Long-term variation of surface phytoplankton chlorophyll a in the Southern Ocean during 1965-2002

Brief description

The variation in the phytoplankton biomass over a decadal time scale, and its relationship with the Antarctic Circumpolar Wave (ACW) and climate change, has been poorly interpreted because of the limited satellite chlorophylla (chl a) data compared with the physical parameters from satellite. We analysed a long-term chl a dataset along the Japanese Antarctic Research Expedition (JARE) cruise tracks since 1965 to investigate inter-annual variation of phytoplankton biomass. In the Southern Ocean, increasing trends of chl a and the spreading of higher chl a area to the north with 3-7 year cycles were found. Although relationships between the decadal change in chl a and climate change such as variation of sea ice extent and the El Nino are still obscure, large variation of primary production in proportion to the chl a is implied.

The chl a concentration of sea surface water has been measured routinely on board the icebreakers Fuji and Shirase during almost every cruise of the JARE.

The download file contains chlorophyll a data collected from ship tracks on JARE voyages between 1965 and 2002.

The field in this dataset are:

Date (local time)
Year
Latitude
Longitude
Corrected Chlorophyll a

See the attached paper for more details.

The publications on the data collected during the 1965-1976 and 1988-1993 cruises are listed in Fukuchi [1980] and Suzuki and Fukuchi [1997], respectively. For data on the 1977-1985 and 1994-1997 cruises, see [Kanda and Fukuchi, 1979; Fukuchi and Tamura, 1982; Tanimura, 1981; Watanabe and Nakajima, 1983; Ino and Fukuchi, 1984; Sasaki, 1984; Hamada et al., 1985; Fukuda et al., 1986; Hattori and Fukuchi, 1988; Midorikawa et al., 2000]. Data post 1998-2002 cruises is in Hirawake and Fukuchi [2004]. Data from the 1986-1987 will be published in the JARE data report of digital media, including all cruise data.

Auxiliary Material for paper 2004GL021394 Long-term variation of surface phytoplankton chlorophyll a in the Southern Ocean during 1965-2002. Toru Hirawake, Tsuneo Odate and Mitsuo Fukuchi (National Institute of Polar Research, Tokyo) Geophys. Res. Lett., Vol (Num), doi:10.1029/2004GL021394

All of the chl a data have been reported in the publications of the National Institute of Polar Research (NIPR).

Lineage

Progress Code: completed

Statement: In the dataset over the 38-year period of 1965-2002, we used the value of water between 25 degrees N to 55 degrees S along the cruise track between Tokyo and Antarctica, during the period between 15 November and 28 December of each year.

Although the sea surface water was sampled with a plastic bucket or pump (8 m), no significant difference in the chl a between sampling procedures was found. The chl a was determined colourimetrically until 1980 (except in 1967 and 1972) and fluorometrically since 1981. The data collected colourimetrically was corrected to a concentration corresponding to the fluorometric measurements. Difference in the chl a between the solvents was not significant.