[LINK] "Deep Waters May Not Run Still"

[rfmcdonald]

The recent discovery that larvae can be swept along the ocean bottom from one deep-sea hydrothermal vent to another has implications for life on other worlds, like Jupiter's Europa and Saturn's Enceladus, which are strongly suspected to be geothermally active and possessors of liquid water oceans. Life need not be isolated on these ocean floors; life can spread.

Deep-sea currents caused by large, swirling eddies at the ocean's surface may carry the larvae (inset) of creatures from one hydrothermal vent (main image) to uninhabited vents hundreds of kilometers away, a new study suggests.

The currents caused by large, swirling eddies at the ocean's surface may reach all the way to the sea floor, a new study suggests. The unexpected finding may help explain how the larvae of organisms living at isolated hydrothermal vents can be transported hundreds of kilometers to colonize new vents. And as climate change affects surface eddies, it may also reach the ocean's depths.

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In a field study, Diane Adams, a marine biologist at Woods Hole Oceanographic Institution in Massachusetts, and her colleagues measured the currents near the seafloor along the East Pacific Rise, a submarine ridge south-southwest of Acapulco, Mexico, that sports many hydrothermal vent systems. They suspended sensors 170 meters above the 2350-meter-deep ridge, high enough to remain unaffected by ridge-related turbulence. They also suspended traps just 4 meters above the sea floor to measure the amount of minerals spewed by the vent systems and settling back to the ocean floor, as well as to count the number of larvae produced by creatures living in the warm oasis. Because the vents usually maintain a steady flow and the creatures that live there reproduce continually, minerals and larvae fall into the traps from the cloudy waters above at fairly steady rates.

From November 2004 through April 2005, typical currents at the site flowed from the north at an average speed of about 5.5 centimeters per second, the researchers report online today in Science. Moreover, says Adams, the currents rarely rose above 10 centimeters per second. But in March 2005, currents shifted suddenly and flowed from the south at speeds that sometimes exceeded 15 centimeters per second. During the same interval, the amounts of sediment and vent-creature larvae that fell into the team's traps dropped dramatically—indicating the cloud of minerals and larvae had been carried away, at least temporarily, as if a strong storm system had swept the stale air from a polluted valley.

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The unusual changes in currents may help explain how the larvae of the heat-loving creatures living around hydrothermal vents are dispersed through long stretches of near-freezing waters to reach other warm havens, says Adams. Lab tests show that such larvae drop into a sort of suspended animation when immersed in cold water but can survive in that state for only 30 days or so. Although the occasional eddy-induced currents would likely sweep many larvae to a frigid doom, some of them would luck out and drift to distant oases that couldn't be reached if currents had remained slow and steady.