Going Deep

Pressure Drop completed an ambitious and scientifically valuable expedition

The primary objective of this expedition was to precisely locate, measure and map the deepest points in each of the world’s five oceans. Dubbed the “Five Deeps Expedition” (FDE), the voyage spanned 10 months and travelled 47,000 nautical miles to execute 39 manned-submersible dives in some of the planet’s most remote and logistically challenging deep-sea locations. Not only did the expedition complete its primary aim, it mapped 550,000sq km of seafloor, discovered more than 40 new species of marine animals, and collected over 400,000 biological, geological and water samples for analysis by scientists.  

The Expeditioners

Through his company, Caladan Oceanic LLC, Vescovo mounted the FDE in partnership with several key stakeholders: Florida-based civil submarine manufacturer Triton Submarines LLC, which designed and built the submersible used in the dives; scientists from the UK’s Newcastle University and the British Geological Survey; the International Hydrographic Organisation and the Nippon Foundation, which provided sonar mapping experts and bathymetric data processing.

The Deep Submergence Support Vessel (DSSV) Pressure Drop

DSSV Pressure Drop

DSSV Pressure Drop was constructed in 1985 by the Tacoma Boatbuilding Company in Tacoma, Washington (USA) as an ocean surveillance ship for the United States Navy. As USNS Indominable, she collected underwater acoustic data in support of Cold War anti-submarine warfare operations and was later deployed on counter-narcotics patrol in the Caribbean Sea and Panama Canal area. 

In 2002, Indomitable was transferred to the National Oceanic and Atmospheric Administration (NOAA), renamed McArthur II and refitted as a dedicated oceanographic research ship, operating throughout the eastern Pacific Ocean until she was retired by the NOAA in 2014.  

In 2017, the vessel was acquired by Caladan Oceanic and renamed Pressure Drop before undergoing a comprehensive refit to serve as the mother ship for the manned deep submergence vessel (DSV) Limiting Factor and the platform for the expedition’s onboard scientific and research projects. Powered by four CAT 850hp diesel electric engines, the 68m ship has a range of more than 15,000nm at a cruising speed of 9kt. 

Pressure Drop also carries three ‘landers’ to support the submersible and carry out additional scientific tasks. The landers are fitted with cameras to record large mobile fauna, traps to recover smaller creatures, push corers to take geological samples and an array of instruments to record hydrographic conditions in the water column.

For hydrographic surveying, the vessel is fitted with a state-of-the-art Kongsberg multibeam echosounder system (MBES), carried in a gondola mounted on the ship's hull behind the bow. Designed to produce high-definition data to full-ocean depth (11,000m), the MBES played a key role in 3D-mapping of the seafloor and in determining with great accuracy the true depths of the Five Deeps. 

Pressure Drop operating in Arctic waters

DSV Limiting Factor

DSV Limiting Factor  was designed and built by Triton Submarines specifically for the FDE as its two-person deep-sea exploration vehicle. As the world’s first fully reusable, commercially-rated, full-ocean depth manned submersible, Limiting Factor  represents a “quantum leap” in deep-sea technology and is one of the most uniquely capable vessels of its kind in seafaring history.

Its defining feature is the hollow 90mm titanium alloy hull filled with a “syntactic foam” of glass beads, which provides a durable, lightweight structure capable of withstanding enormous pressure without significant deformation or stress fractures from repeated use. As Limiting Factor’s movements are primarily vertical, its spherical hull has been precision-engineered to enable high-speed descents and ascents, thereby shortening operational time.

The capsule has space for a pilot and passenger, with three viewports of acrylic-based lenses that provide occupants with a clear view downward and forward. Pilot “situational awareness” is enhanced by high-definition video cameras mounted around the hull to augment the eyes-on view and high-output LEDs to provide illumination at depth. Electrical power is provided by a 12 battery system which enables an operational time of more than 16 hours.

Limiting Factor is the only submersible ever to be certified to go to full ocean depth

The Five Deeps

According to the International   Hydrographic Organisation’s (IHO) guidelines for naming undersea features, ‘deeps’ are defined as “a localised depression within the confines of a larger feature, such as a trough, basin or trench”. A ‘deep’ may also refer to the deepest point of such features. 

Using a combination of MBES bathymetry and direct pressure measurements by the submersible, the FDE successfully located and determined the following as the deepest points in each of the five oceans: the Brownson Deep in the Puerto Rico Trench (Atlantic Ocean, 8,376m / 27,480ft), an unnamed deep (provisionally dubbed the Factorian Deep) in the South Sandwich Trench (Southern Ocean, 7,434m / 24,390ft); an unnamed deep in the Java Trench (Indian Ocean, 7,192m / 23,596ft); Challenger Deep in the Mariana Trench (Pacific Ocean, 10,925m / 35,843ft); and the Molloy Hole in the Fram Strait (Arctic Ocean, 5,550m / 18,210ft).

When considering these measurements, bear in mind that Mount Everest, the highest point on the planet, is 8,849m (29,032ft), although it seems to be growing about half a metre per century.

This map shows the global scale of the expedition

Brownson Deep, Atlantic Ocean 

The FDE began in December 2018 with a mission to the Puerto Rico Trench, an 800km subduction zone parallel to the north coast of Puerto Rico. The trench lies at the boundary between the Caribbean Plate and the North American Plate, both of which are moving in a complex transition that produces considerable seismic activity, including earthquakes greater than 8.0 magnitude.

For several days Pressure Drop surveyed the flat-bottomed basin of the trench to pinpoint the most likely dive site, within an area known as the Brownson Deep - also known as the Milwaukee Deep after the US Coast Guard vessel that first mapped the entire trench. The deep was previously explored by the French submersible Archimede in 1964 and then by a robotic vehicle in 2012, neither of which had reached its deepest point.

During a six-hour solo dive on 19 December, Vescovo piloted Limiting Factor to the bottom of the Brownson Deep at 8,376m (27,480ft). This was the first manned descent to the deepest part of the Atlantic Ocean and the second-deepest solo submersible dive in history, second only to James Cameron’s dive to the Challenger Deep in 2012. The operation also made Limiting Factor the deepest diving operational submersible up to that time, surpassing the previous record (7,062m) of the Chinese submersible Jiaolong.

Factorian Deep, Southern Ocean

For its second mission, the FDE sailed to the South Sandwich Trench in the sub-Antarctic latitudes of the Southern Ocean. This loomed as the expedition’s most difficult assignment of all, with the remote location, near-zero surface temperatures, unpredictable seas and narrow operational window posing many logistical and technical challenges - added to which the dive would take the submersible into the only sub-zero hadal zone (deeper than 6,000m) on Earth.

The  965km South Sandwich Trench extends in an arc spanning the boundary between the Southern and South Atlantic Oceans at the 60 degree south latitude. The trench is formed by the subduction of the South American Plate beneath the South Sandwich Plate at a rate of almost 80mm a year. This rapid tectonic slide has generated significant volcanic activity, having created the South Sandwich Islands 100km to the east and maintaining Mount Belinda as an active volcano on Montagu Island.

For several days in early February 2019, Pressure Down carried out multibeam sonar mapping over more than 15,000sq km along the trench to determine the exact location of its deepest point. This was confirmed as the Meteor Deep (8,266m / 27,119ft), named after the German survey ship that discovered it in 1926, but as this feature lies at 55 degrees south latitude it is technically in the Atlantic Ocean. 

The trench’s deepest point below the 60th parallel, within the Southern Ocean, was found to be an unnamed depression at a depth of 7,434m (24,390ft). It was here, on 4 February, that Vescovo piloted Limiting Factor, reaching the seafloor in just 2.7 hours in what was hailed as “a remarkable achievement in the world of polar exploration”. Vescovo has proposed that this deepest point in the Southern Ocean be named the "Factorian Deep", in honour of the expedition’s record-breaking submersible.

There is a surprising amount of life in the darkness of the Mariana Trench

Java Trench, Indian Ocean

Several tasks confronted the FDE in the Indian Ocean: to identify which of two locations within the Java Trench was the deeper; and to settle the debate about which of the Java Trench or the Dordrecht Deep in the Diamantina Fracture Zone (DFZ) was the deepest point in this ocean. 

The Pressure Down sailed first to the Dordrecht Deep in the Diamantina Trench, 1,125km southwest of Perth. The Dordrecht was a vessel of the Dutch East India Company which explored the Australian west coast in 1619. The trench and larger DFZ are named after HMAS Diamantina which conducted bathymetry and scientific survey here in 1961.

During March 2019, the FDE carried out detailed sonar mapping of more than 5,800sq km of the Dordrecht Deep seafloor and, correlating this data with direct measurement by an ultra-deep-sea lander, determined a maximum depth of 7,019m (23,028ft) for the deep. The FDE then sailed north to explore the Java Trench.

