The oceanography of the northern California national marine sanctuaries is complex and the result of numerous factors. In particular, regional currents such as the California and Davidson Currents are very influential.
Local tidal currents and submarine and terrestrial physical features also influence the area’s oceanographic environment. For example, local outflow from San Francisco Bay affects the Greater Farallones sanctuary.
The calendar year in northern California waters consists of three general oceanographic seasons. Although these occur in each sanctuary at slightly different times (see specific details for Cordell Bank, Greater Farallones and Monterey Bay), the seasons, as they pass through each sanctuary, are characterized by the same phenomena:
- the upwelling period, from early spring to summer: strong southward wind forcing and currents along with cool surface waters
- the relaxation period (or oceanic period), from late summer to early fall: wind relaxation, warmer water temperatures and mainly northward surface currents
- the winter storm period (or Davidson Current period), from late fall to late winter/early spring: rain-bearing cold fronts, rough seas and greater mixing of ocean water
Longer-term climatic variations, principally El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) and global climate change, also affect local physical and biological systems.
ENSO refers to periodic cycling between anomalously warm (El Niño) and cool (La Niña) ocean water temperatures that spread across the equatorial Pacific Ocean. These anomalies indicate perturbations in the ocean and atmosphere that are manifested over broad scales, including the California Current ecosystem. Like ENSO, the PDO comprises a warm and a cool interval (associated with changes in surface water temperatures of several degrees), but over a longer period of time.
Conservation and Management Issues
Offshore waters in the region are in relatively good condition, but nearshore coastal areas, harbors, lagoons, estuaries and tributaries show a number of problems, including elevated levels of coliform bacteria, detergents, oils, nitrates, sediments and persistent pesticides. These contaminants can have a variety of biological impacts – including bioaccumulation, reduced recruitment of anadramous species and transfer of human pathogens – as well as interference with recreational uses due to beach closures.
Phytoplankton blooms, including harmful algal blooms, have increased in frequency and distribution worldwide since 1980. The frequency of such blooms may be increasing with nutrient enrichment from agricultural and urban storm runoff as well as sewage effluent.
All three sanctuaries are involved in a variety of research and monitoring efforts.
PRBO Conservation Science, in collaboration with Cordell Bank and Greater Farallones sanctuaries, study krill and oceanographic processes within these two sanctuaries:
- Distribution and Abundance of Marine Birds, Mammals and Zooplankton Relative to the Physical Oceanography of the Greater Farallones and Cordell Bank
Cordell Bank staff are involved in two projects to learn more about regional oceanographic processes:
The Greater Farallones sanctuary is also involved in other oceanographic studies:
- Sanctuary Ecosystem Assessment Surveys (SEA Surveys)
- Wind to Whales
Examples of the many projects underway with the Monterey Bay sanctuary include the following: