Oden, 10. september 2007, Ice coring in the sea ice north of Greenland
Received from Hans Ramløv, Roskilde University, Denmark
Edited by Jane Holst, Henrik Højmark Thomsen and Torsten Hoelstad, GEUS
During the LOMROG expedition we are collecting ice cores for the investigation of the role of the sea ice in the transport of CO2 from the atmosphere to the ocean. Principal Investigator on the project is professor Søren Rysgaard, Greenland Institute of Natural Resources and participant in the LOMROG expedition is associate professor Hans Ramløv, Roskilde University.
Dissolved inorganic carbon is controlled by biological processes, up-welling of subsurface water enriched in respired CO2 and nutrients, and air-sea exchange. Further, recent work suggests that the dissolved inorganic carbon is rejected from growing sea ice together with brine. Downward rejection of CO2 from growing sea ice together with brine has not been considered previously, and nor has the resulting atmosphere-ice-ocean exchange of carbon resulting from this sea-ice driven carbon pump been quantified. When sea ice is formed the dissolved solutes in the seawater are concentrated into pockets or canals in the ice called “brine pockets”. The ice consists of pure water without salts. The solutes (salts) are therefore “pushed” out of the growing ice into what become the brine pockets.
Recent results suggest that CO2 is sequestered in the brine pockets during the formation of the ice. In the springtime and during summer, when the ice melts, the highly concentrated brine sinks towards the bottom. Thus a relative direct transfer of CO2 from the ice to the intermediate and deep water may occur. When the ice melts during summer, the meltwater has a very low concentration of CO2 which gives rise to a large uptake of CO2 from the atmosphere. As this mechanism is dependent on the formation of sea ice, it seems possible that a future reduction in the sea-ice cover may lead to a reduction in the CO2 uptake by the ocean.
In addition to the physical and chemical measurements of the sea ice, the occurrence of algae in the ice is also investigated. The reason for this is that the role of the algae concerning the chemical conditions in the context of CO2 in the ice is not well known. Thus it is of importance to investigate the algae and their physiology. Ice algae synthesize some substances which can modify the ice surface and optimize the environment in the ice in which the algae are found. It is therefore also one of the aims of the present study to investigate the algae and the synthesized substances.
During the expedition samples of different types of sea ice are collected. The content of CO2 and the alkalinity of these samples are investigated. During the LOMROG expedition ice-core samples are taken with a KOVACS 7 cm ice-core drill. We are dropped on the ice from the ice-breaker either via helicopter or by crane. On the ice a number of physical parameters are measured, i.e. air temperature, snow depth and snow temperature, the latter taken every 5 cm. An approx. one meter long ice core is drilled out of the ice. The temperature of the core is measured at 10 cm intervals and a 10 cm slice is then cut off from the top, the middle and the bottom of the core. These pieces are the taken to the laboratory for further processing. In some cases the ice is drilled all the way through the ice flow and then the same procedure as mentioned above is followed. After having taken the ice core samples, measurements for the calculation of density are also done.
In the laboratory the core pieces are cleaved and one half is transferred to a gas proof plastic bag and sealed. The ice is melted in the bag and the meltwater is transferred to gas proof containers which are brought to the laboratory in Nuuk (Greenland) where the final measurements are done. The other half is melted; some meltwater is transferred to a plastic vial for the measurement of salinity and the rest is filtered through a glass filter and the filter is then frozen for later determination of the chlorophyll a content of the filtrate (i.e. the ice). In addition to the ice cores, water samples from 10 m depth are acquired from the CTD which is operated by one of the Swedish groups participating in the expedition.