Category Archives: Geography

Antarctica – What’s Under All That Ice?

Peter Lobner

From space, Antarctica gives the appearance of a large, ice-covered continental land mass surrounded by the Southern Ocean.  The satellite photo mosaic, below, reinforces that illusion.  Very little ice-free rock is visible, and it’s hard to distinguish between the continental ice sheet and ice shelves that extend into the sea.

Satellite mosaic image of Antarctica created by Dave Pape, 
adapted to the same orientation as the following maps. 
 Source.  https://geology.com/world/antarctica-satellite-image.shtml

The following topographical map presents the surface of Antarctica in more detail, and shows the many ice shelves (in grey) that extend beyond the actual coastline and into the sea.  The surface contour lines on the map are at 500 meter (1,640 ft) intervals.

Map of Antarctica and the Southern Ocean showing the topography of Antarctica (as blue lines), research stations of the United States and the United Kingdom (in red text), ice-free rock areas (in brown), ice shelves (in gray) and names of the major ocean water bodies (in blue uppercase text).
Source: LIMA Project (Landsat Image Mosaic of Antarctica) via Wikipedia

The highest elevation of the ice sheet is 4,093 m (13,428 ft) at Dome Argus (aka Dome A), which is located in the East Antarctic Ice Sheet, about 1,200 kilometers (746 miles) inland.  The highest land elevation in Antarctica is Mount Vinson, which reaches 4,892 meters (16,050 ft) on the north part of a larger mountain range known as Vinson Massif, near the base of the Antarctic Peninsula.  This topographical map does not provide information on the continental bed that underlies the massive ice sheets.

A look at the bedrock under the ice sheets: Bedmap2 and BedMachine

In 2001, the British Antarctic Survey (BAS) released a topographical map of the bedrock that underlies the Antarctic ice sheets and the coastal seabed derived from data collected by international consortia of scientists since the 1950s. The resulting dataset was called  BEDMAP1.  

In a 2013 paper, P. Fretwell, et al. (a very big team of co-authors), published the paper, “Bedmap2: Improved ice bed, surface and thickness datasets for Antarctica,” which included the following bed elevation map, with bed elevations color coded as indicated in the scale on the left.  As you can see, large portions of the Antarctic “continental” bedrock are below sea level.

Bedmap2 bed elevation grid.  Source:  Fretwell 2013, Fig. 9

You can read the 2013 Fretwell paper here:  https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf

For an introduction to Antarctic ice sheet thickness, ice flows, and the topography of the underlying bedrock, please watch the following short (1:51) 2013 video, “Antarctic Bedrock,” by the National Aeronautics and Space Administration’s (NASA’s) Scientific Visualization Studio:

NASA explained:

  • “In 2013, BAS released an update of the topographic dataset called BEDMAP2 that incorporates twenty-five million measurements taken over the past two decades from the ground, air and space.”
  • “The topography of the bedrock under the Antarctic Ice Sheet is critical to understanding the dynamic motion of the ice sheet, its thickness and its influence on the surrounding ocean and global climate. This visualization compares the new BEDMAP2 dataset, released in 2013, to the original BEDMAP1 dataset, released in 2001, showing the improvements in resolution and coverage.  This visualization highlights the contribution that NASA’s mission Operation IceBridge made to this important dataset.”

On 12 December 2019, a University of California Irvine (UCI)-led team of glaciologists unveiled the most accurate portrait yet of the contours of the land beneath Antarctica’s ice sheet.  The new topographic map, named “BedMachine Antarctica,”  is shown below.

BedMachine Antarctica topographical map showing the underlying ground features and the large portions of the continental bed that are below sea level.  
 Credit: Mathieu Morlighem / UCI

UCI reported:

  • “The new Antarctic bed topography product was constructed using ice thickness data from 19 different research institutes dating back to 1967, encompassing nearly a million line-miles of radar soundings. In addition, BedMachine’s creators utilized ice shelf bathymetry measurements from NASA’s Operation IceBridge campaigns, as well as ice flow velocity and seismic information, where available. Some of this same data has been employed in other topography mapping projects, yielding similar results when viewed broadly.”
  • “By basing its results on ice surface velocity in addition to ice thickness data from radar soundings, BedMachine is able to present a more accurate, high-resolution depiction of the bed topography. This methodology has been successfully employed in Greenland in recent years, transforming cryosphere researchers’ understanding of ice dynamics, ocean circulation and the mechanisms of glacier retreat.”
  • “BedMachine relies on the fundamental physics-based method of mass conservation to discern what lies between the radar sounding lines, utilizing highly detailed information on ice flow motion that dictates how ice moves around the varied contours of the bed.”

