The Mutsu Institute for Oceanography (MIO) of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC: Mr. Yasuhiro Kato, President) succeeded for the first time in the world to collect time-series seawater samples for a long period using an automatic water sampler (Remote Access Sampler, RAS) at the Northwestern North Pacific southward off Polustrov Kamchatka, in order to monitor the ocean's ability to absorb atmospheric CO2.
The RAS makes it possible to elucidate in detail the ocean's CO2 absorption mechanism and capacity. CO2 is the main factor of global warming.
This achievement will be published on "Journal of Oceanography" vol. 63 on April 24.
The global warming caused by greenhouse gases, including CO2, has become a global concern. To understand global-scale CO2 cycle correctly, it is necessary to grasp the process of CO2 absorption and transportation in the ocean, which covers 70 % of the surface of the earth and stores as 60 times as much CO2 as in atmosphere.
At the site area in the North Pacific, southward off Polustrov Kamchatka, deep sea water moves upward and abundant nutrients are provided from subsurface to the surface layer, biological production is very active including photosynthesis of phytoplankton, so that it is known that CO2 biological absorb ability is high in this area.
Since the process of CO2 absorption and transportation varies a great deal by season, for more precise understanding, long-term and high-frequency time-series observation data are required. And for previous observations using research vessels, it is difficult, and water sampling in a rough weather is impossible.
Therefore, development and operation of automatic observation systems and automatic samplers for time-series and long-term observations have been expected.
3.Remote Access Sampler (RAS)
The system using this time collects water samples automatically even in several thousands meters depth area, because it is moored the sea floor with mooring cable. 48 sample bags are mounted to store seawater, and collects seawater automatically in accordance with planned schedule. Once it is deployed, long-term and high-frequency water sampling is possible (Fig.1,2).
The MIO started water sampling in 2001 using this system in the pelagic zone. It had several issues back then. It was damaged at the time of installing and recovering, and seawater samples were contaminated. And in the pelagic zone of 5,200m water depth, it was difficult to set the system at a desired depth.
As measures for these problems, such as setting methods, mooring cable design and mooring device materials have been improved, and preservative has been upgraded based on the seawater reserve tests to prevent contamination of seawater samples.
After the improvements, the RAS (Fig.2 (a)) was deployed by Research Vessel "MIRAI" at the Pacific sea area 800km southward off Polustrov Kamchatka (47°N, 160°E, water depth 5280m) on March 17, 2005. The RAS was recovered once in September that year, and reinstalled after collected seawater samples and data, attached new sample bags, and conducted maintenance works including changing batteries. It was recovered on May 30, 2006 and was confirmed its performance of collecting water for over a year every 4 to 8 days automatically at a depth of approximately 40m (refer to pictures). It is the world's first to succeed automatic water sampling at this high-frequency.
Chemical analysis of seawater samples showed as follows:
Concentrations of nutrients (NO3, Si(OH)4) in seawater decrease along with the phytoplankton's increase from spring to summer, and increase from autumn to next spring by winter mixing (Fig.4).
Rapid decrease of concentrations of Si(OH)4 were observed from the late June to July, and rapid increase of opal flux were observed almost at the same time in sediment trap samples at 150m depth. Opal flux, which used to be shells of phytoplankton (diatoms), was quickly transported vertically from surface layer to deep layer after diatoms' death (Fig.5). This result indicates that CO2 assimilated by diatoms photosynthesis were also transported into the ocean interior quickly.
This observation verified utility of the automatic water sampler, RAS, which has made it possible to obtain data useful for elucidations of CO2 absorb mechanism in the ocean.
In the future, at northern Pacific Ocean, comprehensive oceanographic data will be obtained by using RAS with an optical sensor and a sediment trap for a long period, then more precise CO2 absorb ability and cycle process will be clarified. For global-scale oceanographic observation, the same observations will be conducted at various time-series stations in cooperation with foreign institutions.