Browsing by Subject "Geosciences, Multidisciplinary"
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Item Open Access A baseline paleoecological study for the Santa Cruz Formation (late–early Miocene) at the Atlantic coast of Patagonia, Argentina(Palaeogeography, Palaeoclimatology, Palaeoecology, 2010-06) Vizcaíno, SF; Bargo, MS; Kay, RF; Fariña, RA; Di Giacomo, M; Perry, JMG; Prevosti, FJ; Toledo, N; Cassini, GH; Fernicola, JCCoastal exposures of the Santa Cruz Formation (late-early Miocene, southern Patagonia, Argentina) between the Coyle and Gallegos rivers have been a fertile ground for recovery of Miocene vertebrates for more than 100 years. The formation contains an exceptionally rich mammal fauna, which documents a vertebrate assemblage very different from any living community, even at the ordinal level. Intensive fieldwork performed since 2003 (nearly 1200 specimens have been collected, including marsupials, xenarthrans, notoungulates, litopterns astrapotheres, rodents, and primates) document this assertion. The goal of this study is to attempt to reconstruct the trophic structure of the Santacrucian mammalian community with precise stratigraphic control. Particularly, we evaluate the depauperate carnivoran paleoguild and identify new working hypotheses about this community. A database has been built from about 390 specimens from two localities: Campo Barranca (CB) and Puesto Estancia La Costa (PLC). All species have been classified as herbivore or carnivore, their body masses estimated, and the following parameters estimated: population density, on-crop biomass, metabolic rates, and the primary and secondary productivity. According to our results, this model predicts an imbalance in both CB and PLC faunas which can be seen by comparing the secondary productivity of the ecosystem and the energetic requirements of the carnivores in it. While in CB, the difference between carnivores and herbivores is six-fold, in PLC this difference is smaller, the secondary productivity is still around three times that of the carnivore to herbivore ratio seen today. If both localities are combined, the difference rises to around four-fold in favour of secondary productivity. Finally, several working hypotheses about the Santacrucian mammalian community and the main lineages of herbivores and carnivores are offered. © 2010 Elsevier B.V. All rights reserved.Item Open Access A formal Anthropocene is compatible with but distinct from its diachronous anthropogenic counterparts: a response to W.F. Ruddiman’s ‘three flaws in defining a formal Anthropocene’(Progress in Physical Geography, 2019-06-01) Zalasiewicz, J; Waters, CN; Head, MJ; Poirier, C; Summerhayes, CP; Leinfelder, R; Grinevald, J; Steffen, W; Syvitski, J; Haff, P; McNeill, JR; Wagreich, M; Fairchild, IJ; Richter, DD; Vidas, D; Williams, M; Barnosky, AD; Cearreta, A© The Author(s) 2019. We analyse the ‘three flaws’ to potentially defining a formal Anthropocene geological time unit as advanced by Ruddiman (2018). (1) We recognize a long record of pre-industrial human impacts, but note that these increased in relative magnitude slowly and were strongly time-transgressive by comparison with the extraordinarily rapid, novel and near-globally synchronous changes of post-industrial time. (2) The rules of stratigraphic nomenclature do not ‘reject’ pre-industrial anthropogenic signals – these have long been a key characteristic and distinguishing feature of the Holocene. (3) In contrast to the contention that classical chronostratigraphy is now widely ignored by scientists, it remains vital and widely used in unambiguously defining geological time units and is an indispensable part of the Earth sciences. A mounting body of evidence indicates that the Anthropocene, considered as a precisely defined geological time unit that begins in the mid-20th century, is sharply distinct from the Holocene.Item Open Access An improved approach to age-modeling in deep time: Implications for the Santa Cruz Formation, Argentina(Bulletin of the Geological Society of America, 2020-01-01) Trayler, RB; Schmitz, MD; Cuitiño, JI; Kohn, MJ; Bargo, MS; Kay, RF; Strömberg, CAE; Vizcaíno, SF© 2019 Geological Society of America. Accurate age-depth models for proxy records are crucial for inferring changes to the environment through space and time, yet traditional methods of constructing these models assume unrealistically small age uncertainties and do not account for many geologic complexities. Here we modify an existing Bayesian age-depth model to foster its application for deep time U-Pb and 40Ar/39Ar geochronology. More flexible input likelihood functions and use of an adaptive proposal algorithm in the Markov Chain Monte Carlo engine better account for the age variability often observed in magmatic crystal