The net result is a much higher resolution topographical map of the bedrock that underlies the Antarctic ice sheets.  The authors note:“This transformative description of bed topography redefines the high- and lower-risk sectors for rapid sea level rise from Antarctica; it will also significantly impact model projections of sea level rise from Antarctica in the coming centuries.”

You can take a visual tour of BedMachine’s high-precision model of Antarctic’s ice bed topography here.  Enjoy your trip.

There is significant geothermal heating under parts of Antarctica’s bedrock

West Antarctica and the Antarctic Peninsula form a connected rift / fault zone that includes about 60 active and semi-active volcanoes, which are shown as red dots in the following map.  

Volcanoes located along the branching West Antarctic Fault/Rift System.
Source:  James Kamis, Plate Climatology, 4 July 2017

In a 29 June 2018 article on the Plate Climatology website, author James Kamis presents evidence that the fault / rift system underlying West Antarctica generates a significant geothermal heat flow into the bedrock and is the source of volcanic eruptions and sub-glacial volcanic activity in the region.  The heat flow into the bedrock and the observed volcanic activity both contribute to the glacial melting observed in the region.  You can read this article here:

http://www.plateclimatology.com/geologic-forces-fueling-west-antarcticas-larsen-ice-shelf-cracks/

The correlation between the locations of the West Antarctic volcanoes and the regions of higher heat flux within the fault / rift system are evident in the following map, which was developed in 2017 by a multi-national team.

Geothermal heat flux distribution at the ice-rock interface superimposed on subglacial topography.  Source:  Martos, et al., Geophysical Research Letter 10.1002/2017GL075609, 30 Nov 2017

The authors note: “Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent-wide heat flux maps have only been derived from low-resolution satellite magnetic and seismological data. We present a high-resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. …. Our high-resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.”  This Geophysical Research Letter is available here:  

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL075609

The results of six Antarctic heat flux models developed from 2004 to 2017 were compared by Brice Van Liefferinge in his 2018 PhD thesis.  His results, shown below, are presented on the Cryosphere Sciences website of the European Sciences Union (EGU). 

Spatial distributions of geothermal heat flux: (A) Pollard et al. (2005) constant values, (B) Shapiro and Ritzwoller (2004): seismic model, (C) Fox Maule et al. (2005): magnetic measurements, (D) Purucker (2013): magnetic measurements, (E) An et al. (2015): seismic model and (F) Martos et al. (2017): high resolution magnetic measurements.  Source:  Brice Van Liefferinge (2018) PhD Thesis.

Regarding his comparison of Antarctic heat flux models, Van Liefferinge reported:  

  • “As a result, we know that the geology determines the magnitude of the geothermal heat flux and the geology is not homogeneous underneath the Antarctic Ice Sheet:  West Antarctica and East Antarctica are significantly distinct in their crustal rock formation processes and ages.”
  • “To sum up, although all geothermal heat flux data sets agree on continent scales (with higher values under the West Antarctic ice sheet and lower values under East Antarctica), there is a lot of variability in the predicted geothermal heat flux from one data set to the next on smaller scales. A lot of work remains to be done …” 

The effects of geothermal heating are particularly noticeable at Deception Island, which is part of a collapsed and still active volcanic crater near the tip of the Antarctic Peninsula.  This high heat flow volcano is in the same major fault zone as the rapidly melting / breaking-up Larsen Ice Shelf.  The following map shows the faults and volcanoes in this region.  

Key geological features in the Larsen “C” sea ice segment area.  
Source:  James Kamis, Plate Climatology, 4 July 2017
Tourists enjoying the geothermally heated ocean water at Deception Island.  
Source: Public domain

So, if you take a cruise to Antarctica and the Cruise Director offers a “polar bear” plunge, I suggest that you wait until the ship arrives at Deception Island.  Remember, this warm water is not due to climate change.  You’re in a volcano.

