or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] ofor Th e The to: [email protected] Oceanography approval Oceanography correspondence all portionthe Send Society. ofwith any permitted articleonly photocopy by Society, is of machine, reposting, this means or collective or other redistirbution This article has This been published in S P E C I A L Iss U E O N O C E A N E XPL O RATI on Oceanography , Volume 20, Number 4, a quarterly journal of The 20, NumberOceanography 4, a quarterly Society. , Volume Exploring the Submarine Ring of Fire C Mariana Arc - Western Pacific The 2007 by opyright Oceanography Society. B Y Ro B E R T W. E M B L E Y, E D WA R D T. B A K E R , D AV I D A . B UTTERFIELD, WILLIAM W. C HAD W I C K J R . , J O H N E . L UPTon , J os E P H A . R E S I N G , Co R N E L E . J . D E Ron D E , Ko -ICHI NAKAMURA, VERE N A T U nn I C L I F F E , J O H N F. Dow E R , A N D S U S A N G . M ERLE A ll rights reserved. P ermission is granted to copy this article for use in teaching and research. article use for research. and this copy in teaching to granted is ermission P O B ox 1931, ox R ockville, R epublication, systemmatic reproduction, reproduction, systemmatic epublication, MD 20849-1931, U S A . 68 Oceanography Vol. 20, No. 4 Sampling an erupting volcano at 550-m the 65,000-km-long mid-ocean ridge submarine volcanism that creates vol- depth, discovering roiling pools of liq- (MOR) where new oceanic crust is cre- canic arcs along subduction zones land- uid sulfur at 400-m depth, watching ated (Figure 1, green lines). The volcanic ward of oceanic trenches. Most of these tropical fish swimming amid fields of rocks accreted at the MOR are almost intra-oceanic arcs (ocean-ocean colli- black smoker vents, and encounter- entirely basaltic in composition and sions) and island arcs (ocean-continent ing a blizzard of liquid carbon dioxide typically erupt at water depths between collisions) occur in the western Pacific globules rising from fractured lava flows 2000 and 4000 m. The fundamental role (Figure 1). Subduction zones process at 1600-m depth all sound like wishful of Earth’s primary accretion boundaries oceanic crust and upper mantle in a thinking or scenes from a science fiction in creating the ocean basins has provided broad, deep zone that has been called movie. But, we had the good fortune a strong rationale for detailed studies of the “subduction factory” (Stern, 2002). to observe these and other previously the MOR since the 1960s. The discovery These subduction factories are the pri- unseen phenomena between 2004 and of hydrothermal activity and associ- mary agents for recycling oceanic crust 2006 during a series of expeditions to the ated deep chemosynthetic life on MORs back into Earth’s mantle and returning Mariana arc in the western Pacific. We in the late 1970s (see Haymon et al., mantle volatiles to the oceans (Figure 2). describe here several of the most inter- this issue) provided additional impetus Although seafloor drilling is now pro- esting sites, along with their geologic and for this research. viding access to the uppermost portions oceanographic contexts. Although the MOR remains an of subduction zones, seismological and Some 70% of Earth’s volcanism is important research area, the past decade chemical studies are critical to under- B Y Ro B E R T W. E M B L E Y, E D WA R D T. B A K E R , D AV I D A . B UTTERFIELD, submarine, and most of it occurs along has seen new attention focused on the standing the deep regions. The lavas and WILLIAM W. C HAD W I C K J R . , J O H N E . L UPTon , J os E P H A . R E S I N G , Co R N E L E . J . D E Ron D E , Ko -ICHI NAKAMURA, VERE N A T U nn I C L I F F E , J O H N F. Dow E R , A N D S U S A N G . M ERLE Figure 1. Locations of intra-oceanic arcs, island arcs, and other plate boundaries. Modified after de Ronde et al. (2003) Oceanography December 2007 69 Figure 2. Schematic section through the upper 140 km of a subduction zone, showing the principal crustal and upper mantle components and their interactions. Modified after Stern (2002) fluids sampled at the seafloor, in drill 100–250 km from the trench axis along a EXPLORING EARTH’S holes, or on tectonically exposed out- band above the zone of maximum melt InTRA-OCEANIC ARCS crops provide the only direct clues to generation, whose location is determined Interest in submarine arc volcanoes is processes beyond our reach. by the pressure and temperature of the increasing. Because these