Edwards and Coakley

Chem. Erde 63 (2003), 281–328 CHEMIE der ERDE Urban & Fischer Verlag http://www.urbanfischer.de/journals/chemerd GEOCHEMISTRY INVITED REVIEW SCICEX Investigations of the Arctic Ocean System Margo H. Edwards1,* and Bernard J. Coakley2 1 Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii USA 2 Geophysical Institute, University of Alaska, Fairbanks, Alaska USA Received: 7. 7. 2003 · Accepted: 21. 8. 2003 Abstract In 1993 the United States Navy and the marine research community embarked on an ambitious program to study the Arctic Ocean using nuclear-powered submarines. The program, termed SCience ICe EXercise (SCICEX), was designed to simultaneously sample and map the ice canopy, physical, chemical, and biological water properties, seafloor and seabed subsurface. The small size of the Arctic Basin relative to Earth’s other oceans and the unique capabilities of the nuclear submarines, high speed coupled with the ability to operate independently of the sea ice cover, combined to allow the first holistic investigation of an entire ocean basin. The data acquired during eight submarine cruises helped refine hypotheses and models for the broad spectrum of subdisciplines that comprise arctic science and, perhaps more importantly, illuminated the linkages between the various components of the Arctic Ocean system. This paper presents an overview of the SCICEX program, summarizing the results published to date and briefly describing each submarine deployment and the instruments used to acquire various datasets, to demonstrate the important contribution of this collaborative venture to arctic science. Key words: Arctic Ocean, SCICEX, oceanography, ice canopy, seafloor morphology, biogeography * Corresponding address: Margo H. Edwards, Hawaii Institute of Geophysics and Planeto- logy, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822, USA Tel.: ++1-808-956-5232; Fax: ++1-808-956-6530; email: [email protected] 0009-2819/03/63/04-281 $ 15.00/0 282 M. H. Edwards and B. J. Coakley Introduction Surrounding Earth’s northern pole, the Arctic Ocean is a unique, extremely inhospitable environment. For two centuries this region has captured the imaginations of explorers and researchers, who have slowly but persistently investigated it. Results of these expeditions illustrate the extraordinary characteristics of the Arctic Ocean, where rock, water, ice, air and organisms all have important and inextricably linked roles. For example, the weak stratification of the Arctic Ocean below a few hundred meters water depth helps to reveal how the Atlantic and Pacific Oceans mix at their northern bound- aries (Steele and Boyd 1998; Morison et al. 1998; Boyd et al. 2002); when combined with arctic bathymetric data, physical and chemical water properties also validate previously published hypotheses (e.g., Aagaard 1989; Rudels et al. 1994) describing how seafloor morphology regulates the movement of deep and intermediate arctic water masses (Mikhalevsky et al. 1995; Smith et al. 1999; Smethie et al. 2000; Boyd et al. 2000; Gunn and Muench 2001). Perennial ice cover is an exclusive feature of the Arctic Ocean that both influences and is influenced by ocean temperature and circulation (McPhee et al. 1998; Smith and Morison 1998; Björk et al. 2002). The ice canopy affects how much light penetrates the Arctic Ocean, regulating biological growth (Gosselin et al. 1997). Furthermore, the distribution of the arctic ice canopy plays a significant role in the present-day global climate (Clark 1990, and references therein; Aagaard and Carmack 1994, and references therein). Although interconnections between the arctic ice cover and the seabed may seem insignificant given the vertical distance between them in much of the present-day Arctic Basin, arctic ice has in fact provided evidence of ancient climates through apparent and well-preserved evidence of interaction with the seafloor (Polyak et al. 2001). Recognizing the systemic nature of the Arctic Ocean, scientists have developed an array of programs, many of them multidisciplinary, to study the region and describe its contributions to global and local processes. The primary reason cited for studying the present-day Arctic Ocean is to understand its contribution to the global climate. From a planetary perspective, the Arctic Ocean influences both Earth’s surface heat balance and the thermohaline circulation of its oceans (e.g., Johannessen et al. 1994, and references therein). Much of Earth’s atmospheric circulation is generated by gradients that result from heat gain near the equator and heat loss near the poles. The presence of arctic ice cover hinders the heat exchange between the atmosphere and the ocean, effectively suppressing summer heat gain