For more information on Bedmap 2 and BedMachine:

  • “Antarctic Bedrock,” Visualizations by Cindy Starr,  NASA Scientific Visualization Studio, Released on June 4, 2013:  https://svs.gsfc.nasa.gov/4060
  • Morlighem, M., Rignot, E., Binder, T. et al. “Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet,” Nature Geoscience (2019) doi:10.1038/s41561-019-0510-8:  https://www.nature.com/articles/s41561-019-0510-8

More information on geothermal heating in the West Antarctic rift / fault zone:

200th Anniversary of the Discovery of Antarctica: 28 January 2020

Peter Lobner

During his second voyage in 1773, British Captain James Cook became the first to cross the Antarctic Circle, but he was turned back by heavy sea ice without ever sighting the coast of Antarctica.  It took 47 years before a Russian expedition, led by Estonian Fabien von Bellingshausen, sighted the coast of Antarctica. As the expedition leader, Bellingshausen generally is credited with the discovery of Antarctica on 28 January 1820.  Just two days later, on 30 January 1820, a British expedition to the South Shetland Islands, led by Irish Lieutenant Edward Bransfield, sighted the tip of the Antarctic Peninsula.  Bransfield is credited by some with the discovery of Antarctica.  In this post, we’ll take a look at the voyages of these three pioneering Antarctic explorers.


Map of Antarctica and the Southern Ocean showing the topography of Antarctica (as blue lines), research stations of the United States and the United Kingdom (in red text), ice-free rock areas (in brown), ice shelves (in gray) and names of the major ocean water bodies (in blue uppercase text).  Source: adapted from LIMA Project (Landsat Image Mosaic of Antarctica) via Wikipedia

Captain James Cook  – First crossing of the Antarctic Circle,  17 January 1773

Setting out on their second voyage from England in July 1772, Captain James Cook (1728-1779) and his crew, on His Majesty’s Ship Resolution, circumnavigated the globe travelling as far south as possible to determine whether there actually was a great southern continent.  The route covered during this voyage is shown in the following map.

Route of James Cook’s second voyage.  Source:  Jon Platek via Wikipedia

On 17 January 1773, Cook made the first recorded crossing of the Antarctic Circle, which he reported in his log:

“At about a quarter  past 11 o’clock we cross’d the Antarctic Circle, for at Noon we were by observation four miles and a half south of it and are undoubtedly the first and only ship that ever cross’d that line.”

Cook crossed the Antarctic Circle three times during his second voyage.  The last crossing, on 30 January 1773, was to be the most southerly penetration of Antarctic waters, reaching latitude 71°10’ S, longitude 106°54’ W.  The ship was forced back due to solid sea ice.  Cook came within about 240 km (150 mi) of the Antarctic mainland on his second voyage.

Cook’s southernmost approach to Antarctica (yellow pin, left).  Source:  Google Earth

Fabien von Bellingshausen – First sighting of Antarctica, 28 January 1820

In 1818, the Russian Empire, ruled by Czar Alexander I, organized two expeditions to study the polar regions, one for mapping the Arctic and one for sailing further south than Captain James Cook’s second voyage 45 years earlier.  The southern polar expedition was led by the prominent cartographer Fabien Gottlieb Benjamin von Bellingshausen, who was born in 1778 on Saaremaa, the largest island in today’s Republic of Estonia.  This was to became known as the Bellingshausen Expedition. 

The expedition consisted of two ships, Bellingshausen’s 985 ton flagship sloop Vostok, and the 530 ton support sloop Mirnyi, under the command of Mikhail Lazarev (Bellingshausen’s second-in-command).  An exhibit at the Estonian Maritime Museum in Tallinn reported:  “The largest proportion (a whopping 65.8 tons) of the food stock on the Bellingshausen expedition consisted of wheat and rye cookies.  In addition, they brought 28 tons of salted meat and 20.5 tons of dried peas.  In ports, the crew also acquired cereal and fresh food.”  In Antarctic waters, icebergs would supply their fresh water needs.

On 4 June 1819, the expedition departed from the Russian naval island base at Kronstadt, just off the coast from Saint Petersburg. Seven months later, the expedition crossed the Antarctic Circle on 26 January 1820.

The Bellingshausen expedition is credited with being the first to reach Antarctica on 28 January 1820, when the two ships approached to within 20 miles (32 km) of the Antarctic coast, at latitude 69°21’28” S, longitude 2°14’50” W,  in an area now known as Princess Martha Coast in East Antarctica.  Bellingshausen reported sighting an ice shelf that today is known as the Fimbul ice shelf.

