Scientists have identified what they describe as the "heartbeat" of the ocean, a previously unknown cycle of marine fertility near Hawai'i that could be fueling fisheries in ways science has not until now recognized.

The newly identified annual bloom of ocean plants in waters immediately north of Hawai'i involves massive soups of marine plants known as phytoplankton. The blooms are visible from satellites, and University of Hawai'i researchers have followed up on satellite data by going out in ships and sampling the vibrant array of marine life there.

The 2005 bloom was the big-gest in recent history, and its strength drew vast schools of all kinds of marine life, UH oceanographer Dave Karl said.

"There were squid jumping out of the water, probably being chased by predators. Our people fish off the deck of the boat, and they found a feeding frenzy going on," Karl said. "You should have seen all the mahimahi and big pelagics (other deep-ocean fishes) they brought back."

Karl said the oceanic phytoplankton blooms north of Hawai'i appear annually, generally in or around summer. They are denser in some years than others. Another researcher, NOAA Fisheries scientist Cara Wilson of Monterey, Calif., said she sees regular blooms between California and Hawai'i, in an area about 30 degrees north latitude.

"They don't occur every year — but almost. We have 17 years of satellite data for the period when they happen, and they have occurred in at least 11 of those 17 years," Wilson said.

Some blooms can cover as much of the Earth's surface as the state of California, she said.

Are the blooms in the two areas related? That's part of the mystery. "We don't know. They may be separate, or they may be a continuum," Karl said.

Satellites monitoring the ocean surface at different wavelengths pick up the blooms as dappled fields of green on the blue oceanic background. The green represents chlorophyll in ocean plants that are converting the sun's energy into food.

What nobody knows is why, each summer, hundreds of square miles of ocean suddenly erupt with life.

"The deep ocean in the middle of the Pacific is like a desert, and I refer to these blooms as ocean oases," Wilson said.

And just as a desert oasis attracts life from all around, in these ocean blooms "you would expect a cascade effect," she said, with bigger species appearing to take advantage of the sudden source of food, and animals such as albacore and swordfish showing up to pick off the bigger creatures.

Oceanic plants are always present in the open sea, but generally in the deep open ocean they are few and they are tiny. Karl said that Hawai'i researchers have found that during the annual summer blooms, larger phytoplankton dominate.

The oceanic plants that don't get eaten eventually die and drift to the bottom, where they are measured in scientists' ocean-floor sediment traps. Karl said that while these summer blooms occur less than 10 percent of the time, they create as much as a third of all the material that falls into sediment traps each year.

"Our understanding of the ocean is that it has two fundamentally different states. The background state has low nutrients, low biomass, low fishery yield and low carbon-dioxide sequestration potential," he said. The latter term refers to the ocean's ability to remove carbon-dioxide from the atmosphere.

The other state — the summer bloom — is a fundamentally different state, with extremely high density of life. It may ultimately be the main driver of mid-ocean productivity in the Pacific — something marine scientists were not even aware of until recently. This pulse of life may have important implications in the understanding of the ocean's overall productivity.

"The ocean has a heartbeat that we've been missing," Karl said.

But there is still a great deal to learn, including how and why it happens, where the phytoplankton get the nutrients to support their sudden growth, and what causes the whole system to die out again. "Something's triggering this that we don't understand," Karl said.

UH oceanographer Roger Lukas said any or all of a half-dozen theories could be involved. The nutrients may be churned up from deep water by strong trade winds or hurricanes; they may be transported in eddies from the California Current; they could be deposited from the air — perhaps coming from the high-altitude dust kicked up by desert storms in China or Hawaiian volcanic dust transported north of Hawai'i by kona winds.

"We've stretched our minds to try to consider all the alternatives," Lukas said.

Wilson suggested that mats of marine life alternately sink into rich, deep water for nutrients, then rise to the surface to gather sunlight. She hopes to cruise into one of the 30-degree-north blooms soon to study it.

Hawai'i scientists are taking measurements at the deep ocean scientific research site Station Aloha, which is 60 miles north of Kahuku Point on O'ahu. And they plan to add to that next year a free-swimming, self-recharging research torpedo called a solar-powered autonomous underwater vehicle.

This yellow, mobile instrument with solar panels will permanently cruise at 3 miles an hour, rising to the ocean's surface for six hours each day to recharge its batteries and communicate its data to satellites. Then it will dive to take measurements at different depths. Karl said it will record salinity, temperature, oxygen levels, level of green plant life and other information.

"When one of these blooms occurs, we want to look at the edge" to see what's different between the conditions inside the bloom and outside, he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.