populations, whose dispersion can reflect inheritance, crystal residence times and daughter isotope loss. We illustrate this approach by calculating an age-depth model with a contiguous and realistic uncertainty envelope for the Miocene Santa Cruz Formation (early Miocene; Burdigalian), Argentina. The model is calibrated using new, high-precision isotope dilution U-Pb zircon ages for stratigraphically located interbedded tuffs, whose weighted mean ages range from ca. 16.78 ± 0.03 Ma to 17.62 ± 0.03 Ma. We document how the Bayesian age-depth model objectively reallocates probability across the posterior ages of dated horizons, and thus produces better estimates of relative ages among strata and variations in sedimentation rate. We also present a simple method to propagate age-depth model uncertainties onto stratigraphic proxy data using a Monte Carlo technique. This approach allows us to estimate robust uncertainties on isotope composition through time, important for comparisons of terrestrial systems to other proxy records.Item Open Access Biodiversity loss from deep-sea mining(Nature Geoscience, 2017-07-01) Van Dover, CL; Ardron, JA; Escobar, E; Gianni, M; Gjerde, KM; Jaeckel, A; Jones, DOB; Levin, LA; Niner, HJ; Pendleton, L; Smith, CR; Thiele, T; Turner, PJ; Watling, L; Weaver, PPEItem Open Access Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth(Earth Surface Dynamics, 2017-12-18) Brantley, SL; McDowell, WH; Dietrich, WE; White, TS; Kumar, P; Anderson, SP; Chorover, J; Ann Lohse, K; Bales, RC; Richter, DD; Grant, G; Gaillardet, JThe critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.
Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and ahubs-and-campaigns
model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.Item Open Access Distinct contributions of eroding and depositional profiles to land-atmosphere CO 2 exchange in two contrasting forests(Frontiers in Earth Science, 2019-02-26) Billings, SA; Richter, DDB; Ziegler, SE; Prestegaard, K; Wade, AM© 2019 Billings, Richter, Ziegler, Prestegaard and Wade. Lateral movements of soil organic C (SOC) influence Earth's C budgets by transporting organic C across landscapes and by modifying soil-profile fluxes of CO 2 . We extended a previously presented model (Soil Organic C Erosion Replacement and Oxidation, SOrCERO) and present SOrCERODe, a model with which we can project how erosion and subsequent deposition of eroded material can modify biosphere-atmosphere CO 2 fluxes in watersheds. The model permits the user to quantify the degree to which eroding and depositional profiles experience a change in SOC oxidation and production as formerly deep horizons become increasingly shallow, and as depositional profiles are buried. To investigate the relative importance of erosion rate, evolving SOC depth distributions, and mineralization reactivity on modeled soil C fluxes, we examine two forests exhibiting distinct depth distributions of SOC content and reactivity, hydrologic regimes and land use. Model projections suggest that, at decadal to centennial timescales: (1) the quantity of SOC moving across a landscape depends on erosion rate and the degree to which SOC production and oxidation at the eroding profile are modified as deeper horizons become shallower, and determines the degree to which depositional profile SOC fluxes are modified; (2) erosional setting C sink strength increases with erosion rate, with some sink effects reaching more than 40% of original profile SOC content after 100 y of a relatively high erosion rate (i.e., 1 mm y −1 ); (3) even large amounts of deposited SOC may not promote a large depositional profile C sink even with large gains in autochthonous SOC post-deposition if oxidation of buried SOC is not limited; and (4) when modeled depositional settings receive a disproportionately large amount of SOC, simulations of strong C sink scenarios mimic observations of modest preservation of buried SOC and large SOC gains in surficial horizons, suggesting that C sink scenarios have merit in these forests. Our analyses illuminate the importance of cross-landscape linkages between upland and depositional environments for watershed-scale biosphere-atmosphere C fluxes, and emphasize the need for accurate representations and observations of time-varying depth distributions of SOC reactivity across evolving watersheds if we seek accurate projections of ecosystem C balances.Item Open Access Habitat fragmentation and biodiversity conservation: key findings and future challenges(Landscape Ecology, 2016-02-01) Wilson, MC; Chen, XY; Corlett, RT; Didham, RK; Ding, P; Holt, RD; Holyoak, M; Hu, G; Hughes, AC; Jiang, L; Laurance, WF; Liu, J; Pimm, SL; Robinson, SK; Russo, SE; Si, X; Wilcove, DS; Wu, J; Yu, MItem Open Access Ideas and perspectives: Strengthening the