Deep ocean larvae hitch ride on powerful eddies

By Martin Leggett - 28 Apr 2011 18:0:0 GMT
Deep ocean larvae hitch ride on powerful eddies

A new study into the swirling phenomenon of oceanic eddies - massive circling currents up to 300 miles in width - has found that they offer the perfect ride for deep sea organisms, minerals and heat. These were previously though to be trapped over a mile-and-a-half beneath the sea's surface. That's the exciting conclusion from research published in the journal Science today.

It was sparked by a previous study showing the surprisingly fast movement of marine larvae across the sea's bottom. The discovery comes as something of a revelation to marine scientists, because these eddies were previously thought of as relatively shallow expressions on the sea's surface.

But using deep-sea instruments along the East Pacific Rise - for measuring water currents, and studying trapped sediments - the researchers from Woods Hole Oceanographic Institution (WHOI) have confirmed that the eddies reach down to the depths of mid-oceanic ridges. These are sub-sea mountains that form the backbone of much of the oceanic crust.

And it means these volcanically active regions of the ocean, which are home to a bizarre community of bottom-dwelling creatures, black 'smoking' vents and deep-water eruptions, are not as isolated as was believed.

The eddies form on a seasonal basis, when circulating wind jets help whip them into shape - and in the Pacific they are particularly prevalent during an El Nino event. Lead author at WHOI, Diane K. Adams, said ''We knew these eddies existed. But nobody realized they can affect processes on the bottom of the ocean. Previous studies had looked at the upper ocean.''

She had taken part in a prior study which saw that, in an area of the Pacific ridge covered by a new eruption, larvae from marine organisms had rapidly populated the area - from over 200 miles away. The deep and fast roots of the oceanic eddies help to explain how that could happen. And it's not just marine life being swept along the mid-oceanic ridges by these eddies - the warm mineral-rich waters pouring from hydrothermal vents are also likely to be 'mixed' by these seasonal deep-sea 'winds'.

The results of the research are likely to change the way marine scientists look at the dynamics of these most inaccessible parts of our planet. The authors conclude that ''Although the deep sea and hydrothermal vents in particular are often naively thought of as being isolated from the surface ocean and atmosphere, the interaction of the surface-generated eddies with the deep sea offers a conduit for seasonality and longer-period atmospheric phenomena to influence the 'seasonless' deep sea.''