Deciphering Past Climate Change in the High Andes
High above the tropical lowlands, the Andes form a formidable topographic barrier separating the coastal deserts in the west from the Amazon rainforest to the east. The Peruvian Andes are the highest peaks in all the tropics and, despite their proximity to the equator, are mantled with snow and ice. However, the glaciers clinging to the summits today are small remnants of much larger ice caps that grew there during the last ice age, when the tropical climate was very different. Since the first people entered these highlands more than 11,000 years ago, glaciers have played a central role in human land use, providing water, supporting rich biodiversity, directing settlement, and even forming a basis for religion. Now, however, as air temperatures continue to rise in response to greenhouse-gas emissions, these glaciers are disappearing rapidly.
How will tropical glaciers respond to global warming and what will be the repercussions for water resources? These questions are central to our project, which is developing records of past glacier behavior in order to determine the sensitivity of the tropical climate to ongoing change. Glaciers are one of the most sensitive and visible indicators of climate change, advancing and retreating in response to small changes in temperature and precipitation. A valuable record of these glacier events lies in the ridges of rubble, called moraines, deposited along the ice margin. Therefore, our first step will be to visit moraines in the Andes and determine their age using cosmogenic surface-exposure dating. With these new data, we can reconstruct both the timing and magnitude of past climate events in the Andes and, subsequently, learn just how the tropics responded to climate change. The second step will be to collaborate with experts at Columbia University and other institutions to incorporate the geologic data in computer models and project future glacier and hydrological scenarios for the tropical Andes.
The fieldwork – documented in this blog feature – will take our field team to sites in both the arid and humid Andes of Peru. We chose this approach because the tropics consist of starkly different environments and we need to know how these diverse zones respond to climate change. This year, we’ll work primarily at Laguna Aricoma in the Cordillera Carabaya, on the wet side of the Andes. During an exploratory visit to the area in 2009 we found a promising moraine record potentially extending from the last glacial maximum to the present. This year, Gordon will be sampling these moraines for cosmogenic dating, thereby producing a high-resolution record of Pleistocene and Holocene glacier fluctuations in the humid Andes. Three weeks at the lake will be sufficient to map and sample the moraines. The next stop is Nevado Coropuna, in the arid western Andes, to conduct similar mapping and sampling work there. At each of these sites, Kurt will be conducting archeology surveys of the surrounding landscape in addition to our geologic research, searching for artifacts and evidence of early human presence. In all, it promises to be a long and highly productive field season and we are looking forward to their dispatches from the high Andes.