Isabel P. Montañez

Bio: Isabel P. Montañez is an academic researcher from University of California, Davis. The author has contributed to research in topics: Carboniferous & Glacial period. The author has an hindex of 48, co-authored 156 publications receiving 7447 citations. Previous affiliations of Isabel P. Montañez include University of California, Riverside & University of Texas at Austin.

CO 2 as a primary driver of Phanerozoic climate

Abstract: Royer et al. (2004) introduce a seawater pH correction to the Phanerozoic temperature reconstruction based on δO variations in marine fossils. Although this correction is a novel idea and it is likely to have played some role in offsetting the δO record, we show that (a) The correction cannot be as large as claimed by Royer et al. (b) Irrespective of the size of the correction, a CO2 signature cannot possibly be seen in the data. (c) Even though the CO2 signature cannot be seen, the pH correction implies only a somewhat higher global temperature sensitivity than that in Shaviv and Veizer (2003), a sensitivity that is consistent with a “black body Earth”, but only marginally with the lower limit of the IPCC range.

Evolution of the Sr and C Isotope Composition of Cambrian Oceans

Abstract: The recent proliferation of chemostratigraphic studies has clearly documented that systematic fluctuations in the strontium and carbon isotope composition of seawater have occurred throughout Earth history across a range of temporal scales. In particular, significant isotopic variation during key intervals of geologic time has provided unprecedented quantitative constraints on crustal and surficial processes, and enhanced chronostratigraphic resolution for intrabasinal and interbasinal correlations. We present the first set of high-resolution, seawater Sr and C isotope curves for the late Early through early Late Cambrian. These curves are defined in continuous exposures of marine carbonates in the Great Basin and southern Canadian Rockies, and they are used to better constrain primary variations in ocean chemistry during this time period. The Sr curve documents a rapid rate of increase through this period that is comparable to that recorded by the late Cenozoic seawater Sr proxy record of uplift and attendant weathering of the HimalayaTibetan Plateau. The Cambrian rise in Sr values is interpreted to record PanAfrican‐Brasiliano orogenesis, and

CO2-Forced Climate and Vegetation Instability During Late Paleozoic Deglaciation

Abstract: The late Paleozoic deglaciation is the vegetated Earth9s only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO2) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO2, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO2 shifts, illustrating the biotic impact associated with past CO2-forced turnover to a permanent ice-free world.

A 400 million year carbon isotope record of pedogenic carbonate; implications for paleoatomospheric carbon dioxide

Abstract: A 400 record of atmospheric carbon dioxide levels has been estimated by applying a CO{sub 2} paleobarometer to a database of 758 analyses of paleosol (fossil soil) carbonates. This database is a compilation of new data and previously published values from the literature. Many new analyses of Mesozoic paleosols are reported, an era poorly represented in the literature. Results indicate that large fluctuations in atmospheric carbon dioxide levels have occurred over the study interval, ranging from the current level up to ten times the current level. Declining pCO{sub 2} levels through the middle Paleozoic culminate in low levels in the Early Permian. An abrupt increase in pCO{sub 2} in the Early Permian is followed by a decrease prior to the Permo-Triassic boundary. Carbon dioxide levels increase through the Triassic to approx. 3,000 ppmV, a level maintained through the Jurassic period. Levels lowered through the Cretaceous, dropping to less than 1,000 ppmV prior to the Cretaceous-Tertiary boundary. Relatively low levels persisted throughout the Cenozoic, with some evidence of higher levels in the Eocene and Oligocene.

The Late Paleozoic Ice Age: An Evolving Paradigm

Abstract: The late Paleozoic icehouse was the longest-lived ice age of the Phanerozoic, and its demise constitutes the only recorded turnover to a greenhouse state. This review summarizes evidence for the timing, extent, and behavior of continental ice on Pangea in addition to the climate and ecosystem response to repeated transitions between glacial and interglacial conditions. Combined empirical and climate modeling studies argue for a dynamic ice age characterized by discrete periods of glaciation separated by periods of ice contraction during intermittent warmings, moderate-size ice sheets emanating from multiple ice centers throughout southern Gondwana, possible glaciation of the Northern Hemisphere, and atmospheric CO2 as a primary driver of both ice sheet and climate variability. The glacioeustatic response to fluctuations of these smaller ice sheets was likely less extreme than previously suggested. Modeling studies, stratigraphic relationships, and changes in both the geographic patterns and community compositions of marine fauna and terrestrial flora indicate the potential for strong responses to high-latitude glacial conditions in both ocean circulation and low-latitude climate. The forcings and feedbacks of these linkages, as well as existing climate paradoxes, define research targets for future studies of the late Paleozoic.

