12th August 2012
There was excited talk circulating around the cheese table after last night’s dinner. At 0300, the CTD line would take us within 1.5 nautical miles of the magic coast at a place called Henry Land, near Rohmer Fjord. This is some of the world’s most obscure geography even to Greenland junkies like me and several others aboard JCR. I got up at 0330, looked out my port light and saw—nothing, in some of the wooliest fog thus far during this very foggy cruise. I went back to bed. We’ll have another chance later in the week, farther north. Here’s hoping.
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When I was a boy, I’d bug my father to buy me nautical charts of the coast where we lived, but also charts of wild, high-latitude regions on which I’d search for coasts delineated by the dotted lines that mean “position approximate,” places so remote as to be uncharted. Someday, I dreamed, I’d sail to these unknown places, and the charts lent an air of realism to fantasy voyages of exploration. I had at the time no knowledge of physical oceanography (I thought oceanography meant marine biology), of ocean dynamics—and therefore no idea that certain oceans of the world could be delineated by the oceanographic equivalent of dotted lines. This, the northern stretch of the Nordic Seas, is on of these.
Today some parts of the world ocean are well known, the Gulf Stream, for instance, but no credible scientist would claim that we know everything about the Gulf Stream. Day after tomorrow new discoveries could prompt tectonic shifts in knowledge; by such shifts, science advances. And that’s why the theory is the highest form of scientific certainty. Because physical oceanography is expensive, those waters adjoining the world’s wealthier nations with fishing, oil, and other economic interests (the North Atlantic, for example) have been more thoroughly studied than, say, the Indian Ocean. Other oceans defy study due to their remoteness, severe weather conditions, and ice presence. The water presently beneath James Clark Ross’s is among the most defiant. But there is another and perhaps, for our immediate purposes, more compelling reason why gaps in our knowledge still obtain: The ocean action in these waters is mind bendingly complex. Even the East Greenland Current (EGC), once thought to be this relatively simple pipeline turns out to be far less straightforward. So in this introduction, I’ll try to explain the EGC in coarse-grained terms, and as the trip progresses, fill in the blanks as Bob, Kjetil, and Laura explore its ways and means. But before that it might be useful to lay some geographical context.
Bob has called the EGC a “two-headed current.” Perhaps the best perspective from which to understand both is to look down on Earth from above the North Pole in roughly the center of the Arctic Ocean. The Arctic Ocean is a frozen body of water circumscribed by continents (the Antarctic is a frozen continent circumscribed by oceans). It’s not an entirely closed basin, of course, like a giant lake, but the water routes in and out are limited in number and size; in this sense, it’s been compared to the Mediterranean Sea. Pacific Ocean-origin water flows in through the Bering Strait between Russia and Alaska, while Atlantic-origin water flows in via the Barents Sea north of Norway. Among the recurring, bedrock principles in physical oceanography (and for that matter nature itself) is the conservation of mass: If water flows into an ocean basin, water in equal quantities must flow out. The Fram Strait between Greenland and Spitsbergen, our final destination, is the primary outflow pathway. Obviously, this water is cold, but some of it is also quite fresh due to local melting, freshwater disgorged by the gigantic rivers draining western Russia and Siberia, and especially inflow from the Pacific Ocean, which receives considerably more precipitation than the Atlantic.
'The ocean goes about its business impervious to the desires of scientists trying to understand it, let alone amateurs trying to describe it.'
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So one “head” of the EGC is composed of this cold, fresh water exiting the Fram Strait to flow southward along the east coast of Greenland. Because fresh water is lighter—therefore more buoyant than salty water—some portion of the current resides up on Greenland’s “continental” shelf, which sprawls roughly 60 miles seaward of the coast at a depth of about 200 to 400 meters. But most of it hugs the shelf break, that is, the precipice of the submarine cliff that plunges to the seabed some 1,500 to several thousand meters. Another recurring principle of physical oceanography is “stratification,” or layering in common language; in effect, lighter water tends to “float” atop heavier, denser water below. And that brings us to the other “head” of the East Greenland Current.
As we’ve discussed previously (please see
Overturning), that arm of the Gulf Stream, the North Atlantic Current (NAC), transports warm, salty water northward into the Nordic Seas. While there is some penetration into the center of the Nordic basin, and some NAC water slips northward into the Arctic Ocean, much of it hugs the edges of the basin, as ocean currents are wont to do, then makes a U-turn (“retroflects” as they say) to flow southward—beneath the aforementioned cold, fresh part of the EGC. Though stratified because of their density difference, both heads of the East Greenland Current flow as stacked twins roughly along the Greenland shelf break—and into the Denmark Strait, where the EGC combines with that North Icelandic Jet we discussed last time, thence into the deep North Atlantic south of Iceland. And by this means, they sustain the vital Meridional Overturning Circulation.
I wish I could figure out how to describe to you these ocean dynamics without making them sound simple and straightforward while at the same time maintaining a semblance of clarity. For now suffice it to say that the EGC is not a well-behaved stream as one flowing through a conduit. It meanders and mixes; it spins off eddies spilling water out into the center of the basin; winds drive it up on the shelf and blow it off again; it does what it pleases. It’s a confusing oceanographic “mess,” as Bob put it. Though to the scientist beleaguered by the messy circulation in these waters, nothing happens in the ocean without cause and result. The ocean goes about its business impervious to the desires of scientists trying to understand it, let alone amateurs trying to describe it. But then if it were known, if it were as simple as I’ve made it sound, we wouldn’t need be out here.
- Dallas
