Reconstructing Late Quaternary climate variability in the tropical Andes – Gordon Bromley, Brenda Hall
Field parties: Gordon Bromley, Kurt Rademaker, Peter Strand, Ben Gross, Matt Kohler, Claire Todd (Pacific Lutheran University), Matthew Hegland (PLU), Matthew Schmitt (PLU), Brian Donahue (PLU), Kim Martineau (Lamont-Doherty).
Funding provided by Dan & Betty Churchill and the National Science Foundation
This ongoing investigation, which began in 2006, is utilising the geologic record of glaciation preserved in the southern Peruvian Andes in order to improve our understanding of past climate variability in the tropics. In contrast to higher latitudes, the tropical climate record is virtually unknown and outstanding questions remain, including the precise timing of the last glacial maximum (LGM), the magnitude of LGM cooling in the tropics, and the occurrence of abrupt climate events (such as the Younger Dryas and Antarctic Cold Reversal) during the last glacial termination. Even less is known of how the steep precipitation gradients inherent to the Andes might have influenced the tropical response to these important events.
We are exploiting the abundance of moraines preserved at sites in both the humid and arid Peruvian Andes to reconstruct both the timing and magnitude of Late Quaternary climate changes. These landforms record past periods when glaciers were more extensive than today and form the basis for palaeo-snowline reconstruction and glacial chronology, using surface-exposure dating. At Nevado Coropuna, located in the arid Cordillera Occidental, we are employing cosmogenic 3He to date andesitic erratics deposited during and since the LGM. Helium samples are being run at Lamont-Doherty Earth Observatory. Meanwhile, at Laguna Aricoma, located in the relatively humid Cordillera Oriental, we are using cosmogenic 10Be to date quartzite and granite surfaces in glacial contexts. Beryllium samples are prepared at Lamont-Doherty Earth Observatory. Although these chronologies are works in progress, our results to date are compelling and already are offering valuable insights into patterns of glaciation – and therefore climate variability – from the depths of the last ice age to the present interglacial. Moreover, we have documented considerable differences in the magnitude of snowline lowering at the LGM between arid and humid sites. A key challenge now is to determine whether this pattern relates to climate or to other factors, such as topography. Our work also hints at the potentially fundamental role of the tropics in global abrupt climate change, an avenue we are developing further in the northern Andes of Colombia in conjunction with the Escuela de Ingeniería de Antioquia, Medellín.
To learn more about this project, and associated archaeologic investigations in Peru, follow this link to a short video prepared in 2013 by Kim Martineau of Lamont-Doherty Earth Observatory: http://www.ldeo.columbia.edu/news-events/climate-peruvian-andes-early-humans-modern-challenges. Additionally, we maintained a research blog of our 2011 field season that was archived as part of Columbia Earth Institute’s “State of the Planet” series (http://blogs.ei.columbia.edu/tag/peru-glaciers/).
Chronology of the Loch Lomond Advance in Scotland – Gordon Bromley, Aaron Putnam
Field parties: Gordon Bromley, Aaron Putnam, Kurt Rademaker.
Funding provided by Dan & Betty Churchill and the Lamont Climate Center
This research is aimed at placing firm chronologic constraint on the last pulse of glaciation in the British Isles, known locally as the Loch Lomond Advance. Being located on the margin of the North Atlantic Ocean, former glaciers in the Scottish Highlands will have been highly sensitive to changes in upwind sea-surface temperature and circulation changes. Thus, the Scottish moraine record is an unparalleled tool for deciphering the terrestrial impact of North Atlantic ‘stadial’ events such as the Younger Dryas. Specifically, we aim to ascertain whether or not the Loch Lomond Advance was a direct response to cold ocean conditions during the Younger Dryas stadial. Thus far, we have focused on collecting and dating basal sediments overlying Loch Lomond tills at Rannoch Moor – the former centre of the Loch Lomond ice cap – in order to provide robust minimum dates for the end of the event. Our approach incorporates detailed field mapping and sediment coring, using a Livingstone corer, to reach the earliest post-glacial sediments on Rannoch Moor. Plant macrofossils extracted from the basal sections of the cores have been radiocarbon dated to provide the minimum-limiting chronology for deglaciation. Going forward, we will use cosmogenic 10Be surface-exposure dating to refine the chronology and resolve directly the timing of this late-glacial event, from its maximum extent through deglaciation.
Terminal Pleistocene glaciation of high-altitude Andes near Chivay, Peru: Implications for tropical paleoclimate and Paleoindian-age people – Scott Braddock, Paul Pluta
Field Team: Scott Braddock, Gordon Bromley, Paul Pluta
The tropical Andes are an ideal location to study past abrupt climate change and the impacts such events imposed on Paleoindian populations. Previous work by Sandweiss et al. (1998) in southern Peru suggested the glacial history of this region influenced when the Chivay source of obsidian became available to early populations. While continuing to determine the pattern of southern Peru’s late Pleistocene climate, we also can help answer whether glacial fluctuations made certain important resources inaccessible during this period.
Our proposed research aims to use glacial geology to address how glaciers behaved during the Terminal Pleistocene in the tropical Andes and how the impacts of ice-marginal fluctuations may have influenced human-environment interactions in southern Peru. To address these questions we propose to determine: (1) whether glacial features in the Chivay region date to the Younger Dryas, or show a different signal correlated to the Antarctic Cold Reversal, and (2) if the Chivay obsidian source was covered by a glacial readvance at the end of the Pleistocene, making the site inaccessible to early South Americans, such as the occupants of Quebrada Jaguay.
