On the calculation of eddy diffusivity in the shelf water from radium isotopes: High sensitivity to advection

Document Type

Article

Publication Date

5-1-2011

Abstract

The concentrations of the radium isotopes have been used in previous studies to estimate eddy diffusivity on the continental shelf. These studies assume that the advective transport of the radium isotopes is negligible. A theoretical investigation using an analytic model with advection indicates, however, that the eddy diffusivity thus estimated is highly sensitive to the advection. It is shown that the error can be very large even for an advective velocity of the order of 1mm/s-1cm/s. The sensitivity increases with the increase of the half life of the isotope. For a 1mm/s advective velocity, the estimated eddy diffusivity for the radium isotope with the shortest half life (i.e. 224Ra) is almost doubled. In addition, we also conclude that (1) advection has more important effects on smaller values of eddy diffusivity; (2) the effect of advection increases rapidly as advection increases; and (3) offshore advection tends to increase the apparent eddy diffusivity and inshore advection tends to decrease the apparent eddy diffusivity, if the advection is ignored. Based on these facts, an improved model is presented to calculate both advection and eddy diffusivity using the activities of two isotopes, which yields consistent diffusivity and advection from different isotope pairs. © 2011 Elsevier B.V.

Publication Source (Journal or Book title)

Journal of Marine Systems

First Page

28

Last Page

33

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