Collaborative Research: The Pulse of Holocene Glaciations in New Zealand's Southern Alps

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Human civilizations have developed during the Holocene epoch that began approximately 11,500 years ago. The Holocene is classically considered a period of outstanding climate stability. However, recent paleoclimate records suggest that abrupt climatic shifts did occur within the Holocene and that some of those coincided with twists and turns in human history. Although directly influencing human habitat, temporal and spatial patterns, natural variability and driving mechanisms of Holocene climate are not well understood, hampering reliable evaluation of current climate change. Holocene climate swings were large enough to impact humans but small enough to get lost in the ?noise? of natural variability in most geological climate records. Glaciers in many areas on Earth, however, have responded sensitively and quickly to the Holocene climate changes and have produced distinctive landforms, or moraines. The age of these landforms directly indicates when these continental Holocene climate changes occurred, but so far a robust, uniform and reliable dating tool for moraines was lacking. Recent progress in the field of cosmogenic dating demonstrates that moraines can be dated with unprecedented accuracy throughout the Holocene period, allowing novel perspectives on the characteristics of Holocene climate changes. This grant is an interdisciplinary, multi-group effort to date the Holocene moraine sequences in New Zealand?s Southern Alps by applying high-precision 10Be surface exposure dating (SED) combined with local calibration of the 10Be production rate, to evaluate the underlying climate changes, and to analyze the results within an interhemispheric perspective. New Zealand appears to be an ideal location for such a study: (i) terrestrial paleoclimate data from southern mid-latitudes, influenced by tropical and polar signals, are sparse and urgently needed to evaluate the regional footprint of climate changes; (ii) up to five or more different Holocene moraines are preserved in front of individual glaciers, allowing insight into the details of the Holocene climate changes in southern mid-latitudes, including the ?Little Ice Age?; (iii) glaciers in southern mid-latitudes respond to atmospheric/oceanic changes (no continental climate effects); (iv) the general landform setting and rock type is well suited for our SED approach; (v) a suite of detailed glacier landform (geomorphologic) maps of New Zealand?s Southern Alps have been developed, paleo-snowlines have been reconstructed in detail, and glaciological modeling studies are ongoing by our collaborators, making this one of the better investigated glacier records on Earth. To achieve a regional, detailed chronology of glaciations on a prime site in southern mid-latitudes, we will combine large valley glacier systems with smaller valley glaciers on both, the semi-arid east flank as well as on the very humid west flank of the Southern Alps, evaluating the importance of different precipitation regimes for glaciations. We will compare our glacial chronologies to the few records available from New Zealand and elsewhere, testing the regional to inter-hemispheric character of the Holocene glacial pulse-beat. One of the foci herein will be the time period known as the ?Little Ice Age, where detailed historical records are available for European glaciers. Intellectual Merit and Broader Impacts: We expect to greatly improve our understanding of drivers of Holocene glacier fluctuations in southern mid-latitudes by tackling key questions such as: Were Holocene glaciations inter-hemispheric? Were atmospheric circulation changes involved in driving these events or were both, global and regional forces involved? This project represents a unique opportunity to create a reference data set of Holocene glacial fluctuations in southern mid-latitudes. These data should be of high value to calibrate climate models and to the broad community of climate scientists and glacial geologists. We further develop the method of cosmogenic 10Be dating and our geochemical/geochronological tool-kit will be applicable to future Holocene moraine-dating projects. The new atlas of geomorphic maps of the central Southern Alps will be updated with our glacial chronologies during this project. In addition to extending the LDEO/CU curriculum, a female master student will be educated, several early-career scientists will be involved, and high school students and teachers (?Lamont-Doherty Secondary School Field Program?) will actively participate in this project. Beyond standard data dissemination, we will present the project at public events, such as the annual L-DEO Open House (typically 4,000 visitors) and will use our close contacts to New York public media to seek coverage of this project in newspapers (New York Times) and television (History Channel). The project will foster the fruitful collaboration between the Lamont-Doherty Earth Observatory, the University of Maine, the UC Berkeley, and the GNS Science, NZ.