A sea change in the rhythm of life

There's a strong smell of spring off the sea. Standing on the point at Tonakeera, on the little patch of grass littered with cobbles, shells and driftwood from the winter storms, I get this whiff of salty pheromone, prickling the palate like an oyster.

It may not be entirely my fancy. Every bubble in the sea rises with its cargo of gases, among them, in spring, the chemicals released by plant plankton in its sudden surge to life. Maybe what I catch on the wind is a hint of dimethyl sulphide, the stuff by which the ocean sends sulphur into the air and thus returns it, in rain, to the land. I snatch at these glimpses of Gaian regulation like a tribesman negotiating with seasonal gods.

As light levels intensify, this is the season of growth in the sea wherever there's fertility. We need the storms to stir the waters and fetch minerals up from the deeps; we need warm Atlantic currents to help germinate the plants. Without phytoplankton, the sea would be a beautiful, empty, barren blue - the colour of deep ocean - all the way in to the strand.

At Tonakeera, big gullies twist down into the world at the bottom of the tide. Their sides are worn smooth as marble by the assault of waves and yet, glued to these glistening arches of rock are crimson blobs of anemones and sparse little patches of breadcrumb sponge, waiting out the hours until the next surge of water.

In the zone between high and low tide lies Ireland's last margin of wilderness, accessible by humans only on borrowed time. It lives by its own rhythms and rules, its own abundances. On the sheltered inlets, away from the battering surf, and curtained by seaweeds, the abundance is of different species, of diversity. On these outermost rocks, the abundance is of individuals: astronomical numbers of a few, resilient animals.

More than half a million barnacles may coat just one square metre of rock in their fluted white armour; below them, tiny mussels mass at somewhat lesser density, each sharp little bivalve anchored by threads like the guy ropes of a tent. When they spawn, their millions of larvae become temporary members of the zooplankton, mingling with the plants and eating them, and getting eaten.

Anything that could harm the plankton, plant or animal, is bad news for life on the planet - not just marine life but any sort that depends on an equable climate. This is because microscopic plant plankton fixes carbon in its tissues, in the exchange of carbon dioxide between the atmosphere and the sea.

The very skin of the ocean, the boundary layer, has become an intensely interesting and important part of the planet. It does, after all, cover more than two-thirds of Earth - the vast and unique ecosystem known as the "neustonic realm". And an awful lot goes on there, however invisibly to the eye.

The top millimetre, the sea-surface microlayer, is where a lot of chemicals are concentrated. Most of them are natural substances - amino acids, lipids, phenols and the rest - scavenged by bubbles drifting up from below. They form thin organic films, sometimes gathered by the wind into visible slicks, and these can affect the transfer of the ocean's heat into the air. The bursting bubbles also shoot chemicals out into the atmosphere and exchange gases with it.

Man's toxic chemicals, entering the sea all over the globe, often end up in the microlayer, with unpredictable impact on its natural processes. They also contaminate an environment teeming with living organisms, both at the surface and in the next 10 millimetres down. This is where small animals are so abundant and where the eggs and larvae of fish and invertebrates spend a vital part of their lives.

Even more menacing than seaborne chemical pollution is the rise in ultra-violet radiation. Since man's release of chlorofluorocarbons began gobbling holes in the stratospheric ozone layer, people have been urged to cover up in the sun, or slap on screening lotions. But plankton, plant and animal, has no place to hide. Indeed, the sea surface is probably the worst place to be in the mid-day sun, because of what is called the "photon backscatter" from all the particles in the micro layer, and multiple reflections from the waves (rather as tin-foil reflectors are used by fanatics in getting an all-over tan).

Organisms that live at the seasurface should be well-adapted to ultra-violet radiation. Many are highly pigmented; others seem quite transparent or have what seem to be effective UV filters. But many neustonic plants and animals seem to be at the limit of how much of the UV fraction, UV-B, they can take - the summer rise in radiation actually seems to be what switches off the sea's spring uprush of phytoplankton.

Thus, if ultra-violet reaches high enough levels, it seems certain to interfere with the transport of gases like carbon dioxide and dimethylsulphide. It will affect the photochemistry of many other substances in the sea-surface, changing the production of trace gases important to the atmosphere. Some of these changes could trigger feedback mechanisms, perhaps generating iceclouds in the stratosphere or depleting the ozone layer still further . . .

Is this what I spend my time brooding on, as I rummage among the driftwood on the point of Tonakeera? Not, as it were, in much detail. I am content, indeed, to feel quite stupid, amid the wind and the waves, with the sun on the back of my neck.