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If you've ever waded into the ocean for a swim and suddenly realized that the shore is getting farther away, not closer, you may have encountered a rip current (离岸流). Common at beaches worldwide, these powerful currents flow from the shore toward the sea at speeds up to several feet per second.
It's important to know what rip currents are and how to look for them, because they are a leading cause of drownings in the surf zone near shore. Rip currents can form in several ways. One type of rip current, known as a channel rip current, forms when there are gaps between breaking waves. As waves break, they push water toward the beach and raise the level of the water slightly. If waves break on a sandbar (沙洲), but not in a deeper channel that cuts through the sandbar, the extra water that the waves have pushed toward the beacon escapes back to the ocean through the channel. The darker corridor of the escaping water acts like a conveyor belt, moving water, unsuspecting swimmers and small marine organisms offshore.
Another type, known as a transient or flash rip current, forms when surf is choppy (波涛汹涌的). The edges of breaking waves push on the water and make it spin, like a fast ice skater crashing into someone.
Think of a rip current as a swift river cutting through the surf away from the shore. Swimming against the current is going to tire you out and put you at risk of drowning. Instead, swim parallel to the beach—think of heading for the "river banks"—until you are out of the rip current's pull. Once you're no longer fighting it, you can swim back to shore.
Rip currents aren't just a safety issue. Scientists are beginning to better understand the crucial ecological role they play in the ocean. Many marine organisms including oysters, barnacles, fish and coral, rely on ocean currents to find suitable habitats. These organisms swim up or down or attach to floating or sinking material and are transported by multiple ocean processes. Rip currents are a key mechanism for carrying larvae (幼体) to deeper waters or recalculating them in shallow waters. The type and behavior of the rip current may affect the movement of marine organisms.
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