Some Surface Currents

Latest Sea Level Pressure

Introduction Some surface currents influence sea level Some surface currents influence sea level –Therefore, influence coastal erosion –Am excluding tides, longshore currents, etc Currents mostly seasonal Currents mostly seasonal Related to upwelling and downwelling Related to upwelling and downwelling

Upwelling and Downwelling Upwelling Upwelling –Describes process of marine waters rising from some depth in the oceans Downwelling Downwelling –Opposite. Process of marine waters sinking to greater depths.

Ekman 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 H 2 O set ocean surface currents in motionWinds over H 2 O set ocean surface currents in motion Surface H 2 O is deflected 45° by Coriolis EffectSurface H 2 O is deflected 45° by Coriolis Effect In Northern Hemisphere Deflection increases with depthDeflection increases with depth

Upwelling and Downwelling

California & Western U.S. Spring & Summer Spring & Summer –Northerly wind –Promotes upwelling –Lowered sea level Winter and Summer Winter and Summer –Southerly winds –Promotes downwelling –Higher 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 Seasonal Cycles in Sea Level

Divergence and Convergence ConvergenceConvergence – Wind-driven currents collide – Downwelling DivergenceDivergence – Currents move away – Upwelling Equatorial regionEquatorial region – Created by SE and NE trade winds – Divergence – Upwelling

Note Equatorial Upwelling

Peru Upwelling

California Upwelling Spring & Summer High Productivity Diatomaceous sediments accumulate, preserved in basins

Stop Here

Geostrophic Currents Gyres 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 Boundary currents parallel to ocean marginsBoundary currents parallel to ocean margins

Pacific Currents Equatorial and boundary currents  ConvergenceEquatorial and boundary currents  Convergence – Warm currents in West Pacific – Cold currents in East Pacific i.e. Kuroshio, Australia i.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 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-Monterey Rocks Laminated diatomaceous sediment Laminated diatomaceous sediment Changes in forams distinct at 1925 and later. More tropical-subtropical forms Changes in forams distinct at 1925 and later. More tropical-subtropical forms Low oxygen level preserve layers Low oxygen level preserve layers (c) 2005 David Field

Western Intensification Gyres displaced to west by Earth’s rotationGyres displaced to west by Earth’s rotation Western IntensificationWestern Intensification – Faster, narrower currents Eastern CurrentsEastern Currents – Slower, more diffuse currents

El Niño Year Factors producing El Niño yearFactors producing El Niño year – Warmer H 2 O moves east – Rainfall shifts from eastern to western Pacific May result from atmospheric pressure changesMay result from atmospheric pressure changes – Thermocline deepens – Trade winds weaken – Upwelling ceases along western S. America

El 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 Variations britannica

Coriolis on a Cylinder