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In June 1998, Japanese ocean scientists established a time-series observation station in the western North Pacific (left map). The station, located at 44N, 155E, is known as KNOT, short for Kyodo North Pacific Ocean Time-series (Kyodo is a Japanese word meaning "collaborative"). The scientific focus of the program at KNOT is the seasonal carbon cycle.

Although the study region exhibits high seasonal variability in sea surface temperature and biological activity, there have been few observations to document the seasonal variations in carbon concentrations and related parameters. The location was chosen because it is located in the western subarctic gyre, and the travel time from Japan to the station is less than three days. In addition, measurements made by Hokkaido University during summer between 1992 and 1997 can be used for comparison.

KNOT image

The KNOT program was proposed by the JGOFS-Japan committee, led by Nobuhiko Handa of Aichi Prefectural University, Shizuo Tsunogai of Hokkaido University and Toshiro Saino of Nagoya University. It is funded by the Japan Science and Technology Corporation (JST) as one of the Core Research for Evaluational Science and Technology (CREST) Programs. The core members of the CREST program include the organizer Yukihiro Nojiri of the National Institute for Environmental Studies, JST post-doctoral fellows Keiri Imai and Nobuo Tsurushima, and JST technicians Fujio Shimano and Takeshi Egashira. Many other Japanese scientists have joined in this program as well.

The biggest challenge of the KNOT program was securing ship time for the fieldwork. There was no single ship dedicated to these time-series observations. Four research vessels have been used for the observations made to date: T/S Hokusei-maru from Hokkaido University, R/V Bosei-maru from Tokai University, R/V Mirai from Japan Marine Science and Technology and R/V Hakuho-maru from the University of Tokyo. Scientific instruments were packed, moved and set again to accommodate each ship change.

The KNOT station was occupied eight times in 1998 and 10 times in 1999 and 2000 respectively. In addition, observations were sometimes made along north-south transects near the KNOT station. In some cases, the KNOT station was occupied twice during on long cruise, with transect work between occupations.

Measurements made during KNOT include carbonate system parameters, including dissolved inorganic carbon (DIC), alkalinity and the fugacity of carbon dioxide (fCO2) in surface waters, as well as temperature, salinity, nutrients and oxygen. Discrete water samples were collected throughout the water column from the surface to at least 3000 meters.

Surface layer measurements of biological activity, including chlorophyll a concentrations and primary productivity, were also made on nearly every cruise, along with collections of phyto- and zooplankton. For more than half the cruises, floating sediment traps were deployed, and measurements were made of particulate and dissolved organic carbon (POC and DOC), iron, trace metals, halocarbons, methane, nitrous oxide, stable isotopic ratios of DIC, the ratio of nitrogen to Oxygen and argon, and thorium-234.

Funding from JST is limited to five years, and the first cycle of intensive observations was completed in October 2000. Synthesis and interpretation of the three-year data set will take place throughout the coming year, and some of these results will be published in an upcoming Deep-Sea Research II special issue on North Pacific biochemical processes.

This three-year program of observations will greatly expand our information about seasonal variations of chemical parameters in the KNOT region. However, any long-term changes in CO2 concentrations will require both a long-term study and high-frequency observations to capture the extremes in the seasonal variations. The community of ocean scientists in Japan is currently assessing these initial results from KNOT and evaluating options for the next phase of the time-series observation program.

(cited from Tsurushima, N., K.Imai, Y.Nojiri and P.P.Murphy (2002) KNOT: Ocean Time-series Program in western North Pacific completes first phase. US JGOFS News, 11, 4, 11-13. >> PDF file)