[1] The groundwater reservoir and its interaction with surface water facilitate lateral transport of continental water and energy. Current climate models do not account for long-distance groundwater flow between model cells but route the atmospheric surplus (precipitation (P) minus evapotranspiration (ET)) directly to stream discharge within a model grid cell. We ask how much water exits a river basin without ever passing through its surface outlet? What are the climatologic and geologic factors influencing this flux? To answer these questions, a separation of groundwater flow from river flow is necessary. We use the ratio of stream discharge (Qr) to basin recharge (R = P À ET) for this purpose; where Qr:R < 1, a basin is considered a groundwater exporter; and where Qr:R > 1, a basin is considered a groundwater importer. Here Qr is obtained from 39 years of U.S. Geological Survey Hydro-Climatic Data Network observed stream discharge from 1555 basins across the continental United States, and R (P À ET) is derived from 50 years of hydrologic simulation by the Variable Infiltration Capacity model. It was found that the Qr:R ratio deviates significantly from 1 across the continent. Detailed investigations of individual basins suggest that the deviations are primarily a function of geology, while climate and basin scale influence the magnitude of these deviations. Further, a marked incongruity between the surface and groundwater flow directions is apparent, suggesting that surface drainage is only partially indicative of subsurface flow regimes. The apparent significance of this long-distance groundwater flow component reinforces the need for inclusion of the groundwater reservoir in current water cycle and climate modeling efforts.
The effects of a large igneous province on the concentration of atmospheric carbon dioxide (PCO₂) are mostly unknown. In this study, we estimate PCO₂ from stable isotopic values of pedogenic carbonates interbedded with volcanics of the Central Atlantic Magmatic Province (CAMP) in the Newark Basin, eastern North America. We find pre-CAMP PCO₂ values of ~2000 parts per million (ppm), increasing to ~4400 ppm immediately after the first volcanic unit, followed by a steady decrease toward pre-eruptive levels over the subsequent 300 thousand years, a pattern that is repeated after the second and third flow units. We interpret each PCO₂ increase as a direct response to magmatic activity (primary outgassing or contact metamorphism). The systematic decreases in PCO₂ after each magmatic episode probably reflect consumption of atmospheric CO₂ by weathering of silicates, stimulated by fresh CAMP volcanics.
23This paper presents the initial results of a scientific drilling project to recover core 24 and pressurized fluid samples from a natural CO 2 reservoir, near the town of Green River, 25Utah. The drilling targeted a stacked sequence of CO 2 -charged Jurassic sandstone reservoirs 26 and caprocks, situated adjacent to a CO 2 -degassing normal fault. This site has actively 27 leaked CO 2 from deep supercritical CO 2 reservoirs at depth >2km within the basin for over 28 Geyser constrain mixing models which show that, within the Navajo Sandstone, the 49 reservoir fluids are undergoing complex mixing of: (i) CO 2 -saturated brine inflowing from 50 the fault, (ii) CO 2 -undersaturated meteoric groundwater flowing through the reservoir and 51 (iii) reacted CO 2 -charged brines flow through fracture zones in the overlying Carmel 52Formation caprock, into the formations above. Such multi-scale mixing processes may 53 significantly improve the efficiency with which groundwaters dissolve the migrating CO 2 .
