Current Position: 65 54.7626 60 32.3044
On the morning of April 20th, two helicopter missions took off from the ARAON located just southeast of Snow Hill Island in the Weddell Sea. The flights had two purposes: 1) sea ice reconnaissance 2) repairing a GPS station on Robertson Island. The ice pilot, a special crewman who advises the ship’s captain on navigating sea ice, flew in one helo, and within a few minutes of being airborne identified at least two possible courses to penetrate through the sea ice to open water along the former Larsen A ice shelf area. This helo also scouted possible exit paths to ensure the ARAON does not spend the winter in the Weddell Sea.
The other helicopter flew to Robertson Island, the boundary island between the former Larsen A and Larsen B ice shelves. The first visitor to Robertson Island was Sir Earnest Shackleton on the infamous voyage of the Endurance nearly a century ago. Since then, very few people have journeyed there, and now Professor Eugene Domack has been there three times, and by his account more than anyone else!
After the helicopters returned to the ship, the ARAON navigated through a mesh of sea ice and icebergs to break through to open waters along the former Larsen A area. Without the helo flight beforehand, it would have been nearly impossible to spot a path for the ship. After crushing through the ice and cruising by massive tabular icebergs, the ARAON made it to the open water in Larsen A.
Within the Larsen A, the ship’s path crossed close to a mooring placed nearly a year ago by LARISSA scientists on the RVIB Nathaniel B. Palmer. A mooring is essentially an anchored cable with oceanographic and sedimentological instruments attached to it at selected depths in the water column to continuously collect data through time at a given location. The ship positioned itself near the recorded coordinates of the mooring and electronically released it from the anchor allowing it to rise to the surface. As the sun set over the peninsula and James Ross Island, all scientists and crew went on deck to look for the mooring’s buoys. Just as daylight nearly ran out, the captain was able to spot the buoys and brought the ship to the mooring.
After the crew successfully obtained the mooring and carefully brought it on deck, we were able to recover all of the oceanographic instruments and sediment traps flawlessly. Everyone in the marine geology group was ecstatic to obtain this data set from the Weddell Sea, a frontier in the world’s oceans.
The ARAON continued its course south towards the former Larsen B ice shelf area, the site of an ice shelf collapse in 2002. The Larsen B was a stable feature for the entire Holocene, or the last 10,000 years, but due to rising regional surface temperatures and changing atmospheric patterns, broke up over the course of a single month. The ice shelf was nearly 720 feet thick and the area of Rhode Island- a catastrophic example of rapidly changing environmental conditions due to climate change.
Since the breakup event however, access has been highly limited as fast ice, or sea ice that fasts to land and glaciers, has choked much of the Larsen B area. The ARAON cruised as far west into the Larsen B area as possible and stopped along the current fast ice margin. The weather was on our side that morning with clear blue skies, and the glaciology group was able to conduct field activities on several glaciers draining the eastern side of the Bruce Plateau.
Just as the helicopters returned, however, the weather changed quite rapidly, and visibility and temperatures dove and the winds picked up. One of the meteorological stations on a monitored glacier nearby recorded a 20 degree Celsius drop in 30 minutes. We are in Antarctica heading into the winter- insane weather is to be expected! The storm worsened and after the ship encountered 60 knot sustained winds (nearly 70 miles per hour), the ship redirected its course north with haste to avoid the storm and possibly becoming trapped in sea ice.
The following morning the storm had passed leaving the skies clear and frigid dry air. Oceanographic and multibeam surveys were conducted for much of the day to further bolster our understanding of the Larsen A area. With improved weather conditions, the ARAON again headed south towards the Larsen B.
Yesterday I awoke to find that the ARAON returned to the Larsen B. Poor weather conditions canceled all helo operations and the focus of the day would be marine science. Since an ice shelf covered the Larsen B embayment for the past 10,000 years, the marine realm in this region is largely unexplored. Heavy fast ice and sea ice furthered limited access, so it is quite remarkable to be here. The multibeam and chirp data we collect here reveals new information every minute.
We spent the day with our eyes glued to the chirp looking for possible sediment core locations under the former Larsen B ice shelf. An ice shelf is floating glacial ice from land that extends and floats in the ocean, and unlike sea ice, are hundreds of meters thick. Ice shelves are sensitive barometers of climate conditions. They begin to disintegrate when average annual atmospheric temperatures rise above a -9 to -5 degree Celsius. However, ice shelves are also sensitive to oceanic conditions such as water temperature and salinity. If a warm, saline water mass begins to interact with an ice shelf (warm, saline = lower freezing point), the ice shelf can undermelt, placing further strain on its persistence.
When an ice shelf breaks up, it indicates local conditions are in flux. The Larsen B subsisted for the entire Holocene, or period of time since the last ice age. Using sediment cores it is possible to reconstruct past environments as well as use radiocarbon dating to constrain the chronology. Ice shelves limit calving of icebergs and sediment transport from the glaciers, starving these basins of sediment, and therefore, the sedimentation rates are quite low. This is sort of a catch 22 as 1) if we find sediment it provides an extensive time record of sedimentation, but 2) it is hard to find sufficient sediment to core in the first place. Furthermore, during the last ice age the sea floor of the Weddell Sea was englaciated leaving behind hard, compacted till that is difficult to recover with sediment cores. We found a couple sites to core, but just as suspected, the amount of sediment recovered was quite thin and scarce.
In addition to sediment cores, dredging is another common technique used to learn about the seafloor. Along Cape Framnes, remoted operated vehicles (ROVs) discovered corals living on the rocky bottom, and dredging was used to attempt to collect some of these corals. Corals in the Antarctic are akin to extensive tree-ring records from redwoods or sequoias. Corals depend on the influx of moving water containing nutrients in the water column. Since nutrients are remarkably scarce in the Weddell Sea, corals grow very slowly, possibly since the ocean reoccupied the area following deglaciation. Since corals are made of calcium carbonate, the can be radiocarbon dated (telling us how old they are) and grow radially like trees. The layers on coral, therefore record changes in oceanographic conditions that are related to climate variability. Dredging, however, tends to destroy delicate features, so the coral we were able to recover was scarce. Nonetheless, what was recovered, will provide exciting data, and we also obtained a big bucket of rocks / souvenirs :)
The course of the ARAON yesterday took us as far south as sea ice would permit us. We passed Cape Framnes to the Larsen C, the remaining and largest Larsen ice shelf. The vessel dove below 66 degrees south, putting us almost within reach of crossing the Antarctic Circle. The survey, oceanographic, and sedimentological data collected here is particularly valuable as it represents an active, intact ice shelf system. If the recent historical trend of north to south ice shelf collapse along the Antarctic Peninsula continues, this data will provide a baseline dataset to compare against a post-ice shelf collapse environment. Unfortunately it was dark while the ARAON was passing through this section of the Weddell Sea, so I have not seen a living ice shelf quite yet!