The satellite reversion of dissolved organic carbon (DOC) based on the analysis of the mixing behavior of DOC and colored dissolved organic matter: the East China Sea as an example

The retrieval of dissolved organic carbon (DOC) distribution by remote sensing is mainly based on the empirical relationship of DOC concentration and colored dissolved organic matter (CDOM) concentration in many literatures. To investigate the nature of this relationship, the distributions and mixing behaviors of DOC and CDOM are reviewed in the world’s major estuaries and bays. It is found that, generally, the CDOM concentration is well correlated with the salinity in most estuaries, while DOC usually shows a nonconservative behavior which leads to a weak correlation between the DOC concentration and the CDOM concentration. To establish a good satellite reversion of the DOC concentration, the East China Sea(ECS) was taken as an example, and the mixing behavior of DOC and CDOM as well as the influence of biogeochemical processes were analyzed except for the physical mixing process with the data from late autumn (November, 2010) and winter (December, 2009) cruises. In the two ECS cruises, the CDOM concentration was found to be tightly correlated with the salinity, influenced little by the photochemical or biological processes. The data from the winter cruise show that DOC followed a conservative mixing along the salinity gradient, while in the late autumn cruise it was significantly affected by the biological activities, resulting in a poor correlation between the DOC and the CDOM. Accordingly, an improved DOC algorithm (CSDM) was proposed: when the biological influence was significant (Chl a greater than 0.8 μg/dm3 ), DOC was retrieved by the conservative and biological model, and if the conservative mixing was dominant (Chl a less than 0.8 μg/dm3 ), the direct DOC concentration and CDOM concentration relationship was used. Based on the proposed algorithm, a reasonable DOC distribution for the ECS from satellite was obtained in this study, and the proposed method can be applied to the other large river-dominant marginal sea.     

Areas of the global major river plumes

River plumes are the regions where the most intense river-sea-land interaction occurs, and they are characterized by complex material transport and biogeochemical processes. However, due to their highly dynamic nature, global river plume areas have not yet been determined for use in synthetic studies of global oceanography. Based on global climatological monthly averaged salinity data from the NOAA World Ocean Atlas 2009 (WOA09), and monthly averaged salinity contour maps of the East and South China Seas from the Chinese Marine Atlas, we extract the monthly plume areas of major global rivers using a geographic information system (GIS) technique. Only areas with salinities that are three salinity units lower than the average salinity in each ocean are counted. This conservative estimate shows that the minimum and maximum monthly values of the total plume area of the world’s 19 largest rivers are 1.72 × 10 6 km 2 in May and 5.38 × 10 6 km 2 in August. The annual mean area of these river plumes (3.72 × 10 6 km 2 ) takes up approximately 14.2% of the total continental shelves area worldwide (26.15 × 10 6 km 2 ). This paper also presents river plume areas for different oceans and latitude zones, and analyzes seasonal variations of the plume areas and their relationships with river discharge. These statistics describing the major global river plume areas can now provide the basic data for the various flux calculations in the marginal seas, and therefore will be of useful for many oceanographic studies.     

Advances in landslide nowcasting: evaluation of a global and regional modeling approach

The increasing availability of remotely sensed data offers a new opportunity to address landslide hazard assessment at larger spatial scales. A prototype global satellite-based landslide hazard algorithm has been developed to identify areas that may experience landslide activity. This system combines a calculation of static landslide susceptibility with satellite-derived rainfall estimates and uses a threshold approach to generate a set of ‘nowcasts’ that classify potentially hazardous areas. A recent evaluation of this algorithm framework found that while this tool represents an important first step in larger-scale near real-time landslide hazard assessment efforts, it requires several modifications before it can be fully realized as an operational tool. This study draws upon a prior work’s recommendations to develop a new approach for considering landslide susceptibility and hazard at the regional scale. This case study calculates a regional susceptibility map using remotely sensed and in situ information and a database of landslides triggered by Hurricane Mitch in 1998 over four countries in Central America. The susceptibility map is evaluated with a regional rainfall intensity–duration triggering threshold and results are compared with the global algorithm framework for the same event. Evaluation of this regional system suggests that this empirically based approach provides one plausible way to approach some of the data and resolution issues identified in the global assessment. The presented methodology is straightforward to implement, improves upon the global approach, and allows for results to be transferable between regions. The results also highlight several remaining challenges, including the empirical nature of the algorithm framework and adequate information for algorithm validation. Conclusions suggest that integrating additional triggering factors such as soil moisture may help to improve algorithm performance accuracy. The regional algorithm scenario represents an important step forward in advancing regional and global-scale landslide hazard assessment.     

