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The Connecticut River plume interacts with the strong tidal currents of the ambient receiving waters in eastern Long Island Sound. The plume formed during ambient flood tides is studied as an example of tidal river plumes entering into energetic ambient tidal environments in estuaries or continental shelves. Conservative passive freshwater tracers within a high-resolution nested hydrodynamic model are applied to determine how source waters from different parts of the tidal cycle contribute to plume composition and interact with bounding plume fronts. The connection to source waters can be cut off only under low-discharge conditions, when tides reverse surface flow through the mouth after max ambient flood. Upstream plume extent is limited because ambient tidal currents arrest the opposing plume propagation, as the tidal internal Froude number exceeds one. The downstream extent of the tidal plume always is within 20 km from the mouth, which is less than twice the ambient tidal excursion. Freshwaters in the river during the preceding ambient ebb are the oldest found in the new flood plume. Connectivity with source waters and plume fronts exhibits a strong upstream-to-downstream asymmetry. The arrested upstream front has high connectivity, as all freshwaters exiting the mouth immediately interact with this boundary. The downstream plume front has the lowest overall connectivity, as interaction is limited to the oldest waters since younger interior waters do not overtake this front. The offshore front and inshore boundary exhibit a downstream progression from younger to older waters and decreasing overall connectivity with source waters. Plume-averaged freshwater tracer concentrations and variances both exhibit an initial growth period followed by a longer decay period for the remainder of the tidal period. The plume-averaged tracer variance is increased by mouth inputs, decreased by entrainment, and destroyed by internal mixing. Peak entrainment velocities for younger waters are higher than values for older waters, indicating stronger entrainment closer to the mouth. Entrainment and mixing time scales (1–4 h at max ambient flood) are both shorter than half a tidal period, indicating entrainment and mixing are vigorous enough to rapidly diminish tracer variance within the plume.
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This content will become publicly available on August 9, 2026
Tidal Effects on Antarctic Bottom Water Formation in a Changing Climate
Abstract Antarctic bottom water (AABW) forms through the descent of dense shelf waters (DSW) into the abyssal ocean, with tides playing a key role in DSW transport and entrainment. Previous studies suggest that tides can suppress the net overflow entrainment, favoring the formation of denser AABW. However, how tidal effects on AABW formation and associated material sequestration vary with a changing climate remains unclear. In this study, an idealized numerical model is used to investigate potential climatic influences on tidally influenced AABW properties. Experiments are conducted with varying ambient stratifications and rates of DSW supply, inspired by projected future changes over the Antarctic continental shelf. The results show that tidal advection and associated V‐shaped front can modify the vertical diffusivity and the exchanges between DSW and its ambient waters, thereby altering the properties of AABW. For a future warm and salty shelf, AABW will become warmer and saltier accordingly, with the effects of the V‐shaped front weakening significantly. Conversely, for a future cold and fresh shelf, AABW formation is nearly nonexistent due to the stronger dilution of DSW, and the tidal effects become much weaker. Additionally, tidal suppression of overflow mixing is only significant for large DSW fluxes (thickness) and becomes negligible for small DSW fluxes. These findings suggest that the contribution of tides to DSW descent will weaken under global warming, thereby accelerating the slowdown of AABW formation.
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- Award ID(s):
- 2220968
- PAR ID:
- 10636186
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 130
- Issue:
- 8
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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