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1 . American Samoa     American Samoa
American Samoa consists of five main volcanic islands and two atolls, which are situated in the central tropical South Pacific (Figure 10.1) at approximately 14°S and 170°W. American Samoa is the only U.S. territory located south of the equator. It experiences seasons opposite to those in all other U.S. areas, and has atmospheric and oceanic circulation patterns found in the southern hemisphere. The five volcanic islands are part of a hotspot chain that also includes Upolu and Savaii, the two larger volcanic islands of (independent) Samoa to the west of American Samoa, several seamounts west of Samoa, ridges extending southeast from Tutuila and northwest from Ofu, and an active undersea volcano east of the island of Tau in American Samoa, named Vailuluu. American Samoa also includes two atolls, Swains and Rose, both of which are much older than the volcanic islands and not geologically related.



The American Samoa archipelago is composed of high volcanic islands and low-lying atolls that have narrow reef flats (50-500 m) and steep offshore banks dropping to oceanic depths within 0.5-8 km from shore. The shallow water habitats are composed primarily of fringing reefs, a few offshore banks, and the two atolls. The archipelago (Figure 10.2) lies within the South Equatorial Current, characterized by warm (28-30°C) westward flowing, oligotrophic surface waters, with a deep thermocline (approximately 120-200 m). Area winds are generally light and variable during the austral summer rainy season, except during cyclones, with consistently stronger trade winds from theeast-southeastd ominating in other seasons (Figure 10.3). All of the islands are seasonally impacted by episodic long period swell generated from the mid-latitude cyclone belts of both the northern and southern hemisphere (30-60° latitude) and more infrequently by large tropical cyclones, which have historically impacted the islands on 2-7 year timescales. These tropical cyclones and related storms may bring large swells, destructive winds and heavy rains.Spur and groove reef formations are fairly common on the reef slope. On Tututila, the reef slope descends to about 20-30 m where it reaches a rubble or sand covered shelf (Figure 10.4). The shelf extends for about 1-4 km and reaches about 100 m depth at its outer edge, ending in a near-vertical escarpment. The escarpment is composed of layers of limestone about 5-10 cm thick and extends down to at least 350 m, where a talus slope of calcareous sand and debris extends below 400 m depth (Wright, 2005).



Multibeam sonar surveys by the NOAA Pacific Islands Fishery Science Center, Coral Reef Ecosystem Division (PIFSC-CRED) team has revealed that the shelf around Tutuila has a number of banks on it, some of which form an interrupted chain resembling a drowned barrier reef, a term used for it as early as 1921 (Chamberlin, 1921;Davis, 1921). Taema Banks at the mouth of Pago Pago harbor and Nafanua Banks, which extends from Aunuu Island toward Taema Banks, are believed to be part of this drowned barrier reef. Although both banks have coral on their outer slope and a portion of their tops, the banks have not yet been explored.
Source: D. Fenner, M. Speicher, S. Gulick, G. Aeby. S.C. Aletto, P. Anderson, B. Carroll, E. DiDonato, G. DiDonato, V. Farmer, D. Fenner, J, Gove, S. Gulick, P. Houk, E. Lundblad, M. Nadon, F. Riolo, M. Sabater, R. Schroeder, E. Smith, M. Speicher, C. Tuitele, A. Tagarino, S. Vaitautolu, E. caoli, B. Vargas-Angel, P. Vroom, p. Brown, E. Buchan, A. Hall, J. Helyer, S. Heron, J. Kenyon, R. Oram, B. Richards, K.S. Saili, T. Work and B. Zgliczynski , 2008 , The State of Coral Reef Ecosystems of American Samoa. pp. 307-351 . In: J.E. Waddell and A.M. Clarke (eds.), The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2008. NOAA Technical Memorandum NOS NCCOS 73. NOAA/NCCOS Center for Coastal Monitoring and Assessment's Biogeography Team. Silver Spring, MD. 569 pp. (See Document)

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