ABOUT THIS COLLECTION

This open access archive contains publications from University of Arizona faculty, researchers and staff, primarily open-access versions of formally published journal articles. The collection includes published articles and final accepted manuscripts submitted by UA faculty under the UA Open Access Policy. The collection also includes books, book chapters, book reviews, presentations, data, and other scholarly materials submitters have chosen to make available in the repository.


HOW TO SUBMIT

  • Log in to the repository using your NetID and password
  • Click the "Submissions" link in the left sidebar (under "My Account")
  • Start a new submission in the UA Faculty Publications collection.
  • Library staff will check publisher policies, including embargo periods related to your submission.
  • You will receive an email with a persistent link to your submission when it is approved.

QUESTIONS?

Contact open-access@email.arizona.edu with your questions about the UA Faculty Publications collection.

Recent Submissions

  • Triassic–Jurassic Accretionary History and Tectonic Origin of Stikinia From U-Pb Geochronology and Lu-Hf Isotope Analysis, British Columbia

    George, S.W.M.; Nelson, J.L.; Alberts, D.; Greig, C.J.; Gehrels, G.E.; Department of Geosciences, University of Arizona (Blackwell Publishing Ltd, 2021)
    The timing of assembly and tectonic origins of terranes in the northern Cordillera of Alaska, British Columbia, and the Pacific Northwest are debated. Stikinia, a long-lived arc terrane, has an enigmatic regional Mesozoic accretionary history and its tectonic origins remain unconstrained. Zircon U-Pb geochronology and Lu-Hf isotopic data on Triassic–Jurassic sedimentary and igneous rocks from central Stikinia shed light on the terrane-scale effects of a latest Triassic–Early Jurassic collision between Stikinia and pericratonic Yukon-Tanana terrane. Main age peaks from central Stikinia are 250–160 Ma, reflecting ongoing Mesozoic arc-related igneous activity within Stikinia. Comparison of isotopic evolution and unconformity development between central Stikinia and northern Stikinia (Whitehorse trough) provide new constraints on regional latest Triassic–earliest Jurassic deformation. We attribute the shortening-related deformation to variable along-strike interactions during end-on collision with the Yukon-Tanana terrane, with significant crustal thickening at the northern apex of Stikinia that did not persist farther south. A small pre-Devonian zircon population is significant, as the oldest exposed rocks in Stikinia are Early Devonian. Pre-Devonian age peaks differ from those of the northern Yukon-Tanana terrane, but resemble zircons from southern Wrangellia. These zircons are likely multi-cyclic, derived from crust that originated in the Arctic region near the northern end of the Caledonide orogeny. We suggest that Stikinia was an independent crustal block prior to latest Triassic onset of collision with Yukon-Tanana terrane. The ongoing, end-on collision in turn promoted oroclinal assembly of the peri-Laurentian terranes. © 2021. American Geophysical Union. All Rights Reserved.
  • Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica

    Tibbett, E.J.; Scher, H.D.; Warny, S.; Tierney, J.E.; Passchier, S.; Feakins, S.J.; Department of Geosciences, University of Arizona (John Wiley and Sons Inc, 2021)
    The Eocene-Oligocene transition (EOT) marks the onset of Antarctic glaciation at 33.7 Ma. Although the benthic oxygen isotope record defines the major continental ice sheet expansion, recent sedimentary and geochemical evidence suggests the presence of earlier ephemeral ice sheets. Sediment cores from Ocean Drilling Program Legs 119 and 188 in Prydz Bay provide an archive of conditions in a major drainage system of East Antarctica. We study biomarker and microfossil evidence to discern how the vegetation and climate shifted between 36 and 33 Ma. Pollen was dominated by reworked Permian Glossopterid gymnosperms; however, penecontemporaneous Eocene pollen assemblages indicate that some vegetation survived the glacial advances. At the EOT, brGDGT soil biomarkers indicate abrupt cooling from 13°C to 8°C and soil pH increases from 6.0 to 6.7, suggesting drying which is further supported by plant wax hydrogen and carbon isotopic shifts of 20‰ and 1.1‰, respectively, and evidence for drying from weathering proxies. Although the terrestrial soil biomarker influx mostly precludes the use of TEX86, we find sea surface temperatures of 12°C in the late Eocene cooling to 8°C at the EOT. Marine productivity undergoes a sustained increase after the glacial advance, likely promoted by enhanced ocean circulation. Between the two glacial surge events of the Priabonian Oxygen Maximum at 37.3 Ma and the EOT at 33.7 Ma, we observe warming of 2–5°C at 35.7 and 34.7 Ma, with increase in penecontemporaneous pollen and enhanced marine productivity, capturing the last flickers of Antarctic warmth. © 2021. American Geophysical Union. All Rights Reserved.
  • Intermediate Aerosol Loading Enhances Photosynthetic Activity of Croplands

