A helicopter view of the Oden heading home. Credit: Frank Nitsche.

We successfully finished our scientific work in the Amundsen Sea and are now heading back to Punta Arenas, at the tip of South America. It will take eight to nine days to get there depending on the weather and winds. Just before we left the Amundsen Sea we passed the German ice-breaker ship, the Polarstern. They had a helicopter on board, so we we were able to meet and exchange preliminary research results. Because of the preparation and expense to get to this remote location, it is important to avoid duplicating our mapping and sampling efforts.
We were lucky to have favorable weather for most of our expedition–only a few days of strong winds and record low sea ice. It was also unusually warm. Temperatures mostly varied between 28 to 35 degrees F (-5 to 2 degrees C), which is probably related to the low sea ice cover.

Geologists inspect a fresh sediment core. Credit: Frank Nitsche.

The bottom of the seafloor shows us where ice used to flow. To pinpoint when the ice retreated, the geologists on board take samples of mud and sand from the seafloor. Using a weighted steel barrel lowered to the seafloor they bore their way through sand and mud. A catcher at the bottom of the barrel prevents the sediment from falling out when the corer is hoisted up.

Sediment cores are lifted at the back of the boat.

The different layers of sediment help us identify episodes of ice retreat. If we come across shells or tiny plankton fossils in the sediment we can use them to date those episodes. So far we have taken more than 20 cores and and will take several more if the weather holds.

Icebergs gouged furrows on the sea floor as the Antarctic ice sheet started to retreat during the last glaciation.

A few days ago we reached our main study area in the eastern Amundsen Sea. Here we are using sonar to map the contours of the seafloor in great detail. During the last glaciation the Antarctic ice sheet was much larger and covered most of the continental shelf, an underwater extension of the continent that can stretch for miles. The moving ice gouged marks into the seafloor, and those marks now tell us which way the ice was flowing. By analyzing them, we can reconstruct past ice flow. Our ultimate goal is to understand how the ice was flowing, and how fast it retreated as the earth came out of its last glaciation about 18,000 years ago.

An iceberg drifts through open waters. Credit: Frank Nitsche.

Where we work and how we get there depends on the sea ice. The Oden is a powerful icebreaker but it is often faster and more fuel-efficient to go around heavy sea ice then to chop our way through. If the sea ice is several feet thick, we often choose to detour. We actually consult a daily sea-ice map to chart our route each day.

Summer is winding down in Antarctica and the sea ice has been melting for months. Our expedition to the Amundsen Sea was planned for a time when the sea ice could be expected to be at its lowest extent, making more areas accessible. In a few weeks the ocean will start freezing and in a few months thick ice will blanket the region once again.

Our jagged track reflects frequent sea-ice detours.

Moorings Will Continue to Take Measurements After We Leave

After crossing the Ross Sea, we’ve reached our first study area: the “Little America Trough.” The oceanographers on board want to find out if warmer water from the deep ocean is rising onto the continental shelf and reaching the ice, making it melt faster. They measure temperature and salinity as well as the water currents. To collect additional, long term measurements, we leave behind two moorings–a set of instruments attached to a wire or rope that is anchored, or moored, to the seafloor.

Docked on Sea Ice

Today we arrived at McMurdo, an American research station that hosts Antarctica’s largest community—about 1,000 people during austral summer. To get here, a US Air Force cargo plane picked us up in Christchurch, New Zealand, and landed us on the ice nearby.

Today is a balmy summer day of 30°F, not much colder than the weather in New York. We are sweating in the heavy-duty parkas that we picked up in Christchurch. The Oden is currently docked at the edge of the sea ice, waiting to guide a cargo ship out to open water. In the meantime, we visit the ship in a truck designed to travel over ice. In a few days, we will load the last pieces of our equipment and start our journey east.

I will be traveling with an international team of scientists aboard the Swedish ice-breaking ship, the Oden. Our main goal will be to better understand how the West Antarctic ice sheet has changed since the last ice age hit its peak, about 20,000 years ago. Scientists aboard the Oden will map glacial features on the seafloor, take sediment samples, and measure water properties. In addition, some scientists will carry out biological and astrophysical experiments.

From Christchurch, New Zealand, we will fly to the American base on Antarctica, McMurdo Station, and board the Oden, bound for the eastern Ross Sea to deploy oceanographic instruments. From there we will head to the Amundsen Sea, our main study area, and then steam east along the continental shelf and the Antarctic Peninsula. The expedition will end in Punta Arenas, Chile, in mid-March.