Tuesday 6 January 2015

Charting the Deeps

A while ago, I was stitching up the Mid-Atlantic Ridge MAR:  Bouvet - Gough - Tristan - Helena - Pico - Iceland - Jan Meyen without emphasising that the existence of the MAR was an extra-ordinary counter-intuitive hyper-explanatory deduction  . . . by cartographer Marie Tharp from data largely accumulated by marine geologist / oceanographer Bruce Heezen.  Their now-iconic, then wholly unexpected, map of the ocean floor is produced under copyright but currently out of print [tsk! and dang!].

Carl-Friedrich "Princeps mathematicorum" Gauss, and possibly the smartest man ever to walk this Earth, was able to calculate the orbit of the asteroid Ceres from only three timed observations of its position.  But he was only able to do so because the theory of planetary motion had been worked out by Kepler from a great many more observations.  The key [how do the minds of geniuses work this sort of thing out?] was that planets travel in ellipses not circles and sweep out an equal area of the space between themselves and the Sun in equal time. So when they are closer to the Sun they travel faster.  If you are far smarter than me, you can follow the beautifully illustrated explanation of how Gauss thought out the answer from the patchiest of data. [From Metafilter]

In theory, therefore, you might have been able to infer the existence of the MAR from the patchy evidence of super-volanoes poking their heads above the surface in the middle of nowhere; or rather in the middle of the Ocean. Because Gauss was busy [making significant contributions to number theory, algebra, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy, Matrix theory, and optics] elsewhere he never turned his attention to the sea-bed and none of the interested parties was smart enough to do a Gauss from the location of islands.  The complement of sea is land and on 6th January >today< 1912 Alfred Wegener suggested that the continents were drifting about the globe - using such data as the almost perfect fit geologically, bio-geographically and cartographically between, say, the nose of Brazil and the arm-pit of West Africa. Wegener's idea was greeted with ironic sarcasm and hoots of derision by his geological colleagues and it wasn't until a generation after his death that everyone flipped over and started to worship his brilliance and prescience. Whatever we do, we do it together, as the sheep said to the other sheep.

Mais assez sur les moutons: revenons nous a nos cartographes!  Tharp and Heezen worked in the  Lamont Geological Laboratory at Columbia University and the business model was that Heezen would ship out on the RV Vema [L], the three-masted schooner that Columbia U owned and operated out of the Hudson River.  The Vema blew where the wind took her in more-or-less the direction intended by her crew and the strategic plans of head office back in New York. Quite similar therefore to Craig Venter's Sorcerer project. Lots of projects were carried out in parallel but Heezen's job was to gather soundings in the old-fashioned way of heaving a weight over the side and measuring the length of rope when it hit bottom.  This technique could be finessed by filling the base of the weight with wax and obtaining a sample of the sea-floor [black mud or fine sand with crushed shell] to match the 3D coordinates of depth, latitude and longitude.  But Vema also had sonar and Heezen gathered a lot more data in the form of print-outs from the ping scanner.  Nice recent commemorative essay on Mental Floss.

When he returned to port, Heezen would dump the data on Tharp's desk and say "Plot this!" [a little more politely!] The divil is in the detail.  Since the time when submarine telegraph cables had been laid across the Atlantic in the mid-19thC it had been known that a mountain range zig-zagged down the middle of the Atlantic, what Tharp saw in Heezen's data was that the mountains were separated by a zig-zag rift.  We know now that the ridge is an upwelling of magma from below as new Ocean floor is created and spreads out to either side but it initially made no sense to Tharp and she suspected that it was a consistent error in her protocol.  But after double and triple checking her plotting of the raw measurements and getting more confident that she was correctly bridging the inevitable wind-blown gaps in the data, she knew she had discovered something that shook the foundations. It took hootin' and hollerin' battles to persuade Heezen that she was right and that they had discovered crucial evidence that supported Wegener's tectonic theories. But the opposition to continental drift of Doc Ewing, director of the Lamont Lab, escalated to a highly personalised antler clashing that greatly impeded the progress of Ewing's career and led to Tharp's early retirement from Columbia.  But, in a silver lining way, the external aggro forced Heezen & Tharp to iron out their internal disagreements.

One of the absurd but necessary consumers of time in those pre-computer days was that the scale kept changing and Tharp had to recalculate everything to the new standard from fathoms (6 feet, 183 cm to your land-lubbers) to "corrected fathoms" (a fudge factor to account for changes in ping velocity in denser water) and finally in meters (like the rest of the scientific world, Yankee-dogs).  We have it easy, nowadays in a digitised world.

They went out on a limb and published a contour map of the North Atlantic in 1957. It was a milestone in the acceptance of plate-tectonics.  Further maps followed until, in collaboration with a sub-contracted landscape painter Heinrich Berann, in 1977 they produced a undersea map of the whole world, part of which I've clipped for the first picture above.  Some have called it the most beautiful map ever produced.  In forced retirement, Tharp shifted her mapping business to her home in South Nyack, NY where she knew her material and could reliably recall locations and anomalies merely by dredging her mind.  Such immersion in the data is an almost essential prerequisite for creative leaps such as Tharp's identification of the Mid-Atlantic Rift in the Ridge.  I suspect that marietharp.com has lost the plot since The Boss died in 2006: asserting that "We are carrying on her great legacy as she intended" except in the sense of producing maps, all of which are currently unavailable [tsk!].  Nevertheless bonnets off to Marie Tharp!

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