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Fieldwork Methods of the U.S. Antarctic Search for Meteorites Program

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Fieldwork Methods of the U.S. Antarctic Search for Meteorites Program 2 Fieldwork Methods of the U.S. Antarctic Search for Meteorites Program Ralph P. Harvey, John Schutt, and Jim Karner 2.1. INTRODUCTION 1957 International Geophysical Year. The global and developmental nature of that effort led to the high level The U.S. Antarctic Search for Meteorites (ANSMET) of scientific activity in Antarctica that continues today. program has recovered more than 20,000 meteorite speci- During those early years, three meteorites were discov- mens since fieldwork began in 1976. The methods ered during geological surveys: Lazarev, an iron recov- employed during fieldwork have evolved considerably over ered in two fragments from the Humboldt Mountains in that interval in response to demand, logistical support, January of 1961; Thiel Mountains, a pallasite recovered and an improved understanding of the links between in two fragments in December of the same year; and Antarctic meteorite concentrations and their geographical Neptune Mountains, a single iron recovered from the and glaciological setting. This chapter describes how Pensacola Range in February of 1964. Both Lazarev ANSMET fieldwork has evolved over the years to pro- and Neptune Mountains were discovered on mountain duce the current meteorite recovery methods and discusses slopes during geological surveys and were not associated how they relate to the complex phenomena of Antarctic with any obvious glacial processes [Tolstikov, 1961; meteorite concentrations, both in theory and in practice. Turner, 1962; Ravich and Revnov, 1963; Duke, 1965]. Thiel Mountains, on the other hand, was a harbinger of 2.2. ANSMET FIELD SEASONS YESTERDAY the future; the two fragments were found on “hard, irreg- AND TODAY ularly cupped glacier ice” to the northeast of Mount Wrather, associated with morainal debris, as described 2.2.1. ANSMET’s Place Among Modern Antarctic by Ford and Tabor [1971]. These authors also noted that Meteorite Recovery Efforts the association of the specimens with morainal debris implied that the specimens had been transported from Meteorites have played a role in Antarctic science since their original fall site, and that the weathering state of the earliest years of the twentieth century. The first mete- the specimens implied that abrasion in the cold, dry kata- orite recovered from Antarctica, about 10 cm across and batic winds of the polar plateau was extremely effective fully fusion crusted, was found by one of Douglas as a local mechanism of erosion. Their observations Mawson’s field parties in 1912, lying on hard snow on the proved prescient; the Thiel Mountains pallasite deserves Adelie Coast [Mawson, 1915]. F. L. Stillwell, a geologist consideration as the first meteorite recovered from an in the field party, immediately recognized the rock as a Antarctic meteorite concentration surface (as later recov- meteorite and studied it in detail after the expedition eries from the region would confirm). Unfortunately, it returned to Australia [Bayly and Stillwell, 1923]. Four was the only meteorite located at that time, and thus the decades later cooperative international scientific explo- concentration at Thiel Mountains would not be recog- ration of the Antarctic continent commenced with the nized until 1982 [Schutt, 1989]. There is little ambiguity as to the event that revealed Department of Earth, Environmental, and Planetary Science, the existence of Antarctic meteorite concentrations. On Case Western Reserve University, Cleveland, OH, 44106-7216 21 December 1969, Renji Naruse of the tenth Japanese 35 Seasons of U.S. Antarctic Meteorites (1976–2010): A Pictorial Guide to the Collection, Special Publication 68, First Edition. Edited by Kevin Righter, Catherine M. Corrigan, Timothy J. McCoy and Ralph P. Harvey. © 2015 American Geophysical Union. Published 2015 by John Wiley & Sons, Inc. 23 0002150018.indd 23 05/09/2014 16:02:44 24 35 SEASONS OF U.S. ANTARCTIC METEORITES (1976–2010) Antarctic Research Expedition (JARE-10) was one of with durations ranging from as many as six seasons to as several glaciologists establishing a network of survey few as one. Grant proposals may request support for field stations in the East Antarctic ice sheet to allow the study seasons dedicated to systematic meteorite recovery from of glacial movement. As they extended their survey across known sites (hereafter called a systematic activity), recon- a blue icefield uphill from the Yamato (Queen Fabiola) naissance efforts dedicated to improving our under- Mountains, they found a total of nine meteorite speci- standing of poorly known or previously unvisited sites mens [Yoshida et al., 1971; Yoshida, 2010). Within a few (hereafter called a reconnaissance or recon