and winter heat loss (Clark 1990). Arctic snow and ice cover also impact Earth’s albedo, reflecting solar energy back into the atmosphere and influencing atmospheric circulation. In the case of thermohaline circulation, the Arctic Ocean modulates the salinity of the northern Atlantic Ocean, affecting the formation of North Atlantic Deep Water (NADW), an important component of the global ocean conveyor (Broecker 1991). NADW results, in part, from the enhanced salinity of the northern Atlantic Ocean produced by the dise- quilibrium of evaporation and precipitation in the Atlantic and Mediterranean seas. In combination with cold temperatures, the higher salinity yields North Atlantic water that is very dense and thus contributes to deep, cold-water production. Broecker et al. (1985) hypothesize that melting arctic ice would lower salinity in the northern Atlantic and consequently reduce NADW production. The result would be less ocean-to-atmosphere heat flux that could, when combined with other influences on global climate such as SCICEX Investigations of the Arctic Ocean System 283 orbital forcing factors, lead to cooler temperatures and increased snow and ice production. The overall effect would create a global climate that cycles between colder and warmer periods, the type of climatic change that has already been documented for Earth. Studies of such a singular environment as the Arctic Ocean are also important because they provide unique perspectives and/or information for a wide variety of scientific disci- plines. For example, the Arctic Basin is the only ocean basin that is predominantly land- locked. Because of the movement of Earth’s tectonic plates, the Arctic Ocean was likely isolated or nearly isolated from the rest of Earth’s oceans for tens of millions of years between the late Mesozoic and the Early Tertiary (Marincovich et al. 1990, and references therein). Deep-water communication between the Arctic and North Atlantic Oceans was not established until the middle Miocene, ~ 15 mybp, and the Arctic Ocean remained unconnected to the Pacific Ocean until ~ 3 mybp. This isolation is significant to marine biologists as it could result in unique fauna associated with recently discovered hydrothermal venting on Gakkel Ridge (Edmonds et al. 2003). Despite all of the compelling reasons to study the Arctic Ocean, it is an inhospitable place where established procedures can only rarely be used to acquire data. Historically, scientists have studied the Arctic Ocean from the air, from ice islands or from ice- breaking surface ships, but none of these approaches are ideally suited for arctic operations. Although planes and helicopters can cover large research areas, use of these platforms is highly dependent on the weather, fuel supply and distance to the nearest safe landing point. Airborne surveys typically employ only remote sensing instruments as it is time consuming and frequently unsafe to land and acquire physical samples. Ice camps have collected excellent oceanographic data, but they operate at the mercy of the elements, drifting where winds and currents dictate. Even icebreakers, with reinforced hulls to help move through the ice, cannot move freely and are unable to access some parts of the Arctic Ocean. Additionally, the interaction between ice and vessel can degrade the quality of the data collected by icebreakers; for example, the noise generated while underway in ice-covered water interferes with acoustic signals received by towed and hull-mounted sonar systems. Nuclear-powered submarines, which are able to move independently and swiftly below the arctic ice canopy, are well suited as surveying and sampling platforms for arctic research (Newton 1994). For decades submarines have been exploring arctic regions, but the data that they collected could not be made available to the general public for reasons of national security (Newton 2000). Although portions of these historical submarine datasets have recently been declassified and released (e.g., Jakobsson et al. 2000), they were acquired during operations focused first on national security and as such did not collect the type of systematic, detailed datasets that arctic scientists prefer to use when addressing specific research questions. The SCICEX program began in January 1993 when the U.S. Navy announced that a nuclear-powered submarine would survey the Arctic Ocean in the summer of that year and invited the U.S. academic community to help plan and participate in the cruise (Langseth et al. 1993). In contrast to standard operating procedures for naval nuclear submarines, the U.S. Navy agreed to allow data collected during 1993 to be published and disseminated in the

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