FOLLOW THE CURRENT

The steamy Agulhas is back but the whales have left

The steamy Agulhas current is back in full flood along our coast and the humpback whales, seen by the score cavorting with calves for weeks off East London port, have left.

This happened within days this week, and it is time to try to put the pieces of this vital puzzle together.

Weather anomalies, suggestive of a climate change link, have been observed but none explain why the whales, which “milled about” for months, have carried on their southwards migration.

Two global features affect all of this: the hot Agulhas current running south hugging our East Coast — and its returning cold deep Agulhas current — in conjunction with the global weather pattern known as the El Niño-southern Oscillation (ENSO) which is now in a La Niña ('little boy') state for an unprecedented third year in a row.

La Niña is responsible for unrelenting northeast winds off the east coast, driving cold water from deep down up to the shore, and an above-normal summer rainfall and climate turbulence for much of eastern SA, while the west remains dry.

East London falls within the eastern rainfall area.

Dr Els Vermeulen, senior lecturer and research manager at the Mammal Research Institute’s whale unit at the University of Pretoria, said: “There are signs of changes in whale migration patterns, humpback and southern rights, likely due to changes in food supplies and ocean conditions in the Southern Ocean feeding grounds, but to my knowledge there is no suspension of humpback whale migration along South Africa’s east coast.

“There may be a large number of whales passing, and even hanging about for a little while, but not a full suspension of migration, as the eastern coast of SA is nutrient poor and would not provide enough food supply for these whales to feed on,” she said.

This week, recreational anglers and wild ocean tour guide John Barry of Southern Cruises in East London port confirmed that the Agulhas — which vanished offshore weeks ago — was suddenly back in full force, bringing warm waters and sea life down from the subtropics.

One expert, who asked not to be named, said major ocean currents were in a state of climate flux and governments did not want people to know that they could be slowing down as this would bring massive changes to people’s lives.

Was it possible that the whales jumped on the watery food train and rode south?

No-one could say, which is a common position for reporters trying to delve into the murky, vested world of climate change explanations.

The Agulhas, according to Windy.com on Tuesday, is drawing hot water straight from the equator, down through the Mozambique eddies and the east Madagascar current.

The Agulhas is forming at Richards Bay, and compresses from Durban down the south coast at a rocking speed of 4.6km/h.

At Wavecrest on the Wild Coast, the current compresses even more by a total of 34% in width and almost doubles its speed to 8km/h as it races past East London, only slowing down at Kidds Beach where it leaves the shore and heads south-south west.

When it is 51km off Gqeberha, the Agulhas lights out into the ocean, this time hugging the edge of the Agulhas Bank, a broad, shallow part of the continental shelf which falls away steeply into the cold southern oceans.

The Agulhas, which influences many weather patterns, as far north as Europe, then runs way down south to 750km off the Cape.

There, it does a dramatic Uturn and heads straight back to the Eastern Cape, this time known as the colder deep Agulhas undercurrent which SA Weather Service senior marine scientist Prof Tammy Morris has said flows at a depth of 1.2km on its long way to the equator in the Indian Ocean.

What is startling is that this cold current is only 300km off Port Alfred and not far from what oceanographer Mike Roberts and other scientists are calling the Port Alfred upwelling cell.

It is this mysterious appearance of prolonged cold water, sometimes as frigid as only 12°C, which has shocked East London anglers and open water swimmers because it is unprecedented for it to hang around for so long in spring and summer.

The SA Weather Service has also produced data which shows that Buffalo City’s climate has cooled by almost a degree since the 1940s, while other scientists are saying the interior is heating up by as much as 4°C to 6°C since industrialisation in the 1840s.

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, said emphatically: “We have found that the upwelling zone between Port Alfred and East London has become more intense over a 40year time frame due to climate change.”

Neither Roberts nor Morris were prepared to suggest that Antarctic ice melt was featuring in the cold Agulhas undercurrent and was hooking up with the Port Alfred upwelling cell and La Niña east winds and was hitting the shoreline.

Roberts believed the cold water was simply being thrown up by the persistent easterlies, while Morris said that though the Agulhas undercurrent “can include some Antarctic waters from the frontal zone in the Southern Ocean” it was “impossible” to include Antarctic ice melt.

Morris said it took tens or hundreds of years for fresh water to mix out with surrounding saline waters and join the mighty system of hot and cold currents called thermohaline circulation, which is basically Earth’s air con.

She said the “massive Antarctica circumpolar current” flowing continuously around Antarctica would be “unhindered by [currents from the] continents”.

But a Daily Maverick report suggests that Antarctic ice melt could be a feature in the cooling oceans and immediate coastal climate off Buffalo City, the Sunshine Coast, East Coast and the Wild Coast.

The paper reported that University of Washington atmospheric science researcher Prof Robert Jnglin Wills had said in recent research published by the journal Geophysical Research Letters that climate change might trigger more La Niñas.

Wills, a lead researcher for the paper, said ocean temperatures in the southern Pacific had cooled between 1979 and 2020, and no-one knew why.

One suggestion was that deep, cool ocean waters were surfacing and having a cooling effect, which was not being captured by computed climate models.

Wills, reported the paper, said: “It could also be related to changes as far away as Antarctica, where the Antarctic ice sheet is melting.

“And this adds freshwater to the ocean, changing the whole Southern Ocean temperature structure.”