Ranasinghe P N, Hughen K A, Wijewardhana T U T, Ortiz J D, Kapuge A K I U, Ratnayake Kalpani M, Nanayakkara N U, Hewawasam A L T, Siriwardana Y P S, Kodithuwakku S
Lake Superior State University, Sault Ste. Marie, USA.
Woods Hole Oceanographic Institution, Woods Hole, USA.
Sci Rep. 2024 Sep 27;14(1):22178. doi: 10.1038/s41598-024-71940-z.
Precipitation variations in the tropical Indian Ocean region result from changes in the Indian Summer Monsoon (ISM), as well as convective and cyclonic rainfall. The relative roles of such forcing can be elucidated by constructing robust paleoclimate records, which help to better predict future variability in precipitation due to rising greenhouse gases. This study was carried out using a suite of paleoclimate proxies on a combination of marine and terrestrial sediment cores from Sri Lanka. The sites receive differing amounts of precipitation from the ISM versus convective and cyclone-driven intermonsoon rainfall and allow differentiation of precipitation sources through time. The constructed 80000-year-long precipitation record for the ISM-dominant regions of Sri Lanka shows strong sensitivity to orbital scale insolation variations as well as to millennial-scale events in the North Atlantic region. This precipitation response to external and internal forcings is a result of the combined effects of ISM and Intermonsoon intensity either of which dominated periodically. The strong positive correlation between different periods in the precipitation record and different monthly insolation curves shows that changes in solar insolation due to precession decide the dominant rainfall mechanism in the region, suggesting the ISM dominated after 13 ka (MIS1) while the first intermonsoon dominated between 29 and 13 ka (MIS2) and the second intermonsoon dominated period between 77 and 40 ka.
热带印度洋地区的降水变化是由印度夏季风（ISM）以及对流降雨和气旋降雨的变化引起的。通过构建可靠的古气候记录可以阐明这种强迫作用的相对作用，这有助于更好地预测由于温室气体增加导致的未来降水变化。本研究使用了一套古气候代理指标，对来自斯里兰卡的海洋和陆地沉积岩芯进行了综合分析。这些地点从ISM获得的降水量与对流降雨和气旋驱动的季风降雨不同，并且可以随时间区分降水来源。为斯里兰卡ISM主导地区构建的长达80000年的降水记录显示，其对轨道尺度的日照变化以及北大西洋地区的千年尺度事件具有很强的敏感性。这种降水对外部和内部强迫的响应是ISM和季风强度周期性主导的综合作用的结果。降水记录中不同时期与不同月份日照曲线之间的强正相关表明，由于岁差导致的太阳日照变化决定了该地区的主要降雨机制，这表明ISM在13 ka（MIS1）之后占主导地位，而第一次季风在29至13 ka（MIS2）之间占主导地位，第二次季风主导期在77至40 ka之间。
