Scientists Discover Huge Phytoplankton Bloom in Ice Covered Waters
“Although the under-ice light field was less intense than in ice-free waters, it was sufficient to support the blooms of under-ice phytoplankton, which grew twice as fast at low light as their open ocean counterparts,” the study notes.
The ship conducted transects into the ice pack to determine how far and deep the bloom extended. Measurements of biomass showed the largest part of the bloom occurred far away from the open ocean, under thick ice and close to water upwelling at the continental shelf break, where the shallow coastal shelf plunges steeply into deeper water.
Another member of the ICESCAPE team, WHOI physical oceanographer Bob Pickart showed that easterly winds churned out by monster storm systems along the Aleutian Islands can reverse the current along the shelf break. The change in circulation drives cold, nutrient-rich water up from the abyss and refreshes the supply of nutrients available to phytoplankton growing near the surface.
“Without a doubt the bloom was enhanced at the shelf break,” Pickart said.
As the melt pools introduced light through the ice, phytoplankton in shelf break waters likely experienced something akin to an all-you-can-eat buffet.
What types of organisms participated in the bloom? Laney caught them on camera with an instrument he had brought to sea—the Imaging FlowCytobot, an automated microscopic imaging system invented at WHOI and built by Laney and co-developer Dr. Rob Olson.
Since their return, Laney and MIT/WHOI Joint Program graduate student Emily Brownlee have been working with the Imaging FlowCytobot’s other co-developer and ICESCAPE team member, WHOI biologist Heidi Sosik, to sort through and classify organisms in the millions of images collected by the instrument and unravel intricacies of the under-ice bloom. The images showed that the bloom was not caused by fallout from algae growing on the ice, but rather it contained different organisms that seized the confluence of currents, light, and nutrients.
The Imaging FlowCytobot offers tantalizing insights into the microbial dynamics and food web of this dramatic Arctic algal boom. For example, the images consistently showed some phytoplankton in the bloom in a half-munched state, offering clues to the planktonic grazers that might be eating them.
Discovering the under-ice bloom “was very serendipitous,” Pickart said, but the difficulty of exploring the harsh, remote region also leaves it wide open for surprises.
The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans’ role in the changing global environment. For more information, please visitwww.whoi.edu.
