California Current
Encyclopedia
The California Current is a Pacific Ocean
current
that moves south along the western coast of North America
, beginning off southern British Columbia
, and ending off southern Baja California
. There are five major coastal currents affiliated with upwelling
zones. These are the California Current (located off the coast of Oregon and California), the Humboldt Current (located off the coast of Chile and Peru), the Canary Current (located off the coast of northwest Africa), the Benguela Current (located off the coast of southwest Africa), and the Somali Current (located in the western Indian Ocean) (Mann and Lazier, 2006). The five major coastal currents are parts of the global ocean gyre system and as such, these currents are driven by wind and deflected by landmasses. Each of the major ocean basins has both a western boundary current and an eastern boundary current. The western boundary currents tend to be deep and fast and the eastern boundary currents are mainly shallow, broad, and less-defined (Mann and Lazier, 2006).
The California Current is an Eastern boundary current and is part of the North Pacific Gyre
, a large swirling current that occupies the northern basin of the Pacific. The movement of northern waters southward makes the coast
al waters cooler than the coastal areas of comparable latitude
on the east coast of the United States
. Additionally, extensive upwelling
of colder sub-surface waters occurs, caused by the prevailing northeasterly winds acting through the Ekman Effect. The winds drive surface water to the right of the wind flow, that is offshore, which draws water up from below to replace it. The upwelling further cools the already cool California Current. This is the mechanism that produces California's characteristic coastal fog
and the negative temperature anomaly we measure in California's coastal waters during summer (Mann and Lazier, 2006). This translates into cold coastal waters during the summer, stretching from Oregon to Baja California. Note, this does not include the coastal water surrounding San Diego. There is a warm water anomaly off San Diego (Mann and Lazier, 2006).
The cold water is highly productive due to the upwelling
, which brings to the surface nutrient-rich sediments, supporting large populations of whale
s, seabird
s and important fisheries. Winds of the appropriate direction and strength to induce upwelling are more prevalent in the presence of Eastern boundary currents, such as the California Current (Mann and Lazier, 2006). Phytoplankton production is dramatically increased in these areas because the nutrient-rich water lying below the pycnocline
is relatively close to the surface and is thus easily upwelled (Mann and Lazier, 2006). Scientists at Scripps Institution of Oceanography
said in 2011 that the average surface temperature of the water at Scripps Pier has increased by almost 3 degrees since 1950.
A narrower, weaker counter current, the Davidson Current
, occasionally moves somewhat warmer water northwards during the winter months. During El Niño events, the California Current is disrupted, leading to declines in phytoplankton
, resulting in cascading effects up the food chain, such as declines in fisheries, seabird breeding failures and marine mammal mortality (Schwing et al., 2003). In 2005, a failure in the otherwise predictable upwelling events, unassociated with El Niño, caused a collapse in krill
in the current, leading to similar effects (Schwing et al., 2003).
Bakun (1973) calculated a 20-year average of the monthly mean Ekman transport for different regions off the California coast. His 'Bakun upwelling index' ranges from 300 meters-cubed/second (in the offshore direction) to -212 meters-cubed/second (toward the coast, or onshore direction) (Mann and Lazier,2006). Bakun's index showed there is year-round upwelling off Southern California's coast, but it is strongest in the summer months. Bakun's work also shows that off the coast of Oregon and Washington, there is forceful downwelling in the winter months, and upwelling in the region is restricted to the months of April through September (Mann and Lazier, 2006).
) and upwelled water. Several studies have investigated the carbon flow from primary production to the pelagic fish stocks which depend on the California Current. Lasker (1988) described powerful 'jets and squirts' off northern and central California. These 'jets and squirts' move large quantities of cold, nutrient rich water offshore. This water then gets carried by the southward bound California Current and adds significant primary production to the sardine population (Mann and Lazier, 2006).
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
that moves south along the western coast of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, beginning off southern British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, and ending off southern Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
. There are five major coastal currents affiliated with upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
zones. These are the California Current (located off the coast of Oregon and California), the Humboldt Current (located off the coast of Chile and Peru), the Canary Current (located off the coast of northwest Africa), the Benguela Current (located off the coast of southwest Africa), and the Somali Current (located in the western Indian Ocean) (Mann and Lazier, 2006). The five major coastal currents are parts of the global ocean gyre system and as such, these currents are driven by wind and deflected by landmasses. Each of the major ocean basins has both a western boundary current and an eastern boundary current. The western boundary currents tend to be deep and fast and the eastern boundary currents are mainly shallow, broad, and less-defined (Mann and Lazier, 2006).
