Hydrodynamic properties of San Quintin Bay, Baja California: Merging models and observations Donata Melaku Canu a , Leslie Aveytua-Alcázar a,b , Victor F. Camacho-Ibar c , Stefano Querin a , Cosimo Solidoro a,b a Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Borgo Grotta Gigante 42/C, 34010, Sgonico, Trieste, Italy b ICTP, The Abdus Salam International Centre for Theoretical Physics – Strada Costiera, 11I-34151 Trieste, Italy c Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas, km 103 Autopista Tijuana-Ensenada, 22860, Baja California, Mexico abstract article info Article history: Received 15 January 2016 Received in revised form 17 March 2016 Accepted 14 April 2016 Available online xxxx We investigated the physical dynamics of San Quintin Bay, a coastal lagoon located on the Pacific coast of north- ern Baja California, Mexico. We implemented, validated and used a finite element 2-D hydrodynamic model to characterize the spatial and temporal variability of the hydrodynamic of the bay in response to variability in the tidal regime and in meteorological forcing patterns. Our analysis of general circulation, residual currents, res- idence times, and tidal propagation delays allowed us to characterize spatial variability in the hydrodynamic basin features. The eulerian water residence time is –on average and under reference conditions– approximately 7 days, although this can change significantly by region and season and under different tidal and meteorological conditions. Ocean upwelling events that bring colder waters into the bay mouth affect hydrodynamic properties in all areas of the lagoon and may affect ecological dynamics. A return to pre-upwelling conditions would take approximately 10 days. © 2016 Elsevier Ltd. All rights reserved. Keywords: Modeling Coastal lagoon Tidal advection Upwelling SHYFEM San Quintin Bay 1. Introduction Coastal lagoons are almost fully enclosed shallow water bodies that are connected to a sea by one or more inlets. Typically being shallow, these lagoons respond quickly to meteorological conditions and exter- nal forcing and present marked seasonality in terms of water tempera- ture, salinity and other environmental parameters (Möller et al., 2001; Solidoro et al., 2004). Lagoons are often very productive systems and are exploited for fishing and aquaculture. However, they can also be fragile ecosystems, vulnerable to a variety of effects originating from an- thropogenic sources (Bricker et al., 2003, Newton et al., 2014, Solidoro et al., 2010, Elliott and Quintino, 2007). An understanding of lagoon dy- namics and responses to natural and anthropogenic variability is thus needed to support ecosystem-based management of these water bodies. Transitional waters are often classified on the basis of exchange pat- terns with adjacent seas (Basset et al., 2013, Melaku Canu et al., 2012), basin morphologies (Kjerfve, 1994) and the relative importance of dif- ferent factors (river discharges, winds, and tides) in defining internal general circulation and biogeochemical properties. The role of tides is particularly relevant among coastal lagoons connected to oceans. In fact, as observed in several lagoons along the Pacific US coast, even in es- tuarine lagoons (i.e., lagoons that originate at a river mouth and that therefore are heavily influenced by river discharge such as Willapa Bay, Yaquina Bay, Tillamook Bay and Tomales Bay) oceanic supplies become the most significant source of nutrients during the upwelling season (Smith and Hollibaugh, 1997; Hickey and Banas, 2002; Colbert and McManus, 2003). Oceanic contributions are even more influential in the southern region of the California Current domain (e.g., San Quintin Bay (SQB), Ojo de Liebre Lagoon and Magdalena Bay), where freshwater inputs are scarce (Valle-Levinson et al., 2009). However, each of these coastal lagoons follows a different exchange pattern that is forced mainly by tides and intermittently by wind and that is constrained by basin morphology. SQB is a coastal lagoon (sensu Largier et al., 1997) located on the Pa- cific coast of Mexico and in the southern region of the California Current domain (Fig. 1). SQB dynamics are dominated by tidal exchanges with the Pacific Ocean and are characterized by minor anthropogenic im- pacts, strong atmospheric thermal exchanges, sporadic freshwater in- puts and coastal upwelling that is considered to be the main source of nutrients for the Bay, as already shown for other similar systems (Ribas-Ribas et al., 2011). Although several studies (Lara-Lara et al., 1980; Farfán and Álvarez-Borrego, 1983; Camacho-Ibar et al., 2003, Ribas-Ribas et al., 2011, Carriquiry et al., 2015) have already explored the patterns and ex- tents of the exchange of biogeochemical properties between SQB and the sea, less is known of the role of physical forcing and upwelling in shaping hydrodynamic and thermohaline properties in SQB. Over the past decades, monitoring activities have been carried out in the bay to address its biogeochemistry and to support aquaculture management (García-Esquivel et al., 2004). Conversely, in a very few cases, numerical models have been applied with a focus on specific and limited issues. Marine Pollution Bulletin xxx (2016) xxx–xxx MPB-07642; No of Pages 12 http://dx.doi.org/10.1016/j.marpolbul.2016.04.030 0025-326X/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Please cite this article as: Melaku Canu, D., et al., Hydrodynamic properties of San Quintin Bay, Baja California: Merging models and observations, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.04.030