三亚鹿回头岸礁区人类活动及其对珊瑚礁的影响

通过在三亚鹿回头岸礁区开展人类活动的现场调查,发现礁区目前人类活动主要为以船捕鱼钓鱼、个人涉水捕鱼、采挖螺贝和潜水为主的水域活动和以养殖、餐饮为主的沿岸活动;人类活动强度和分布密度保持较低水平,水下人类活动印迹反映出过去礁区相对较频繁的人类活动状况。认为人类活动是导致三亚鹿回头珊瑚礁衰退的主要原因。基于以往定性资料,利用层次分析法计算了人类活动影响因子权重,并根据人类活动等级估算其影响指数,评价人类活动对珊瑚礁的影响。结果显示,近40年来人类活动对三亚鹿回头珊瑚礁总体为负面影响,但影响程度呈下降趋势,其中,上世纪70、80年代人类活动负面影响大,90年代小,目前的负面影响程度较小。主要原因在于上世纪90年代建立的三亚珊瑚礁国家级保护区和珊瑚礁立法保护,以及逐步加强的日常管理和环保宣传。但当前珊瑚礁仍面临不断增加的各类污染物排放活动的巨大威胁。     

基于高频观测数据的徐闻青安湾海滩对台风“贝碧嘉”的响应研究

风暴是造成海滩剧烈变化的重要因子。由于观测环境的恶劣,目前极少有风暴过程中海滩响应的现场高频观测工作。本研究在2018年台风“贝碧嘉”期间对徐闻青安湾海滩开展了历时6天半的高频观测,获得了全时水动力要素和164组逐时海滩滩面高程变化数据。通过分析表明:(1)青安湾海域风暴增水及波浪受控于海南岛?雷州半岛特有的地形地貌和台风“贝碧嘉”的多变路径,增水稳定在0.38～0.5 m之间,而波高先由0.78 m衰减至0.43 m,再增加至0.56 m;(2)海滩剖面地形变化总体表现为滩肩侵蚀,形成水下沙坝,滩肩响应过程分为快速向下侵蚀、缓慢侵蚀至最大值、振荡回淤恢复3个阶段,台风期间滩肩振荡恢复幅度可达最大侵蚀深度的1/4;(3)海滩的风暴响应过程主要由4个模态耦合而成:第一模态体现大潮滩肩侵蚀生成水下沙坝过程;第二模态体现风暴滩肩侵蚀,补偿大潮滩肩侵蚀位置和进一步促进沙坝形成过程;第三模态揭示了波浪二次破碎位置的上冲流和离岸底流使泥沙发生双向输移过程;第四模态表明台风大浪使得碎波带内泥沙大量悬浮,在沿岸流和离岸流作用下部分悬沙进入深水区,可能造成海滩泥沙的永久亏损。     

南海北部珊瑚生长率对4.2 ka气候事件的记录

The 4.2 ka event that occurred during the period from 4 500–3 900 a BP was characterized by cold and dry climates and resulted in the collapse of civilizations around the world. The cause of this climatic event, however, has been under debate. We collected four corals(Porites lutea) from Yongxing Island, Xisha Islands, South China Sea, dated them with the U-series method, and measured the annual coral growth rates using X-ray technology. The dating results showed that the coral growth ages were from 4 500–3 900 a BP, which coincide well with the period of the4.2 ka event. We then reconstructed annual sea surface temperature anomaly(SSTA) variations based on the coral growth rates. The growth rate-based SSTA results showed that the interdecadal SSTA from 4 500–3 900 a BP was lower than that during modern times(1961–2008 AD). A spectral analysis showed that the SSTA variations from4 500–3 900 a BP were under the influence of El Ni?o-Southern Oscillation(ENSO) activities. From 4 500–4 100 a BP, the climate exhibited La Ni?a-like conditions with weak ENSO intensity and relatively stable and lower SSTA amplitudes. From 4 100–3 900 a BP, the climate underwent a complicated period of ENSO variability and showed alternating El Ni?o-or La Ni?a-like conditions at interdecadal time scales and large SSTA amplitudes. We speculate that during the early and middle stages of the 4.2 ka event, the cold climate caused by weak ENSO activities largely weakened social productivity. Then, during the end stages of the 4.2 ka event, the repeated fluctuations in the ENSO intensity caused frequent extreme weather events, resulting in the collapse of civilizations worldwide. Thus, the new evidence obtained from our coral records suggests that the 4.2 ka event as well as the related collapse of civilizations were very likely driven by ENSO variability.