2007 Annual Report - jamstec japan agency for marine-earth ...

station K2 (47N, 160E) and shipboard observation around
the K2 station in the northwestern North Pacific to obtain quantitative
and mechanistic understanding of key processes of carbon
cycle in the western subarctic Pacific.
Efforts were also made for development of an autonomous
surface CO 2 partial pressure observing floats, with financial
support by the Ministry of Education, Culture, Science and
Technology (MEXT) as a part of Japan Earth Observation
System Promotion Program.
b. Achievements
1) Distribution of nutrients and phytoplankton in the western
subarctic Pacific during MR07-05
R/V Mirai cruise MR07-05 was conducted to study
dynamics of nutrients and phytoplankton at the time-series station
in autumn 2007. Concentration of nitrate plus nitrite at the
surface seawater of Sta. K2 and its inventory in the upper 100m
water column was 8 - 10mole kg -1 and 1.9mol m -2 during this
cruise, respectively (Fig. 4). Primary productivity was measured
twice during the cruise and valued 460 mg-C m -2 day -1 and 300
mg-C m- 2 day -1 (Fig. 5). Those are typical values in the early
autumn at Sta. K2.
Chlorophyll a concentration and phytoplankton community
structure obtained during MR07-05 cruise were compared with
those captured during MR05-04 in October, 2005 and MR06-03
in early summer, 2006 as shown in Fig. 6 and 7. In early summer,
chlorophyll a concentration was over 1mg m -3 and diatom
was predominant. However, haptophyceae was the most dominant
phytoplankton taxa, and contributed to a half of total
chlorophyll a concentration during this cruise. This result is
consistent with a size distribution of phytoplankton.
Fig. 4 Seasonal variation of water column inventory of nitrate and
nitrite normalized to salinity 33 above 100m depth at Sta. K.
Data obtained in 2007 cruise (MR07-05).
Data obtained before 2007
Fig. 5 Seasonal variation of primary production at Sta. K.
Data obtained in 2007 cruise (MR07-05)
Data obtained before 2007
2) Seasonal and interannual change of shallow carbonate chemistry
and settling particle
Due to increasing input of anthropogenic carbon, biogeochemical
cycle (carbon cycle) in the ocean can be affected and
ocean acidification may be taking place. We have continued
observations at the time-series stations K2 and KNOT (44N,
155E) to detect the seasonal and long term changes in the
western subarctic Pacific.
Seasonal variability in normalized DIC (nDIC) and nitrate
concentration at the sea surface in the Western Subarctic Gyre
were from 81 to 113 mol kg -1 and 12.7-15.7 mol kg -1 ,
respectively. Inventories of DIC and nitrate in the upper 100m
water column showed maximum in March and the minimum in
October. Based on the inventory change between March and
October, seasonal new production was estimated to be 39 - 61
gC m -2 , about twice higher than that in the North Pacific subtropical
gyre and the northeastern North Pacific (Kawakami et
Fig. 6 Typical vertical distributions of chlorophyll a during MR05-
04MR06-03 and MR07-05 cruise.
Fig. 7 Water column inventory of biomass in term of chlorophyll a
obtained during MR05-04 cruise in October, 2005, MR07-05 cruise in
September, 2007, and MR06-03 cruise from May to July, 2006.
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