If you see a flash of a blonde haired female scientist on the deck that seems to be everywhere at once, then that would be Dr. Jackie (Jacqueline) Grebmeier from the University of Maryland. Her team is studying various parameters such as the ecological forces or biological factors of the benthos (bottom dwellers) in the Chukchi Sea with emphasis on the Hanna Shoal region. They run various chemical analysis of the CTD water too. For example, the ratio of isotopes in the water (O18 to O16) can determine how much of the fresh water lens originates from melt water from sea ice versus runoff from precipitation. Chlorophyll and nutrients in the water column are other chemical analyses that will result from this cruise. For this journal, I will discuss the benthos only.
Van Veen Grab
At each station, five single van Veen grabs are deployed; four are used for quantitative analysis, as the number is sufficient to describe the benthic community at any particular station statistically. An additional grab is used for sediment characteristics and organisms collected are used for other analysis. In the chemical analysis total organic carbon and chlorophyll inventories of surface sediments are determined. Another interesting component of sampling the top layer of the mud is recording the grain size of the sediments. Grain size can tell a researcher about the currents in the area and the physical environment of the infuana (organisms in the mud).
Christina and Holly adding acetone to sediment samples for chlorophyll analysis.
Christina washing a mud sample in the box sieve.
Box sieves are used in quantitative analysis and the complete grab sample is preserved and identified back in Maryland. The quantitative analysis can indicate the dominant species in the biomass and the infaunal wet weight is converted to number of grams carbon per square meter. Why does a dominant species matter? One example is if clams are abundant then, this could be a feeding area for walrus. The infaunal dominant species can be related to what is the top predator in that area.
Jackie is on the right next to the mulit-HAPS core.
Another type of sediment sampler the team uses is a multi-HAPS core, which collects several cores at once. This sample of sediment is less disturbed then the van Veen and normally is brought up to the deck with the water above the sediment (the interface) along with the sediment. This water is carefully replaced with the bottom water from the CTD. Next, respiration experiments are conducted in the dark at bottom water temperatures on these cores that provide data on total community metabolism. The community includes microphytobenthos, small bottom photosynthesizers that are targeted in the sediment chlorophyll measurements. For the most part the main changers of dissolved oxygen in the water are benthic animals that use oxygen in the overlying water as they consume food. Oxygen respiration rates are directly related to the deposition rate of food to the sea floor. Nutrient levels and pH (alkalinity) exchange rates are measured too. After experimentation, the organisms in the sediment are preserved for further study including wet weight measurements so oxygen utilization can be corrected to wet weight biomass.
Sediment sample from the milit-HAPS core.