Northern Monterey Bay upwelling shadow front: Observations of a coastally and surface‐trapped buoyant plume

Abstract

[1] During the upwelling season in central California, northwesterly winds along the coast produce a strong upwelling jet that originates at Point Año Nuevo and flows southward across the mouth of Monterey Bay. A convergent front with a mean temperature change of 3.77 ± 0.29°C develops between the warm interior waters and the cold offshore upwelling jet. To examine the forcing mechanisms driving the location and movement of the upwelling shadow front and its effects on biological communities in northern Monterey Bay, oceanographic conditions were monitored using cross-shelf mooring arrays, drifters, and hydrographic surveys along a 20 km stretch of coast extending northwestward from Santa Cruz, California, during the upwelling season of 2007 (May-September). The alongshore location of the upwelling shadow front at the northern edge of the bay was driven by: regional wind forcing, through an alongshore pressure gradient; buoyancy forces due to the temperature change across the front; and local wind forcing (the diurnal sea breeze). The upwelling shadow front behaved as a surface-trapped buoyant current, which is superimposed on a poleward barotropic current, moving up and down the coast up to several kilometers each day. We surmise that the front is advected poleward by a preexisting northward barotropic current of 0.10 m s À1 that arises due to an alongshore pressure gradient caused by focused upwelling at Point Año Nuevo. The frontal circulation (onshore surface currents) breaks the typical two-dimensional wind-driven, cross-shelf circulation (offshore surface currents) and introduces another way for water, and the material it contains (e.g., pollutants, larvae), to go across the shelf toward shore.

Shoreward swimming boosts modeled nearshore larval supply and pelagic connectivity in a coastal upwelling region

“…Fronts are associated with phytoplankton blooms and aggregate phytoplankton and larvae, and these phenomena are well-documented in central California (Bjorkstedt et al, 2002;Graham et al, 1992;Ryan et al, 2010Ryan et al, , 2014Traganza and Conrad, 1981;Woodson et al, 2009). Fronts are common and persistent in the CCS (Castelao et al, 2006;Shanks et al, 2003a), and are spatially correlated with higher recruitment of both intertidal and subtidal species .…”

Seasonal behavior of dissolved cadmium and Cd/PO4 ratio in Todos Santos Bay: A retention site of upwelled waters in the Baja California peninsula, Mexico

“…2b). The phenomenon of bays and capes acting as retention centers, with surface water much warmer than the adjacent ocean, has been observed in other upwelling areas such as the Bay of Antofagasta (Piñones et al, 2007) and Mejillones Bay (Marín et al, 2003;Valdés et al, 2006) within the Humboldt Current System, as well as Point Reyes (Vander Woude et al, 2006) and Monterey Bay along the California Current System (Graham and Largier, 1997;Ryan et al, 2008;Woodson et al, 2009;Berdalet et al, 2014). The retentive circulation and its effect on the temperature and stability of the water column inside these systems are important in terms of the biogeochemical processes because water retention allows for the increase of phytoplankton biomass and the intensification of biological processes, such as photosynthesis and respiration.…”

“…Graham, 1993;Graham and Largier, 1997;Marín et al, 2003) and whose fate is distinct from those waters transported to the open ocean. Although their dynamics are not entirely clear, the retention sites are typically located in sections of the coast where wind stress is reduced, causing the upwelled waters to rapidly warm up, creating a thermal front between the retention center (RC) and the open ocean (Piñones et al, 2007;Woodson et al, 2009). Such water warming up is considered a symptom of increased residence time of upwelling water "inside" the RC (Graham and Largier, 1997).…”

Harmful phytoplankton ecology studies using an autonomous molecular analytical and ocean observing network

“…Diurnal and semidiurnal variations in water column structure were pronounced throughout the time series. Variation in this frequency band is related to tidal and wind-forced advection (Petruncio et al 1998;Woodson et al 2007Woodson et al , 2009). The highest frequency of variability resolved with hourly profiles was due to internal waves (Figs.…”