Journeys of the high seas

Friday, 12 March, 2004
Leonie Joubert
Something far greater than a sail or motor will power your journey
Imagine you’re planning an ocean adventure. Looking at your atlas, you want to get from Antarctica in the south to, say, Greenland in the north and it looks like your highway of choice slices up through the Atlantic Ocean. You stock up with supplies, drop your tiny vessel into the water and away you go!

You won’t need a sail or motor because something far greater will power your journey – the Global Conveyor Belt or, more technically, the Atlantic thermohaline circulation. This is the massive journey which ocean waters take from the frozen continent in the south, along the surface of the Atlantic Ocean, snaking between the continents on either side, across the equator and into the north.

When you arrive in the north, you may want to get yourself out of the water smartly. Here the surface waters plunge down to the bottom of the ocean at a phenomenal rate – equivalent to all the world’s river water per second – and begin their journey back south, this time following the trenches of the ocean floor.

It’s an 800-year journey that these waters take. You may want to pack a few good books.

The first part of the journey spins you off the giant Antarctic Circumpolar Front into an anti-clockwise pirouette, which brushes your starboard side against the arid west coast of the African sub-continent. Similar currents spin off the Front, taking equally frigid waters with them to the westerly facing shores of Australia and South America.

Where these cold currents meet land, they may bring with them a phenomenon known as the Mediterranean climate. Here summers are long, dry months. Winters bring rain and, when the sun is low in the sky, a ripple of growth fans out across the plants of the region. Vegetation in all these places is typically scrub-like and resilient to drought; much of it is rare and endemic.

Similar climatic areas occur on the west coast of North America – California – and around the edge of the Mediterranean Sea.

These areas have also proved to be ideal for grapevines, which prefer winter rainfall to fill up their reserves and long, dry-ish summer months in which to ripen their fruit without disease and rot. These are the now hallowed places in the exclusive club of cult wines where names such as Hunter Valley, Napa, Barossa and Stellenbosch, have become legendary regions, producers and personalities.

Chilly sea breezes
Every farmer likes to claim them, no matter how far inland they may be: those cooling sea breezes which move in with the late afternoon, chilling the berries after a hot day in the sun and protecting their delicate flavours from being reduced to jam.

In the Western Cape, where summertime temperatures may creep towards the upper 30s, this is often the case as warm air rises over the land, sucking in cooler air from the ocean, which refrigerates the fruit of the vine. You’d be surprised just how far inland it reaches.

Fans of South African wine owe everything to the Atlantic. Or, more specifically, to the Benguela current, which rips up the planet from the frozen wastes of the south, clipping the west Cape coast as it goes.

If the Benguela were just a few degrees warmer, the Cape Floral Kingdom and the Namib Desert would never have happened. Vineyards would not have found a workable home here, either.

How different the resulting coastline is from that of the east, where the warm waters of the south-flowing Mozambique and Agulhas currents bring heat down from the tropics. They throw moisture up into the air for it to be blown in overland where it douses everything with summer rain. Entirely different ecosystems spring from the ground.

Of course, these bodies of water must meet somewhere. Cape Point, the tip of the Cape peninsula, was fêted for years as the place where the mighty Atlantic and Indian Oceans met. In fact the exact point is 150-odd kilometres to the south-east, at Cape Agulhas.

The line dividing the Atlantic from the Indian Ocean is an arbitrary, man-made thing, of which the waters flowing in and around it take little notice. The currents mentioned here are wind-driven and cross this border without passports.

The Agulhas’s warmer waters usually spin away from the coast a while before reaching the Cape peninsula so the region’s climate is almost entirely courtesy of the Benguela.

The so-called Mediterranean conditions have been enjoyed by the Western Cape for about eight million years. So as long as the oceans keep interacting with winds and the spinning of the planet to churn around water as they do, conditions will continue for a long time to come.

In the mean time, if you were to embark on as absurd a journey as the one mentioned here, it’ll be a long one indeed. Better fill the hold with plenty of good Cape wine.