    Wang, X.; Wang, C.; Wu, J.; Miao, G.; Chen, M.; Chen, S.; Wang, S.; Guo, Z.; Wang, Z.; Wang, B.; et al. (Blackwell Publishing Ltd, 2021)
    Aerosols can affect crop photosynthesis by altering radiation and meteorological conditions. By combining field observations, mechanistic modeling, and satellite-retrieved solar-induced chlorophyll fluorescence (SIF), we assessed aerosols' impacts on crop photosynthesis from leaf to regional scale. We found that the initial increase in aerosol optical depth (AOD) enhanced photosynthesis of sun leaves, shade leaves, and canopy, which reached their maximum at AOD = 0.76, 1.13, and 0.93, respectively, and then decreased. Aerosol-induced changes in radiation regime and the concurrent high relative humidity led to such nonlinear responses. Similarly, the SIF of croplands in the North China Plain (NCP) also showed a bell-shaped response to aerosols. The optimal AOD level at which SIF reached the maximum value varied from 0.56 to 1.04, depending on the background meteorological conditions. Approximately 76%–90% of the NCP exceeded the optimal AOD level, suggesting that stringent aerosol pollution control could promote cropland productivity in this region. © 2021. American Geophysical Union. All Rights Reserved.
  • Large-Scale Reductions in Terrestrial Carbon Uptake Following Central Pacific El Niño

    Dannenberg, M.P.; Smith, W.K.; Zhang, Y.; Song, C.; Huntzinger, D.N.; Moore, D.J.P.; School of Natural Resources and the Environment, University of Arizona (Blackwell Publishing Ltd, 2021)
    The El Niño–Southern Oscillation (ENSO) affects global climate and ecosystems, but a recent shift toward more frequent central Pacific (CP) El Niño events could alter these relationships. Here, we show strong responses of the terrestrial carbon cycle to CP ENSO, exceeding even those to canonical eastern Pacific (EP) ENSO. Annual GPP of both global tropical forests and semiarid ecosystems were reduced by ∼0.3–0.5 Pg C yr−1 K−1 increase in CP sea surface temperatures (SSTs), which also reduced net ecosystem production of key tropical and semiarid regions like the Amazon and Australia, but with smaller (and generally not significant) responses to EP SSTs. Given these large negative responses of ecosystem production to CP SSTs, our results suggest that a recent shift toward CP-dominated ENSO events could further alter Earth's terrestrial carbon cycle, especially when coupled with possible increases in ENSO amplitude with continued warming. © 2021. American Geophysical Union. All Rights Reserved.
  • The Preservation of Climate-Driven Landslide Dams in Western Oregon

