Observations of upwelling and relaxation events in the northern Monterey Bay during August 2000

Abstract

[1] The interplay between the Point Año Nuevo upwelling center, an offshore anticyclonic mesoscale eddy, and the waters of the Monterey Bay was studied during a series of up-and downwelling favorable wind events during August 2000. The upwelling events were characterized by the appearance of cold, salty water at Point Año Nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued. During the downwelling/relaxation events, the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself. The circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing. The ICON model, a nested, data assimilating, sigma coordinate model, was used to simulate the upwelling and relaxation events and calculate the subsurface current and density fields. The model reproduced the dominant current and temperature patterns outside the bay, including the southward flowing upwelling filament, the movement of the offshore eddy, the poleward flow off Point Sur, and the circulation within the bay. The model salinity fields at the surface and 100 m levels show that during upwelling, the bay was filled with higher-salinity water stemming from the Point Año Nuevo upwelling center to the north. During downwelling, the source water for both the surface and 100 m levels was the colder, fresher California Current water offshore, which had advected southward well past Point Piños during the previous upwelling event.

Oceanographic and atmospheric conditions on the continental shelf north of the Monterey Bay during August 2006

“…This clear maximum in the alongshore wind stress may contribute to the formation of the upwelling center off Año Nuevo. Consistent with previous studies, there was a wind shadow behind the coastal mountains in the northeast corner of the Monterey Bay (Graham and Largier, 1997;Ramp et al, 2005). This lead to a very strong gradient in the wind stress extending southwest from Santa Cruz.…”

“…When the feature has moved inshore, the combination of blocking and geostrophic current force the plume to move southward across the mouth of the bay. Time series of sea surface temperature from aircraft and AVHRR images show that the MBE moves rapidly onshore during wind relaxation events and retreats back offshore when the winds re-intensify (Rosenfeld et al, 1994;Ramp et al, 2005). Moored observations however have also shown an onshore and southward translation of the MBE without a wind relaxation (Ramp et al, 1997a,b).…”

“…As the wind continues to blow for 5-10 days, a cold plume forms which may move further offshore or turn southward across the Monterey Submarine Canyon (MSC) (Rosenfeld et al, 1994;Ramp et al, 2005;Haley et al, 2009). A warm, fresh, anticyclonic feature (the "Monterey Bay Eddy" or MBE) often exists offshore, which interacts with the cold plume in some complex way (Rosenfeld et al, 1994;Paduan and Rosenfeld, 1996;Ramp et al, 2005). It has now been determined during the second Autonomous Ocean Sensing Network (AOSN-II) experiment that the position and strength of the anticyclonic feature can determine the bifurcation of the upwelling front .…”

Nutrient Loading through Submarine Groundwater Discharge and Phytoplankton Growth in Monterey Bay, CA

“…9−11 The advective supply of nutrients to Monterey Bay from regional upwelling originates at upwelling centers north and south of the bay. 7,8 Upwelling can also occur within the bay, in response to diurnal sea-breeze forcing. 12 In addition to wind-forced upwelling, internal oscillations over Monterey Canyon can force nutrient fluxs from the canyon onto the shelf.…”

The California Current System: A multiscale overview and the development of a feature-oriented regional modeling system (FORMS)

“…The upwelling activity subsides in September, when the northwesterlies die down, which leads to downwelling in October. The relaxation of the upwelling in August is described by Ramp et al (2005) and in Rosenfeld et al (1994). Haley et al (2009) The inshore region of the CTZ is complicated by the poleward flow being interrupted by the summer upwelling jets flowing equatorward near the mouth of Monterey Bay .…”