and paleolimnological studies in this environmentally sensitive region.

FRESHWATER DIATOM ASSEMBLAGES FROM 23 LAKES LOCATED NEAR NORILSK, SIBERIA: A COMPARISON WITH ASSEMBLAGES FROM OTHER CIRCUMPOLAR TREELINE REGIONS

Knowledge of the composition and ecological preferences of diatom assemblages in northern regions is important for paleoenvironmental reconstructions of variables related to climate and/or anthropogenic disturbances. Relatively little is presently known about diatoms from circumpolar treeline areas, especially for lakes located in northern Russia. Our study set included lakes in the Siberian tundra, forest-tundra, and boreal forest regions close to Norilsk, of which nine sites were subject to anthropogenic disturbances, such as mining and housing developments. We enumerated surficial sediment diatom assemblages and used multivariate statistical techniques to investigate which environmental variables were important in explaining the variation in diatom assemblages within our lake set. Deeper lakes were associated with higher abundances of planktonic centric taxa, such as Cyclotella Kützing species. Warmer, higher conductivity forested lakes were associated with higher abundances of planktonic pennate taxa, such as Fragilaria nanana Lange-Bertalot. Diatom assemblages in the colder tundra lakes were significantly different from those in forested regions, and were dominated by small benthic Fragilaria Lyngbye species. Disturbed lakes near the Norilsk smelters exhibited slightly higher metal (Cu) concentrations and conductivities, and were associated with pollution-tolerant Nitzschia Hassall taxa, as well as species associated with higher electrolyte concentrations, such as Navicula capitata Ehrenberg. However, in comparison with diatom assemblages from other regions of intense mining (e.g. Sudbury, Canada), the assemblages appear relatively unaffected by mining activities, most likely reflecting the suppression of aqueous metal concentrations due to the alkaline nature of these lakes. Overall, diatom assemblages were very similar to those found in northern Canadian and Fennoscandian lakes, suggesting mat the Siberian taxa are representative of a circumpolar arctic diatom flora.

Diatom flux and species composition in the Greenland Sea and the Norwegian Sea in 1991–1992

Vertical diatom fluxes were investigated in sediment trap material from June 1991 to July 1992 from the Greenland Sea at 72 °N, 007 °W and the Norwegian Sea at 70 °N, 000 °E in order to determine seasonal species compositions and alterations that affect settling assemblages. Different hydrographical conditions, including seasonal ice coverage, are reflected in seasonal variations of total diatom flux and species composition. The purpose of this study is to achieve a better understanding of pelagic and sedimentary processes. The quantification of the annual diatom fluxes with respect to accumulation rates of underlying sediments is a suitable approach in reconstructing palaeoceanographic changes and their effects on the productivity of the oceans. The influx of laterally advected material and the alteration of sedimenting assemblages due to silica dissolution are also considered in this approach. A strong pulse-like sedimentation pattern was observed in the Greenland Sea. Highest values of up to 7.7 × 10 6 valves m −2 d −1 were recorded during the summer (second half of July 1991). Allochthonous diatoms, such as benthic and subtropical-boreal, as well as enriched autochthonous species found in the deep water trap indicate the sporadic occurrence of lateral advection and resuspension processes in the Greenland Sea. In the Norwegian Sea, low diatom flux was observed and three distinct sedimentation events could be differentiated at 500 m water depth. At this site, Zooplankton grazing pressure during spring is known to have more influence on the phytoplankton stock than in the Greenland Sea, which causes a delay in diatom accumulation. This is evident from maximum values of 0.3 × 10 6 valves m −2 d −1 during November/December 1991. Significant enrichment of Arctic diatom species suggests a transport from the Greenland Sea into the Norwegian Sea via deep currents. The assemblages of diatom species that are preserved in underlying surface sediments reflect the local oceanographic conditions and are quite similar to the assemblages found in deep water traps from both regions. However, they do not necessarily reflect the composition of the main sedimentation event, but rather the typical post-bloom species composition with stronger silicified diatoms. Despite the absence of weakly silicified species due to silica dissolution, diatom assemblages were useful in reconstructing modern and ancient oceanographic conditions.

Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea

Large phytoplankton biomass accumulates during ice‐edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophyte Phaeocystis pouchetii usually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance by P. pouchetii as opposed to periods when diatoms dominated. This alternation of P. pouchetii and diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. Although P. pouchetii contributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice‐edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north‐south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom‐ and P. pouchetii‐rich phytoplankton was observed in these stations. In contrast, the station located in ice‐free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom‐ and P. pouchetii‐dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice‐edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOC, than previously thought.

Light-dependence of carbon and sulfur production by polar clones of the genus Phaeocystis

