Browsing by Author "Norton, KP"

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    Controls on 10Be dilution in catchments affected by coseismic landsliding: a 2016 Kaikōura earthquake case-study
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Wilkinson, C; Stahl, T; Jones, K; Fujioka, T; Fink, D; Norton, KP
    The 2016 Mw 7.8 Kaikōura earthquake triggered tens of thousands of landslides across the northern Canterbury and southern Marlborough regions in the South Island of Aotearoa New Zealand. The influence of landslides generated by this earthquake on sediment generation, transport and deposition in stream networks has varied across the region and through time — some catchments show significant and near-immediate responses while others show little to no change despite the extensive landsliding. We measured 10Be concentrations in detrital quartz sands over a two-year period in the Conway River catchment, which has a total area of ~475 km2 and had ~13 M m3 of new landslide material liberated from hillslopes during the 2016 Kaikōura earthquake. Samples for 10Be analysis were collected at the rangefront of the Seaward Kaikōura Mountains and near the catchment outlet on three sampling campaigns between 2017-2018. We also carried out a similar sampling regime in the nearby Hurunui catchment, which was unaffected by the 2016 Kaikōura earthquake. Measured 10Be concentrations were converted to basin wide mean denudation rates using accepted GIS-based elevation and shielding programs. Our results indicate that apparent catchment-wide erosion rates in the Conway River (i) did not change through time, (ii) have remained similar to basin mean erosion rates for the Hurunui, (iii) overlap with the range of values for exhumation rates of the region (from previously published low-temperature thermochronology data), and (iv) are influenced in part by selection of grain size. We also compared our 10Be concentrations for the Conway catchment to values derived by modelling mean landslide 10Be concentrations constrained by local production rates, detailed mapping of all landslides across the catchment, area-volume scaling, and landslide-channel connectivity estimates. Our modelling estimates show that the mean 10Be concentrations derived from landslide sediment would have been sufficient to dilute pre-earthquake catchment-wide 10Be values by up to a factor of 3. We explore various landscape and landslide parameters that may explain the mismatch between measured and modelled 10Be and ascertain that the combination of storage, site specific channel connectivity, and landslide geometries/failure mechanisms likely exert first-order controls on in-situ 10Be concentrations following such a large catchment-wide disturbance event. We conclude that using fluvial quartz grains to characterise catchment response to landsliding and the mass balance of earthquakes, is subject to a number of factors that are highly site-specific. © The Authors
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    Cosmogenic nuclides constrain surface fluctuations of an East Antarctic outlet glacier since the Pliocene
    (Elsevier, 2017-12-05) Jones, JS; Norton, KP; Mackintosh, AN; Anderson, JTH; Kubik, P; Vockenhuber, C; Wittmann, H; Fink, D; Wilson, GS; Golledge, NR; McKay, RM
    Understanding past changes in the Antarctic ice sheets provides insight into how they might respond to future climate warming. During the Pliocene and Pleistocene, geological data show that the East Antarctic Ice Sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior, but oscillating at its marine-based margin. It is currently not clear how outlet glaciers, which connect the ice sheet interior to its margin, responded to these orbitally-paced climate cycles. Here we report new ice surface constraints from Skelton Glacier, an outlet of the East Antarctic ice sheet, which drains into the Ross Ice Shelf. Our multiple-isotope (10Be and 26Al) cosmogenic nuclide data indicate that currently ice-free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past. We use an exposure-burial model driven by orbitally-paced glacial–interglacial cycles to determine the probable ice surface history implied by our data. This analysis shows that: 1) the glacier surface has likely fluctuated since at least the Pliocene; 2) the ice surface was >200 m higher than today during glacial periods, and the glacier has been thicker than present for ∼75–90% of each glacial–interglacial cycle; and 3) ice cover at higher elevations possibly occurred for a relatively shorter time per Pliocene cycle than Pleistocene cycle. Our multiple-nuclide approach demonstrates the magnitude of ice surface fluctuations during the Pliocene and Pleistocene that are linked to marine-based ice margin variability. © 2017 Elsevier B.V.
