LARISSA - LARsen Ice Shelf System, Antarctica, a NSF-funded project.

LARISSA - LARsen Ice Shelf System, Antarctica, a NSF-funded project.
We are conducting an integrated, multi-disciplinary field program to address the rapid and fundamental changes occurring in the Antarctic Peninsula region as a consequence of the abrupt collapse of the Larsen B Ice Shelf in the fall of 2002. A profound transformation in ecosystem structure and function is occurring in coastal waters of the western Weddell Sea. This transformation appears to be yielding a redistribution of energy flow between chemoautotrophic and photosynthetic production, and to be causing the rapid demise of the extraordinary seep ecosystem discovered beneath the ice shelf, providing an ideal opportunity to test fundamental paradigms in ecosystem evolution.

Monday, March 26, 2012

17-19 March 2012 - Throughout March 17th, we ground through heavy sea ice, making our way south into the Weddell Sea, heading for our work area in the Larsen B embayment. On the day before, we had moved rapidly through the ice-free Prince Gustav Channel to enter the Weddell Sea, one of the coldest bodies of water along the Antarctic continent. This is one of two regions cold enough to form Antarctic bottom water, the densest water in most of the ocean. On entering the Weddell, we quickly encountered sea ice, and our intrepid icebreaker, the Nathaniel B. Palmer (or “NBP”), ground its way through heavy sea ice most of March 17th. The ice was a mixture of new ice formed this late summer season (about 4-6 inches thick), one-year old ice form last fall (2-4 feet thick) and large floes of multi-year ice that can be more than 2 meters thick. Icebergs up to 50 m (165 ft) that had broken off the ice shelves and glaciers in the region loomed over the ship in some areas. The NBP can grind through new and year-old ice, but it is a noisy process, filling the forward parts of the ship, such as the galley were we eat, with a cacophony of roars, bangs, scraping, and thumps as sea ice grates along the metal hull. When the ship is breaking through ice, it is impossible to carry on a conversation in the galley with a ship mate seated next to you. As the ship hits a floe of multi-year ice, there is a loud band, the ship grinds to a halt, and then backs up and rams forward (the “back and ram” icebreaking), or simply circles around thick ice. We stay well clear of icebergs because they can protrude far out under the water, or drop large chunks of ice. Progress through sea ice has been slow, with the ship making 2-4 knots, and often being forced off our desired heading. Work in the frozen Weddell Sea certainly requires patience and flexibility because you often cannot get to a particular location targeted for study.

After a night of raucous ice-breaking, were arrived at the southwest tip of Robertson Island on the morning of 18 March. One of our goals in the LARISSA project is to figure out what food materials are reaching the seafloor in our Larsen B study area. One possibility is that large algae growing in shallow water around the edges of the Weddell sea sink to the seafloor floor to provide food for scavengers such as Antarctic shrimp and sea urchins. Thus, at Robertson Island, Craig and our collaborators from Duke (Dave Honig and Jamieson Clarke) went ashore by Zodiac inflatable boat to sample algae in the island’s shallows. We donned weatherproof Helly exposure suites, and filled a waterproof bag and buckets with sampling gear, drinking water and emergency food (you never know when you might become stranding in Antarctica!). The emergency kit in the Zodiac (a large plastic crate) included tents, more emergency rations, a satellite phones, and other materials. Our shore party also included geologists bent on sampling rocks and servicing an electronic observation station (collecting GPS and weather data) installed on the island two years ago. Our Zodiac boat was operated by two of our Marine Technicians, Buzz and Julian, who steered us through a mile of ice floes past seals and an occasional emperor penguin. We landed on a narrow beach caked with sea-ice and strewn with small icebergs. Most of the coastline of the island was barricaded by sea-ice and bergie bits (small icebergs) making access the shallow water along the beach very difficult

An ice armored beach on Roberston Island- C Smith

We spent four hours on shore, wading in the shallows collecting algae within arms reach, and using a dip net from the Zodiac to sample algae from 3-4 meters depth.

Sampling seaweed in the Robertson Island subtidal - E Hutt

We collected samples of four species of algae for stable-isotope analyses, which will allow us to trace this “food” into seafloor food webs. In the process, our exposure suites leaked, soaking our arms up to our shoulders with frigid (-1.8 C or 29 F), water and we experienced the extreme wind chill of Antarctic islands --- the wind chill was about -25 C (-13F) our entire time on shore, numbing our toes through two pair of heavy woolen socks. Surviving a year in these conditions as did Shackelton’s men on Elephant Island is difficult to imagine! After we collected our seaweed samples, we hiked to the top of Roberston Island (about 200 m, or 650 ft, high) to get the blood flowing back into our toes and fingers. We were treated to a spectacular view looking south into the Larsen B embayment. While extraordinarily beautiful, the view also yielded some disappointing news – our path south into the Larsen B region is blocked by very heavy sea ice and lines of icebergs. Our hopes of getting all the way south to our primary study area appear a bit dimmer!

Craig modeling a Helly suit atop Robertson Island looking south into the ice-clogged Larson B Embayment with the NBP in the background - D Honig)

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