Description: Interactions between dissolved trace elements and organic ligands in seawater play an important role in ocean biogeochemistry, ranging from regulating primary production in surface waters to element cycling on basin-wide scale, with strong feedbacks to climate variability. In this study, we review different aspects in the field of marine trace elements and their organic ligands: recent instrumental innovation, factors that affect the fate of trace element complexes at the molecular level, spatial distribution of organic matter – trace element complexes in the ocean, modeling approaches as well as prospect in the scenarios of climate variability. We also assess the critical issues of parameterization in the numerical simulation that incorporate the trace elements – organic ligands interactions. Given the predicted climate changes, we examine the potential of exchange between inorganic and organic complexes for trace elements in different oceanic provinces.

Description: Phytoplankton distribution and concentrations of macronutrients and iron were studied in the Polar Frontal Zone (PFZ) and the eastern Weddell Gyre of the Southern Ocean, during austral autumn. HPLC analysis of algal pigments was combined with microscopy observations to assess algal distribution. Patterns of algal distribution were dictated by the frontal systems. Travelling from north to south, four distinctively different algal communities were observed, the composition of which could be explained by variations in nutrients, light climate and grazing pressure. North of the PFZ, low silicate levels (〈3 μM) were limiting diatom growth, and the algal community was dominated by prasinophytes. Silicate concentrations increased over the PFZ, which coincided with the dominance of diatoms. South of the PFZ, the open waters of the Weddell Gyre are characterised as a high nutrient low-chlorophyll area. Low iron concentrations (〈0.4 nM on average) supported an algal community that was dominated by smaller size algae (〈20 μm). Deep wind-mixed layers (〉100 m depth) together with low incident irradiance in autumn were likely limiting algal growth. At the Marginal Ice Zone (MIZ), the phytoplankton community consisted mainly of low numbers of flagellates (Chlorophyceae and haptophytes) and high numbers of microzooplankton, indicating phytoplankton control by grazing. The phytoplankton distribution patterns presented here and the relation with potential growth-controlling factors provides more insight in the mechanisms that control carbon fluxes from the atmosphere into the ocean interior.

Description: We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14 °C for 14 days after which ice decay was induced by increasing the air temperature to −1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.

Description: Sea-surface microlayers and the corresponding underlying waters of the karstic Krka Estuary (Croatia) were studied with respect to optical and molecular properties of dissolved organic matter (DOM). Solid-phase extracted DOMwas separated by reversed-phase chromatography and analyzedwith ultra-high resolution Fourier transformion cyclotron resonance mass spectrometry (FT-ICRMS). The number and summedmagnitudes of FT-ICR MS peaks, enriched in themicrolayer, increased with increasing salinity along the estuary. The molecular hydrogen to carbon ratio (as ameasure of polarity) of enriched compounds was higher for the low salinity samples than for a high salinity marine station, which we propose is a consequence of a salt-mediated separation mechanism. Absorption and fluorescence of all samples decreased along the estuarywith themicrolayer samples showing higher absorption than the underlying water. Chromatographic and FT-ICR MS data revealed a distinct shift towards a smaller molecular size in the microlayer compared to the underlyingwater. The redistribution of dissolved organic carbonwithin chromatographic fractions and the decrease inmolecular sizewas interpreted to result from photo-degradation and/or microbial reprocessing. Collision induced dissociation of selected FT-ICR MS mass peaks revealed the presence of sulfur containing anthropogenic surfactants enriched in themicrolayer. Molecular level investigation of estuarine surfacemicrolayers will help to better understand the highly dynamic character of these systems, the accumulation of natural organicmatter and anthropogenic pollutants and the role of surface microlayers for the sea-air energy exchange.

Description: Two of the dominant Southern Ocean copepods, Calanus simillimus and Calanus propinquus, are known for their lipid storage via triacylglycerols indicating year-round activity, as opposed to diapausing species, which accumulate wax esters. We studied the lipid and fatty acid compositions of C. simillimus (CV stages) with focus on its ability to produce unusually long-chain monounsaturated fatty acids. Besides the biosynthesis of high-energy fatty acids with 20 and 22 carbon atoms, the occurrence of fatty acids with 24 carbon atoms accounting for up to 15% of total fatty acids is intriguing. Their double bond positions were unequivocally determined as (n-9), (n-11) and (n-13) by DMOX derivatisation. The dominant isomer was 24:1(n-11) contributing up to 8% to the total fatty acids. The major fatty acids were the isomers 22:1(n-11) and (n-9) averaging 20% and 10%, respectively. A re-evaluation of fatty acid data of C. propinquus also revealed 24:1 fatty acids exhibiting on average 5% with (n-11) and (n-9) as main isomers. The principal fatty acids were also 22:1(n-11) and (n-9), but in contrast to C. simillimus both fatty acids occurred in equally high amounts of about 20%. The de novo biosynthesis of these long-chain monounsaturated fatty acids generally represents a very efficient energy storage mode. Chain elongation to 22 and even to 24 carbon atoms in C. propinquus and further optimized by C. simillimus yields high-energy compounds for these triacylglycerol-storing copepods. Biosynthetic pathways for the fatty acids are proposed and discussed in view of the well-adapted life cycle strategies of the two species, which have to cope with a pronounced seasonal food supply in the Southern Ocean.

Description: Summer sea ice cover in the Arctic Ocean has undergone a reduction in the last decade exposing the sea surface to unforeseen environmental changes. Melting sea ice increases water stratification and induces nutrient limitation, which is also known to play a crucial role in methane formation in oxygenated surface water. We report on an excess of methane in the marginal ice zone in the western Fram Strait. Our study is based on measurements of oxygen, methane, DMSP, nitrate and phosphate concentrations as well as on phytoplankton composition and light transmission, conducted along the 79°N oceanographic transect from Svalbard to the Northwest Water Polynya region off Greenland. Between the eastern Fram Strait, where Atlantic water enters from the south and the western Fram Strait, where Polar water enters from the north, different nutrient limitations occurred and consequently different bloom conditions were established. Ongoing sea ice melting enhances the environmental differences and initiates regenerated production in the western Fram Strait. In a unique biogeochemical feedback process, methane production occurs despite an oxygen excess. We postulate that DMSP (dimethylsulfoniopropionate) released from sea ice may serve as a precursor for methane formation. Thus, feedback effects on cycling pathways of methane are likely and could constitute an additional component in biogeochemical cycling in a seasonal ice-free Arctic Ocean. The metabolic activity (respiration) of unicellular organisms explains the presence of anaerobic conditions in the cellular environment. Therefore we present a theoretical model which explains the maintenance of anaerobic conditions for methane formation inside bacterial cells, despite enhanced oxygen concentrations in the environment.