Marine Benthic Ecosystems
Figure 1. A satellite image from NASA's MODIS sensor take in November 2003. The red dots indicate where the ice flow speed was measured and the colored lines illustrate the retreat of the Larsen B during the past 6 years. Credit National Snow and Ice Data Center (NSIDC)
Satellites have been tracking the changes in the Larsen B Ice Shelf since 1990. The Larsen B Ice Shelf System (LARISSA) is located in the northwest embayment of the Weddell Sea on the east coast of the Antarctic Peninsula (Figure 1). In 2002, a 3,200 km² section, (almost 770,000 acres) of the Larsen B disintegrated into the Southern Ocean in nearly one month. Approximately 600 ft thick, scientists are led to believe the ice shelves demise might be the result of long term gradual thinning due to increased surface air temperatures. The physical and biological oceanography of the region is now being investigated by an international team of marine biologists, geologists, physical oceanographers, marine ecologists, and glaciologists . This NSF-funded "LARISSA" (LARsen Ic Shelf System, Antarctica) initiative seeks to understand why the Larsen B Ice Shelf collapsed, to use this knowledge to forecast future ice shelf disintegration elsewhere in Antarctica, and to understand how the benthic community responds to the change in ice cover.
The Marine Ecosystem
Figure 2. (a) View of the pustular white mat covering 75% of the seafloor under the Larsen B Ice Shelf. Yellow scale bar is 20 cm across and the yellow circle represent unknown gas bubbles ascending. Water depth is 840 m. (b) Small boulder dropstone resting on white mat in 850m water. (c)Close up of seafloor at 840m. Greenish fringe along mat edge is diatomaceous fluff. (d) View of seep mound with surrounding bivalve community. Credit: E. Domack et. al. July 2005.
The environment below the Larsen B Ice Shelf had been hidden for nearly 10,000 years (Domack et al. 2005); the ice playing a major role in the ecology of the marine ecosystem. As these ice-protected areas had virtually no light (aphotic), input of photosynthetically - derived materials thought to drive open-water Antarctic marine ecosystems was severely limited. In the absence light energy, chemical energy (chemosynthesis) may have played a large role in the Larsen B sub-shelf marine ecosystem. While exploring the newlyvacated Laresn B embayment, Domack et al (2005) found evidence of chemosynthesis in the form of clam beds associated with methane bubbling from the seafloor. These clam beds resemble "cold seeps" - seafloor communities known from other parts of the world to be fueled principally by chemicals seeping from the seafloor instead of sunlight. This would be the first active cold seep ever found in the Antarctic.
The collapse of the Larsen B ice shelf in 2002 exposed 1.5 million square kilometers of seafloor, much of which remains unexplored. The LARISSA marine biology team will survey a subset of the vast Larsen B embayment to better understand how seafloor communities respond to the loss of the ice shelf. Are the clam beds true "cold seeps"? If so, how common were seeps under the Larsen B Ice Shelf? How are the dynamics of cold seeps being affected by photosynthesis and organic inputs from the surface waters above? Does enhanced sedimentation result in an influx of new organisms? If so, how quickly does this process occur?