Activity in 2020

Cruise observation in FY2020

Western Pacific subarctic – subtropical regions

R/V Mirai (MR21-01: 2021/2/13-3/24)
「Influence on Marine ecosystem at western north Pacific by Atmospheric Chemical Trace Species from East Asia（“IMPACT-SEA” project）」

Recovery / Redeployment of sediment trap mooring system, and interdisciplinary observations at KEO, K2 and other stations.

Details of the cruise observations (1): Time-Series Sediment Trap Experiment at KEO

Time-series sediment traps at 1800 m and 4800 m of station KEO were recovered and re-deployed.

Mar. 6 Recovery
Mar. 7 Deployment
Temporal variability in Total Mass Flux at 1800 m and 4800 m (preliminary result）

○The first data from 1800 m
●Missing nutrients source in the subtropical region
●Origin of terrestrial materials including micro plastic
●Interannual variability in settling particles

Details of the cruise observations (2): Experiments of primary production

Primary production of phytoplankton were measured in subarctic and subtropical waters in winter.

Phytoplankton incubation experiment
Rain-chase observations were conducted to evaluate the impact of rainfall-induced aerosol deposition into the ocean on primary production.
Comparison of vertical primary production in subarctic (KNOT) and subtropical (KEO) waters during winter and early summer (preliminary result). KNOT and KEO stations were in bloom and stratification conditions, respectively, in summer.

Topics

Topic 1: Effective CO2 transport to the ocean interior in the North Pacific Subarctic Gyre

Background

Particulate Organic Carbon (POC) plays a crucial role in atmospheric CO2 transport to the ocean interior. For better understanding the global carbon cycle, the intensity of POC vertical transport, i.e. the Biological Carbon Pump (BCP), should be quantified precisely.

Knowledge gap

What mechanism control the intensity of the BCP ?

This study

Vertical change in POC flux in the North Pacific Subarctic gyre (station K2) and Subtropical gyre (station S1) were compared and the mechanism to control the BCP was discussed.

Honda MC (2020) Effective Vertical Transport of Particulate Organic Carbon in the Western North Pacific Subarctic Region. Front. Earth Sci. 8:366. doi: 10.3389/feart.2020.00366

Topic 2: Subtropical blooms dictated by water column stability in the northwestern Pacific

Background

Phytoplankton blooms observed between winter and spring in the northwestern Pacific subtropics.

Knowledge gap

Less observational knowledge compared to the summer bloom in the central Pacific subtropics.

This study

Blooms by episodic stratification in winter, seasonal stratification in early-spring, stratification breakdown in late-spring, with smaller bloom when winter mixing is weak and larger bloom when it is strong.

Matsumoto, K., Y. Sasai, K. Sasaoka, E. Siswanto, M. C. Honda (2021), The formation of subtropical phytoplankton blooms is dictated by water column stability during winter and spring in the oligotrophic northwestern North Pacific. Journal of Geophysical Research: Oceans,126, e2020JC016864. https://doi.org/10.1029/2020JC016864

Topic 3: Development of satellite-based near-real-time observing system

Background

The Asian coastal waters are surrounded by densely populated countries and are vulnerable to climate changes.

Knowledge gap

Eutrophication and red tide outbreaks are common problems that lead to ecological, economic, and societal adverse impacts in the Asian coastal waters.

This study

For the purpose of monitoring ocean color properties, particularly red tide outbreaks, development of a near-real-time satellite-based observing system (NRT-OS) that covers the Asian waters has been initiated. The NRT-OS will relay NASA/MODIS moderate-resolution (1000-m) and Japanese GCOM-C/SGLI high-resolution (250-m) data/images through the Japan-Asia Coastal Monitoring System web (JASCOMS). Red tide and eutrophication algorithms are now being developed to be implemented in this system.