Claudia I. Mora

Middle to Late Paleozoic Atmospheric CO2 Levels from Soil Carbonate and Organic Matter

The stable carbon isotope compositions of ancient soil carbonate and coexisting soil organic matter indicate that atmospheric CO2 levels decreased by a factor of 10 during the middle to late Paleozoic era. Proxy measurements of CO2 were made by application of a soil carbonate CO2 paleobarometer to a suite of paleosols that share key physical and chemical characteristics. The estimates agree with theoretical models that imply that a decrease in Paleozoic atmospheric CO2 levels was associated with afforestation of the land surface by terrestrial plants and with global climate change leading to the extensive Permo-Carboniferous glaciation.

Tree-ring isotope records of tropical cyclone activity

The destruction wrought by North Atlantic hurricanes in 2004 and 2005 dramatically emphasizes the need for better understanding of tropical cyclone activity apart from the records provided by meteorological data and historical documentation. We present a 220-year record of oxygen isotope values of α-cellulose in longleaf pine tree rings that preserves anomalously low isotope values in the latewood portion of the ring in years corresponding with known 19th and 20th century landfalling/near-coastal tropical storms and hurricanes. Our results suggest the potential for a tree-ring oxygen isotope proxy record of tropical cyclone occurrence extending back many centuries based on remnant pine wood from protected areas in the southeastern U.S.

Mass-balance reconstruction of a modern Vertisol: implications for interpreting the geochemistry and burial alteration of paleo-Vertisols.

Abstract Utilizing identical sampling and analytical techniques, the morphological and chemical characteristics of a modern Vertisol (Houston Black series, central Texas) can be directly compared with an Upper Mississippian paleo-Vertisol from the Appalachian basin (Pennington Formation, east-central Tennessee). Mass-balance reconstructions suggest retention of primary pedochemical patterns in the paleo-Vertisol, including patterns of soil volume change (strain) and transport functions (translocations) of many major and trace elements. Retention of primary pedochemical patterns suggests that Vertisols constitute nearly closed systems during burial diagenesis. Chemical and mineralogical changes associated with burial diagenesis of the paleo-Vertisol include oxidation of organic carbon (OC), illitization of smectites, dehydration and recrystallization of Fe–Mn oxyhydroxides, and dolomitization of pedogenic calcite. Significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern Vertisols have implications for interpretation of geochemical data obtained from paleo-Vertisols. Overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox-sensitive trace elements, including Co, Cr, Cu, Mn, Ni, and V. Gilgai microhighs behave as evaporative “wicks” that draw moisture and soluble phases towards the soil surface, resulting in precipitation of metal hydrosylate complexes and sulfates (gypsum) at the capillary fringe and shallower depths of leaching and fixation of trace elements. Paleoprecipitation estimates from paleosols, based on the depth to the top of the pedogenic carbonate horizon, should therefore utilize field, petrographic and geochemical data for characterizing maximum depths of leaching, loss or gain of exchangeable bases, and calcification, rather than relying solely upon field data.

Carbon dioxide in the Paleozoic atmosphere: Evidence from carbon-isotope compositions of pedogenic carbonate

Stable carbon-isotope compositions of pedogenic carbonate occurring in three clay-rich vertic paleosols within Paleozoic red-bed successions in central Pennsylvania provide a record of past pedogenic environments and can be used to estimate CO{sub 2} pressure (P{sub CO{sub 2}}) of the Paleozoic atmosphere. The {delta}{sup 13}C values of carbonate nodules from paleosols in the deltaic lower Bloomsburg Formation (Upper Silurian) reflect the contribution of carbon from marine groundwater or fossils, coupled with low biological activity. The {delta}{sup 13}C values of carbonate rhizocretions from stratigraphically high paleosols in the Bloomsburg Formation, and in the alluvial Catskill (Upper Devonian) and Mauch Chunk (Upper Mississippian) Formations, suggest an extensive C{sub 3} flora and significant contribution of atmospheric CO{sub 2}. Paleozoic atmospheric CO{sub 2} levels inferred from {delta}{sup 13}C of pedogenic carbonate are significantly higher than present levels.

Pedogenic processes and domain boundaries in a Vertisol climosequence: evidence from titanium and zirconium distribution and morphology

Abstract The occurrences of titanium (Ti) and zirconium (Zr) within eight Vertisols formed in a climosequence on the Upper Beaumont Formation of the Texas Gulf Coastal Plain were investigated in order to determine processes responsible for Ti and Zr redistribution during pedogenesis. Discontinuities defined by significant shifts in particle size distribution and the content (in volume percent) of Zr are present at 160 to 260 cm depth in each pedon. The discontinuities are interpreted to be functional boundaries, i.e., physico-chemical expressions of pedogenic domains, between an upper soil domain dominated by open-system pedogenesis and a lower, more closed-system domain dominated by chemical weathering. The depth at which the functional boundary occurs is dependent on physical and hydrogeochemical influences, which are largely a function of available water. Soil materials above the discontinuities are slightly coarser textured and enriched in Zr, whereas below the sediments are finer textured and have lower and more constant Zr contents. The Zr is associated almost exclusively with zircon and Zr contents correlate positively to the weight percent sand+coarse silt, with negligible Zr present in the Profile volume loss/gain (i.e., soil strain, e), a mass-balance calculation that assumes Zr or Ti immobility during pedogenesis, indicate eZr values nearly four times greater than eTi. Large values of eZr within the upper soil domains are due primarily to sand and coarse silt additions to the Vertisols and preclude use of Zr as a basis of mass-balance calculations in these soils, despite its relative chemical stability. By comparison, Ti is generally conserved within the clay-rich soil profiles and is therefore better suited for mass-balance calculations of volume change and mobile element translocation during pedogenesis.

