Download the full cruise report as an PDF file.
The Arctic GAkkel Vents Expedition (AGAVE) took place on the IB Oden from July 1 – August 10, 2007. Major funding for the cruise came from the United States through the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the Woods Hole Oceanographic Institution (WHOI). The expedition represented an international collaboration between scientists in the United States, Sweden, Japan, and Germany, and was part of an International Polar Year (IPY) project entitled, “Biogeography and Geological Diversity of Hydrothermal Venting on the Ultra-Slow Spreading Arctic Mid-Ocean Ridge.” The participant list for the expedition can be found in Table 1.
The AGAVE expedition incorporated two sets of complementary, but nevertheless separate, objectives – scientific goals pertaining to hydrothermal venting and engineering goals pertaining to the development of robotic vehicles for deep-sea research under ice. To first-order the scientific goals are associated with the NSF-funded portion of the research and the engineering goals are associated with the NASA-funded portion, but this categorization is not strict. Some of the NSF research was focused on vehicle development, and some of the NASA research was focused on astrobiological science. The complete set of cruise objectives is described below.
The overarching scientific objective of the AGAVE expedition is to study the geological, chemical, and biological characteristics of hydrothermal venting on the Gakkel Ridge.
The Gakkel Ridge in the Eastern Arctic Basin is the ultra-slow spreading end-member in the global mid-ocean ridge (MOR) system. The North American and Eurasian plates diverge at rates of 3-7 mm/yr along the Gakkel Ridge (Figure 1), nearly two orders of magnitude slower than the fast spreading end-member (southern East Pacific Rise). This ultra-slow divergence completely changes the geologic nature of the ridge, and the results of recent work make it clear that many geologic processes have a completely different character in these environments. We are only just beginning to understand how basic ridge processes such as deformation and extension, crustal accretion, and hydrothermal flow play out at such slow spreading rates [Michael et al., 2003; Jokat et al., 2003; Dick et al., 2003; Edmonds et al., 2003].
The unique geology of the Gakkel Ridge affects all of the first-order parameters that control hydrothermal circulation. The thermal structure, permeability, and chemistry of the host rock on the Gakkel Ridge are all directly impacted by the extremely slow spreading rate. Intuitively, hydrothermal systems might be expected to be rare on the magmatically starved Gakkel Ridge, but thermal and particulate signatures indicative of hydrothermal fluids were found in nearly 80% of the CTD casts from the 2001 Arctic Mid-Ocean Ridge Expedition (AMORE) expedition to the ridge (Edmonds et al., 2003; Michael et al., 2003). How do these water column anomalies relate to hydrothermal discharge on the seafloor and fluid circulation within the crust? Are there massive hydrothermal systems that generate pervasive, large-scale anomalies in the water column? Are hydrothermal systems densely distributed along the ridge? Or perhaps are the currents along the ridge and within the axial valley limited such that hydrothermal fluids linger exceptionally long periods of time in the water column? The AGAVE expedition seeks to answer these first order questions so that we can begin to understand the geological and chemical aspects of hydrothermal processes on the Gakkel Ridge.
Along with being an end-member geological environment, the Gakkel Ridge is also a unique MOR in that it is hydrographically isolated within the Arctic Basin. Communication with the rest of the world's oceans is limited to exchange across shallow sills, and this has important implications for the evolution and ecology of resident chemosynthetic vent fauna. Vent-endemic fauna have been characterized in all of the major ocean basins except for the Arctic, and therefore we 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 end-member, hydrographically isolated Arctic ridge system. Characterizing vent fauna on the Gakkel Ridge is the last major piece of the global biogeographic puzzle.
The overarching engineering objective of the AGAVE expedition is to develop new technologies to enable deep-sea research in ice covered oceans.
In order to develop an understanding of hydrothermal processes on the Gakkel Ridge it is necessary to conduct detailed investigations of the deep seafloor in regions that are permanently covered in ice. The ice cover inhibits or precludes many of the standard oceanographic and deep-sea technologies employed to find and study hydrothermal systems in the open ocean. In particular, remotely operated vehicle (ROV) operations are not presently feasible in ice-covered bodies of water, and submersible operations are considered too risky owing to the difficulties of recovery through the ice. Even relatively straightforward operations, such as CTD casts, are hindered owing to the fact that the tending icebreaker cannot make way in the ice with a wire over the side, but rather must drift in the ice pack. These considerations motivate the development of new techniques that decouple the deep-sea surveying process from the drifting ice.