    Struble, W.T.; Roering, J.J.; Burns, W.J.; Calhoun, N.C.; Wetherell, L.R.; Black, B.A.; Department of Geosciences, University of Arizona; Laboratory of Tree Ring Research, University of Arizona (Blackwell Publishing Ltd, 2021)
    Bedrock landsliding, including the formation of landslide dams, is a predominant geomorphic process in steep landscapes. Clarifying the importance of hydrologic and seismic mechanisms for triggering deep-seated landslides remains an ongoing effort, and formulation of geomorphic metrics that predict dam preservation is crucial for quantifying secondary landslide hazards. Here, we identify >200 landslide-dammed lakes in western Oregon and utilize dendrochronology and enhanced 14C dating (“wiggle matching”) of “ghost forests” to establish slope failure timing at 20 sites. Our dated landslide dataset reveals bedrock landsliding has been common since the last Cascadia Subduction Zone earthquake in January 1700 AD. Our study does not reveal landslides that date to 1700 AD. Rather, we observe temporal clustering of at least four landslides in the winter of 1889/1890 AD, coincident with a series of atmospheric rivers that generated one of the largest regionally recorded floods. We use topographic and field analyses to assess the relation between dam preservation and topographic characteristics of the impounded valleys. In contrast to previous studies, we do not observe systematic scaling between dam size and upstream drainage area, though dam stability indices for our sites correspond with “stable” dams elsewhere. Notably, we observe that dams are preferentially preserved at drainage areas of ∼1.5 to 13 km2 and valley widths of ∼25 to 80 m, which may reflect the reduced downstream influence of debris flows and the accumulation of mature conifer trees upstream from landslide-dammed lake outlets. We suggest that wood accumulation upstream of landslide dams tempers large stream discharges, thus inhibiting dam incision. © 2021. American Geophysical Union. All Rights Reserved.
  • Extreme Precipitation Across Adjacent Burned and Unburned Watersheds Reveals Impacts of Low Severity Wildfire on Debris-Flow Processes

    McGuire, L.A.; Youberg, A.M.; Rengers, F.K.; Abramson, N.S.; Ganesh, I.; Gorr, A.N.; Hoch, O.; Johnson, J.C.; Lamom, P.; Prescott, A.B.; et al. (Blackwell Publishing Ltd, 2021)
    In steep landscapes, wildfire-induced changes to soil and vegetation can lead to extreme and hazardous geomorphic responses, including debris flows. The wildfire-induced mechanisms that lead to heightened geomorphic responses, however, depend on many site-specific factors including regional climate, vegetation, soil texture, and soil burn severity. As climate and land use change drive changes in fire regime, there is an increasing need to understand how fire alters geomorphic responses, particularly in areas where fire has been historically infrequent. Here, we examine differences in the initiation, magnitude, and particle-size distribution of debris flows that initiated within the area burned by the 2019 Woodbury Fire in central Arizona, USA, and those that initiated in a nearby unburned area. Despite similar rainfall intensities, unburned watersheds were less likely to produce debris flows. Debris flows in unburned areas initiated from both runoff and shallow landslides, while debris flows only initiated from runoff-related processes in the burned area. The grain-size distribution making up the matrix of debris-flow deposits within the burned area generally had a lower ratio of sand to silt relative to debris flows that initiated in the unburned area, though there were no systematic differences in the coarse fraction of debris-flow sediment between burned and unburned areas. Results help expand our ability to predict postwildfire debris-flow activity in a wider range of settings, specifically the Sonoran Desert ecoregion, and provide general insight into the impact of wildfire on geomorphic processes in steep terrain. © 2021. American Geophysical Union. All Rights Reserved.
  • An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast—Part 2: Circulation, Boundary Layer, and Clouds

    Painemal, D.; Corral, A.F.; Sorooshian, A.; Brunke, M.A.; Chellappan, S.; Afzali Gorooh, V.; Ham, S.-H.; O'Neill, L.; Smith, W.L., Jr; Tselioudis, G.; et al. (Blackwell Publishing Ltd, 2021)
    The Western North Atlantic Ocean (WNAO) is a complex land-ocean-atmosphere system that experiences a broad range of atmospheric phenomena, which in turn drive unique aerosol transport pathways, cloud morphologies, and boundary layer variability. This work, Part 2 of a 2-part paper series, provides an overview of the atmospheric circulation, boundary layer variability, three-dimensional cloud structure, and precipitation over the WNAO; the companion paper (Part 1) focused on chemical characterization of aerosols, gases, and wet deposition. Seasonal changes in atmospheric circulation and sea surface temperature explain a clear transition in cloud morphologies from small shallow cumulus clouds, convective clouds, and tropical storms in summer, to stratus/stratocumulus and multilayer cloud systems associated with winter storms. Synoptic variability in cloud fields is estimated using satellite-based weather states, and the role of postfrontal conditions (cold-air outbreaks) in the development of stratiform clouds is further analyzed. Precipitation is persistent over the ocean, with a regional peak over the Gulf Stream path, where offshore sea surface temperature gradients are large and surface fluxes reach a regional peak. Satellite data show a clear annual cycle in cloud droplet number concentration with maxima (minima) along the coast in winter (summer), suggesting a marked annual cycle in aerosol-cloud interactions. Compared with satellite cloud retrievals, four climate models qualitatively reproduce the annual cycle in cloud cover and liquid water path, but with large discrepancies across models, especially in the extratropics. The paper concludes with a summary of outstanding issues and recommendations for future work. © 2021. American Geophysical Union. All Rights Reserved.
  • Reproducibility of Coral Mn/Ca-Based Wind Reconstructions at Kiritimati Island and Butaritari Atoll

