Fatty acid composition, element concentration and isotope ratios of sea ice algae sampled in Rijpfjorden, Svalbard

The accelerating decrease of Arctic sea ice substantially changes the growth conditions for primary producers, particularly with respect to light. This affects the biochemical composition of sea ice algae, which are an essential high-quality food source for herbivores early in the season. Their high nutritional value is related to their content of polyunsaturated fatty acids (PUFAs), which play an important role for successful maturation, egg production, hatching and nauplii development in grazers. We followed the fatty acid composition of an assemblage of sea ice algae in a high Arctic fjord during spring from the early bloom stage to post bloom. Light conditions proved to be decisive in determining the nutritional quality of sea ice algae, and irradiance was negatively correlated with the relative amount of PUFAs. Algal PUFA content decreased on average by 40 % from April to June, while algal biomass (measured as particulate carbon, C) did not differ. This decrease was even more pronounced when algae were exposed to higher irradiances due to reduced snow cover. The ratio of chlorophyll a (chl a) to C, as well as the level of photoprotective pigments, confirmed a physiological adaptation to higher light levels in algae of poorer nutritional quality. We conclude that high irradiances are detrimental to sea ice algal food quality, and that the biochemical composition of sea ice algae is strongly dependent on growth conditions.

Occurrence of metazoans, and gut pigments and fatty acid composition of Acartia bifilosa in ice and under-ice water samples from Santala Bay

A field study was conducted in Santala Bay with weekly samplings during February and March 2000. Ice thickness was 20-28 cm, snow cover 0-1 cm. The under-ice water column was stratified with a cold (-0.3 - 0.2°C) and less saline (S = 2.1-4.9) interface layer. Concentrations of particulate organic carbon (0.5-5.8 mg POC/l) and algal pigments (0.3-18.2 µg chlorophyll a/l) were higher in the ice than in the water (0.2-0.5 mg POC/l, 1.6-7.1 µg chlorophyll a/l) and peaked mostly in the bottom part of the ice. The thin ice and almost lacking snow cover had favoured an early ice-algal and phytoplankton bloom. The diversity of metazoans was low, with six species in the ice and eight species in the under-ice water. The rotifer Synchaeta cf. littoralis dominated both in ice and water, with maximum abundances of 230 individuals/l in the bottom part of the ice. Rotifer eggs were also observed in the ice. Baltic sea ice seems to be a suitable habitat for rotifers. Nauplii and copepodids of the calanoid Acartia longiremis in the under-ice water showed some herbivorous feeding (<0.1-0.23 ng gut pigment/individual), but analysis of fatty acids, fatty alcohols and biomarker ratios indicated a more omnivorous/carnivorous diet. Despite low temperatures, this copepod showed growth and development below the ice, doubling in numbers (mainly CI, CII) from 118 to 230 individuals m during the third week of March.

Geochemical analysis of sediments and interstitial water in sediment cores from the North-West African continental margin and from the Central Pacific

