Southern African sea levels: corrections, influences and trends

Abstract

The tidal records of existing South African and Namibian tide gauges are examined and corrected. Regional sea level trends vary, with the  West Coast rising by +1.87 mm y^–1 (1959–2006), the southern coast by +1.48 mm y^–1 (1957–2006) and the East Coast by +2.74 mm y^–1 (1967–2006). The effects of barometric pressure and vertical crustal movement changes on these trends are examined. The derived relationship between sea levels and barometric pressure changes varied between 5.71 and 7.67 mm hPa^–1, significantly less than the theoretical inverse barometric correction. Barometric pressure has been dropping along the west coast at 1.63 hPa per decade (1987–2006), has remained fairly static along the southern coast and is rising  at 0.30 hPa per decade (1970–2007) along the east coast of southern Africa. The West Coast barometrically corrected sea level trends show that most of the change can be attributed to falling barometric pressure, whereas along the East Coast, the barometric pressure increase is suppressing sea level by 0.2 mm y^–1. Vertical crust movements vary, with the largest recorded movements of +1.11 ± 0.25 mm y^–1 found along the East Coast. Movement rate reduces southwards. Eustatic sea level trends vary from +3.55 mm y^–1 along the East Coast and +1.57 mm y^–1 along the southern coast to +0.42 mm y^–1 along the West Coast.

Keywords: barometric pressure; sea level rise; tide levels

African Journal of Marine Science 2009, 31(2): 145–156