Long-term change study on biogeochemical cycles and marine ecosystems: developing New Ocean Provinces through observational data analysis and modeling
Sanae Chiba, JAMSTEC
We investigate long-term variations in biogeochemical properties and the structure of marine ecosystems, as well as regional differences across the North Pacific using in situ and satellite observation data sets. The goals of our study are: (1) to reveal the regionally specific responses of biogeochemical and ecological processes to the specific climatic forcing and global environmental changes including warming trends, and understand physical, chemical and ecological properties of each region that cause such regional differences; (2) to evaluate how changes in ecosystem structure (species diversity, functional diversity, and food web structure, etc.) in response to various environmental stresses would influence regional biogeochemical processes, such as air-sea CO2 flux and vertical carbon export. Through these studies, we would like to contribute to the development of new ocean provinces that NEOPS aims to propose for sustainable ecosystem management.
By analyzing pCO2 and nutrients data obtained from volunteer ship observations, and chlorophyll a (Chl a) data obtained from ocean color satellite observations, we have developed biogeochemical provinces and Chl a provinces for the end of FY2014 (Figure); we divided the North Pacific into 10~15 sub-regions based on the seasonal variation pattern of pCO2 and nutrients for the biogeochemical provinces (Yasunaka et al., 2013 & 2014), and that of satellite chlorophyll a for the Chl a province, respectively. In our proposed provinces, the boundaries between sub-regions are not fixed but rather vary interannualy depending on spatio-temporal variations in hydrographic conditions. Therefore, those boundary areas could indicate the regions in which ecosystems might be susceptible to environmental change. We also proposed alternative ocean provinces, with boundaries determined based on a combination of distribution of the phytoplankton functional type (size-based: micro, nano and pico) and the distribution of respective limiting nutrients (N, P, Si and Fe) (Figure). Using these relationships between phytoplankton types and nutrients, we are conducting a prognostic study to see how future climatic change would affect global distribution of nutrients and subsequently phytoplankton compositions.
Yasunaka, S., Y. Nojiri, S. Nakaoka, T. Ono, H. Mukai and N. Usui (2013), Monthlymaps of sea surface dissolved inorganic carbon in the North Pacific: Basin-wide distribution and seasonal variation, J. Geophys. Res. Oceans, 118, 3843–3850, doi:10.1002/jgrc.20279.
Yasunaka, S., Y. Nojiri, S. Nakaoka,T. Ono, F. A. Whitney and M. Telszewski (2014), Mapping of sea surface nutrients in the North Pacific: Basin-wide distribution and seasonal to interannual variability, J. Geophys. Res. Oceans, 119, 7756–7771, doi:10.1002/2014JC010318.