- Title
- Lagoon stratification in Manihiki Atoll, Cook Islands
- Creator
- Power, Hannah E.; Cossu, Remo; Callaghan, David P.; Nielsen, Jesper; Hughes, Michael G.; Nielsen, Peter
- Relation
- Coasts and Ports 2017 Conference. Australasian Coasts and Ports 2017: Working With Nature (Cairns, Qld 21-23 June, 2017) p. 886-892
- Publisher
- Engineers Australia
- Resource Type
- conference paper
- Date
- 2017
- Description
- Manihiki Atoll is an enclosed atoll in the Northern Group of the Cook Islands, South Pacific, with depths in the lagoon up to 70 m. The enclosed rim of the atoll causes the primary lagoon flushing mechanism to be driven by the ocean waves rather than tides with one-way wave driven flows in the lagoon. Historically, there have been varying degrees of stratification in the lagoon water column with a higher density, de-oxygenated bottom water layer and a lower density, oxygenated upper layer. The relative thicknesses of these two water layers have varied through time with the depth of transition from low to high density water varying from 20 m to 50 m. Observations in 2016 revealed a stable temperature anomaly near the interface of the dense bottom water and the well mixed lagoon surface waters. The bottom water had a salinity 1 psu and density 1 kg/m3 greater than the surface water. Warm ocean water entering the lagoon through the wave pumping mechanism was quickly mixed through the upper 50m of lagoon water while the properties of the bottom water remained stable. Two potential mechanisms for generation of bottom water are proposed: 1) dense pools of ocean water entering the lagoon through wave flushing, and 2) hypersaline water forming through evaporation in shallow ponds around the reef edge. The mechanism driving build-up of bottom water was unclear with the volume of bottom water reducing during the observation period.
- Subject
- coral atoll; lagoon mixing; stratification
- Identifier
- http://hdl.handle.net/1959.13/1393038
- Identifier
- uon:33491
- Identifier
- ISBN:9781922107916
- Language
- eng
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