biogeosciences in environmental research networks(Biogeosciences, 2018-08-15) Richter, DD; Billings, SA; Groffman, PM; Kelly, EF; Lohse, KA; McDowell, WH; White, TS; Anderson, S; Baldocchi, DD; Banwart, S; Brantley, S; Braun, JJ; Brecheisen, ZS; Cook, CS; Hartnett, HE; Hobbie, SE; Gaillardet, J; Jobbagy, E; Jungkunst, HF; Kazanski, CE; Krishnaswamy, J; Markewitz, D; O'Neill, K; Riebe, CS; Schroeder, P; Siebe, C; Silver, WL; Thompson, A; Verhoef, A; Zhang, G© Author(s) 2018. Long-term environmental research networks are one approach to advancing local, regional, and global environmental science and education. A remarkable number and wide variety of environmental research networks operate around the world today. These are diverse in funding, infrastructure, motivating questions, scientific strengths, and the sciences that birthed and maintain the networks. Some networks have individual sites that were selected because they had produced invaluable long-term data, while other networks have new sites selected to span ecological gradients. However, all long-term environmental networks share two challenges. Networks must keep pace with scientific advances and interact with both the scientific community and society at large. If networks fall short of successfully addressing these challenges, they risk becoming irrelevant. The objective of this paper is to assert that the biogeosciences offer environmental research networks a number of opportunities to expand scientific impact and public engagement. We explore some of these opportunities with four networks: the International Long-Term Ecological Research Network programs (ILTERs), critical zone observatories (CZOs), Earth and ecological observatory networks (EONs), and the FLUXNET program of eddy flux sites. While these networks were founded and expanded by interdisciplinary scientists, the preponderance of expertise and funding has gravitated activities of ILTERs and EONs toward ecology and biology, CZOs toward the Earth sciences and geology, and FLUXNET toward ecophysiology and micrometeorology. Our point is not to homogenize networks, nor to diminish disciplinary science. Rather, we argue that by more fully incorporating the integration of biology and geology in long-term environmental research networks, scientists can better leverage network assets, keep pace with the ever-changing science of the environment, and engage with larger scientific and public audiences.Item Open Access Inorganic carbon speciation and fluxes in the Congo River(Geophysical Research Letters, 2013-02-16) Wang, ZA; Bienvenu, DJ; Mann, PJ; Hoering, KA; Poulsen, JR; Spencer, RGM; Holmes, RMSeasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville-Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge-correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO2*, the sum of dissolved CO2 and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11-61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO2* and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO2 at a rate of ~109 mol m-2 yr-1. The basin-wide DIC yield was ~8.84 × 104 mol km-2 yr-1. The discharge normalized DIC flux to the ocean amounted to 3.11 × 1011 mol yr-1. The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers. Key Points The carbonate chemistry near the Congo River mouth is comprehensively studied Organic acids have a titration effect on the inorganic carbon system Surface CO2 and inorganic carbon fluxes to the ocean are characterized ©2013. American Geophysical Union. All Rights Reserved.Item Unknown Iron Age landscape changes in the Benoué River Valley, Cameroon(Quaternary Research (United States), 2019-09-01) Wright, DK; MacEachern, S; Ambrose, SH; Choi, J; Choi, JH; Lang, C; Wang, HCopyright © 2019 University of Washington. Published by Cambridge University Press. The introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon (13C/12C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen (15N/14N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ15N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ13C and δ15N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.Item Unknown Mammalian faunas, ecological indices, and machine-learning regression for the purpose of paleoenvironment reconstruction in the Miocene of South America(Palaeogeography, Palaeoclimatology, Palaeoecology, 2019-03-15) Spradley, JP; Glazer, BJ; Kay, RF© 2019 Elsevier B.V. Reconstructing paleoenvironments has long been considered a vital component for understanding community structure of extinct organisms, as well as patterns that guide evolutionary pathways of species and higher-level taxa. Given the relative geographic and phylogenetic isolation of the South American continent throughout much of the Cenozoic, the South American fossil record presents a unique