Climate Variability OCEA 101
Why should you care? - the associated atmospheric and oceanic changes accompanying climate variability yield significant changes in the distribution of nutrients and marine organisms
Outline El Nino Southern Oscillation Pacific Decadal Oscillation North Atlantic Oscillation Influences on marine environments
The El Nino Southern Oscillation Additional information available at: enso.ucsc.edu
Normal Conditions in the tropical Pacific L H Low P HIgh P
Equatorial Upwelling Ekman Transport NE Trades Warm SST High Sea Level The West Pacific Warm Pool Cold SST Low Sea Level The Equatorial Cold Tongue SE Trades Equator Ekman Transport
Idealized Vertical Section in the Ocean along Equator (Normal Conditions) West Strong Trades Ocean surface East Depth Warm surface layer Strong Upwelling Thermocline Cold subsurface layer
Upper Ocean Temperature Structure: Normal Year
Equatorial Upwelling Normal Year
Equatorial Upwelling and Ocean Chlorophyll
Sea Level Normal Conditions During a normal year, the sea-level stands about 16 inches higher in the equatorial west Pacific than in the east.
Normal Conditions in the Tropical Pacific
El Nino Conditions
West Idealized Vertical Section at Equator (El Nino Year) Weak Trades Ocean surface East Depth Warm surface layer Weak upwelling Thermocline Cold subsurface layer
Upper Ocean Temperature Structure: El Nino Year
El Nino SST
El Nino Sea Level Changes
Irregular Occurrence of El Nino A timeseries of a temperature index of El Nino and La Nina
Equatorial Kelvin Waves Sea level signals propagate eastward as an equatorial Kelvin wave. Equatorial Kelvin waves have very long wavelengths, only propagate east, and rely on both gravity and the Coriolis Force as a restoring force. They move at about 3 m/s crossing the Pacific in about 3 months.
Strong Trades Weak Trades Kelvin Wave Kelvin Wave Kelvin Wave
What happens when an equatorial Kelvin Wave reaches the coast of central America? Coastal Kelvin Waves Coastal Kelvin Waves
Coastal Kelvin Waves Coastal Kelvin propagate with the coast on their right (left) in the NH (SH): - they propagate polewards along eastern boundaries - they propagate equatorwards along western boundaries Coastal Kelvin waves move the thermocline up and down as they pass by. The coastal Kelvin waves along US west coast during El Nino years lower the thermocline.
California Coastal Upwelling During a Normal Year Equatorward Wind California Coastal Upwelling During an El Nino Year Equatorward Wind Thermocline Thermocline Cold, nutrient rich upwelled waters from below the thermocline Warm, nutrient deplete upwelled waters from above the now deeper thermocline due to passage of a coastal Kelvin wave
Influence of El Nino on Marine organisms Normal Year 1962 Maps of Sea Surface Temperature (SST) during a normal year (1962) and an El Nino year (1958) El Nino Year 1958
Euphausid Distributions During Normal and El Nino Years El Nino 1958 El Nino 1958 Subarctic krill (cold species) Tropical krill (warm species) Note the change in distribution of cold and warm species of krill during the El Nino Normal 1962 Normal 1962 Also note low krill abundance in SCB during El Nino Affects entire marine food chain Subarctic krill (cold species) Tropical krill (warm species)
El Niño Impacts on Coastal California
Mean weaning weights for Elephant Seal pups during 1997-98 were at an all time low 75% first-year mortalities for marine mammals (seals, sea lions) was reported Monterey was inundated by starving marine mammals
Monterey Bay Whale Abundance During El Niño Courtesy of B. Marinovic
Changes in Phytoplankton Populations Along Coast of Peru Distributional shifts in dinoflagellate populations during the 1982/83 El Nino: Ceratium breve equatorial species (A) A B Protoperidinium obtusum subantarctic species (B) Before El Nino: upwelling cold waters favored by B El Nino peak: warmer surface waters favored by A
Dinoflagellate Ceratium breve equatorial species
Pacific Decadal Oscillation (PDO) Warm Phase Cold Phase Notice the similarity between the tropical warm phase of the PDO and El Nino.
Positive (warm phase) of PDO during 1990s reinforced El Nino events.
A Pacific interdecadal climate oscillation with impacts on salmon production Mantua et al. (1997, Bull Amer. Met Soc.) Note the change in relative abundance Alaskan salmon and WA-OR-CA (WOC) Salmon In relation to the PDO. Note also the out of phase of relation Between Alaskan and WOC Salmon. Note the shading convention is reversed for WOC and Columbia
The North Atlantic Oscillation (NAO) Associated with changes in strength in the Icelandic Low and Bermuda/Azores High
Aleutian Low Azores High Icelandic Low Siberian High
The prevailing winds deliver iron-rich dust to the ocean in the north Atlantic. The rate of dust delivery to the Mediterranean and North Atlantic is correlated with the NAO.
NAO Index
Calanus Abundance NE of British Isles and the NAO Northern species -NAO vs C. Fin. -1*NAO index Southern species NAO vs C. Hel. NAO index
Calunus Distributions and Spawing: Calunus have several distinct life stages Low NAO more N transport more mothers more C. finmarchicus Low NAO less S transport fewer mothers fewer C. helgolandicus High NAO less N transport fewer mothers fewer C. finmarchicus High NAO more S transport more mothers more C. helgolandicus