The ocean has an important role in controlling atmospheric CO2 that has been drastically increasing since the industrial revolution. Recently it has been detected that the environmental changes in the ocean such as warming, freshening (decrease of salinity), stratification and acidification have started. It is predicted that the oceanic change leads the change in oceanic ecosystem and, sequentially, the change in marine biogeochemical cycle. It is possible that, consequentially, the ocean’s role in controlling the atmospheric CO2 will change (weaken) and its change will accelerate the global climate change. MBCRT has conducted the research of interactions between climate variability and changing marine ecosystem dynamics and biogeochemical cycles.
Research area and tactics
Research area is the Western North Pacific where is known as a terminal area of deep-sea water circulation. In this area, two time-series stations have been set: One is the station K2 (47N / 160E) located in the western Pacific subarctic gyre, and the other is station S1 (30N / 145E) located in the subtropical gyre. These stations have contrasting oceanic properties as follows:
|Sea Surface Temperature||Low||High|
|Winter CO2 balance||CO2 source||CO2 sink|
|Eolian dust input||Low (?)||High (?)|
|Zoo / Phytoplankton abundance||High||Low|
In addition, it has been suspected that both gyre respond differently to the atmospheric / oceanic events and decadal oscillation such as Asia monsoon, El Nino and the Arctic oscillation. Shipboard observation/experiments will be conducted at K2 and S1 to study responses of ecosystem dynamics and biogeochemical cycles to atmospheric and oceanic events in two contrasting oceanographic conditions. Emphasis will be placed on describing seasonal variability of oceanic responses in order to detect long-term variability and/or trend. Processes to be studied include every aspect of end-to-end food web dynamics and biogeochemical cycles. Intra-seasonal short-term variability will be studied by visiting the stations with aid of various moored instruments and satellite (see below). It is envisioned that an integrated and comprehensive understanding on seasonal variability of end-to-end food web dynamics and biogeochemical cycles in response to seasonal change and response to atmospheric / oceanic events could be achieved from as many as possible viewpoints and disciplines by close collaboration with external participants of widely distributing disciplines and ideas.
Our research is conducted by scientific cruise, mooring system and satellite.
(1) Scientific cruise
MBCRT visit two time-series stations in different season by various research vessels, mainly R/V MIRAI and interdisciplinary observations / experiments are conducted with external participants. The following Table is tentative cruise plan between 2010-2013 (Closed circles are cruises already done or scheduled robustly).
Major observation items are as follows:
A） Dissolved components
Salinity, oxygen, nutrients, carbonate components（pH, dissolved inorganic / organic carbon, alkalinity, pCO2, carbon isotope）, phytoplankton pigments, trace gasses, natural radio / stable isotopes and trace metals.
B） Particulate materials
Spatial and temporal variation of suspended / sinking particle and its chemical compositions（major / trace elements, isotopes, micro fossil）and Transparent ExoPolymer (TEP).
C） Zoo / Phytoplankton, Bacteria
Spatial and temporal variation of species of zoo / phytoplankton, primary productivity, N2 fixation, grazing pressure, fecal pellet production and bacteria production.
D） Sea floor sediment
Sedimentation rate and microfossil for paleoceanography.
E） Seawater bio-optics
F） Physics (advection, diffusion and current etc.)
(2) Mooring system
The Western North Pacific, especially the subarctic gyre, has the large seasonal variability in marine physics, biology and chemistry. Thus high-frequency time-series observation should be conducted in order to verify ecosystem dynamics and biogeochemical cycle precisely. MBCRT has been deploying two types mooring systems at time-series stations.
A） Sediment trap mooring system (BGC ms)
Time-series sediment trap collects sinking particles at any interval. The BGC ms consists of several time-series sediment traps installed at different depths from subsurface to deep sea. After recovery, chemical and biological analysis of collected particles is conducted and process of vertical transport and regeneration of particulate materials are studied.
B） Primary Productivity Profiler
Main gear of this mooring system is Fast Repetition Rate Fluorometer (FRRF) that measures gross primary productivity in the surface sunlit layer (euphotic zone). An observation buoy which equipped with FRRF, CTD, oxygen sensor and optical sensor is supported by an underwater winch located at subsurface (ca. 200m). The observation buoy ascends to the sea surface, basically, once a day (at noon time) measuring vertical profile of temperature, salinity, oxygen, chlorophyll and bio-optical condition. After data transmission via satellite, the observation buoy descends and returns to its home position (ca. 200m).
C） Satellite observation
In order to observe spatial and temporal variability of oceanography in the whole Western North Pacific including two time-series stations, MBCRT also conducts satellite data analysis. Satellite observation enables us to know spatial and temporal variability of sea surface temperature, ocean color, solar irradiance, sea level and wind. These data are helpful for the study of horizontal distribution of abundance and productivity of phytoplankton, and relation between ocean ecosystem, biogeochemical cycle and ocean structure such as current and eddy.