Using hourly measurements to explore the role of secondary inorganic aerosol in PM2.5 during haze and fog in Hangzhou,China

This paper explores the role of the secondary inorganic aerosol （SIA） species ammonium,NH4＋,nitrate,NO3-,and sulfate,SO24-,during haze and fog events using hourly mass concentrations of PM2.5 measured at a suburban site in Hangzhou,China.A total of 546 samples were collected between 1 April and 8 May 2012.The samples were analyzed and classified as clear,haze or fog depending on visibility and relative humidity （RH）.The contribution of SIA species to PM2.5 mass increased to ～50％ during haze and fog.The mass contribution of nitrate to PM2.5 increased from 11％ during clear to 20％ during haze episodes.Nitrate mass exceeded sulfate mass during haze,while near equal concentrations were observed during fog episodes.The role of RH on the correlation between concentrations of SIA and visibility was examined,with optimal correlation at 60％-70％ RH.The total acidity during clear,haze and fog periods was 42.38,48.38 and 45.51 nmol m-3,respectively,indicating that sulfate,nitrate and chloride were not neutralized by ammonium during any period.The nitrate to sulfate molar ratio,as a function of the ammonium to sulfate molar ratio,indicated that nitrate formation during fog started at a higher ammonium to sulfate molar ratio compared to clear and haze periods.During haze and fog,the nitrate oxidation ratio increased by a factor of 1.6-1.7,while the sulfur oxidation ratio increased by a factor of 1.2-1.5,indicating that both gaseous NO2 and SO2 were involved in the reduced visibility.     

RCP2.6: exploring the possibility to keep global mean temperature increase below 2��C

The RCP2.6 emission and concentration pathway is representative of the literature on mitigation scenarios aiming to limit the increase of global mean temperature to 2°C. These scenarios form the low end of the scenario literature in terms of emissions and radiative forcing. They often show negative emissions from energy use in the second half of the 21st century. The RCP2.6 scenario is shown to be technically feasible in the IMAGE integrated assessment modeling framework from a medium emission baseline scenario, assuming full participation of all countries. Cumulative emissions of greenhouse gases from 2010 to 2100 need to be reduced by 70% compared to a baseline scenario, requiring substantial changes in energy use and emissions of non-CO₂ gases. These measures (specifically the use of bio-energy and reforestation measures) also have clear consequences for global land use. Based on the RCP2.6 scenario, recommendations for further research on low emission scenarios have been formulated. These include the response of the climate system to a radiative forcing peak, the ability of society to achieve the required emission reduction rates given political and social inertia and the possibilities to further reduce emissions of non-CO₂ gases.     

Extraction of P-wave reflections from microseisms

The last few years there has been a growing number of body-wave observations in noise records. In 1973, Vinnik conjectured that P-waves would even be the dominant wavemode, at epicentral distances of about 40 degrees and onwards from an oceanic source. At arrays far from offshore storms, surface waves induced by nearby storms would not mask the body-wave signal and hence primarily P-waves would be recorded. We measured at such an array in Egypt and indeed found a large proportion of P-waves. At the same time, a new methodology is under development to characterize the lithosphere below an array of receivers, without active sources or local earthquakes. Instead, transmitted waves are used which are caused by distant sources. These sources may either be transient or more stationary. With this new methodology, called seismic interferometry, reflection responses are extracted from the coda of transmissions. Combining the two developments, it is clear that there is a large potential for obtaining reflection responses from low-frequency noise. A potential practical advantage of using noise instead of earthquake responses would be that an array only needs to be deployed for a few days or weeks instead of months, to gather enough illumination. We used a few days of continuous noise, recorded with an array in the Abu Gharadig basin, Egypt. We split up the record in three distinct frequency bands and in many small time windows. Using array techniques and taking advantage of all three-component recordings, we could unravel the dominant wavemodes arriving in each time window and in each frequency band. The recorded wavemodes, and hence the noise sources, varied significantly per frequency band, and – to a lesser extent – per time window. Primarily P-waves were detected on the vertical component for two of the three frequency bands. For these frequency bands, we only selected the time windows with a favorable illumination. By subsequently, applying seismic interferometry, we retrieved P-wave reflection responses and delineated reflectors in the crust, the Moho and possibly the Lehmann discontinuity.     

