The south shore of Clew Bay might have been tropical, driving west on the first weekend in March, if one didn’t look up to the left and the cold white capped reek. To the right, the underwater reefs and the sand filled spaces between them were shimmering beneath a translucent green sea, remarkably clear and suggesting a temperature far greater than its actual 9 or 10 degrees.
An extraordinary three month episode of east winds and hushed seas meant the water column, usually so clouded with sediment and nutrients stirred up from below by the hefty swells of winter, was settled and clear. Divers across the fjord at ScubaDiveWest in the Little Killary were describing unusually sharp visibility in the month where one’s hand often murkily disappears at arms length underwater.
In the strict calendar of marine ecosystems, where everything has a function, such nutrients are hungrily awaited. The Spring phytoplankton bloom is this months big event; an event where the tiniest of marine organisms hint at their importance in an explosion of life.
Phytoplankton (microscopic algae) need light to grow and when daylight levels reach a critical point at the end of March and beginning of April, the abundance of nutrients in the water causes the sudden and out of control growth in their population resulting in a discolouring bloom stretching over hundreds or thousands of square kilometres in places.
Though tiny, phytoplankton’s contribution to the planet is not insignificant; it is know believed they contribute as much, if not more, oxygen to the earth as the rainforests do and soak up carbon dioxide equally industriously.
The Spring Bloom is all over in a few weeks as growth is so wild and uninhibited that the nutrient supply is rapidly used up. But what happens when the daylight hours come and nutrients still sit unroused on the sea floor? Such a run of inactivity as we have had is almost unprecedented so it’s hard to say, but swell is promised for next week; the water column will likely become replenished in time.
Blooms which occur from time to time in nutrient loaded estuaries, and can be dangerous to shellfish, are sometimes obvious to coastal observers; the Spring bloom however usually comes and goes unnoticed. Occurring offshore and covering large expanses of surface ocean it is best appreciated from above. Satellite images of Ireland are a good place to view it, or maybe if one timed it right, the top of Croagh Patrick.