Mangrove forest degradation indicated by mangrove-derived organic matter in the Qinzhou Bay,Guangxi,China,and its response to the Asian monsoon during the Holocene climatic optimum

The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum（HCO）, using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources： mangrove-derived, terrigenous,and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope（δ13Corg） and the molar ratio of total organic carbon to total nitrogen（C/N）. The percentage of mangrove-derived organic matter（MOM） contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.

Was the 4.2 ka Event an Anthropogenic Disaster?

The article describes a possible impact of demographic explosion during the Neolith on local ecosystems and on the global climate as well as the role of this explosion in aggravating the course of 4.2 ka cooling event. A possible role of human activity in changing the pattern of mid-latitudes westerlies, monsoons and Walker circulation throughout the Holocene is analyzed. It is explained why during the Holocene Climatic Optimum (HCO) monsoons could have been weaker than today, not stronger, as it is commonly stated. It is described how during the HCO the humid Tibetan Plateau could have repelled the Indian monsoon to the west and the East Asian monsoon to the north. The explanation for weaker El Ni&#241o-Southern Oscillation (ENSO) during HCO is proposed.

Mammal diversity during the Pleistocene-Holocene transition in Eastern Europe

Fossil record data on the mammal diversity and species richness are of importance for the reconstruction of the evolution of terrestrial ecosystems during the Late Pleistocene-Holocene transition.In Eastern Europe,the transformations during the Pleistocene-Holocene transition consisted mainly in changes in zonal structure and local fauna composition(Markova&Kolfschoten 2008).We investigated the species richness and the an­alogues of theα,βdiversity indexes(in the sense of Whittaker 1972)of large and medium size mammals for 13 climate-stratigraphic units dating to the Late Pleistocene and the Holocene,from the Hasselo Stadial(44-39 kBP)to the Subatlantic period and the present day.The biological diversity of the Last Glacial Maximum(LGM)and the Holocene thermal optimum was investigated in more detail using information about all mamma­lian taxa(PALEOFAUNA database;Markova 1995).One of our results show that theα,βdiversity values show only a negative correlation with the temperature conditions during the Late Pleistocene,the period that is char­acterized by the so-called‘Mammoth Fauna’complex.For the Holocene faunas the diversity indexes are nearly independent from physical conditions;theαdiversity index decreased and theβdiversity index increased.The relatively lowαdiversity and highβdiversity indexes for the present-day faunas are referred to the decrease of the population number of some forest species in historical time and the increase of the dominance of unspecial­ized species or the species connected with intra-zonal ecosystems.The study shows furthermore the occurrence of several East European‘centers’with a high mammal diversity,which are relatively stable during the Pleis­tocene-Holocene transition.The orientation of the boundaries between the large geographical mammal assem­blages depended,particularly in the northwestern part of Eastern Europe,on the expansion of the Scandinavian ice sheet.