Temperature drop a risk to sealife

One of the biggest climate breakdown events affecting the Eastern Cape is happening now. The fiery Agulhas ocean current, which normally hugs our coastline, has vanished, and drifted off somewhere southeast of us.

The Agulhas is normally pumped with heat and energy from equatorial and subtropical currents – eddies in the Mozambican channel and the east Madagascar current – and when it hits SA off KwaZulu-Natal, it compresses into a torrent, hitting speeds of up to 13km/h and bringing waters of up to 27°C.

It carries with it an entire living ecosystem, from tiny micro-organisms to marlin.

A scientist, who asked not to be named, said: “The Agulhas [at present] is very weak. Currents about the world are changing directions. Many governments don’t want to tell their people this.”

Today, in place of the Agulhas are weird upwellings of frigid water between East London and Port Alfred ocean temperature terms dubbed the Port Alfred upwelling cell – which is affecting the local climate as part of climate change, according to leading SA marine scientist Prof Mike Roberts.

There are many unknowns in this scenario, but on Sunday, Gonubie Marine Club commodore Hercules Nel, who fishes regularly in the Agulhas current, said they had gone the farthest yet to find it – 27km out, and found no current and no fish. Just cold water.

Prof Tommy Bornman, of Nelson Mandela University’s Institute for Coastal and Marine Research, and a research leader at the SA Environment Observation Network, previously told Off Track that in 2021 a sudden temperature crash within hours from 26°C to 11°C had caused fish to go into thermal shock, die and wash up.

He spoke of occasional sudden, intense “Natal pulses” causing meandering, which had knock-on effects on the coastal environment.

Adding to the mystery is official air temperature data provided last year by the SA Weather Service’s Gqeberha office, which shows t East London has experienced a startling 1°C of cooling since 1940.

Off Track asked if the local upwellings were linked to Antarctic icemelt, and the SA Weather Service’s senior marine scientist, Prof Tammy

Morris, said this was impossible. Icemelt from Antarctica was “caught up in the massive circulation of the Antarctica Circumpolar Current” which flowed continuously about Antarctica and took tens or hundreds of thousands of years to “mix out” with waters to its north.

However, another current, the deep Agulhas undercurrent, flowing past SA at a depth of 1.2km, on its way to the equator in the Indian Ocean, was made up of “waters flowing from the North Atlantic, and can include some Antarctic waters from the frontal zone in the Southern Ocean”.

She said the most probable explanation for the cold conditions was a combination of the Agulhas meandering off shore to follow the

Agulhas bank, “allowing colder waters to travel northwards along the coast, and the Port Alfred Upwelling Cell.”

All of this was influenced by “wind conditions”. She did not know if this was the climate changing, saying: “The simple answer, we do not know.”

However, Prof Roberts, said: “We have found that the upwelling zone between Port Alfred and East London has become more intense over a 40year timeframe due to climate change.

“The Indian Ocean is one of the fastest-warming ocean basins and convincing evidence now exists that demonstrates climate change is affecting ocean upwelling one of the most fundamental and powerful mechanisms in ocean dynamics that underpins the critical supply of nutrients to sustain ecosystems and marine food resources.”

He said the Port Alfred upwelling zone was driven by easterly winds “which are now seen to be increasing as the high pressure belt gradually pushes the westerly wind belt south over time. A significant drop in the ocean temperature of an average 8°C has been detected. This can have a devastating effect on the ecosystem.”

We have found that the upwelling zone between Port Alfred and East London has become more intense over a 40-year timeframe due to climate change