volcanoes are The major volcanic-tectonic features mantle and the rate of dehydration of the main portals through which volatiles of an intra-oceanic subduction zone the downgoing plate (Stern, 2002). The (primarily H2O, CO2, and SO2) released (Figure 2) are summarized in several release of water from the slabs down to from the downgoing oceanic plate are review papers (Fryer, 1996; Stern, 2002; depths of 100 km or more decreases the returned to the ocean, their output rep- Stern et al., 2003), so we provide only melting point of the mantle and initi- resents an important but as yet unknown a brief synopsis here. The trench is the ates magma accumulations that eventu- part of the oceanic volatile budget. Their depression caused by bending and frac- ally erupt onto the ocean floor, forming volcanic emissions are injected into the turing of the subducting oceanic plate. chains of volcanoes. Approximately 75% ocean at relatively shallow depths, mostly The forearc is the site of initial interac- of all subduction-zone-related subma- less than 1000 m, providing opportuni- tion between the two plates, marked by rine volcanoes occur within the Tonga- ties to study the interaction of volcanic fracturing, serpentinization, accretion of Kermadec, Izu-Bonin-Mariana, and New and hydrothermal chemicals and upper- sediments, or subduction erosion. The Hebrides intra-oceanic arcs (de Ronde ocean biological processes. In addition, back-arc spreading centers and back-arc et al., 2001, 2003). These and other the wide range of host-rock composi- rift zones result from seaward migration intra-oceanic arcs account for more than tion and high gas content produces a of the trench and/or plate divergence 15% of the total length of Earth’s sub- chemical variability of hydrothermal (Karig, 1971). The magmatic arc lies duction zones (Bird, 2003). emissions much broader than found on 70 Oceanography Vol. 20, No. 4 MORs. Finally, because of these systems’ et al., 2001), expanding to the mid html). These surveys of the Mariana and isolation from one another (the “point to northern reaches of the Kermadec Tonga-Kermadec arcs were followed by source” nature of their emissions), arc arc in 2002 and 2004 (de Ronde et al., dive campaigns using manned submers- volcanoes sponsor distinct, sometimes 2007) and farther north to the Tonga ibles and remotely operated vehicles unique, hydrothermal fauna from vol- arc in 2003 (Massoth et al., 2005). (ROVs) to target some of the most active cano to volcano, resulting in enhanced Similar work on the Mariana arc began sites. As of 2007, more than 80 dives with biogeographical diversity. The modern era of subduction- zone exploration began in the 1980s with large-scale mapping using then Some 70% of Earth’s volcanism is submarine, new multibeam and side-scan sonars and most of it occurs along the 65,000-km-long along with human-occupied vehicles such as the Japanese Shinkai 2000 and mid-ocean ridge (MOR) where new oceanic 6500 and the American Alvin. Though crust is created... these pioneering studies of the Izu Bonin (Glasby et al., 2000; Ishibashi and Urabe, 1995) and Mariana (Fryer et al., 1997; McMurtry et al., 1993; Stuben in 2003 (Embley et al., 2004; Resing et submersibles (Shinkai 6500, PISCES V) et al., 1992) arcs focused on only a few al., 2003b; http://oceanexplorer.noaa. and ROVs (ROPOS, Jason 2, and Hyper- active sites, they provided impetus for gov/explorations/03fire/welcome. Dolphin 3000) have been conducted on subduction-zone emphasis that began html), and was followed by in situ stud- more than 26 submarine volcanoes in in the late 1990s. ies using remotely operated vehicles the Mariana (12), Kermadec (10), and Systematic bathymetric and water- in 2004 (http://oceanexplorer.noaa. Tonga (4) arcs (Embley and Investigators, column surveys of the major intra- gov/explorations/03fire/welcome.html), 2006; Massoth et al., 2005; Stoffers et oceanic arcs were initiated in 1999 along 2005, and 2006 (http://oceanexplorer. al., 2006). In this paper, we highlight the southern Kermadec arc (de Ronde noaa.gov/explorations/06fire/welcome. the results of 2003–2006 expeditions to the Mariana Arc. RoBERT W. EMBLEY ([email protected]) is Senior Research Scientist, Pacific Marine Environmental Laboratory (PMEL), National Oceanic and Atmospheric MARIANA ARC Administration (NOAA), Newport, OR, USA. EDWARD T. BAKER is Supervisory The Izu-Bonin-Mariana subduction zone Oceanographer, PMEL/NOAA, Seattle, WA, USA.