气候与环境演变中的非线性关系——以末次冰期为例

通过末次冰消期国内外实例,说明在气候和环境演变中广泛存在非线性关系,简单地将辐射量增大→气温增高→海面上升→岸线后退视作线性系统,会导致错误的模式和错误的预测。由于非线性反馈的结果,当末次冰消期辐射量最大时,反而出现新仙女木期突然变冷事件,在我国也已发现相应或近似事件的证据;冰后期海面随气候转暖的上升,同样也包含曲折和反复;海面上升在某些河口可以促使沉积加速,岸线并不向后退。

NONLINEAR INTERACTIONS IN CLIMATIC AND ENVIRONMENTAL EVOLUTION:EXAMPLES FROM THE LAST DEGLACIATION

The climatic and environmental system is highly nonlinear in nature,and each link inthe chain of interactions increase of isolation→climate warming→sea-level rising→retreat ofcoastline has its own nonlinear feedback.Failure to realize the complexity of the interactionscan lead to erroneous models and prediction.Though ultimately the Milankovitch orbital forcing is responsible for glacial-interglacialcycles,the warming process during the last deglaciation does not always follow the increasingisolation.The abrupt cooling event “Younger Dryas” occurred just at the maximum of postgla-cial summer isolation at 60°N,suggesting a nonlinear feedback related obviously to the reor-ganization of oceanic circulation and the changes in CO₂ budget.As shown by recent studies inChina,the Younger Dryas event or its analogues have been recognized in the Transfer Func-tion based paleo-SST of Core V36-06-3 taken from the northern slope of the South China Sea（19°00.5′N,116°05.6′E,water depth 2809m）,in the marine transgression curve based on drillholes at the eastern end of the subaerial delta of the Changjiang （Yangtze） River to the east ofShanghai,as well as in the susceptibility curve from a loess profile at Baxie,Gansu Province,and in water-level fluctuations of the Dai Hai Lake,Nei Monggol,although all these occur-rences are still awaiting more precise datings.An adequate knowledge of geographic distri-bution of the event is of great significance for correct understanding of its origin.Nonlinearity is shown to be inherent in the climate/sea-level interactions.The sea level ris-ing process near Shanghai,for example,has a reverse excursion early in the last deglaciation.The nonlinear response of coast-line migra ion to the sea-level fluctuations is demonstratedon an example from the South Alligator River in northern Australia.According to Chappell（MS）,the mid-Holocene sea-level rising there has given rise to intensified deposition of ma-rine sediments in the river area,and the resulted aggregation of mangrove swamps,keepingpace with the rising sea-level,has compensated the effects of marine transgression.