Activity in 2015

Cruise observation in FY2015

The following three observational cruises were conducted.

  • (1) M/V Blue Fin/NOAA-PMEL (2015.8.28～9.10)
    　　Subtropical region in the northwestern Pacific Ocean
    　　Recovery and redeployment of the sediment trap at stn. KEO

  • (2) R/V Shinsei-maru (KS-15-13: 2015.10.6～10.16) 　Off Fukushima
    　 　Recovery and redeployment of the sediment trap at stn. F1
    　 　(Investigation of radionuclides derived from nuclear accident)

  • (3) R/V Mirai (MR15-05：2015.12.22～2016.1.12)
    　　Eastern Indian Ocean
    　　Relationship between aerosol and marine ecosystem

Topics

（１）Study of Missing Source of Nutrients to support primary productivity in the oligotrophic region ー Time-series sediment trap experiment at KEO station and analysis of NOAA-KEO buoy data -

Time-series sediment trap was turned around during NOAA cruise in August-September 2015. Chemical analysis of collected settling particles and analysis of NOAA-KEO meteorological / physical oceanographic data started.


（２）Impact assessment of aerosol into marine ecosystem

Aerosol dissolution experiment

To estimate the impact of aerosol into marine ecosystem, we started an experiment of phytoplankton incubation with an aerosol dissolution by using the seawater of KEO site.

Phytoplankton growth experiment in response to an aerosol input

Observational cruise in the eastern Indian Ocean

Estimations of phytoplankton composition and primary productivity were conducted at MR15-05 cruise. We evaluate the impact of nutrient input into marine ecosystem via aerosol or upwelling in the eastern Indian Ocean.

Experiment of primary productivity

（３）Visiting scientist at the South China Sea Institute of Oceanology

As a visiting scientist at the South China Institute of Oceanology, Chinese Academy of Sciences from August 24 to September 25, 2015, a research collaboration to investigate the impacts of tropical cyclone passage and El Nino on phytoplankton biomass variability was conducted.

Changes of MODIS Chlorophyll and SST due to the passage of tropical cyclone
Spatial variation of correlations between Nino3.4 (index of El Nino) and Chlorophyll (a), SST (b), meridional winds (c), and zonal winds (d). During El Nino, anti-cyclonic wind circulation occurred (c, d) leading to downwelling favorable condition which causes SST increase (b). Decreased in chlorophyll during El Nino (a) was thus likely ascribed to reduction of nutrients associated with strengthened stratification and/or water mass convergence. Panel (e) shows mean surface current during El Nino exhibiting several anti-cyclonic circulations.

（４）The 3rd Asian Workshop on Ocean Color 2015

The 3rd Asian Workshop on Ocean Color 2015 was held from 8 to 10 December 2015 in Miyoshi Memorial Hall, JAMSTEC. Attended by scientists from China, Japan, Korea, US, and southeast Asian countries, new research collaborations have been established among the participating countries.

Research result

Investigation of radiocesium in the ocean emitted from Fukushima Daiichi Nuclear Power Plant (FDNPP) accident ー Re-suspension and lateral transport of radiologically contaminated seafloor sediment -

Buesseler, K.O., C.R. German, M.C. Honda, S. Otosaka, E.E. Black, H. Kawakami, S.J. Manganini and S.M. Pike (2015) Tracking the fate of particle associated Fukushima daiichi cesium in the ocean off Japan. Environmental Science and Technology 49, 9807-9816, doi: 10.1021/acs.est.5b02635.
（2015.8.15 Press release）

→ When will radiocesium disappear from seafloor sediment off Fukushima? ? ?

Possible contribution of aerosols from wildfires in enhancing ocean primary productivity during positive Indian Ocean Dipoles (+IODs)

Siswanto, E (2015) Atmospheric deposition—Another source of nutrients enhancing primary productivity in the eastern tropical Indian Ocean during positive Indian Ocean Dipole phases. Geophysical Research Letters, 42, doi:10.1002/2015GL064188.

Primary productivity in the eastern tropical Indian Ocean increases significantly during the positive phase of Indian Ocean Dipole. Such an increase is widely considered to be ascribed to elevated nutrients due to coastal upwelling. This work however indicates that besides upwelled nutrients, deposition of aerosols from wildfires might also be important source of nutrients enhancing ocean primary productivity.

Long-term trend of chlorophyll in the northwestern Pacific Ocean

Siswanto, E, Honda MC, Matsumoto K, Sasai Y, Fujiki T, Sasaoka K, Saino T (2016) Sixteen-year phytoplankton biomass trends in the northwestern Pacific Ocean observed by the SeaWiFS and MODIS ocean color sensors. Journal of Oceanography. doi:10.1007/s10872-016-0357-1

Chlorophyll in high latitudes of northwestern Pacific Ocean has tended to increase in recent 16 years (1997 to 2013). Such an increasing trend in chlorophyll was likely attributed to increasing trend in sea surface temperature that promoted phytoplankton net growth. The trend was likely also modulated by weakened Aleutian Low pressure.

K2S1 project・seasonal variation of primary productivity

K. Matsumoto, O. Abe, T. Fujiki, C. Sukigara and Y. Mino (2016) Primary productivity at the time-series stations in the northwestern Pacific Ocean: Is the subtropical station unproductive?, Journal of Oceanography, doi: 10.1007/s10872-016-0354-4

In the subtropical region, photosynthetically assimilated carbon was largely lost via respiration and dissolved organic carbon (DOC). However, if the released DOC is accounted for as primary production, the location of subtropical station “S1” is suggested as more productive region, contrary to the traditional expectation.