Pedogenic iron-manganese nodules in Vertisols: A new proxy for paleoprecipitation?

The total Fe content of pedogenic iron-manganese (Fe-Mn) nodules taken from a Vertisol climosequence on the Texas Gulf Coastal Plain correlates with mean annual precipitation (MAP, r 2 = 0.92). No significant trend of total Fe (FeTOT) with depth was noted in profiles. Using the regression developed from modern Vertisol data, FeTOT contents of Paleozoic paleo-Vertisol Fe-Mn nodules yielded MAP regimes comparable to previously inferred paleoenvironmental interpretations. Paleoprecipitation estimates derived from Fe-Mn nodules for an uneroded, Late Mississippian paleo-Vertisol are very close to estimates determined from a depth to pedogenic carbonate horizon (DCH) proxy determined from the modern Vertisol climosequence. The lack of soil depth dependence of the Fe-Mn nodule proxy provides a consistent paleoprecipitation estimate even in eroded paleo- Vertisols and, in combination with the DCH, may be useful in determining original paleosol thickness.

Preservation of a Paleo-vertisol and an Estimate of Late Mississippian Paleoprecipitation

ABSTRACT A Late Mississippian paleosol satisfying all of the morphological criteria required for classification of Holocene Vertisols provides quantitative paleoclimate information, in addition to the now commonplace interpretation of precipitation seasonality based on the presence of vertic features. Paleoprecipitation was estimated using the empirical relationship between depth to pedogenic carbonate horizon in Quaternary soils. Burial compaction, erosional truncation, and high paleoatmospheric CO2 concentration, all factors that complicate paleoprecipitation estimates, are unusually well constrained for this paleosol. Allowing for 10% compaction, the paleosol had a pre-burial depth of 100 cm for the pedogenic carbonate horizon, yielding a mean annual paleo-precipitation estimate f 648 ± 141 mm. This is comparable to the mean annual precipitation for Brownsville, Texas, where similar soils are found today. A dolomicrite crust, developed in gilgai microlows, is well preserved in the paleo-Vertisol. Higher Late Mississippian paleotemperatures and rates of evapotranspiration associated with a lower-latitude paleogeography for central Tennessee during the Late Mississippian may explain in part why Holocene coastal Vertisols in the Brownsville region lack surficial crusts similar to that of the paleo-Vertisol. We qualitatively define the Late Mississippian climate of central Tennessee as semiarid.

Very large plant and root traces from the Early to Middle Devonian: Implications for early terrestrial ecosystems and atmospheric p(CO2)

Plant and root traces from the Fort Prevel Member of the Battery Point Formation (late Early Devonian, Emsian), Gaspe Bay, Quebec (Canada), are larger and more complex than previously postulated for land plants of this time. The traces are preserved as clay- and silt-lined casts in or near growth position and provide evidence that early vascular land plants achieved substantial stature (2–3 m) and were capable of deep rooting (to nearly 1 m). The root traces and alluvial deposits in which they occur suggest increased landscape stabilization and root system and paleosol morphologies that were influenced by a water-stressed, episodically energetic environment. Early Devonian plants of such large stature may have been partly responsible for initiation of a steep decline in atmospheric p (CO 2 ), through organic carbon burial and accelerated terrestrial weathering.

Correlations between components of the water balance and burned area reveal new insights for predicting forest fire area in the southwest United States

We related measurements of annual burned area in the southwest United States during 1984-2013 to records of climate variability. Within forests, annual burned area correlated at least as strongly with spring-summer vapour pressure deficit (VPD) as with 14 other drought-related metrics, including more complex metrics that explicitly represent fuel moisture. Particularly strong correlations with VPD arise partly because this term dictates the atmospheric moisture demand. Additionally, VPD responds to moisture supply, which is difficult to measure and model regionally due to complex micrometeorology, land cover and terrain. Thus, VPD appears to be a simple and holistic indicator of regional water balance. Coupled with the well-known positive influence of prior-year cold season precipitation on fuel availability and connectivity, VPD may be utilised for burned area forecasts and also to infer future trends, though these are subject to othercomplicatingfactorssuchaslandcoverchangeandmanagement.Assuminganaggressivegreenhousegasemissions scenario, climate models predict mean spring-summer VPD will exceed the highest recorded values in the southwest in nearly40%ofyearsbythemiddleofthiscentury.Theseresultsforewarnofcontinuedincreasesinburnedforestareainthe southwest United States, and likely elsewhere, when fuels are not limiting. Additional keywords: fire danger, tree mortality, warming.

Causes and Implications of Extreme Atmospheric Moisture Demand during the Record-Breaking 2011 Wildfire Season in the Southwestern United States

AbstractIn 2011, exceptionally low atmospheric moisture content combined with moderately high temperatures to produce a record-high vapor pressure deficit (VPD) in the southwestern United States (SW). These conditions combined with record-low cold-season precipitation to cause widespread drought and extreme wildfires. Although interannual VPD variability is generally dominated by temperature, high VPD in 2011 was also driven by a lack of atmospheric moisture. The May–July 2011 dewpoint in the SW was 4.5 standard deviations below the long-term mean. Lack of atmospheric moisture was promoted by already very dry soils and amplified by a strong ocean-to-continent sea level pressure gradient and upper-level convergence that drove dry northerly winds and subsidence upwind of and over the SW. Subsidence drove divergence of rapid and dry surface winds over the SW, suppressing southerly moisture imports and removing moisture from already dry soils. Model projections developed for the fifth phase of the Coupled Mod...