Assessment of salinity status in intensively cultivated soils under semiarid climate, Murcia, SE Spain

This research presents the results from the assessment of the salinity status of a highly productive agricultural area, under a semiarid climate. The objectives were to: identify the origin of salts, assess seasonal changes of salt contents, and examine spatio-temporal and vertical variability of the presence and composition of salts. Soil samples from the surface horizon, and topsoil samples, soil profiles, water samples and salt precipitates on aggregates were collected in January and July 2009. High electrical conductivity was mainly the result of the poor low quality irrigation water. However, ions responsible for salinity were chlorides, sulfates, calcium, magnesium and sodium, while phosphates, ammonium, nitrates, and potassium were associated with fertilizers. SEM-EDX (scanning electron microscope-energy dispersive X-ray) analyses suggested that calcium sulfate came from both irrigation water and from a pedogenic source, as indicated by differences in crystal morphology and seasonal occurrence, which indicates that primary salinization is also a contributor to soil salinity in the area studied. Significant differences were reported between seasons. The electrical conductivity and concentrations of chloride, sulfates, calcium, magnesium, sodium, potassium, and nitrite are significantly higher in July. The observed differences were caused by the effect of soluble salt movement through evaporation and capillary rise, resulting in precipitation of salts on the surface. Multivariable, GIS and advanced laboratory analysis have confirmed to be useful techniques to identify the salts sources, spatial distribution of anions, and identification of vulnerable areas.     

Quaternary stratigraphy of the fladen area,central North Sea: A multidisciplinary study

Based on detailed stratigraphic investigations on a 200.6m long core (BGS borehole No. 81/26) from the Fladen Ground area (British sector), core material from the Sleipner field (Norwegian sector) and shallow seismic profiles between the core-sites, the following conclusions are drawn: (1) The North Sea was glaciated sometime during th elaterpart of Matuyama reversed period. A complete glacial-interglacial-glacial cycle is recorded in these sediments. (2) In a period of marine sedimentation in the Middle Pleistocene, a transgression-regression cycle under boreal-arctic regime is recorded. (3) The Fladen area has subsided between 0.9 and 0.6 m/ka through the later parts of the Quaternary (4) A major glacial event dated at between 130 and 200 ka is recorded as a thick till unit in 81/26. This till, which was deposited by ice moving from the southwest (Scotland), probably represents a period when the Scandinavian and British ice sheets coalesced in the North Sea. (5) Based on the seismic data and the stratigraphy of the Sleipner core, an ice-free, open embayment/dry land is favoured for the central North Sea during the Late Weichselian. (6) From the amino-acid data, it is shown that there has been an episodic style of sedimentation through the Quaternary. (7) of the investigated sediments (which span the last 1 mill. year) ca 98% have been deposited under arctic to boreal-arctic conditions.     

Variations in temperature and extent of Atlantic Water in the northern North Atlantic during the Holocene

We compare six high-resolution Holocene, sediment cores along a S–N transect on the Norwegian–Svalbard continental margin from ca 60°N to 77.4°N, northern North Atlantic. Planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties, including summer sea-surface temperatures (SST). The cores are located below the axis of the Norwegian Current and the West Spitsbergen Current, which today transport warm Atlantic Water to the Arctic. Sediment accumulation rates are generally high at all the core sites, allowing for a temporal resolution of 10–10² years. SST is reconstructed using different types of transfer functions, resulting in very similar SST trends, with deviations of no more than ±1.0/1.5 °C. A transfer function based on the maximum likelihood statistical approach is found to be most relevant. The reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the Younger Dryas–Preboreal transition. The earliest part of the Holocene was characterized by large temperature variability, including the Preboreal Oscillations and the 8.2 k event. In general, the early Holocene was characterized by SSTs similar to those of today in the south and warmer than today in the north, and a smaller S–N temperature gradient (0.23 °C/°N) compared to the present temperature gradient (0.46 °C/°N). The southern proxy records (60–69°N) were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening. The northern records (72–77.4°N) display a millennial-scale change associated with reduced insolation and a gradual weakening of the North Atlantic thermohaline circulation (THC). The observed northwards amplification of the early Holocene warming is comparable to the pattern of recent global warming and future climate modelling, which predicts greater warming at higher latitudes. The overall trend during mid and late Holocene was a cooling in the north, stable or weak warming in the south, and a maximum S–N SST gradient of ca 0.7 °C/°N at 5000 cal. years BP. Superimposed on this trend were several abrupt temperature shifts. Four of these shifts, dated to 9000–8000, 5500–3000 and 1000 and 400 cal. years BP, appear to be global, as they correlate with periods of global climate change. In general, there is a good correlation between the northern North Atlantic temperature records and climate records from Norway and Svalbard.     

