Lake ice thickness changes with regional hydrometeorology and is closely associated with global climate change.We tested the detection of ice thickness using ground penetrating radar（GPR）in the Hongqipao reservoir.I...Lake ice thickness changes with regional hydrometeorology and is closely associated with global climate change.We tested the detection of ice thickness using ground penetrating radar（GPR）in the Hongqipao reservoir.Ice crystals,gas bubbles,ice density and ice thickness were also determined by concurrently drilling for validation.During the tests the gas bubble content was high in the upper and low in the bottom,ice density varied with the bubble content,and the ice thickness was not homogeneous.By comparisons between radar detected and in-situ measured ice thicknesses with theoretical analyses of the influence of gas bubble content on the dielectric constant,a three-layer model with snow, granular ice,and columnar ice was established and the transmission speed of radar wave within the ice was determined.Experience reveals that the equivalent dielectric constant can be used to evaluate the wave speed and the values at 1/3 ice cover depth can be used as equivalent values.Besides,the difference between the theoretical transmission time and the real detection time induced by large gas bubbles increases nonlinearly with the theoretical transmission time or ice thickness.展开更多
To constrain short-term changes of climate and oceanography in the northern South China Sea （SCS） over interglacial marine isotope stage （MIS） 5.5, we studied planktic and benthic δ18O records of seven marine sed...To constrain short-term changes of climate and oceanography in the northern South China Sea （SCS） over interglacial marine isotope stage （MIS） 5.5, we studied planktic and benthic δ18O records of seven marine sediment cores with a time resolution of 70-700 yr. Using 6-8 tie points the planktic records were tuned to the U/Th chronology of speleothem δ180 records in China and Europe. The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11 （HS-11） near 128.4 ka. HS-11 matches a 2300-yr long positive δ180 excursion by 1.5/0.8‰ both in planktic and benthic δ18O records. Hence half of the planktic δ180 signal was linked to increased upwelling of δ18O- and 12C-enriched deep waters in the southwestern SCS. The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait, that form a boundary current along the northern slope of the SCS, building a major sediment drift. At its lower margin near 2300-2400 m water depth （w.d.） Parasound records reveal a belt of modern erosion. At the end of glacial termination 2, stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144. Likewise hiatuses probably earmarked all preced- ing glacial terminations at Site 1144 back to 650 ka. Accordingly, boundary current erosion then shifted -300 m upslope to ~2040-2060 m w.d. These vertical shifts imply a rise in boundary current buoyancy, that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.展开更多
基金supported by the National Natural Science Foundation of China(Grant No50879008,40930848)the Open Fund of State Key Laboratory of Frozen Soil Engineering(Grant No SKLFSE200904)
文摘Lake ice thickness changes with regional hydrometeorology and is closely associated with global climate change.We tested the detection of ice thickness using ground penetrating radar（GPR）in the Hongqipao reservoir.Ice crystals,gas bubbles,ice density and ice thickness were also determined by concurrently drilling for validation.During the tests the gas bubble content was high in the upper and low in the bottom,ice density varied with the bubble content,and the ice thickness was not homogeneous.By comparisons between radar detected and in-situ measured ice thicknesses with theoretical analyses of the influence of gas bubble content on the dielectric constant,a three-layer model with snow, granular ice,and columnar ice was established and the transmission speed of radar wave within the ice was determined.Experience reveals that the equivalent dielectric constant can be used to evaluate the wave speed and the values at 1/3 ice cover depth can be used as equivalent values.Besides,the difference between the theoretical transmission time and the real detection time induced by large gas bubbles increases nonlinearly with the theoretical transmission time or ice thickness.
基金the National Natural Science Foundation of China(Grant Nos.91028004 and 41023004)
文摘To constrain short-term changes of climate and oceanography in the northern South China Sea （SCS） over interglacial marine isotope stage （MIS） 5.5, we studied planktic and benthic δ18O records of seven marine sediment cores with a time resolution of 70-700 yr. Using 6-8 tie points the planktic records were tuned to the U/Th chronology of speleothem δ180 records in China and Europe. The last occurrence of pink Globigerinoides ruber marks the top of Heinrich stadial 11 （HS-11） near 128.4 ka. HS-11 matches a 2300-yr long positive δ180 excursion by 1.5/0.8‰ both in planktic and benthic δ18O records. Hence half of the planktic δ180 signal was linked to increased upwelling of δ18O- and 12C-enriched deep waters in the southwestern SCS. The increase was possibly linked to a strengthened inflow of Pacific deep waters through the Bashi Strait, that form a boundary current along the northern slope of the SCS, building a major sediment drift. At its lower margin near 2300-2400 m water depth （w.d.） Parasound records reveal a belt of modern erosion. At the end of glacial termination 2, stratigraphic gaps deleted HS-11 in core MD05-2904 and subsequent peak MIS 5.5 at ODP Site 1144. Likewise hiatuses probably earmarked all preced- ing glacial terminations at Site 1144 back to 650 ka. Accordingly, boundary current erosion then shifted -300 m upslope to ~2040-2060 m w.d. These vertical shifts imply a rise in boundary current buoyancy, that in turn may be linked to transient events of North Pacific deepwater formation similar to that traced in SCS and North Pacific paleoceanographic records over glacial termination 1.
