RESEARCH HIGHLIGHT

Contacts

Kohei Mizobata
IARC-JAXA Information Systems, University of Alaska Fairbanks
kmizobata@iarc.uaf.edu

Sei-Ichi Saitoh
Graduate School of Fisheries Sciences, Hokkaido University
ssaitoh@salmon.fish.hokudai.ac.jp

Links

Arctic Modeling Group
IARC-JAXA Information Systems Research Group

Photos

zooplankton sampling using closing net

deployment of CTD (Conductivity - Temperature - Depth) rosette water sampler

filtering for size-fractionated chlorophyll-a concentration

photos by K.Mizobata

Oshoro-maru cruise in the Chukchi Sea, August 5th-15th, 2007

September 14, 2007

Kohei Mizobata, a researcher from the IARC Arctic Modeling/IARC-JAXA Information System (IJIS) Research Group, joined a JAXA Arctic Research Project summer cruise in the eastern Chukchi Sea from August 5th – 15th aboard the training ship Oshoro-maru from the Faculty of Fisheries, Hokkaido University, Japan.

The IJIS Research Group objectives during this cruise were to take heat and salt measurements in the eastern Chukchi Sea and to examine the linkage between physical environments and phytoplankton distribution.

In the eastern Chukchi Sea, the warm Pacific Summer Water flows northwardly along the Alaska coastal area. This warm water is thought to be a trigger of sea ice melting along the northern Alaska coastal area, resulting in drastic sea ice reduction in the western Arctic Ocean (Shimada et al., 2006). To measure the heat and salt contents, 32 hydrographic observations were made. Figure 1 shows temperature at the ocean surface along the cruise track. Very warm waters were observed (over 14 degrees C) along the Alaska coastal area. The warm water extended to the Barrow Canyon. Their measurements confirmed the same kind of warm water at the northernmost station along the Alaska coast as well. Those warm waters may have an impact on sea ice melt during summer and the delay of sea ice freezing during winter in the western Arctic Ocean.

Warm conditions were also observed and they had 3 clear-sky days during short 10-day cruise. Absorption of solar radiation may accelerate ocean warming and contribute heat input into the Arctic Ocean.

Less phytoplankton was observed in the surface warm layer, but sometimes they observed a relatively high abundance of the phytoplankton just under the thermocline (mixed layer base). In the Chukchi Sea, phytoplankton biomass supports the benthic animals and marine mammals (Grebmeier and Dunton, 2000). The pathway of the surface warm water may alter not only the fate of sea ice in the western Arctic Ocean but also the phytoplankton distribution and biomass in the Chukchi Sea. They expect more interesting results to be revealed through the ongoing analysis of cruise data.

Japanese scientists joined with researchers from the United States and Korea under the Chief Scientist Professor Sei-ichi Saitoh of Hokkaido University, making this cruise an international effort. U.S. participation included scientists from the University of Alaska Fairbanks, University of Washington, and University of Hawaii. From Korea, scientists from the Korea Polar Research Institute participated.

The overall target research objectives of the cruise included examination of physical parameters such as temperature and salinity, the optical properties within the water column*, population assessments (phyto/zooplankton, salmon, whale, and benthic animals), and general observations of the marine ecosystem. The cruise will be repeated in the Chukchi Sea in the summer of 2008.

* Optical properties are needed for the validation and calibration of the satellite ocean color sensor to measure chlorophyll-a concentration. Chlorophyll-a is the green pigment that all phytoplankton have, and which can be used as an index of phytoplankton biomass.

References:
Shimada, K., T. Kamoshida, M. Itoh, S. Nishino, E. Carmack, F. MacLaughlin, S. Zimmermann and A. Proshutinsky (2006), Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean, Geophys. Res. Lett., 33, L08605, doi:10.1029/2005GL025624.

Grebmeier, J. M. and K. H. Dunton (2000), Benthic processes in the northern Bering/Chukchi seas: status and global change, pp. 61-71.Impacts of Changes in Sea Ice and other Environmental parameters in the Arctic. Report of the Marine Mammal Commission Workshop,15-17 February 2000, Girdwood, Alaska. Available from the Marine Mammal Commission, Bethesda, Maryland.

Figure: