Toward a High-Resolution Monitoring of Continental Surface Water Extent and Dynamics,at Global Scale: from GIEMS (Global Inundation Extent from Multi-Satellites) to SWOT (Surface Water Ocean Topography)

Up to now, high-resolution mapping of surface water extent from satellites has only been available for a few regions, over limited time periods. The extension of the temporal and spatial coverage was difficult, due to the limitation of the remote sensing technique [e.g., the interaction of the radiation with vegetation or cloud for visible observations or the temporal sampling with the synthetic aperture radar (SAR)]. The advantages and the limitations of the various satellite techniques are reviewed. The need to have a global and consistent estimate of the water surfaces over long time periods triggered the development of a multi-satellite methodology to obtain consistent surface water all over the globe, regardless of the environments. The Global Inundation Extent from Multi-satellites (GIEMS) combines the complementary strengths of satellite observations from the visible to the microwave, to produce a low-resolution monthly dataset (\(0.25^\circ \,\times \,0.25^\circ\)) of surface water extent and dynamics. Downscaling algorithms are now developed and applied to GIEMS, using high-spatial-resolution information from visible, near-infrared, and synthetic aperture radar (SAR) satellite images, or from digital elevation models. Preliminary products are available down to 500-m spatial resolution. This work bridges the gaps and prepares for the future NASA/CNES Surface Water Ocean Topography (SWOT) mission to be launched in 2020. SWOT will delineate surface water extent estimates and their water storage with an unprecedented spatial resolution and accuracy, thanks to a SAR in an interferometry mode. When available, the SWOT data will be adopted to downscale GIEMS, to produce a long time series of water surfaces at global scale, consistent with the SWOT observations.     

Large‐scale erosion and overbank deposition caused by the July 2013 flood of the Abu River,Yamaguchi City,Japan

This paper reports on the erosion, transport, and deposition processes associated with an overbank deposit formed by the flooding of the Abu River on July 28, 2013, in Yamaguchi City, Japan. At the study site, river flows overtopped the levee revetment upstream of a meander bend cutting it off and flowing back into the main channel downstream. In this sequential process, it deposited large amounts of sediments, ranging from mud to cobbles, on the floodplain. The surface of paddy fields adjacent to a railway line, located at the center of the affected floodplain, was severely eroded by the flood flows. Overbank deposits composed of both upstream finer sediments and eroded coarser terrestrial sediments are laid down in the affected area. Large amounts of pebbles and cobbles originating from the eroded terrestrial area formed a gravelly pile on top of the sand and gravel sediments derived from the river. This finding indicates that sands and gravels were deposited prior to the formation of the gravelly pile, probably before and during peak flood flows. An inverse grading structure is evident in the lower to middle part of these comparatively thick deposits, most likely due to differences in transport pattern between entrained terrestrial gravels and upstream finer sediments.     

Authigenic carbonates from active methane seeps offshore southwest Africa

The southwest African continental margin is well known for occurrences of active methane-rich fluid seeps associated with seafloor pockmarks at water depths ranging broadly from the shelf to the deep basins, as well as with high gas flares in the water column, gas hydrate accumulations, diagenetic carbonate crusts and highly diverse benthic faunal communities. During the M76/3a expedition of R/V METEOR in 2008, gravity cores recovered abundant authigenic carbonate concretions from three known pockmark sites—Hydrate Hole, Worm Hole, the Regab pockmark—and two sites newly discovered during that cruise, the so-called Deep Hole and Baboon Cluster. The carbonate concretions were commonly associated with seep-benthic macrofauna and occurred within sediments bearing shallow gas hydrates. This study presents selected results from a comprehensive analysis of the mineralogy and isotope geochemistry of diagenetic carbonates sampled at these five pockmark sites. The oxygen isotope stratigraphy obtained from three cores of 2–5?m length indicates a maximum age of about 60,000–80,000?years for these sediments. The authigenic carbonates comprise mostly magnesian calcite and aragonite, associated occasionally with dolomite. Their very low carbon isotopic compositions (–61.0?<?δ¹³C ‰ V-PDB?<?–40.1) suggest anaerobic oxidation of methane (AOM) as the main process controlling carbonate precipitation. The oxygen isotopic signatures (+2.4?<?δ¹⁸O ‰ V-PDB?<?+6.2) lie within the range in equilibrium under present-day/interglacial to glacial conditions of bottom seawater; alternatively, the most positive δ¹⁸O values might reflect the contribution of ¹⁸O-rich water from gas hydrate decomposition. The frequent occurrence of diagenetic gypsum crystals suggests that reduced sulphur (hydrogen sulphide, pyrite) from sub-seafloor sediments has been oxidized by oxygenated bottom water. The acidity released during this process can potentially induce the dissolution of carbonate, thereby providing enough Ca²⁺ ions for pore solutions to reach gypsum saturation; this is thought to be promoted by the bio-irrigation and burrowing activity of benthic fauna. The δ¹⁸O–δ¹³C patterns identified in the authigenic carbonates are interpreted to reflect variations in the rate of AOM during the last glacial–interglacial cycle, in turn controlled by variably strong methane fluxes through the pockmarks. These results complement the conclusions of Kasten et al. in this special issue, based on authigenic barite trends at the Hydrate Hole and Worm Hole pockmarks which were interpreted to reflect spatiotemporal variations in AOM related to subsurface gas hydrate formation–decomposition.     