perspective of mammalian community evolution in the context of changing climates and environments. Here we focus on one line of evidence for paleoenvironment reconstruction: ecological diversity, i.e. the number and types of ecological niches filled within a given fauna. We propose a novel approach by utilizing ecological indices as predictors in two regressive modeling techniques—Random Forest (RF) and Gaussian Process Regression (GPR)—which are applied to 85 extant Central and South American localities to produce paleoecological prediction models. Faunal richness is quantified via ratios of ecologies within the mammalian communities, i.e. ecological indices, which serve as predictor variables in our models. Six climate/habitat variables were then predicted using these ecological indices: mean annual temperature (MAT), mean annual precipitation (MAP), temperature seasonality, precipitation seasonality, canopy height, and net primary productivity (NPP). Predictive accuracy of RF and GPR is markedly higher when compared to previously published methods. MAT, MAP, and temperature seasonality have the lowest predictive error. We use these models to reconstruct paleoclimatic variables in two well-sampled Miocene faunas from South America: fossiliferous layers (FL) 1–7, Santa Cruz Formation (Early Miocene), Santa Cruz Province, Argentina; and the Monkey Beds unit, Villavieja Formation (Middle Miocene) Huila, Colombia. Results suggest general concordance with published estimations of precipitation and temperature, and add information with regards to the other climate/habitat variables included here. Ultimately, we believe that RF and GPR in conjunction with ecological indices have the potential to contribute to paleoenvironment reconstruction.Item Unknown Mercury Sourcing and Sequestration in Weathering Profiles at Six Critical Zone Observatories(Global Biogeochemical Cycles, 2018-10-01) Richardson, JB; Aguirre, AA; Buss, HL; Toby O'Geen, A; Gu, X; Rempe, DM; Richter, DDB©2018. American Geophysical Union. All Rights Reserved. Mercury sequestration in regolith (soils + weathered bedrock) is an important ecosystem service of the critical zone. This has largely remained unexplored, due to the difficulty of sample collection and the assumption that Hg is predominantly sequestered within surface soils (here we define as 0–0.3 m). We measured Hg concentrations and inventories in weathering profiles at six Critical Zone Observatories (CZOs): Boulder Creek in the Front Range of Colorado, Calhoun in the South Carolina Piedmont, Eel River in coastal northern California, Luquillo in the tropical montane forest of Puerto Rico, Shale Hills of the valley and ridges of central Pennsylvania, and Southern Sierra in the Sierra Nevada range of California. Surface soils had higher Hg concentrations than the deepest regolith samples, except for Eel River, which had lower Hg concentrations in surface soils compared to regolith. Using Ti normalization, CZOs with <12% rock-derived Hg (Boulder Creek, Calhoun, and Southern Sierra) had Hg peaks between 1.5 and 8.0 m in depth. At CZOs with >50% rock-derived Hg, Eel River Hg concentrations and pools were greatest at >4.0 m in the weathering profile, while Luquillo and Shale Hills had peaks at the surface that diminished within 1.0 m of the surface. Hg and total organic C were only significantly correlated in regolith at Luquillo and Shale Hills CZOs, suggesting that Hg sorption to organic matter may be less dominant than clays or Fe(II) sulfides in deeper regolith. Our results demonstrate the importance of Hg sequestration in deep regolith, below typical soil sampling depths.Item Unknown Modifications of 2:1 clay minerals in a kaolinite-dominated Ultisol under changing land-use regimes(Clays and Clay Minerals, 2018-02-01) Austin, JC; Perry, A; Richter, DD; Schroeder, PA© 2018, Clay Minerals Society. All rights reserved. Chemical denudation and chemical weathering rates vary under climatic, bedrock, biotic, and topographic conditions. Constraints for landscape evolution models must consider changes in these factors on human and geologic time scales. Changes in nutrient dynamics, related to the storage and exchange of K+ in clay minerals as a response to land use change, can affect the rates of chemical weathering and denudation. Incorporation of these changes in landscape evolution models can add insight into how land use changes affect soil thickness and erodibility. In order to assess changes in soil clay mineralogy that result from land-use differences, the present study contrasts the clay mineral assemblages in three proximal sites that were managed differently over nearly the past two centuries where contemporary vegetation was dominated by old hardwood forest, old-field pine, and cultivated biomes. X-ray