Location of Bellingshausen’s first sighting of Antarctica on 28 January 1820 
(yellow pin, upper right).  Source:  Google Earth

Bellingshausen did not claim to have discovered Antarctica, but his descriptions of what he saw agree very well with what the Princess Martha Coast is now known to look like.  On the basis of this sighting and the coordinates given in his log book, Bellingshausen generally is credited (e.g., the British polar historian A. G. E. Jones) with the discovery of  the Antarctic continent.

In their subsequent circumnavigation of the Antarctic continent, Bellingshausen and Lazarev became the first explorers to see and officially discover several parts of the Antarctic landmass.   On 22 February 1820, the Vostok and Mirnyi were hit by the worst storm of the voyage and were forced to sail north, arriving in Sydney, Australia in April.  After several months exploring the South Pacific and then hearing about the sighting of Antarctica by the British (Edward Bransfield and William Smith), the Bellingshausen Expedition sailed from Sydney on 11 November 1820 to continue exploring the Antarctic. On 24 December 1820, the two ships once again were south of the Antarctic Circle.  On this part of the voyage, Bellingshausen discovered and named Peter I Island and the Alexander Coast, now known as Alexander Island, along the west coast of the Antarctic Peninsula.

The circumnavigation route followed by the Bellingshausen Expedition is shown in the following map.  Bellingshausen became only the second explorer, after Cook, to have circumnavigated Antarctica.

Route map of the Bellingshausen Expedition to Antarctica: 1819-21.
Source:  Bourrichon via Wikipedia

The Bellingshausen expedition returned to Kronstadt on 4 August 1821, ending a voyage that had lasted two years and 21 days and covered about 50,000 miles (80,467 km).  After his return, Bellingshausen was promoted to the rank of Admiral and Lazarev was promoted to the rank of Lieutenant–Captain.  His travel account was not published until ten years later.

As part of the International Geophysical Year (IGY) in the mid-1950s, the Soviet Union established its first two Antarctic bases, which were named Mirnyi (established 13 February 1956) and Vostok (established 6 December 1957), in honor of the ships in the Bellingshausen Expedition.

2003 Estonian stamp commemorating Bellingshausen’s 
discovery of Antarctica.  Source: eBay

The Bellingshausen expedition was commemorated on a 2003 Estonian stamp that features a portrait of Bellingshausen and a drawing of his flagship Vostok over a map showing the route of his Antarctic expedition.

Edward Bransfield – Sighting of Antarctica, 30 January 1820

In February 1819, British merchant ship owner William Smith, aboard his vessel The Williams, was sailing from Buenos Aires, Argentina to Valparaiso, Chile.   To catch the prevailing winds, he sailed unusually far south of Cape Horn and, on 19 February 1819, sighted previously unknown islands in the Southern Ocean.  To confirm his sighting and to chart the islands, Royal Navy officials in Valpariso chartered his ship and assigned Sailing Master Lieutenant Edward Bransfield, from Ballinacurra, Ireland (near Cork), to accompany Smith on an expedition back to the islands, which would become known as the South Shetland Islands.  During this expedition,  Bransfield landed on King George Island and took formal possession on behalf of King George III.  

On 30 January 1820, Bransfield sighted the Trinity Peninsula, which is the northernmost tip of the Antarctic Peninsula.  His sighting was made at about latitude 63°50’S and longitude 60°30’W.

Location of Bransfield’s first sighting of Antarctica (yellow pin, top center) on 30 January 1820.  Source:  Google Earth

After the initial sighting, Bransfield charted a segment of the Trinity Peninsula and followed the edge of the ice sheet in a north-easterly direction, where he discovered various points on Elephant Island and Clarence Island, which he formally claimed for the British Crown. In his log, Bransfield made a note of two “high mountains, covered with snow”, one of which subsequently was named Mount Bransfield in his honor.  The Bransfield Strait between the South Shetland Islands and the Antarctic Peninsula also was named in his honor in 1822 by Antarctic explorer James Weddell. 

Bransfield’s track in Antarctic.  Source:  Edited version by Jim Wilson, http://rememberingedwardbransfield.ie/voyage-of-discovery/

Since Bransfield’s sighting, the tip of the Antarctic Peninsula has been known variously as Trinity Land, Palmer Land, Graham Land, and Land of Louis Philippe.  Prime Head is the northernmost point of this peninsula. 

