LOCATED AT a staggering altitude of 5,100 metres, Lake Puma Yumco (普莫雍错) would most certainly deter the amateur and the faint-hearted – but not a group of exploratory divers set out to conduct wildlife investigations in one of Earth’s most challenging freshwater environments.
According to the Professional Association of Diving Instructors (PADI), any time you scuba dive at an altitude higher than 300 metres above sea level, you’re altitude diving. Wu Lixin, one extraordinary tek diver and underwater photographer – together with his team – decided to take on Puma Yumco in February 2014, a wintry season when streams of water from the surrounding snow-capped mountains feed the freezing lake.
To date, there are no reference materials available for diving at an altitude beyond 3,000 metres. This historic photography project, commissioned by China Central Television (commonly known as CCTV), was targeted at documenting life beneath the surface of the Tibetan Plateau’s waters – a long-held East Asian mystery.
As they journeyed to the dive site, burdened by the weight of their equipment, Wu and his contemporaries were not spared the unforgiving effects of the extreme elevation. The lack of oxygen brought about impaired body movement and lethargy the team had never felt before while preparing to dive. In hindsight, Wu deems such debilitating environmental effects “unprecedented” – even for highly experienced dive “warriors”. At these altitudes, the actual maximum depth of 11 metres translated to a theoretical depth of 20 metres, demanding stepped-up planning, safety measures and adjustments made to their dive.
At the height of winter, the picturesque Puma Yumco, devoid of an outlet, develops intricate ice block patterns, caused by repeated cycles of freezing, fracturing and refreezing of the ice due to temperature variations as well as wind-induced ice motion. The name of this obscure geographical feature, 普莫雍错 (pronounced “pu-mo yong-cuo”), translates as “blue jewel that floats in the sky” – an apt description given that the lake inclines towards a blue to blue-green colour. This is due to the water’s ultra-oligotrophic nature – meaning that nutrient concentrations in both the water column and lake sediments are extremely low.
As February rolled around, the lake’s icy covering gave way to a water temperature of 2°C, guiding Wu’s choices of equipment: a DUI TLS350 drysuit, a 12-litre single cylinder tank with a Y-valve, a Halcyon Eclipse BC system (for single-tank diving) fitted with a stainless steel backplate, and two Apeks XTX200 regulators, ideal for cold-water diving (one intended as a back-up). Upon descending, the team was immediately accosted by several difficulties, the most impacting being drastic variations in buoyancy, typical at an altitude beyond 3,000 metres. This caused the divers to battle the risk of a sudden ascension due to loss of buoyancy control.
Contrary to common expectations, the environmental limitations prevented Wu from conducting any decompression stops at all. The key procedure aimed at minimising unforeseen contingencies was simply reducing bottom time. The team also stuck to a conservative ascension rate of three metres per minute, instead of the usual nine metres per minute.
For the rest of this article and other stories from this issue, see Asian Diver 2014 Issue 5, Volume 135