The Java Trench (also known as the Sunda Trench) stretches more than 3,200km from the Lesser Sunda Islands, past the south coasts of Java and Sumatra to the Andaman Islands. It is formed by the Indo-Australian Plate subducting beneath the Eurasian (Sunda) Plate.

Surveys in April/May 2019 acquired nearly 40,000km of bathymetric data and revealed that the trench was deepest in its central part - not in the east as was previously thought to be the case - and that became the designated dive area. Here, on 16 April, Vescovo made his third successful solo dive in Limiting Factor to confirm that the deepest point in the Indian Ocean was in the Java Trench at 7,192m (23,596ft). A second dive was piloted by Patrick Lahey, president of Triton Submarines, accompanied by Dr Alan Jamieson, the FDE’s chief scientist. At the bottom of the trench, video footage was captured of many marine organisms believed to be species entirely new to science.

Challenger Deep, Pacific Ocean

Challenger Deep in the Mariana Trench is indisputably the deepest point on planet Earth. To put this into perspective, if Mount Everest were placed into Challenger Deep, its peak would still be submerged by more than two kilometres. The FDE’s mission here was to refine its exact location and depth.

The Mariana Trench lies east of the Mariana Islands, which lend their name to it, and is 300km southeast of Guam. It extends 2,550km in an arc along the seafloor where the Pacific Plate subducts beneath the Philippine Plate. The Challenger Deep is a small slot-shaped valley at the southern end of the trench, consisting of three basins, each over 10,850m (35,597ft) deep. It is named after the British survey ship HMS Challenger, whose expedition of 1872–1876 first attempted to sound its depth (using a weighted rope).

Before FDE’s mission here in April/May 2019, there had only been two manned-submersible explorations of the deep: by Don Walsh and Jacques Piccard’s bathyscaphe Trieste in 1960 (10,912m); and James Cameron’s Deepsea Challenger in 2012 (10,908m) - both of which only descended once. The FDE successfully completed not one, but four, manned dives to the bottom of Challenger Deep, and a fifth in the Sirena Deep 200km to the northeast. Vescovo piloted Limiting Factor on four occasions (twice solo), becoming the first person to dive into Challenger Deep more than once. Don Walsh, on board the Pressure Drop during the mission, described these historic achievements as “an impressive tour de force”.

Direct pressure measurements by sensors on the submersible and survey by the Kongsberg MBES enabled the maximum depth of Challenger Deep to be determined as 10,928m. However, following a subsequent review of the bathymetric data and sensor recordings this was revised to 10,925m (35,843ft). (At this depth, the water column exerts a pressure of 15,750psi, more than 1,000 times the standard atmospheric pressure at sea level.)

An historical footnote to this remarkable operation concerns the retrieval of one of the unmanned landers used during the second dive on 1 May. Due to a technical problem, the lander became stuck on the bottom for two days before it was freed and recovered using Limiting Factor - making it the deepest marine salvage operation ever attempted.

Before leaving the Pacific, the FDE conducted further operations on Horizon Deep in the Tonga Trench, part of a subduction zone stretching 2,550km between New Zealand’s North Island and Tonga. Detailed sonar mapping was conducted over 13,100sq km of ocean floor and, on 10 June, Vescovo piloted Limiting Factor to the bottom of the deep, confirming it as the deepest point in the Southern Hemisphere (at 10,823m / 35,509ft) and the second deepest on the planet.

Retrieving Limiting Factor after a deep dive

Molloy Deep, Arctic Ocean

In August 2019, the FDE reached the near-freezing waters of the Arctic Ocean for its final mission: to survey and refine the exact location and depth of the Molloy Deep, in the Fram Strait, 275km west of Svalbard, Norway. Also known as the Molloy Hole, the deep is a broadly circular, topographically featureless depression of the seafloor, overlying the point where the Eurasian and North American tectonic plates are separating.

It was discovered in 1972 by the USNS Hayes, the first of a new class of catamaran-hulled oceanographic research vessels, and named after Arthur E Molloy, a US Navy research scientist who worked in the North Atlantic and Arctic Oceans in the 1950s-1970s.

Cruising at about 80 degree north latitude, just 70km from the edge of the pack ice, Pressure Down collected 1,850sq km of bathymetric data over the Hole and identified the precise dive site for the submersible. On 24 August, with external sea temperatures dropping to -2 degrees Celsius, Vescovo piloted Limiting Factor to the bottom of the Arctic Ocean, measured as 5,550m (18,210ft), becoming the first person to dive to the deepest point of all five of the world’s oceans.