In work never done before, scientists are extracting mud from the depths of Doubtful Sound to gain a deeper understanding of how effective fjords are at absorbing carbon.
But in a twist of irony, they've discovered human efforts to create renewable energy might be undoing the fjords' natural carbon storage.
Breathtakingly beautiful and vitally important in reversing the effects of climate change, New Zealand's fjords bury around 20 percent of the country's annual emissions.
"All of that soil and all of the vegetation that falls into them sinks, so a lot of that carbon is buried and stored for thousands of years," said Jacob Anderson, Blake Expeditions director.
Blake Expeditions took a group of teens to Doubtful Sound to help with an $8.6 million Otago Uni research project - mapping the sea floor to understand how carbon is buried and why fjords must be protected.
"I mean it is the biggest challenge for our generation but it's going to be an even bigger challenge for the next generation, right," said GNS chief scientist Professor Gary Wilson.
Deeper sediment samples show how the fjords have absorbed carbon over time while the shallower mud and water samples show how the flushing of freshwater can prevent the fjord from soaking up carbon.
"You see that hazy shimmer that exists right at the boundary between the fresh water at the very top of the water column and the salty water below," said geologist Professor Chris Moy.
That mixing might be hampering our 2050 carbon-neutral goal.
The Manapōuri Power Station flushes fresh water through a 10km tunnel into Doubtful Sound and scientists say that oxygenation could be disturbing the natural burial of carbon.
"Yes we're emitting carbon dioxide but we're also preventing the natural sequestration of carbon dioxide," said Prof Wilson.
Opposition to the Manapōuri Power Station sparked Aotearoa's green activist movement. Now 50 years on, the dam is key to meeting the country's 100 percent renewable energy ambitions, but it also might be threatening one of our best natural weapons in the climate change arsenal.
The depths are hiding huge implications for New Zealand's hydroelectric power generation.
