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current meter observations, diurnal fish migration, Cariaco Basin

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Multiple years of moored current meter observations from the Cariaco Basin show low‐frequency variations along with near‐inertial waves and further imply the persistent diurnal movement of fish species known to populate the basin. In agreement with short‐term observations from 1979, the more recent observations with acoustic Doppler current profilers provide evidence of the multidecadal presence and behavior of these species. An unwanted corollary, however, is a bias in both the vertical and horizontal components of velocity due to the fish movements. Removal of this fish bias results in large data loss (approximately 72%); however, an interpolated, non‐biased data set is developed with depth‐averaged horizontal velocities comparable to the observations, demonstrating successful elimination of the bias. Further comparisons show that the interpolated data result in minimal variance density loss at low frequencies and a reduction of variance density at high frequencies such that the interpolated data in the internal wave range more closely fit the Garrett‐Munk spectrum. The net result is a data set appropriate for further analysis. A mean downward velocity of 0.18 cm s−1 is a reflection of a biogenic particle flux and some residual fish contamination. The mean settling speed of particles in the Cariaco Basin is calculated, via Stokes law, to be smaller than 0.04 cm s−1. Velocity observations from acoustic current meters at depths greater than 400 m are impacted by the water clarity; therefore alternate methods should be used to make velocity measurements at depth.

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Journal of Geophysical Research - Oceans, v. 114, issue C3, art. C03028

Copyright 2009 by the American Geophysical Union.