Bransfield’s expedition charts were given to the Admirality and currently are in the possession of the UK Hydrographic department in Taunton, Somerset.

In 2000, Bransfield’s historic achievement was recognized when the Royal Mail issued a stamp in his honor. Since no likeness of the man survives, the stamp depicted an image of the RRS Bransfield, a British Antarctic surveying vessel.

2000 Royal Mail commemorative stamp. 
Source: Commonwealth Stamps Opinion

To commemorate the 200th anniversary of Edward Bransfield’s sighting of Antarctica (and some say, his discovery of Antarctica), a memorial by sculptor Matt Thompson will be erected in Ballinacurra, Ireland in January 2020.

Edward Bransfield memorial, work in progress.
Source: Tony Whelan photo, Afloat.ie

Estonia’s Antarktika 200 expedition

To commemorate the 200th anniversary of the discovery of Antarctica by the Bellingshausen Expedition, the Estonian Maritime Museum and NGO Thetis Expeditions have organized a scientific expedition from Kronstadt, Russia to the Antarctic peninsula by a crew of 12 aboard the 24 meter, 95 ton, Estonian-registered sailing yacht S/Y Admiral Bellingshausen.

S/Y Admiral Bellingshausen.
Source: maritimetraffic.com

The planned route, which includes about 50 stops, and approximately follows the Bellingshausen’s route to and from the Southern Ocean, is shown in the following map.  The crew will take samples of pollen, water and microplastics while on the voyage, for researchers at Estonia’s University of Tartu.  The expedition includes food of Estonian origin to the largest possible extent, and probably a better selection of food than on Bellingshausen’s 1819 – 1821 voyage.

Antarktika 200 route map.  Source: International Maritime Rescue Federation

The ship departed Tallinn harbor on 14 July 2019, and headed for its first port of call at the historic Russian naval island base at Kronstadt, which was the starting point for the Bellingshausen Expedition.  

You can follow the current position on the S/Y Admiral Bellingham at the following link:

https://www.marinetraffic.com/en/ais/details/ships/shipid:5929279

On 3 January 2020, the ship was moored in Ushuaia, Argentina, in preparation for its voyage across the Drake Passage to Antarctica.  The ship is scheduled to reach Antarctica in time to celebrate the 200th anniversary of Bellingshausen’s discovery on 28 January 2020.

This voyage will be the subject of a TV documentary.  For more information on the Antarktika 200 expedition, visit the following website:

https://www.international-maritime-rescue.org/news/the-estonian-maritime-expedition-to-celebrate-the-discovery-of-antarctica-200-years-ago

Best wishes to the crew of S/Y Admiral Bellingshausen for a safe and successful voyage.

Composite map of early expeditions in Antarctic waters

The following map provides a good overview of the routes taken by the early Antarctic explorers, none of whom went ashore.  

Source: Antarctic Logistics

The first landings in Antarctica

An unconfirmed first landing at Hughes Bay, on the northwest coast of the Antarctic Peninsula, may have been made on 7 February 1821 by Captain John Davis and crew members from the American sealing ship Cecilia, which had been sailing in the vicinity of the South Shetland Islands in search of seals. The ship’s log recorded that men were ashore to look for seals at latitude 64°01’S.  The logbook entry concluded with the statement, “I think this Southern Land to be a Continent.”

The first substantiated landing in Antarctica was not made until 74 years later, on 24 January 1895, when seven men from the Norwegian whaling and sealing ship Antarctic, came ashore in the vicinity of Cape Adare, on the Ross Sea almost due south of New Zealand.  New Zealander Alexander Francis Henry von Tunzelmann is sometimes credited as being the first person to set foot on the Antarctic mainland.

For more information on Fabien Bellingshausen & Mikhail Lazarev

Fabien Gottlieb Von Bellingshausen (1778-1852):  https://antarctic-logistics.com/2010/08/28/fabian-gottlieb-von-bellingshausen/

Mikhail Lazarev (1788-1851):  https://antarctic-logistics.com/2010/08/28/mikhail-lazarev/

For more information on Edward Bransfield:

Remembering Edward Bransfield:  http://rememberingedwardbransfield.ie

What’s been happening in your neighborhood for the past 750 million years?

