Nutrient and Silicon Isotope Dynamics in the Laptev Sea and Implications for Nutrient Availability in the Transpolar Drift

Realistic prediction of the near-future response of Arctic Ocean primary productivity to ongoing warming and sea ice loss requires a mechanistic understanding of the processes controlling nutrient bioavailability. To evaluate continental nutrient inputs, biological utilization and the influence of mixing and winter processes in the Laptev Sea, the major source region of the Transpolar Drift, we compare observed with preformed concentrations of dissolved inorganic nitrogen (DIN), phosphorus (DIP), silicic acid (DSi) and silicon isotope compositions of DSi (δ30SiDSi) obtained for two summers (2013, 2014) and one winter (2012). In summer, preformed nutrient concentrations persisted in the surface layer of the southeastern Laptev Sea, while diatom-dominated utilization caused intense northward drawdown and a pronounced shift in δ30SiDSi from +0.91 to +3.82 ‰. The modeled Si isotope fractionation suggests that DSi in the northern Laptev Sea originated from the Lena River during the spring freshet, while in the southeastern Laptev Sea it was continuously supplied by it during the summer. Primary productivity fueled by river-borne nutrients was enhanced by admixture of DIN- and DIP-rich Atlantic-sourced waters to the surface, either by convective mixing during the previous winter or by occasional storm-induced stratification breakdowns in late summer. Substantial enrichments of DSi (+240 %) and DIP (+90 %) beneath the Lena River plume were caused by sea ice-driven redistribution and remineralization. Predicted weaker stratification on the outer Laptev shelf will enhance DSi utilization and removal through greater vertical DIN supply, which will limit DSi export and reduce diatom-dominated primary productivity in the Transpolar Drift. Key Points - Surface DIN, DIP, DSi and Si isotope dynamics are controlled by marine and riverine inputs and uptake by phytoplankton - Strong DIP and DSi enrichments beneath the Lena River plume are due to sea ice-driven nutrient redistribution and remineralization - Enhanced DSi utilization in the Laptev Sea will lead to a reduced diatom-dominated primary productivity in the Transpolar Drif

Observational program tracks Arctic Ocean transition to a warmer state

Over the past several decades, the Arctic Ocean has undergone substantial change. Enhanced transport of warmer air from lower latitudes has led to increased Arctic surface air temperature. Concurrent reductions in Arctic ice extent and thickness have been documented. The first evidence of warming in the intermediate Atlantic Water (AW, water depth between 150 and 900 meters) of the Arctic Ocean was found in 1990. Another anomaly, found in 2004, suggests that the Arctic Ocean is in transition toward a new, warmer state [Polyakov et al., 2005, and references therein]

Dissolved iron in the Arctic shelf seas and surface waters of the Central Arctic Ocean: Impact of Arctic river water and ice-melt

Key Points - DFe in the Arctic shelves and surface is linked to freshwater and alkalinity - Fluvial input main contributor to high DFe, low alkalinity in Central Arctic - Remineralisation and biological depletion determine DFe in the Arctic Shelf Seas Abstract Concentrations of dissolved (10 nM) in the bottom waters of the Laptev Sea shelf may be attributed to either sediment resuspension, sinking of brine or regeneration of DFe in the lower layers. A significant correlation (R2 = 0.60) between salinity and DFe is observed. Using δ18O, salinity ,nutrients and total alkalinity data, the main source for the high (>2 nM) DFe concentrations in the Amundsen and Makarov Basins is identified as (Eurasian) river water, transported with the Transpolar Drift (TPD). On the North American side of the TPD, the DFe concentrations are low ( 4) above the shelf and low ( < 4) off the shelf)

Sea-ice dynamics in an Arctic coastal polynya during the past 6500 years

The production of high-salinity brines during sea-ice freezing in circum-arctic coastal polynyas is thought to be part of northern deep water formation as it supplies additional dense waters to the Atlantic meridional overturning circulation system. To better predict the effect of possible future summer ice-free conditions in the Arctic Ocean on global climate, it is important to improve our understanding of how climate change has affected sea-ice and brine formation, and thus finally dense water formation during the past. Here, we show temporal coherence between sea-ice conditions in a key Arctic polynya (Storfjorden, Svalbard) and patterns of deep water convection in the neighbouring Nordic Seas over the last 6500 years. A period of frequent sea-ice melting and freezing between 6.5 and 2.8 ka BP coincided with enhanced deep water renewal in the Nordic Seas. Near-permanent sea-ice cover and low brine rejection after 2.8 ka BP likely reduced the overflow of high-salinity shelf waters, concomitant with a gradual slow down of deep water convection in the Nordic Seas, which occurred along with a regional expansion in sea-ice and surface water freshening. The Storfjorden polynya sea-ice factory restarted at ~0.5 ka BP, coincident with renewed deep water penetration to the Arctic and climate amelioration over Svalbard. The identified synergy between Arctic polynya sea-ice conditions and deep water convection during the present interglacial is an indication of the potential consequences for ocean ventilation during states with permanent sea-ice cover or future Arctic ice-free conditions

Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)3 Project

Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)3 project has been established in 2016. It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, ship-borne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data

Development of a plate-based scintillation proximity assay for the mycobacterial AftB enzyme involved in cell wall arabinan biosynthesis

A number of mycobacterial arabinosyltransferases, such as the Emb proteins, AftA, AftB, AftC, and AftD have been characterized and implicated to be involved in the cell wall arabinan assembly. These arabinosyltransferases are essential for the viability of the organism and are logically valid targets for developing new anti-tuberculosis agents. For instance, Ethambutol, a first line anti-tuberculosis drug, targets the Emb proteins involved in the formation of the arabinan of cell wall arabinogalactan. Among these arabinosyltransferases, the terminal β-(1→2) arabinosyltransferase activity has been associated with AftB. The predicted topology of AftB in Mycobacterium tuberculosis has 10 N terminal transmembrane domains and a C terminal hydrophilic domain similar to the Emb proteins. It has a conserved GT-C motif and is difficult to express. In a cell free assay, synthetic disaccharide, α-d-Araf-(1→5)-α-d-Araf-octyl, has been used as a substrate to explore the function of AftB. In our work, the disaccharide was synthesized in its pentenylated and biotinylated form, and the enzymatic product formed was identified as the β-(1→2) arabinofuranose adduct. When synthetic tri- and tetra-saccharides were used as substrates, a mixture of products containing both β-(1→2) and α-(1→5) linkages were formed. Therefore, the biotinylated disaccharide was selected to develop a scintillation proximity assay