Stuck on an island: land area changes during Holocene sea-level rise and implications for species evolution

Abstract

Global biogeographic models are essential for reconstructing paleo-environments and understanding species evolution and modern biodiversity. Present state-of-the-art models include the effects of sea-level rise and isostasy on Holocene biogeography but so far do not take sediment deposition and erosion into account. This could be a major issue near river deltas, where pronounced morphologic change due to high fluvial sediment fluxes has large potential effects on reconstruction of the past coastline positions. Here we attempt to resolve that knowledge gap by using sediment cores input to reconstruct the Holocene evolution of the Vietnamese Mekong Delta (VMD) from 11ka BP to the present. For each time slice on a gridded surface, we calculate terrestrial and marine sedimentation rates and include this dynamic topography in a novel numerical paleo-coastline model. Model results simulate delta formation and its dynamic evolution during the Holocene period and show important consequences of the past wetland extent and connections between fresh-water environments. The period of 11-7 ka BP marked a significant retreat of coastlines and expansion of shelf areas followed by a relative temporary equilibrium in landmass change for the next 3 kyr. The latest phase from 4 ka BP to the present indicated a regression phase, where the coastline notably progradated seawards, shaping the modern landscape.