No abstract

This paper reconstructs the evolutionary history of the Pearl River delta over the last 9000 years and investigates land—sea interaction in a large deltaic complex which formed under the influence of Asian monsoon climate. Specifically, this research examines the delta evolution in the context of three driving mechanisms: (1) rising sea level that influences the available accommodation space, (2) fluvial discharge as influenced by monsoon climate and (3) human activities that alter sedimentation within the deltaic system. Results reveal that the formation of deltaic sequences was initiated as a consequence of rapid sea-level rise between 9000 and 7000 cal. yr BP. The rate of sea-level rise slowed down markedly around 7000 cal. yr BP and sedimentation switched from transgressive to regressive. Initially, both the progradation of the delta plains near the apex and aggradation of delta front sedimentation in the central and lower parts of the receiving basin were fast owing to strong monsoonal-driven runoff. The progradation rate gradually slowed down between 6800 and 2000 cal. yr BP as monsoonal-driven runoff weakened. Rapid shoreline advances during the last 2000 years were the result of significantly increased human activities, a practice that trapped sediments in the encircled tidal flats along the front of delta plains. The evolutionary history of the Pearl River delta demonstrates the interplay between the three driving mechanisms.

This study employs a multiproxy approach in the reconstruction of Holocene monsoon history from sedimentary sequences obtained from the Pearl River Estuary, southern China. A set of modern surface sediment samples were collected within and outside the estuary, and a sediment core was obtained from the mouth of the estuary. A range of modern environmental variables were recorded including water salinity (summer, winter and annual average) and water depth. The diatom results show a good relationship with water salinity, with marine diatoms dominating the more distal samples from outside the main estuary and freshwater diatoms dominating the proximal samples influenced by higher freshwater flux. This pattern is matched by the bulk organic carbon isotopes. The isotope values vary between -21.1 +0.3%0 for samples from the fully marine environment, between -23.2±0.8%. and -23.7±0.8%. for samples from the mid to outer estuary brackish water environment and less than -24.7 + 1.3%. for samples from the inner estuary close to the freshwater sources. Similarly, the C/N ratios vary from below 7+0.6 in the marine end-members to over 14.8 + 3.0 in the freshwater end-members. Both the diatom and carbon data from the sediment core reveal a significant increase in freshwater flux from 8500 cal. yr BP resulting from the enhanced summer monsoon regime in early Holocene. The strength of freshwater flux reached its highest between 7500 and 6000 cal. yr BP. In the last 6000 years, freshwater flux decreased towards present, reflecting a gradual weakening of the summer monsoon.