Geochemical evidence for abrupt changes in relative strength of the Arabian monsoons during a stadial/interstadial climate transition

The occurrence and propagation of abrupt climate change between the high and low-latitudes has become an important focus of paleoclimatic and paleoceanographic research. The causes of abrupt change have significant implications for understanding future manifestations of similar forcings under late Holocene (‘Anthropocene’) boundary conditions. Of particular interest are signals indicative of sub-millennial scale climate change in the sub-tropics of similar magnitude and frequency to those recorded in Greenland ice cores. Earlier research in the Arabian Sea has highlighted the sensitivity of sedimentary organic carbon and nitrogen isotope measurements for recording the state of the SW monsoon and associated Arabian Sea Oxygen Minimum Zone. In this study, we exploit the unprecedented fidelity of the sedimentary δ¹⁵N record to identify a 20 cm interval at ODP Site 723 containing a stadial/inter-stadial interval between 43-42 Kyr BP. We employ sedimentary nitrogen isotopes, chlorin pigment and alkenone abundances, major and minor element analyses of highly-resolved (2 mm ≈ 10 yr) samples across this interval to compare a comprehensive, multi-proxy data set to understand (a) the processes contributing to the δ¹⁵N signal in the longer records of denitrification; and (b) the associated climatic events, especially the relative intensity of summer and winter monsoons at these times. A lack of evidence for bioturbation in excess of our 2 mm sampling resolution facilitates decadal-scale oceanographic and climatic reconstructions. Using a four-component flux-dilution model, we show that the deposition of carbonate decreased in parallel with an increase in Total Organic Matter flux from stadial to inter-stadial time. This interval is also marked by a significant drop in lithogenic (dust) accumulation, analogous to a similar decrease noted during deglaciation in the Western Arabian Sea. Combined with alkenone U₃₇^K′-derived estimates for sea surface temperature (SST), we conclude that the climatological shift from stadial to inter-stadial conditions at low latitudes was characterized by repeated switches in mean monsoon state approximately every 200 yr. The winter monsoon was the dominant mode during maximum stadial conditions; conversely the summer monsoon was dominant during maximum interstadial-like conditions. However, each interval was separated by a distinct ‘inter-monsoon’ mode, indicated by a higher continental dust flux but warmer SST. Proxy records for changing bottom-water oxygenation show near-identical results down to the mm-scale, but hint at increased export production leading the onset of anoxia during the stadial/inter-stadial transition. The coherence of all sedimentary signals depicts a wholesale reorganization of the Arabian Sea climate and marine ecosystem over approximately 200 years, a period that may be associated with monsoon modulation by small oscillations in solar irradiance.     

Economic‐Development Stakeholder Perspectives on Boomtown Dynamics in the Eagle Ford Shale,Texas

Unconventional oil and gas production in the United States reversed a decades‐old trend of rising oil imports, provided an argument for lifting the U.S. crude oil export ban and motivated the development of domestic natural gas export facilities. But the most visible impact of unconventional‐hydrocarbon extraction is the creation of boomtowns in rural regions. Despite widespread media coverage, scholarly analysis of boomtowns is restricted to regional econometric studies with little attention to how economic stakeholders understand and respond to booming economies. Here we analyze interviews with key economic stakeholders in the Eagle Ford Shale in Texas. Respondents consider their community's economic success relative to the price of oil and indicate concerns about the deterioration of roads, high housing demand, and skyrocketing wages. We also re‐examine John Gilmore's foundational work on boomtowns in the 1970s in the context of contemporary unconventional extraction.     

A Comparative Plume Study of DRO,GRO, Benzene,and MTBE: Implications for Risk Management

Groundwater remediation and no-further action decision making at petroleum underground storage tank (UST) sites has largely been based on an understanding of plume length, plume stability, and attenuation rates for key hydrocarbon constituents. Regulatory guidance to support and guide such decisions is based in part on plume studies involving individual hydrocarbon constituents, namely benzene and methyl tert-butyl ether (MTBE). Questions remain regarding whether current guidance is applicable to chemical mixtures such as gasoline range organics (GRO), diesel range organics (DRO), and oxygen containing organic compounds (OCOCs) resulting from hydrocarbon biodegradation. To help address this concern, data from California's GeoTracker database were used to estimate maximum plume lengths, plume stability, and attenuation rates of DRO (which can be used as an analytical surrogate for OCOCs) and GRO relative to benzene and MTBE. The distributions of maximum plume lengths were similar for the four constituents with medians ranging from 27 to 32 m. The fraction of monitoring wells with a decreasing concentration trend ranged from 19% for DRO to 40% for MTBE, while fewer than 7% of the wells had an increasing concentration trend for any of the constituents. Median attenuation rates ranged from 0.10% day⁻¹ for DRO to 0.17% day⁻¹ for MTBE. The results suggest attenuation based risk management is appropriate for DRO and GRO plumes at most petroleum UST sites.     