    Sayani, H.R.; Thompson, D.M.; Carilli, J.E.; Marchitto, T.M.; Chapman, A.U.; Cobb, K.M.; Department of Geosciences, University of Arizona (Blackwell Publishing Ltd, 2021)
    Global surface temperatures during the twentieth century are characterized by multidecadal periods of accelerated or reduced warming, which are thought to be driven by Pacific decadal variability, specifically changes in trade-wind strength. However, the relationship between trade-wind strength and global surface warming remains poorly constrained due to the scarcity of instrumental wind observations. Previous work has shown that corals growing at Tarawa Atoll (1.3°N, 173°E) incorporate dissolved Mn flushed from lagoon sediments by El Niño-related westerly wind events (WWEs), providing records of both westerly wind variability and trade-wind strength (on decadal time scales). Here, we explore the utility of this novel coral Mn/Ca-wind proxy at two nearby islands that also feature west-facing lagoons. Short coral Mn/Ca records from Butaritari (3°N, 173°E) and Kiritimati (2°N, 157.5°W) track WWEs, albeit with some intercolony variability in the magnitude and timing of the signal. Variability in coral Mn/Ca signal intensity among records from Butaritari suggests that wind-driven mixing of the sediment Mn reservoir may be finite and/or localized. At Kiritimati, a coral growing outside the lagoon shows higher Mn/Ca concentrations during the 1997/1998 El Niño event, suggesting that nearshore sediments may be an overlooked dissolved Mn reservoir. Taken together, these results highlight a need for additional studies of Mn reservoir variability within and across atolls that hold promise for recording WWEs. These results also suggest that Mn/Ca records from multiple coral colonies and sites are needed to generate robust coral-based wind reconstructions, particularly from sites with unknown or complex Mn transport pathways. © 2021. American Geophysical Union. All Rights Reserved.
  • Was Gale Crater (Mars) Connected to a Regionally Extensive Groundwater System?

    Roseborough, V.; Horvath, D.G.; Palucis, M.C.; Lunar & Planetary Laboratory, University of Arizona (Blackwell Publishing Ltd, 2021)
    Gale crater, home of the Curiosity rover, contains some of the best geomorphic and sedimentologic evidence on Mars for large lakes during the Hesperian and Amazonian. Orbital data and rover observations of delta deposits and terminations of gully networks suggest several phases of stable lake levels. However, the regional extent, water source (groundwater vs. surface water), and climate during each lake stand are debated. Consistent gully network termination elevations (GNTEs) within Gale and 17 regional craters suggest that GNTEs record paleolake levels. Hydrologic modeling indicates these lakes may have been coeval and the result of a regional groundwater table, recording a drying trend from subhumid conditions to semiarid conditions. Crater counting indicates that most lake-hosting craters impacted after ∼3.7 Ga and surface water persisted intermittently until the Early Amazonian, constraining the timing but not duration of lakes. This work has implications for understanding water sources and volumes affecting sediments investigated by Curiosity. © 2021. American Geophysical Union. All Rights Reserved.
  • Five Decades of Observed Daily Precipitation Reveal Longer and More Variable Drought Events Across Much of the Western United States

