Papers by Gary Stinchcomb
Frontiers in Earth Science, 2018
Paleosols (fossil soils) are abundant in the sedimentary record and reflect, at least in part, re... more Paleosols (fossil soils) are abundant in the sedimentary record and reflect, at least in part, regional paleoclimate. Paleopedology thus offers a great potential for elucidating high resolution, deep-time paleoclimate records. However, many fossil soils did not equilibrate with climate prior to burial and instead dominantly express physical and chemical features reflective of other soil forming factors. Current models that use elemental oxides for climate reconstruction bypass the issue of soil-climate equilibration by restricting datasets to narrow ranges of soil properties, soil-forming environments and mean annual precipitation (MAP) and mean annual temperature (MAT). Here we evaluate a data-driven paleosol-paleoclimate model (PPM 1.0) that uses subsoil geochemistry to test the ability of soils from wide-ranging environments to predict MAP and MAT as a joint response with few initial assumptions. The PPM 1.0 was developed using a combined partial least squares regression (PLSR) and a nonlinear spline on 685 mineral soil B horizons currently forming under MAP ranging from 130 to 6900 mm and MAT ranging from 0 to 27 °C. The PLSR results on 11 major and minor oxides show that four linear combinations of these oxides (Regressors 1-4), akin to classic oxide ratios, have potential for predicting climate. Regressor 1 correlates with increasing MAP and MAT through Fe oxidation, desilication, base loss and residual enrichment. Regressor 2 correlates with MAT through temperature-dependent dissolution of Na-and K-bearing minerals. Regressor 3 correlates with increasing MAP through decalcification and retention of Si. Regres-sor 4 correlates with increasing MAP through Mg retention in mafic-rich parent material. The nonlinear spline model fit on Regressors 1 to 4 results in a Root Mean Squared Error (RMSE MAP) of 228 mm and RMSE MAT of 2.46 °C. PPM 1.0 model simulations result in Root Mean Squared Predictive Error (RMSPE MAP) of 512 mm and RMSPE MAT of 3.98 °C. The RMSE values are lower than some preexisting MAT models and show that subsoil weathering processes operating under a wide range of soil forming factors possess climate prediction potential, which agrees with the state-factor model of soil formation. The nonlinear, multivariate model space of PPM 1.0 more accurately reflects the complex and nonlinear nature of many weathering processes as climate varies. This approach is still limited as it was built using data primarily from the conterminous USA and does not account for effects of diagenesis. Yet, because it is calibrated over a broader range of climatic variable space than previous work, it should have the widest array of potential applications. Furthermore, because it is not dependent on properties that may be poorly preserved in buried paleosols, the PPM 1.0 model is preferable for reconstructing deep time climate transitions. In fact, previous studies may have grossly underestimated paleo-MAP for some paleosols.
Geoderma, 2016
At Earth's surface, bedrock transforms to regolith in a process that has many implications for wa... more At Earth's surface, bedrock transforms to regolith in a process that has many implications for water storage, soil formation, and nutrient availability to ecosystems. To understand deep regolith formation, we investigate three zones demarcating changes in mineralogy, chemistry and Fe isotopic composition in a 4-m thick regolith profile developed at a ridge top in Pennsylvania (U.S.A.) that is underlain entirely by diabase. Relative to the unweathered diabase, Zone 1 at the bottom is characterized by major element depletion, abrupt oxidation of Fe(II), a rapid decrease in sulfur concentrations and the presence of short-range ordered (SRO) Fe with depleted δ 56 Fe values relative to unweathered diabase. We attribute many of the observations at this depth (which we refer to as the lithogenic zone) to the effects of spheroidal weathering, which may be releasing a flux of Fe(II) with low δ 56 Fe values as the mineral pyroxene is weathered. This Fe(II) is oxidized due to the presence of oxygen at the bottom of the profile and is likely precipitated as isotopically light SRO Fe phases, which then recrystallize with time. Zone 2 is interpreted as a region of crystallization in which minimal bulk chemical changes occur. Finally, SRO Fe isotopic compositions become lighter again near the land surface in Zone 3, the zone of most intense biogenic weathering. Biological Fe weathering likely involves enhanced microbial activity, exudation of protons and organic acids by plant roots and fungi, and plant uptake. This pattern of SRO Fe isotopic variability (with isotopically depleted values both at depth and near the surface) has been observed in another regolith profile on spheroidally weathering bedrock in Puerto Rico. We further used pore-water concentrations and soil chemistry to calculate rates of diabase weathering. While pore-water concentrations yield modern rates, soil chemistry concentrations indicate longer-term rates. The similarity in the diabase dissolution rates using modern pore fluids and soil chemistry is consistent with steady-state weathering. Similar approaches can be applied to other Appalachian soil profiles in the future.