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

Abstract: Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

The Neogene Period

Abstract: An Astronomically Tuned Neogene Time Scale (ATNTS2012) is presented, as an update of ATNTS2004 in GTS2004. The new scale is not fundamentally different from its predecessor and the numerical ages are identical or almost so. Astronomical tuning has in principle the potential of generating a stable Neogene time scale as a function of the accuracy of the La2004 astronomical solution used for both scales. Minor problems remain in the tuning of the Lower Miocene. In GTS2012 we will summarize what has been modified or added since the publication of ATNTS2004 for incorporation in its successor, ATNTS2012. Mammal biostratigraphy and its chronology are elaborated, and the regional Neogene stages of the Paratethys and New Zealand are briefy discussed. To keep changes to ATNTS2004 transparent we maintain its subdivision into headings as much as possible.

Strontium Isotope Stratigraphy: LOWESS Version 3: Best Fit to the Marine Sr‐Isotope Curve for 0–509 Ma and Accompanying Look‐up Table for Deriving Numerical Age

Abstract: An improved and updated version of the statistical LOWESS fit to the marine 87Sr/86Sr record and a revised look-up table (V3:10/99; available from j.mcarthur@ucl.ac.uk) based upon it enables straightforward conversion of 87Sr/86Sr to numerical age, and vice versa, for use in strontium isotope stratigraphy (SIS). The table includes 95% confidence intervals on predictions of numerical age from 87Sr/86Sr. This version includes the Triassic and Paleozoic record (0509 Ma) omitted from previous versions because of the paucity of adequate data at the time of preparation. We highlight differences between the previous versions of the table and the current version and discuss some aspects of the 87Sr/86Sr record that may have geological significance. We give examples of how the table can be used and where it has proven useful.

Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification

Abstract: Anthropogenic elevation of atmospheric carbon dioxide ( p CO2) is making the oceans more acidic, thereby reducing their degree of saturation with respect to calcium carbonate (CaCO3). There is mounting concern over the impact that future CO2-induced reductions in the CaCO3 saturation state of seawater will have on marine organisms that construct their shells and skeletons from this mineral. Here, we present the results of 60 d laboratory experiments in which we investigated the effects of CO2-induced ocean acidification on calcification in 18 benthic marine organisms. Species were selected to span a broad taxonomic range (crustacea, cnidaria, echinoidea, rhodophyta, chlorophyta, gastropoda, bivalvia, annelida) and included organisms producing aragonite, low-Mg calcite, and high-Mg calcite forms of CaCO3. We show that 10 of the 18 species studied exhibited reduced rates of net calcification and, in some cases, net dissolution under elevated p CO2. However, in seven species, net calcification increased under the intermediate and/or highest levels of p CO2, and one species showed no response at all. These varied responses may reflect differences amongst organisms in their ability to regulate pH at the site of calcification, in the extent to which their outer shell layer is protected by an organic covering, in the solubility of their shell or skeletal mineral, and in the extent to which they utilize photosynthesis. Whatever the specific mechanism(s) involved, our results suggest that the impact of elevated atmospheric p CO2 on marine calcification is more varied than previously thought.

Geochemistry of oceanic anoxic events

Abstract: [1] Oceanic anoxic events (OAEs) record profound changes in the climatic and paleoceanographic state of the planet and represent major disturbances in the global carbon cycle. OAEs that manifestly caused major chemical change in the Mesozoic Ocean include those of the early Toarcian (Posidonienschiefer event, T-OAE, ∼183 Ma), early Aptian (Selli event, OAE 1a, ∼120 Ma), early Albian (Paquier event, OAE 1b, ∼111 Ma), and Cenomanian–Turonian (Bonarelli event, C/T OAE, OAE 2, ∼93 Ma). Currently available data suggest that the major forcing function behind OAEs was an abrupt rise in temperature, induced by rapid influx of CO2 into the atmosphere from volcanogenic and/or methanogenic sources. Global warming was accompanied by an accelerated hydrological cycle, increased continental weathering, enhanced nutrient discharge to oceans and lakes, intensified upwelling, and an increase in organic productivity. An increase in continental weathering is typically recorded by transient increases in the seawater values of 87Sr/86Sr and 187Os/188Os ratios acting against, in the case of the Cenomanian-Turonian and early Aptian OAEs, a longer-term trend to less radiogenic values. This latter trend indicates that hydrothermally and volcanically sourced nutrients may also have stimulated local increases in organic productivity. Increased flux of organic matter favored intense oxygen demand in the water column, as well as increased rates of marine and lacustrine carbon burial. Particularly in those restricted oceans and seaways where density stratification was favored by paleogeography and significant fluvial input, conditions could readily evolve from poorly oxygenated to anoxic and ultimately euxinic (i.e., sulfidic), this latter state being geochemically the most significant. The progressive evolution in redox conditions through phases of denitrification/anammox, through to sulfate reduction accompanied by water column precipitation of pyrite framboids, resulted in fractionation of many isotope systems (e.g., N, S, Fe, Mo, and U) and mobilization and incorporation of certain trace elements into carbonates (Mn), sulfides, and organic matter. Sequestration of CO2 in organic-rich black shales and by reaction with silicate rocks exposed on continents would ultimately restore climatic equilibrium but at the expense of massive chemical change in the oceans and over time scales of tens to hundreds of thousands of years.