Pressure-temperature-fluid constraints for the Emmaville-Torrington emerald deposit, New South Wales, Australia: Fluid inclusion and stable isotope studies

The Emmaville-Torrington emeralds were first discovered in 1890 in quartz veins hosted within a Permian metasedimentary sequence, consisting of meta-siltstones, slates and quartzites intruded by pegmatite and aplite veins from the Moule Granite. The emerald deposit genesis is consistent with a typical granite-related emerald vein system. Emeralds from these veins display colour zonation alternating between emerald and clear beryl. Two fluid inclusion types are identified: three-phase (brine+vapour+halite) and two-phase (vapour+liquid) fluid inclusions. Fluid inclusion studies indicate the emeralds were precipitated from saline fluids ranging from approximately 33 mass percent NaCl equivalent. Formational pressures and temperatures of 350 to 400 °C and approximately 150 to 250 bars were derived from fluid inclusion and petrographic studies that also indicate emerald and beryl precipitation respectively from the liquid and vapour portions of a two-phase (boiling) system. The distinct colour zonations observed in the emerald from these deposits is the first recorded emerald locality which shows evidence of colour variation as a function of boiling. The primary three-phase and primary two-phase FITs are consistent with alternating chromium-rich ??striped?? colour banding. Alternating emerald zones with colourless beryl are due to chromium and vanadium partitioning in the liquid portion of the boiling system. The chemical variations observed at Emmaville-Torrington are similar to other colour zoned emeralds from other localities worldwide likely precipitated from a boiling system as well.     

Glacially derived material in an Inner Mongolian desert lake during Marine Isotope Stage 2

Establishing the precise timing of continental glacial dynamics and abrupt high‐latitude climate events is crucial to understanding the causes of global climate change. Here we present multi‐proxy records in a lake sediment core from arid Inner Mongolia (Wuliangsuhai Lake) that show two distinct glacially derived sedimentation events at ～26.2–21.8 and ～17.3–11.5k cal a BP. Fine sediments from the Last Glacial Maximum separate these glacially derived coarse sediments. Within these intervals, the occurrence of granite clasts at ～24–23.5, 17.3–17 and 15.6–14.1k cal a BP implies either sediment discharge by meltwater as well as strong current flow in the Yellow River and/or sediment influx through hill‐slope mass wasting and landsliding from the nearby Yin Mountains. Surface microfeatures of quartz grains and spot elemental analysis of black specks in these intervals, however, indicate that physical weathering is dominant and that the provenance of the rocks is probably from a glacial source. To the best of our knowledge, this is the first time glacier‐derived materials have been detected in any desert lake in the Yellow River basin. The occurrence of granite clasts roughly correlates with Heinrich events in the North Atlantic, suggesting synchronous ice sheet dynamics in high‐ and mid‐latitude regions during the Last Glacial period. Although our data provide unprecedented evidence for the influence of glacier‐related processes in arid Inner Mongolia, further well‐dated records are clearly needed to re‐evaluate the correlative inference drawn between granite clast layers in Wuliangsuhai Lake and Heinrich events in the North Atlantic. Copyright © 2012 John Wiley & Sons, Ltd.     

