What’s up with GP15?

“GP15” is the code name of this GEOTRACES research expedition from Alaska to Tahiti. GP15 draws a vertical line down the middle of the Pacific Ocean at longitude 152° West. The 67-day voyage aboard the Research Vessel Roger Revelle spans more than 5,000 miles of ocean.

Clouds off the stern of the Research Vessel Roger Revelle near Vancouver Island. Photo: Alex Fox

“GP15 is like the Pacific Ocean’s greatest hits album,” says Co-chief Scientist Phoebe Lam of the University of California, Santa Cruz. “If you were going to choose one track to understand every major ocean process, this would be a strong contender.”

This expedition is a study of extremes. It begins collecting samples of seawater in the marine equivalent of a rainforest and ends in an underwater desert.

GP15 cruise-track
The path of GP15 along longitude line 152° West. Each dot represents a station where the expedition will pause to collect samples. The different colors indicate how many measurements must be retrieved from each station. Red dots are “Super Stations,” which take multiple days to complete. Blue and purple dots are different kinds of “Full Stations,” typically requiring 24 or 36 hours. White dots are “Demi-Stations,” that can be completed in less than a day. Finally, green dots are places the R/V Roger Revelle will stop in port. Image: GEOTRACES

The waters off Alaska are filled with microscopic plants called phytoplankton. They are what drive Alaska’s productive fisheries and are the dinner bell to which giant whales are drawn. But phytoplankton depend on abundant nutrients like nitrogen and rare trace nutrients like iron to turn the sun’s energy into food. GP15’s investigations will probe where exactly those nutrients and others can be found, how abundant they are and where they’re coming from.

Tahiti may be known for rainbow studded coral reefs, but the ocean surrounding those reefs is crystal clear precisely because it is so devoid of nutrients. Without abundant nutrients, phytoplankton become scarce and different ocean processes come into play, all of which will be captured by GP15’s samples.

A sunset at sea from the bridge of the Roger Revelle. Photo: Kenneth Olsen

Bookended by these two divergent undersea ecosystems, GP15 will chart how one extreme transforms into the other. Along the way, the 37 scientists aboard the Roger Revelle will sample water that hasn’t seen the sun in 1000 years, pass by hydrothermal vents—thought to be a potentially significant source of iron—and skirt a hotbed of deep sea mining activity.

Deep sea mining has the potential to stir up toxic trace elements, and this GEOTRACES expedition is perfectly positioned to take a chemical snapshot of these waters before any underwater excavation begins. An unbiased baseline of the area’s ocean chemistry will ensure that the environmental impacts of deep sea mining can be laid bare.

Members of the science team work around the clock to make the most of GP15’s time at sea. Photo: Alex Fox

The data collected on GP15 will complement the findings of the last GEOTRACES expedition, conducted in 2013, from Peru to Tahiti—the horizontal to GP15’S vertical line.

At a time when the world’s climate is changing ever more rapidly, the oceans remain a bellwether. The oceans absorb more and more carbon dioxide and heat every year, and unless large scale studies like GP15 continue, the consequences may blindside humanity.

GP15 blog posts written by Alex Fox unless otherwise stated.

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GEOTRACES GP15 is supported by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.

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