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    Rapid carbon accumulation in soil rapidly forming in the Southern Alps of New Zealand
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Raines, E; Hua, Q; Dosseto, A; Lukens, CE; Deslippe, JR; Norton, KP
    Biota contribute 3-7 orders of magnitude more potential energy to landscapes than climate or tectonics alone. This potential energy is quantified as the system’s net primary productivity (NPP), i.e., the net gain of photosynthetically sourced carbon. The effects of biological energy on landscape evolution is likely highly non-negligible, yet, has proven difficult to properly quantify in the past. Current methods for quantifying NPP vary in accuracy and can involve careful and costly study over the course of many years. The associated costs are often prohibitive for geomorphic studies. Therefore, NPP is not a commonly included measurement made in such studies. While relating biological to geomorphic processes in rapidly forming soils could help increase the predictive ability of current geomorphic models, a more suitable method for quantifying NPP is required to make this possible. Here, we present a novel method combining uranium and carbon isotopes that can be used for quantifying soil NPP. The study was carried out on a rapidly forming, New Zealand soil. The uranium isotope composition of the soil was used to derive a soil age of 178 years. Given the soil’s age, the soil production rate is 1.7 mm yr-1 which is one of the most rapid every quantified. Geomorphic models fail to predict such rapid soil production by a factor of ~2. Carbon-14 (14C) was also isolated from the same soil and quantified by AMS. The 14C measurements allow for the soil organic carbon (SOC) mean residence time (MRT) to be calculated. Utilizing a commonly employed biogeochemical model, the MRT allows for the calculation of the concentration of SOC as a function of time. In the rapidly forming soil, we measured a SOC content of 536 g-C m-1. Employing MRT and SOC to calculate the expected age of soil yielded a predicted soil age of 408 years. The discrepancy in MRT predicted age and the observed soil age indicates that the biogeochemical model fails to predict the rate of carbon accretion in the rapidly forming soil by a factor of ~2. The work presented here is the first biogeochemical characterization of a soil forming more rapidly than current geomorphic models can accurately determine. Both the observed soil NPP and the soil formation rate exceed current model predictions. It is possible that a causal relationship exists, however, further cocharacterization of biological energy input rates and soil formation rates is needed to test this hypothesis. © The Authors
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    Using in situ 14C to unravel complex exposure histories along the David Glacier, Antarctica
    (Australian Nuclear Science and Technology Organisation, 2021-11-17) Stutz, J; Fülöp, RH; Norton, KP; Mackintosh, AN; Whitemore, R; Yang, B; Smith, AM
    Understanding the past Antarctic Ice Sheet (AIS) is critical to forecast the impacts of future of the AIS and its contribution to sea level rise. Ice sheet models constrained by geological data provide improved confidence in future projections. Both marine and terrestrial geologic data are required for a robust reconstruction of both the extent and thickness of the AIS. On land, cosmogenic nuclides have transformed the ability to constrain reconstructions of the past AIS through time. Highresolution, low-inheritance chronologies focused on large outlet glaciers provide enhanced understanding on the timing, rate and potential mechanisms driving past ice sheet change. Using the ‘glacial dip stick’ approach at each site, we sample glacial debris and bedrock from the local peak down to the modern ice surface. While field sampling strategies and analytical capability continues to improve, ‘complex’ exposure histories remain a common occurrence in practice. Inheritance, or a signal of cumulative exposure, can arise due to burial by cold-based, non-crosive nature of the AIS. At Mt. Kring along the upper David Glacier, previous studies show a distinct mid-Holocene signal of glacier thinning as well as at least two populations of apparent older glacial thinning events. Here, we use 14C measurements on samples suspected of having an inherited signal. We show that samples with >30 ka 10Be exposure ages indeed carry a mid-Holocene 14C exposure age and improve the existing thinning history. This multi-nuclide comparison approach provides a preliminary data set to bolster previous and emerging studies where complex exposure histories occur around Antarctica. © The Authors