Holocene Climate Change Recorded Mainly By Pollen From Northern Beibu Gulf

The Northern Beibu gulf is a natural semi-closed shallow gulf, which is bounded by Chinese Guangxi coast, peninsula Leizhou of Guangdong, western Hainan, northern Vietnam. It is one of the most significant areas by Asian monsoon, so palaeoclimate research helps to understand climate change process in monsoon area, and rapid climate change events and their driving mechanism.At present, the research about palaeoclimate of Northern Beibu gulf is very few, and the dating precision is also very low. Besides, high sedimentation rate of Beibu gulf during the Holoeene has been shown in previous studies, which makes it possible to exact information from sea sedimenis.,so it has certain theoretical value to study palaeoclimate here.This paper studied particle size, pollen and 210Pb of surface sediment adequately, as a basis for explaining the palaeoclimate characteristic in core. Then we chose two samples of surface sediments from core Q24 (6.25 m) and core Q43 (5.13 m) to 210Pb date, and nine samples to AMS14C date, in order to build the sedimentary-date framework. Then according to the significance of climate proxies pollen, grain size, charcoal, C/N,δ13C, XRF, the history of the environmental changes of Northern Beibu gulf in the past 8.50 cal. kyr BP was reconstructed. The main results of this study include the followings:1.The surface pollen regularities of distribution in Northern Beibu gulfThe sea area,where drilling is located, is affected by monsoon, land stream, tidal, the residual current, so the environmental condition is relatively complicated, and makes pollen distribution rule is very complex. When sediment particle size is small, pollen concentration generally is high; the content of fern spores and pinus become higher and herb lower as farther from the offshore.2.The climate change process and modelThis research use particle size as the proxy of the hydrodynamic of sedimentary environment, and C/N,813C,Al/Ti as the proxies of the land-originchange, and pollen and charcoal as the main proxy of the climate change. We extract information about climate change by correcting the influence of sedimentary environmental and land-originc changes on terrestrial pollen distribution.Qiongzhou Strait was opened fully about 8.50 cal. kyr BP and modern Beibu Bay was formated. Study area was in the stable shallow marine environment, so environmental impacted the climate proxies weakly.According to sedimentary facies and AMS14C age framework, we can found that the deposition of Q24 core during 8.5-4.0 cal. kyr BP was continuous, and Q43 core recorded mainly 4.0 cal. kyr BP deposition, so comprehensive this two cores about the climate and sedimentary environment, we recoveried the climate change process since 8.50 cal. kyr BP:In the study area of core Q24, before 7.84 cal. kyr BP, the climate is humid and warm; during 7.84～7.36 cal. kyr BP, the temperature and humidity are declined; and during 7.36～6.51 cal. kyr BP, the temperature gradually increased, at the same time the humidity is down, but the Sediment grain sizeand other changes inenvironmental indicators,three sub-stages can be identified:6.51-6.00 cal. kyr BP, the climate was a little cooler and wetter,6.00-5.80 cal. kyr BP, it need further information to separate of climate change,5.80-4.09 cal. kyr BP, the climate was warmer; during 4.09-1.84 cal. kyr BP, Because there was only one undisturbed samples in this stage sampling, so we cannot achieve high resolution research. the climate characteristics is cool and dry; during 2.20-1.84 cal. kyr BP the climate was cooler and drier; during 1.84-1.40 cal. kyr BP, the temperature is still low, but humidity gradually increased; during 1.40 -0.33 cal. kyr BP, the climate characteristics is warm and humid.3. The Northern Beibu gulf recorded rapid climate change events and its driving mechanismAccording to partical size, Al/Ti,δ13C, pollen volume concentration, pollen flux, RCC events 7.8-8.0 cal. kyr BP,5.8-6.0 cal. kyr BP,1.4-1.8 cal. kyr BP was recorded in Northern Beibu gulf, Global RCC events of 7.8-8.0 cal. kyr BP,5.8-6.0 cal. kyr BP,1.4-1.8 cal. kyr BP are associated with the solar radiation and Thermohaline Current(THC). Besides,1.4-1.8 cal. kyr BP event may be the main reason that couse continuous wars and regime change frequently in Wei, Chin and the South and North Dynasties.