A novel technique for detection of the toxic dinoflagellate, Karenia brevis, in the Gulf of Mexico from remotely sensed ocean color data

Karenia brevis, a toxic dinoflagellate that blooms regularly in the Gulf of Mexico, frequently causes widespread ecological and economic damage and can pose a serious threat to human health. A means for detecting blooms early and monitoring existing blooms that offers high spatial and temporal resolution is desired. Between 1999 and 2001, a large bio-optical data set consisting of spectral measurements of remote-sensing reflectance (R_rs(λ)), absorption (a(λ)), and backscattering (b_b(λ)) along with chlorophyll a concentrations and K. brevis cell counts was collected on the central west Florida shelf (WFS) as part of the Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) and Hyperspectral Coastal Ocean Dynamics Experiment (HyCODE) programs. Reflectance model simulations indicate that absorption due to cellular pigmentation is not responsible for the factor of ∼3–4 decrease observed in R_rs(λ) for waters containing greater than 10⁴ cells l⁻¹ of K. brevis. Instead, particulate backscattering is responsible for this decreased reflectivity. Measured particulate backscattering coefficients were significantly lower when K. brevis concentrations exceeded 10⁴ cells l⁻¹ compared to values measured in high-chlorophyll (>1.5 mg m⁻³), diatom-dominated waters containing fewer than 10⁴ cells l⁻¹ of K. brevis. A classification technique for detecting high-chlorophyll, low-backscattering K. brevis blooms is developed. In addition, a method for quantifying chlorophyll concentrations in positively flagged pixels using fluorescence line height (FLH) data obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is introduced. Both techniques are successfully applied to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and MODIS data acquired in late August 2001 and validated using in situ K. brevis cell concentrations.     

Seismic evidence for the Pleistocene depositional changes in Lake Hovsgol, Mongolia, and implications for the age model and the sediment grain size record of KDP-01 drill core

This paper seeks to arrive at a consistent interpretation of (1) the age model, (2) the grain size record, and (3) seismic reflection data from Lake Hovsgol (a.k.a Khubsugul or Hövsgöl), Mongolia, reported by Fedotov et al. (2007, earlier by Fedotov et al. 2002, 2004). In their most recent contribution, the grain size record of the KDP-01 drill core is interpreted as a climatic signal while little consideration is given to lake-level changes and hence to basin-wide changes in depositional setting evident from seismic profiles; also, a nearly linear age model is at odds with the seismic evidence for a major angular unconformity in the sediment strata. The lack of regional seismic stratigraphic analysis has thus led to an improbable interpretation of the Lake Hovsgol sediment grain size record and ultimately to an improbable scenario of Mongolian glaciation history. Using the available seismic profiles, here we show that the drill core penetrated several transgressive/regressive sedimentary sequences and a major angular unconformity. Therefore, the drilled sediment section cannot represent continuous sediment accumulation and the Brunhes age model across the unconformity cannot be nearly linear; the time interval representing a hiatus remains to be determined. The assumed nearly linear age/depth relationship in the upper 23 m above the angular unconformity is also an unlikely relationship, given the evidence of repeated changes in lake level, and hence in the depositional setting and sedimentation rates. We further propose a qualitative reference model for changes in the Lake Hovsgol depositional setting (presented as a step-by-step animation – see supplementary material) based on manually ‘backstripping and rebuilding’ the seismic pattern. We argue that this model provides a useful template of the likely sediment facies changes in the deep axial part of the Hovsgol basin: our crude model in fact captures the major depositional trends in the KDP-01 drill core section located some 10 km NW along the seismic line. We contend that changes in the depositional setting provide the first-order control on sediment grain size in the Hovsgol record. Our study provides important new constraints on the nature of sedimentary proxy records in Lake Hovsgol and on their interpretation as a record of Mongolian glaciation history.     

Primary feldspar in the Semarkona LL3.00 chondrite: Constraints on chondrule formation and secondary alteration

Feldspar in ordinary chondrites (OCs) is often associated with thermal metamorphism, as a secondary mineral that forms from the crystallization of matrix and chondrule mesostasis. However, studies of feldspar in equilibrated OCs show that there is a range of plagioclase compositions within chondrules, some of which may be primary products of chondrule crystallization. It is important to recognize primary feldspar within chondrules because it can be used to help understand the secondary effects of thermal metamorphism and aqueous alteration. The presence of primary feldspar also provides important petrologic constraints on chondrule formation time scales. We undertook a careful study of Semarkona (LL3.00) and observed feldspar in 18% of chondrules. The feldspar is plagioclase covering a wide range of compositions (An₂–An₉₉) with little K‐feldspar component (<Or₃). We show that plagioclase is a primary igneous phase, based on grain morphology and compositions consistent with growth from a melt having the bulk compositions of the host chondrules. Based on experimental studies, the presence of plagioclase suggests chondrules cooled slowly at temperatures close to the solidus. We also observed several secondary features consistent with the aqueous alteration. These features include zoning of Na and Ca in plagioclase, heterogeneity in plagioclase compositions in altered chondrules, development of porosity from the dissolution of chondrule glass, and alteration of glass to phyllosilicates. Alteration of major Al‐bearing phases, like plagioclase and glass, has important implications for interpretations of ages derived from Al‐Mg dating of chondrules, if they have been affected by secondary processes.     