Pb–Nd isotopic constraints on sedimentary input into the Lesser Antilles arc system

The Lesser Antilles arc is a particularly interesting island arc because it is presently very active, it is located perpendicular to the South American continent and its chemical and isotopic compositions display a strong north–south gradient. While the presence in the south of a thick pile of sedimentary material coming from the old South American continent has long been suspected to explain the geochemical gradient, previous studies failed to demonstrate unambiguously a direct link between the arc lava compositions and the subducted sediment compositions.Here, we present new Nd, Sm, Th, U and Pb concentrations and Nd–Pb isotopic data for over 60 sediments from three sites located in the fore arc region of the Lesser Antilles arc. New data for DSDP Site 543 drill core located east of Dominica Island complement the data published by White et al. [White, W.M., Dupré, B. and Vidal, P., 1985. Isotope and trace element geochemistry of sediments from the Barbados Ridge–Demerara Plain region, Atlantic Ocean. Geochimica et Cosmochimica Acta, 49: 1875–1886.] and confirm their relatively uniform isotopic compositions (i.e., ²⁰⁶Pb/²⁰⁴Pb between 19.13 and 19.53). In contrast, data obtained on DSDP Site 144 located further south, on the edge of the South American Rise and on sediments from Barbados Island are much more variable (²⁰⁶Pb/²⁰⁴Pb ranges from 18.81 to 27.69). The very radiogenic Pb isotopic compositions are found in a 60 m thick black shale unit, which has no age equivalent in the Site 543 drill core. We interpret the peculiar composition of the southern sediments as being due to two factors, (a) the proximity of the South American craton, which contributes coarse grain old detrital material that does not travel far from the continental shelf, and (b) the presence of older sediments including the thick black shale unit formed during Oceanic Anoxic events 2 and 3.The north–south isotopic change known along the Lesser Antilles arc can be explained by the observed geographical changes in the composition of the subducted sediments. About 1% contamination of the mantle wedge by Site 543 sediments explains the composition of the northern islands while up to 10% sediments like those of Site 144 is required in the source of the southern island lavas. The presence of black shales in the subducted pile provides a satisfactory explanation for the very low Δ8/4 values that characterize the Lesser Antilles arc.     

An alternative measure of discharge effectiveness

Since 1960, geomorphic effectiveness has been quantified by analytically combining measures of the frequency and the magnitude of geomorphic processes, most often for the case of sediment yield in rivers via the calculation of effective discharge, Q_eff. Here we leverage the Q_eff analysis approach to develop an alternative metric, the functional‐equivalent discharge Q_fed, which is the discharge that will reproduce the magnitude of the sediment load generated by the full hydrologic distribution. Q_fed is intended to be a more representative metric of hydrologic variability than Q_eff: whereas Q_eff provides a measure of the effectiveness of individual flow rates, Q_fed incorporates a measure of the average effectiveness of the entire flow distribution. We develop an analytical approximation of Q_fed based on relatively few parameters, apply the approach to a set of suspended sediment load data and describe how Q_fed varies broadly with sediment and hydrologic conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

New Olivine Reference Material for In Situ Microanalysis

A new olivine reference material – MongOL Sh11‐2 – for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn‐Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5–2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA‐ICP‐MS, SIMS and bulk analytical methods (ID‐ICP‐MS for Mg and Fe, XRF, ICP‐MS) for major, minor and trace elements at six institutions world‐wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1–2). The presence of some mineral and fluid‐melt micro‐inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty‐seven major, minor and trace elements.     

