William Riedel: 1927-2020

William Riedel, a long-time scientist at Scripps Institution of Oceanography at UC San Diego and renowned micropaleontologist, died Dec. 14, 2020, in Adelaide, South Australia. He was 93. 

Over a career of more than 50 years, Riedel became known worldwide for his expertise in radiolarians, single-celled microscopic organisms known for their intricate mineral skeletons. Riedel’s work on fossilized radiolarians was foundational in the expanding field of oceanography in the second half of the 20th century, redefining the understanding of Earth’s geologic history. 

As a young graduate student, Riedel’s interest in radiolarians was sparked when he discovered they were a neglected group in paleontology. He found that they defy easy classification, but that they can be useful indicators of geologic age. During his career analyzing marine sediment cores from around the world as well as on land, he established a radiolarian zonation that divides the Cretaceous period into seven parts.

William Rex Riedel was born in Tanunda, South Australia on Sept. 5, 1927. He studied at the University of Adelaide, majoring in geology and zoology and got a bachelor’s degree with first class honors in 1947, a master’s degree in 1952, and a Doctor of Science degree in 1976.

From 1947-50 and again from 1954-55, Riedel served as assistant paleontologist at the South Australia Museum. The Royal Society awarded Riedel the John Murray Traveling Studentship in Oceanography, which brought him to Scripps Oceanography in 1951. Riedel worked at Scripps as a graduate research geologist and became curator of Scripps’ collection of seafloor cores and dredged rocks in 1955. His later work included writing a manual on curating marine geological specimens. 

Riedel returned to Scripps in 1955 as a junior research geologist after spending a year in Australia and became curator of Scripps’ collection of seafloor cores and dredged rocks. He was promoted to assistant research geologist in 1958, associate research geologist in 1962, and research geologist in 1968. 

Riedel gained a great deal of experience at sea. He participated in the Northern Holiday Expedition, which looked at the geology of mid-Pacific submerged mountains. He was scientific leader on R/V Horizon during the Capricorn Expedition in 1952-1953, and on many Scripps expeditions after that. Riedel was a member of the Argentine Antarctic Expedition organized by the Argentine Navy in 1955-1956 and spent three months in the Weddell Sea on the icebreaker General San Martin, and on the same ship in the Bellingshausen Sea during the following southern summer. 

In 1961, Riedel served as scientific leader for Project Mohole, an effort to drill through the thin ocean crust and directly sample Earth’s mantle undertaken on the drilling vessel CUSS I off Guadalupe Island. This test proved the feasibility of drilling in very deep water. Riedel wrote the summary of coring operations on that expedition, and he was a co-author of the proposal to the National Science Foundation for the establishment of Mohole’s successor, the Deep Sea Drilling Program. The drilling program continues today as the Ocean Drilling Program.

Though they never met, fellow micropaleontologist and Scripps Oceanography scientist Richard Norris knows Riedel’s research well. 

“He used his knowledge of radiolarians to tell the age of mud collected during the first oceanic deep sea drilling effort – the CUSS expedition, immortalized in an article written by John Steinbeck,” said Norris. “That expedition was such a success that it garnered a telegram of congratulations from President Kennedy.” 

Riedel’s work on stratigraphy and on the analysis of sediment cores was especially important to the Deep Sea Drilling Program, and he invested a significant amount of time on the JOIDES Planning Committee which oversaw DSDP. Riedel was named curator of DSDP cores and served on the JOIDES Information Handling Panel beginning in 1990. He also served as chair of the Scripps Geological Research Division from 1978-1983. He was appointed senior lecturer in 1981, and authored more than 40 research papers during his career.

While most of his work focused on radiolarians, Riedel ventured into other fossils, most notably ichthyoliths, fish teeth and scales. Parts of the deep Pacific sea floor are coated with pelagic clay from which nearly all the microfossils have been dissolved away. Riedel discovered that although there were no radiolarians in the clay to date it, there were many ichthyoliths. He worked for decades to develop a new chronometer based on these teeth and scales that could tell time in pelagic clay. As a consequence, Scripps has the largest collections of both ichthyoliths and radiolarians in the world. 

During the last decade of his career at Scripps Oceanography, Riedel experimented with the use of computer-based technologies to create tools for paleontology and biostratigraphy. He helped develop databases and expert systems to assist non-specialists in the identification of radiolarians and the interpretation of ocean sediments. Subsequently, he was one of the founders of the electronic journal Palaeontologia Electronica. 

Riedel retired to Marananga in Australia in June 2000. He is survived by his daughter Catherine of Hamilton, New South Wales, and his sons Philip of Seattle, Wash., and David of Greenbrae, Calif. Due to travel restrictions, no memorial service is planned at this time, but donations to the Australian Conservation Foundation at https://support.acf.org.au/gift_in_memory# are welcome.