Abstract
Well-preserved sediment from closed water bodies of atolls such as Lib Pond are rare opportunities to reconstruct the past regional climate, which pieced together across a latitude and longitude range identify the range of movement patterns of wider scale climate phenomena such as the Intertropical Convergence Zone (ITCZ) and El Niño Southern Oscillation (ENSO). We conducted the first physico-chemical survey of Lib Pond, a shallow, closed-water saline lake located on remote and difficult to access Lib Island in the Marshall Islands at 8° 18′ 48.99″ N, 167 22′ 51.90″ E in the Pacific Ocean, in July 2009. We performed a bathymetric survey, recorded salinity, dissolved oxygen, pH, and temperature profiles, monitored the tidal variability, and conducted a vegetation survey surrounding the lake. From bathymetric data we calculated the lake volume, which we used to estimate the lake's salt budget, and ultimately the residence time of water in the lake basin. We took a series of sediment cores from the lake, cores which indicate Lib Island's changing environment and climate. Radiocarbon measurements determined sediment age, and reveal significant mixing over the last 2 ka of deposition. We conclude that prior to 3 ka, Lib Island was an atoll with a central lagoon connected to the open ocean, which was then closed off from the open ocean to form the brackish system that exists today. We predict that the sediment accumulation in Lib Pond evident today will continue. As seawater is inhibited from exchanging with fresh water, Lib Pond will become a shallower lake with increasingly fresh water.
Highlights
Lib island Lib, called Ellep, is a coral island that is part of the RalikChain in the Republic of the Marshall Islands
We describe Lib Island’s lacustrine body in terms of geology, morphometry, ecology and physico-chemistry, combining water property measurements of salinity, pH, temperature, and dissolved oxygen (DO) with water level fluctuations and macroscale stratigraphic observations to generate a physico-chemical overview
Using GPS data and computer modeling we created a bathymetric map of Lib Pond with estimated ranges for surface area, perimeter and volume using two methods
Summary
Lib island Lib, called Ellep, is a coral island that is part of the RalikChain in the Republic of the Marshall Islands. Lib Island today has a wet tropical climate, based on data from the nearby meteorological station on Kwajalein Atoll (58 km to the NE, 8u 439N 167u 449E) (Table 1, Table 2). Three-quarters of annual rainfall occurs during the wet season (June – Dec), influenced by the El Nino Southern Oscillation (ENSO) [1]. This precipitation distribution is consistent with the annual migration of the Intertropical Convergence Zone (ITCZ). In this regard, drought periods on Lib – inferred from decreased rainfall on neighboring Kwajalein – commonly follow El Nino events [2]
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