activity), or years, mounting numbers of meteorite recoveries by the some combination of these. A typical proposal will there- Japanese eventually convinced the United States Antarctic fore include a list of sites prioritized from among poten- Program (USAP) to begin supporting active searches, as tial targets based on our understanding of each site’s described in chapter 1 [Marvin, 2014 (this volume)]. potential. The highest-priority fieldwork targets are, not As of this writing, ANSMET has recovered more surprisingly, those we think will yield the most meteorite than 20,000 meteorites, but these numbers account for specimens. However, this is typically based on prior expe- only part of the program’s success. Consistent initial rience at the site, which is always incomplete during early characterization of recovered specimens, curation at the visits. More practical issues such as logistical availability highest level, and rapid, cost-free availability have given can trump potential meteorite yield. For example, when a ANSMET meteorites unique value within the planetary remote helicopter camp allows us to reach otherwise materials research community, as described in chapter 3 inaccessible locations, those targets become a higher pri- [Righter et al., 2014 (this volume)]. ority; and when aircraft support is predicted to be limited, The early successes of the U.S. Antarctic meteorite we may choose targets demanding fewer flight hours. program quickly led to increasing demand for new spec- Recon and systematic targets are both mixed into the imens and to the well-supported, institutionalized pro- long-term plan; the former typically result in fewer mete- grams of recovery in place today. With a strong backbone orite recoveries but are essential to ensure a continuous of aerial logistics, U.S. expeditions have ranged widely supply of new specimens. On a few occasions we have across Antarctica, predominantly in East Antarctica also adjusted the recon/systematic activity mix to reduce along the Transantarctic Mountains. ANSMET has stress on the curatorial system, favoring recon activities been one of the most active governmentally-supported when a characterization backlog is growing. The desire meteorite recovery programs, with 45 independent for geographical separation between ANSMET field field parties deployed to more than 75 different sites parties (to minimize the effects of individual weather sys- during 36 seasons of fieldwork (Figure 2.1 a through e). tems) is also considered. Every ANSMET proposal also Continued demand for specimens recovered by ANSMET includes alternate targets for either style of activity, has been the primary driver for annual field parties, allowing the project to adjust to rapid changes in USAP which are enabled by improvements in remote sensing of logistics and programmatic issues. polar regions, an increased understanding of meteorite Meteorite concentration sites tend to occur on exposed concentrations, and better access to remote locations. blue ice in a variety of specific geographical and glacio- The fieldwork has evolved with these changes, resulting logical settings; the characteristics of these icefields and in a field program that is highly adapted to available meteorite concentration mechanisms are discussed in logistics and the needs of the planetary materials detail in Harvey [2003]. Identification of such sites through community. This chapter documents the field practices examination of maps and imagery has been a natural first that have helped ANSMET support research through step in ANSMET’s work since the program began. USAP- the past four decades. produced topographic maps and aerial photography doc- umenting much of the Transantarctic Mountains became 2.2.2. Preseason Planning and Site Selection available throughout the 1960s and 1970s, and during ANSMET’s early years these served as a primary means U.S. activities in the Antarctic are carried out within for identification of meteorite concentration sites. These the U.S. Antarctic Program (USAP), funded and maps, however, were primarily meant to serve naviga- managed by the Office of Polar Programs (OPP) of the tional and geological needs, and do not document blue National Science Foundation. During its history, ice. Similarly, while aerial photography coverage was ANSMET has been supported through USAP, both excellent, many blue ice areas were visible only in low- directly (through OPP grants) and indirectly (through angle oblique images that mask their full extent. The most logistical support funded by NASA). As a result, planning powerful “remote sensing” tool employed by ANSMET for any given season may begin as many as seven years in this era was opportunistic reconnaissance flights, dur- before deployment (at the time a grant is funded). Grants ing which field personnel would sit glued to the windows supporting
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