Multi-scale Variations In The Long Time Series Of Phytoplankton From Satellite Data

The relationship between marine ecosystem and climate change has received rising attention. As the main producer of marine ecosystem, phytoplankton is particularly good indicator of climate change in the marine environment. The accumulation of remote sensing data provides a reliable data source for studying the marine multi-scale ecological responses to marine environment. In this thesis, we study the multi-scale variations of chlorophyll a (Chl-a) concentration and timing of phytoplankton bloom in the Western North Pacific (WNP) and Eastern North Indian Ocean (ENIO)(10°S～60°N,75°E～160°E) and their relationship with multiple forcings by utilization of ocean color data, microwave data and in situ data. Specifically, the climatic forcing on the phytoplankton is the key issue that we are concerned about. The results let us futher understand the coupling effect between marine ecosystem and physical processes and provide evidence of how the global warming will change the marine ecosystem in the furture. The main contents and conclusions are as follows:(1) By analyzing the seasonal and interannual variability in Chl-a concentration, most regions of the ENIO and the WNP subtropical grye show a significant downward trend with the rate of less than1%/yr during September1997and December2011. All other regions show a significant upward trend. The annual rate is more than1%/yr in the Yellow Sea, the Bohai Sea and the Okhotsk Sea, even more than4%/yr in some regions. The regions with significant interannual variarion include the tropical Indian Ocean (TIO), the South China Sea (SCS). Pacific Warm Pool (PWP) and the subtropical grye in the Western North Pacific (SG). Short-term climate variability is an important factor that regulating the interannual variation of Chl-a concentration. During the event of El Nino-Southern Oscillation (ENSO) or Indian Ocen Dipole (IOD), the abnormal zonal wind controls the interannual variation of Chl-a concentration in the TIO and PWP. For the SCS, increasing SST during El Nino years induces the decrease of Chl-a concentration while it seems that La Nina events have less impact on the SCS Chl-a concentration. Contrary to the other regions’response to ENSO, the Chl-a concentration is high during El Nino years while low during La Nina years in the SG region. The trend of Chl-a concentration is mainly negatively related to the change of sea surface temperature while has little relationship with sea surface height anomaly and wind speed.(2) By analyzing the seasonal and interannual variability of the timing of phytoplankton bloom, the results show spring bloom starts during March to May and the duration is shorter than50d in the mid-high latitude.Winter bloom starts during Novermber to December and the duration is nearly200d in the subtropical grye in the WNP (20°N-30°N) and northern part of SCS. Summer bloom only occurs in the upwelling regions such as Vietnam and Sri Lanka and begins during May to June. The duration is more than100d. The interannual variability of the timing of phytoplankton bloom is significant in the regions of the Sri Lanka upwelling, the Japan Sea and the Okhotsk Sea but minor in the the subtropical grye in the WNP (20°N-30°N) and northern part of SCS. For the Sri Lanka upwelling region, the southwest monsoon is the main factor that influences the bloom timing and duration. At the same time, the bloom iniation time in this region is also impacted by SST. For the Japan Sea, the spring bloom starts earlier and lasts longer during El Nino years while the situation is contrary during La Nina years. The SST and wind speed modulated by ENSO envents are the driving forcings. However, the influence of La Nina events is weaker than that of El Nino events.The start time of phytoplankton in the El Nino year of2005is late due to the deep mixed layer depth induced by highest average wind speed of all years.(3) The total annual primary production enhancements induced by typhoons during the recent ten years are evaluated. The estimated annual mean carbon fixation in the SCS is0.54Mt while only0.26Mt in the ocean desert of the Western North Pacific and0.21Mt in the continental shelf of the East China Sea. However, only typhoon-forced primary production enhancement in the ocean desert of the Western North Pacific corresponds with climate variability. The contribution tends to be higher during El Nino years while lower during La Nina years.(4) We analyze the extreme phytoplankton blooms in the Bay of Bengal triggered by multiple forcings, which include short-term events such as typhoons and eddies as well as climatic events such as ENSO and IOD. The mechanisms between phytoplankton bloom and multiple forcings can be used as the basis of analysis of similar events in the future.