Morphometric comparisons between automated and manual karst depression inventories in Apalachicola National Forest,Florida, and Mammoth Cave National Park,Kentucky, USA

Karst depression catalogs are critical to assessing the hydrology and geohazards of an area; yet, the delineation of these features within a landscape can be a difficult, time-consuming and subjective task. This study evaluates the efficacy of karst depression inventorying using an automated fill-difference method operating on high-resolution lidar-derived digital elevation models (DEMs). The resulting catalog is compared with existing karst depression inventories for two low-development areas of the USA, Mammoth Cave National Park (MACA) and Apalachicola National Forest (ANF), where karst depressions have been mapped previously using a manual closed-contour approach. The automated fill method captures 93 and 85 % of these previously mapped karst depressions at MACA and ANF, respectively. Field observations and topographic analysis suggest that the omitted features were likely misclassified within the existing catalogs. The automated routine returns 797 and 3377 additional topographic depressions, at MACA and ANF, respectively, which are not included in the existing catalogs. While the geology of ANF is mostly homogenous Quaternary deposits, the newly identified, typically smaller-scale depressions found within MACA tend to be disproportionally located in non-carbonate-dominated formations, where the development of karst may be restricted by geologic heterogeneity. Within both areas, the size distributions of the two inventories are statistically identical for features larger than ~10³ m² in area or ~3 m in depth. For individual depressions captured by both methods at MACA, the automated fill-difference routine tends to return a slightly larger estimate of depression size and aggregate small depressions into larger ones. Conversely, at ANF, some low-relief depressions may be disaggregated by the fill-difference technique, with a trend toward smaller estimated depression areas when the automated method is employed. The automated fill-difference method, operating on high-resolution lidar-derived DEMs, can reproduce and expand the existing inventories of karst depressions, while minimizing false detections that may be inherent within pre-existing catalogs.     

Sea surface wind stress and drag coefficients: The hexos results

Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age.     

南海南部巽他陆架氧同位素3期粘土矿物记录及其古环境意义

南海南部低海平面时期巽他陆架陆源碎屑的物源区变化,对于研究海陆变迁过程古环境演化具有重要意义.选择巽他陆架外缘对海平面变化影响非常敏感的氧同位素3期岩心记录(18282-2孔),开展高分辨率陆源碎屑粘土矿物分析,以期获得海平面变化影响下的物源区演化历史.研究结果显示,在氧同位素3期44.5～36.0 cal ka BP期间,巽他陆架外缘含有较高的蒙脱石(29%～44%)与中等含量的高岭石(21%～27%)、伊利石(19%～27%)和绿泥石(14%～20%).物源区分析表明,这个时期的蒙脱石主要由苏门答腊岛和泰国中部河流提供,高岭石主要由马来半岛、苏门答腊岛和婆罗洲西部河流提供,而伊利石和绿泥石主要由湄公河提供.在此期间,海平面长时间位于-80 m以下,巽他出露陆架上发育的大型古河流(北巽他河、古昭披耶河及古湄公河)可将来自周边物源区的陆源碎屑物质直接输送到陆架外缘.研究岩心的蒙脱石/(伊利石+绿泥石)比值与海平面变化具有良好的对应关系:当海平面下降时,蒙脱石/(伊利石+绿泥石)比值增大;反之亦然.这一现象表明海平面变化是影响巽他陆架外缘氧同位素3期沉积环境演化的最重要因素,即海平面升降...