diffraction (XRD) of the oriented clay fraction using K-, Mg-, and Na-saturation treatments for the air-dried, ethylene glycol (Mg- EG and K-EG) solvated, and heated (100, 350, and 550ºC) states were used to characterize the clay mineral assemblages. XRD patterns of degraded biotite (oxidized Fe and expelled charge-compensating interlayer K) exhibited coherent scattering characteristics similar to illite. XRD patterns of the Mg-EG samples were, therefore, accurately modeled using NEWMOD2® software by the use of mineral structure files for discrete illite, vermiculite, kaolinite, mixed-layer kaolinite-smectite, illite-vermiculite, kaolinite-illite, and hydroxy-interlayered vermiculite. The soil and upper saprolite profiles that formed on a Neoproterozoic gneiss in the Calhoun Experimental Forest in South Carolina, USA, revealed a depth-dependence for the deeply weathered kaolinitic to the shallowly weathered illitic/vermiculitic mineral assemblages that varied in the cultivated, pine, and hardwood sites, respectively. An analysis of archived samples that were collected over a five-decade growth period from the pine site suggests that the content of illite-like layers increased at the surface within 8 y. Historical management of the sites has resulted in different states of dynamic equilibrium, whereby deep rooting at the hardwood and pine sites promotes nutrient uplift of K from the weathering of orthoclase and micas. Differences in the denudation rates at the cultivated, pine, and hardwood sites through time were reflected by changes in the soil clay mineralogy. Specifically, an increased abundance of illite-like layers in the surface soils can serve as a reservoir of K+.Item Unknown Persistent anthropogenic legacies structure depth dependence of regenerating rooting systems and their functions(Biogeochemistry, 2020-02-01) Hauser, E; Richter, DD; Markewitz, D; Brecheisen, Z; Billings, SA© 2020, Springer Nature Switzerland AG. Biotically-mediated weathering helps to shape Earth’s surface. For example, plants expend carbon (C) to mobilize nutrients in forms whose relative abundances vary with depth. It thus is likely that trees’ nutrient acquisition strategies—their investment in rooting systems and exudates—may function differently following disturbance-induced changes in depth of rooting zones and soil nutrient stocks. These changes may persist across centuries. We test the hypothesis that plant C allocation for nutrient acquisition is depth dependent as a function of rooting system development and relative abundances of organic vs. mineral nutrient stocks. We further posit that patterns of belowground C allocation to nutrient acquisition reveal anthropogenic signatures through many decades of forest regeneration. To test this idea, we examined fine root abundances and rooting system C in organic acid exudates and exo-enzymes in tandem with depth distributions of organically- and mineral-bound P stocks. Our design permitted us to estimate C tradeoffs between organic vs. mineral nutrient benefits in paired forests with many similar aboveground traits but different ages: post-agricultural mixed-pine forests and older reference hardwoods. Fine roots were more abundant throughout the upper 2 m in reference forest soils than in regenerating stands. Rooting systems in all forests exhibited depth-dependent C allocations to nutrient acquisition reflecting relative abundances of organic vs. mineral bound P stocks. Further, organic vs. mineral stocks underwent redistribution with historic land use, producing distinct ecosystem nutritional economies. In reference forests, rooting systems are allocating C to relatively deep fine roots and low-C exudation strategies that can increase mobility of mineral-bound P stocks. Regenerating forests exhibit relatively shallower fine root distributions and more diverse exudation strategies reflecting more variable nutrient stocks. We observed these disparities in rooting systems’ depth and nutritional mechanisms even though the regenerating forests have attained aboveground biomass stocks similar to those in reference hardwood forests. These distinctions offer plausible belowground mechanisms for observations of continued C sink strength in relatively old forests, and have implications for soil C fates and soil development on timescales relevant to human lifetimes. As such, depth-dependent nutrient returns on plant C investments represent a subtle but consequential signal of the Anthropocene.Item Unknown Postseismic coastal development in Aceh, Indonesia - Field observations and numerical modeling(Marine Geology, 2017-10-01) Monecke, K; Meilianda, E; Walstra, DJ; Hill, EM; McAdoo, BG; Qiu, Q; Storms, JEA; Masputri, AS; Mayasari, CD; Nasir, M; Riandi, I; Setiawan, A; Templeton, CKWe model postseismic changes