Marie Tharp is the subject of today’s Google Doodle, with an interactive narration of her life story. That story—how Tharp’s pioneering work mapping the ocean floor helped prove the theory of continental drift—is familiar to long-time readers of this blog: this is the 12th post I’ve made about the legendary cartographer. But someone is going to be one of today’s lucky 10,000 because of this, and that’s not a bad thing.
Scientists have now mapped the seafloor around the Hunga Tonga-Hunga Ha‘apai volcano, and as a result we have learned just how massive the January 2022 eruption was. By comparing their soundings with 2017 data, they determined that at least 9.5 km3 of material was discharged. Debris was found 80 km from the volcano, and the volcano’s caldera has been replaced by a cavern 850 m deep. More from the NIWA media release and from ABC (Australia).
Europe’s summer heat wave wasn’t just felt on land; the Mediterranean Sea saw surface temperatures as much as 5°C above the average. The ESA’s animated map, above, shows the difference between sea surface temperatures from March to August 2022 and the 1985-2005 average for those months. The redder, the hotter than average. [ESA]
In their paper, the complete text of which is available online, physical geographer Simon Haslett and professor of Celtic David Willis are trying to reconstruct the post-glacial evolution of Wales’s Cardigan Bay using historical and folklore sources as well as bathymetric data and geological evidence. (It’s pretty obvious which author contributed what.) The Gough Map shows two islands that don’t correlate to any real island in Cardigan Bay; the study suggests that the islands may have in fact existed and have since been lost to flooding, erosion and other post-glacial changes to the shorelines. There are several submarine highs in the bay that may match up with the lost islands. The paper hypothesizes that the Cantre’r Gwaelod legend is a folk memory from when the coast was much different: that there were islands in Cardigan Bay, that they disappeared during the human era, and this legend is one of their traces.
In other words, a bit different from taking an old map at entirely too much face value (which, to be sure, has been enough of a thing that it was first to mind when I saw the story). They’re using the map and the legend to try and figure out the shoreline’s history—not using the map to prove the legend.
NASA Earth Observatory: “Researchers at the University of Michigan (UM) recently developed a new method to map the concentration of ocean microplastics around the world. The researchers used data from eight microsatellites that are part of the Cyclone Global Navigation Satellite System (CYGNSS) mission. Radio signals from GPS satellites reflect off the ocean surface, and CYGNSS satellites detect those reflections. Scientists then analyze the signals to measure the roughness of the ocean surface. These measurements provide scientists with a means to derive ocean wind speeds, which is useful for studying phenomena like hurricanes. It turns out that the signals also reveal the presence of plastic.”
In 2021, Nathan Thomas and Lola Fatoyinbo of NASA’s Goddard Space Flight Center, along with colleagues from three countries, took another step by mating ICESat-2 measurements with images from Copernicus Sentinel-2 to derive bathymetry at better resolution. The team mapped the shallows down a depth of 26 meters (85 feet) around Biscayne Bay in Florida, the Gulf of Chania in Crete, and the island of Bermuda.
Thomas and colleagues compared their satellite-derived bathymetry with maps made from traditional topographic surveys, multibeam sonar, and nautical soundings. Their new maps had a resolution of 10 meters, improving upon the current 115-meter resolution dataset for Crete and the 30- to 90-meter datasets for Florida and Bermuda. The existing data for Florida and Bermuda are composites of lots of sources spanning 63 years, while the ICESat-2/Sentinel-2 maps offer a contemporary assessment of underwater structure.
A new article on the life and career of Marie Tharp, written by our friend Betsy Mason, was published by Science News earlier this month. Plenty has been written about Tharp, whose work mapping the ocean floor helped provide the evidence for continental drift: numerous articles, a 2012 biography, two books for children just last year. But that doesn’t mean that there aren’t still people who still haven’t heard of her, and should.
Zealandia (Te Riu-a-Māui) is the name given to a proposed, and largely submerged eighth continent, of which New Zealand (Aotearoa) is the largest above-water remnant. Explore Zealandia is geoscience company GNS Science’s web portal to their maps of this largely submerged continent, including bathymetry, tectonics, and other data; the data is also available for download. [WAML]
The Guardian looks at efforts to map Doggerland, a prehistoric area of land in the North Sea between Britain and continental Europe that was submerged by rising sea levels at the end of the last ice age. “Using seabed mapping data the team plans to produce a 3D chart revealing the rivers, lakes, hills and coastlines of the country. Specialist survey ships will take core sediment samples from selected areas to extract millions of fragments of DNA from the buried plants and animals.”
The bare bones of Tharp’s story are therefore fairly well known: while mapping the floor of the Atlantic Ocean, she discovered the presence of the Mid-Atlantic Ridge—and, more specifically, its rift valley, providing tangible evidence of continental drift. Because continental drift was at that point considered to be a crackpot theory, it took some doing for Tharp’s discovery to be accepted; and when it was her contributions were to some extent minimized.
While Felt’s book is positioned as a biography, its strength is in the details of that pivotal discovery: how and where it was made, and by whom, and in what context. Tharp’s work was not done in a vacuum, and how and why she was where she was is important. Felt sets the stage for us: not only does she take us through Tharp’s early childhood and rather variegated education and her arrival in 1948 at the Lamont Observatory, she gives us a short history of that Observatory, of the theory of continental drift, of her colleagues—notably her lifelong collaborator (and possibly life partner) Bruce Heezen and Observatory director (and sometime antagonist) Maurice Ewing. More than anything else, Soundings provides context for Tharp’s discovery: by the time we’re done, we know how important it was, and why. We’ve been well briefed.
Felt is less successful in building a portrait of Tharp herself. Some areas of her non-work life—her childhood, family and college education, for example—are extremely well covered, but other areas have considerable gaps, particularly those involving her personal life. The nature of Tharp’s relationship with Heezen is only hinted at, as is an early, unsuccessful marriage to someone else. Her later life, supported by a motley gang of eccentrics called Tharpophiles, is also incompletely covered. The elisions, however unintended, are frustrating. I suspect the author was a prisoner of her source material, which in places she follows very closely; I would have liked it if more had been done to fill in the gaps.
Soundings was published in hardcover by Henry Holt in 2012. It’s available in paperback and ebook from Picador.
This image went a bit viral earlier this week. Some context. It’s from an August 2015 blog post at Le Cartographe, in which Alexandre Nicolas discussed (and rendered, above) a projection produced in 1942 by South African oceanographer Athelstan Spilhaus. In Spilhaus’s oceanic projection, centred on Antarctica, the world’s oceans form a single, uninterrupted body of water. Which, you know, it is. The continents form the edges of the map; there is … some … spatial distortion. As Alexandre wrote in 2015, “This projection is rarely used and it’s a real shame!”