Browsing by Author "Smith, JA"

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    A community-based geological reconstruction of Antarctic ice sheet deglaciation since the last glacial maximum
    (Elsevier, 2014-09-15) Bentley, MJ; O'Cofaigh, C; Anderson, JB; Conway, H; Davies, B; Graham, AGC; Hillenbrand, CD; Hodgson, DA; Jamieson, SSR; Larter, RD; Mackintosh, AN; Smith, JA; Verleyen, E; Ackert, RP; Bart, PJ; Berg, S; Brunstein, D; Canals, M; Colhoun, EA; Crosta, X; Dickens, WA; Domack, E; Dowdeswell, JA; Dunbar, R; Ehrmann, W; Evans, J; Favier, V; Fink, D; Fogwill, CJ; Glasser, NF; Gohl, K; Golledge, NR; Goodwin, I; Gore, DB; Greenwood, SL; Hall, BL; Hall, K; Hedding, DW; Hein, AS; Hocking, EP; Jakobsson, M; Johnson, JS; Jomelli, V; Jones, RS; Klages, JP; Kristoffersen, Y; Kuhn, G; Leventer, A; Licht, K; Lilly, K; Lindow, J; Livingstone, SJ; Massé, G; McGlone, MS; McKay, RM; Melles, M; Miura, H; Mulvaney, R; Nel, W; Nitsche, FO; O'Brien, PE; Post, AL; Roberts, SJ; Saunders, KM; Selkirk, PM; Simms, AR; Spiegel, C; Stolldorf, TD; Sugden, DE; van der Putten, N; van Ommen, TD; Verfaillie, D; Vyverman, W; Wagner, B; White, DA; Witus, AE; Zwartz, D
    A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community. © 2014 The Authors. CC BY license
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    Convictfish on the move: variation in growth and trophic niche space along a latitudinal gradient
    (Oxford Academic, 2019-06-30) Miranda, T; Smith, JA; Suthers, IM; Mazumder, D; Cruz, DO; Schilling, HT; Searle, K; Vergés, A
    The range expansion of tropical fish into temperate waters is increasing markedly in response to climate change. Range-expanding fish encounter novel diets and environments, but we know little about how these conditions facilitate or hinder distribution shifts. Here, we quantified relative growth rate, morphometric condition and trophic niche of juvenile Acanthurus triostegus, a dominant range-expanding tropical surgeonfish, at four locations across 10° of latitude off eastern Australia. We related these metrics to differences in temperature and nutritional quality of dominant seaweeds and the epilithic algal matrix. Temperate food sources were richer in nitrogen than tropical diets. Stable isotope analysis (δ13 carbon and δ15 nitrogen) of fish muscle revealed a large trophic niche breadth at the highest latitude indicating a generalist foraging strategy, and more nitrogen-enriched isotopic signatures compared to tropical regions. Fish length was strongly correlated to δ13C in all regions, suggesting an ontogenetic shift in diet independent of latitude. Despite temperature differences of 4°C, fish growth and body condition were similar across tropical and temperate regions. These results suggest that more nutritious temperate diets may compensate for the effects of cooler water temperatures. Neither summer water temperatures nor dietary factors appear to limit the success of juvenile tropical vagrants as they continue to expand their range along eastern Australia. © 2019 ICES/CIEM
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    To fit or not to fit: evaluating stable isotope mixing models using simulated mixing polygons
    (Wiley-Blackwell, 2013-07-01) Smith, JA; Mazumder, D; Suthers, IM; Taylor, MD
    1. Stable isotope analysis is often used to identify the relative contributions of various food resources to a consumer's diet. Some Bayesian isotopic mixing models now incorporate uncertainty in the isotopic signatures of consumers, sources and trophic enrichment factors (e.g. SIAR, MixSIR). This had made model outputs more comprehensive, but at the expense of simple model evaluation, and there is no quantitative method for determining whether a proposed mixing model is likely to explain the isotopic signatures of all consumers, before the model is run. 2. Earlier linear mixing models (e.g. IsoSource) are easier to evaluate, such that if a consumer's isotopic signature is outside the mixing polygon bounding the proposed dietary sources, then mass balance cannot be established and there is no logical solution. This can be used to identify consumers for exclusion or to reject a model outright. This point-in-polygon assumption is not inherent in the Bayesian mixing models, because the source data are distributions not average values, and these models will quantify source contributions even when the solution is very unlikely. 3. We use a Monte Carlo simulation of mixing polygons to apply the point-in-polygon assumption to these models. Convex hulls (mixing polygons') are iterated using the distributions of the proposed dietary sources and trophic enrichment factors, and the proportion of polygons that have a solution (i.e. that satisfy point-in-polygon) is calculated. This proportion can be interpreted as the frequentist probability that the proposed mixing model can calculate source contributions to explain a consumer's isotopic signature. The mixing polygon simulation is visualised with a mixing region, which is calculated by testing a grid of values for point-in-polygon. 4. The simulation method enables users to quantitatively explore assumptions of stable isotope analysis in mixing models incorporating uncertainty, for both two- and three-isotope systems. It provides a quantitative basis for model rejection, for consumer exclusion (those outside the 95% mixing region) and for the correction of trophic enrichment factors. The simulation is demonstrated using a two-isotope study (N-15, C-13) of an Australian freshwater food web. © 2013, Wiley-Blackwell.