Recent coastal evolution and sea-level rise, Setiu Wetland, Peninsular Malaysia

Abstract Sea-level reconstructions based on foraminiferal assemblage data are common for temperate salt-marsh settings. In comparison, the widespread mangrove swamps of equatorial to subtropical settings have received considerably less attention due to enhanced taphonomic loss of specimens, extensive bioturbation, abundant infaunal foraminifera and irregular intertidal topography. The tropics, however, provide the best possible estimate of “eustatic function” and thus are important for testing earth-ice models. In this paper, we use foraminiferal data, in a chronologic framework provided by optically stimulated luminescence, radiocarbon and Pb-210 age estimates, to determine coastal evolution and rates of sea-level rise in the Setiu wetland of northeastern peninsular Malaysia on the western margin of the southern South China Sea over the past ca. 200 years. Foraminiferal data from three surface transects across fringing mangrove swamps were used to interpret four cores from mid to high mangrove swamp settings. Patterns of foraminiferal distribution were determined by correspondence analysis, canonical correspondence analysis and detrended canonical correspondence analysis of dead assemblage data. We used weighted averaging as the transfer function model to reconstruct sea-level curves for the cores and to provide a composite reconstruction for the last ca. 200 years. Based on one C-14 estimate, sea level rose during the 19th century at 1.26 mm yr − 1 . The rate increased to 3.2 ± 0.6 mm yr − 1 .around 1900 CE, roughly coincident with rate increases recorded globally. However, the 20th century rate in the Setiu wetland is considerably greater than that of global estimates (ca. 1.8 mm yr − 1 ) for this period. Rates of sea-level rise in the Gulf of Thailand (immediately to the north of the Setiu wetland) determined from GPS-corrected tide gauge data and multi-satellite altimetry are geographically variable but also greater than the global rate. The data from the Setiu wetland provide the first foraminifera-based sea-level reconstruction of the past few hundred years from the southeastern South China Sea (SCS) and they represent the first time the early 20th century increase in rate of sea-level rise has been identified using proxy foraminiferal data in an equatorial setting.