Icebergs cool and dilute the ocean water they pass through and may stimulate the uptake of carbon dioxide by phytoplankton in the Southern Ocean. The findings have global implications for climate research, according to a paper published by a team of scientists that includes a University of San Diego professor.
The findings “demonstrate that icebergs influence oceanic surface waters and mixing to a greater extent than previously realized,” said USD Associate Professor of Marine Science and Environmental Studies Ronald S. Kaufmann, PhD.
“The implications of this result for climate change are important,” he explained. “Increasing numbers of icebergs that are produced through the breakup of ice shelves could release nutrients into the Southern Ocean as they melt, enhancing the activity of phytoplankton and increasing the rate at which they remove carbon dioxide from the ocean and atmosphere.”
The research, supported by the National Science Foundation, found a persistent change in the physical and biological characteristics of surface waters after the transit of an iceberg. The changes in surface water properties such as salinity lasted at least 10 days, far longer than had been expected.
“The extent and persistence of the iceberg meltwater effects were surprising,” Dr. Kaufmann said. “We knew that iceberg melting affected the upper ocean in the Antarctic. However we didn’t expect that the meltwater from an individual iceberg would be detectable as long as 10 days after the iceberg had passed.”
Icebergs affect the upper ocean ecosystem in multiple ways, Dr. Kaufmann said. “As they melt, they release fresh water that changes the salinity and stability of surface waters. In addition, icebergs contain chemicals that act as nutrients to stimulate phytoplankton growth.”
The new results were published in the journal Deep Sea Research II in a paper titled, “Cooling, dilution and mixing of ocean water by free-drifting icebergs in the Weddell Sea.” The main results of the paper were also highlighted in the March issue of Nature Geoscience.
The research was conducted as part of a multi-disciplinary project that involved scientists from the University of California, San Diego; Monterey Bay Aquarium Research Institute; University of South Carolina; University of Nevada, Reno; Brigham Young University and the Bigelow Laboratory for Ocean Sciences.
Sampling was conducted by a surface-mapping method used to survey the area around a large iceberg more than 32 kilometers (20 miles) long. When the same area was surveyed 10 days later, after the iceberg had drifted away, scientists observed increased concentration of chlorophyll a and reduced concentrations of carbon dioxide compared to nearby areas without icebergs.
“These findings confirm that icebergs contribute yet another dimension of physical and biological complexity to the polar ecosystems,” said Roberta L. Marinelli, program director of the Antarctic Organisms and Ecosystem Program at the National Science Foundation, which supported the study.
— Liz Harman
Photo Credit: Ron Kaufmann