SUNDIALS is a suite of advanced computational codes for solving large-scale problems that can be modeled as a system of nonlinear algebraic equations, or as initial-value problems in ordinary differential or differential-algebraic equations. The basic versions of these codes are called KINSOL, CVODE, and IDA, respectively. The codes are written in ANSI standard C and are suitable for either serial or parallel machine environments. Common and notable features of these codes include inexact Newton-Krylov methods for solving large-scale nonlinear systems; linear multistep methods for time-dependent problems; a highly modular structure to allow incorporation of different preconditioning and/or linear solver methods; and clear interfaces allowing for users to provide their own data structures underneath the solvers. We describe the current capabilities of the codes, along with some of the algorithms and heuristics used to achieve efficiency and robustness. We also describe how the codes stem from previous and widely used Fortran 77 solvers, and how the codes have been augmented with forward and adjoint methods for carrying out first-order sensitivity analysis with respect to model parameters or initial conditions.

The balance between photosynthetic organic carbon production and respiration controls atmospheric composition and climate 1,2. The majority of organic carbon is respired back to carbon dioxide in the biosphere, but a small fraction escapes remineralization and is preserved over geologic timescales 3. By removing reduced carbon from Earth's surface, this sequestration process promotes atmospheric oxygen accumulation 2 and carbon dioxide removal 1. Two major mechanisms have been proposed to explain organic carbon preservation: selective preservation of biochemically unreactive compounds 4,5 and protection resulting from interactions with a mineral matrix 6,7. While both mechanisms can play a role across a range of environments and timescales, their global relative importance on 10 3-to 10 5-year timescales remains uncertain 4. Here we present a global dataset of the distributions of organic carbon activation energy and corresponding radiocarbon ages in soils, sediments, and dissolved organic carbon; we find that activation energy distributions broaden over time in all mineral-containing samples. This result requires increasing bondstrength diversity, consistent with the formation of organo-mineral bonds 8 but inconsistent with selective preservation. Radiocarbon ages further reveal that high-energy, mineralbound organic carbon persists for millennia relative to low-energy, unbound organic carbon. Our results provide globally coherent evidence for the proposed 7 importance of mineral protection in promoting organic carbon preservation. We suggest that similar studies of bond-strength diversity in ancient sediments may elucidate how and why organic carbon preservation-and thus atmospheric composition and climate-has varied over geologic time. Two classes of mechanisms-selectivity and protection-have been proposed to explain why some organic carbon (OC) escapes remineralization in soils and sediments 4-7. Biochemical selectivity hypotheses state that intrinsically bioavailable compounds such as sugars and amino acids are rapidly respired, whereas "recalcitrant" (macro)molecules such as lignin are selectively preserved due to their low energy yield, large size, and/or a lack of enzymes that can decompose them 4,5. Selective preservation has been extensively documented in dissolved OC (DOC) 9 , decaying woody tissue 10 , and sapropel sediments containing almost exclusively organic matter 5. In contrast, protection hypotheses state that particles shield OC from respiration regardless of intrinsic recalcitrance, potentially due to occlusion within pore spaces that are inaccessible to microbes and their extracellular enzymes 4,8,11-14. Specifically, protection often involves inspiration was always invaluable. We thank the National Ocean Sciences Accelerator Mass Spectrometer staff, especially A

An atmospheric general circulation model is coupled to an atmospheric chemistry model to calculate the radiative forcing by anthropogenic sulfate and carbonaceous aerosols. The latter aerosols result from biomass burning as well as fossil fuel burning. The black carbon associated with carbonaceous aerosols is absorbant and can decrease the amount of reflected radiation at the top-of-the-atmosphere. In contrast, sulfate aerosols are reflectant and the amount of reflected radiation depends nonlinearly on the relative humidity. We examine the importance of treating the range of optical properties associated with sulfate aerosol at high relative humidities and find that the direct forcing by anthropogenic sulfate aerosols can decrease from !0.81 W m\ to !0.55 Wm\ if grid box average relative humidity is not allowed to increase above 90%. The climate forcing associated with fossil fuel emissions of carbonaceous aerosols is calculated to range from #0.16 to #0.20 Wm\, depending on how much organic carbon is associated with the black carbon from fossil fuel burning. The direct forcing of carbonaceous aerosols associated with biomass burning is calculated to range from !0.23 to !0.16 Wm\. The pattern of forcing by carbonaceous aerosols depends on both the surface albedo and the presence of clouds. Multiple scattering associated with clouds and high surface albedos can change the forcing from negative to positive.