The Paleocene/Eocene thermal maximum (PETM) and associated carbon isotope excursion (CIE) are often touted as the best geologic analog for the current anthropogenic rise in pCO 2. However, a causal mechanism for the PETM CIE remains unidentified because of large uncertainties in the duration of the CIE's onset. Here, we report on a sequence of rhythmic sedimentary couplets comprising the Paleocene/Eocene Marlboro Clay (Salisbury Embayment). C-depleted carbon to the ocean-atmosphere system in a geologically short interval of time (1-3). Proposed mechanisms include the destabilization of the global methane reservoir by a thermal trigger (2, 4) or physical disturbance (5), production of thermogenic CH 4 and CO 2 during the emplacement of a large igneous province (6, 7), wildfires burning peatlands (8), desiccation of a large epicontinental sea (9), decomposition of terrestrial permafrost (10), and bolide impact (11,12). The only consensus is that a precise chronology providing rates for the onset of the CIE is essential to distinguish among these mechanisms. Efforts to establish such a chronology have relied on average sedimentation rates based on integrated magneto-and biostratigraphic constraints (1), identifying cycles in deep sea cores and assigning an orbital periodicity (13,14), or measuring the concentration of extraterrestrial 3 He and applying an estimated flux to establish sedimentation rates (15,16). The lack of a precise timescale for the δ 13 C excursion precludes further advances in identification of the source(s) of the light carbon and calculation of the release rates and magnitudes. Until these are better quantified, the relevance of the CIE as an analog for the Anthropocene remains speculative.Deep sea bulk carbonate records show that the CIE began with an abrupt initial δ 13 C decrease of ∼1‰ followed by a more gradual decrease of similar magnitude (17). Bulk carbonate δ implications for the size of the carbon release necessary to produce the CIE. This uncertainty highlights the dire need for a precise chronometer for the onset of the carbon isotope excursion.Here, we present high-resolution bulk stable isotope and % CaCO 3 records from the northern Salisbury Embayment [35°N paleolatitude (18)] on the Atlantic coastal plain, using the Millville (ODP 174X) and newly recovered Wilson Lake B cores. Both of these cores contain the upper Paleocene-lower Eocene Marlboro Clay unit that has been correlated to deep sea CIE sections using carbon isotope and biostratigraphy (19,20). These cores have two unique features that distinguish them as outstanding temporal archives for the onset of the CIE: (i) expanded sections of the Marlboro Clay in both the Wilson Lake B (15.5 m) and Millville (12.6 m) cores and (ii) distinct and rhythmic bedding of silty clays through the entire section containing the δ 13 C excursion. The δ 13 C excursions in the Wilson Lake B and Millville cores have amplitudes of −6‰ and −4.5‰, respectively (Fig. S1), with ∼3.5‰ of the decrease representing the virtually instantaneous initia...
Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.
Recent evidence from the~201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO 2 , followed by a falloff to pre-eruptive concentrations over~300 kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO 2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO 2 levels for pre-CAMP background of 2000 ±700 ppm (at S(z)=3000±1000 ppm), increasing to~5000±1700 ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO 2 to~4500 ± 1200 ppm, about 240 kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840 ± 60 kyr. The Portland also records a post-eruptive decrease in pCO 2 reaching pre-eruptive background concentrations of~2000 ppm in only~300 kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO 2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall netcooling effect on global climates due to a long-term net-decrease in pCO 2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps.
A major unresolved aspect of the rise of dinosaurs is why early dinosaurs and their relatives were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, a pattern persisting 30 million years after their origin and 10-15 million years after they became abundant and speciose at higher latitudes. New palynological, wildfire, organic carbon isotope, and atmospheric pCO 2 data from early dinosaur-bearing strata of low paleolatitudes in western North America show that large, high-frequency, tightly correlated variations in δ 13 C org and palynomorph ecotypes occurred within a context of elevated and increasing pCO 2 and pervasive wildfires. Whereas pseudosuchian archosaur-dominated communities were able to persist in these same regions under rapidly fluctuating extreme climatic conditions until the end-Triassic, large-bodied, fastgrowing tachymetabolic dinosaurian herbivores requiring greater resources were unable to adapt to unstable high CO 2 environmental conditions of the Late Triassic.Early Mesozoic | carbon cycling | atmospheric CO 2 | terrestrial ecosystems | wildfires
Marine diatoms are silica-precipitating microalgae that account for over half of organic carbon burial in marine sediments and thus they play a key role in the global carbon cycle. Their evolutionary expansion during the Cenozoic era (66 Ma to present) has been associated with a superior competitive ability for silicic acid relative to other siliceous plankton such as radiolarians, which evolved by reducing the weight of their silica test. Here we use a mathematical model in which diatoms and radiolarians compete for silicic acid to show that the observed reduction in the weight of radiolarian tests is insufficient to explain the rise of diatoms. Using the lithium isotope record of seawater as a proxy of silicate rock weathering and erosion, we calculate changes in the input flux of silicic acid to the oceans. Our results indicate that the long-term massive erosion of continental silicates was critical to the subsequent success of diatoms in marine ecosystems over the last 40 My and suggest an increase in the strength and efficiency of the oceanic biological pump over this period.
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