January 11: Sea Ice Sampling at the Mertz Glacier

Post from VIMS graduate student Mar Arroyo.

11 Jan 2017
65° 7’ S, 121° 19’ E
Sea ice sampling at the Mertz Glacier

One of the main marine science projects onboard this voyage is looking into the links between the iron and carbon cycles around East Antarctica and the Southern Ocean, led onboard by Dr. Delphine Lannuzel, with my supervisor, Dr. Elizabeth Shadwick. In the Southern ocean, the availability of iron as a micronutrient limits primary production for marine phytoplankton. Around Antarctica, melting sea ice releases iron and other trace elements to the surface waters. This input of iron makes the phytoplankton happy, and they take up CO2 out of the ocean to make organic matter during photosynthesis. The drawdown of CO2 in the ocean allows for more CO2 to be drawn out of the atmosphere.

Delphine and her team on the Aurora have collected cores of sea ice to measure the concentration of iron and other parameters within pack ice while we steam around East Antarctica. In order to leave the ship and step foot onto the ice, safety training and inductions need to be completed. Tents, fire starting kits, radios, GPSs, food, and more are taken onto the ice at every station, just in case.

The tent that the sea ice team brings out onto the ice. This tent could sleep five people comfortably.
The tent that the sea ice team brings out onto the ice. This tent could sleep five people comfortably.

To prepare for a sea ice station, a field training officer first goes onto the sea ice to make sure it is stable and thick enough to work on. The ice station is located upwind from the ship, to prevent any trace metal contamination from the ship and exhaust. Once everything is clear, Delphine and the team go out onto the ice and drill for sea ice cores. Clean suits are worn to prevent any contamination from clothing.

Dr. Julie Janssens (left) using the sea ice corer as Dr. Sebastian Moreau moves snow out of the way. Ice cores are typically over three feet in length and weigh over 20 pounds!
Dr. Julie Janssens (left) using the sea ice corer as Dr. Sebastian Moreau moves snow out of the way. Ice cores are typically over three feet in length and weigh over 20 pounds!

For this project, four main sea ice cores are collected. One for temperature and salinity, another for trace metals, a third for total alkalinity and dissolved CO2, and a final fourth for exopolysaccharides (EPS). Duplicate cores are sometimes also taken at the same site. The cores are cut into sections every 10 cm from top to bottom and separated into buckets to give a vertical profile of each parameter measured. Snow and seawater from under the ice are also sampled for the same measurements. The core sections and snow are brought back onto the ship and are melted down for analysis.

I joined Delphine’s team for the final sea ice station on the pack ice next to the Mertz Glacier! The Aurora crunched through along the eastern side of the Glacier. The starting time for ice stations is quite variable and depends on the location and thickness of the ice flow, among other things. I was on call from 8 PM onward and had all of my survival gear packed and ready to go. I was finally woken up at 4:30 AM to go out onto the ice.

The sea ice team post-sampling at Mertz station, (from L to R) Sebastian, Me, Julie, and Delphine, in front of the Aurora and Mertz glacier.
The sea ice team post-sampling at Mertz station, (from L to R) Sebastian, Me, Julie, and Delphine, in front of the Aurora and Mertz glacier.

Walking out onto the ice was a bit like walking out onto snow-covered land. It didn’t feel like there was only a 4-foot layer of ice separating me with the seafloor ~400m below. I helped the team core through the ice and separate the cores into sections for melting. Roughly four hours and eight ice cores later, we were packed back up onto the ship. This was hands down the best experience of the voyage so far.

Mar