Rapid water exchange between the lagoon and the open ocean at Majuro Atolldue to wind, waves, and tide

Current measurements and conductivity-temperature-depth surveys of the lago on and ocean at Majuro Atoll, the Republic of the Marshall Islands, were ma de from January 10 to 24, 1997. A vertically integrated tidal current model reproduced qualitatively well tidal ellipses calculated from the observed current measurements py Fourier transform. A three-dimensional, robust diag nostic residual current model explained the major features observed in the current measurements averaged over the dominant tidal cycles. We used the d iagnostic model to examine the effects of wind stress, radiation stress, de nsity gradients, and tidal stress on the exchange of water between the lago on and the ocean. Wind effectively mixes the lagoon water in approximately 2 weeks. Tidal flushing appears to be restricted to a small area near the m ain channels connecting the lagoon to the ocean. Cross-reef-flat currents i nduced by radiation stress and flowing to the deep channels in the center o f the northern boundary form the dominant mechanism for exchange between th e lagoon and the open ocean, causing water to exchange completely with the ocean in about 15 days. Computer-generated particles tracked through the la goon showed that radiation stress is also the main forcing mechanism for pa rticle export from the lagoon. However, the coupling of tidal exchange thro ugh the Calalin Channel and wind-stress-induced mixing in the lagoon could also provide a significant export mechanism, particularly for particles ori ginating uniformly inside the lagoon.