to the shoreline of West Aceh, Indonesia, a region largely affected by the December 2004 Sumatra-Andaman earthquake and ensuing Indian Ocean tsunami, using a cross-shore morphodynamic model. Subsidence of 0.5–1.0 m and tsunami scouring during the 2004 event caused the complete destruction of the beach and the landward displacement of the western coast of Aceh by an average of 110 m. Comparing a series of satellite images and topographic surveys, we reconstruct the build-up of a new beach ridge along a 6 km long stretch of coastline in the years following the event. We then use the cross-shore model UNIBEST-TC developed for a wave-dominated sandy shoreline to determine the controlling factors of shoreline recovery. Input parameters include bathymetric data measured in 2015, grain size characteristics of offshore sediment samples, modeled wave data, tidal elevations from a nearby tide-gauge station as well as measured and modeled postseismic uplift data. After establishing a cross-shore profile in equilibrium with the prevailing hydrodynamic conditions, we simulate the post-tsunami recovery, the effect of the monsoon seasons, as well as the influence of postseismic land level changes for up to 10 years and compare them to the observed coastal development. Our modeling results indicate that the recovery of the western Acehnese shoreline after the 2004 tsunami was quick with littoral sediment transport normalizing to pre-tsunami conditions within two to four years following the event. However, field data shows that the shoreline stabilized 50–90 m landward of its pre-2004 tsunami position, most likely due to the build-up of a prominent higher beach ridge in response to coseismic subsidence. Observed variability in shoreline position in the order of a few tens of meters since 2009 can be attributed to seasonal wave climate variability related to the monsoon cycle. The effect of postseismic uplift on shoreline position is small and in the order of only a few meters over 10 years, which is 3 to 5 times smaller than long-term coastal progradation rates that are driven by abundant sediment supply to the littoral zone. This overall progradational trend will promote preservation of seismically modified beach ridges, which can serve as paleoseismic indicators.Item Unknown Quantification of Mixed-Layer Clays in Multiple Saturation States Using NEWMOD2: Implications for the Potassium Uplift Hypothesis in the SE United States(Clays and Clay Minerals, 2020-02-01) Austin, JC; Richter, DD; Schroeder, PA© 2020, The Clay Minerals Society. Quantification of mineral assemblages in near-surface Earth materials is a challenge because of the often abundant and highly variable crystalline and chemical nature of discrete clay minerals. Further adding to this challenge is the occurrence of mixed-layer clay minerals, which is complicated because of the numerous possible combinations of clay layer types, as defined by their relative proportions and the ordering schemes. The problem of ensuring accurate quantification is important to understanding landscape evolution because mineral abundances have a large influence on ecosystem function. X-ray diffraction analysis of the variable cation-saturated clay fraction in soil and regolith from the Calhoun Critical Zone observatory near Clinton, South Carolina, USA, was coupled with modeling using NEWMOD2 to show that mixed-layer clays are often dominant components in the mineral assemblages. Deep samples in the profile (>6.5 m) contain mixed-layer kaolinite/smectite, kaolinite/illite-like, kaolinite-vermiculite, illite-like/biotite, and illite-like/vermiculite species (with ‘illite-like’ defined herein as Fe-oxidized 2:1 layer structure with a negative layer charge of ~0.75 per unit formula, i.e. weathered biotite). The 2:1 layers in the mixed-layer structures are proposed to serve as exchange sites for K+, which is known to cycle seasonally between plant biomass and subsurface weathering horizons. Forested landscapes have a greater number of 2:1 layer types than cultivated landscapes. Of two nearby cultivated sites, the one higher in landscape position has fewer 2:1 layer types. Bulk potassium concentrations for the forested and two cultivated sites show the greatest abundances in the surface forested site and lowest abundance in the surface upland cultivated site. These observations suggest that landscape use and landscape position are factors controlling the mixed-layer mineral assemblages in Kanhapludults typical of the S.E. United States Piedmont. These mixed-layer clays are key components of the proposed mechanism for K+ uplift concepts, whereby subsurface cation storage may occur in the interlayer sites (with increased negative 2:1 layer charge) during wetter reduced conditions of the winter season and as