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J2 Cave Expedition and the Birth of the Poseidon MkVI Rebreather



J2 Cave Expedition and the Birth of the Poseidon MkVI Rebreather 


By Jonas Brandt



Background - History of the J2 Cave Expeditions


In February and March 2013 the J2 Cave Expedition Crew teamed up with Poseidon Diving Systems, who provided MkVI Rebreathers to give the team the "extra edge" they needed to push through the boundaries met by previous explorers. This expedition was so groundbreaking, Discovery Channel had their crew on site to film a documentary about it which will air in the Fall of 2013.  


J2 is located high in the remote cloud forest of Ocotal, 5 kilometers northeast of Cheve. To back track a bit, J2 was discovered because of two initial explorations in 1987 and 2003 where Cueva Cheve, located at high elevation in the Sierra Juárez of northeastern Oaxaca, México, was explored by 2 teams of cave explorers who ultimately, in 2003, were able to explore a total of 9.3 kilometers into the cave. Cueva Cheve is 1,484 meters deep and is the deepest known cave in the Western Hemisphere as well as the world's 11th deepest. Needless to say it is one of the most remote locations ever attained inside any cave on Earth. The exploration in 2003 was ultimately halted by an ancient tunnel collapse that blocked the route forward. (


J2According to the U.S. Deep Caving Team (, in 2004 an international expedition led by the led by the USDCT discovered a new cave named J2 which was determined to be incredibly deep and headed in the direction of Cueva Cheve. In addition, there was a predicted intersection beyond the location of the collapse in the 2003 expedition, giving the team an opportunity to connect into Cueva Cheve from J2 and explore further into the cavern. During the course of four major expeditions in 2004, 2005, 2006, and 2009 J2 was explored to a distance of 11.5 kilometers from the nearest entrance at a depth of -1,222 meters. To get there the team explored four underwater tunnels. Based from Camp 4, a final 19-day underground push in 2009 reached a point 300 meters into Sump 4 where the team ran out of safety guideline with the tunnel surfacing. The 3D computer map of the mountain predicted that the tunnel would surface to air soon and then descend more than 800 meters vertically to cross under Star Gorge on its long way to the Mano Resurgence. Getting there would require pushing the envelope. To do this 11 members of the over-100 person international 2013 J2 team used a custom-designed, long-range variant of the Poseidon MkVI rebreather.  The briefcase-sized system was small enough to be transported to Sump 4 where the main push began in March of 2013. 


How Poseidon Became Involved in J2 and Developed the MkVI Rebreather

To explain Poseidon's involvement in the J2 expedition we have go back to the early days of the CisLunar Mk6 project which eventually became the Poseidon MkVI.


Dr. Bill Stone, myself (Jonas Brandt), Kurt Sjöblom, Rich Pyle, Nigel Jones, Barry Coleman, Hempa Henriksson and Paul Heinerth met in early 2006 in New Port Richey, Florida for one of the first project meetings bound to create the Cis Lunar mk6 around a variety of radical and revolutionary design ideas. The group gathered in a small conference room in a motel for three days to discuss the next generation of rebreathers. Some of the discussions that took place during these days I would still classify as revolutionary and up until today would be quite controversial within the rebreather community.


It may sound weird at this stage to say, but back then I did not realize that Dr. Bill Stone had his mind set to develop not only the first true recreational rebreather but also to develop a new tool, to break the frontiers in cave diving. Dr. Stone knew very well that a fully automated, lightweight rebreather would be the key factor to penetrate the deepest known caves in the world. With the much bigger and heavier rebreather CisLunar mk5 the J2 expedition would have been more or less impossible due to its size and weight.


Perfecting the Poseidon MkVI for J2 2009

Poseidon Gear for J2 ExplorationSince the birth of the MkVI, Dr. Stone's cave diving team has been very important for the development of the MkVI. Tests started in early 2008 in Lake Travis on pre-production units prior to the 2009 J2 expedition. Apart from Bill Stone, people like Jose Morales, Yuri Schwartz, James C. Brown and Marcin Gala spent hours and hours on the MkVI prior to the expedition, providing valuable feedback to the development team about what could be enhanced. In total, Poseidon provided quite a remarkable amount of equipment to the first J2 expedition. Eight (8) MkVI rigs four (4) of these were pre-production models and four (4) were from one of the early production lots.  Apart from rebreather’s Poseidon also provided dry suits, gloves, hoods, regulators, harnesses with BCD’s, tank valves and of course also regulators.


One pre-production unit remained in New Jersey for team training after the start of the expedition on March 5, 2009 since not all team members arrived on the mountain at the beginning.  Seven units were transported to base camp and were assembled and tested there.  Of those, three units were subsequently designated for transport to Sump 2 at the -1,200 meter level of the cave.  All MkVI’s arrived at J2 base camp without any damage. For a full Photo Summary of the J2 Expedition, click here. 


At DEMA 2009 Jose Morales held a lecture about the expedition in front of a stunned audience, it is up until today one of the most thrilling presentations I have ever witnessed.


The Route Towards J2 2013

I have known for a long time that the cave diving team was to go back into the J2 to explore the deepest parts of the cave. To prepare ourselves for that and for the release to the sport diver market, the MkVI development team spent a significant amount of hours going through the performance of the MkVI after the first J2 expedition. It boiled down to a list of at least 20 action points hardware wise and quite a significant list of firmware improvements. One of the key experiences was that handling 420 bar tanks is not an easy task for the 1st stages. For the J2 2013 expedition, Poseidon provided special diluent Cyklon 1st stages, tuned to handle the cylinder pressures in the composite tanks of 420 bar. Those were used both on the rebreathers and the stage cylinders together with Xstream durations.


To prepare the diving team for the second push into the J2 cave set for March 2013, Poseidon sent in their software manager Thomas Oskarsson to the J2 equipment configuration exercise in High Springs, Florida from February 18 to February 26, 2012. The main purpose of Thomas being on site was to learn more about their specific demands and adapt various parts of the equipment. The report I got when the engineer came back to Sweden was not in line with what I expected. He reported “those guys are crazy, the first thing they do is to rip all the equipment apart in microns and then rebuild it in a completely different way." These reconfigurations boiled down to a rather sophisticated harness and BCD configuration; the One Wing harness was put together with the One Wing BCD mounted upside down for perfect leveling, low drag, and effortless swimming. Having Thomas, an electronics developer, on site made it possible to test different MkVI configurations and in real time through a “livelink” measure the O2/diluent consumption with various setups.


Later in 2012 one of the lead divers from the 2009 J2 expedition, Marcin Gala, came to the Poseidon HQ in Gothenburg Sweden to get the latest service training from our Service Manger Jörgen Nilsson. Once certified for service training, Marcin and myself took the equipment into our pool for some exercises and to test the latest developments. During 2012 and 2013 another lead diver from the cave diving team, Yuri Schwarts, came to Posidon Gothenburg to train in the Poseidon facilities.


For the J2 2013 expedition Poseidon provided not only MkVI’s and spares, Poseidon provided items like; 1st stages, tank valves, gauges, multitools, QMR’s, fittings and 2nd stages, all of which were essential for mission success.


During the 70 day exploration the team spent 45 days in the cave, totaling "1000 hours under the earth." 


For more detailed information about this expedition and personal blogs about the experience, visit these links: