ABOARD THE JOIDES RESOLUTION, IN TRANSIT TO HOBART, TASMANIA– The work of the ship ended as quickly as it started nearly two months ago. We finished drilling Site 1361 and logged the hole. The drillers tripped 3500 meters of pipe and prepped it for storage as the ship will not drill again until July – off the coast of British Columbia. Everyone on board is absolutely brain dead from the non-stop grind of 12-hour shifts day after day. But all are happy as well. We’ve completed most of our objectives and made some exciting discoveries. When we did not meet with complete success it was always because of weather and ice, either encroaching sea ice or fields of icebergs so thick that we had no chance to pass.

Relaxing with some music after the work is done.

Now we have some days in transit. These days are filled with meetings to design our post-cruise research. We will all spend much more time at home working on the cores than our actual days at sea on this expedition. Some of the methods we will employ are expensive and difficult and we have recovered nearly 2000 meters of core. This means that we must carefully select the intervals we will study, so that we can answer the most important questions about Antarctic climate change as quickly as we can. For some of us, the analytical work will extend over the next 4 years. Then other scientists will work on these cores for decades to come. They will be stored in a vast library of ocean cores in College Station, Texas, at the IODP core repository where they are available to scientists from all over the world.

What I like most about these days in transit is going off shift. I no longer set my alarm to awake at 11PM. The two shifts mingle at meals and in the labs, almost as strangers at first as they have not seen much of each other for more than 7 weeks.

The whole team for Expedition 318. Photo courtesy of John Beck, IODP.

Working groups between the shifts assemble to design research strategies and timetables. I will lead a group that will make oxygen isotopic measurements of the small shells of amoeba-like organisms called foraminifera. Forams, as we call them, live for about 4 weeks during the brief Antarctic summer. They build their tiny shells out of calcium carbonate, the main mineral that makes up limestone. By measuring the ratios of two types of oxygen in the carbonate we can tell the temperature of the water in which the forams grew. We will make these analyses on forams that were living in Antarctic surface waters hundreds, thousands, and even millions of years ago to see how warm the water was next to the Wilkes Land coast. We already know from our microscope work on board that this part of Antarctica has been very warm at times, maybe 10 to 15 degrees centigrade warmer when we go back 35 million years. The foram work will help tell us exactly how warm the waters may have been during more recent periods when we know the ice sheet became much smaller. The results will help us predict the behavior of Antarctic ice in the future.

What a trip it’s been! I hope you’ve enjoyed these blogs. If you live in the Bay Area, please look for a notice about a talk I’ll likely give on this expedition in 6 months or so, after we’ve had a chance to start the shore-based part of the work. As we pull ever closer to Hobart we are very much aware that we are simply reaching the end of the beginning.

Christina and Joerg at the bow at sunset. Photo courtesy of John Beck, IODP.

Early drill and recovery attempts of the buried glacier ice.

Sediment lenses cross cutting through a 30 cm ice core.

The outstanding question is how old is the ice? Ash deposits overlying the ice are dated to as old as 8.1 Ma (million years ago) which would make the underlying glacier the oldest ice yet discovered on our planet. To further convince skeptics that the ice is indeed old, the principal investigators of the grant (David Marchant, Boston University, and Michael Bender, Princeton University) are attempting to date the age of the ice directly.

An in-situ ash wedge in debris overlying buried ice. The wedge is approximately 30 cm across and 40 cm tall. Such deposits can be dated to give a minimum age for the overlying glacial debris.

To understand how this is done we need to go back to when the planet was forming 4.6 billion years ago. Since the formation of the earth, there has been a slow release of gas from the interior of the planet to the atmosphere (i.e. degassing via volcanic activity). One gas in particular is an isotope of Argon. This isotope does not decay thus its concentration is slowly building up in the earth’s atmosphere over time. Atmospheric gas trapped in old ice would have less Argon isotope compared to recently formed glacier ice. The principal investigators will use this technique to analyze the gases trapped within the glacier ice we collect during this field season and determine an age of the ice. If indeed it is the oldest ice yet found on earth, we will have the opportunity to directly measure important greenhouse gases such as CO2 at timescale millions of years back into earth’s history.

For field work, we have very nice accommodations here in Deadhorse including occasional meals at one of the hotels in town. Polar bears do not have the luxury of eating regularly – sometimes they must go for days or even weeks and months without having the opportunity to kill a seal for food.

Site of a seal kill by polar bears, probably a sow and cub we spotted nearby that afternoon. Seals – here, likely ringed seals (Phoca hispida) – maintain lairs carved out in snow drifts on the sea ice, in which females give birth and nurse their young. The lair is over a hole in the ice, allowing the seals to come and go without being seen. Polar bears seek out lairs and pounce through the snow roof to catch the seals inside – this likely created the hole in the center of the photo. We hovered about fifteen feet above the site for this photo.

Polar bears specialize in hunting seals and seals provide most, if not all, of the polar bear diet. During summer, some bears remain on shore as the sea ice retreats far north; seals are typically not available for hunting on shore during summer, so these bears probably have little to eat. Some bears follow the retreating sea ice north; however, if the sea ice retreats too far north (as has happened in recent years) it moves beyond productive near-shore waters where it is thought that seals congregate. In that situation bears spending the summer on the sea ice may find little to eat as well.

To find out if bears are getting by without food during the summer, we are taking samples indicative of fed status for bears on shore and those on ice. One sample is exhaled breath. Once the bear is anesthetized, we place a mask over its snout; the mask is connected to a two-way valve and the exhaled air fills a collection bag. Usually it takes less than a minute for the bear to fill the bag.

The mask and two-way valve at the right, connected the collection bag at the left.

One analysis estimates how much of the carbon in the exhaled carbon dioxide is actually carbon-thirteen (13C). This is a stable isotope of carbon; unlike a radioactive isotope, it does not readily break down (thus the term “stable” isotope). 13C is slightly heavier than regular carbon and is present in small amounts in most things. The carbon in exhaled carbon dioxide comes from digested food – and, the amount of 13C in carbon dioxide will be slightly different if a polar bear is breaking down its own fat stores for energy than if a polar bear is digesting a seal it has killed. Once our collection bag is full of exhaled breath, we take a small sample of the breath and inject it into an airtight container for stable isotope analysis back at the University of Wyoming.

Another site of a seal kill by a polar bear. Nearby we caught a 940 lb male.

A back paw of the male captured near the seal kill, with a glove for perspective. We had to move quickly to finish this capture and fly back to Deadhorse because a snowstorm moved in and we were losing visibility fast.