Experiments by Invited Researchers



Project acronym: HyIV-HSVA-01
Name of Group Leader: Prof. David Thomas
User-Project Title: INTERICE 5
Data Management Report: Report

User-Project Objectives

INTERICE 5 was a 31 day programme of research that included 14 researchers from Belgium, Denmark, Finland, Germany and U.K. The interests focused on the effects of sea ice formation on the dissolved organic matter in seawater and the resulting bacterial activity, and linking this to the carbon fluxes into and out of the ice during the freezing process. This was a truly multidisciplinary team, including chemists, glaciologists and biologists. In short, 22 experimental bags were each filled with 1m3 of North Sea water. When cooled to around 0ºC, 100 litres of river water were added to half of the bags in order to enrich them with DOM. Therefore there were two series of bags: north sea water (NSW) with normal DOM concentrations and the DOM enriched bags (R). The salinity of the latter was adjusted to that of the NSW bags by adding artificial seawater salts. Inorganic nitrogen and phosphorus were added to all bags to ensure that there was no nutrient limitation of the bacteria during the subsequent experiment. On 3 of the bags we placed flux chambers to measure the CO2 fluxes into and/or out of the ice. One bag had a thermistor chain for detailed temperature profiles of ice, water and air, and in the same bag we placed a CTD that logged the salinity and temperature changes in the water underlying the ice. Although discrete oxygen samples were taken, in 4 bags we also placed optodes to continually measure the oxygen concentration in the under-ice water. After the additions the experimental basin was cooled to an air temperature of -14ºC, and ice formed, growing at a rate between 1 or 2 cm per day. The last 6 days of the experiment were a “warming phase” where the air temperature was increased to -1ºC in order to observe the influence of increasing temperature shifts on the biogeochemical parameters being studied. During the course of the experiment samples were taken from the water underlying the ice, from the bulk ice itself directly from ice brines. The parameters measured during the experiment and the sample types collected are: Bacteria & Viruses: Activity ; Cell numbers/size (flow cytometry) ; Population succession/dynamics ; Microscopy/enumeration Ice growth dynamics: Thickness; Texture; Temperature Atmosphere: CO2 flux chambers CTD Thermistor chain Chemistry: Inorganic macro-nutrients ; DOC & DON ; Oxygen isotopes ; Winkler O2 ; Optode O2 ; Salinity ; pCO2 ; Gas content (total CO2, CH4, O2, Ar, N2) ; CO2, CH4, N20 ; DOM Absorption ; DOM Fluorescence ; Alkalinity The nature of biogeochemical sampling such as that undertaken during INTERICE 5 is that there was 2 year of sample analyses in the home laboratories before synthesis of the results was possible and manuscripts written.

Short description of the work carried out

All of the objectives were achieved, although the melt phase that we induced, was on reflection, rather too drastic and future experiments would have a more gradual warming than the one we adopted. Despite this, the INTERICE 5 experiment was the first successful attempt to measure gas fluxes from a growing sea ice sheet in an experimental facility. It is virtually impossible to make such measurements in the field and so the results are unique. To be able to link these measurements to biological activity and chemical changes have resulted in a rather unique data set that will be highly pertinent to researchers working on biogeochemical processes in ice-covered oceans. Because of the tightly constrained experimental conditions and the suite of measurements it was possible to collect this experiment should be highly pertinent for modelers trying to model these processes in natural sea ice. The INTERICE 5 team did not encounter any difficulties while carrying out the work, and the experience was immensely rewarding scientifically for the time that was invested. One of the problems about making measurements of CO2 fluxes in an experimental facility such as this is that the measurements when researchers are working inside of the basin cannot be used since naturally they are producing CO2 themselves. Therefore we were only able to use the measurements made at night and the weekends when there was no researcher activity in the basin.

Highlights of important research results

We secured funding to support a workshop in Finland in September 2013 to synthesise results. The first important highlights are presented in the following publications: J Zhou, B. Delille, H Kaartokallio, G Kattner, H Kuosa, J-L Tison, R. Autio, GS Dieckmann, K-U Evers, L. Jørgensen, H Kennedy, M Kotovitch, A-M Luhtanen, CA Stedmon & DN Thomas. 2014. Physical and bacterial controls on the distribution of inorganic nutrients and DOC in sea ice during an experimental ice growth and decay cycle. Marine Chemistry, doi: 10.1016/j.marchem.2014.09.013 The work was also presented at the Hydrolab IV Closing Event, Lisbon in July 2014: DN Thomas, J Zhou, H Kaartokallio, J-L Tison, B Delille, L Jørgensen, A-M Luhtanen, G Kattner, CA Stedmon, R Autio, H Kuosa, GS Dieckmann, H Kennedy, K-U Evers. 2014. Using the Arctic Environment test basin to study the dynamics of dissolved organic matter in sea ice. Proceedings of the Hydrolab IV Closing Event, Lisbon, July 2014, In Press. In summary we were able to measure CO2 fluxes during both freezing and melting phases. These were at rates that are realistic to field conditions. We were also able to measure bacterial growth and activity in relation to the DOM content of the parent water from which the ice was formed. Such detailed measurements are seldom possible in the field due to obvious logistical constraints. In addition we were able to document the changes in the nature and bioavailability of the organic matter over time. This helps us relate the chemical signatures of organic matter measured in field studies to processes that may have gone on to produce such chemical characteristics.

Zhou, Jiayun et al.Factors driving pCO2 dynamics in sea ice during a large-scale ice tank experiment , 2014 International Symposium on Sea Ice in a Changing Environment 10-14 March 2014 in Hobart, Australia organized by IGS International Glaciology Society
Zhou, Jiayun et al. Physical and bacterial controls on the distribution of inorganic 1 nutrients and DOC in sea ice during an experimental ice growth and decay cycle. , 2014 Manuscript submitted to Elsevier ? Marine Chemistry, 2014
Thomas, D. et al. INTERICE 5 HyIV-HSVA‐01 Final Report , 2013