Arctic seawater flows south along an unexpected route

Textbooks depict the Gulf Stream, the Kuroshio, and other great ocean currents as smooth, river-like streams. Reality is messier. Gravitationally bound to the spinning globe, the oceans constitute a complex, turbulent system. How turbulence influences one particular ocean current is revealed in a new field and computational study led by Amy Bower of Woods Hole Oceanographic Institution. In 2003--05 her team released 76 floats off the Newfoundland coast at a rate of about six every three months. Her aim was to trace the southward flow of cold arctic water in the Deep Western Boundary Current (DWBC), which hugs the continental slope of the Eastern Seaboard and eventually meets the Gulf Stream off Cape Hatteras. The floats recorded their courses by triangulating signals from a set of moored sound beacons along the route. Like nuclear submarines, the floats surfaced at the end of their voyage and beamed up their recordings to a satellite. To their surprise, Bower and her colleagues found that only seven floats followed the DWBC’s coastal route. Most took a wide, irregular path farther east in the Atlantic interior. The same behavior showed up in the team’s simulation of the two-year field study. Emboldened by that resemblance, the researchers simulated a further 13 years of flow and found a richer, more complex pattern than appears in textbooks. Understanding such patterns in the present-day ocean, says Bower, is an essential ingredient for predicting the effects of global warming on Earth’s future climate. (A. S. Bower, M. S. Lozier, S. F. Gary, C. W. Böning, Nature 459, 243, 2009 .)--Charles Day