Peter Lobner

A 15 February 2019 article by Meilan Solly in the Smithsonian online magazine describes a recently released interactive map of the world that shows how the Earth’s continents have moved since 750 million years ago.   With your cursor, you can zoom in and rotate the globe in any direction. Using a pull-down menu at the top center of the screen, you can see the relative positioning of the landmasses at the point in time you selected.  A similar selection box in the upper right corner of the screen allows you to select a particular geological or evolutionary milestone (i.e., first land animals) in Earths’ development.  Even better, you can enter an address in the text box in the upper-left corner of the screen and then see how your selected location has migrated as you explore through the ages.

You can read the Smithsonian article here:

https://www.smithsonianmag.com/smart-news/map-lets-you-plug-your-address-see-how-neighborhood-has-changed-over-past-750-million-years-180971507/?utm_source=smithsoniandaily&utm_medium=email&utm_campaign=20190215-daily-responsive&spMailingID=38891027&spUserID=ODE1MzYyNTI5NjM5S0&spJobID=1461358228&spReportId=MTQ2MTM1ODIyOAS2

You can directly access the interactive globe here:

http://dinosaurpictures.org/ancient-earth#0

Following are screenshots showing what’s happened to the Lyncean Group’s meeting site in San Diego during the past 750 million years.

I hope you enjoy the interactive globe, with visualization created and maintained by Ian Webster, plate tectonic and paleogeographic maps by C.R. Scotese, and the address search tool by LocationIQ.

Current world map
20 million years ago
66 million years ago – dinosaur extinction
105 million years ago
240 million years ago – Pangea supercontinent
400 million years ago – first land animals.  Looks like the first land animals couldn’t have emerged from the sea in San Diego.
600 million years ago – Pannotia supercontinent
750 million years ago

Antediluvian Continents and Modern Sovereignty Over Continental Seabeds

Peter Lobner

Ignatius Donnelly was the author of the book, Atlantis: The Antediluvian World, which was published in 1882. I remember reading this book in 1969, and being fascinated by the concept of a lost continent hidden somewhere beneath today’s oceans. While Atlantis is yet to be found, researchers have reported finding extensive continental landmasses beneath the waters of the South Pacific and Indian Oceans. Let’s take a look at these two mostly submerged continents and how improved knowledge of their subsea geography and geology can affect the definition of sovereign maritime zones.

Zealandia

In a 2016 paper entitled, “Zealandia: Earth’s Hidden Continent,” the authors, N. Mortimer, et al., reported on finding a submerged, coherent (i.e., not a collection of continental fragments) continental landmass about the size of India, located in the South Pacific Ocean off the eastern coast of Australia and generally centered on New Zealand. The extent of Zealandia is shown in the following map.

Source: N. Mortimer, et al., “Zealandia: Earth’s Hidden Continent,” GSA Today

The authors explain:

“A 4.9 Mkm2 region of the southwest Pacific Ocean is made up of continental crust. The region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent—Zealandia. Zealandia was formerly part of (the ancient supercontinent) Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup.”

The authors claim that Zealandia is the seventh largest continental landmass, the youngest, and thinnest. While they also claim it is the “most submerged,” that claim may have been eclipsed by the discovery of another continental landmass in the Indian Ocean.

You can read the complete paper on Zealandia on the Geological Society of America (GSA) website at the following link:

http://www.geosociety.org/gsatoday/archive/27/3/pdf/GSATG321A.1.pdf

Mauritia

In the February 2013 paper, “A Precambrian microcontinent in the Indian Ocean,” authors T. Torsvik, et al., noted that an arc of volcanic islands in the western Indian Ocean, stretching from the west coast of India to the east coast of Madagascar, had been thought to be formed by the Réunion mantle plume (a hotspot in the Earth’s crust) and then distributed by tectonic plate movement over the past 65 million years. Their analysis of ancient rock zircons 660 million to 2 billion years old, found in beach sand, led them to a different conclusion. The presence of the ancient zircons was inconsistent with the geology of the more recently formed volcanic islands, and was evidence of “ancient fragments of continental lithosphere beneath Mauritius (that) were brought to the surface by plume-related lavas.”

