Reverse Estuarine Circulation Due to Local and Remote Wind Forcing, Enhanced by the Presence of Along‐Coast Estuaries

Abstract

Estuarine exchange flow governs the interaction between oceans and estuaries and thus plays a large role in their biogeochemical processes. This study investigates the variability in estuarine exchange flow due to offshore oceanic conditions including upwelling/downwelling, and the presence of a river plume offshore (from a neighboring estuary). We address these processes via numerical simulations at the mouth of the Salish Sea, a large estuarine system in the Northeast Pacific. An analysis of the Total Exchange Flow indicates that during the upwelling season, the exchange flow is fairly consistent in magnitude and oriented in a positive (into the estuary at depth and out at the surface) direction. However, during periods of downwelling favorable winds, the exchange flow shows significantly more variability including multiple reversals, consistent with observations, and surface intrusions of the Columbia River plume which originates 250 km to the south. Numerical along‐strait momentum budgets show that the exchange flow is forced dominantly by the pressure gradients, particularly the baroclinic. The pressure gradient is modified by Coriolis and sometimes advection, highlighting the importance of geostrophy and local adjustments. In experiments conducted without the offshore river plume, reversals still occur but are weaker, and the baroclinic pressure gradient plays a reduced role. These results suggest that estuaries along strong upwelling coastlines should experience significant modulation in the exchange flow during upwelling versus downwelling conditions. Additionally, they highlight the importance of nearby estuaries impacting one‐another, not only in terms of connectivity, but also altering the exchange flow.

Modulation of the Semidiurnal Cycle of Turbulent Dissipation by Wind‐Driven Upwelling in a Coastal Embayment

“…In fact, diffusive nitrate fluxes due to the enhanced dissipation, as observed during CHAOS 1‐springs, could be responsible for about half of the phytoplankton primary production estimated in this system during periods of upwelling relaxation‐stratification (Villamaña et al, ). Interactions between upwelling circulation and tides, similar to those described here, could occur in other upwelling systems, particularly bays with a bi‐directional response to the forcing winds, like the Gulf of Arauco (Valle‐Levinson, ) and Concepción Bay (Valle‐Levinson et al, ) in the Chile coastal upwelling region, the Sermilik Fjord in Greenland (Straneo et al, ), the Lyse Fjord in Norway (Erga et al, ), or the Salish Sea in the Pacific coast of North America (Giddings & Maccready, ). Future studies should be addressed to determine the spatial extension and temporal persistence of this phenomenon in the Galician Rías, and in similar systems worldwide, and to assess the biogeochemical relevance of this process.…”

Estuarine Circulation, Mixing, and Residence Times in the Salish Sea

“…[references from the supplement: (Babson et al, 2006) (Brasseale et al, 2019) (Codiga, 2011) ( Davis et al, 2014) (Egbert & Erofeeva, 2002) (Emery & Thomson, 1998) (Feely et al, 2016) (Finlayson, 2005) (Foreman et al, 1995) (Fredrickson et al, 2019) (Giddings & MacCready, 2017) (Giddings et al, 2014) (Haidvogel et al, 2000) (Khangaonkar et al, 2017) (Lavelle et al, 1988) (Liu et al, 2009) (Mass et al, 2003 Each panel represents three segments (i-iii) divided by sections 0 and 1. Each segment has two layers in the vertical, a deep saltier one and a shallow fresher one.…”

“…Here we use the cast data averaged over the upper and lower parts of the water column at CTD stations to test the model skill at reproducing the along‐channel salinity gradient and stratification. The along‐channel salinity gradient is thought to provide the driving pressure gradient for the estuarine exchange flow (Giddings & MacCready, 2017; MacCready & Geyer, 2010) and the size of the exchange flow as estimated from Knudsen's Relations depends critically on the stratification. Evaluating these for the three Puget Sound along‐channel sections shown in Figure 2 we find that the model salinity gradient is somewhat too weak, being 78%–85% of that observed.…”

Intratidal and Subtidal Circulation in a Tropical Estuary during Wet Season: The Maroni, French Guiana

“…The Northern coast of South America, including French Guiana, Suriname, Guyana and Venezuela experience persistent southwesterly winds that are therefore blowing directly on-shore and thus, up-estuary [7]. This could be an important (yet unexplored) feature of this region in terms of estuarine dynamics since studies have found that onshore winds can reduce or even reverse estuarine exchange flows [8,9]. In fact, [8] used observations from the microtidal and partially mixed York River Estuary in Virginia to demonstrate how along-channel wind plays a dominant role in governing the estuarine circulation.…”