Osmund Holm-Hansen Jr., a research biologist at UC San Diego’s Scripps Institution of Oceanography who revealed long-invisible secrets of microbial life in Antarctica, died Nov. 25, 2021, at home in his sleep at the age of 93.
Holm-Hansen conducted extensive ecological fieldwork in Antarctica, where a mountain is named for him, as well as in coastal southern California, Alaska's North Slope, and the Barents Sea north of Scandinavia.
“Osmund Holm Hansen II was an American hero of Antarctic exploration and discovery,” said Christopher Hewes, a Scripps Oceanography marine biologist, and longtime collaborator.
Holm-Hansen was born Sept. 9, 1928, the youngest of four children, in Sandefjord, Norway. He immigrated to Connecticut with his parents, Osmund Holm-Hansen Jr. and Bergliot Peterson Holm-Hansen, at age 6. Osmund Sr., who held more than 20 patents, was an engineer at Sikorsky Helicopter and later at General Electric.
Holm-Hansen won the Connecticut High School Tennis Championship twice. He attended Harvard University on a four-year scholarship and in 1954 received his PhD in botany at the University of Wisconsin-Madison. In Madison, he met his future wife, Tanya Sprager of Los Angeles.
Holm-Hansen spent 1954-55 at the University of Oslo as a Fulbright Scholar. There he became introduced to polar oceanography and its link to plant physiology. He then became a postdoctoral scholar of Melvin Calvin at the University of California, Berkeley. Holm-Hansen conducted photosynthesis research with Calvin, who would receive the 1961 Nobel Prize in Chemistry.
After three years in Calvin’s laboratory, Holm-Hanson joined the faculty at the University of Wisconsin-Madison in 1958. During the 1959-60 field season he made his first research trip to Antarctica, where he collected water and soil samples from the continent’s dry valleys.
In 1997 the Advisory Committee on Antarctic Names assigned the title of Mount Holm-Hansen in his honor on a peak in the Asgard Range rising 1,920 meters (6,299 feet) between the David Valley and Bartley Glacier. Holm-Hansen explored the area alone, a feat that would never be allowed with today’s safety protocols, said his son, Osmund Holm-Hansen III.
Holm-Hansen left Wisconsin in 1963 to join the Food Chain Research Group of Scripps Oceanography. Over the next decade, he devoted himself to FCRG cruises into the waters off Southern California, laboratory studies, and new research methods.
He developed the fluorometric measurement method of chlorophyll-a that is used today. He also developed, with Rocky Booth of Biospherical Instruments, a method to measure adenosine triphosphate (ATP)—a molecule that stores and transports energy in biological cells—to identify microbial populations in ocean water (1966). Holm-Hansen and Booth patented their ATP instrument, which Science Applications, Inc., Technologies began producing and selling in 1978.
Holm-Hansen took part in three Eltanin cruises to Antarctica (1969-73) to measure chlorophyll and ATP in the Southern Ocean. On these cruises, he found low nutrients and low chlorophyll concentrations in the subtropical waters to the north, and high nutrients and low chlorophyll concentrations (HNLC) in the colder southerly waters around Antarctica.
“He called this the ‘Antarctic Paradox’ since light and macronutrients, the major limiting factors of phytoplankton growth known at the time, were abundant, but there was little phytoplankton,” Hewes said.
In the early 1980s, Holm-Hansen assessed the ecological impact of oil drilling in Prudhoe Bay, Alaska, in connection with the adjacent Arctic National Wildlife Refuge. He also collaborated with Egil Sakshaug of the Norwegian University of Science and Technology. He worked with Sakshaug during the Norwegian Research Program for Marine Arctic Ecology (1984-89) in the Barents Sea and nearby areas of the sub-Arctic.
In 1981, Holm-Hansen served as a chief scientist for one leg of the Vulcan Expedition to Antarctic waters. He again served as a co-chief scientist in 1983 aboard the U.S. Coast Guard Cutter Polar Star on its historic expedition that circumnavigated Antarctica. This earned him the Antarctic Service Medal.
In 1986, Holm-Hansen co-established the Research on Antarctic Coastal Ecosystem Rates (RACER, 1986-1992) group. This study was designed to test several hypotheses regarding the interaction of biological and physical processes in the coastal areas of the Antarctic Peninsula and especially the importance of this region as a nursery for Antarctic krill (Euphausia superba).
International concern began emerging in the late 1980s over the opening of the Ozone Hole in the skies above the Antarctic Peninsula, the result of increasing atmospheric inputs of greenhouse gases. Holm-Hansen’s team working at Palmer Station, Antarctica, found—in conflict with other claims—that the resulting increase in ultraviolet light had little effect on photosynthetic productivity in the water column.
Starting in 1990, Holm-Hansen joined NOAA’s Antarctic Marine Life Resources (AMLR, 1990-2010) Program. These annual ship surveys occurred around the Elephant Island region off the northwestern tip of the Antarctic Peninsula.
Holm-Hansen and team, performing both experiments and studies at sea, found considerable evidence that both light availability and iron concentrations regulated phytoplankton productivity. The nature of the Antarctic Paradox became clearer when Hewes brought him satellite imaging data of surface chlorophyll concentrations off the coast of Western Antarctica in 1998.
“Oz immediately pinned the color printout of this image front and center of his office, and claimed it was the most significant ‘Aha!’ moment of his life,” Hewes recalled.
After nearly 30 years, Holm-Hansen, Hewes, and other scientists finally resolved the complex and nuanced conditions that caused the Antarctic Paradox and more. They found that two different sources of high nutrient, low chlorophyll water sources were blending. One source was iron-rich and highly saline, but deep mixing limited phytoplankton growth through light availability. The opposite source was iron-poor water (the paradox), but its less saline property provided a shallow mixing layer that maximized the exposure to light. The blending of these source waters created a condition of both available iron and light that allowed phytoplankton growth, thus blooming, to occur.
Holm-Hansen is survived by his son, Osmund Holm-Hansen III, and a grandson, Per Holm-Hansen, of La Jolla, Calif.