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Experiments by Invited Researchers

 

INTERICE 4

Project acronym: HyIII-HSVA-07
Name of Group Leader: Professor David Thomas, School of Ocean Sciences,
User-Project Title: INTERICE 4
Facility: Arctic Environmental Test Basin (AETB)
Proceedings TA Project: Using the arctic environment test basin for measuring carbon dynamics in rapidly growing ice sheets
Data Management Report: There is no Data Management Report available for this project

User-Project Objectives

Summary:

Interice 4 was a programme of research that included 20 researchers from Denmark, Belgium, Finland, Germany, Norway and U.K. The interests focused on two very different key topical issues for sea ice biogeochemistry and therefore the work was conducted during two phases of experimentation:

Phase One (01.09.09 to 23.09.09) was designed to investigate the production of calcium carbonate (in particular the form ikaite) in sea ice. Carbonate minerals and their production in sea ice is an, as yet, unquantified component of the polar carbon cycle, and key aspects of their dynamics need to be studied before a true appreciation of their role can be assessed.

Phase Two (28.09.09 to 09.10.09) was designed to investigate the fractionation of dissolved organic matter (DOM) during sea ice formation, consolidation and ice melt. The objective of the work was to determine whether DOM and constituents of the DOM behave conservatively during brine exclusion caused by sea-ice formation, and the degree to which fractionation of DOM constituents takes place. In parallel the influence of these processes on bacteria activity and diversity were investigated.

During Phase One 24 experimental bags were each filled with approximately 1m3 of North Sea water. When cooled to around 0ºC, additional phosphate was added and the pH elevated slightly in 12 of the bags. These manipulations were designed to promote calcium carbonate formation in the ice formed in these bags. After the additions the experimental basin was cooled to an air temperature of -12ºC. During the course of the experiment samples were taken from the water underlying the ice, from the bulk ice itself directly from ice brines. These samples included: salinity, temperature, dissolved inorganic carbon and oxygen concentrations, inorganic nutrient concentrations, stable isotope composition of dissolved and particle fractions as well as samples for calcium carbonate determination. Measurements were also made in air, water and ice brines to measure the CO2 gas fluxes into and out of the ice sheets formed in the bags.

During Phase Two 18 experimental bags were each filled with approximately 1.2 m3 of North Sea water. 9 of these were enriched with a dissolved organic matter (DOM) concentrate derived from microalgae. These additions were designed to enhance the organic matter signature over that from the seawater alone. After the additions the experimental basin was cooled to an air temperature of -15ºC. As in Phase One during the course of the experiment samples were taken from the water underlying the ice, from the bulk ice itself directly from ice brines. Samples were taken for: bacterial activity, enumeration and diversity of bacteria and flagellates, absorbance and fluorescence characterization of DOM, chemical characterization of DOM fractions, salinity, temperature, dissolved inorganic carbon and oxygen concentrations and inorganic nutrient concentrations. Due to the unexpected growth of copious frost flowers on the surface of the ice in the bags during Phase Two, a systematic study was initiated to investigate the bacterial activity & composition as well as DOM characteristics in frost flowers on top of our original research programme.

In both phases samples were taken of the ice in order to conduct structural analyses. In addition during both phases an imaging Infrared (IR) camera (temperature resolution: 80 mK), was used to monitor the spatio-temporal evolution (resolution: 2 mm x 2 mm; footprint area: 66 cm x 52 cm) of the surface temperature within a single bag in which a thermistor chain had also been placed.

The nature of biogeochemical sampling such as that undertaken during Interice 4 is that there will be about 1 year of sample analyses in the home laboratories before synthesis of the results will be possible and manuscripts written. It is anticipated that initital reports will be presented at the International Glaciology Society International Symposium on Sea Ice in the Physical and Biogeochemical System to be held in Tromsø, Norway, 31 May–4 June 2010.

Fig 1. (Top) Launching of plastic bags into the basin

Fig 2. Seeding procedure after the
bags have been filled with water from
the North Sea
Fig 3. Sampling of bacteria from underneath
the ice sheet
Fig 4. Measurement of released carbon dioxide

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