    Zhang, F.; Biederman, J.A.; Dannenberg, M.P.; Yan, D.; Reed, S.C.; Smith, W.K.; School of Natural Resources and the Environment, University of Arizona (Blackwell Publishing Ltd, 2021)
    Multiple lines of evidence suggest climate change will result in increased precipitation variability and consequently more frequent extreme events. These hydroclimatic changes will likely have significant socioecological impacts, especially across water-limited regions. Here we present an analysis of daily meteorological observations from 1976 to 2019 at 337 long-term weather stations distributed across the western United States (US). In addition to widespread warming (0.2 °C ± 0.01°C/decade, daily maximum temperature), we observed trends of reduced annual precipitation (−2.3 ± 1.5 mm/decade) across most of the region, with increasing interannual variability of precipitation. Critically, daily observations showed that extreme-duration drought became more common, with increases in both the mean and longest dry interval between precipitation events (0.6 ± 0.2, 2.4 ± 0.3 days/decade) and greater interannual variability in these dry intervals. These findings indicate that, against a backdrop of warming and drying, large regions of the western US are experiencing intensification of precipitation variability, with likely detrimental consequences for essential ecosystem services. © 2021. American Geophysical Union. All Rights Reserved.
  • New Observational Constraints on Warm Rain Processes and Their Climate Implications

    Dong, X.; Wu, P.; Wang, Y.; Xi, B.; Huang, Y.; Department of Hydrology and Atmospheric Sciences, University of Arizona (Blackwell Publishing Ltd, 2021)
    Low stratiform clouds have profound impacts on the hydrological cycle and the Earth’s radiation budget. However, realistic simulation of low clouds in climate models presents a major challenge. Here we employ the newly retrieved cloud and drizzle microphysical properties to improve the autoconversion and accretion parameterizations in a microphysical scheme. We find that the new autoconversion (accretion) rate contributes 14% lower (greater) to total drizzle water content than the original scheme near the cloud top. Compared to satellite results, the simulated cloud liquid water path (LWP) and shortwave cloud radiative effect using the original scheme in a climate model agree well on global average but with large regional differences. Simulations using the updated scheme show a 7.3% decrease in the light rain frequency, and a 10% increase in LWP. The updated microphysics scheme alleviates the long-lasting problem in most climate models, that is “too frequent and too light precipitation.”. © 2021. American Geophysical Union. All Rights Reserved.
  • Regional Exhumation and Tectonic History of the Shanxi Rift and Taihangshan, North China

    Clinkscales, C.; Kapp, P.; Thomson, S.; Wang, H.; Laskowski, A.; Orme, D.A.; Pullen, A.; Department of Geosciences, University of Arizona (Blackwell Publishing Ltd, 2021)
    This study presents a comprehensive low-temperature thermochronometric data set from the Shanxi Rift, Taihangshan, and eastern Ordos block in North China, including new apatite fission track and apatite (U-Th-Sm)/He data and published apatite and zircon fission track and (U-Th-Sm)/He data. We use these data and new thermal history inversion models to reveal that the Shanxi Rift and Taihangshan experienced an increase in cooling rates between ca. 110–70 Ma and ca. 50–30 Ma. A preceding ca. 160–135 Ma cooling event is generally restricted to the western rift margin in the Lüliangshan and Hengshan. In contrast, the ca. 50–30 Ma cooling event was widespread and occurred coevally with the opening of the Bohai Basin and slip across the NNE-striking Eastern Taihangshan fault. In the southern rift zone, however, exhumation beginning ca. 50 Ma was likely associated with fault block uplift across the ESE–striking Qinling and Huashan faults, which accompanied the extensional opening of the Weihe Graben. Coeval fault slip along the NNE–striking Eastern Taihangshan faults and ESE–striking Qinling and Huashan faults was associated with NW-SE extension in North China related to oblique subduction of the Pacific plate under Eastern Asia and slow convergence rates. The Shanxi Rift is commonly attributed to Late Miocene and younger extension, but our new thermochronologic data do not precisely record the onset of rifting. However, our inversion models do suggest ≤∼50°C of Neogene–Quaternary cooling, consistent with ≤∼2 km of footwall uplift across most range-bounding faults. © 2021. American Geophysical Union. All Rights Reserved.
  • Physical and Chemical Evolution of Lunar Mare Regolith