Effect of anorthite on granite phase relations: Experimental data and models

New experimental data on the effect of anorthite (An) on liquidus phase equilibria in the system Qz–Ab–Or are presented. The data were obtained for 5 wt% An added to variable Qz/Ab/Or compositions at 300 MPa and under H₂O-saturated conditions. Crystal–liquid equilibria were determined for 13 synthetic glass compositions made from gels in experiments performed between 660 and 750 °C in cold-seal pressure vessels. Forward and reversal experiments were systematically conducted on each composition to demonstrate equilibrium. A total of 51 charges was examined. Three crystalline phases, quartz, alkali feldspar and plagioclase appear on the H₂O-saturated liquidus surface. The determined minimum liquidus 5 wt% An “piercing” point (39% Qz, 33% Ab, 28% Or) is shifted away from the Ab apex toward the Qz–Or sideline when compared with the An-free 300 MPa H₂O-saturated minimum. This shift is of the same type as that observed at 100 MPa in the same system and at 200 MPa in a rhyolitic system. The new experimental results are used to test both empirical and thermodynamic models for silicic magmas. Empirical models reproduce reasonably well the new experimental data, although more sophisticated calculations schemes appear to be required to improve their accuracy. The new experimental results in the haplogranodiorite system are not well reproduced with the model of Holland and Powell (2001), mainly because plagioclase stability appears greatly enhanced in the model. Rhyolite-MELTS satisfactorily reproduces the Qz-, Pl- and Af-liquid phase equilibria, but model H₂O solubilities are significantly lower and crystallization temperatures higher than in experiments.     

Variability in the annual cycle of vertical particulate organic carbon export on Arctic shelves: Contrasting the Laptev Sea,Northern Baffin Bay and the Beaufort Sea

The ongoing regression of sea ice cover is expected to significantly affect the fate of organic carbon over the Arctic continental shelves. Long-term moored sediment traps were deployed in 2005–2006 in the Beaufort Sea, Northern Baffin Bay and the Laptev Sea to compare the annual variability of POC fluxes and to evaluate the factors regulating the annual cycle of carbon export over these continental shelves. Annual POC fluxes at 200 m ranged from 1.6 to 5.9 g C m⁻² yr⁻¹ with the highest export in Northern Baffin Bay and the lowest export over the Mackenzie Shelf in the Beaufort Sea. Each annual cycle exhibited an increase in POC export a few weeks before, during, or immediately following sea ice melt, but showed different patterns over the remainder of the cycle. Enhanced primary production, discharge of the Lena River, and resuspension events contributed to periods of elevated POC export over the Laptev Sea slope. High POC fluxes in Northern Baffin Bay reflected periods of elevated primary production in the North Water polynya. In the Beaufort Sea sediment resuspension contributed to most of the large export events. Our results suggest that the outer shelf of the Laptev Sea will likely sustain the largest increase in POC export in the next few years due to the large reduction in ice cover and the possible increase in the Lena River discharge. The large differences in forcing among the regions investigated reinforce the importance of monitoring POC fluxes in the different oceanographic regimes that characterize the Arctic shelves to assess the response of the Arctic Ocean carbon cycle to interannual variability and climate change.     

Large and growing environmental reservoirs of Deca-BDE present an emerging health risk for fish and marine mammals

Polybrominated diphenyl ethers (PBDEs) have been the subject of intense scientific and regulatory scrutiny during recent years. Of the three commercial forms (Penta, Octa and Deca) of PBDEs that have been widely used as flame retardants in textiles, furniture upholstery, plastics, and electronics, only Deca-BDE remains on the general market in North America, while a recent ruling of the European Court spells an impending end to its use in Europe. We review here highlights of aquatic research documenting the rapid emergence of PBDEs as a high priority environmental concern in Canada. PBDEs are being introduced in large quantities to the aquatic environment through sewage discharge and atmospheric deposition. In certain environmental compartments, the single congener BDE-209, the main ingredient in the Deca-BDE formulation, has surpassed the legacy PCBs and DDT as the top contaminant by concentration. Limited biomagnification of BDE-209 in aquatic food webs reflects its high log K_ow and preferential partitioning into the particle phase. As a result, large environmental reservoirs of BDE-209 are being created in sediments, and these may present a long-term threat to biota: BDE-209 breaks down into more persistent, more bioaccumulative, more toxic, and more mobile PBDE congeners in the environment.