Tide and wind forced nearshore dynamics in Nuevo Gulf (Northern Patagonia, Argentina): Potential implications for cross-shore transport

The coastal hydrodynamics of an eastward-facing bay (Nueva Bay) located in the west coast of Nuevo Gulf (42.76° S, 65.03° W) was inferred using time series of seawater temperature, winds and tides. Temperature was measured at surface and near the bottom at a station with a maximum depth of 18 m. Concurrent observations of wind intensity and direction were registered at ~ 3 km from the station. Tidal levels were predicted using the WXTide software. Surface heat flux explained the observed annual cycle of seawater temperature and the seasonal thermal stratification. Events of upwelling/downwelling were observed associated to offshore/onshore winds, with lags of approximately 5–6 hours. Spectral analysis of the temperature time series showed significant diurnal and semidiurnal peaks during the warm season (spring and summer), when the water column was stratified. The semidiurnal peaks of spectral energy were correlated with the main components of the tidal cycle. Diurnal thermal variability was driven by diurnal cycles of wind (sea breeze) occurring during 52% of spring days and 61% of summer days. We present two conceptual models of nearshore dynamics that are coherent with the observed thermal variability (up to 4 °C in 6 hours).

► Near-shore hydrodynamics is inferred from the analysis of seawater temperature time-series.
► Off-shore/on-shore winds generate upwelling/downwelling events.
► Sea-breeze generates downwelling-relaxation cycles associated with day-night cycles.
► These mechanisms could play a role in the transport of diel-vertical-migrating plankton on-shore/off-shore.