Study Of Seasonal And Interannual Variations Of Mid-cretaceous East Asian Paleoclimate

The modern East Asian monsoon?EAM?has been undergoing significant changes under current global warming.In order to better predict future climate change in East Asia,deep-time greenhouse climate characteristics become the hotspot of geosciences,and investigating it is conductive to explore the genetic mechanism of climate change.Utilizing the Community Earth System Model?CESM?,the mid-Cretaceous?90 Ma?is simulated,and the seasonal and interannual variations of the mid-Cretaceous East Asian paleoclimate are discussed,which are compared with geological evidences.The main contents are as follows.I.Simulation of mid-Cretaceous climate with 10 times pre-industrial CO₂ level?2800ppmv?shows that global mean surface temperature?ST?is 25.5°C,with equatorial zonal mean ST 34°C,and decreases toward poles.In the warm mid-Cretaceous,global mean annual precipitation is 3.46 mm/day,exceeding the pre-industrial modeling result?2.63mm/day?.Mid-Cretaceous three-meridional cell structure is similar to that of modern,and strength and positions of pressure belts vary with seasons.II.East Asia is a typical monsoon region in mid-Cretaceous,and the spacial structure of mid-Cretaceous winter/summer atmospheric circulation resembles that of modern EAM,but their precipitation patterns differ from each other.The four-season rainfall pattern at mid-Cretaceous East Asian mid-latitude is similar to that of modern East Asian low-latitude with the most in summer and least in winter,while the four-season rainfall pattern at mid-Cretaceous East Asian low-latitude is similar to that of modern East Asian mid-latitude with the more in spring and summer and less in autumn and winter.III.Mid-Cretaceous East Asian Winter Monsoon?EAWM?shows evident interannual variations,exhibiting opposite phase relationship of mid-to high-latitude?north of 45°N?and low-to mid-latitude?south of 45°N?ST at Asia Paleocontinent,i.e.,in strong?weak?EAWM years,mid-to high-latitude STs increase?decrease?and low-to mid-latitude STs decrease?increase?.Under the background of mid-Cretaceous greenhouse climate,the North Atlantic Oscillation-like?NAO-like?and North Pacific Oscillation-like?NPO-like?exist in Northern Hemisphere.Correlation analysis and Composite analysis indicates that the NAO-like and NPO-like collectively control the interannual variation of mid-Cretaceous EAWM.The influence of the NAO-like at the mid-to high-latitude of Asia Paleocontinent is stronger than that of the NPO-like,but weaker at low-to mid-latitude than NPO-like.IV.Mid-Cretaceous East Asian Summer Monsoon?EASM?shows significant interannual variations,exhibiting out-of-phase relationship of East Asia-Northwest Pacific?EANWP?region,i.e.,in strong?weak?EASM years,precipitation increases?decreases?south of 15°N and at mid-latitude of EANWP region,and decreases?increases?between15³0°N.Under the background of mid-Cretaceous greenhouse climate,the El Ni?o-Southern Oscillation-like?ENSO-like?exists around the equatorial Paleopacific-East Tethys Ocean in winter,summer and autumn.Summer ENSO-like correlates significantly with EASM,and the correlation coefficient is-0.63?99.9%?.Composite analysis indicates that the mid-Cretaceous EASM is weak/strong and precipitation decreases/increases when ENSO-like is in warm/cold phase.