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Title: Decomposition of Vertical Velocity for Nutrient Transport in the Upper Ocean

Within the pycnocline, where diapycnal mixing is suppressed, both the vertical movement (uplift) of isopycnal surfaces and upward motion along sloping isopycnals supply nutrients to the euphotic layer, but the relative importance of each of these mechanisms is unknown. We present a method for decomposing vertical velocity w into two components in a Lagrangian frame: vertical velocity along sloping isopycnal surfaces [Formula: see text] and the adiabatic vertical velocity of isopycnal surfaces [Formula: see text]. We show that [Formula: see text], where [Formula: see text] is the isopycnal slope and [Formula: see text] is the geometric aspect ratio of the flow, and that [Formula: see text] accounts for 10%–25% of the total vertical velocity w for isopycnal slopes representative of the midlatitude pycnocline. We perform the decomposition of w in a process study model of a midlatitude eddying flow field generated with a range of isopycnal slopes. A spectral decomposition of the velocity components shows that while [Formula: see text] is the largest contributor to vertical velocity, [Formula: see text] is of comparable magnitude at horizontal scales less than about 10 km, that is, at submesoscales. Increasing the horizontal grid resolution of models is known to increase vertical velocity; this increase is disproportionately due to better resolution of [Formula: see text], as is shown here by comparing 1- and 4-km resolution model runs. Along-isopycnal vertical transport can be an important contributor to the vertical flux of tracers, including oxygen, nutrients, and chlorophyll, although we find weak covariance between vertical velocity and nutrient anomaly in our model.

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Author(s) / Creator(s):
Publisher / Repository:
American Meteorological Society
Date Published:
Journal Name:
Journal of Physical Oceanography
Page Range / eLocation ID:
p. 1561-1575
Medium: X
Sponsoring Org:
National Science Foundation
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