Collaborative Research: Testing Mechanisms for Holocene Climate Change in the Southern Tropical and Mid-Latitude Andes

该合作基金正在收集南半球热带和中纬度地区的古气候代理数据，并利用这些数据来约束全球环流模型（GCM）对气候变化的模拟。通过这种协调努力，这项研究提高了我们对影响全新世气候事件（如小冰河期）的潜在机制的认识。研究人员有三个具体目标：1)利用多种古气候代用物，包括湖泊沉积物中的chironomid和硅藻组合，在最大的热带冰盖秘鲁的Quelccaya冰盖附近建立全新世气候变化的连续记录；2)在南纬~13 ~ 40°的安第斯山脉更大范围内追踪小冰期气候条件；3)利用GCM评估哪些机制假设可以解释重建的古气候波动的地理和时间模式。本研究建立了奎尔卡亚冰冠附近南热带地区全新世古气候和古环境的详细的多代用记录。该年表由放射性碳年龄确定，并辅以地表暴露年龄（10Be），可与北半球和南半球的高纬度记录相比较。除了Quelccaya的时间详细记录外，该研究还提供了南热带和中纬度地区小冰期气候的空间分辨率重建。小冰期安第斯冰川在多种气候条件下波动的更广泛模式也为研究温度和降水对这种波动的相对影响提供了宝贵的数据。这些努力与正在进行的美国国家科学基金会资助的研究（EAR-0902363）相结合，研究巴塔哥尼亚全新世冰川波动，加强两个研究项目。本研究为进一步认识南热带和中纬度地区全新世和近期气候变化提供了古气候代用数据和模拟结果。这项研究测试了小冰期的各种机制。例如，它检查了小冰期太阳强迫模拟的结果，这些结果表明，除了北半球的气候变化之外，热带环流也发生了变化。由于来自Quelccaya冰盖附近的古气候数据跨越了一个受不同边界条件（如南方夏季高日照和低日照）影响的时期，因此应该有可能研究快速气候事件的各种机制。可能的机制包括热带辐合带的纬向转移和El Niño南方涛动（ENSO）的增强/减弱。本研究的广泛影响包括：(1)在一个新的地区（热带安第斯山脉）应用和评价一种有前途的替代方法（chironomid组合），并存档沉积物岩心；(2)加强和建立包括秘鲁佩德罗·塔皮亚博士和智利科学家在内的科学家之间新的国际和跨学科合作；(3)培养研究生和本科生；(4)确保向公众宣传和传播气候变化信息。

This collaborative grant is collecting paleoclimate proxy data from locations in Southern Hemisphere tropical and mid-latitudes and using these data to constrain global circulation model (GCM) simulations of climate change. Through this coordinated effort, the research enhances our knowledge of potential mechanisms which influenced Holocene climate events such as the Little Ice Age. The investigators have three specific aims: 1) developing a continuous record of Holocene climate change near the largest tropical ice mass, Peru's Quelccaya Ice Cap, using multiple paleoclimate proxies, including chironomid and diatom assemblages in lake sediments; 2) tracking Little Ice Age climatic conditions over a broader area of the Andes, from ~13 to 40°S latitude; and 3) using a GCM to evaluate which mechanistic hypotheses explain the geographical and temporal patterns of reconstructed paleoclimatic fluctuations.This research establishes a detailed multi-proxy record of the Holocene paleoclimate and paleoenvironment in the southern tropics near the Quelccaya Ice Cap. Defined by radiocarbon ages and supplemented by surface exposure (10Be) ages, this chronology is comparable with higher-latitude records from both Northern and Southern Hemispheres. In addition to the temporally detailed record from Quelccaya, the research provides a spatially resolved reconstruction of climate during the Little Ice Age in the southern tropics and mid-latitudes. The broader pattern of Little Ice Age Andean glacier fluctuations in multiple climatic regimes also provides valuable data for examining the relative influences of temperature and precipitation on such fluctuations. These efforts interface with ongoing NSF-funded research (EAR-0902363) investigating Holocene glacier fluctuations in Patagonia, enhancing both research projects.This research provides both paleoclimate proxy data and modeling results to further the understanding of Holocene and recent climate change in the southern tropics and mid-latitudes. The research tests various mechanisms for the Little Ice Age. For example, it examines results from modeling of solar forcing during the Little Ice Age which suggest that there were changes in tropical circulation in addition to Northern Hemisphere climate changes. Since the paleoclimate data from near Quelccaya Ice Cap spans a time period influenced by differing boundary conditions, such as high and low austral summer insolation, it should be possible to examine various mechanisms for rapid climate events. Possible mechanisms include a latitudinal shift of the Intertropical Convergence Zone and the strengthening/weakening of the El Niño Southern Oscillation (ENSO).The broader impacts of the research include (1) applying and evaluating a promising proxy (chironomid assemblages) method in a new area (tropical Andes) and archiving sediment cores; (2) strengthening and establishing new international and interdisciplinary collaborations among scientists including Dr. Pedro Tapia of Peru and Chilean scientists; (3) training graduate and undergraduate students; and (4) ensuring outreach and dissemination to the general public of information regarding climate change.