The microstructure of sea ice and its impact on nutrient dynamics in the Arctic
The microstructure of sea ice is an important variable that determines primary production rates within and directly underneath the ice. To quantify the magnitude of biomass production, permeability of the ice and nutrient flux from the deeper layers of the ocean toward the surface are being investigated as part of this project. A permeameter was built according to specifications by Dr. Johannes Freitag of the Alfred-Wegner-Institute für Polar- und Meeresforschung in Bremen, Germany which enables me to determine the permeability of sea ice core samples under varying temporal and spatial conditions. Ice core samples were collected during the spring of 2003 in the shore-fast ice off of the coast of Barrow and on an ice breaker expedition (HLY-04-02) into the Arctic Ocean in May/June of 2004. The samples were centrifuged and preserved for experiments which were conducted in the cold room at the Geophysical Institute here in Fairbanks. Under-ice currents have also been measured with a SonTek Argonaut-ADV at various depths during the respective field trips and will be used to calculate the nutrient flux in and out of the ice. Experiments were set up in Barrow, AK in the spring of 2005 where the influence of under-ice currents on the growth rate of biomass in the ice was investigated. The biological component looked at alterations in nutrients, salinity and light conditions whereas the physical component looked for a correlation between ice growth conditions and primary production rates. Since the currents were shut off from the ice bottom during the biological experiments, ice growth and the associated microstructure were researched by taking samples in the field at the time of the onset of the experiment as well as after the conclusion. One set of experiments was conducted in March 2005, a second in May 2005; both over a time span of 7 days. Also, a 4 x 4 feet rectangular ice block was cut loose in a level ice floe and 4-feet wide by 8-feet long UHMW plastic sheets was installed into those slots to simulate ice growth under no-current conditions. Experiments in this rectangle looked at biomass production rates in ice that grew with no currents present as opposed to the previous samples which investigate biomass in virgin ice with only the no-current option during a 7-day period. Furthermore, under-ice velocities were measured during those 2 field trips and correlated to the primary production rates in regard to nutrient uptake. Data are currently processes. The outcome is expected to show how a change in current speeds and directions influences primary production rates and with it the whole Arctic marine system.
A poster with the permeability measurements was presented at the Gordon Research Conference for Polar Marine Science in Ventura in March 2007: Arctic sea ice permeability measurements in the context of ice-associated biological production.
Pictures of some thin sections can be found here
Field Work Pictures:
SBI Ice Breaker Cruise May/June 2004
My committee members:
Dr. Hajo Eicken (Adviser)
Dr. Rolf Gradinger
Dr. Thomas Weingartner
Dr. David Newman
