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Mechanisms controlling the distribution of nutrients in the Laptev Sea (TRANSDRIFT XXIV + XXV)

The goal of this task is to determine the mechanisms controlling the supply, distribution and utilization of nutrients, their biogeochemical cycling in the Laptev Sea and their implications for changes in biological productivity related to the rapid warming of the Arctic region and the associated sea-ice loss. This will be achieved by combining for the first time an investigation of the dissolved stable-silicon(Si)-isotope compositions (used to trace the utilization of silicate by diatom growth) and barium(Ba)-isotope compositions (used to trace riverine inputs and the effects of particle interaction). These parameters will be complemented by dissolved silicate (Task B) and Ba concentrations, selected applications of established geochemical tracers of water-mass advection and mixing (neodymium (Nd) isotopes and rare earth elements (REEs)), and by stable oxygen isotope compositions of the water, which together with the salinity and alkalinity allow identifying freshwater sources including sea-ice-related processes and water-mass pathways.

The isotopic composition of dissolved Ba and Si together with Ba concentrations will be determined through state-of-the-art mass spectrometry on well-characterized samples obtained during the expeditions TRANSDRIFT XX (March-April 2012), TRANSDRIFT XXI (August-September 2013) and TRANSDRIFT XXII (September-October 2014) and compared to available Nd isotope, REE concentration, nutrient, stable-oxygen-isotope and CTD data derived from these samples. This dataset will be complemented by data from water samples to be obtained during two sea-going expeditions to the Laptev Sea in 2017 and 2018 (TRANSDRIFT XXIV and XXV). In addition to the dissolved Ba, Si and Nd isotope compositions, these parameters will also be determined on suspended particles and surface sediments in order to be able to characterize their complete biogeochemical cycles.

While Task A will carry out a systematic investigation of silicate cycling and biological utilization, as well as the impact of riverine inputs and water mass advection, Task B will provide essential information on changes in the cycling and the reservoirs of all nutrients on the Laptev Sea shelf and in their controlling factors. Task A will characterize the influence of changes in distinct freshwater sources such as rivers and sea ice on the biogeochemical cycling of silicate and assess and quantify the riverine inputs. This task will also address the question of how the seasonal and interannual variability of silicate distribution and utilization is linked to changes in biological productivity related to sea-ice loss.

The GEOMAR team will determine the isotopic composition of dissolved Ba, Si and Nd as well as Ba and REE concentrations and stable oxygen isotopes (see below for a detailed description of the research in Task 3A for which the CATS scientists apply for funding on the German side). The AARI team will contribute the determination of dissolved nutrients (Si, P, N), total alkalinity and pH, and their linkage to the hydrographic data. The team of Kiel University will provide information on the distribution of suspended material and will evaluate the findings with regard to the functioning of the marine ecosystems of this Arctic region.

 

Task coordinator
Georgi Laukert	GEOMAR Helmholtz Centre for Ocean Research Kiel

 

Key collaborators
Dorothea Bauch	GEOMAR Helmholtz Centre for Ocean Research Kiel
Martin Frank	GEOMAR Helmholtz Center for Ocean Research Kiel
Andrey Novikhin	Arctic and Antarctic Research Institute
Dieter Piepenburg	Christian Albrechts University Kiel
Vasily Povazhnyy	Arctic and Antarctic Research Institute