Regional differences in decadal changes of diatom primary productivity in the eastern Chinese shelf sea over the past 100 years

Contradicting findings were observed when decadal changes of primary productivity in the eastern Chinese shelf sea were learnt through examination of sediment cores (Lv, 2007; Zhou, 2007; Jin, 2009; Zhao, 2010; Yang et al., 2012). This inconformity may imply the regional differences of decadal environmental changes in different types of seas. To verify the possible regional differences, we examined sediment cores collected in different types of seas in the eastern Chinese shelf sea. 210Pb activity in the sediment was used to estimate sediment rate, while biogenic silica (BSi) was applied to indicate diatom paleoproductivity. And then the decadal change trends of diatom primary productivities (DPP) over the past 100 years in different areas were achieved. Subsequently, the differences in these DPP changes and the possible controlling mechanism were also discussed. Results reveal the presence of regional differences in DPP decadal changes in the eastern Chinese shelf sea. In all coastal seas, DPP followed similar trends before the 1980s; after the 1980s, DPP increased obviously in Shandong coastal waters where no large river mouth exists nearby, but decreased in the Yangtze River estuary. By contrast, in open waters, DPP in the past 100 years followed almost opposite trends against that in Shandong coastal waters. The differences in DPP changes between coastal and open sea areas before the 1980s could be attributed to the distinct influence mechanism of Pacific Decadal Oscillation (PDO) on DPP variation. However, the regional differences of DPP changes after the 1980s were probably attributed to the differences in influence type and intensity of human activities. Summarily, the disproportion of the influence of human activities and PDO could induce regional differences in DPP decadal changes in the Chinese shelf sea. These actual and probably general existences of regional differences prompt us to comprehensively assess long-term environmental changes in the complex shelf seas, rather than rebuild paleoenvironmental change patterns by using only one or limited sediment cores.