Abstracts

The nature of hydrothermal circulation along the Gakkel Ridge in the eastern Arctic Basin is presently unknown, but the limited data acquired to date is enigmatic. Thermal and particulate signatures indicative of hydrothermal fluids were found in nearly 80% of the CTD casts from the recent AMORE expedition to the ridge, an astonishing number considering that hydrothermal activity is generally expected to decrease as the spreading rate, and hence thermal structure, of a ridge decreases. Is hydrothermal activity truly ubiquitous on the Gakkel Ridge, or are there a few very large systems that fill the axial valley with hydrothermal tracers, or is it even possible that circulation in the deep axial valley is so restricted that plumes linger exceptionally long periods of time?

The biological characteristics of vent fauna on the Gakkel Ridge are also of great interest. Vent-endemic fauna have been characterized in all of the major ocean basins except for the Arctic, and thus we presently do not know how vent fauna on the Gakkel Ridge relate to species found in the nearby Atlantic and Pacific basins. Nor do we know how Arctic vent fauna may have evolved in an isolated Arctic system since hydrographic communication with the rest of the world’s oceans is limited to exchange across shallow sills. Vent fauna on the Gakkel Ridge constitute the last major piece of the global biogeographic puzzle, with implications that extend beyond domain characterization.

 In order to develop an inter-disciplinary understanding of hydrothermal processes on the Gakkel Ridge a comprehensive set of geological, chemical, and biological data is needed. The data will be difficult to obtain, however, because the ridge is covered with a permanent layer of ice that precludes many of the standard oceanographic and deep-sea technologies employed to find and study hydrothermal systems in the open ocean, including towed vehicles and ROVs.

Building on AUV technology developed to enable ocean bottom seismic studies in the Arctic, we have devised an AUV-based, nested survey strategy that will allow us to map hydrothermal plumes in the water column, find and image vent fields on the seafloor, and obtain biological samples of vent fauna. The major technological challenges include under-ice navigation for surveys, acoustic communication in the Arctic sound channel, and recovery of AUVs through the ice sheet.