© 2011 Pearson Education, Inc.

Gulf Stream Best studied of all

ocean currents Meanders and

loops Merges with

Sargasso Sea Circulates

around center of North Atlantic Gyre

Unique biology – Sargassum

© 2011 Pearson Education, Inc.

Gulf Stream Meanders or loops

may cause loss of water volume and generate:

Warm-core rings – warmer Sargasso Sea water trapped in loop surrounded by cool water

Cold-core rings – cold water trapped in loop surrounded by warmer water

Unique biological populations

© 2011 Pearson Education, Inc.

El Nino – Southern Oscillation (ENSO)High pressure in

eastern Pacific weakens

Weaker trade windsWarm pool migrates

eastwardThermocline deeper in

eastern PacificDownwellingLower biological

productivityPeruvian fishing

suffers

Downwelling

© 2011 Pearson Education, Inc.

ENSO Conditions in the Pacific Ocean

© 2011 Pearson Education, Inc.

La Nina – ENSO Cool PhaseIncreased pressure

difference across equatorial Pacific

Stronger trade winds

Stronger upwelling in eastern Pacific

Shallower thermocline

Cooler than normal seawater

Higher biological productivity

Stronger upwelling

© 2011 Pearson Education, Inc.

La Nina Conditions

© 2011 Pearson Education, Inc.

Occurrence of ENSO EventsEl Niño warm phase about every

2–10 yearsHighly irregularPhases usually last 12–18 months10,000-year sediment record of eventsENSO may be part of Pacific Decadal

Oscillation (PDO) Long-term natural climate cycleLasts 20–30 years

© 2011 Pearson Education, Inc.

ENSO Occurrences

© 2011 Pearson Education, Inc.

ENSO has Global Impacts

© 2011 Pearson Education, Inc.

Notable ENSO Events1982 – 19831997 – 1998 Flooding,

drought, erosion, fires,tropical storms, harmful effects on marine life

Unpredictable

© 2011 Pearson Education, Inc.

Predicting El Nino Events Tropical Ocean−Global Atmosphere (TOGA)

program1985Monitors equatorial South PacificSystem of buoys

Tropical Atmosphere and Ocean (TOA) projectContinues monitoring

ENSO still not fully understood

© 2011 Pearson Education, Inc.

Ocean Currents and ClimateWarm ocean currents

warm the air at the coast.Warm, humid airHumid climate on

adjoining landmassCool ocean currents

cool the air at the coast.Cool, dry airDry climate on

adjoining landmass

© 2011 Pearson Education, Inc.

Upwelling and DownwellingUpwelling – Vertical

movement of cold, nutrient-rich water to surfaceHigh biological

productivity

Downwelling – Vertical movement of surface water downward in water column

© 2011 Pearson Education, Inc.

Coastal UpwellingEkman transport

moves surface seawater offshore.

Cool, nutrient-rich deep water comes up to replace displaced surface waters.

Example: U.S. West Coast

© 2011 Pearson Education, Inc.

Other Types of UpwellingOffshore windsSeafloor

obstruction Coastal geometry

change

© 2011 Pearson Education, Inc.

Coastal DownwellingEkman transport

moves surface seawater toward shore.

Water piles up, moves downward in water column

Lack of marine life