    O'Brien, P.; Byrne, S.; Lunar and Planetary Laboratory, University of Arizona (Blackwell Publishing Ltd, 2021)
    The lunar landscape evolves both physically and chemically over time due to impact cratering and energetic processes collectively known as space weathering. Despite returned soil samples and global remote sensing reflectance measurements, the rate of space weathering in the lunar regolith is not well understood. To address this, we developed a novel three-dimensional landscape evolution model to simulate the physical processes that control the burial, excavation, and transport of regolith on airless bodies. Applying this model to the lunar mare, we find that over billions of years of surface evolution, material typically spends only a few million years on the surface where it is exposed to the effects of space weathering. The small surface residence times are a result of vigorous mixing by small-scale impacts, predominantly driven by secondary crater formation. We deduce the rate of space weathering by comparing our modeled distribution of surface residence times on the lunar mare to measurements of space weathering maturity from Apollo soil samples and orbital surface reflectance datasets. These chemical constraints indicate that soil on the lunar mare reaches maturity in 7 Myr of cumulative surface exposure though due to uncertainties in the rate of small secondary crater production, this timescale could be 2–3 times higher. Weathering progresses more rapidly upon initial exposure to space but the surface residence time required to achieve maturity is realized over billions of years as regolith is repeatedly buried and exposed by small impacts. © 2020. American Geophysical Union. All Rights Reserved.
  • Sequential Abiotic-Biotic Processes Drive Organic Carbon Transformation in Peat Bogs

    Fudyma, J.D.; Toyoda, J.G.; Chu, R.K.; Weitz, K.K.; Heyman, H.M.; Eder, E.; Hoyt, D.W.; Gieschen, H.; Graf Grachet, N.; Wilson, R.M.; et al. (Blackwell Publishing Ltd, 2021)
    Peatlands, which store one third of the terrestrial carbon (C), are subject to large disturbances under a changing climate. It is crucial to understand how microbial and physiochemical factors affect the vulnerability of these large C stores to predict climate-induced greenhouse gas fluxes. Here, we used a combination of mass spectrometry and spectroscopy techniques, to understand sequential biotic and abiotic degradation pathways of Sphagnum fallax leachate in an anaerobic incubation experiment, in the presence and absence of microorganisms. Removal of microorganisms was carried out by passing aqueous samples through 0.2-µm filters. Our results revealed that S. fallax leachate degradation by abiotic reactions is a significant contributor to CO2 production. Further, abiotic factors, such as low pH, are responsible for partial dissolved organic carbon (DOC) degradation that produces bioavailable compounds that shift microbial metabolic pathways and stimulate respiration in peat bogs. Acid-catalyzed hydrolysis of Sphagnum- produced glycosides can provide the microbial communities with glucose and stimulate microbial respiration of DOC to CO2. These results, while unique to peatlands, demonstrate the importance and underscore the complexity of sequential abiotic and biotic processes on C cycling in peat bogs. It is therefore crucial to incorporate abiotic degradation and sequential below-ground biotic and abiotic interactions into climate models for a better prediction of the influence of climate change on DOC stability in peatlands. These findings might not be representative of other ecosystems with different environmental conditions including mineral-rich peatlands and plant matter in surface peat horizons that comprise discrete microbial populations, and DOC composition. © 2021. American Geophysical Union. All Rights Reserved.
  • Discerning Changes in High-Frequency Climate Variability Using Geochemical Populations of Individual Foraminifera

    Glaubke, R.H.; Thirumalai, K.; Schmidt, M.W.; Hertzberg, J.E.; Department of Geosciences, University of Arizona (John Wiley and Sons Inc, 2021)
    Individual foraminiferal analysis (IFA) has proven to be a useful tool in reconstructing the amplitude of high-frequency climate signals such as the annual cycle and the El Niño-Southern Oscillation (ENSO). However, using IFA to evaluate past changes in climate variability is complicated by many factors including geographic location, foraminiferal ecology, methods of sample processing, and the influence of multiple, superimposed high-frequency climate signals. Robust statistical tools and rigorous uncertainty analysis are therefore required to ensure the reliability of IFA-based interpretations of paleoclimatic change. Here, we present a new proxy system model—called the Quantile Analysis of Temperature using Individual Foraminiferal Analyses (QUANTIFA)—that combines methods for assessing IFA detection sensitivity with analytical tools for processing and interpreting IFA data to standardize and streamline reconstructions employing IFA-Mg/Ca measurements. Model exercises with simulated and real IFA data demonstrate that the dominant signal retained by IFA populations is largely determined by the annual-to-interannual ratio of climate variability at a given location and depth and can be impacted by seasonal biases in foraminiferal productivity. In addition, our exercises reveal that extreme quantiles can be reliable indicators of past changes in climate variability, are often more sensitive to climate change than quantiles within the distributional interior, and can be used to distinguish changes in interannual phenomena like ENSO from seasonality. Altogether, QUANTIFA provides a useful tool for modeling IFA uncertainties and processing IFA data that can be leveraged to establish a history of past climate variability. © 2021. American Geophysical Union. All Rights Reserved.
  • Magnetic Anomalies in Five Lunar Impact Basins: Implications for Impactor Trajectories and Inverse Modeling

