Extensive sampling will help assess future changes
By Summit Voice
SUMMIT COUNTY — As the Earth’s atmosphere warms and oceans become more acidic, the carbon cycle has become the subject of intense study for climate scientists. And new research by researchers with the Woods Hole Oceanographic Institution that establishes a baseline for Arctic ocean carbon levels should provide a yardstick against which to measure future changes.
The study, recently published in the journal Biogeosciences, will help researchers better understand how carbon enters and is used by the marine ecosystem.
Some researchers think that global warming could lead to a more intense precipitation cycle over northern Canada, Alaska, and Siberia, resulting in more runoff from melting permafrost and eroded soil — both rich sources of organic carbon. That could result in a net gain of carbon, as bacteria in Arctic Ocean use the new influx of carbon as a food source, they may create CO2 as a byproduct.
“Carbon is the currency of life. Where carbon is coming from, which organisms are using it, how they’re giving off carbon themselves—these things say a lot about how an ocean ecosystem works,” said lead author David Griffith. “If warming temperatures perturb the Arctic Ocean, the way that carbon cycles through that system may change.”
Griffith’s team sampled suspended particles of organic matter, as well as organic carbon and carbon dioxide (CO2) dissolved into the surrounding water. This is the first time that researchers have focused broadly on measuring multiple types of carbon at the same time and place in the Arctic Ocean. Only few carbon surveys had previously been conducted in the remote ocean, due partly to the challenges of operating in the Arctic environment.
Griffith and his colleagues conducted their fieldwork in 2008 aboard the Canadian Coast Guard icebreaker Louis S. St. Laurent. At two different spots in the Canada Basin, an area northwest of the Canadian coast, they gathered samples from 24 depths ranging from the surface to the ocean floor 3800 meters (roughly 12,500 feet) below.
Collecting samples at those intervals was necessary because the Arctic Ocean is separated into distinct layers, each with its own unique carbon characteristics,” he explained. At the surface is a freshwater layer from river runoff and sea-ice melt. Below that is a layer of cold water from the Pacific, and below that is a warm, salty Atlantic layer. The deepest layer is slowly replaced by mixing with overlying Atlantic water.
Measuring the different amounts of carbon in each layer (and determining its source) is an essential step in understanding the flow of carbon through the marine ecosystem.
“It’s kind of like understanding how freight and people move in a city. If you don’t know what’s coming in and out, it’s really hard to understand how the city works.”
The samples were analyzed down to the atomic levels by Ann McNichol, a WHOI senior researcher and staff chemist. McNichol tallied the total number of carbon atoms in each specimen, including carbon-13, a stable isotope of the element. McNichol said that it can be used to determine where a particular pool of carbon originated, and how it may have been utilized by the marine ecosystem.
“Carbon-13 is primarily a source indicator,” she said. “By measuring levels of carbon-13 at different depths, it’s possible to determine if the carbon there was generated by the marine environment, ocean ice environment, or by terrestrial sources.” The team also examined levels of carbon-14, a radioactive isotope that can help determine the age of each sample to further determine its source.
In addition to understanding the basic carbon cycle in the Arctic Ocean, Griffith’s team hopes that the results of this baseline study will help evaluate how Arctic Ocean carbon levels and global climate interact.
Griffith said it’s also possible that warming temperatures and melting sea ice might boost the production of phytoplankton, tiny plant-like organisms that live near the ocean’s surface and thrive on carbon dioxide in the water. As those phytoplankton die (or are eaten by other organisms and released as waste), they would sink to the sea floor, causing the carbon in their bodies to be sequestered in thick sediments—effectively removing the increased carbon from the environment.
“We don’t yet have the kind of data to say anything definitive about how the Arctic would be affected by warming climate,” Griffith said. “But what we do have is a very important baseline of data to help evaluate changes that will happen in the future. Without that, you‘re unfortunately just guessing at how things change over time.”
This research was funded by the WHOI Arctic Research Initiative, Fisheries and Oceans Canada, the Canadian International Polar Year Office, and the U.S. National Science Foundation.