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 , the southern coast by +1.48 mm y -1 and the East Coast by +2.74 mm y -1 . 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)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(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.

A Perspective on Sea Level Rise and Coastal Storm Surge from Southern and Eastern Africa: A Case Study Near Durban, South Africa

“…Recent sea-level analysis in the region has shown that there is variation in the rate of sea-level change in the region [7,8,47]. Virtually all tide gauges show a rise with the exception of Zanzibar at −3.6 mm/yr) [47].…”

“…Studies of SLR in Durban [7] and SLR in Namibia and South Africa [8] and regional impacts of climate change in the Western Cape [9] have recently been completed. Three of South Africa's major coastal cities, Durban [10][11][12][13][14], Cape Town [15] and Port Elizabeth have embarked on studies to understand and address these impacts.…”

Extant shore-platform stromatolite (SPS) assemblage

“…The sea level has risen 125 m since the end of the last glacial maximum (Ramsay & Cooper, 2002) and is subject to thermal-expansion sea-level rise (SLR), currently measured at 2.7mm (Mather et al, 2009) and 1.23 mm/yr (http://tidesandcurrents.noaa.gov/sltrends/sltrends.html) for Durban, and 2.39mm/yr for 20 Port Elizabeth, on which both references agree (Fig. 1).…”

“…Sea level rise is ongoing SLR (Mather et al, 2009; http://tidesandcurrents.noaa.gov/sltrends/sltrends.html). The stromatolites and shore-platform contact is an unconformity.…”

The Ecology and Food Web Dynamics of South African Intermittently Open Estuaries

“…By contrast, SSTs along the west coast have decreased resulting from the increased frequency and intensity of coastal upwelling due to upwelling favourable southerly winds [47,49]. The warming of the Agulhas Current waters has through thermal expansion contributed to a rise in sea levels, estimated at approximately 2.74 mm y À1 [50], while increased wind stress has resulted in an increase in wave height (5 cm per decade), since the mid 1950s [51].…”