Carbon isotopic composition and lattice-bound carbonate of Peru-Chile margin phosphorites

New light-stable carbonate-carbon isotope and lattice-bound CO₂ data from Quaternary Peru-Chile margin phosphatic nodules, crusts and pelletal grains, and from associated dolomicritic concretions, are presented, which provide constraints on the timing and mechanisms of growth of these phases in organic carbon-rich sediments. Comparison of δ¹³C values from carbonate fluorapatite (CFA) nodules and pelletal grains (−4.8 to 0.0‰ and −2.9 to +1.0‰ PDB, respectively) with pore-water total dissolved δ¹³C values from these sediments suggests early authigenic CFA precipitation from pore waters within a few centimeters of the sediment-water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter. In contrast, the dolomicritic cores of nodules recovered from about 12°S display both strongly negative to positive δ¹³C values (−10.8 to +6.1‰) characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes.

The amount of structural carbonate in CFA suggests that carbonate substitution generally increases as δ¹³C in CFA decreases, a probable consequence of increasing carbonate and accompanying charge-balancing substitutions in the CFA lattice in response to increasing pore-water carbonate ion concentrations with depth below the sediment-water interface. In one buried upward-growing nodule, decreasing CFA δ¹³C and increasing structural CO₂ also correspond to decreasing CFA growth rates. These data suggest that in addition to other constraints such as pore-water phosphorus and fluoride availability, the lower limit of CFA precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations. In organic-rich Peru-Chile margin sediments this depth threshold appears to be at approximately 5–10 cm below the sediment-water interface where maximum CFA CO₂ contents of about 6 Wt.% occur; in less organic-rich settings, greater depths of precipitation of CFA may be anticipated. Below this relatively shallow depth of CFA precipitation on the Peru shelf, high pore-water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates.     

Using entropy theory to improve the definition of homogeneous regions in the semi-arid region of Brazil

ABSTRACT

Although the semi-arid region of Brazil appears to be homogeneous due to drought conditions, there is a great deal of variability in climatic elements in the region, so that the definition of homogeneous regions will provide the deployment of measures appropriate for each locality. However, the limited information on climatic parameters in the region makes it difficult to define these regions. This problem can, however, be alleviated by the use of entropy theory. Therefore, this study aimed to investigate the potential of the theory to identify hydrologically homogeneous regions for conditions of the semi-arid region of Brazil. Entropy-based Disorder Index (DI) data were computed, based on monthly precipitation and monthly water balance (precipitation – reference evapotranspiration) for 290 gauge stations. For defining homogeneous regions, cluster analysis was utilized, using the data on geographical information about rain gauges (latitude and longitude), annual precipitation, annual water balance, coefficient of skewness, coefficient of kurtosis and DI. The identification of homogeneous regions in the Brazilian semi-arid region was only possible when the grouping of stations was performed, based on DI for precipitation and latitude. Results showed the definition of seven homogeneous regions in the semi-arid region of Brazil.     

Regional coupled ocean–atmosphere downscaling in the Southeast Pacific: impacts on upwelling, mesoscale air–sea fluxes, and ocean eddies

