Late Holocene variations in Arctic shelf hydrology and sea-ice regime: evidence from north of the Lena Delta   总被引：1，自引：0，他引：1  

Henning A. Bauch  Yelena I. Polyakova 《International Journal of Earth Sciences》2000,89(3):569-577

Diatom assemblage studies are used to interpret past changes in river runoff (salinity) and sea-ice regime in the vicinity of the vast Lena River delta, southern Laptev Sea shelf. On the basis of their distribution in surface sediments, the shelf region outside the strong influence of riverine waters is characterized by a dominance in sea-ice diatoms and other marine species. Their numbers increase steeply (>20%) within the area of drifting pack ice. In contrast, the marginal zone of the delta, where exceedingly low salinities prevail, is marked by freshwater diatoms showing values higher than 70%. Using the environmental information from the surface sediments, the downcore distribution patterns of the main ecological groups of diatoms were investigated on a sediment core that covers the past 2800 cal. years BP. Although the freshwater group indicates some temporal variations in salinities, the study site north of the Lena River delta remained under a dominantly riverine influence for most of the three recognized phases. In contrast, the relative abundance of sea-ice species gives evidence that pack-ice conditions were more severe during the oldest phase (older than ~2700 cal. years BP). The most significant changes are observed in the uppermost core section (younger than ~300 cal. years BP) when the relative abundance of freshwater diatoms decreases from 80% down to below 20%. This dramatic decrease is interpreted as a major shift from a more northward-directed to the modern, dominantly eastern outflow pattern. Because the dispersal and fate of riverine waters and its role on the ice regime as well as on water mass properties is a central issue in understanding short- and longer-term climatic changes in the Arctic and beyond, it needs to be tested using more cores if this most recent change in outflow pattern from the delta is connected to climate change or simply a result of channel migration within the delta.  相似文献   

Probleme bei der Nutzung von Offshore-Wind-energie aus Sicht des Naturschutzes     

Merck  Thomas  von Nordheim  Henning 《Ocean Dynamics》1999,51(10):79-88

Ocean Dynamics - Allein für den Bereich der deutschen Ausschließlichen Wirtschaftszonen von Nord-und Ostsee sind Anfragen zur Genehmigungsfähigkeit von Windparken mit zusammen weit...  相似文献   

Geochemical signals of the late Jurassic,marine Mjølnir impact     

Henning DYPVIK  Moses ATTREP 《Meteoritics & planetary science》1999,34(3):393-406

Abstract— Of the only seven submarine impact craters that have been found globally, the Mjølnir crater is one of the best preserved and retains crater and ejecta. Geochemical studies (organic pyrolysis using the Rock Eval technique and XRF analysis for major, minor, and trace elements) of the Institute for Petroleum Research (IKU) core 7430/10-U-01 that was taken from a drillhole located ～30 km north-northeast of the crater rim show gradual establishment of anoxic sea floor conditions through the late Jurassic. These poorly ventilated water conditions were overturned due to the Mjølnir impact event. Waves and currents transported impact glass (which is now partly weathered to smectite) into the depositional area where the drillhole is located. The succeeding crater collapse transported impact material (e.g., shocked quartz and Ir) from the crater rim and deeper levels to the core site. Normal marine depositional conditions were established a short time after the crater collapsed.  相似文献   

Machine learning based identification of dominant controls on runoff dynamics     

Henning Oppel  Andreas H. Schumann 《水文研究》2020,34(11):2450-2465

Hydrological models used for flood prediction in ungauged catchments are commonly fitted to regionally transferred data. The key issue of this procedure is to identify hydrologically similar catchments. Therefore, the dominant controls for the process of interest have to be known. In this study, we applied a new machine learning based approach to identify the catchment characteristics that can be used to identify the active processes controlling runoff dynamics. A random forest (RF) regressor has been trained to estimate the drainage velocity parameters of a geomorphologic instantaneous unit hydrograph (GIUH) in ungauged catchments, based on regionally available data. We analyzed the learning procedure of the algorithm and identified preferred donor catchments for each ungauged catchment. Based on the obtained machine learning results from catchment grouping, a classification scheme for drainage network characteristics has been derived. This classification scheme has been applied in a flood forecasting case study. The results demonstrate that the RF could be trained properly with the selected donor catchments to successfully estimate the required GIUH parameters. Moreover, our results showed that drainage network characteristics can be used to identify the influence of geomorphological dispersion on the dynamics of catchment response.  相似文献