skip to main content

Title: Cosmogenic nuclide techniques
Cosmogenic nuclide techniques have advanced the geosciences by providing tools for exposure age dating, burial dating, quantification of denudation rates and more. Advances in geochemistry, accelerator mass spectrometry and atom trap trace analyses are ushering in a new cosmogenic nuclide era, by improving the sensitivity of measurements to ultra- trace levels that now allow new applications of these techniques to numerous Earth surface processes. The advances in cosmogenic nuclide techniques have equipped the next generation of geoscientists with invaluable tools for understanding the planet, but addressing pressing needs requires rising to an even greater challenge: imbuing within the cosmogenic community, and the geosciences as a whole, a commitment to justice, equity, diversity and inclusion that matches our dedication to scientific research. In this Primer, we review the state of the art and recent exciting breakthroughs in the use of cosmogenic nuclide techniques, focusing on erosion factories over space and time, and new perspectives on ice sheet stability. We also highlight promising ways forward in enhancing inclusion in the field, as well as obstacles that remain to be overcome.
; ; ; ; ; ;
Award ID(s):
Publication Date:
Journal Name:
Nature reviews methods primers
Sponsoring Org:
National Science Foundation
More Like this
  1. The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10 Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is inmore »stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.« less
  2. Important information about past climates can be determined from reconstructed equilibrium line altitudes (ELA) of mountain paleoglaciers, specifically the temperature and precipitation accompanying a glacier in equilibrium. Previous reconstructions of Late Pleistocene ELAs of mountain glaciers across the western United States have been used to infer the pattern of temperature and precipitation change across the region, although most of the work was based on presumed ages and limited mapping of glacial deposits and landforms. Cosmogenic nuclide exposure dating of moraines combined with updated mapping and aerial imagery afford an opportunity to revisit the pattern of regional ELAs during multiple episodes of the last Pleistocene glaciation. The goal of this research is to reconstruct ELAs in the same region of previous reconstructions based on glacial sediments that have been dated using cosmogenic nuclide exposure ages. We focus on the large number of glacial valleys with moraines corresponding to the Last Glacial Maximum (LGM; 26.5-19.0 ka). Paleo-ELAs are estimated using the toe to headwall altitude ratio and the accumulation area ratio determined from published glacier reconstructions and existing glacial mapping. Cosmogenic-exposure ages of moraines are compiled from the informal cosmogenic nuclide exposure age database for alpine glacial features (ICE-D Alpine) and representedmore »in a geographic information system along with ELAs for each glacial valley. A reconstructed ELA surface spanning the conterminous western United States is produced using existing algorithms in ArcGIS. Results show reconstructed ELAs generally lower than initially estimated and a larger range of ELAs across the region. In the Sierra Nevada, ELAs increase southeastward, which is consistent with previous estimates, spanning a range from 1800 to 2800 m asl. ELAs rise eastward across the Basin and Range toward the western shore of the area covered by Lake Bonneville, and then decrease eastward toward the Wasatch Mountains. This pattern is inconsistent with previous estimates and may reflect a west-to-east precipitation gradient that differs from modern climate. We discuss this pattern and broader features of the ELA surface of the LGM and later episodes of the last Pleistocene glaciation.« less
  3. Cosmogenic nuclide surface exposure dating and erosion rate measurements in basaltic landscapes rely primarily on measurement of 3He in olivine or pyroxene. However, geochemical investigations using 3He have been impossible in the substantial fraction of basalts that lack separable olivine or pyroxene crystals, or where such crystals were present, but have been chemically weathered. Fine-textured basalts often contain small grains of ilmenite, a weathering-resistant mineral that is a target for cosmogenic 3He production with good He retention and straightforward mineral separation, but with a poorly constrained production rate. Here we empirically calibrate the cosmogenic 3He production rate in