October’s big spring tide coincided with days of very high pressure, so that the memorable calm of the hillside was echoed in the rise of the sea. It brimmed out of the channel more like slow mercury than water, creeping over sand and grass in a gradual, silent glaze. On the outer strand it rose to the lowest hummocks of the dunes and fell smoothly back, hemming the sand with lacy lines stitched by the smallest of bubbles.
The boreen to the sea was fringed by finches and linnets, dancing ahead of me and away over sandy pastures and cotton-wool sheep gilded by the sun. With no rumble of surf, the whirr of their wings was the day’s loudest sound. At the channel the tide was still ebbing, to be waded in bare feet and trousers rolled up above the knee. It’s ages since I did this, toes reaching for the softer, sandy bits, my balance not quite as sure as it was.
I have met baby flounders here, and sticklebacks, but the swift, glassy flow had sent them to shelter in cowlicks of green weed. The water was thrillingly cold and then not cold at all.
The strand was ribbed in the flood’s withdrawal and scattered with dark furls of Laminaria seaweed. The sand around them was pitted by the shore birds probing after burrowing sandhoppers. Otherwise, only random blobs, sheets and shards of plastic flotsam drew the eye.
I have gathered many useful plastic things: fish boxes and bottle crates, buoys and bits of net, tangles of cord – all grist to the landlubbing gardener. I have enough now, quite enough. And all, anyway, are the sweepings of storms, of which we’ve had few in a long time.
The sea has returned a great mass of sand, clothing the ribs of black rock. The cliffs it had carved in the dunes have had time to slide to a stable slope and grow a new haze of marram.
Other delicate tides have brought me whole window sills of collectibles – sea beans and sea-urchin globes, the fragile violet sea snail, and more – none on this day. But the sand at the foot of the dunes was swagged with fresh drifts of seashells: limpet, mussel, razor, cockle, venus, carpet, trough, otter, wedge, tellin and the rest, a jumble of shapes, colours and fragments of small ocean lives.
The substance of them all is calcium – or, rather, the kind of calcium carbonate known as aragonite, named for an eccentric twinning of its crystals in rocky veins of that part of Spain that produced a famous Catherine (I’ve started, so I’ll finish). Aragonite also gives pearls their sheen, and abalone shells their rainbow iridescence. More essentially, it builds the shells and skeletons of billions of sea organisms, from deep-sea corals to the bivalves of the Irish shore. For others the main building block is calcite, a tougher, less soluble form of carbonate.
The ocean is still alkaline, its upper layers saturated with carbonate ions. But the extra CO2 absorbed into the sea from human industry has already swung its pH the other way, by almost a third. The acidification of the ocean is now “the other CO2 problem”, looming ever more urgently in scenarios of climate change.
Human-generated carbon has penetrated deeply into the North Atlantic, becoming more corrosive with greater cold and pressure, and in the long term the surface layer of shell-friendly water could get shallower and shallower. But already there are forecasts that, in the Arctic, aragonite could begin to diminish at the surface within a few decades.
What happens when marine animals are bathed in acidifying seawater? Research is still in its infancy and full of paradoxical results.
In some studies sea urchins and brittlestars have lost their body functions, oyster growth has dwindled, marine snails have started losing their shells. Other molluscs have damaged immune systems or have forgotten how to dodge their predators. Not every species reacts severely. Crabs, lobsters, starfish, barnacles and even limpets seem better able to cope with changes in pH, but even these are vulnerable in the early stages of life.
If dissolved aragonite disappears from the deep Atlantic, the slow-growing cold-water corals off Ireland seem likely to be among the first organisms to suffer. The point was made strongly this summer in a robust review from the Marine Institute, Ocean Acidification: An Emerging Threat to Our Marine Environment (available to download at marine.ie).
The waters around Ireland have distinctive patterns of seasonal upwellings, raising deep water, lower in aragonite, to spill across the continental shelf. Our coastal topographies, currents and plankton fronts can all affect the pace and degree of acidification.
Michael Viney, The Irish Times, 23 October 2010. Article.
