Brace yourselves swimmers

Nov 30, 2022

Eastern Cape climate warning as Agulhas current drifts off

Thank you Mike Loewe and DispatchLIVE for kind permission to include this article in our Newsletter.

Weird upwellings of frigid water between East London and Port Alfred are affecting local climate, says leading SA marine scientist

A significant drop in the ocean’s temperature has been observed, says NMU’S Professor Mike Roberts.

Image: FILE, Dispatch Live

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 compresses into a torrent hitting speeds of up to 13km/h bringing, in ocean temperature terms, scorching waters up to 27°C.

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

It is so powerful it sends eddies across the Atlantic to hook up with the Gulf Stream off the US east coast and heads to Europe, where it contributes to the snow and cold weather.

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 — 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.

EL open water swimmer and former international SA deaf champion Mark Roach, who swims daily off East London, said his Garmin had started recording cold water readings of 18°C trending down to 15°C from June already.

But November had been consistently cold, with temperatures plummeting from 18°C last Tuesday, to 15°C the next day and there it has stuck, bumping along the bottom, going as low as 13°C on Tuesday.

His mother, Joy Roach, said her Garmin had measured the temperature at 12.8°C at Orient Beach on Monday.

Dispatch swam in this water. It takes a few minutes to acclimatise, then there is the infamous “ice-cream headache”, and after that the body burns, counter-intuitively as if it is on fire.

Professor 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 on the shore.

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 that East London has experienced a startling one-degree of cooling since 1940.

Average global air temperatures are 1.1°C higher and headed for 3°C, or 4°C and even 6°C in the SA interior, and unprecedented heatwaves have recently roasted the US, Europe and China.

Off Track asked the SA Weather Service if the local upwellings were linked to Antarctic icemelt, and the 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 said: “All in all, while the conditions are perhaps unusual, they are unlikely to be anomalous”.

She did not know if this was the climate changing, saying: “The simple answer, we do not know.

“Some studies have shown the Agulhas current is changing, particularly in terms of the meanders that flow south-westward. But we do not have enough information.

“There have been model studies done, but a model is only as good as the physical observations that are used to validate such information and we have very little now monitoring the Agulhas Current. We know there will be changes.”

“If the Agulhas Current slows, weakens, changes, we could see very real changes to the global climate system. Not tomorrow … that was just a movie. But as a slow progression”

However, Prof Roberts, who holds the chair of ocean science and food security at Nelson Mandela University, and has chaired a number of large international science panels on the major Indian Ocean currents and actively led more than 30 science ship missions, said emphatically: “We have found that the upwelling zone between Port Alfred and East London has become more intense over a 40-year time frame due to climate change.”

He said: “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”.

The scientist said: “A significant drop in the ocean temperature of an average 8°C has been detected.

“This can have a devastating effect on the ecosystem. The Agulhas is very weak. One of the reasons is a strange and unusual undercurrent from the south was detected. It brings cooler waters to the coast. This is still being investigated.”

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