冰层覆盖下的浮游植物也会开花

A team of researchers, including scientists from Woods Hole Oceanographic Institution (WHOI), discovered a massive bloom of phytoplankton（浮游植物） beneath ice-covered Arctic waters. Until now, sea ice was thought to block sunlight and limit the growth of microscopic marine plants living under the ice. The amount of phytoplankton growing in this under-ice bloom was four times greater than the amount found in neighboring ice-free waters. The bloom extended laterally more than 100 kilometers (62 miles) underneath the ice pack, where ocean and ice physics combined to create a phenomenon that scientists had never seen before.

The study, published June 8 in the journal Science, concluded that ice melting in summer forms pools of water that act like transient（短暂的） skylights and magnifying lenses. These pools focused sunlight through the ice and into waters above the continental shelf north of Alaska, where currents steer nutrient-rich deep waters up toward the surface. Phytoplankton under the ice were primed to take advantage of this narrow window of light and nutrients.

"Way more production is happening under the ice than we previously thought, in a manner that's very different than we expected," said WHOI biologist Sam Laney, who was part of the multi-institutional team led by Kevin Arrigo of Stanford University.

Just as a rainstorm in the desert can cause the landscape to explode with wildflowers, this research shows that events like pooling melt water can happen on very short timescales in the Arctic yet have major effects on the ecosystem.

"If you don't catch these ephemeral events, you're missing a big part of the picture," Laney said.

The unexpected discovery occurred during a 2011 expedition aboard the U.S. Coast Guard icebreaker Healy. It was part of the NASA-funded ICESCAPE program to investigate the impact of climate change in the polar Chukchi and Beaufort seas.

The scientists found themselves in the right place at the right time in early July of 2011, as the Healy made its way above the Arctic Circle and into year-old ice. Atop the meter-thick ice, pools of sky-blue melt water were accumulating as the Arctic summer progressed.

Researchers expected that, as in years past, the waters beneath the ice would have minimal amounts of chlorophyll -- the fluorescing hallmark of photosynthetic（光合作用的） marine plants. Instead, they observed the opposite. As the ship broke further into the ice, chlorophyll in the dark waters below shot up to levels rarely observed even in the most productive ocean regions. It became evident that there was a phytoplankton bloom of astonishing magnitude happening under the ice. Optical measurements showed that four times as much light penetrated ice covered by meltwater ponds than ice covered by snow.