Circulation and Retention of River Plumes Around Capes

• Published in: Journal of geophysical research. Oceans 2024-04, Vol.129 (4), p.n/a
• Main Authors: Pareja‐Roman, L. Fernando, Chant, Robert J., Mazzini, Piero L. F., Cole, Kelly
• Format: Article
• Language: English
• Subjects: capes; Capes (landforms); Downwelling; Earth rotation; flow separation; Fresh water; Freshwater; freshwater bulge; geophysics; Headlands; Hydrodynamics; Inland water environment; Marine ecosystems; Numerical experiments; Oceans; Plumes; Radius of curvature; Retention; River discharge; River flow; river plume; River plumes; Rivers; Rossby number; Scalars; Separation; Water discharge; Water quality; Wind; Winds
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2023JC020645

River plumes often interact with capes in the coastal ocean, impacting local hydrodynamics and the transport of scalars. However, our current knowledge on how capes affect river plume separation, mixing, and retention is limited. Here, we conducted idealized numerical experiments with Gaussian‐shaped capes of varying curvature radii, constant river discharge, a sloping bottom, and scenarios with and without downwelling winds. We found that river plumes separate from capes when the Rossby number is above 1, a criterion that had not been tested for plume separation. This Rossby number is based on the plume velocity, the Coriolis factor, and the radius of curvature of the cape. Freshwater accumulation is greatest at the lee of narrow (i.e., pointy) capes under calm winds, but decreases significantly in downwelling winds or around broader capes. Plain Language Summary The interaction of river plumes with capes and headlands can affect the circulation and transport of substances and organisms in the coastal ocean. However, not much is known regarding the impact of capes on the retention of freshwater and any substances or organisms present in river plumes. To address this research gap, we conducted simulations, exploring various scenarios with differing cape shapes, constant river flow, and variable winds. Our findings underscore the roles of capes, wind, and the Earth's rotation in freshwater retention dynamics. At narrow capes without wind, freshwater accumulates predominantly on the lee side, forming a bulge. In contrast, broader capes lead to reduced freshwater retention. This research advances our understanding of plume‐cape interactions in the coastal ocean, with implications for marine ecosystems dynamics and water quality. Key Points River plume separation at capes occurs when the Rossby number exceeds 1, but separation patterns are also largely influenced by wind Cape geometry and wind modulate freshwater retention at capes, with maximum retention at pointy capes in calm winds and minimal over flatter capes under downwelling winds The farthest offshore displacement of the plume was at the lee of pointy capes under calm winds, favoring the development of a freshwater bulge