Late Holocene ITCZ Shifts from Sedimentary Lipids on Tropical Pacific Islands

这一建议将支持重建过去2000年热带辐合带（ITCZ）位置的尝试，方法是测量来自太平洋上2°S和10°N之间13个岛屿上淡水、咸水和高咸水盆地的沉积物中的氢同位素比率，这些沉积物年代明确，快速积累。尽管来自树木年轮和高山冰川的令人信服的证据表明，在中纬度北部出现了公元800-1300年的中世纪温暖期和公元1400-1850年的小冰期，但人们对与这些事件相关的气候变化的幅度和地理足迹知之甚少，尤其是在热带地区。然而，由于从那里散发出大量的潜热和水汽，热带地区在气候系统中发挥着中心作用，而且存在这样一种可能性，即过去2000年的中纬度气候异常是由热带地区的气候变化引起或放大的。无论是在这两个事件中的被动反应者还是主动参与者，该团队的初步结果表明，热带降雨模式在这些事件中发生了很大的变化。脂质氢同位素数据表明，在小冰期，与现代和中世纪暖期相比，加拉帕戈斯群岛（1°S, 90°W）是湿润的，而华盛顿岛（5°N, 160°W）和帕劳岛（7°N, 134°E）是干燥的。对这些发现最简单的解释是，在小冰期，ITCZ位于其目前平均位置~7°N的南部。在中世纪暖期，加拉帕戈斯群岛和华盛顿岛比现在更干燥，这表明ITCZ当时位于其现在位置的北部。为了证实这些发现并获得对过去2000年太平洋ITCZ变化的详细了解，需要在现代ITCZ范围内北部和南部的湖泊和泻湖中进行年代际分辨率的脂质äD记录，并排除直接的季风和大陆影响。马绍尔群岛和吉尔伯特群岛（15°N至3°S， 162°E至177°E）是理想的，在ITCZ的北部和南部跨越准对称的降雨梯度，并有许多合适的淡水和咸水盆地。克利珀顿环礁（北纬10°，西经109°）和圣诞岛（北纬2°，西经157°）以及加拉帕戈斯群岛、华盛顿岛和帕劳提供了重建ITCZ位置变化所需的剩余地点。本项目将资助一名女研究生，并促进环境研究方面的本科生教育。拟议中的研究将促进与几个太平洋岛国、法国和厄瓜多尔的科学家和政府的国际合作。

This proposal will support an attempt to reconstruct the position of the Intertropical Convergence Zone (ITCZ) during the last 2,000 years by measuring hydrogen isotope ratios in lipids from well-dated, rapidly accumulating sediments from freshwater, saline and hypersaline basins on 13 islands between 2°S and 10°N across the Pacific Ocean.Despite convincing evidence from tree rings and mountain glaciers for a Medieval Warm Period 800-1300 A.D. and a Little Ice Age 1400-1850 A.D. in Northern middle latitudes, there is little known about the magnitude and geographic footprint of the climate changes associated with those events, especially in the tropics. Yet the tropics play a central role in the climate system owing to the massive fluxes of latent heat and moisture that emanate from there, and the possibility exists that mid-latitude climate anomalies of the last 2,000 years were caused or amplified by climate changes in the tropics. Whether passive responders or active players in these two events, initial results from this team suggest that tropical rainfall patterns underwent large changes during those episodes. Lipid hydrogen isotope data indicate that the Galapagos (1°S, 90°W) were wet, and both Washington Island (5°N, 160°W) and Palau (7°N, 134°E) were dry during the Little Ice Age compared to the modern and Medieval Warm Periods. The simplest interpretation of these findings is that the ITCZ was located south of its present mean position of ~7°N during the Little Ice Age. Drier than modern conditions in both the Galapagos and Washington Island during the Medieval Warm Period suggest that the ITCZ was positioned north of its present location at that time. In order to confirm these findings and gain a detailed understanding of Pacific ITCZ changes during the last 2,000 years, decadally-resolved lipid äD records from lakes and lagoons within, north and south of the modern ITCZ range, and removed from direct monsoonal and continental influences, are required. The Marshall and Gilbert Islands (15°N to 3°S, 162°E to 177°E) are ideal, spanning quasi-symmetric gradients of rainfall to the north and south of the ITCZ and having many suitable fresh and saline basins to core. Clipperton Atoll (10°N, 109°W) and Christmas Island (2°N, 157°W), along with the Galapagos, Washington Island and Palau provide the remainder of sites needed to reconstruct changes in the position of the ITCZ.This project will support a female graduate student and facilitate the education of undergraduate students in environmental research. The proposed research will foster international collaborations with scientists and governments in several Pacific Island nations, France and Ecuador.