The Fate of the Ocean
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Along with thermal expansion, melting ice also adds freshwater to the ocean. Until recently, many researchers believed this freshening would have a negligible impact on sea levels or ocean chemistry. But the effects are proving unpredictable. In the Antarctic Peninsula, lubricated by summer temperatures registering 3.6 degrees Fahrenheit warmer than 40 years ago, ancient ice shelves are disintegrating, enabling the glaciers behind them to surge into the sea with a rapidity startling to scientists. Consequently, fears are growing that if the West Antarctic Ice Sheet, currently contained by the Ronne and Ross ice shelves, ever surges, it would raise sea levels by as much as 23 feet worldwide.
Curry’s work aboard Oceanus is part of a five-year study monitoring the ocean conveyor belt and its reaction to the freshening ocean. In a 2005 paper published in Science, she calculates that 4,558 cubic miles of freshwater from rivers and ice melt have been added to the cold waters between Labrador and northern Europe since 1965. Based on the trends of the past 40 years, it would take another 100 years of similar freshening to shut down a critical element of the ocean conveyor belt known as the Atlantic meridional overturning circulation (MOC), the primary heat-transport mechanism that awards northern Europe a climate more like that of New England than Alaska—Europe’s latitudinal counterpart.
Add enough warming, evaporation, and freshwater, however, and there is potential for enormous change on an accelerated schedule, including the possibility that the Atlantic MOC could shut down faster than expected, which would make Europe colder, possibly cold enough to grow new glaciers. Hollywood sensationalized this scenario in the film The Day After Tomorrow and was widely accused of scaremongering. Yet John Schellnhuber, research director of the Tyndall Centre for Climate Change Research in the United Kingdom, calls the Atlantic MOC one of the earth’s most critical tipping points, which, if triggered, could initiate rapid changes across the entire planet.
No one knows if we’re instigating another ice age. But what we do know is that the tropical ocean is saltier than it was 40 years ago, and the polar ocean fresher. Furthermore, this salinity differential accelerates the earth’s freshwater cycle—creating faster rates of evaporation and precipitation, which release more water vapor into the atmosphere, thereby increasing the greenhouse effect and invigorating the global warming that caused the whole problem in the first place.
CURRY AND I SHARE THE TWO BUNKS in the chief scientist’s cabin, distinct from the other berths aboard by the presence of a private head and shower. She has refreshed our tiny corner of the ship with a cheerful string of white Christmas lights, an antidote to the overhead fluorescents. Curry doesn’t spend much time below, however, even though most of the science team, when not on their 12-hour watches, are bunked out, hoping for unconsciousness. Curry is usually on station in the dry lab, a space kept water-free to protect sensitive scientific equipment, where she straddles a chair strapped to the counter while working on a laptop secured with a rope tied in half hitches.
She will celebrate her 48th birthday aboard during this trip, though she looks years younger. Fit, with a runner’s frame, long blond hair, and steady blue eyes, she is the Hollywood ideal of a female scientist, yet she possesses the keen mind the movies never capture, and she bears the weight of responsibility of managing a $300,000 research cruise in bad weather. Already she has been forced to reverse the order in which Oceanus normally visits each of the 22 stations on the transect. And already she’s suspended deck operations for one critical night, when huge waves washed aboard in the darkness, swamping her to her waist and knocking her off her feet, nearly sweeping her overboard. When I ask why she doesn’t use lifelines on deck, she says the risk of entanglement in the equipment is greater than the benefit of staying tethered to the ship.
