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.
The processes that drive climate change over centuries and millennium during the current warm time, the Holocene, are still poorly understood. Change in incoming solar radiation have been identified as one important component, but significant changes imposed on that trend have multiple possible explanations. These possibilities imply different temporal and spatial evolution. Thus proxies that record both the entire Holocene as well as a single time slice over a wide spatial range can provide key constrains on climate models. Peru’s Quelccaya Ice Cap provides the anchor for a long Holocene record. Glaciers are a sensitive proxy that can yield quantitate temperature changes with appropriate schemes. In that view the ice core record from Quelccaya serves as calibration point. Detailed mapping of glacial features, study of stratigraphic sections, and coring of lake sequences along with dating by radiocarbon and surface exposure techniques revealed a millennium rhythm of the ice cap. During the early Holocene the ice cap was more restricted than at the present as it was from 7,200-5,200; 4,200-3,800; and 1000-800 yr BP with expansion of the ice cap between those times (Fig. 1). Preliminary glacier modeling experiments suggest these expansions reflect <0.5 degree cooling. The timings of expansions and contractions has a strong similarity to glacial sequences in North America and Europe implying these temperatures variations are present across at least the northern hemisphere. The pattern of late Holocene expansions of glaciers across the Andes represent the spatial imprint of the processes that drove millennium climate changes. The Andes span multiple climate regimens and one preliminary research task was to understand if the relative importance of temperature and precipitation differ in these regimes. Surface energy modeling of the atmospheric level between positive snow accumulation and removal show that temperatures dominates, but by varying amounts (Fig. 2). Mapping and dating of four glacier systems indicate that no single combination of temperature and precipitation changes can accommodate the observed glacier length changes. For example temperature ranges from -0.7 to -1.3 degree C. Only climate models that explain this spatial pattern likely have tenable hypothesis to explain the major cooling during the last millennium. The broader impacts relate to improved ability to understand how climate patterns are expressed across the backbone of South America. This work supported students training at all levels. It includes a PhD student who has taken a position at university in Chile. This coupled with collaboration with Peruvian colleges is fostering stronger education and research ties with counties lying along the Andes.
