Chapter 9 - Currents

What is ocean circulation driven by?

it is driven by winds and by differences in water density

What two forces of nature distribute tropical heat worldwide?

winds and ocean currents

• Surface currents are wind-driven movements of water at or near the ocean’s surface

• Thermohaline currents are the slow, deep currents that affect the vast bulk of seawater beneath the pycnocline

Gyre

any large system of ocean surface currents moving in a circular fashion driven by wind movements around the peripheries of major ocean basins

El Niño

climate patterns in the Pacific Ocean that can affect weather worldwide. during this climate pattern, trade winds weaken. warm water is pushed back east, toward the west coast of the Americas

La Niña

climate patterns in the Pacific Ocean that can affect weather worldwide. during this climate pattern, trade winds are even stronger than usual, pushing more warm water toward Asia. Off the west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the surface

What are the three main ocean layers?

1. Surface zone/mixed layer

2. Pycnocline

3. Deep zone

How does temperature change with depth in the thermocline?

The deeper into the ocean you go, the more drastic the temperature drop is

How does temperature change below the thermocline?

Below the thermocline, temperatures experience a steep drop

Ocean current

regular movement of large amounts of water along defined paths

What are the two primary ocean currents?

• Surface Currents (at surface, to a depth of about 400 m)

  • Driving factor: Wind

• Deep Currents (entirely below the effect of wind)

  • Driving factor: Density differences

  • Slow, deep currents

Thermohaline circulation

Ocean circulation driven by differences in density caused by temperature and salinity variations

Why are currents so important?

• Influence world climate and weather

• Ocean navigation and transportation

• Support marine life (transport mechanism, food source)

• Transport of materials (both helpful and harmful) and energy to different regions and depths of the ocean

The primary driving force of ocean currents

Wind

Where do surface currents flow?

around the periphery of ocean basins

Why can’t water flow uphill?

• Hills in the mid-oceans

• Maintained by wind energy (waves are pushed forward and down, cannot be pulled upwards)

Geostrophic gyres

The horizontal movement of surface water arising from a balance between the pressure gradient force and the Coriolis force

What are the five major gyres?

• North Atlantic Gyre

• South Atlantic Gyre

• North Pacific Gyre

• South Pacific Gyre

• Indian Ocean Gyre

Boundary current

ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents

Western boundary currents

• Narrow, deep, fast currents

• Western boundaries of ocean basins

Eastern boundary currents

• Cold, shallow, broad currents

• Boundaries not well defined

Countercurrents

a current running in an opposite direction to another current

Undercurrents

a current of water below the surface and moving in a different direction from any surface current

What is the role of warm water?

to transfer heat to higher latitudes

What is the role of cold water?

to cool down lower latitudes

Upwelling/downwelling

wind-induced vertical circulation

Langmuir circulation

long sets of counter-rotating gyres at the ocean surface

Southern Oscillation

changes in winds across the tropical Pacific

“Global conveyor belt”

a constantly moving system of deep ocean circulation driven by temperature and salinity. regulates temperatures and salinities throughout the world

What drives ocean currents?

• Density gradients (differences) drive deep ocean currents

• Upwelling brings cold, nutrient-rich water from the depths up to the surface

• Wind is one of the primary drivers of surface currents

Water masses

• Surface water (to 200 meters)

• Central water (to bottom of main thermocline)

• Intermediate water (to 1500 meters)

• Deep water (below intermediate water to 4000 meters)

• Bottom water (in contact with seafloor)

How is Thermohaline and Surface Flow connected?

• Polar regions – formation of bottom water

  • Downwelling

• Water masses move slowly across ocean bottom, rise slowly

• Convergence zones

• Contour currents – bottom currents

How does ocean water circulate?

in currents which move all around the world

What percentage of the uppermost ocean do surface currents affect?

10%

Surface currents

currents that are driven by global wind systems that are fueled by energy from the sun. flows horizontally and transfers heat from the equator to the poles