Field work was completed this summer during July. The team successfully collected samples from glacial erratics that will be used to determine when local glaciers had receded and exposed the Chivay source of obsidian.
Funding for this field expedition provided by Dan and Betty Churchill Exploration Fund.
Dating the LGM in Tierra del Fuego – Jennifer Lennon, Brenda Hall
Field Team Members: Brenda Hall, Alex Introne, Mike Kaplan, Jen Lennon, Tom Lowell, Aaron Putnam
Chilean Tierra del Fuego, March 25, 2013- April 2, 2013
Funding provided by Dan and Betty Churchill
Introduction One implication of Milankovitch’s orbital theory of ice ages is that glacial cycles should be asynchronous between the northern and southern mid-latitudes, because insolation forcing is out of phase between the two hemispheres. However, evidence at present points to a near-synchronous termination (a rapid transition from glacial to interglacial conditions) at the end of the last glacial maximum (LGM) in both hemispheres. One way to test hypotheses for the ice ages and their terminations is to create detailed glacial chronologies that record the timing of past ice fluctuations.Globally distributed records allow one to make geographic comparisons to isolate potential mechanisms that drive ice ages.
The glacial history of southernmost South America is not well-documented at present, but is important for understanding the characteristics of the Southern Hemisphere ice age and termination. During March and April of 2013, a field team from the University of Maine (along with colleagues from Lamont-Doherty Earth Observatory and the University of Cincinnati) traveled to Bahía Inútil, Chile, to collect data to improve the local glacial record, and that allow for the testing of larger hypotheses concerning the termination of the last ice age. The field work consisted of glacial mapping and the collection of rock samples from boulder surfaces for surface-exposure age dating. This technique results in precise dates of glacial landform construction. When a quartz-bearing boulder melts out of a receding ice lobe, the boulder surface is exposed to cosmogenic rays. When these rays strike the surface, spallation reactions occur within the quartz and produce 10Be atoms at known production rates.
Location and Setting The Bahía Inútil field area lies at 53°S and 69ºW on the equatorial side of the Antarctic Frontal Zone. The Straights of Magellan and Bahía Inútil are large marine inlets surrounded on all sides by low elevation coastal areas. During the LGM (~26,000 -18,000 years before present) ice flowed through the Straits of Magellan from mountains to the west and south, such as Cordillera Darwin. The moraines adjacent to Bahía Inútil represent the fluctuations of a major ice lobe during the LGM until the start of the last termination. The moraines examined during this field season lie just to the south of Bahía Inútil, on the Chilean side of Tierra del Fuego. The landscape is covered with heath-like vegetation and few trees. The moraines here are subtle, appearing as boulder strings on low, curving ridges. The windward surfaces of the boulders are very weathered.
Field Season The field party arrived in Punta Arenas, Chile, on the 25th of March, and by the next day, we had 4×4 vehicles loaded to the brim with field team members and equipment. To get to the field site, we first took a ferry across the Straits of Magellan. We drove south through Tierra del Fuego until arrival in Bahía Inútil. Most of Tierra del Fuego is privately owned, and the field work completed during this expedition was done on two large estancias, Estancia Tres Hermanos, and Estancia Rosa Irene, with landowner permission.
On Estancia Tres Hermanos, we sampled ten ideal boulders from two closely-spaced moraines. Estancia Rosa Irene contained a younger moraine set than those found at Estancia Tres Hermanos, and we took twenty-three samples from this location.For the purposes of cosmogenic surface exposure dating, an ideal boulder should be in place, and have its original surface. In addition, the boulders should be shielded only minimally. Corrections can be made for shielding effects, but to introduce the least error, our field crew tried to select boulders where shielding was minimal. After each boulder was approved by the field team, a surface-slab was taken using either a small charge or a set of wedges and shims. The surface characteristics of the boulder and its geomorphological setting were then recorded in field notebooks, photographed, and logged as points on a Trimble GPS.
Conclusions The samples collected at Bahía Inútil are currently being processed at Lamont-Doherty Earth Observatory for 10Be surface-exposure dating. When geochemical processing at LDEO is complete, the samples will be sent to Lawrence-Livermore National Laboratory, where the 10Be/9Be ratio will be measured. This dating method is highly precise, and should result in a new chronology of glacial recession in Tierra del Fuego, allowing for the testing of larger hypotheses that aim to solve the mystery of the ice ages.
This field excursion was made possible by the generous support of the Churchill Fund- Thank you!
Holocene climate change – McMurdo Sound region, Antarctica –Scott Braddock, Brenda Hall
Field Team – University of Maine (Brenda Hall, Scott Braddock, Audra Norvaisa) University of California – Santa Cruz (Paul Koch, Rachel Brown, Jon Nye)
The aim of this project is to create a Holocene water temperature reconstruction for the Ross Sea region of Antarctica using oxygen isotopes from scallop shells (Adamussium colbecki). Shells found in raised marine terraces and deltas span from the late to mid Holocene, roughly the last 6000 years. Results from this study will provide a proxy for fluctuations in water temperature after the retreat of grounded ice in the Ross Sea. Samples were collected along the Scott Coast in January, 2013, with a field team consisting of three members from the University of Maine and three members from the University of California – Santa Cruz (UCSC). I will use oxygen isotope analysis and radiocarbon dating of the scallop shells to develop this temperature reconstruction and travel to UCSC’s stable isotope laboratory over the summer to begin analyzing data.
An understanding of temperature variations in the Ross Sea region during the Holocene will provide better insight into how the West Antarctic Ice Sheet and local alpine glaciers may react to changing climate in the future.
Funding provided by the National Science Foundation.