Synchrosqueezing transform for geoacoustic inversion with air-gun source in the East China Sea
APPLIED ACOUSTICS
Authors: Liu, Hong; Yang, Kunde; Ma, Yuanliang; Yang, Qiulong; Huang, Chunlong
Abstract
This paper presents a geoacoustic inversion method combining with warping transform and synchrosqueezing transform to improve the precision of extracting modal dispersion curves in shallow water waveguide. Dispersive characteristic is often used to invert geoacoustic parameters, while the dispersion curves are hard to be extracted in short range. Warping transform can compensate the nonlinearity of received signal but the frequency resolution is still inaccurate. Synchrosqueezing transform sharpens the frequency resolution of warped modes, which makes the extracted dispersion curves more accurate. The comparison of simulation shows that the result using combined method is closer to the preset value when implementing geoacoustic inversion of dispersion characteristics. Furthermore, this method is used to invert the sea bottom parameters of a shallow water experiment in the East China Sea. The Bayesian method and in situ measurement are used to verify the reliability of inversion results. (C) 2020 Elsevier Ltd. All rights reserved.
Glacial-interglacial variation in catchment weathering and erosion paces the Indian summer monsoon during the Pleistocene
QUATERNARY SCIENCE REVIEWS
Authors: Jin, Zhangdong; Yu, Jimin; Zhang, Fei; Qiang, Xiaoke
Abstract
Silicate weathering via CO2 consumption is considered to regulate the long-term climate change. Discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate. However, owing to the paucity of welldated and continuous records of weathering and erosion, the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial-interglacial climate remain elusive. Geochemical analysis of a 666 m core from the Heqing basin, a paleolake situated at the southeastern margin of the Tibetan Plateau, demonstrates silicate versus carbonate weathering and erosion changes under Indian summer monsoon (ISM) conditions spanning the entire Pleistocene, via respective tracing between Rb/Sr and Al/Na ratios. The Rb/Sr record is interpreted as reflecting a competition between clayey silicate-origin Rb versus carbonate-origin Sr fluxes, whereas Al/Na ratio is a balance between weathering and erosion of silicate minerals, both pacing the glacial-interglacial cycles of the ISM. During interglacials, strong silicate weathering intensity reflected by low Al/Na values is mainly controlled by warmer temperatures, with the reduced variability during 1.82-0.92 Ma, recalling the pacing of the Arabian Sea surface temperature amplitudes. Within glacials, the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval. In conclusion, the Heqing Rb/Sr and Al/Na records reveal the sensitivity of catchment weathering and erosion to ISM changes over glacial-interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials. (C) 2020 Elsevier Ltd. All rights reserved.