[1] Present-day global anthropogenic emissions contribute more than half of the mass in submicron particles primarily due to sulfate and carbonaceous aerosol components derived from fossil fuel combustion and biomass burning. These anthropogenic aerosols increase cloud drop number concentration and cloud albedo. Here, we use an improved version of the fully coupled climate/chemistry models to investigate cloud susceptibility and the first indirect effect of anthropogenic aerosols (the Twomey effect). We examine the correspondence between the model simulation of cloud susceptibility and that inferred from satellite measurements to test whether our simulated aerosol concentrations and aerosol/cloud interactions give a faithful representation of these features. This comparison provides an overall measure of the adequacy of cloud cover and drop concentrations. We also address the impact of black carbon absorption in clouds on the first indirect forcing and examine the sensitivity of the forcing to different representations of natural aerosols. We find that including this absorption does not change the global forcing by more than 0.07 W m À2 , but that locally it could decrease the forcing by as much as 0. Citation: Chuang, C. C., J. E. Penner, J. M. Prospero, K. E. Grant, G. H. Rau, and K. Kawamoto, Cloud susceptibility and the first aerosol indirect forcing: Sensitivity to black carbon and aerosol concentrations,

[1] We present a global chemical transport model called the Integrated Massively Parallel Atmospheric Chemical Transport (IMPACT) model. This model treats chemical and physical processes in the troposphere, the stratosphere, and the climatically critical tropopause region, allowing for physically based simulations of past, present, and future ozone and its precursors. The model is driven by meteorological fields from general circulation models (GCMs) or assimilated fields representing particular time periods. It includes anthropogenic and natural emissions, advective and convective transport, vertical diffusion, dry deposition, wet scavenging, and photochemistry. Simulations presented here use meteorological fields from the National Center for Atmospheric Research (NCAR) Middle Atmospheric Community Climate Model, Version 3 (MACCM3). IMPACT simulations of radon/lead are compared to observed vertical profiles and seasonal cycles. IMPACT results for a full chemistry simulation, with approximately 100 chemical species and 300 reactions representative of a mid-1990s atmosphere, are presented. The results are compared with surface, satellite, and ozonesonde observations. The model calculates a total annual flux from the stratosphere of 663 Tg O 3 /year, and a net in situ tropospheric photochemical source (that is, production minus loss) of 161 Tg O 3 /year, with 826 Tg O 3 /year dry deposited. NO x is overpredicted in the lower midlatitude stratosphere, perhaps because model aerosol surface densities are lower than actual values or the NO x to NO y conversion rate is underpredicted. Analysis of the free radical budget shows that ozone and NO y abundances are simulated satisfactorily, as are HO x catalytic cycles and total production and removal rates for ozone.

The eruption of Mount Pinatubo introduced large amounts of sulfur‐containing particles into the stratosphere. Stratospheric ozone measured by ozonesondes and satellites is significantly lower following the June 1991 eruption and throughout 1992 and 1993. To clarify the mechanisms leading to effects on stratospheric ozone, time‐dependent stratospheric aerosol and gas experiment II (SAGE II) and cryogenic limb array elaton spectrometer (CLAES) aerosol optical extinction data and SAGE II surface area density are used as parameters in a two‐dimensional (2‐D) zonally averaged chemical radiative transport model. The model was integrated with time from before the eruption through December 1993. The modeled impact on global ozone results from increased rates of heterogeneous reactions on sulfate aerosols and from the increased radiative heating and scattering caused by these aerosols. The model's dynamical response to changes in forcing (from changes in radiatively active trace gas concentrations and from aerosol heating) is treated in one of three ways: (1) the stratospheric temperature is perturbed, with fixed seasonal circulation, (2) the circulation is perturbed, with fixed seasonal temperature, or (3) both circulation and temperature are unperturbed, when investigating only the impact of Mount Pinatubo increased aerosol surface area density (SAD) and aerosol scattering of actinic solar radiation, When the aerosol heating is allowed to modify the temperature distribution, the maximum change calculated in equatorial column ozone is −1.6%. The calculated equatorial temperature change and peak local ozone change in October 1991 are +6 K and −4%, respectively. When aerosol heating perturbs the circulation in the model, the maximum change in equatorial column ozone is −6%. Increased heterogeneous processing on sulfate aerosols is calculated to have changed equatorial column ozone in late 1991 by −1.5%. Global column ozone in the model in 1992 and 1993 changed by −2.8% and −2.4%, respectively. The relationship of ozone‐controlling processes in the lower stratosphere is altered as well; HOx becomes the most important catalytic cycle, followed by ClOx and NOx. This is driven by significant changes in trace gas concentrations. In October 1991, lower stratospheric, equatorial NOx decreased by 40%, ClOx increased by 60%, and HOx increased by 25%. When the effect of heterogeneous chemical processing on sulfate aerosols is combined with aerosol heating, modifying either circulation or temperature, dramatically different ozone fingerprints with time and latitude are predicted. Model‐derived changes in the equatorial region in column ozone best represented the observed data when perturbed circulation was combined with heterogeneous chemical effects. However, at high latitudes, the increased ozone production from the strengthening of the mean circulation tends to cancel the heterogeneous reduction of ozone. This is not in good agreement with observed data, especially in 1992 and 1993. When the circulation is held fixed and the tempe...

We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min–1) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ13C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ13C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ13C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n=66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n=36). Lastly, we show there exists no significant intra-sample δ13C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13C- and 12C-containing compounds (13–12∆E) of 0.3–1.8 J×mol–1, indicating that blank and mass-balance corrected RPO δ13C values accurately retain carbon source isotope signals to within 1–2‰.

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