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Mechanisms driving stratification in Delaware Bay estuary

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Abstract

An observational study in the middle reach of Delaware Bay shows that vertical stratification is often enhanced during flood tide relative to ebb tide, contrary to the tidal variability predicted by the tidal straining mechanism. This tidal period variability was more pronounced during times of high river discharge when the tidally mean stratification was higher. This tidal variability in stratification is caused by two reinforcing processes. In the along-channel direction, the upstream advection of a salinity front at mid-depth causes an increase of the vertical stratification during the flood tide and a decrease during the ebb tide. In the cross-channel direction, the tilting of isohalines during the ebb reduces vertical stratification, and the subsequent readjustment of the salinity field during the flood enhances the water column stability. A diagnosis of the cross-channel momentum balance reveals that the lateral flows are driven by the interplay of Coriolis forcing and the cross-channel pressure gradient. During the flood tide, these two forces mostly reinforce each other, while the opposite occurs during the ebb tide. This sets up a lateral circulation that is clockwise (looking landward) during the first half of the flood and then reverses and remains counterclockwise during most of the ebb tide. Past maximum ebb, the cross-channel baroclinic term, overcomes Coriolis and reverses the lateral flows.

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Acknowledgments

We thank Eli Hunter, Chip Haldeman, Joe Jurisa, Dove Guo, and the captain of the ship Ken Roma for all their dedication in collecting the data. This work was supported by a National Science Foundation grant OCE-0928567 and OCE-0825833. The author María Aristizábal was supported by a Dupont fellowship and the Institute of Marine and Coastal Sciences at Rutgers University. We also thank Jack McSweeney for closely reading the manuscript. We are also very thankful to the reviewers who insisted in the importance of the along-channel advection of stratification.

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  1. Rutgers University, 71 Dudley Road, New Brunswick, NJ, 08901, USA

    María Aristizábal & Robert Chant

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  1. María Aristizábal
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  2. Robert Chant
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Correspondence to María Aristizábal.

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Responsible Editor: Rockwell Geyer

This article is part of the Topical Collection on Physics of Estuaries and Coastal Seas 2012

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Aristizábal, M., Chant, R. Mechanisms driving stratification in Delaware Bay estuary. Ocean Dynamics 64, 1615–1629 (2014). https://doi.org/10.1007/s10236-014-0770-1

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  • DOI: https://doi.org/10.1007/s10236-014-0770-1

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