Holocene sea level trend on the west coast of Bohai Bay,China: reanalysis and standardization

摘要

Using 110 newly revised Holocene sea level indicators categorized into three types,sediments(67),shelly cheniers(27)and oyster reefs(16),this paper firstly provides a Holocene relative sea level curve,based on multiple approaches of litho-and biostratigraphies and sedimentary faces analysis,for the west coast of Bohai Bay,China.Following considerations,including indicative meaning,the paleo tidal pattern and range and conversion from mean tidal level to mean sea level,an apparent relative mean sea level(RMSL)curve was further reconstructed.After systematical calibration using CALIB,those of the 48 reworked samples were further corrected for the residence-time effect.Similarly,the younger ages for another 35 samples were chosen at the subsample level.These result in a younger-oriented shift for about 0.5 ka.Three local spatial factors,including neotectonic subsidence(average rate about 0.1 mm/a),self-compaction of unconsolidated sediments(between a few decimeters to about 6 m)and subsidence due to groundwater withdrawal(between a few centimeters to about 2.5 m),were quantitatively corrected.Finally,the amended RMSL curve after eliminating all these local temporo-spatial factors is very likely to show non-existence of mid-Holocene highstand and imply potential influences of both ice-volume equivalent sea level and regional glacial isostatic adjustment.Although it is still unable to divide both global and regional factors,the slowdown of sea level rise,in 7.5–6.8 ka with a maximum height less than+1 m,may constrain the model effort in the near future.