What is happening with the Arctic Sea Ice?
If you think seawater should taste pretty much the same everywhere around the world, think again. In the Arctic, the salt content of the surface seawater has always been below the global range of 3.1 to 3.8 percent, and it’s becoming even less salty in recent years.
Experts point to the increasing amount of water flowing into the Arctic Ocean from the surrounding rivers as the culprit of the reduced salinity. The diluted seawater doesn't freeze the way saltier seawater does. That sparks a chain of events that can exacerbate global warming.
From salinity to chemical balance, all data related to the Arctic water cycle provides clues for understanding the intricate workings of the Arctic and global climate systems.
Now, we would like to invite you to take a closer look at what’s happening with the Arctic sea ice and how that helps fuel the climate change with the help of our expert.
Ask an Expert: Associate Prof. Kazutaka Tateyama (Kitami Institute of Technology)
Dr. Tateyama is one of the few scientists in the world conducting research on the changes of sea ice volume in the Arctic and Antarctic oceans and the Sea of Okhotsk. He is working to develop a system that pulls satellite observation data to estimate the thickness of sea ice, which is currently impossible to do without getting hands on the ice. While monitoring climate changes related to sea ice, Dr. Tateyama helps lead research projects on Arctic and Antarctic developments, including sea route and coastal oilfield developments in the Arctic Ocean. He participates in the GRENE Arctic Climate Change Research Project and the Arctic Challenge for Sustainability (ArCS).
Distinguishing Between Sea Ice and Iceberg
In the Arctic, ice comes in all shapes and forms. Sea ice refers to frozen seawater with thickness ranging from a few meters to 10 meters. An iceberg, on the other hand, is compressed snow layers that forms on a glacier or an ice shelf and breaks away from it after repeatedly washed by tides. It floats into the ocean like the one that crashed into and destroyed the Titanic. Icebergs are particularly abundant in Central Greenland where ice mountains of various sizes continuously break away from the shorelines that look up to 500- to 1,000-meter-high ice sheets.
“You listen to the sounds of the vessel hitting and crushing the ice below while moving through the Arctic Ocean, and you know how old the ice is,” says Dr. Kazutaka Tateyama, associate professor at Kitami Institute of Technology. “New ice under a year old sounds like shaved ice. Ice that’s gone through two or more summers makes thumping noises or squeaks like pieces of Styrofoam rubbing against each other.”
Sea ice and icebergs look alike from the above because they are both covered in snow.
“You need to look at the cross-section of ice. Newly formed ice looks greyish and you can see seawater through it. One- to two-year-old ice has blueish tones to it, and it turns greener as it ages.”
Dr. Tateyama studies Arctic sea ice with a focus on ice volume changes. He says local animals often approach the research crew during the fieldwork. They include polar bear, which use sea ice as a foothold to hunt seals. For polar bear, sea ice plays a crucial role in their survival, Dr. Tateyama says.
“Some years, I run into polar bear every day. Some other years, little sea ice would be left, and bear don’t come, either,” he says.
Heavy Brine Makes Seawater to Circulate Around the World
The lower the salt content of water is, the faster it freezes. When new sea ice begins to form, a matrix of freshwater ice crystals develops. These ice crystals contain pockets of high salinity sea water known as brine cells in them. The freezing temperature in the Arctic is minus 2 degrees Celsius (28.4 degrees Fahrenheit). This means brine hardly ever freezes and only grows more concentrated and heavier, sinking towards the bottom of the ocean to become part of the “global ocean conveyor belt” -- deep seawater that circulates around the globe. Temperature and salinity along with energy from the wind received by the surface seawater drive this down-reaching current southward across the Atlantic Ocean and then eastward to the Pacific Ocean past the north of the Antarctic. Deep seawater then moves up and down the Pacific and returns to the Atlantic Ocean. The round-the-world journey of deep seawater takes about 1,000 years to complete.
The deep ocean circulation shows how heat transfer and salinity balance of snow and ice in the Arctic contribute to climate events a halfway around the world.
“Over the past two to three decades, which is a short term when you are discussing climate, we have been seeing more and more thin ice and less aged ice in the Arctic. This is a direct result of global warming,” Dr. Tateyama says. “Thin ice quickly melts in summer heat, leaving a larger section of ocean surface directly exposed to the atmosphere. This causes more seawater to evaporate, triggering heavier and more frequent rain and snow. The salinity of the Arctic surface seawater is declining as the volume of water streaming into the ocean is increasing. This may cause the Arctic to regain some of the lost sea ice area because lower salt content helps water to freeze. Sea ice extent may also grow if a lot of snow falls on the ocean and freezes.
Such seemingly “cooling” phenomena may not last too long, however, as they are symptoms of global warming. The Syowa Station in Antarctica observed the fast ice at record thickness recently, and this can also be explained by global warming.
Decoding the Arctic Climate Through On-site Verification of Aerial Monitoring Data
Dr. Tateyama and his research team visit the Arctic every September or October to find out what’s happening at ground zero of climate change. Sea ice is a relatively new area of study led by Japan’s Tateyama team. Experts believe obtaining accurate and detailed information about sea ice can reveal how climate and those which live in it are intertwined. Such data can also help improve weather forecasting, along with other benefits. This is why the global science community is paying close attention to Dr. Tateyama group’s research projects.
For the monitoring of sea ice, researchers use remote-sensing instruments that do not damage the environment, such as electro-magnetic inductive device and microwave radiometer. Dr. Tateyama is experienced with the technology as he has used it since 2003 when he was a university student.
“We want to be able to not only remotely detect ice and its age but also its thickness preferably in 10 cm increments. We are trying to develop a remote-sensing system for that,” Dr. Tateyama says. “We also hope our use of numerical models for the analysis of satellite and field data will help us overcome some challenges, such as dealing with multi-layered, oddly shaped ice and distinguishing between seawater and a pool of water on sea ice.”
Dr. Tateyama is unique in that he combines surface and aerial observation data to improve the data accuracy for to obtain more accurate and precise data.
“In April 2016, our surface observation team drove dog sleds along Greenland’s shores to stake flags in the fast ice there while our aerial team followed the markings by helicopter to gather data.
Dr. Tateyama’s research project is a collaborative one with the Arctic Challenge for Sustainability (ArCS), and his team closely works with the ArCS team led by Arctic glacier experts.
“We are focusing on the points of contacts between the land and sea. We research the water cycle and mass balance of glaciers that flow into the ocean and dissolve into the seawater. Much of what we do has never been tried before, and so it’s very exciting. We are hopeful that a lot of useful information will come out of the work,” Dr. Tateyama says.
Interviewer: Rue Ikeya
Photographs: Yuji Iijima unless noted otherwise
Released on: July 10, 2017 (The Japanese version released on Jan. 20. 2017)