CalClim: California Climate Data Archive

CALIFORNIA CLIMATE WATCH
CURRENT ISSUE: January 2005

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Motions of the Ocean: The California Current

By Laura Edwards
Western Regional Climate Center

Whenever we hear about climate variability, we usually hear about temperature and precipitation trends on land, generally speaking where the people live. It is sometimes easy to forget the role of the Pacific Ocean in California's climate, despite its intricate connection to atmospheric conditions over land. The California Current System (CCS) is one near-shore phenomenon that has an impact on the terrestrial climate, as well as the economical livelihood, and beach environments from Oregon to Baja California.

Figure 1 (right). Ocean currents and location of California Current System.

Figure 2 (left). Satellite image of spring upwelling in May 1998. http://www.mbari.org/bog/Projects/Satellite/Default.htm

The CCS forms the eastern boundary of the North Pacific subtropical gyre, a wind-driven clockwise circulation in the Pacific basin. The western side of this gyre is formed by the Kuroshio current off Japan, bounded in the south by the North Equatorial current (east to west flow) and in the north by the North Pacific current (west to east flow). The California Current surface flows equatorward, or north to south, in a region within about 1000 km of the shoreline. Eastern boundary currents are generally shallower than western currents, and the CCS is about 500 m deep, with a peak speed of about 10 cm per second, or .22 miles per hour. There is also an undercurrent at about 200 m deep that flows poleward (south to north) at a speed of about 15 cm per second, or .33 miles per hour, in addition to another surface counter current.

The CCS was once thought of as a weak eastern boundary current, but research using CalCOFI (California Cooperative Oceanic Fisheries Investigations), a project to observe and monitor conditions of the CCS, and other data networks have shown that it has a strong seasonality and diverse characteristics (1). Timescales of days to weeks are affected by weather patterns and upwelling, when deep, nutrient-rich water rises to the surface along the coast, especially when offshore winds are strong. Seasonality has been detected in strength of winds, currents, salinity and water temperature. Interannual variability, such as El Niño and La Niña, and interdecadal phenomenon such as the Pacific Decadal Oscillation, also affect the CCS. Additionally, the strength and position of the Aleutian Low and the Madden-Julian Oscillation impact the CCS. All of these factors combine to make cycles in the physical and biological properties off California's coast (1,2,3).

Figure 3. Average atmospheric and surface currents in winter and summer in the North Pacific. http://www-odp.tamu.edu/publications/167_SR/chap_32images/38_f03.gif

The importance of the CCS is particularly evident in the fishing industries. CalCOFI was developed after a sharp decline in the sardine fishery. This network of offshore observations provided a goldmine of data on the physics of the current itself, but also the biology and productivity of the region. The species studied included not only sardine, but also anchovy, salmonids, kelp, seabirds and plankton. Researchers found large fluctuations in abundance of the individual species between 1950s and 1990s, but there is evidence for stability at the assemblage, or community level (2). Some species thrive when water temperatures are cooler, some in warmer temperatures, as well as in different strengths of the current and upwelling. North/South variability has been detected, and the historical patterns have suggested that the coastal California Current and Gulf of Alaska/Aleutian Low systems are coupled, but out of phase (4).

In investigating the trends and cycles of biology in the CCS, models have been developed using our current knowledge. Regimes, or periods of a decade or longer during which climatic and oceanographic variables fluctuate around some average value, have been detected. Regime shifts have been known to occur around 1910, 1925, 1947, 1976-77 and perhaps 1998. These regimes have consisted of cooler/warmer ocean temperatures, shifts in upwelling-favorable winds and biological productivity. Predicting these regime shifts and the accompanying impacts on the CCS are important for climate modeling regionally and globally.

Almost all of the researchers note that long-term, continuous data sets are needed for further development of our knowledge of the California Current System (2,3). Our historical records of oceanic properties and biology are scattered and short. It is easy to forget the effect of the CCS on our terrestrial lives, but it is intricately connected and we may not be able to afford the cost of overlooking it.

References:
1. Miller, A. J. et al, 1999. Observing and modeling the California Current System. Eos, Transactions, AGU, 80, 533-539.

2. Rebstock, G. A., 2003. Long-term change and stability in the California Current System: lessons from CalCOFI and other long-term data sets. Deep-Sea Res. II, 50, 2583-2594.

3. Peterson, W. T. and F. B. Schwing, 2003. A new climate regime in northeast Pacific ecosystems. Geophys. Res. Lett., 30, 17, doi:10.1029/2003GL017528.

4. Mantua, N., et al., 1997. A Pacific interdecadal climate oscillation with impacts on salmon production, Bull. Am. Meteorol. Soc., 78, 1069-1079.

For more information:
1. Wind-driven circulation, http://www.glacier.rice.edu/oceans/4_windcirculation.html
2. California Current Ecosystem, http://lternet.edu/sites/cce/
3. California Current System, ocean drilling, and paleoclimate, http://www-odp.tamu.edu/publications/167_SR/chap_32/c32_2.htm

Page last updated 2/11/05.

