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The Way North The Gulf Stream: A River in the Sea? The Great Merry-Go-Round Winds Good and Bad Variability in Space and Time Currents of the Abyss A mighty ocean current runs north and east offshore from the East Coast, between the Florida Keys and Cape Hatteras (fig. 6.1). It moves warm water northward, from the Gulf of Mexico into the northern North Atlantic, on the way entraining warm water from the Sargasso Sea. It is one of the two most powerful warm currents on the planet.1 The heat it transports feeds the storms of the northern Atlantic and helps maintain low air pressure in the vicinity of Iceland, stabilizing the Iceland Low. In turn, the anticlockwise winds running about the Iceland Low direct the heat-bearing marine air and associated rainstorms into northwestern Europe, from the British Isles and the Netherlands to Denmark and Norway. The origin of this great weather-making current was a mystery well into the twentieth century . In the 1940s, it was realized that the current represents the western boundary of the spinning wheel of warm water that is centered on the Sargasso Sea, in the desert belt of the North Atlantic. This wheel is made to spin by winds, but not any winds over the Gulf Stream itself. As long as there are trade winds and westerlies , the great wheel will spin, and the Gulf Stream will move warm water from low to temperate latitudes. THE WAY NORTH The city of Bergen in western Norway, the second largest of its country and once the nation’s royal capital and its main port, has a number of outstanding assets. As a port, it is ice free all year, despite its latitude, which is just slightly poleward of 60⬚ N. The equivalent position on Greenland is Julianehåb, surrounded by glaciers terminating in the ocean. In Canada, the 60⬚ line runs through the center of Hudson Bay, which is full of sea ice until early summer. In Alaska, Glacier Bay is at this latitude, an enormous fjord system where tourists on cruise ships watch glacier tongues feed icebergs to the 151 SIX Unraveling the Gulf Stream Puzzle ON A WARM CURRENT RUNNING NORTH sea. In the Southern Hemisphere, the latitude of 60⬚ is positively uninviting—it runs through the desolate and windswept islands north of the Antarctic Peninsula, where sea ice is common. The point is that the citizens of Bergen bene fit from the greatest warm-water anomaly on the planet (fig. 6.2). The sea off their shores is some 5 ⬚C (9 ⬚F) warmer than is typical for the latitude. Springtime in Bergen arrives in May as a glorious spectacle of greening and flowering, with daylight breaking early and extending far into the late evening. Front yards are blazing with lilacs, hedge roses, poppies, and ubiquitous rhododendron and azalea, while dandelions grace niches and cracks in sidewalks and church walls. At the fish market, pansies are for sale next to gutted mackerel and live crabs. Bergen’s festive spring—celebrated with pageants of parades and musical events—contrasts with May in Hudson Bay, at the same latitude , a bleak scene with but little green, where sea ice still rules the seascape. The warm water bathing Bergen’s shores, with a temperature near 10 ⬚C (50 ⬚F), arrives from the south with the Norwegian Current, and this water has access deep into the countryside through the fjords, which act like so many pipes of a central heating system. The warm Norwegian Current, in turn, is a branch from the North Atlantic Current, which receives heat from the Gulf Stream and carries some of it toward northwestern Europe. All of northwestern Europe depends on this heat supply, much of which was gathered in the subtropical Atlantic and in the sunny Caribbean. The westerly winds of the North Atlantic drive the currents bringing heat, and they themselves bring even more heat—heat locked into the vapor they bear. These are the same winds, of course, that powered the sailing vessels making their way back from the New World to the Old before steam and diesel engines took over this task. The delivery of subtropical heat to high northern latitudes by the winds and currents toward the shores of Norway generates a great temperature anomaly (fig. 6.3). As mentioned, it is the largest such anomaly on the planet, and Bergen happens to be at its center. Offshore of Norwegian shores, in the...

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