biomass decay releases cation nutrients. Cation release from the mixed-layer clays (by decreased 2:1 layer charge) occurs under drier oxidized conditions during the growing seasons as biota utilize cation nutrients. The types and abundances of mixed layers also reflect long-term geologic factors including dissolution/alteration of primary feldspar and biotite and the subsequent transformation and dissolution/precipitation reactions that operate within the soil horizons. Thus, the resulting mixed-layer clay mineral assemblages are often complex and heterogeneous at every depth within a profile and across landscapes. X-ray diffraction (XRD) assessment, using multiple cation saturation state and modeling, is essential for quantifying the clay mineral assemblage and pools for cation nutrients, such as potassium, in the critical zone.Item Open Access Quantification of Peat Thickness and Stored Carbon at the Landscape Scale in Tropical Peatlands: A Comparison of Airborne Geophysics and an Empirical Topographic Method(Journal of Geophysical Research: Earth Surface, 2019-12-01) Silvestri, S; Knight, R; Viezzoli, A; Richardson, CJ; Anshari, GZ; Dewar, N; Flanagan, N; Comas, X©2019. The Authors. Peatlands play a key role in the global carbon cycle, sequestering and releasing large amounts of carbon. Despite their importance, a reliable method for the quantification of peatland thickness and volume is still missing, particularly for peat deposits located in the tropics given their limited accessibility, and for scales of measurement representative of peatland environments (i.e., of hundreds of km2). This limitation also prevents the accurate quantification of the stored carbon as well as future greenhouse gas emissions due to ongoing peat degradation. Here we present the results obtained using the airborne electromagnetic (AEM) method, a geophysical surveying tool, for peat thickness detection at the landscape scale. Based on a large amount of data collected on an Indonesian peatland, our results show that the AEM method provides a reliable and accurate 3-D model of peatlands, allowing the quantification of their volume and carbon storage. A comparison with the often used empirical topographic approach, which is based on an assumed correlation between peat thickness and surface topography, revealed larger errors across the landscape associated with the empirical approach than the AEM method when predicting the peat thickness. As a result, the AEM method provides higher estimates (22%) of organic carbon pools than the empirical method. We show how in our case study the empirical method tends to underestimate the peat thickness due to its inability to accurately detect the large variability in the elevation of the peat/mineral substrate interface, which is better quantified by the AEM method.Item Open Access Stratigraphic and Earth System approaches to defining the Anthropocene(Earth's Future, 2016-08-01) Steffen, W; Leinfelder, R; Zalasiewicz, J; Waters, CN; Williams, M; Summerhayes, C; Barnosky, AD; Cearreta, A; Crutzen, P; Edgeworth, M; Ellis, EC; Fairchild, IJ; Galuszka, A; Grinevald, J; Haywood, A; Ivar do Sul, J; Jeandel, C; McNeill, JR; Odada, E; Oreskes, N; Revkin, A; Richter, DDB; Syvitski, J; Vidas, D; Wagreich, M; Wing, SL; Wolfe, AP; Schellnhuber, HJ© 2016 The Authors. Stratigraphy provides insights into the evolution and dynamics of the Earth System over its long history. With recent developments in Earth System science, changes in Earth System dynamics can now be observed directly and projected into the near future. An integration of the two approaches provides powerful insights into the nature and significance of contemporary changes to Earth. From both perspectives, the Earth has been pushed out of the Holocene Epoch by human activities, with the mid-20th century a strong candidate for the start date of the Anthropocene, the proposed new epoch in Earth history. Here we explore two contrasting scenarios for the future of the Anthropocene, recognizing that the Earth System has already undergone a substantial transition away from the Holocene state. A rapid shift of societies toward the UN Sustainable Development Goals could stabilize the Earth System in a state with more intense interglacial conditions than in the late Quaternary climate regime and with little further biospheric change. In contrast, a continuation of the present Anthropocene trajectory of growing human pressures will likely lead to biotic impoverishment and a much warmer climate with a significant loss of polar ice.Item Open Access Submarine landslide geomorphology, US continental slope(Marine Geology, 2000-09-15) McAdoo, BG; Pratson, LF; Orange, DLThe morphometric analysis of submarine landslides in four distinctly different tectonic environments on the continental