Observations of divergence and upwelling around Point Loma, California

Abstract

[1] Historical records of near-surface water temperatures in the Southern Californian Bight often show a preferential cooling in the lee of headlands such as Point Dume, Palos Verdes, and Point Loma. At times, this cooler water is associated with an increase in chlorophyll-a as is evident in satellite images of ocean color from the region. Here we combine hydrographic data from a 1 day cruise aboard the RV Roger Revelle (a precursor to the 0304 California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruise) with high-frequency (HF) radar (CODAR) measurements, satellite images, and long-term thermistor records of near-surface temperature to identify a small-scale, isolated upwelling in the lee of Point Loma (32.5°N). Associated with the more saline water downstream of the headland are higher nutrient concentrations, an increase in chlorophyll-a concentration, and a bloom of chain-forming diatoms, indicative of a mature upwelling system. It is suggested that this upwelling is not primarily due to local or remote wind forcing but rather to the divergence of the prevailing southerly flow as it passes the Point Loma headland. Time series of surface vorticity calculated from HF radar measurements of sea surface velocity show that as the flow separates from the headland, relative vorticity increases offshore of the cape. Inshore, the time series of divergence/convergence shows a tendency toward divergence at the surface, indicating a preferential upwelling which appears to raise the thermocline, thus resulting in a flux of cold nutrient-rich water to the surface. In the presence of high nutrients and light, photosynthetic organisms bloom in these upwelled waters as they are advected away from the headland and offshore by the prevailing surface currents.

Measuring pH variability using an experimental sensor on an underwater glider

“…values are likely the result of changes in the carbon equilibrium due to the consumption of CO 2 (Cornwall et al, 2013;Rivaro et al, 2010;Copin-Montégut and Bégovic, 2002). A similar relationship between pH and primary production was described by Álvarez et al (2014) in the western Mediterranean Sea.…”

“…Some water makes its way northward and follows the shelf back west towards the Atlantic Ocean (Rivaro et al, 2010;Millot, 1999). At deeper depths, warmer saltier waters were found east of 7.5 • E, which is likely to be Levantine Intermediate Water (LIW) identified in the western Mediterranean Sea by a salinity range of 38.45 to 38.65 and θ between 13.07 and 13.88 • C (Rivaro et al, 2010), typically found at depths between 200 and 800 m close to the shelf slope (Millot, 1999). The c(O 2 ) maxima were found at depths between 20 and 90 m. The Mediterranean Sea on the whole is considered to be oligotrophic (Álvarez et al, 2014).…”

“…However, there is a drive to improve spatial and temporal data coverage via autonomous means, similar to what was experienced for temperature and salinity with Argo floats 16 years ago (Roemmich et al, 2003). There is demand to develop a reliable autonomous sensor with a precision and accuracy of 10 −3 that is affordable to the scientific community .…”

Phytoplanktonic primary production modulated by coastal geomorphology in a highly dynamic environment of central Chile

“…In highly dynamic coastal systems where circulation and wind regimes interact with the local geomorphology it is possible to identify sites with higher retention of phytoplanktonic biomass (Roughan et al 2005a, Mace & Morgan 2006, Henríquez et al 2007). In our case, and during normal summer conditions, the wind typically comes from the south and south west with magnitudes that generate coastal upwelling events which in turn promote high levels of primary production (Daneri et al 2000, Poulin et al 2002.…”

“…Another important factor that affects the distribution and the amount of PP and Chl-a is the interaction of coastal geomorphology with nearshore circulation processes (Signell & Geyer 1991, Wing et al 1998, Pawlak et al 2003, Gan et al 2004, Roughan et al 2005a, Mace & Morgan 2006. From local to regional scales, several studies agree that geomorphological factors may influence the occurrence of coastal fronts or the presence of nearshore retention zones that may modify patterns of aggregation and transport of benthic invertebrate larvae (Wing et al 1998, Archambault & Bourget 1999, Botsford 2001, Poulin et al 2002, Palma et al 2006 and furthermore, geomorphological factors influence the distribution of phytoplankton biomass and production (Archambault et al 1999, Shanks & McCulloch 2003, Henríquez et al 2007.…”