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Feature Article

High-Resolution Seismic Survey Off South Shetland Island, Antarctica
Using a Sub-Bottom Profiler to Acquire High-Resolution Data In Deepwater Areas With Challenging Environmental Conditions

By Arthur Ayres Neto
Professor of Marine Geology
Luiz Antonio Pierantoni Gamboa
Professor of Marine Geophysics
Universidade Federal Fluminense
Niterói, Brazil

Luiz Carlos Torres
Retired Hydrographer
Brazilian Navy
Niterói, Brazil

Antarctica, with an area of 14 million square kilometers and an average ice thickness of three kilometers, remains relatively unknown and unexplored. Harsh weather is common year-round, with temperatures that reach -80° C in its interior. The Antarctic Circumpolar Current flows clockwise around the continent, moving the entire water column from the surface to the seafloor, thermally isolating the continent.

Understanding the evolution of the Antarctic continent in detail throughout geologic time is critical to foreseeing both the continent's future and its impact on the planet as a whole. Moreover, comparative studies between Antarctica and other fragments of the Gondwana supercontinent, the study of climatic variations and the influence of human action on this peculiar environment are critical to understanding the evolution of local biological communities and their interaction with other organisms outside the Antarctic region.

Regional Setting
The Southern Ocean is a deep ocean with a great part of its seafloor at depths between 4,000 meters and 5,000 meters. The ocean has few restricted shallow-water zones and a narrow and relatively deep continental shelf. The shelf break is between the 400-meter and 800-meter isobath, much deeper than the worldwide average of 133 meters.

The Bransfield Strait, a 200-mile back-arc basin between South Shetland Island and the Antarctic Peninsula, is relatively young (estimated to be 5 million years old) and was formed by the extensional tectonics responsible for the separation of the Antarctic Peninsula from the South Shetland Islands archipelago.

The basin is limited to the northeast and the southwest by the Shackleton and Hero fracture zones, respectively, and it presents an asymmetrical profile with the basin axis located closer to the South Shetland archipelago. At this side the continental margin is narrower and presents a steeper continental slope. On the side of the Antarctic Peninsula, the basin has a wider continental shelf, thicker sediment packages and a softer slope, suggesting that the peninsula has supplied greater volumes of sediment to the basin than the archipelago. Land-based glaciers on both sides of the basin have generated deep canyons and gullies along the continental slope as they have moved toward the sea.

The SEASOAM Project
A study of the separation between Antarctica and South America (SEASOAM) was approved by the subcommittee of the International Polar Year, part of the Scientific Committee on Antarctic Research, and it is funded by the Brazilian National Council for Scientific and Technological Development. The research aims to study regional depositional sequences and to identify related erosional surfaces that resulted from sea-level variations. The project ended in June 2010, and data processing and analysis are ongoing.

Coordinated by Universidade Federal Fluminense, the SEASOAM study consisted of high-resolution seismic and magnetic surveys as well as the recovery of marine sediment cores offshore the South Shetland Islands. The study's purpose was to investigate the relationship between the geologic evolution of the region and climatic changes of the Southern Hemisphere. Two cruises—a 2008 expedition in October and November and a 2009 expedition in November—were conducted with the Brazilian navy's Antarctic research vessel Ary Rongel. During these cruises, a total of 350 kilometers of high-resolution seismic data, 600 kilometers of magnetic data and six gravity cores were acquired in the study area. To continue this article please click here.

Arthur Ayres Neto is a marine geologist with a Ph.D. in marine geophysics from the University of Kiel. After 17 years of working in the survey industry, he is now a professor of engineering and environmental marine geophysics at Universidade Federal Fluminense.

Luiz Antonio Pierantoni Gamboa is a geologist working for Petrobras (Rio de Janeiro, Brazil) conducting seismic interpretation on the Santos and Campos basins. He is also a professor at Universidade Federal Fluminense and has been involved with Antarctic projects since 1989.

Luiz Carlos Torres is a retired Brazilian navy hydrographer and holds an M.S. in geology and marine geophysics from Universidade Federal Fluminense. For the past 15 years, Torres has worked on a wide variety of multidisciplinary governmental and academic projects.

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