Journal of Archaeological Science: Reports, 2015
Archived soil samples hold important information for reconstructing ancient environments and can ... more Archived soil samples hold important information for reconstructing ancient environments and can provide data on prehistoric land use, manipulation and changes over time. Archeological investigations at the Abbott FarmNational Historic Landmark (NHL) located near Trenton, NewJersey recovered occupations fromPaleoindian to Late Woodland periods. Soil samples collected during the 1930s WPA excavations have never been analyzed until now. This paper discusses the results of a carbon isotope analysis of soil organic carbon, δ13Csoc, performed on 54 samples from a number of archeological contexts from the Abbott Farm NHL. Data from Early and Middle Woodland pits and associated soils exhibit average δ13Csoc values of −25.0 ± 1.0‰ suggesting that the suite of samples have an isotopic signature that primarily reflects aboveground C3 vegetation. These values agree with current interpretations of an Early andMiddle Woodland that had no maize and a gradual LateWoodland introduction of maize (C4 plant) into the Lower Delaware River Valley. Assuming these samples have not experienced significant organic matter oxidation in their ~80 years of storage, the Abbott Farmresults suggest that preserved archeological feature and soil samples in other collections that have been desiccated and housed in climate controlled facilities serve as an untapped resource for paleoenvironmental reconstruction for sites that either no longer exist or where access is limited. In the case of Abbott Farm NHL, the archeological feature and soil samples provide information on prehistoric site vegetation and paleoenvironment before the beginnings of agriculture in the Delaware Valley.
Frontiers in Earth Science, 2015
Forman SL and Stinchcomb GE (2015) Views on grand research challenges for Quaternary geology, geo... more Forman SL and Stinchcomb GE (2015) Views on grand research challenges for Quaternary geology, geomorphology and environments.
Applied Geochemistry, 2015
Accurate measurements of soil CO 2 concentrations (pCO 2 ) are important for understanding carbon... more Accurate measurements of soil CO 2 concentrations (pCO 2 ) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO 2 , most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO 2 distribution can predictably vary with topographic position. We measured soil pCO 2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO 2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO 2 generally at 0.1e0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO 2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO 2 diffusive fluxes. The highest pCO 2 values were observed in the valley floor and swales where soils are deep (!0.7 m) and wet, resulting in low CO 2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO 2 because they are shallower ( 0.6 m) and drier, resulting in high CO 2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO 2 : the north (i.e., south-facing) swale generally had lower soil moisture content and pCO 2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO 2 was similar across the watershed, the amplitude of the pCO 2 peak was higher in the deep soils due to more variable moisture content. The high pCO 2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO 2 alone. CO 2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO 2 dynamics would be improved by including landscape controls on soil pCO 2 .
Method and Theory in Paleoethnobotany, 2015
Magnetic susceptibility is an increasingly popular low-cost method for rapidly assessing paleocli... more Magnetic susceptibility is an increasingly popular low-cost method for rapidly assessing paleoclimate and paleoenvironmental impact on buried soils. The goal of this study is to determine the primary influence(s) on soil magnetic susceptibility along floodplain, terrace and upland soils in the middle Delaware River Valley, USA, using environmental magnetic, pedologic, and stratigraphic techniques. Two-hundred thirty samples were collected from age-constrained sandy, quartz-rich, floodplain, terrace, and upland soils (Entisols, Inceptisols). A Kruskal-Wallis (K-W) and post-hoc Tukey-Kramer (T-K) (α=0.05) multiple comparisons analysis on 176 mass-specific low-field susceptibility (Xlf) assays show that A and B horizons are magnetically enhanced compared to C and E horizons (p<0.0001). Results of descriptive soil micromorphology show that A and B horizons contain anywhere from 10-50% more amorphous organic matter and clay films along pores than do C and E horizons. Enhanced Xlf valu...
Antiquity
http://antiquity.ac.uk/projgall/ferraro338/
Pennsylvania archaeologist
Anthropocene, 2013
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.