A. Continental slope sediments off Spanish-Sahara and Senegal contain up to 4% organic carbon and up to 0.4% total nitrogen. The highest concentrations were found in sediments from water depths between 1000 and 2000 m. The regional and vertical distribution of organic matter differs significantly. Off Spanish-Sahara the organic matter content of sediment deposited during glacial times (Wuerm, Late Riss) is high whereas sediments deposited during interglacial times (Recent, Eem) are low in organic matter. Opposite distribution was found in sediments off Senegal. The sediments contain 30 to 130 ppm of fixed nitrogen. In most sediments this corresponds to 2-8 % of the total nitrogen. Only in sediments deposited during interglacial times off Spanish-Sahara up to 20 % of the total nitrogen is contained as inorganically bound nitrogen. Positive correlations of the fixed nitrogen concentrations to the amounts of clay, alumina, and potassium suggest that it is primarily fixed to illites. The amino acid nitrogen and hexosamine nitrogen account for 17 to 26 % and 1.3 to 2.4 %, respectively of the total nitrogen content of the sediments. The concentrations vary between 200 and 850 ppm amino acid nitrogen and 20 to 70 ppm hexosamine nitrogen, both parallel the fluctiations of organic matter in the sediment. Fulvic acids, humic acids, and the total organic matter of the sediments may be clearly differentiated from one another and their amino acid and hexosamine contents and their amino acid composition: a) Fulvic acids contain only half as much amino acids as humic acids b) The molar amino acid/hexosamine ratios of the fulvic acids are half those of the humic acids and the total organic matter of the sediment c) The amino acid spectra of fulvic acids are characterized by an enrichment of aspartic acid, alanine, and methionine sulfoxide and a depletion of glycine, valine, isoleucine, leucine, tyrosine, phenylalanine, lysine, and arginine compared to the spectra of the humic acids and those of the total organic matter fraction of the sediment. d) The amino acid spectra of the humic acids and those of the total organic matter fraction of the sediments are about the same with the exception that arginine is clearly enriched in the total organic matter. In general, as indicated by the amino compounds humic acids resemble closer the total organic matter composition than the low molecular fulvic acids do. This supports the general idea that during the course of diagenesis in reducing sediments organic matter stabilizes from a fulvic-like structure to humic-like structure and finally to kerogen. The decomposition rates of single aminio acids differ significantly from one another. Generally amino acids which are preferentially contained in humic acids and the total organic matter fraction show a smaller loss with time than those preferably well documented in case of the basic amino acids lysine and arginine which- although thermally unstable- are the most stable amino acids in the sediments. A favoured incorporation of these compounds into high molecular substances as well as into clay minerals may explain their relatively high "stability" in the sediment. The nitrogen loss from the sediments due to the activity of sulphate-reducing bacteria amounts to 20-40 % of the total organic nitrogen now present. At least 40 % of the organic nitrogen which is liberated by sulphate-reducing bacteria can be explained ny decomposition of amino acids alone. B. Deep-sea sediments from the Central Pacific The deep-seas sediments contain 1 to 2 orders of magnitude less organic matter than the continental slope sediments off NW Africa, i.e. 0.04 to 0.3 % organic carbon. The fixed nitrogen content of the deep-sea sediments ranges from 60 to 270 ppm or from 20 to 45 % of the total nitrogen content. While ammonia is the prevailing inorganic nitrogen compound in anoxic pore waters, nitrate predominates in the oxic environment of the deep-sea sediments. Near the sediment/water interface interstital nitrate concentrations of around 30 µg-at. N/l were recorded. These generally increase with sediment depth by 10 to 15 µg-at. NO3- N/l. This suggests the presence of free oxygen and the activity of nitrifying bacteria in the interstitial waters. The ammonia content of the interstitial water of the oxic deep-sea sediments ranges from 2 to 60 µg-at. N/l and thus is several orders of magnitude less than in anoxic sediments. In contrast to recorded nitrate gradients towards the sediments/water interface, there are no ammonia concentration gradients. However, ammonia concentrations appear to be characteristic for certain regional areas. It is suggested that this regional differentiation is caused by ion exchange reactions involving potassium and ammonium ions rather than by different decomposition rates of organic matter. C. C/N ratios All estimated C/N ratios of surface sediments vary between 3 and 9 in the deep-sea and the continental margin, respectively. Whereas the C/N ratios generally increase with depth in the sediment cores off NW Africa they decrease in the deep-sea cores. The lowest values of around 1.3 were found in the deeper sections of the deep-sea cores, the highest of around 10 in the sediments off NW Africa. The wide range of the C/N ratios as well as their opposite behaviour with increasing sediment depth in both the deep-sea and continental margin sediment cores, can be attributed mainly to the combination of the following three factors: 1. Inorganic and organic substances bound within the latticed of clay minerals tend to decrease the C/N ratios. 2. Organic matter not protected by absorption on the clay minerals tends to increase C/N ratios 3. Diagenetic alteration of organic matter by micro-organisms tends to increase C/N ratios through preferential loss of nitrogen The diagenetic changes of the microbially decomposable organic matter results in both oxic and anoxic environments in a preferential loss of nitrogen and hence in higher C/N ratios of the organic fraction. This holds true for most of the continental margin sediments off NW Africa which contain relatively high amounts of organic matter so that factors 2 and 3 predominate there. The relative low C/N ratios of the sediments deposited during interglacial times off Spanish-Sahara, which are low in organic carbon, show the increasing influence of factor 1 - the nitrogen-rich organic substances bound to clay minerals. In the deep-sea sediments from the Central Pacific this factor completely predominates so that the C/N rations of the sediments approach that of the substance absorbed to clay minerals with decreasing organic matter content. In the deeper core sections the unprotected organic matter has been completely destroyed so that the C/N ratios of the total sediments eventually fall into the same range as those of the pure clay mineral fraction.

