EXPERIMENTS (WP2)

WP2 EXPERIMENTAL AND LAB WORK AND DATA PROCESSING (NIVA lead, NTNU, MSUG)

Objectives: i) Conduct shipboard experiments to address Hg methylation/demethylation rates and the potential impacts of pH on particulate Fe (Pfe) solubility in natural plankton communities from the polar ecosystems in the Siberian Shelf Break region; ii) Process the data received in the cruise and experiments available to scientific community.

Description: The experimental work conducted will have a two-fold approach: (i) study the response of phytoplankton and bacterial to manipulations and (ii) study how these processes will affect the biogeochemical behavior of Pfe in Arctic waters.

T2.1 On-board experiments (NTNU/2). We will perform a microcosm incubation using natural plankton communities collected at the depth of the Chlorophyll-a (Chl-a) peak. pH will be manipulated by one-time addition of hydrochloric acid (HCL 32% trace select ultra) and sodium bicarbonate (NaHCO3) using projected conditions under the RCP8.5 scenario to set low treatment levels. Hg methylation and demethylation rates at selected sampling stations will be measured using 24-hour shipboard experiments, incubating water and sediment spiked with isotopically-labelled 200HgII and Me199Hg.

T2.2 Laboratory experiments (NTNU/5). We will conduct the same measurements and analysis as for the on-deck experiment (T2.1) using the laboratory facilities at NTNU. These experiments will use non-axenic, ecologically relevant phytoplankton strains from Arctic waters, and will allow us to compare biological responses according to varying species (different from the on-deck experiments) or varying environment (same main species from on deck experiment but different environment). An abiotic experiment will also be carried out in order to test for the influence of only chemically mediated changes on the solubility of different forms of Pfe under a pH gradient. Here we will add water from Trondheim fjord (filtered and UV- C treated seawater to eliminate organic matter) to the same forms of Pfe employed in the biotic experiments. Possible changes in the solubility of Fe minerals will be followed by regular additions (every 2h) of the selected Pfe following the one-time pH manipulation by continuous measurement of FeII during a continuous cycle of 24–48 hrs.

T2.3 Processing of existing data (NIVA/2). Any relevant observational/experimental data existing prior to the project (literature) will be collated and quality-controlled for use in WP3.

T2.4 Processing of new data (NIVA/2). All data obtained from the cruise and experiments will be collated, quality-controlled, shared with WP3 and uploaded to international databases.

Deliverables: D2.1 Report on the main results obtain on the experimental incubations. D2.2 Manuscript on on-deck experiment. D2.3 Manuscript on on-lab experiments. D2.4 Report on data availability and methods description

Milestones: M2.1 On-deck experiment accomplished. M2.2 Laboratory experiments (biotic and abiotic conditions) accomplished. M2.3 Existing data analysed and made available to WP3 and WP4 as well as WP1 (expedition planning). M2.4 New data uploaded to the databases.