Expedition Report
Jeff Standish, Joint Program Student,
and Henry Dick, Senior Scientist

Of all the world's oceans, the most inaccessible is the Arctic. Covered by ice and shrouded in darkness for six months of the year, it represents the last great frontier for ocean sciences. The few reliable maps available at the turn of the century were made by nuclear submarine only in the last few years. To those of us studying ocean ridges and the evolution of Earth's deep interior, it was the last unexplored ocean ridge—a key gap in our global collection of rock from the ocean basins.

Some three-fifths of Earth's crust forms at ocean ridges, and the Gakkel Ridge occupies a unique and important place within the global ridge system. It runs over the top of the world, extending 1,080 miles from off the northeastern corner of Greenland, across the Eurasian Basin, to the continental margin in the Laptev Sea. It is the deepest ocean ridge, and it has the slowest spreading rate, decreasing rapidly west to east from one inch per year near Greenland to a half an inch per year at its eastern end.

Because fast and slow-spreading ridges exhibit great differences in the composition and structure of the ocean crust, theory predicted that as seafloor spreading slows along the Gakkel Ridge, a major change would occur. Namely, volcanism would wither as seafloor spreading decreased, and the ridge would become essentially a crack in the planet where solid mantle rock from depth would be pulled up by the spreading plates to form new seafloor.

Lavas erupting from deep within the earth at mid-ocean ridges provide the principle means for inferring the composition of the mantle and its global variation. The Gakkel Ridge has long tantalized geochemists because sampling rocks along its length promised a view into the interior of the earth beneath the pole of planetary rotation. It also presented, however, the possibility of sampling mantle peridotite over a large region and directly observing lateral variations in mantle composition—a unique opportunity simply not available anywhere else.

In July 2001, US oceanographers not only got their first detailed look at the Gakkel Ridge but also gained a new ocean to explore when the US Coast Guard's icebreaker Healy made its first research voyage. Along with WHOI Research Specialist Jim Broda and Postdoctoral Investigator Deborah Hassler, we were fortunate to be among 21 US scientists embarking from Tromso, Norway, for an epic two-ship expedition to the Arctic Ice Cap.

Among the scientific party were Joint Program graduates David Graham (Oregon State University) and Hedy Edmonds (University of Texas at Austin) and a former Summer Student Fellow, Peter Michael (University of Tulsa), the lead scientist aboard Healy. We were accompanied by German scientists aboard R/V Polarstern, including another Joint Program graduate, Jon Snow (Max Planck Institute for Chemistry, Mainz, Germany). Our objective was to do detailed rock sampling along a 1,000-kilometer (690-mile) section of actively spreading ridge and to monitor for hydrothermal plume activity within the rift valley.

A great deal of logistical and scientific planning preceded this expedition, yet the largest unknown remained: How would Healy perform on its first scientific voyage? One old Arctic hand predicted we wouldn't be able to do "dredge 1." No one even contemplated collecting high-quality SWATH bathymetery data while pounding through the ice. It did not take long for Healy to impress us, both with its ice breaking and its technological strength. Any doubts about Healy's capabilities were quickly put to rest, as we, along with the Polarstern scientific party, proceeded to conduct 200 successful dredges and to produce a high resolution bathymetry map.

The character of the Gakkel Ridge turned out to be a bit different than predicted. As we moved from west to east, instead of gradually dying away, the volcanoes abruptly stopped at 3°E. From there, for nearly 100 kilometers (60 miles), we found mantle rock from deep within the earth rising up in great solid slabs to form new seafloor.

Then, surprisingly, a new volcano appeared. Further east, there was more mantle rock, then another volcano, and so on as far as we surveyed. This showed for the first time that ocean ridge volcanism isn't simply a primary function of spreading rate. The generation of magmas deep within the earth's interior is more complicated than ever imagined!

Based on the ultra-slow spreading rate, current dogma also predicted near absence of hydrothermal vent activity—as spreading rate slows, less volcanism should also mean that hydrothermal vents disappear. However, on a Knorr cruise in 2000 to the slow-spreading Southwest Indian Ridge, we sampled six new hydrothermal deposits in a relatively small area of ridge.

Did this mean that hydrothermal venting was more frequent than predicted for ultra-slow spreading ridges? This was dramatically confirmed when we dredged several hydrothermal deposits on the Gakkel Ridge and our sensors registered hydrothermal plume anomalies at 12 separate sites. Nearly as many hydrothermal plumes were discovered in this one cruise as in the last 20 years of Mid-Atlantic Ridge exploration.

Along with vent sulfides dredged from an active black smoker, we recovered a variety of biological fauna—a discovery of great potential importance. Like the Mediterranean Sea, the Arctic Ocean is unusual because of its limited connections to other major oceans-with the extraordinary feature of being covered by ice. The abundant biology we found, then, was a great surprise.

In addition to the unexpected scientific discoveries and the overall success of the cruise, we all became "polar explorers." On September 6, 2001, Healy reached 90°N latitude. None of us will ever forget the exhilaration of stepping off Healy to stand at the point where all Earth's lines of latitude converge and having the entire world directly below our feet!

In addition to the many scientific discoveries of this cruise, to many, its most important aspect was the remarkable capabilities of the ship. With the advent of Healy, carefully planned by a cooperative Coast Guard/US science community effort, the US has gone in a single season from a minor presence in the Arctic Ocean to perhaps the principal player.

First printed in the Woods Hole Oceanographic Institution 2001 Annual Report