South Africa: Our Coast, our Climate and our Currents

by Prof Ticky Forbes

The climate and the sea
People living in South Africa are not always aware of the significance of the seas around us in terms of their influence on our climate. No matter what we might think about how hot or how cold we might get, we have a relatively mild climate with few extremes in comparison with many other parts of the world, even those at similar latitudes. We might see something different in future with climate change but that is a story for another blog. Our present conditions can be attributed to the fact that most places are not that far from the sea – again in comparison with many other parts of the world.

A beast of a current on the east coast

image source NOAA

The different conditions in the marine environments on the east and west coasts are determined by oceanic processes, specifically the Agulhas Current on the east and the combination of the Benguela Current and upwelling of deep, cold water on the west. The Agulhas is a western boundary current, referred to as such because, while it flows from north to south down the east coast of Africa towards Cape Agulhas, from which it gets its name, its influence is in the western Indian Ocean.
It ranks highly amongst the ocean currents of the world and is rated as a major current. The following statistics give some idea of the amount of water involved: It is the world’s second fastest ocean current moving at a maximum speed of 150km/day; it is up to 60 km wide and 2 000 m deep with temperatures between 22 and 27 degrees Celsius. The flow volume is up to 1 400 times that of the Amazon river and 250 000 times that of the Orange River. The narrow continental shelf off our east coast allows this mass of warm water to closely approach the shore line and has a significant warming effect on the coastal climate – Durban never stays cold for long! This southward extension of a warm water environment allows many tropical marine fish and invertebrates, including the coral reefs in the Sodwana Bay area, to occur at relatively high latitudes. A comparison of air and sea temperatures at similar latitudes on our east and west coasts will clearly demonstrate the effect of the Agulhas current.

A moderating influence on the land but very different marine environments on the east and west coast
While the overall moderating influence of the sea on the land is there, the marine environments on the east and west coasts are nevertheless very different, although strong wave action is a feature of our entire coast. The differences that do exist translate into very different temperatures and nutrient levels which are reflected in the faunal diversity and productivity. See Part 2 of this blog for more on this interesting difference between South Africa’s east and west coasts.

MER is situated at the coast and tries to participate meaningfully in change and adaptation.
Our ocean and coasts affect us — and we affect them. Almost 60 percent of the country’s population lives at the coast. These coastal communities along with large harbour cities contribute significantly to the South African economy. Climate change, sea level rise, more intense storms, and population growth are all challenges for our coastal environments. MER is part of helping decision makers find solutions. We participate in observing, measuring, assessing, protecting, and managing coastal habitats including dune forests, beaches, estuaries and the inshore marine environment.