    Hood, L.L.; Oliveira, J.S.; Andrews-Hanna, J.; Wieczorek, M.A.; Stewart, S.T.; Lunar and Planetary Laboratory, University of Arizona (Blackwell Publishing Ltd, 2021)
    A recent large-scale map of the lunar crustal magnetic field is examined for the existence of magnetic anomalies internal to ringed impact basins. It is found that, of 25 basins with upper preNectarian and younger ages, 18 contain mapped internal anomalies with amplitudes of at least 1 nT at 30 km altitude. Of these, five are most confidently judged to contain intrinsic anomalies (i.e., anomalies located within the inner basin rims and originating at the times of basin formation): Crisium, Humboldtianum, Mendel-Rydberg, Moscoviense, and Nectaris. Comparing the anomaly distributions with previous numerical simulations of the impact of iron-rich planetesimals to form a large (SPA-sized) basin, inferences are drawn about the likely trajectories of the impactors. Specifically, results suggest that impactor trajectories for these basins were within ∼45° of being vertical and tended to lie on average parallel to the lunar equatorial plane and the ecliptic plane. Inverse modeling of anomalies within these basins yields inferred directions of magnetization that are difficult to reconcile with the axial centered dipole hypothesis for the geometry of the internal lunar dynamo field: Paleomagnetic pole positions are widely scattered and, in agreement with a recent independent study, the two main anomalies within Crisium yield significantly different directions of magnetization. © 2020. American Geophysical Union. All Rights Reserved.
  • A New Large-Scale Map of the Lunar Crustal Magnetic Field and Its Interpretation

    Hood, L.L.; Torres, C.B.; Oliveira, J.S.; Wieczorek, M.A.; Stewart, S.T.; Lunar and Planetary Laboratory, University of Arizona (Blackwell Publishing Ltd, 2021)
    A new large-scale map of the lunar crustal magnetic field at 30 km altitude covering latitudes from 65°S to 65°N has been produced using high-quality vector magnetometer data from two complementary polar orbital missions, Lunar Prospector and SELENE (Kaguya). The map has characteristics similar to those of previous maps but better resolves the shapes and distribution of weaker anomalies. The strongest group of anomalies is located on the northwest side of the South Pole-Aitken basin approximately antipodal to the Imbrium basin. On the near side, both strong isolated anomalies and weaker elongated anomalies tend to lie along lines oriented radial to Imbrium. These include named anomalies such as Reiner Gamma, Hartwig, Descartes, Abel, and Airy. The statistical significance of this tendency for elongated anomalies is verified by Monte Carlo simulations. Great circle paths determined by end points of elongated anomaly groups and the locations of five individual strong anomalies converge within the inner rim of Imbrium and intersect within the Imbrium antipode zone. Statistically significant evidence for similar alignments northwest of the Orientale basin is also found. The observed distribution of anomalies on the near side and the location of the strongest anomaly group antipodal to Imbrium are consistent with the hypothesis that iron from the Imbrium impactor was mixed into ejecta that was inhomogeneously deposited downrange in groups aligned radial to the basin and concentrated antipodal to the basin. © 2021. American Geophysical Union. All Rights Reserved.
  • An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast – Part 1: Analysis of Aerosols, Gases, and Wet Deposition Chemistry

