Diving under the frozen surface of a lake in the middle of Antarctica's dry valleys is like "flying through a cathedral". That is according to Tyler Mackey, a PhD student from the University of California.
He has spent December studying Lake Vanda's microbial communities for an international project, led by Canterbury University scientists and supported by Antarctica New Zealand.
His unusual subject means he has needed to master the rare skill of diving under ice-covered lakes to gather samples of bacteria.
On diving days, he and a fellow scientist don warm gear under a dry suit and a 90-metre tether for safety before slipping under the 3m to 4m-thick ice via a dive hole, which a heater keeps open.
Swimming below ice is far from terrifying, Mr Mackey says.
"When we're diving down there through the clear water with this glassy ceiling above us, it really is like flying through a cathedral because you're weightless and in your dry suit, just floating through crystal clear water with diffuse light coming in from everywhere. This sort of pale blue light sort of permeates everything."
The lake is about 77m deep but Mr Mackey's dives are limited to about 28m so the lake's shallower edges are the main target for collecting samples.
There are no animals or plants in the water, unlike lakes elsewhere in the world. Instead, the floor is covered with a thick carpet of bacteria, which is completely undisturbed.
During dives, samples of the carpet are carefully cut out using a spatula "like a piece of lasagne" and put into a container or a tube.
Mr Mackey's research examines climate impact on the bacteria, which grow a few millimetres annually and depend on light levels penetrating the water.
New Zealand has been involved with studies in the area since about 1970, when monitoring began on the Onx River, which flows into Lake Vanda and is Antarctica's longest river.
Since the 1960s, the lake's level has risen more than 10m due to climate change and that affects the amount of light reaching its bed.
The river is having more frequent high-flow years and the Lower Wright Glacier, which also feeds the lake, is generating more melt water as Antarctic temperatures rise. The lake has no outlet.
Mr Mackey is deeply passionate about his climate change studies and his work environment. While the lake's bacteria forest is not a typical "charismatic rainforest", he says it is as diverse and interesting.
"You're really swimming through the forest of these bacteria.
"It just happens to be on a much smaller scale than we think of ecosystems that we see around us. It's also a much more temperate environment.
"It's a very other-worldly experience and rather transcendent just being in a system so far outside of yourself and so apart from daily experience."