Evidence of early Flandrian tidal surges in Lower Strathearn,Scotland

Detailed stratigraphic, palaeobotanical (diatom and pollen) and radiometric evidence from a sequence of buried estuarine deposits, buried peat and overlying estuarine ‘carse’ deposits at Wester Rhynd, in Lower Strathearn, suggests the occurrence of two brief marine incursions between the abandonment by the sea of a buried estuarine flat, probably the Low Buried Beach, at about 8765 ± 75 BP, and c. 8500 BP. The first incursion, shortly after 8565 ± 85 BP, caused bottom-living marine diatoms to be thrown without clastic material onto the rapidly accumulating terrestrial peat. The second, bracketed by dates of 8485 ± 80 and 8510 ± 85 BP, deposited an extremely thin (1 mm) layer of fine sand that interrupts an otherwise unbroken buried peat succession covering the period 8765 ± 75 to 7710 ± 70 BP. The marine diatom, lithostratigraphic and ¹⁴C evidence together are consistent with a storm, storm-surge or tsunami origin for these events, which are recognised principally from the diatom evidence, having left no mark in the pollen record.     

An algorithm for mesh simplification applied to fracture hydrology

Numerically generated discrete fracture networks are used to simulate the flow of water through rock fractures. The fractures are modeled as random assemblages of conductive elements in a nonconductive matrix. Because large numbers of fractures often are needed to represent fractured rock adequately, minimizing the required computer time and memory is crucial. For steady-state flow, any portion of the mesh that is linked to the rest of the mesh by only one point is a dead end and does not contribute to water flow. The removal of such dead-end clusters simplifies the mesh and therefore speeds up computation, without changing its response. An algorithm for removing these dead ends is described in detail. Its effectiveness is discussed with regard to the connectivity of a network.     

Bifurcations of plane with three-dimensional periodic orbits in the elliptic restricted problem

We show that the procedure employed in the circular restricted problem, of tracing families of three-dimensional periodic orbits from vertical self-resonant orbits belonging to plane families, can also be applied in the elliptic problem. A method of determining series of vertical bifurcation orbits in the planar elliptic restricted problem is described, and one such series consisting of vertical-critical orbits (a _v=+1) is given for the entire range (0,1/2) of the mass parameter . The initial segments of the families of three-dimensional orbits which bifurcate from two of the orbits belonging to this series are also given.     

Stable carbon and oxygen isotope record of central Lake Erie sediments

Stable carbon and oxygen isotope data from mollusc aragonite extracted from sediment cores provide new information on the origin and history of sedimentation in the southwestern area of the central basin of Lake Erie. Sediments infilling the Sandusky subbasin consist of three lithologic units overlying glacial deposits. The lowest of these is a soft gray mud overlain by a shell hash layer containing Sphaerium striatinum fragments. A fluid mud unit caps the shell hash layer and extends upwards to the sediment-water interface. New stable isotope data suggest that the soft gray mud unit is of postglacial, rather than proglacial, origin. These data also suggest that the shell hash layer was derived from erosional winnowing of the underlying soft gray mud layer. This winnowing event may have occurred as a result of the Nipissing flood.The Pelee-Lorain moraine, which forms the eastern boundary of the Sandusky subbasin, is an elevated area of till capped by a sand deposit that originated as a beach. The presence of both the shell hash layer and relict beach deposit strengthens the interpretation that the Nipissing flood was a critical event in the development of the southwestern area of the central basin of Lake Erie. This event, which returned drainage from the upper lakes to the Lake Erie basin, was a dominant influence on regional stratigraphy, bathymetry, and depositional setting.     

2021: A Year of Unprecedented Climate Extremes in Eastern Asia,North America,and Europe

The year 2021 was recorded as the 6th warmest since 1880. In addition to large-scale warming, 2021 will be remembered for its unprecedented climate extremes. Here, a review of selected high-impact climate extremes in 2021, with a focus on China, along with an extension to extreme events in North America and Europe is presented. Nine extreme events that occurred in 2021 in China are highlighted, including a rapid transition from cold to warm extremes and sandstorms in spring, consecutive drought in South China and severe thunderstorms in eastern China in the first half of the year, extremely heavy rainfall over Henan Province and Hubei Province during summer, as well as heatwaves, persistent heavy rainfall, and a cold surge during fall. Potential links of extremes in China to four global-scale climate extremes and the underlying physical mechanisms are discussed here, providing insights to understand climate extremes from a global perspective. This serves as a reference for climate event attribution, process understanding, and high-resolution modeling of extreme events.     

The Anomalous Mei-yu Rainfall of Summer 2020 from a Circulation Clustering Perspective: Current and Possible Future Prevalence※

Highly unusual amounts of rainfall were seen in the 2020 summer in many parts of China, Japan, and South Korea. At the intercontinental scale, case studies have attributed this exceptional event to a displacement of the climatological western North Pacific subtropical anticyclone, potentially associated Indian Ocean sea surface temperature patterns and a mid-latitude wave train emanating from the North Atlantic. Using clusters of spatial patterns of sea level pressure, we show that an unprecedented 80％ of the 2020 summer days in East Asia were dominated by clusters of surface pressure greater than normal over the South China Sea. By examining the rainfall and water vapor fluxes in other years when these clusters were also prevalent, we find that the frequency of these types of clusters was likely to have been largely responsible for the unusual rainfall of 2020. From two ensembles of future climate projections, we show that summers like 2020 in East Asia may become more frequent and considerably wetter in a warmer world with an enhanced moisture supply.     

Characterizing aquatic sediment-oil aggregates using in situ instruments

The effects of emulsified crude oil and salinity (15, 30 per thousand ) on the steady state aggregate volume distributions and fractal dimensions were determined for a range of mean velocity gradients, (G(m) =5-50 s(-1)). Aggregation was performed in a 40-L cylindrical tank with a 4-blade paddle mixer. Three-dimensional fractal dimensions (D3) and volume distributions were determined using a procedure integrating data from an electrozone and an in situ light scattering instrument. Two-dimensional fractal dimensions (D2) and derived volume distributions were determined using a recently developed submersible flow cytometer equipped with a digital camera and image analysis software. For latex beads or emulsified crude oil systems, the above listed instruments yielded consistent size distributions and fractal dimensions (D2=1.92 +/- 0.16, D3=2.94 +/- 0.12). Mean volume aggregate diameters determined using the FlowCAM were consistently larger that those determined using the LISST-100 or Coulter Multisizer due to aggregate orientations during measurements. With increasing G(m) values, all colloidal aggregates showed increasing D3 values due to reduced aggregate length. Because of the compactness of all the aggregates (D3 >2), D2 values remained constant at 2. Neither salinity nor sediment type significantly affected D2 values calculated for sediment-crude oil aggregates. However, clay-oil aggregates showed higher D3 values than clay aggregates. This suggests that colloidal oil and mixing shear are the more dominant factors influencing aggregate morphology in nearshore waters. Overall, the data suggests that the analysis methods provide consistent size distribution results. However, because of the shear and salinity of coastal waters, resulting aggregates are too compact to estimate their D3 values using image analysis alone.