Some Surface CurrentsSome Surface Currents

Latest Sea Level Latest Sea Level PressurePressure

IntroductionIntroduction

• Some surface currents influence sea Some surface currents influence sea levellevel– Therefore, influence coastal erosionTherefore, influence coastal erosion– Am excluding tides, longshore currents, Am excluding tides, longshore currents,

etcetc

• Currents mostly seasonalCurrents mostly seasonal

• Related to upwelling and Related to upwelling and downwellingdownwelling

Upwelling and DownwellingUpwelling and Downwelling

• UpwellingUpwelling– Describes process of marine waters Describes process of marine waters

rising from some depth in the oceansrising from some depth in the oceans

• DownwellingDownwelling– Opposite. Process of marine waters Opposite. Process of marine waters

sinking to greater depths.sinking to greater depths.

Ekman TransportEkman Transport

•Net water movement 90° to right of wind direction in N. Hemi.Net water movement 90° to right of wind direction in N. Hemi.

• Winds over HWinds over H22O set ocean surface currents in motionO set ocean surface currents in motion• Surface HSurface H22O is deflected 45° by O is deflected 45° by Coriolis EffectCoriolis Effect

In Northern Hemisphere

• Deflection increases with depthDeflection increases with depth

Upwelling and DownwellingUpwelling and Downwelling

California & California & Western U.S.Western U.S.

• Spring & SummerSpring & Summer– Northerly windNortherly wind– Promotes upwellingPromotes upwelling– Lowered sea levelLowered sea level

• Winter and SummerWinter and Summer– Southerly windsSoutherly winds– Promotes Promotes

downwellingdownwelling– Higher sea levelHigher sea level

Aleutian Low A semi-permanent, subpolar area of low pressure located in the Gulf of Alaska near the Aleutian Islands. It is a generating area for storms and migratory lows often reach maximum instensity in this area. It is most active during the late fall to late spring. During the summer, it is weaker, retreating towards the North Pole and becoming almost nonexistent. During this time, the North Pacific High pressure system dominates. NWS

Los Angeles & San Diego Average Los Angeles & San Diego Average Seasonal Cycles in Sea LevelSeasonal Cycles in Sea Level

Divergence and Divergence and ConvergenceConvergence

•ConvergenceConvergence

– Wind-driven currents collideWind-driven currents collide

– DownwellingDownwelling

• DivergenceDivergence– Currents move awayCurrents move away– UpwellingUpwelling

• Equatorial regionEquatorial region– Created by SE and NE Created by SE and NE

trade windstrade winds– DivergenceDivergence

– UpwellingUpwelling

Note Equatorial UpwellingNote Equatorial Upwelling

Peru UpwellingPeru Upwelling

California Upwelling Spring & California Upwelling Spring & SummerSummer

High Productivity

Diatomaceous sediments accumulate, preserved in basins

Stop HereStop Here

Geostrophic CurrentsGeostrophic CurrentsGyresGyres

•Convergence thickens surface layer – builds a domeConvergence thickens surface layer – builds a dome

• Circular current systems in major ocean basins: GyresCircular current systems in major ocean basins: Gyres

gyre gyre

gyre gyre gyre

• Boundary currents parallel to ocean marginsBoundary currents parallel to ocean margins

Pacific CurrentsPacific Currents

•Equatorial and boundary currents Equatorial and boundary currents Convergence Convergence– Warm currents in West PacificWarm currents in West Pacific

– Cold currents in East PacificCold currents in East Pacifici.e. Kuroshio, Australiai.e. Kuroshio, Australia

i.e. California, Perui.e. California, Peru

California Current

•Most studied-separates from east flowing North Pacific Current•Flow from shelf break to 1000km offshore•Movement down to 500m, speeds to .5m\sec•Interacts with sea floor•Eddy produces counter current

California CurrentCalifornia Current

Colder water transported southward

Changes in current strenght,position impacts sediment accumulation

Changes associated with El Nino/La Nina events, glacial/interglacial period

Santa Barbara Basin Core-Santa Barbara Basin Core-Monterey RocksMonterey Rocks

• Laminated Laminated diatomaceous diatomaceous sedimentsediment

• Changes in Changes in forams distinct forams distinct at 1925 and at 1925 and later. More later. More tropical-tropical-subtropical formssubtropical forms

• Low oxygen level Low oxygen level preserve layerspreserve layers

www.sakura.cc.tsukuba.ac.jp (c) 2005 David Field

Western IntensificationWestern Intensification

•Gyres displaced to west by Earth’s rotationGyres displaced to west by Earth’s rotation

• Western IntensificationWestern Intensification– Faster, narrower currentsFaster, narrower currents

• Eastern CurrentsEastern Currents– Slower, more diffuse currentsSlower, more diffuse currents

El Niño YearEl Niño Year

•Factors producing El Niño yearFactors producing El Niño year

– Warmer HWarmer H22O moves eastO moves east

– Rainfall shifts from eastern to western PacificRainfall shifts from eastern to western Pacific• May result from atmospheric pressure changesMay result from atmospheric pressure changes

– Thermocline deepensThermocline deepens

– Trade winds weakenTrade winds weaken

– Upwelling ceases along western S. AmericaUpwelling ceases along western S. America

El Niño ImpactEl Niño Impact

•Leads to death of cold-water organismsLeads to death of cold-water organisms• Warm-water organisms migrate north and southWarm-water organisms migrate north and south

Temperature VariationsTemperature Variations

britannica

Coriolis on a CylinderCoriolis on a Cylinder