Downscaling reveals diverse effects of anthropogenic climate warming on the potential for local environments to support malaria transmission

The potential impact of climate warming on patterns of malaria transmission has been the subject of keen scientific and policy debate. Standard climate models (GCMs) characterize climate change at relatively coarse spatial and temporal scales. However, malaria parasites and the mosquito vectors respond to diurnal variations in conditions at very local scales. Here we bridge this gap by downscaling a series of GCMs to provide high-resolution temperature data for four different sites and show that although outputs from both the GCM and the downscaled models predict diverse but qualitatively similar effects of warming on the potential for adult mosquitoes to transmit malaria, the predicted magnitude of change differs markedly between the different model approaches. Raw GCM model outputs underestimate the effects of climate warming at both hot (3-fold) and cold (8–12 fold) extremes, and overestimate (3-fold) the change under intermediate conditions. Thus, downscaling could add important insights to the standard application of coarse-scale GCMs for biophysical processes driven strongly by local microclimatic conditions.     

Storm track response to ocean fronts in a global high-resolution climate model

Synoptic atmospheric eddies are affected by lower tropospheric air-temperature gradients and by turbulent heat fluxes from the surface. In this study we examine how ocean fronts affect these quantities and hence the storm tracks. We focus on two midlatitude regions where ocean fronts lie close to the storm tracks: the north-west Atlantic and the Southern Ocean. An atmospheric climate model of reasonably high resolution (~50 km) is applied in a climate-length (60 year) simulation in order to obtain stable statistics. Simulations with frontal structure in the sea surface temperature (SST) in one of the regions are compared against simulations with globally smoothed SST. We show that in both regions the ocean fronts have a strong influence on the transient eddy heat and moisture fluxes, not just in the boundary layer, but also in the free troposphere. Local differences in these quantities between the simulations reach 20–40 % of the maximum values in the simulation with smoothed SST. Averaged over the entire region of the storm track over the ocean the corresponding differences are 10–20 %. The effect on the transient eddy meridional wind variance is strong in the boundary layer but relatively weak above that. The potential mechanisms by which the ocean fronts influence the storm tracks are discussed, and our results are compared against previous studies with regional models, Aquaplanet models, and coarse resolution coupled models.     

Momentum and Turbulent Kinetic Energy Budgets Within the Park Avenue Street Canyon During the Joint Urban 2003 Field Campaign

Very few attempts have so far been made to quantify the momentum and turbulent kinetic energy (TKE) budgets within real urban canopies. In this study, sonic anemometer data obtained during the Joint Urban 2003 field campaign in Oklahoma City, U.S.A. were used for calculating the momentum and TKE budgets within a real-world urban street canyon. Sonic anemometers were deployed on multiple towers in the lower half of the canyon. Gradients in all three principal directions were included in the analyses. The storage and buoyancy terms were found to have negligible contributions to both the momentum and TKE budgets. The momentum budgets were generally found to be more complex than a simple balance of two physical processes. The horizontal terms were found to have significant and sometimes dominant contributions to the momentum and TKE budgets.     

Assessing the simulation and prediction of rainfall associated with the MJO in the POAMA seasonal forecast system

We assess the ability of the Predictive Ocean Atmosphere Model for Australia (POAMA) to simulate and predict weekly rainfall associated with the MJO using a 27-year hindcast dataset. After an initial 2-week atmospheric adjustment, the POAMA model is shown to simulate well, both in pattern and in intensity, the weekly-mean rainfall variation associated with the evolution of the MJO over the tropical Indo-Pacific. The simulation is most realistic in December?CFebruary (austral summer) and least realistic in March?CMay (austral autumn). Regionally, the most problematic area is the Maritime Continent, which is a common problem area in other models. Coupled with our previous demonstration of the ability of POAMA to predict the evolution of the large-scale structure of the MJO for up to about 3?weeks, this ability to simulate the regional rainfall evolution associated with the MJO translates to enhanced predictability of rainfall regionally throughout much of the tropical Indo-Pacific when the MJO is present in the initial conditions during October?CMarch. We also demonstrate enhanced prediction skill of rainfall at up to 3?weeks lead time over the north-east Pacific and north Atlantic, which are areas of pronounced teleconnections excited by the MJO-modulation of tropical Indo-Pacific rainfall. Failure to simulate and predict the modulation of rainfall in such places as the Maritime Continent and tropical Australia by the MJO indicates, however, there is still much room for improvement of the prediction of the MJO and its teleconnections.