Early and late Holocene paleoenvironmental reconstruction of the Pearl River estuary, South China Sea using foraminiferal assemblages and stable carbon isotopes

摘要

Proxy reconstructions of estuarine evolution provide perspectives on regional to global environmental changes, including relative sea-level changes, climatic changes, and agricultural developments. Here, we present a new benthic foraminiferal record along with delta C-13 and C/N, and lithological data from a sediment core in the Pearl River estuary (Lingding Bay) adjacent to the South China Sea. The core has relatively thick Holocene sediments ( 40 m) due to its location in the paleo-valley of the Pearl River. The lithologic and foraminiferal record reveal an evolution in paleoenvironment from fluvial, inner estuary to middle estuary between 11300 and 8100 cal a BP in response to rapid sea-level rise. delta C-13 and C/N data indicate high freshwater discharge from 10500 to 8100 cal a BP driven by a strong Asian monsoon. The middle Holocene (8100 - 3300 cal a BP) sediment is absent in the core due to subaqueous erosion resulting from the unique geomorphology of the Pearl River Delta. In the late Holocene from 3300 cal a BP to the present, the lithology and foraminiferal assemblages suggest a further evolution from outer estuary, middle estuary channel, to middle estuary shoal, resulting from deltaic pro gradation under stable relative sea levels. In the last 2000 years, delta C-13 and C/N values reveal the intensive development of agriculture coupled with the reduction of freshwater input derived from a weakening Asian monsoon.