The motivation to develop novel under-ice survey capabilities is not limited to missions on Earth. The search for life on other planets includes the possibility of volcanically hosted vent fields beneath the ice-covered ocean of Europa, a moon of Jupiter. The search for vent fields under the Arctic ice cap on Earth thus presents a technical analogy for similar missions on Europa. In both cases the most efficient technical solution appears to be the development of robotic vehicles that are capable of being deployed and recovered from within the ice, and that are capable of carrying sensors for the detection and localization of chemosynthetic biological communities hosted by vent fields on the deep seafloor. To this end a major objective of the AGAVE expedition is the development of autonomous underwater vehicle (AUV) technology for under-ice missions. AUVs are presently being used at an ever-increasing rate to conduct science missions in the open ocean, but their operation under-ice has been limited to deployments from the ice edge, with limited success to this point. AUVs have never been deployed and recovered from an icebreaker within the ice pack, and all of the previous AUV missions under-ice have operated at shallow depths less than a few hundred meters. A major objective of the AGAVE expedition is to develop and demonstrate AUV technology for deep-sea missions within the permanent pack ice.
Ultimately the AUVs must also be capable of acquiring biological samples, particularly for astrobiology missions to Europa. The development of computer vision and dexterous manipulation systems for an AUV is an active area of research in collaboration between WHOI and the University of Maryland's Space Systems Lab, but these systems were not sufficiently advanced to allow for their utilization on the AGAVE expedition. Therefore it was also necessary to develop a separate wireline platform for imaging and sampling, and the development and demonstration of such a system was a second major engineering objective.
In all three new vehicles were developed for the AGAVE expedition. The PUMA AUV was designed to map hydrothermal plumes in the water column. The JAGUAR AUV was designed to conduct high-resolution bathymetric, magnetic, and photographic surveys on the seafloor. The CAMPER wireline vehicle was designed to conduct high-resolution digital imaging surveys and to acquire geological and biological samples from the deep seafloor. The development and demonstration of these three vehicles and the support systems for their operation under-ice constitute the major engineering activities for the AGAVE expedition.
Ultra-slow spreading ridges are characterized by a heterogeneous crustal structure. The generation and delivery of magma is restricted by a relatively cold thermal structure, and tends to be focused to discrete regions along-strike. As a result, some ridge segments have a reasonably well-developed igneous layer, while others are magma starved and consist primarily of peridotite terrains exhumed by tectonic extension. Hydrothermal circulation in these disparate environments is expected to be fundamentally different in nature owing to the differences in thermal structure, host rock substrate, and permeability structure between basaltic (magmatically robust) and peridotitic (magmatically starved) geologic settings.
Intriguingly, evidence of hydrothermal venting in the form of water column plume anomalies was ubiquitous in wireline sensor data from dredges along essentially all portions of the Gakkel ridge during the AMORE expedition in 2001, including tectonic regions with predominantly peridotite exposures on the seafloor. As a result, one of the objectives of the AGAVE expedition was to conduct a direct comparison between venting in basaltic vs. peridotitic settings. To this end two field areas were chosen for plume mapping and seafloor surveys – the 7°E segment, which is a peridotite environment, and the 85°E segment, which is a basalt environment that is believed to have experienced a large magmatic event in 1999. Given the ports of call for the expedition (Longyearbyen to Tromso) it made sense to begin by working at the 7°E site, and then to finish at the 85°E site (Figure 1).
Figure 1. Oden's trackline during the AGAVE leg (Longyearbyen to Tromso via the Gakkel Ridge) and multibeam fieldsheets.
Table 1. Participant List.
|Reves-Sohn, Robert||WHOI||Chief scientist, lead geophysicist||USA|
|Singh, Hanumant||WHOI||Co-chief, lead engineer||USA|
|Shank, Timothy||WHOI||Co-chief, lead biologist||USA|
|Humphris, Susan||WHOI||Co-chief, lead geologist||UK|
|Edmonds, Henrietta||U. Texas, Austin||Co-chief, lead chemist||USA|
|Winsor, Peter||WHOI||Physical oceanographer||Sweden|
|Helmke, Elisabeth||AWI||Sediment microbiologist||Germany|
|Liljebladh, Bengt||Goteburg University||Physical oceanographer||Sweden|
|Nakamura, Ko-ichi||AIST||Water chemistry||Japan|
|Engineering and Instrumentation|
|Kemp, John||WHOI||Deck operations||USA|
|Upchurch, Lucia||U. Texas, Austin||Science||USA|
|Sato, Taichi||ORI, U. Tokyo||Engineering||Japan|
|Media and Outreach|