Ocean–atmosphere coupling in the Humboldt Current System (HCS) of the Southeast Pacific is studied using the Scripps Coupled Ocean–atmosphere Regional (SCOAR) model, which is used to downscale the National Center for Environmental Prediction (NCEP) Reanalysis-2 (RA2) product for the period 2000–2007 at 20-km resolution. An interactive 2-D spatial smoother within the sea-surface temperature (SST)–flux coupler is invoked in a separate run to isolate the impact of the mesoscale (～50–200 km, in the oceanic sense) SST field felt by the atmosphere in the fully coupled run. For the HCS, SCOAR produces seasonal wind stress and wind stress curl patterns that agree better with QuikSCAT winds than those from RA2. The SCOAR downscaled wind stress distribution has substantially different impacts on the magnitude and structure of wind-driven upwelling processes along the coast compared to RA2. Along coastal locations such as Arica and Taltal, SCOAR and RA2 produce seasonally opposite signs in the total wind-driven upwelling transport. At San Juan, SCOAR shows that upwelling is mainly due to coastal Ekman upwelling transport, while in RA2 upwelling is mostly attributed to Ekman pumping. Fully coupled SCOAR shows significant SST–wind stress coupling during fall and winter, while smoothed SCOAR shows insignificant coupling throughout, indicating the important role of ocean mesoscale eddies on air–sea coupling in HCS. Coupling between SST, wind speed, and latent heat flux is incoherent in large-scale coupling and full coupling mode. In contrast, coupling between these three variables is clearly identified for oceanic mesoscales, which suggests that mesoscale SST affects latent heat directly through the bulk formulation, as well as indirectly through stability changes on the overlying atmosphere, which affects surface wind speeds. The SST–wind stress and SST–heat-flux couplings, however, fail to produce a strong change in the ocean eddy statistics. No rectified effects of ocean–atmosphere coupling were identified for either the atmospheric or oceanic mean conditions, suggesting that mesoscale coupling is too weak in this region to strongly alter the basic climate state.     

Deep Impact: Optical spectroscopy and photometry obtained at MIRA

We present spectroscopic and photometric observations, spanning the optical UV to the far red, before, during, and after the NASA Deep Impact event of July 4, 2005. The inner 2000 km of the pre- and post-impact coma was about 0.3 magnitude redder in B-R than in the outer coma. The pre-impact spectrum was a faint reflected solar spectrum dominated by molecular emissions extending >40,000 km from the nucleus. The post-impact light curve in R and I showed a rapid rise consistent with an expanding optically thick cloud during the first 18 min after impact. During the next 8 min the cloud became optically thin. Sixty minutes after impact the impact R-band flux reached a plateau at , the comet brightening by a factor of ∼4.3 above its pre-impact value observed in a 15″ aperture. The mean expansion velocity of the grains during the first 49 min was . The spectrum became dominated by scattered sunlight during the first hour after impact. The volume scattering function (VSF) observed 32 min after impact shows strong reddening. At 49 min, however, the VSF shows an additional twofold increase in the blue but only a 20% increase at 5500 Å. Post-impact spectra and R-I photometry showed rapid reddening. The particle size distribution, dominated by 1-2.5 μm particles shortly after impact, changed dramatically during the first hour due to sublimation of water-ice particles of this size. On the night following impact the comet was still substantially brighter than before impact, but R-I had returned to its pre-impact value. B-R remained significantly redder. The ejecta 25 h after impact was fan-shaped subtending ∼180° roughly symmetrical about position angle 225°. The mean expansion velocity 90° from the direction to the Sun was .     

Application of Gibbs’ model to urban drainage networks: a case study in southwestern Chicago,USA

Hydrologic analysis of urban drainage networks often encounters a number of issues, including data acquisition and preparation for modelling, which can be costly and time‐consuming processes. Moreover, it can get more challenging with missing data and complex loops inside networks. In this article, Gibbs’ model is applied to urban drainage networks to investigate the possibility of replacing an actual existing urban drainage network in terms of the shape and peak flow of the hydrographs at the outlet. The characteristic network configuration is given as a value of a parameter β of Gibbs’ model. Instead of the actual network, stochastic networks from Monte‐Carlo simulation are utilized to obtain a synthetic width function from the generated networks, and runoff hydrographs are estimated based on it. The results show that the synthetic width function and the resulting hydrographs obtained from the networks simulated by Gibbs’ model are close to those from the actual network. The result also shows that even the behaviour of a looped network can be approximated by equivalent dendritic networks generated by Gibbs’ model. The applicability of a stochastic network model in urban catchment implies a complement to modelling approaches in case of data unavailability. Moreover, the network property (β) is utilized not only to estimate the discharge hydrograph of a catchment but also as a key link to evaluate the effect from rainstorm movement in urban catchments. Copyright © 2012 John Wiley & Sons, Ltd.