    Corral, A.F.; Braun, R.A.; Cairns, B.; Gorooh, V.A.; Liu, H.; Ma, L.; Mardi, A.H.; Painemal, D.; Stamnes, S.; van Diedenhoven, B.; et al. (Blackwell Publishing Ltd, 2021)
    The Western North Atlantic Ocean (WNAO) and adjoining East Coast of North America are of great importance for atmospheric research and have been extensively studied for several decades. This broad region exhibits complex meteorological features and a wide range of conditions associated with gas and particulate species from many sources regionally and other continents. As Part 1 of a 2-part paper series, this work characterizes quantities associated with atmospheric chemistry, including gases, aerosols, and wet deposition, by analyzing available satellite observations, ground-based data, model simulations, and reanalysis products. Part 2 provides insight into the atmospheric circulation, boundary layer variability, three-dimensional cloud structure, properties, and precipitation over the WNAO domain. Key results include spatial and seasonal differences in composition along the North American East Coast and over the WNAO associated with varying sources of smoke and dust and meteorological drivers such as temperature, moisture, and precipitation. Spatial and seasonal variations of tropospheric carbon monoxide and ozone highlight different pathways toward the accumulation of these species in the troposphere. Spatial distributions of speciated aerosol optical depth and vertical profiles of aerosol mass mixing ratios show a clear seasonal cycle highlighting the influence of different sources in addition to the impact of intercontinental transport. Analysis of long-term climate model simulations of aerosol species and satellite observations of carbon monoxide confirm that there has been a significant decline in recent decades among anthropogenic constituents owing to regulatory activities. © 2021. American Geophysical Union. All Rights Reserved.
  • The effect of anthropogenic aerosols on the aleutian low

    Dow, W.J.; Maycock, A.C.; Lofverstrom, M.; Smith, C.J.; Department of Geosciences, University of Arizona (American Meteorological Society, 2021)
    Past studies have suggested that regional trends in anthropogenic aerosols can influence the Pacific decadal oscillation (PDO) through modulation of the Aleutian low. However, the robustness of this connection is debated. This study analyzes changes to the Aleutian low in an ensemble of climate models forced with large, idealized global and regional black carbon (BC) and sulfate aerosol perturbations. To isolate the role of ocean feedbacks, the experiments are performed with an interactive ocean and with prescribed sea surface temperatures. The results show a robust weakening of the Aleutian low forced by a global tenfold increase in BC in both experiment configurations. A linearized steady-state primitive equation model is forced with diabatic heating anomalies to investigate the mechanisms through which heating from BC emissions influences the Aleutian low. The heating from BC absorption over India and East Asia generates Rossby wave trains that propagate into the North Pacific sector, forming an upper-tropospheric ridge. Sources of BC outside of East Asia enhance the weakening of the Aleutian low. The responses to a global fivefold and regional tenfold increase in sulfate aerosols over Asia show poor consistency across climate models, with a multimodel mean response that does not project strongly onto the Aleutian low. These findings for a large, idealized step increase in regional sulfate aerosol differ from previous studies that suggest the transient increase in sulfate aerosols over Asia during the early twenty-first century weakened the Aleutian low and induced a transition to a negative PDO phase. © 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).
  • The amazon water cycle: perspectives from water budget closure and ocean salinity

    Eyre, J.E.J.R.; Zeng, X.; Department of Hydrology and Atmospheric Sciences, University of Arizona (American Meteorological Society, 2021)
    Global and regional water cycle includes precipitation, water vapor divergence, and change of column water vapor in the atmosphere, and land surface evapotranspiration, terrestrial water storage change, and river discharge, which is linked to ocean salinity near the river mouth. The water cycle is a crucial component of the Earth system, and numerous studies have addressed its individual components (e.g., precipitation). Here we assess, for the first time, if remote sensing and reanalysis datasets can accurately and self-consistently portray the Amazon water cycle. This is further assisted with satellite ocean salinity measurements near the mouth of the Amazon River. The widely used practice of taking the mean of an ensemble of datasets to represent water cycle components (e.g., precipitation) can produce large biases in water cycle closure. Closure is achieved with only a small subset of data combinations (e.g., ERA5 precipitation and evapotranspiration plus GRACE satellite terrestrial water storage), which rules out the lower precipitation and higher evapotranspiration estimates, providing valuable constraints on assessments of precipitation, evapotranspiration, and their ratio. The common approach of using the Óbidos stream gauge (located hundreds of kilometers from the river mouth) multiplied by a constant (1.25) to represent the entire Amazon discharge is found to misrepresent the seasonal cycle, and this can affect the apparent influence of Amazon discharge on tropical Atlantic salinity. Ó 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy

View more