The Transient Response of Dense Water Storage in a Hydraulically Drained Ocean Basin through One or Two Passages, in the Context of the Greenland–Iceland– Scotland Ridge

Abstract

To investigate dense water hydraulics under transient conditions, we examine the time-dependent adjustment of circulation in an ocean basin drained by one or two hydraulically controlled straits. Adjustment is triggered by a sudden in-creaseintheimposed inflow to the upstream basin and is communicated to the draining strait(s) by a coastal Kelvin wave. Hydraulic control at a sill causes partial reflection of the transport anomaly back into the upstream basin, while the remaining signal is transmitted to the downstream basin. The resulting adjustment process and draining time scale can be interpreted in terms of these wave pathways and their reflection coefficients. The dynamics become more complex in the presence of two draining straits separated by an island. Using numerical experiments with a 1.5-layer model including an active lower layer, we explore the effects of strait width and sill depth, as well as rotation and stratification. While the presence of a second strait increases Kelvin wave reflection at each individual strait, the combined effect of both straits enhances the net volume transmission to the downstream basin, significantly reducing the upstream draining time scale relative to a single-strait configuration. A theoretical estimate of the reflection coefficient underestimates the reflection values diagnosed in the model by a factor of 4, and we propose an empirical parameterization that better fits the experiments. Applied to the Nordic seas, the results suggest a characteristic draining time scale of 2–3 months, largely independent of perturbation amplitude.