Grosvenor Mountains 95 howardite pairing group: Insights into the surface regolith of asteroid 4 Vesta

Regolithic howardites are analogs for the surface materials of asteroid 4 Vesta, recently mapped by the Dawn spacecraft. Rigorously evaluating pairing of howardites recovered in 1995 in the Grosvenor Mountains (GRO 95), Antarctica, enables an examination of a larger, more representative regolith sample. Previous work on two of the howardites studied here concluded that GRO 95602 and GRO 95535 are solar wind‐rich surface regolith samples and that they are not paired with each other, leading to uncertainty regarding pairing relationships between the other GRO 95 howardites. Based on petrology, cosmic‐ray exposure history, and terrestrial age, four GRO 95 howardites are paired. The paired howardites (GRO 95534, 95535, 95574, 95581) were from a meteoroid with radius of 10–15 cm, a preatmospheric size comparable to that of Kapoeta, the largest known regolithic howardite. The paired GRO 95 howardites contain clasts of at least 18 separate HED lithologies, providing evidence they were assembled from diverse source materials. The total eucrite:diogenite mixing ratio (ratio of all eucrite lithologies to all diogenite lithologies) in the paired GRO 95 howardites is ~2:1. Petrographically determined basaltic eucrite:cumulate eucrite ratios in regolithic howardites, studied here and previously, vary more widely than total eucrite:diogenite ratios. Relative to eucritic pyroxene, plagioclase is depleted in these howardites, which provides evidence that plagioclase is preferentially comminuted in the vestan regolith. The extent of plagioclase depletion could be an indicator of regolith maturity.     

Challenges in adjoint-based optimization of a foam EOR process

We apply adjoint-based optimization to a surfactant-alternating gas foam process using a linear foam model introducing gradual changes in gas mobility and a nonlinear foam model giving abrupt changes in gas mobility as function of oil and water saturations and surfactant concentration. For the linear foam model, the objective function is a relatively smooth function of the switching time. For the nonlinear foam model, the objective function exhibits many small-scale fluctuations. As a result, a gradient-based optimization routine could have difficulty finding the optimal switching time. For the nonlinear foam model, extremely small time steps were required in the forward integration to converge to an accurate solution to the semi-discrete (discretized in space, continuous in time) problem. The semi-discrete solution still had strong oscillations in gridblock properties associated with the steep front moving through the reservoir. In addition, an extraordinarily tight tolerance was required in the backward integration to obtain accurate adjoints. We believe the small-scale oscillations in the objective function result from the large oscillations in gridblock properties associated with the front moving through the reservoir. Other EOR processes, including surfactant EOR and near-miscible flooding, have similar sharp changes and may present similar challenges to gradient-based optimization.     

Shell Middens,Cultural Chronologies,and Coastal Settlement on the Rhode River Sub‐Estuary of Chesapeake Bay,Maryland, USA

North America's Atlantic Coast has been a focus of human settlement and subsistence for millennia, but sea‐level rise, sedimentation, and other processes pose significant challenges for archaeological research. Radiocarbon dating of 31 shell middens near the Rhode River Estuary, Maryland provides an opportunity to evaluate human land use, settlement, and cultural chronologies on the Chesapeake Bay. Sixty calibrated radiocarbon dates on eastern oyster (Crassostrea virginica) shell and charcoal demonstrate that Native Americans, colonial, and historic peoples harvested oysters and other shellfish from at least 3200 years ago through the 19th century. The number of dated sites increases during the Late Woodland period after about 1000 cal yr B.P., a factor probably related to greater site visibility and preservation, as well as increased human exploitation of the watershed. Accumulation rates for five of the shell middens provide preliminary indications that some of the sites accumulated rapidly suggesting, along with other evidence, that many of the region's shell middens were logistical or perhaps seasonal camps. Our study demonstrates the importance of regional watershed surveys and radiocarbon dating programs to help build and refine cultural chronologies in coastal regions threatened by sea‐level rise and other processes.     

A 300-kyr record of aridity and wind strength in southwestern Africa: inferences from grain-size distributions of sediments on Walvis Ridge, SE Atlantic

The terrigenous fraction of sediments recovered from Walvis Ridge, SE Atlantic Ocean, reveals a history of southwestern African climate of the last 300 kyr. End-member modelling of a data set of grain-size distributions (n=428) results in three end members. The two coarsest end members are interpreted as eolian dust, the third end member as hemipelagic mud. The ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the SE trade winds. Trade winds were intensified during glacials compared to interglacials. Changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern African aridity. Late Quaternary southwestern African climate was relatively arid during the interglacial stages and relatively humid during the glacial stages, owing to meridional shifts in the atmospheric circulation system. During glacials the polar front shifted equatorward, resulting in a northward displacement of the zone of westerlies, causing increased rainfall in southwestern Africa. The equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient, leading to enhanced atmospheric circulation and increased trade-wind intensity.