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Climate Watch Archive All data in the Climate Watch is provisional and subject to change. Jan 2005 [PDF] [Word] For 2004 stories, click here Monthly Summaries by Bill Mork 2005 2004	CALIFORNIA CLIMATE WATCH CURRENT ISSUE: January 2005 Read the full newsletter here: Word Format or PDF format Motions of the Ocean: The California Current By Laura Edwards Western Regional Climate Center Whenever we hear about climate variability, we usually hear about temperature and precipitation trends on land, generally speaking where the people live. It is sometimes easy to forget the role of the Pacific Ocean in California's climate, despite its intricate connection to atmospheric conditions over land. The California Current System (CCS) is one near-shore phenomenon that has an impact on the terrestrial climate, as well as the economical livelihood, and beach environments from Oregon to Baja California. Figure 1 (right). Ocean currents and location of California Current System. Figure 2 (left). Satellite image of spring upwelling in May 1998. http://www.mbari.org/bog/Projects/Satellite/Default.htm The CCS forms the eastern boundary of the North Pacific subtropical gyre, a wind-driven clockwise circulation in the Pacific basin. The western side of this gyre is formed by the Kuroshio current off Japan, bounded in the south by the North Equatorial current (east to west flow) and in the north by the North Pacific current (west to east flow). The California Current surface flows equatorward, or north to south, in a region within about 1000 km of the shoreline. Eastern boundary currents are generally shallower than western currents, and the CCS is about 500 m deep, with a peak speed of about 10 cm per second, or .22 miles per hour. There is also an undercurrent at about 200 m deep that flows poleward (south to north) at a speed of about 15 cm per second, or .33 miles per hour, in addition to another surface counter current. The CCS was once thought of as a weak eastern boundary current, but research using CalCOFI (California Cooperative Oceanic Fisheries Investigations), a project to observe and monitor conditions of the CCS, and other data networks have shown that it has a strong seasonality and diverse characteristics (1). Timescales of days to weeks are affected by weather patterns and upwelling, when deep, nutrient-rich water rises to the surface along the coast, especially when offshore winds are strong. Seasonality has been detected in strength of winds, currents, salinity and water temperature. Interannual variability, such as El Niño and La Niña, and interdecadal phenomenon such as the Pacific Decadal Oscillation, also affect the CCS. Additionally, the strength and position of the Aleutian Low and the Madden-Julian Oscillation impact the CCS. All of these factors combine to make cycles in the physical and biological properties off California's coast (1,2,3). Figure 3. Average atmospheric and surface currents in winter and summer in the North Pacific. http://www-odp.tamu.edu/publications/167_SR/chap_32images/38_f03.gif The importance of the CCS is particularly evident in the fishing industries. CalCOFI was developed after a sharp decline in the sardine fishery. This network of offshore observations provided a goldmine of data on the physics of the current itself, but also the biology and productivity of the region. The species studied included not only sardine, but also anchovy, salmonids, kelp, seabirds and plankton. Researchers found large fluctuations in abundance of the individual species between 1950s and 1990s, but there is evidence for stability at the assemblage, or community level (2). Some species thrive when water temperatures are cooler, some in warmer temperatures, as well as in different strengths of the current and upwelling. North/South variability has been detected, and the historical patterns have suggested that the coastal California Current and Gulf of Alaska/Aleutian Low systems are coupled, but out of phase (4). In investigating the trends and cycles of biology in the CCS, models have been developed using our current knowledge. Regimes, or periods of a decade or longer during which climatic and oceanographic variables fluctuate around some average value, have been detected. Regime shifts have been known to occur around 1910, 1925, 1947, 1976-77 and perhaps 1998. These regimes have consisted of cooler/warmer ocean temperatures, shifts in upwelling-favorable winds and biological productivity. Predicting these regime shifts and the accompanying impacts on the CCS are important for climate modeling regionally and globally. Almost all of the researchers note that long-term, continuous data sets are needed for further development of our knowledge of the California Current System (2,3). Our historical records of oceanic properties and biology are scattered and short. It is easy to forget the effect of the CCS on our terrestrial lives, but it is intricately connected and we may not be able to afford the cost of overlooking it. References: 1. Miller, A. J. et al, 1999. Observing and modeling the California Current System. Eos, Transactions, AGU, 80, 533-539. 2. Rebstock, G. A., 2003. Long-term change and stability in the California Current System: lessons from CalCOFI and other long-term data sets. Deep-Sea Res. II, 50, 2583-2594. 3. Peterson, W. T. and F. B. Schwing, 2003. A new climate regime in northeast Pacific ecosystems. Geophys. Res. Lett., 30, 17, doi:10.1029/2003GL017528. 4. Mantua, N., et al., 1997. A Pacific interdecadal climate oscillation with impacts on salmon production, Bull. Am. Meteorol. Soc., 78, 1069-1079. For more information: 1. Wind-driven circulation, http://www.glacier.rice.edu/oceans/4_windcirculation.html 2. California Current Ecosystem, http://lternet.edu/sites/cce/ 3. California Current System, ocean drilling, and paleoclimate, http://www-odp.tamu.edu/publications/167_SR/chap_32/c32_2.htm Page last updated 2/11/05.