Hokkaido University · Earth and Planetary Sciences
Professor Hisatomo Waga's research lab specializes in Arctic marine ecology and remote sensing, focusing on the impacts of climate change on phytoplankton dynamics, sea-ice properties, and marine ecosystem structure. The lab investigates spatiotemporal variations in phytoplankton blooms—particularly spring and fall blooms—using satellite-derived chlorophyll-a data and advanced radiative transfer modeling. Key research directions include understanding the role of mesoscale eddies in shaping phytoplankton size structure, monitoring sediment-laden sea ice through spectral albedo analysis, and improving predictions of species shifts using phytoplankton size structure dynamics. The lab integrates satellite observations with biophysical modeling to address critical questions in polar oceanography and ecosystem responses to environmental change.
Figures are computed from collected data and may differ slightly.
Phytoplankton blooms in the Pacific Arctic have been characterized as a huge single bloom in spring. However, several studies have reported recent increases in the occurrence of fall blooms during the period after dissipation of the spring bloom. Here, we explored spatiotemporal variations in the occurrence of fall blooms in the region, using satellite remote-sensing data for 2003–2017. Seasonal time-series variation in satellite-derived chlorophyll-a concentrations (chla) was modeled using a Ga
Sediment-laden sea ice is a ubiquitous phenomenon in the Arctic Ocean and its marginal seas. This study presents a satellite-based approach at quantifying the distribution of sediment-laden ice that allows for more extensive observations in both time and space to monitor spatiotemporal variations in sediment-laden ice. A structural-optical model coupled with a four-stream multilayer discrete ordinates method radiative transfer model was used to examine surface spectral albedo for four surface ty
Abstract The impact of mesoscale eddies on phytoplankton communities attracts considerable research attention because phytoplankton play numerous roles in marine ecosystems. Using remote sensing techniques, this study considered a synoptic relationship between phytoplankton size structure, which is a determinant of energy transfer efficiency in marine ecosystems, and mesoscale eddies, which are ubiquitous ocean features. We found clear spatial variation in the impacts of mesoscale eddies on phyt
The Arctic is experiencing rapid changes in sea-ice seasonality and extent, with significant consequences for primary production. With the importance of accurate monitoring of spring phytoplankton dynamics in a changing Arctic, this study further examines the previously established critical relationship between spring phytoplankton bloom types and timing of the sea-ice retreat for broader temporal and spatial coverages, with a particular focus on the Pacific Arctic for 2003-2019. To this end, ti
Species distributions are changing with various rates and directions in response to recent global warming. The velocity of sea surface temperature (SST) has been used to predict species migration and persistence as an expectation of how species track their thermal niches; however, several studies have found that evidence for species shifts has deviated from the velocity of SST. This study investigated whether estimation of the velocity of shifts in phytoplankton size structure using remote sensi
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