slopes of Oregon, central California, Texas, and New Jersey provides useful insight into submarine process, including sediment transport mechanisms and slope stability. Using Geographic Information System (GIS) software, we identify landslides from multibeam bathymetric and GLORIA sidescan surveys based solely on surficial morphology and reflectivity. This method provides useful data in a time- and cost-efficient manner. We measure various aspects of the failures, including landslide area, runout distance, and headscarp height, along with the slope gradient of the runout zone, the failure's scar, headscarp, and adjacent slopes. The largest failures of the four study areas occur in the Gulf of Mexico, adjacent to Mississippi Canyon, and between salt withdrawal basins. Smaller landslides occur within the basins, and at the base of the Sigsbee Escarpment. These smaller landslides tend to have higher headscarps than the larger ones, and often have cohesive material at the base, suggesting a stronger rheology. Oregon has the steepest local slopes, but surprisingly few large failures for a seismically active margin (especially in the north), implying that slope angle and seismic activity may not be the most important slope stability controls. The California continental slope is heavily incised, which makes failure isolation difficult. Most of the landslides occur within the larger canyons (Vizcaino, Pioneer, Monterey) and adjacent to a pock mark field in the Point Arena basin. The majority of landslides offshore New Jersey occur on the open slope between Lindenkohl and Carteret Canyons. Morphometric statistics give us insight into where mass movements occur, how big they are likely to be, their relative importance as sediment transport mechanisms, and the overall slope stability of a given margin. Most landslides occur on slopes less than 10°. Curiously, the steepness of the slope adjacent to the failure tends to be inversely proportional to the runout length. In both California and Oregon, slope failures tend to make the local slope steeper, whereas failures in the Gulf of Mexico and offshore New Jersey will tend to make the local slope less steep. Landslides with rubble beneath the scar are mostly smaller than those without, are deep seated, and make the slope steeper. We use the ratio of headscarp height to runout length as a measure of the failure's dynamic rheology. This ratio in the submarine case is orders of magnitude less than subaerial landslides. Hydroplaning of the failed mass may be responsible for the very long runout lengths. These morphometric relationships give us important insight into landslide dynamics and process in different sedimentary and tectonic environments. (C) 2000 Elsevier Science B.V.Item Open Access The Anthropocene: A conspicuous stratigraphical signal of anthropogenic changes in production and consumption across the biosphere(Earth's Future, 2016-03-01) Williams, M; Zalasiewicz, J; Waters, CN; Edgeworth, M; Bennett, C; Barnosky, AD; Ellis, EC; Ellis, MA; Cearreta, A; Haff, PK; Ivar Do Sul, JA; Leinfelder, R; McNeill, JR; Odada, E; Oreskes, N; Revkin, A; Richter, DDB; Steffen, W; Summerhayes, C; Syvitski, JP; Vidas, D; Wagreich, M; Wing, SL; Wolfe, AP; Zhisheng, A© 2016 The Authors. Biospheric relationships between production and consumption of biomass have been resilient to changes in the Earth system over billions of years. This relationship has increased in its complexity, from localized ecosystems predicated on anaerobic microbial production and consumption to a global biosphere founded on primary production from oxygenic photoautotrophs, through the evolution of Eukarya, metazoans, and the complexly networked ecosystems of microbes, animals, fungi, and plants that characterize the Phanerozoic Eon (the last 541 million years of Earth history). At present, one species, Homo sapiens, is refashioning this relationship between consumption and production in the biosphere with unknown consequences. This has left a distinctive stratigraphy of the production and consumption of biomass, of natural resources, and of produced goods. This can be traced through stone tool technologies and geochemical signals, later unfolding into a diachronous signal of technofossils and human bioturbation across the planet, leading to stratigraphically almost isochronous signals developing by the mid-20th century. These latter signals may provide an invaluable resource for informing and constraining a formal Anthropocene chronostratigraphy, but are perhaps yet more important as tracers of a biosphere state that is characterized by a geologically unprecedented pattern of global energy flow that is now pervasively influenced and mediated by humans, and which is necessary for maintaining the complexity of modern human societies.