ilmenite by measuring 3He concentrations in basalts with fine-grained (~20 lm cross-section) ilmenite and co-existing pyroxene or olivine from the Columbia River and Snake River Plain basalt provinces in the western United States. The concentration ratio of ilmenite to pyroxene and olivine is 0.78 ± 0.02, yielding an apparent cosmogenic 3He production rate of 93.6 ± 7.7 atom g-1 yr-1 that is 20–30% greater than expected from prior theoretical and empirical estimates for compositionally similar minerals. The production rate discrepancy arises from the high energy with which cosmic ray spallation reactions emit tritium and 3He and the associated long stopping distances thatmore »cause them to redistribute within a rock. Fine-grained phases with low cosmogenic 3He production rates, like ilmenite, will have anomalously high production rates owing to net implantation of 3He from the surrounding, higher 3He production rate, matrix. Semi-quantitative modeling indicates implantation of spallation 3He increases with decreasing ilmenite grain size, leading to production rates that exceed those in a large grain by ~10% when grain radii are <150 lm. The modeling predicts that for the ilmenite grain size in our samples, implantation causes production rates to be ~20% greater than expected for a large grain, and within uncertainty resolves the discrepancy between our calibrated production rate, theory, and rates from previous work. The redistribution effect is maximized when the host rock and crystals differ substantially in mean atomic number, as they do between whole-rock basalt and ilmenite.« less
  4. Abstract. We collected a debris-rich ice core from a buried icemass in Ong Valley, located in the Transantarctic Mountains in Antarctica. Wemeasured cosmogenic nuclide concentrations in quartz obtained from the icecore to determine the age of the buried ice mass and infer the processesresponsible for the emplacement of the debris currently overlaying the ice.Such ice masses are valuable archives of paleoclimate proxies; however, thepreservation of ice beyond 800 kyr is rare, and therefore much effort hasbeen recently focused on finding ice that is older than 1 Myr. In Ong Valley,the large, buried ice mass has been previously dated at > 1.1 Ma.Here we provide a forward model that predicts the accumulation of thecosmic-ray-produced nuclides 10Be, 21Ne, and 26Al in quartzin the englacial and supraglacial debris and compare the model predictionsto measured nuclide concentrations in order to further constrain the age.Large downcore variation in measured cosmogenic nuclide concentrationssuggests that the englacial debris is sourced both from subglacially derivedmaterial and recycled paleo-surface debris that has experienced surfaceexposure prior to entrainment. We find that the upper section of the icecore is 2.95 + 0.18 / −0.22 Myr old. The average ice sublimation rate duringthis time period is 22.86 + 0.10 / −0.09 m Myr−1, and the surfaceerosion rate of the debris is 0.206 + 0.013 / −0.017 m Myr−1. Burialdating of the recycled paleo-surfacemore »debris suggests that the lower sectionof the ice core belongs to a separate, older ice mass which we estimate tobe 4.3–5.1 Myr old. The ages of these two stacked, separate ice masses canbe directly related to glacial advances of the Antarctic ice sheet andpotentially coincide with two major global glaciations during the early andlate Pliocene epoch when global temperatures and CO2 were higher thanpresent. These ancient ice masses represent new opportunities for gatheringancient climate information.« less
  5. Abstract The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/-0.22 Ma to 1.06 +0.23/-0.26 Ma, and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastward from 0.60 +0.05/-0.06 Ma to 3.30 +0.30/-0.41 Ma. Our geochronology is used to calculate rapid long-term reverse fault slip rates of 8.6–12.6 mm yr–1 since ca. 1.0 Ma for the San Cayetano fault and 1.3–3.0 mm yr–1 since ca. 1.0 Ma for the Oak Ridge fault, which are both broadly consistent with contemporary reverse slip rates derived from mechanical models driven by global positioning system (GPS) data. We also calculate terrestrial cosmogenic nuclide (TCN)-derived, catchment-averaged erosion rates thatmore »range from 0.05–1.14 mm yr–1 and discuss the applicability of TCN-derived, catchment-averaged erosion rates in rapidly uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly uplifting mountain belts, catchments may attain a quasi-steady-state on timescales of <105 years even if catchment-averaged erosion rates are still adjusting to tectonic forcing.« less