Warm and Cool Nearshore Plumes Connecting the Surf Zone to the Inner Shelf

Abstract

Transport pathways of pollutants, nutrients, sediment, larvae, and heat in the transition from the shoreline to the shelf are important for coastal ecosystem health and water quality (Boehm et al., 2017;Grant et al., 2005). Bathymetric rip currents, strong seaward currents generated by wave breaking on channels and other alongshore-varying bathymetry in the surf zone (Bowen, 1969), are a dominant driver of cross-shore exchange in this region (Morgan et al., 2018). Signatures of rip-current circulation patterns can be observed extending onto the shelf, sometimes in the form of a turbid plume with elevated surface roughness (Haller et al., 2014;Smith & Largier, 1995) (Figure 1a). While the dynamics of bathymetric rip currents in the wellmixed surf zone are well understood and have been the subject of many observational and modeling studies (Castelle et al., 2016;Dalrymple et al., 2011), few studies have measured or assessed the importance of horizontal temperature and salinity variations as these currents evolve on the shelf.Several field studies have observed that the surf zone may have a different temperature or salinity than water on the adjacent shelf, which is often stratified (

Long‐Distance/Time Surf‐Zone Tracer Evolution Affected by Inner‐Shelf Tracer Retention and Recirculation

“…In contrast, the afternoon period alongshore averaged surf-zone (red triangles, top of Figures 11e) was consistently 0.5°C warmer than the z ≈ −1 m inner-shelf T. Surf-zone tracer exported onto the inner-shelf with positive T-anomaly would preferentially spread offshore at, or near the surface due to buoyancy (e.g., Molina et al, 2014;Moulton et al, 2021). In idealized modeling studies, diurnal thermally driven circulation modulates the inner-shelf vertical distribution of surf-zone released tracers, with a near surface inner-shelf plume for warm surf-zones and sub-surface plume for cool surf-zones (Grimes, Feddersen, & Kumar, 2020).…”

“…Inner-shelf tracer evolution is affected by various processes ranging from surf-zone origin transient rip-currents (Hally-Rosendahl et al, 2015) to stratified dynamics, such as internal waves (Grimes, Feddersen, Giddings, & Pawlak, 2020;Omand et al, 2011) and cross-shore buoyancy gradients (Grimes, Feddersen, & Kumar, 2020;Moulton et al, 2021). However, the fully coupled surf-zone/inner-shelf tracer model does not distinguish between specific process contributions to γ or k IS ; nor whether the inner-shelf region is vertically well mixed or stratified (cross-hatch patterns in Figure 8).…”

“…Also, the morning diffuse inner-shelf D does not have strong coherence with T′ (Figures 11a and 11b), in contrast to mid-afternoon inner-shelf D and T′ (Figures 11c and 11d) when surf-zone/inner-shelf temperature anomaly ΔT is a factor of 2 larger. Recent observations and modeling suggest that a larger surf-zone/inner-shelf temperature anomaly (ΔT) induce larger cross-shore surface extent of rip-current thermal plumes (Moulton et al, 2021).…”

“…Inner-shelf alongshore momentum dynamics also differ from the surfzone, with dominant contributions from wind and waves (e.g., Austin & Lentz, 2002;Lentz & Fewings, 2012), and alongshore pressure gradients (Wu et al, 2020). Under realistic conditions, numerous processes affect inner-shelf tracer evolution (e.g., Fong & Stacey, 2003;Jones et al, 2008), including internal waves (e.g., Moniz et al, 2014;Sundermeyer & Ledwell, 2001), baroclinic circulation (e.g., Grimes, Feddersen & Kumar, 2020;Kumar & Feddersen, 2017;Molina et al, 2014;Moulton et al, 2021), and cross-shore oriented coastal sub-mesoscale fronts (e.g., Wu et al, 2020). However, limited observations from surf-zone dye release experiments suggest inner-shelf mixing is weaker than in the surf-zone (e.g., Brown et al, 2019, among others;Clark et al, 2010).…”

Interactions Between Internal Tidal Bores and Submesoscale Currents on the Continental Shelf

“…We output fields with a 30 min average to better resolve the rapid evolution of interactions between internal tidal bores and submesoscale currents. The dense ISDE data set (August–November 2017; Kumar et al., 2021) highlights the prevalence of internal tidal bores (Becherer et al., 2020; Haney et al., 2021; McSweeney, Lerczak, Barth, Becherer, Colosi, et al., 2020; McSweeney, Lerczak, Barth, Becherer, MacKinnon, et al., 2020), topographic wakes (Kovatch et al., 2021), and surf‐zone plumes (Moulton et al., 2021) in this same region. We do not intend this study to serve as a direct comparison with the ISDE observations due to the different time periods (discussed further in Section 6.2).…”