Frontiers in Earth Science, 2014
Magnetic susceptibility of soils is a common proxy for rainfall, but other factors can contribute... more Magnetic susceptibility of soils is a common proxy for rainfall, but other factors can contribute to magnetic enhancement in soils. Here we explore influence of centuryto millennial-scale duration of soil formation on periglacial and alluvial soil magnetic properties by assessing three terraces with surface and buried soils ranging in exposure ages from <0.01 to ∼16 kyrs along the Delaware River in northeastern USA. The A and B soil horizons have higher X lf , Ms, and S-ratios compared to parent material, and these values increase in a non-linear fashion with increasing duration of soil formation. Magnetic remanence measurements show a mixed low-and high-coercivity mineral assemblage likely consisting of goethite, hematite, and maghemite and/or magnetite that contributes to the magnetic enhancement of the soil. Room-temperature and lowtemperature field-cooled and zero field-cooled remanence curves confirm the presence of goethite and magnetite and/or maghemite and show an increase in magnetization with increasing soil age. These data suggest that as the Delaware alluvial soils weather, the concentration of secondary ferrimagnetic minerals increase in the A and B soil horizons. We then compared the time-dependent X lf from several age-constrained buried alluvial soils with known climate data for the region during the Quaternary. Contradictory to most studies that suggest a link between increases in magnetic susceptibility and high moisture, increased magnetic enhancement of Delaware alluvial soils coincides with dry climate intervals. Early Holocene enhanced soil X lf (9.5-8.5 ka) corresponds with a welldocumented cool-dry climate episode. This relationship is probably related to less frequent flooding during dry intervals allowing more time for low-coercive pedogenic magnetic minerals to form and accumulate, which resulted in increased X lf . Middle Holocene enhanced X lf (6.1-4.3 ka) corresponds with a wet to dry transitional phase and a previously documented incision event along the valley bottom. In this case the incision and terrace development resulted in prolonged surface exposure and more time for the accumulation of secondary ferrimagnetic minerals, enhancing X lf . The results of this study agree with previous modeling efforts, and show that in Quaternary (and possibly pre-Quaternary) periglacial and alluvial soils and paleosols that weathered for 10 1 -10 4 years, duration of pedogenesis, rather than climate, is an important control on magnetic enhancement.
Encyclopedia of Scientific Dating Methods, 2013
Quaternary Research, 2013
A paleoenvironmental time-series spanning the Holocene was constructed using 29 radiocarbon ages ... more A paleoenvironmental time-series spanning the Holocene was constructed using 29 radiocarbon ages and 149 standardized δ 13 C som values from alluvial terrace profiles along the middle Delaware River valley. There is good agreement between increasing δ 13 C som and Panicoideae phytolith concentrations, suggesting that variations in C 4 biomass are a major contributor to changes in the soil δ 13 C. A measurement error deconvolution curve over time reveals two isotope stages (II-I), with nine sub-stages exhibiting variations in average δ 13 C som (average %C 4 ). Stage II,~10.7-4.3 ka, shows above-average δ 13 C som (increase %C 4 ) values with evidence of an early Holocene warming and dry interval (sub-stage IIb, 9.8-8.3 ka) that coincides with rapid warming and cool-dry abrupt climate-change events. Sub-stage IId, 7.0-4.3 ka, is an above average δ 13 C som (increase %C 4 ) interval associated with the mid-Holocene warm-dry hypsithermal. The Stage II-I shift at 4.3 ka documents a transition toward below average δ 13 C som (decrease %C 4 ) values and coincides with decreasing insolation and hydroclimatic change. Sub-stages Ib and Id (above average %C 4 ) coincide with the first documented occurrence of maize in the northeastern USA and a substantial increase in human population during the Late Woodland. These associations suggest that people influenced δ 13 C som during the late Holocene.
Geology, 2011
Despite the importance of understanding the effect of land use on fl oodplains in eastern North A... more Despite the importance of understanding the effect of land use on fl oodplains in eastern North America, few studies have directly addressed the possibility and extent of prehistoric indigenous land use on fl oodplain development. Here we report geoarchaeological evidence of increasing fl oodplain sedimentation and prehistoric land-use intensifi cation in the Delaware River Valley (eastern United States) during the Medieval Climate Anomaly-Little Ice Age transition. The evidence of this anthropogenic sedimentation event, documented throughout eastern North America, is designated here as pre-colonial sediment (PCS), ca. A.D. 1100-1600. The data demonstrate that the combined effects of prehistoric land use and climate change affected eastern North American fl oodplain development several hundred years prior to the onset of major European settlement.
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Papers by Gary Stinchcomb