He and his team found that the West Antarctic Ice Sheet, thought to be a thin layer covering high mountains, was two miles thick at some points and extended as far below sea level as the highest mountains rose above the surface. In their travels they discovered a trench the size of Mexico. Now known as the Bentley Subglacial Trench, it is the deepest spot on Earth not covered by ocean.
Professor Bentley made more than 15 trips to the Antarctic, the last in 2009, mapping the structure and physical properties of the ice sheet and probing the continent beneath it. In 1986, he and several colleagues reported in a cover article in Nature magazine that the glaciers known as ice streams do not rest on rock but rather move rapidly over water-saturated till.
By explaining the mechanics of ice-stream movement, he opened the way for research into the instability of the ice sheet and its potential for collapse, a subject of increasing concern as evidence on global warming accumulated.
“Charlie Bentley was the absolute polar scientist, going where nobody else had gone and measuring what nobody else had measured,” Richard Alley, a former student of Professor Bentley’s and now a geoscientist at Penn State University, wrote in an email. “Concern about rapid sea-level rise from ice-sheet collapse grew out of his early discoveries, and many of the tools to answer the big questions come from his research since then.”
Charles Raymond Bentley was born on Dec. 23, 1929, in Rochester. His father, also named Charles but known as Raymond, was a successful lawyer. His mother, the former Janet Everest, was the granddaughter of a founder of Vacuum Oil, which later merged with Standard Oil. She was unconventional: Before marrying, she had already adopted two children on her own.
After graduating from Phillips Academy in Andover, Mass., Professor Bentley earned a physics degree from Yale University in 1950. He planned to study law but changed his mind after spending a summer on a research ship in the Atlantic led by the oceanographer Maurice Ewing of Columbia University.
He enrolled in Columbia to study geophysics and, after spending two years on the Greenland ice shelf, where he developed a seismic method of measuring ice depth, defended his dissertation at the end of 1956. The degree was not awarded until 1959 because he had forgotten to pay a $50 dissertation fee before setting off for Antarctica.
Professor Bentley joined the department of geology and geophysics (now the department of geosciences) at the University of Wisconsin in 1961. On retiring in 2000, he became the head of Ice Drilling Design and Operations, a program at the university’s Space Science and Engineering Center that designs and deploys drills for collecting ice samples.
Professor Bentley’s scientific exploits combined the derring-do of the great polar explorers with the painstaking work of measurement and calibration. On his first expedition, he and his team discovered a mountain range as large as the Rockies running parallel to the Weddell Sea. They were the first to visit and partly survey the Sentinel Range, one of whose peaks was named after him.
To measure the ice shelf’s depth, he set off explosions that sent sound waves to the bottom of the ice sheet. Geophones on the surface picked up the waves on their return and provided a depth reading.
It would be many decades before such discoveries captured the imagination of the general public.
“There was no particular effort to reach the public at all,” he told The Antarctic Sun, a newsletter published by the United States Antarctic Program, in 2007. “Furthermore, we didn’t really understand back 50 years ago the connections between the polar regions and the rest of the world. They seemed isolated and remote, and of interest as part of the earth; but it took quite a while to learn how closely related they are to the rest of the world.”
In addition to his daughter, Professor Bentley is survived by a son, Alex; a grandson; and two step-grandsons.
Professor Bentley served as the chairman of the Polar Research Board of the National Academy of Sciences from 1981 to 1985. His work was honored by the Soviet Academy of Sciences with the Bellingshausen-Lazarev Medal in 1971, and in 1990 the International Glaciological Society gave him its highest honor, the Seligman Crystal.