Amino acid concentrations in interstitial waters from ODP Sites 113-689 and 113-690

Biogenic calcareous and siliceous sediments were drilled at ODP Sites 689 and 690 on the Maud Rise, Antarctic Ocean. We analyzed dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA) in interstitial waters in order to characterize the amino acids in dissolved organic matter. The DFAA was predominant over the DCAA in interstitial waters at Sites 689 and 690, which contradicted the previous results from interstitial water and seawater studies. The DCAA in the interstitial waters probably originated from calcareous biogenic debris with less amounts of siliceous debris. Although glutamic acid constituted 41% of the total concentration of DCAA, it accounted for only 1% of the total concentration of DFAA due to the adsorption and/or reaction with biogenic carbonate. Ornithine, a nonprotein amino acid, is a decomposed product of arginine and made up 17 mol% of the total DFAA and. The total hydrolyzable amino acids (=DCAA + DFAA) accounted for 5 to 28% of the dissolved organic carbon (DOC) concentration, which implied that high molecular weight organic matter was a major contributor for the DOM (dissolved organic matter) in interstitial waters. Fairly positive correlation between the dissolved manganese and the total DCAA values suggested that the redox condition plays a significant role in controlling the total DCAA content. A small decrease in the sulfate concentration in the interstitial waters from both sites suggested fairly low microbial activity by sulfate-reducing bacteria.

Photosynthetically active radiation during the experiment, and lipid content of sub- and intertidal specimens of the endemic Antarctic red alga, Palmaria decipiens

In coastal waters, Antarctic rhodophytes are exposed to harsh environmental conditions throughout the year, like low water temperatures ranging from -1.8°C to 2°C and high light during the summer season. Photosynthetic performance under these conditions may be affected by slowed down enzymatic reactions and the increased generation of reactive oxygen species. The consequence might be a chronic photoinhibition of photosynthetic primary reactions related to increased fragmentation of the D1 reaction centre protein in photosystem II. It is hypothesized that changes in lipid composition of biomembranes may represent an adaptive trait to maintain D1 turnover in response to temperature variation. The interactive effects of high light and low temperature were studied on an endemic Antarctic red alga, Palmaria decipiens, sampled from two shore levels, intertidal and subtidal, and exposed to mesocosm experiments using two levels of natural solar radiation and two different temperature regimes (2-5°C and 5-10°C). During the experimental period of 23 days, maximum quantum yield of photosynthesis decreased in all treatments, with the intertidal specimens exposed at 5-10°C being most affected. On the pigment level, a decreasing ratio of phycobiliproteins to chlorophyll a was found in all treatments. A pronounced decrease in D1 protein concentration occurred in subtidal specimens exposed at 2-5°C. Marked changes in lipid composition, i.e. the ratio of saturated to unsaturated fatty acids, indicated an effective response of specimens to temperature change. Results provide new insights into mechanisms of stress adaptation in this key species of shallow Antarctic benthic communities.

Impact of elevated pCO2 on paralytic shellfish poisoning toxin content and composition in Alexandrium tamarense

Ocean acidification is considered a major threat to marine ecosystems and may particularly affect primary producers. Here we investigated the impact of elevated pCO2 on paralytic shellfish poisoning toxin (PST) content and composition in two strains of Alexandrium tamarense, Alex5 and Alex2. Experiments were carried out as dilute batch to keep carbonate chemistry unaltered over time. We observed only minor changes with respect to growth and elemental composition in response to elevated pCO2. For both strains, the cellular PST content, and in particular the associated cellular toxicity, was lower in the high CO2 treatments. In addition, Alex5 showed a shift in its PST composition from a nonsulfated analogue towards less toxic sulfated analogues with increasing pCO2. Transcriptomic analyses suggest that the ability of A. tamarense to maintain cellular homeostasis is predominantly regulated on the post-translational level rather than on the transcriptomic level. Furthermore, genes associated to secondary metabolite and amino acid metabolism in Alex5 were down-regulated in the high CO2 treatment, which may explain the lower PST content. Elevated pCO2 also induced up-regulation of a putative sulfotransferase sxtN homologue and a substantial down-regulation of several sulfatases. Such changes in sulfur metabolism may explain the shift in PST composition towards more sulfated analogues. All in all, our results indicate that elevated pCO2 will have minor consequences for growth and elemental composition, but may potentially reduce the cellular toxicity of A. tamarense.