Radiative Properties Of Euphotic Layer And Their Impacts On Satellite Remote Sensing Of Ocean Primary Productivity

Ocean primary productivity (OPP) controls the exchange of carbon dioxide at the air–sea interface and plays an important role in the global carbon cycle and climate change. The objective of this dissertation is to study long-time OPP in the whole China seas by satellite remote sensing and the impacts of variation in optical properties of various waters on chlorophyll a (Chl a in short) concentration and OPP through radiative transfer model in the euphotic layer. At the same time, we analyzed the spatiotemporal variability of OPP in the China seas and tried to give the answer to explain the variability. In addition, the probable effects of Asian dust year after year on ocean ecosystem were studied preliminarily. The study in this dissertation can complement the spatiotemporal limitation of in situ investigation, and it's also very important to understand the biogeochemical processes and the probable climate and environment effects. Moreover, the study on probable impacts of Asian dust on Chl a concentration and OPP will be an implication to the study on the indirect climate and environment effects of dust which was still not concerned so much, and can be took as the basis of further study on this problem.There are 4 parts in this dissertation: to establish the retrieval model for OPP in the China seas and its accuracy analysis after introduction of the principle and methods of remote sensing of ocean color and OPP; to study the impacts of various ocean waters on remote sensing of OPP using sensitivity experiments and radiative transfer model; to analyze the spatiotemporal variability of OPP in the China seas and its possible reasons; to study the effects of Asian dust on ocean ecosystem in the China seas preliminary. The first part is the basis of the latter three parts.In the first part, the principle of remote sensing of ocean color and OPP was introduced first and the retrieval methods of OPP was summarized, then the modified Vertically-Generalized Productivity Model (VGPM) which is the very popular model and the most usable for primary production estimation was selected to establish OPP retrieval model in the China seas. We discussed the factors influencing the accuracy of OPP in detail and summarized the result based on the analysis of the difference between data from remotely sensed and in situ measurements. The results show that Chl a concentration, euphotic layer depth and the maximum photosynthetic rate are the most important factors that influence the accuracy of remote sensing of OPP in the China seas and the trends of OPP in the China seas still can be reflected by OPP estimated through the modified VGPM.In the second part, sensitivity experiments was done by using radiative transfer model in the euphotic layer to study the impacts of variation in optical properties of various waters on remote sensing of Chl a concentration and OPP. The results indicate: for the water with different constituents, the potential error of Chl a concentration and OPP will increase along with the increasing of error of remote sensing reflectance. When the Chl a concentration was in the range of 0.2-1 mg m -3, we can get the best results no matter what algorithms were selected; if not, none of these methods can be expected to get the compatible accuracy. Moreover, the error of OPP decreases along with the decreasing of total suspended substance concentration. The difference of OPP caused by uniform and non-uniform Chl a profile can be 71% in the South China Sea (SCS) and 29% in the Yellow Sea (YS), respectively.In the third part, the OPP in the China seas from 1998 to 2005 was estimated by the modified VGPM, and then its spatiotemporal variability together with the relationship between OPP and some physiochemical environmental factors were analyzed. The results show: the OPP in the Bohai Sea, northern YS, southern YS, northern East China Sea (ECS), southern ECS, and SCS has obvious seasonal variation, and two peaks distribution of primary production with the larger of the first peak was also clear (it appeared in early summer and fall in the Bohai Sea, spring and fall in the YS and ECS, winter and summer in the SCS, respectively). The lowest OPP was occurred in summer in the southern ECS and SCS, while in winter in the other sea areas. Temperature and light penetrating into the water (it relates to radiance on the sea surface and transparency) are the most important factors which influence the spatiotemporal variability of OPP in the Bohai Sea, YS and ECS, while in the SCS nutrients are the most important factor.In the fourth part, the probable effects of Asian dust deposition to the YS and SCS on phytoplankton growth and OPP were discussed by using the data of Chl a concentration, SST and aerosol index from remotely sensed and OPP retrieved by us. The main results show: the promotion impacts of Asian dust on phytoplankton growth and OPP in the oligotrophic open ocean are very notable, while that in the coastal waters are relatively small maybe due to its eutrophic environment; Asian dust may initiated the early spring bloom in the YS; the increasing of Chl a concentration and OPP after a delay of about one to two weeks as Asian dust deposition to the YS and SCS is clearly seen from several typical long-range distance dust events in the year of 1998, 2001, 2002 and 2006; and it'll delay about one month just during a few dust storm events.The innovation of this dissertation is as follows:○1 The retrieval model for OPP in the China seas was established by using the modified VGPM which is the very popular model and the most usable for primary production estimation, and then the spatial and long-time temporal variability of OPP was analyzed, which can complement the spatiotemporal limitation of in situ measurement.○2 The influence of variation in optical properties of various waters on the accuracy of OPP retrieval was studied through radiative transfer model in the euphotic layer, which may be more sufficient to determine the level of uncertainty of OPP product.○3 The probable effects of Asian dust on chlorophyll and OPP in the China seas during recent ten years were discussed in this dissertation, and the date, days and intensity of Asian dust storm deposition to ocean were analyzed using the satellite remote sensing aerosol index data compared with the detail records of strong and very strong dust storm, which maybe catch the dust storm deposition to ocean more accurately, and consequently become more reliable basis for studying the effects of dust on ocean.We try to find out the rule of the spatiotemporal variability of OPP in the China seas by satellite remote sensing, expect to uncover the probable effects of various waters on the uncertainty of remote sensing of OPP, and attempt to find out the primary factor. In addition, we expect to uncover the rule of"fertilization"effects of Asian dust on ecosystem in the YS and SCS after deposition to the ocean through long-distance transportation, which need to be studied and confirmed further in future.