Abstract:

New insights from an in situ coastal temperature climatology for South Africa: static patterns and long-term change

Albertus J Smit 1, Francois Du Fois 2, Robert J Anderson 3,4, John J Bolton 4, Sheldon Dudley 5, Michael Roberts 6, Jennifer Olbers 7

1 School of Life Sciences, University of KwaZulu-Natal, Westville Campus, PO Box X54001, Durban, South Africa. Tel.: +27 (0)31 260 7410.

2 Department of Oceanography, University of Cape Town, Rondebosch 7701, South Africa.

3 Seaweed Unit, Fisheries Research, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, Cape Town, South Africa.

4 Botany Department, University of Cape Town, Rondebosch 7701, South Africa.

5 KwaZulu-Natal Sharks Board, Private Bag 2, Umhlanga 4320, South Africa.

6 Physical and Applied Oceanography, Oceans and Coasts, Department of Environment Affairs, Private Bag X2, Roggebaai, 8012, Cape Town, South Africa.

7 Ezemvelo KZN Wildlife, 3 Elton Place, Congela, Durban, 4001

Seawater temperature is the most important environmental variable that determines the distribution of marine species at regional and global scales. For coastal applications, offshore gridded sea surface temperatures (SST) are generally extrapolated to the shore for correlation with biogeographic patterns at the land-sea edge. The recent development of a high-resolution alongshore in situ seawater temperature climatology now allows detailed comparisons with gridded SSTs, and reveals surface temperature gradients close to the coast (<20 km). These gradients are very pronounced when compared with reprocessed MODIS Terra SSTs at 1 and 4 km resolutions, and they have been generally overlooked by oceanographers, for whom shallow coastal waters are out of their depth. Measured seawater temperatures are lower at the coast with respect to their offshore analogues, and consequences for biologists modelling species distribution limits relative to temperature minima and maxima could be far reaching. For some sites, the in situ data used to calculate climatological averages are of up to 30 years in duration, and this allows us to study the temporal dynamics of temperature. Insights from these data are applied to the recent finding of the eastward migration of kelp at Cape Agulhas; it highlights the importance of long-term, high-resolution data in climate change studies.

Presentation Topic

New insights from an in situ coastal temperature climatology for South Africa: static patterns and long-term change

 

Contact Albertus J Smit:

School of Life Sciences, University of KwaZulu-Natal

 

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