Locating microseismic events using borehole data

Constraining microseismic hypocentres in and around hydrocarbon reservoirs and their overburdens is essential for the monitoring of deformation related to hydraulic fracturing, production and injection and the assessment of reservoir security for CO₂ and wastewater storage. Microseismic monitoring in hydrocarbon reservoirs can be achieved via a variety of surface and subsurface acquisition geometries. In this study we use data from a single, subsurface, vertical array of sensors. We test an existing technique that uses a 1D velocity model to constrain locations by minimizing differential S‐to‐P arrival times for individual sensors. We show that small errors in either arrival time picks or the velocity model can lead to large errors in depth, especially near velocity model discontinuities where events tend to cluster. To address this issue we develop two methods that use all available arrival times simultaneously in the inversion, thus maximizing the number of potential constraints from to N, where N is the number of phase picks. The first approach minimizes all available arrival time pairs whilst the second approach, the equal distance time (EDT) method defines the hypocentre as the point where the maximum number of arrival time surfaces intersect. We test and compare the new location procedures with locations using differential S‐to‐P times at each individual sensor on a microseismic data set recorded by a vertical array of sensors at the Ekofisk reservoir in the North Sea. Specifically, we test each procedure's sensitivity to perturbations in measured arrival times and the velocity model using Monte Carlo analysis. In general, location uncertainties increase with increasing raypath length. We show that errors in velocity model estimates are the most significant source of uncertainty in source location with these experiments. Our tests show that hypocentres determined by the new procedures are less sensitive to erroneous measurements and velocity model uncertainties thus reducing the potential for misinterpretation of the results.     

Natural Disturbance Shapes Benthic Intertidal Macroinvertebrate Communities of High Latitude River Deltas

Unlike lower latitude coastlines, the estuarine nearshore zones of the Alaskan Beaufort Sea are icebound and frozen up to 9 months annually. This annual freezing event represents a dramatic physical disturbance to fauna living within intertidal sediments. The main objectives of this study were to describe the benthic communities of Beaufort Sea deltas, including temporal changes and trophic structure. Understanding benthic invertebrate communities provided a baseline for concurrent research on shorebird foraging ecology at these sites. We found that despite continuous year-to-year episodes of annual freezing, these estuarine deltas are populated by a range of invertebrates that represent both marine and freshwater assemblages. Freshwater organisms like Diptera and Oligochaeta not only survive this extreme event, but a marine invasion of infaunal organisms such as Amphipoda and Polychaeta rapidly recolonizes the delta mudflats following ice ablation. These delta sediments of sand, silt, and clay are fine in structure compared to sediments of other Beaufort Sea coastal intertidal habitats. The relatively depauperate invertebrate community that ultimately develops is composed of marine and freshwater benthic invertebrates. The composition of the infauna also reflects two strategies that make life on Beaufort Sea deltas possible: a migration of marine organisms from deeper lagoons to the intertidal and freshwater biota that survive the 9-month ice-covered period in frozen sediments. Stable isotopic analyses reveal that both infaunal assemblages assimilate marine and terrestrial sources of organic carbon. These results provide some of the first quantitative information on the infaunal food resources of shallow arctic estuarine systems and the long-term persistence of these invertebrate assemblages. Our data help explain the presence of large numbers of shorebirds in these habitats during the brief summer open-water period and their trophic importance to migrating waterfowl and nearshore populations of estuarine fishes that are the basis of subsistence lifestyles by native inhabitants of the Beaufort Sea coast.     

Global correlation of the Vazante Group, São Francisco Basin, Brazil: Re–Os and U–Pb radiometric age constraints

The Vazante Group consists of Precambrian carbonate-dominated platform deposits that extend along more than 300 km in the external zone of the Brasilia Fold Belt of the São Francisco Basin in east central Brazil. The sequence is about 4.8 km thick and contains a preserved glaciomarine diamictite unit (containing dropstone) at the top and a lower diamictite unit at the bottom. Previous C- and Sr-isotope profiles suggested the correlation of the upper diamictite unit with the “Sturtian” glacial event (ca. 750–643 Ma). However, new Re–Os isotope data from the shales associated with the upper diamictites yield radiometric age estimates between 993 ± 46 and 1100 ± 77 Ma. U–Pb measurements on a suite of clear euhedral zircon crystals that were separated from the same shales associated with the upper diamictite and from the arkosic sandstone above the lower diamictite yield ages as young as 988 ± 15 and 1000 ± 25 Ma, respectively. Based on the Re–Os and U–Pb ages, the best age estimate of the Vazante Group is constrained to be 1000–1100 Ma and thus the two diamictite units are not correlative with the Sturtian glaciation(s) but most likely are records of glacial events that occurred during the late Mesoproterozoic.     

Measurement of ocean temperature and salinity via microwave radiometry

Sea-surface temperature with an accuracy of 1 °C and salinity with an accuracy of 1 were measured with a 1.43 and 2.65 GHz radiometer system after correcting for the influence of cosmic radiation, intervening atmosphere, sea-surface roughness, and antenna beamwidth. The radiometers are a third-generation system using null-balancing and feed-back noise injection. Flight measurements from aircraft over bay regions and coastal areas of the Atlantic resulted in contour maps with spatial resolution of 0.5 km.