Photo Credit: Anna-Carlijn Alderkamp

Scientist Matt Mills carryies a Go-Flow bottle to the trace metal clean lab on the research vessel Nathaniel B. Palmer during a previous cruise. The instrument collects water samples.

Polynyas are important sink for carbon

Is the meltwater releasing nutrients, including trace metals like iron, into the near-shore environment? Or is the iron coming from somewhere else? Is it even the iron that’s driving the increased productivity?

To help answer those questions, the USAP recently acquired a new state-of-the-art trace metal system with a National Science Foundation (NSF) grant to Rob Sherrell at Rutgers University . Sherrell is a co-PI on ASPIRE. 

The system helps ensure any trace metal samples collected by a conductivity, temperature and depth (CTD) sensor and rosette — a circular frame that holds canisters that collect water — haven’t been contaminated by the instrument itself. A thick, Kevlar-coated cable lowers the CTD from a trace-metal clean winch.

“This system makes it possible for us, and for other trace metal investigators, to sample seawater at any depth down to about 3,000 [meters] without contamination of the samples by the equipment, as would happen for at least some important metals if we used the ship’s conventional CTD,” Sherrell said by e-mail as the system was being installed in Punta Arenas.  

Photo Credit: Anna-Carlijn Alderkamp

Dotson Ice Shelf

Photo Credit: Johan Engelbrektsson

A convential CTD used aboard the Oden.

Photo Credit: Patricia Yager

Rob Sherrell, right, looks over a trace metal clean CTD on the Oden.

“We’re excited to see the system work correctly, both mechanically, and in terms of returning clean samples. Iron is one of the most contamination-prone metals,” he added.

Another key goal of the project is to figure out what occurs post-bloom.

Phytoplankton are important to the carbon cycle because as they die, they fall from the surface to the deeper ocean, keeping that carbon from returning to the atmosphere. Carbon dioxide in the atmosphere is the key greenhouse gas in global warming.

“When that [carbon] sinks, it’s gone for a while,” Yager said. The timeframe in this case is at least centuries.

Scientists believe the polynya’s intense productivity will be matched by high level of carbon export to ocean depth. In addition to measuring the drawdown of CO2 at the surface, the ship will deploy a sediment trap attached to a mooring to capture the organic carbon particles as they settle from the surface to the bottom of the ocean. The mooring will sit on the ocean floor at about a depth of a thousand meters for a year.

Many of the measurements and techniques the scientists use will mirror those of the Palmer Long Term Ecological Research (PAL LTER) project , a nearly 20-year-long program to study the marine environment of the western Antarctic Peninsula.

For example, they will release a glider — a winged, torpedo-shaped robot that moves autonomously through the water — to take physical oceanographic measurements like temperature and salinity in the polynya. Oscar Schofield at Rutgers University, a co-PI on ASPIRE, first brought the instrument to the PAL LTER program about three years ago.

The western Antarctic Peninsula is one of the fastest warming regions on the planet, with average temperatures increasing nearly 3 degrees Celsius since the 1950s — and even more in the winter.

Additionally, the winter sea ice duration in an area stretching from the west Antarctic Peninsula to the eastern Amundsen Sea is in decline. Data between 1979 and 2006 show sea ice advancing later and retreating earlier. In the greater PAL LTER study area, the life of winter sea ice has shrunk by almost three months.

Graphic Credit: Sharon Stammerjohn

This graph shows the decline of sea ice duration over 30 years.

Citing previous studies published in the journal Nature, Sharon Stammerjohn said by e-mail, “These large trends toward shorter sea ice seasons are offshore of the coastal regions showing the largest ice mass losses from the Antarctic continent.

“Both sea ice and land ice appear to be responding to changes in atmospheric and ocean circulation,” added Stammerjohn, an assistant professor in Ocean Sciences at the University of California, Santa Cruz , who is a co-PI on both ASPIRE and the PAL LTER.

Stammerjohn said the ASPIRE team hopes to better identify the physical and chemical environmental factors in the polynya, like surface stratification and the presence of trace metals, that boost the region’s productivity. Once the researchers understand what’s happening, they can predict how changes in the future might influence the Amundsen Sea marine ecosystem.

“This is an important region because it’s where the West Antarctic Ice Sheet meets and interacts with the ocean,” noted Hugh Ducklow , the lead principal investigator for the PAL LTER program and co-PI for ASPIRE.

“ASPIRE, through comparison and coordinated study with LTER, will gauge the extent of change in the south,” said Ducklow, director of The Ecosystems Center at the Marine Biological Laboratory in Woods Hole, Mass. “This will give us a much better understanding of the extent of climate change continent-wide, and how it will proceed in the future.”

One concern is that as sea ice disappears, so will the polynyas and their highly productive carbons sinks.

“It’s possible that carbon fixation and storage will decrease — leading to more CO2 in the atmosphere, more warming, and so on — another positive feedback [loop]. Polynyas are on the front lines of global change,” Ducklow said.

NSF-funded research in this story: Patricia Yager, University of Georgia, Award No. 0839069 ; Robert Sherrell and Oscar Schofield, Rutgers University, Award No. 0838995 ; Hugh Ducklow, Marine Biological Laboratory, Award No. 0839012 ; Sharon Stammerjohn, University of California Santa Cruz, Award No. 0838975 ; and Kevin Arrigo, Stanford University, Award No. 0944727 . Back   1 2