The California Current is an Eastern boundary current and is part of the North Pacific Gyre
North Pacific Gyre
The North Pacific Gyre, located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre comprises most of the northern Pacific Ocean. It is the largest ecosystem on our planet...
, a large swirling current that occupies the northern basin of the Pacific. The movement of northern waters southward makes the coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
al waters cooler than the coastal areas of comparable latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
on the east coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Additionally, extensive upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
of colder sub-surface waters occurs, caused by the prevailing northeasterly winds acting through the Ekman Effect. The winds drive surface water to the right of the wind flow, that is offshore, which draws water up from below to replace it. The upwelling further cools the already cool California Current. This is the mechanism that produces California's characteristic coastal fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
and the negative temperature anomaly we measure in California's coastal waters during summer (Mann and Lazier, 2006). This translates into cold coastal waters during the summer, stretching from Oregon to Baja California. Note, this does not include the coastal water surrounding San Diego. There is a warm water anomaly off San Diego (Mann and Lazier, 2006).
The cold water is highly productive due to the upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...
, which brings to the surface nutrient-rich sediments, supporting large populations of whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s, seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s and important fisheries. Winds of the appropriate direction and strength to induce upwelling are more prevalent in the presence of Eastern boundary currents, such as the California Current (Mann and Lazier, 2006). Phytoplankton production is dramatically increased in these areas because the nutrient-rich water lying below the pycnocline
Pycnocline
A pycnocline is the cline or layer where the density gradient is greatest within a body of water. An ocean current is generated by the forces such as breaking waves, terms of temperature and salinity differences, wind, Coriolis effect, and tides caused by the gravitational pull of the Moon and the...
is relatively close to the surface and is thus easily upwelled (Mann and Lazier, 2006). Scientists at Scripps Institution of Oceanography
Scripps Institution of Oceanography
Scripps Institution of Oceanography in La Jolla, California, is one of the oldest and largest centers for ocean and earth science research, graduate training, and public service in the world...
said in 2011 that the average surface temperature of the water at Scripps Pier has increased by almost 3 degrees since 1950.
A narrower, weaker counter current, the Davidson Current
Davidson Current
In oceanography, the Davidson Current is a coastal countercurrent of the Pacific Ocean running north along the western coast of the United States from Baja California Mexico to northern California to at least latitude 40°N. It prevails during the winter months, generally from September through...
, occasionally moves somewhat warmer water northwards during the winter months. During El Niño events, the California Current is disrupted, leading to declines in phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
, resulting in cascading effects up the food chain, such as declines in fisheries, seabird breeding failures and marine mammal mortality (Schwing et al., 2003). In 2005, a failure in the otherwise predictable upwelling events, unassociated with El Niño, caused a collapse in krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
in the current, leading to similar effects (Schwing et al., 2003).
Bakun (1973) calculated a 20-year average of the monthly mean Ekman transport for different regions off the California coast. His 'Bakun upwelling index' ranges from 300 meters-cubed/second (in the offshore direction) to -212 meters-cubed/second (toward the coast, or onshore direction) (Mann and Lazier,2006). Bakun's index showed there is year-round upwelling off Southern California's coast, but it is strongest in the summer months. Bakun's work also shows that off the coast of Oregon and Washington, there is forceful downwelling in the winter months, and upwelling in the region is restricted to the months of April through September (Mann and Lazier, 2006).
Primary production
Primary production is a topic of interest among those who study the California Current. In their study, Hayward and Venrick (1982) found great variability in both biomass and the productivity of phytoplankton in the California Current. The differences observed by Hayward and Venrick in carbon-fixation rates (0.2-2.0 grams Carbon/(meter-squared x day)) show the heterogeneous nature of the California Current, with its combination of advected (see advectionAdvection
Advection, in chemistry, engineering and earth sciences, is a transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid's bulk motion in a particular direction. An example of advection is the transport of pollutants or silt in a river. The motion of the water carries...
) and upwelled water. Several studies have investigated the carbon flow from primary production to the pelagic fish stocks which depend on the California Current. Lasker (1988) described powerful 'jets and squirts' off northern and central California. These 'jets and squirts' move large quantities of cold, nutrient rich water offshore. This water then gets carried by the southward bound California Current and adds significant primary production to the sardine population (Mann and Lazier, 2006).