By Valerie Nikolas, Jan. 14, 2019 – Glaciers in the Northern and Southern Hemispheres are rapidly retreating in sync, a trend unique to the accelerating pace of warming in which the Earth is currently caught. Researchers such as University of Maine geologist Noel Potter, who studies glacial retreat in New Zealand, observe this trend with increasing frequency.
Unlikely partnerships in drones and cosmic rays are helping to uncover insights unique to New Zealand’s Southern Alps. Using drone technology, PhotoScan software and isotope dating, Potter and his team mapped changes in the Hooker Glacier, located on the flank of Mount Cook, New Zealand’s highest mountain. His results show unprecedented levels of recession in the Hooker Glacier now compared to the last 1,500 years.
“The Southern Alps are really falling apart,” Potter said during his presentation at the fourteenth annual Comer Climate Conference held in October in southwest Wisconsin. “Collapse is immense. And the ice likely has not been as far back as it is today since these moraines were deposited.”
Researchers often refer to glaciers as the Earth’s “thermometers.” Because they are more sensitive to changes in temperature than other landforms, they can give a more accurate indication of regional climate variations.
Potter and his team flew a DJI Phantom 4 drone above the Hooker Glacier, where it took thousands of aerial videos and photographs. They then stitched the photos together in Agisoft Photoscan software to make an “orthomosaic,” a highly detailed, 3-dimensional model of the landscape. Potter says the team’s orthomosaics are so detailed they can pick out individual boulders in the landscape.
The team used the orthomosaics to determine particular boulders to study, extracted pieces of quartz from those boulders and then used isotope dating to determine when and where ice was present at each site. Beryllium-10 is an isotope that gives scientists a glimpse into the past. The isotope is created as cosmic rays hurling through the solar system strike rock.
If you’ve ever peered out at a mountainous landscape, you’ve probably noticed long, narrow ridges in the side of the mountains. These ridges that form from sediment deposits on the sides of glaciers are called moraines, and glacial geologists like Potter study their rough edges to determine where a glacier’s ice reached and retreated at certain points in time.
“We use cosmogenic dates from boulders collected on these moraines to tell us when the glacier occupied the position marked by those moraines,” Potter said.
When a glacier retreats from a moraine, the isotope beryllium-10 collects at predictable levels once it shakes free of ice. Determining when the glacier freed the rock is called “cosmogenic dating” and it tells scientists how old particular moraines are. The term relates to the clock created as cosmic rays strike the rock and react with quartz to generate beryllium-10.
Potter and his colleagues collected data from 11 moraines just east of the main divide of the Southern Alps.
The outermost, oldest left moraine was deposited roughly 1,500 years ago—around 497 A.D. The next oldest moraine studied was deposited around 1,100 years ago in 1066 A.D.
“We had moraines forming here in New Zealand when glaciers in the Alps of Europe were retreating,” Potter said. These New Zealand moraines were deposited well within the range of what is referred to as the Medieval Climate Optimum, the warm period in Europe which took place between 750 and 1250 A.D. This shows that more snow was accumulating in the Southern Alps during this time, meaning the Northern and Southern Hemispheres were not experiencing the same temperature fluctuations–the Southern Alps retreated later.
The terminal moraines are the most recent and were deposited as the ice began to retreat from what was once its point of furthest advance. These moraines were deposited between approximately 700 and 250 years ago, sometime between the years 1321 and 1787 A.D. These moraines were deposited during the time of the Little Ice Age, a cold snap in Europe that lasted roughly from 1250 to 1850 A.D.
Potter’s colleague Peter Strand explained that glaciers are high energy systems. Despite fluctuations in temperature, glaciers try to maintain a constant equilibrium between the area above the snow line and the area below, called the ablation area. The ablation area and the accumulation area must maintain a constant ratio, thus causing advances in colder temperatures and retreats in warmer conditions.
The Hooker Glacier in particular features a long ablation area, which is the only area where moraines form. This makes it an ideal area for studying the fluctuations in temperature during certain time periods.
“There’s so much moisture being added in the top and so much being lost through ablation at the bottom that the turnover time for ice going through these systems is quick, which makes them more responsive to changes in climate,” Potter explained.
The differences in the landscape are so dramatic, they can even be observed by the naked eye through comparing photographs of today with those of the early twentieth century.
Potter’s team also found that the Hooker Lake, located at the foot of the Hooker Glacier, did not begin to form until between 1965 and 1976.
“Retreat from the terminal position has really accelerated since the lake began to form,” said Potter. “When a glacier like the Hooker is rocketing back to that lake it is just catching up quickly to a climate signal that has been imposed upon it for a while before.”
The changes in glacial position and appearance of a lake highlight the delicate balance between warming and cooling in the Earth’s “thermometers.”
“To counteract one Fahrenheit degree of warming [in this area], precipitation would have to increase 50 to 80 percent,” said Aaron Putman, a colleague of Potter’s at University of Maine.
The Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report, released in 2007, was one of the first major publications to shed light on the temperature differences in the Northern and Southern Hemispheres during the Little Ice Age.
Potter’s finding that the climate of New Zealand was independent of temperature fluctuations seen throughout Europe during the same time adds to a growing body of evidence that supports the IPCC’s report and confirms the paradigm shift about this time in the planet’s history.
“My research shows pretty clearly that natural variations in climate have regional, not global, effects in geologically recent times,” Potter said. “Only since the Industrial Revolution have we seen climate doing the same thing all around the world. The  IPCC is warning about the consequences of the same warming we see in the glaciers when it starts to affect other systems with more chance to do harm to people.”
Photo at top: An aerial photograph of Mount Cook and the Hooker Glacier. (Drone footage from glaciologist Noel Potter’s DJI Phantom 4)