The ages of the zircon samples were determined using U-Pb (uranium-lead) dating. This dating technique is particularly effective with zircons, which originally contain uranium and thorium, but no lead. The lead content of a present-day zircon is attributed to uranium and thorium radioactive decay that has occurred since the zircon was formed. The authors also used gravity data inversion (a technique to extract 3-D structural details from gravity survey data) to map crustal thicknesses in their areas of interest in the Indian Ocean.

The key results from this study were:

“…..Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia.”

This paper is available for purchase on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/v6/n3/full/ngeo1736.html

This ancient continent of Mauritia is better defined in the 2016 article, “Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius,” by L. Ashwai, et al.. The authors provide further evidence of this submerged continental landmass, the approximate extent of which is shown in the following map.Source: L. Ashwai, et al., Nature Communications

The authors report:

“A fragment of continental crust has been postulated to underlie the young plume-related lavas of the Indian Ocean island of Mauritius based on the recovery of Proterozoic zircons from basaltic beach sands. Here we document the first U–Pb zircon ages recovered directly from 5.7 Ma (million year old) Mauritian trachytic rocks (a type of igneous volcanic rock). We identified concordant Archaean xenocrystic zircons ranging in age between 2.5 and 3.0 Ga (billion years old) within a trachyte plug that crosscuts Older Series plume-related basalts of Mauritius. Our results demonstrate the existence of ancient continental crust beneath Mauritius; based on the entire spectrum of U–Pb ages for old Mauritian zircons, we demonstrate that this ancient crust is of central-east Madagascar affinity, which is presently located ∼700 km west of Mauritius. This makes possible a detailed reconstruction of Mauritius and other Mauritian continental fragments, which once formed part of the ancient nucleus of Madagascar and southern India.”

Starting about 85 million years ago, the authors suggest that the former contiguous continental landmass of Mauritia was “fragmented into a ribbon-like configuration because of a series of mid-ocean ridge jumps,” associated with various tectonic and volcanic events.

You can read the complete article on the Nature Communications website at the following link:

http://www.nature.com/articles/ncomms14086

Implications to the definition of maritime zones

The UN Convention on the Law of the Sea (UNCLOS) provides the basic framework whereby nations define their territorial sea, contiguous zone, and exclusive economic zone (EEZ). These maritime zones are depicted below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

UNCLOS Article 76 defines the basis whereby a nation can claim an extended territorial sea by demonstrating an “extended continental shelf,” using one of two methods: formula lines or constraint lines. These options are defined below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

You’ll find more details (than you ever wanted to know) in the paper, “A Practical Overview of Article 76 of the United Nations Convention on the Law of the Sea,” at the following link:

http://www.un.org/depts/los/nippon/unnff_programme_home/fellows_pages/fellows_papers/persand_0506_mauritius.pdf

New Zealand’s Article 76 application

New Zealand ratified UNCLOS in 1996 and undertook the Continental Shelf Project with the firm GNS Science “to identify submarine areas that are the prolongation of the New Zealand landmass”. New Zealand submitted an Article 76 application on 19 April 2006. Recommendations by the UN Commission on the Limits of the Continental Shelf (CLCS) were adopted on 22 August 2008. A UN summary of New Zealand’s application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_nzl.htm

The detailed CLCS recommendations are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/nzl06/nzl_summary_of_recommendations.pdf

Additional information in support of New Zealand’s application is available on the GNS Science website here:

https://www.gns.cri.nz/static/unclos/

Seychelles and Mauritius joint Article 76 application

The Republic of Seychelles ratified UNCLOS on 16 November 1994 and the Republic of Mauritius followed suit on 4 December 1994. On 1 December 2008, these countries jointly made an Article 76 application claiming continental shelf extensions in the region of the Mascarene Plateau. A UN summary of this joint application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_musc.htm

The CLCS recommendations were adopted on 30 March 2011, and are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/musc08/sms08_summary_recommendations.pdf

Implications for the future

The recent definitions of the mostly submerged continents of Zealandia and Mauritia greatly improve our understanding of how our planet evolved from a supercontinent in a global sea to the distributed landmasses in multiple oceans we know today.

Beyond the obvious scientific interest, improved knowledge of subsea geography and geology can give a nation the technical basis for claiming a continental shelf extension that expands their EEZ. The new data on Zealandia and Mauritia postdate the UNCLOS Article 76 applications by New Zealand, Seychelles and Mauritius, which already have been resolved. It will be interesting to see if these nations use the new research findings on Zealandia and Mauritia to file new Article 76 applications with broader claims.