Blooms of the marine prymnesiophyte genus Phaeocystis link the oceanic and atmospheric compartments of the carbon and sulfur cycles. Modeling the fluxes of dimethylsulfide from the ocean to the atmosphere has been limited due to a lack of information on functional responses to environmental variables. In this study, the light-dependence of extracellular carbon production and dimethyl sulfide (DMS) production by non-axenic polar clones of Phaeocystis spp. was examined at different growth stages. Comparative experiments were run with non-axenic arctic clones of the diatoms Thalassiossira nordenskioeldii and Skeletonema costatum. A large portion of carbon incorporated by the colonial stage of Phaeocystis spp. is released extracellularly, in particular in stationary colonies. This extracellular production can be modeled as a function of irradiance, as for carbon incorporation. In Phaeocystis spp., cellular and extracellular carbon incorporation represent different uptake rates, indicating the formation of two distinct carbon pools. The release of extracellular carbon by polar Phaeocystis spp. was not a constant fraction of total production over the irradiance range used. We observed little extracellular carbon production by cells at high irradiance, and maximal rates were observed at intermediate irradiance. Newly incorporated carbon that accumulates in the mucilage of the colonial stage of antarctic Phaeocystis sp. during photosynthesis was not reutilized for cellular growth during the dark period, as observed for temperate clones. In contrast, only a minor fraction of the radiocarbon incorporated by the diatoms was released extracellularly for all growth stages. The production of DMS was an order of magnitude higher for Phaeocystis spp. than for diatoms. The chlorophyll-specific production of DMS and DMSP (dimethylsulphoniopropionate, the precursor to DMS) by Phaeocystis spp. showed a hyperbolic response to irradiance, while arctic diatoms (weak or non-producers of DMS), on the other hand, did not show any light-dependency of DMS production. An inverse relationship between DMS and DMSP production in stationary clones of arctic P. pouchetii was observed, but not for the exponentially growing antarctic clone. Stationary colonies also had higher DMS and dissolved DMSP production rates than exponentially growing ones. These relationships can be extrapolated to the field in areas where Phaeocystis spp. dominates.

Thraustochytrid protists in Antarctic fast ice?

Sea ice provides a habitat for a conspicuous and productive assemblage of autotrophic microalgae and for heterotrophs ranging from bacteria to vertebrates (Horner 1990, Garrison 1991). With the exception of a reference to chytridiaceous fungi that were found infecting Arctic ice diatoms (Horner 1977) and a note in a cruise report (Schnack-Schiel 1987, p. 153), it appears that fungi and similar organisms have until now not been mentioned as members of the heterotrophic sea ice community. In the present short note we report on the abundant occurrence of apparently thraustochytrid fungus-like protists associated with mucilage tubes of pennate diatoms, encountered in the lower section of a fast ice core drilled close to the southern shelf ice margin of the Weddell Sea.

Growth rates of ten diatom species from the Barents Sea at different irradiances and day lengths

Nutrient-sufficient cultures of 10 arctic diatom species were grown at a combination of 9 irradiances and 4 day lengths at 0 . 5 'C. The growth rate was calculated on the basis of in vivo fluorescence measurements. Maximum recorded growth rates ranged from 0.41 d-' (Amphiprora sp.) to 0.60 d-' (Thalassiosira antarctica and T. bulbosa). Growth rates generally increased with irradiance up to 50 or 70 pm01 rn-2s-', above which they depended mainly on day length. The day length response of light-saturated cultures was satisfactorily described by a rectangular hyperbola.

Distribution of carbon among photosynthetic end products in the bloom-forming arctic diatom Thalassiosira antarctica COMBER

Investigations of the bloom-forming arctic diatom Thalassiosira antarctica COMBER show that at all temperature and light conditions tested, the 14C-incorporation rates in lipids averaged 20% and in carbohydrates 12%. The percentage of 14C in proteins and small metabolites ranged from 30% to 50% respectively, with contrary trends. The production rate of protein per generation time was not temperature and light dependent. The changes in percent carbon incorporated into proteins may be due to enhanced metabolite synthesis at high irradiances and/or temperatures above 0° C.

Photoadaptation in marine Arctic diatoms

Photoadaptation in some marine Arctic diatoms has been studied. Thalassiosira antarctica, Nitzschia delicatissima and Chaetoceros furcellatus were grown at-0.5°C and various irradiances and continuous light. Growth and cellular chlorophyll were followed during transitional phase after the algae had been transferred from one irradiance to another. Adaptation time for cellular chlorophyll was linearly related to the gradient in irradiance, and adaptation to transfer from high to low light was faster than from low to high light. Adaptation time was found to be species dependent, and Arctic diatoms growing at low temperature seemed to adapt as fast as temperate species.

Paleoclimate proxy data from freshwater arctic diatoms

(1988). Paleoclimate proxy data from freshwater arctic diatoms. SIL Proceedings, 1922-2010: Vol. 23, No. 2, pp. 837-844.

Arctic Medusæ

WE have received copies of parts of the Report of the Canadian Arctic Expedition, 1913–18; the Medusæ and Ctenophora are dealt with by Dr. H. B. Bigelow, the Polychæta by Dr. R. V. Chamberlin, and, in the portion devoted to the Crustacea, the Cumacea bv Dr.W. T. Caiman, the Isppoda by Mr. P. L. Boone, the Amphipoda by Mr. C. R. Shoemaker, and the parasitic Copepoda by Dr. C. B. Wilson. The collection of Medusæ, which is only the second which has been made on the Arctic coast of America, comprises species well known either from some part of the North Atlantic or from its Arctic tributaries. One species only is new. Dr. Bigelow refers to the importance, especially to ths oceanographer, of establishing definitely which of the Arctic Medusæ are certainly produced in those seas; for such floating buoys are sometimes of great assistance in indicating the origin, northern or southern, of the constituent waters of ocean currents. The Medusæ have the advantage, as compared with Arctic diatoms, of larger size and easy identification. Dr. Bigelow points out that there is at least one Anthomedusa, Sarsia princeps, which has now been recorded from so many parts of the Arctic and from currents flowing from it (e.g. the Labrador current), but from nowhere else, that it can safely be taken as an indicator of Arctic water. The report on the Isopoda has been extended to include other material from the Arctic, and forms a summary of our present knowledge of the Isopoda of that region. The Amphipoda reported are, for the most part, well-known Arctic species, but one—a species of Synurella—is new, and this genus is recorded for the first time in American waters. Katius obesus, known previously only from the Atlantic, is now reported for the first time from the Pacific. Appended to the report on parasitic Copepoda is a useful list of the species which have been recorded from the Arctic up to the present.