Archaeological Investigation of the Landscape History of an Oceanic Atoll: Majuro, Marshall Islands

Abstract

Historical ecology has provided the field of geoarchaeology in Oceania with the concept of an island landscape as a historical product, invented from the dynamic interactions between natural processes and human agency. Since Davidson's work in Nukuoro (1971) and Dye's introduction to the prehistory of Majuro in the Marshall Islands (1987), systematic excavations of atoll islets have also been based on this tenet. Following this concept, this study presents a geoarchaeological examination of the long-term history of the pitagricultural landscape in Laura Islet of Majuro Atoll, which now consists of 195 pits showing remarkable undulation and anthropogenic vegetation on their spoil banks. Our excavations, conducted since 2003, have revealed that human habitation on Laura began as early as 2,000 years ago, soon after the emergence of the core islet, which probably followed a relative drop in sea level in the late Holocene. Some centuries later, the inhabitants started excavating agricultural pits for the cultivation of wet taro, probably Cyrtosperma spp. The subsequent sea-level decline would have enlarged the foraminiferal sediment; the islet then extended its landform both oceanward and lagoonward as well as along the longitudinal axis stretching north to south. The land accretion caused its inhabitants to increasingly extend their activity space and readjust areas for habitation. It would also have enlarged the volume of the freshwater lens, prompting additional construction of agricultural pits even in the area just behind the lagoonside beach ridge. Most of the current landscape was formed by around 1,000 years ago at the latest. Geoarchaeological synthesis of Pacific atolls will enable the precise elucidation of local chronological relationships between land accretion and expansion of human activities.More than 170 coral atolls are scattered in the trade-wind zone from the westernmost Caroline Islands to the easternmost Tuamotu Islands (Figure 1). Their islets of foraminiferal sand and coral shingle lie on mid-Holocene emergent reef flats, and a chain of these islets, which are covered with coconut trees, separate a turquoise lagoon from the surrounding navy blue ocean. On the surface, the scene appears to be a typical oceanic paradise. Most of the subaerial landforms, however, are no more than 2-3 m in elevation and a few hundred meters to less than a few kilometers at most in width. As such, they are highly susceptible to inundation by storm surges. Moreover, in the absence of running surface water, some atolls frequently suffer from droughts. Because of these and other factors, atolls have often been stereotyped as being extremely marginal environments for human settlement. This oversimplified image tends to be reflected even in the latest scientific reports on global warming,

Rapid settlement of Majuro Atoll, central Pacific, following its emergence at 2000 years CalBP

“…We excavated one of the largest banks at the center of Laura Island. The archaeological results, which were reported by Yamaguchi et al [2009], are reassessed in this study in relation to late Holocene sea level change and the history of island formation. To reconstruct a detailed time sequence of human settlement and island formation, it is necessary to obtain a precise calibration of the local ocean reservoir effect (ΔR).…”

“…On the other hand, foraminifera sand from the top of naturally deposited layer (Layer 7) in this section yields an age of 2100–1970 years CalBP. The ages of the earth ovens in the layers overlying the Layer 6 in Figure 3 and at other archaeological sites in Laura Island [ Yamaguchi et al , 2009] distribute later than 1900 years CalBP, and thus the date of U1/Fe6 shows the oldest date of human settlement. On the other hand, the age of top surface of Layer 7 falls within the island exposure age of 2100–1940 years CalBP shown in the previous section.…”

“…The bank sediment was dug out from the taro pits and indicates that pit agriculture was being practiced at this time. The age reversal between U1/Fe5 and U2/Fe0 within an error range in the bank shows it was heaped within a short period, and about 200 agricultural pits had been excavated since then [ Yamaguchi et al , 2009]. Human modification of the island's vegetation and landforms is evident in the bank sediment overlying the layer.…”

Marginalization of the Margins: The Importance of Smaller Islands in Human Prehistory

“…In the Pacific, some of the gaps in our knowledge of small island colonization and adaptations have been filled by work on atolls or small limestone islands in Micronesia, including the Marshall Islands (e.g., Weisler 2001aWeisler , 2001bWeisler , 2002Weisler et al 2012;Yamaguchi et al 2009), Mwoakilloa (Poteate et al 2016), Fais (Intoh 2008;Intoh and Shigehara 2004), Kiribati (e.g., Thomas 2007aThomas , 2007bThomas , 2009Thomas , 2014, and Palau (e.g., Clark 2005;Clark et al 2006;Fitzpatrick 2003;Fitzpatrick et al 2011). There are also many other similar ones in Polynesia such as the Cook Islands (e.g., Allen and Craig 2009; Allen and Steadman 1990; Allen and Wallace 2007; Kirch et al 1995), the Tuamotu archipelago (e.g., Conte and Dennison 1995), the remote islands of Henderson, Pitcairn (Weisler 1995), and Rapa Nui (e.g., Hunt and Lipo 2011), and even the Arawe Islands of Papua New Guinea (Specht et al 2016), all of which have enhanced our understanding of small island adaptations.…”

Classifying Pacific islands

“…The large number of reef islands is explainable by their tendency to develop on broad reef surfaces throughout the low-latitude Pacific. Yet this tendency has also been assisted by Late Holocene sea-level fall within the Pacific that has seen some reef surfaces emerge by around 1 m within the past few thousand years, providing foci for sediment accumulation that has manifestly aided the growth of large reef islands (Dickinson 2004); examples have been described from the Marshall Islands and Tuvalu (McLean and Hosking 1991;Yamaguchi et al 2009). Yet it is also worth noting that reef islands are generally more vulnerable than other island types to size reduction (and even erasure) under conditions of sealevel rise; projections of this event occurring this century have been made (Dickinson 2009), although there are studies that demonstrate the dynamic nature of reefisland shorelines and emphasizes the point that sea-level rise does not uncritically equate with reef-island 'disappearance' (Webb and Kench 2010;Woodroffe 2008).…”