Chapter 2.3 Tides and Ocean currents

Tides

the regular rise and fall of the ocean's surface influenced by the gravitational interactions of the Moon, Earth and Sun.

Tides are found in

all costal areas as well as large lakes. Ex: Bay of Fundy in Canada

Tidal Pattern: Semi-Diurnal

a tidal cycle with two high tides and two low tides of approximately equal height each lunar day.

Semidiurnal tide = 2 high tides and 2 low tides per day

Diurnal

Diurnal tide = 1 high tide and 1 low tide per day

Tidal range / Amplitude

The difference in height between the low-water mark and the high-water mark on a coastline.

What is the average Tidal Range ?

In SOME PLACES the average Tidal Range is 12m while in others, the tidal range is close to zero, due to:

-Gravitational effects on the Moon, Earth and Sun

- physical features of the coastline where the tide is occurring

- environmental factors such as wind, air pressure and size of the body of water.

Tidal Range in small bodies of water.

Small bodies of water, such as Mediterranean or Red Sea, also have tidal ranges, but they are minimal. Small tidal ranges also occur in large lakes, such as Lake Superior in the northern United States, but the effect is usually masked by the winds blowing across the lake.

Shape of the coastline

The shape of the coastline plays a significant role in the size of the tidal range. If the tide is entering a NARROW channel ( a river mouth or entrance to an estuary ) the tidal height is increased because the water is being forced into a smaller area.

IF, however the tide is happening along an open beach(WIDE) , the tidal height is much shorter because the same volume of water is more spread out.

EX- The Bay of Fundy in Canada, home to the highest tidal range in the world. The highest water level recorded there was 21.6 m,

Ex- The Mediterranean and Baltic Sea ( really small tidal range )

Weathers affect on Tidal Range

-Changes in wind and air pressure can have incredible effects on tidal range

-During a cyclone, air pressure is much lower than usual, allowing water to swell

- as-well as high winds capable of pushing water onto shore (combined these two factors can create a tidal surge)

Tidal Surge

- A dangerous rising of water higher than the predicted levels of the tide.

Spring Tides

-create greatest tidal range

-Occurs during the phases of new moon and full moon

-Straight Line configuration

-amplifies the gravitational effects the moon and sun have on earth, creating a larger ocean bulge

-creates highest of high tides (HH) and Lowest of low tides (LL)

Spring Tide (Full Moon)

Sun, Earth, Moon

Spring Tide (new moon)

Sun, Moon, Earth

It's always low tide in the

North and South Poles

Neap Tides

Neap Tides have the smallest tidal range, with the highest low-tide marks (HL) and the lowest high-tide (LH) marks. During these tides the Sun and Moon are at a right angle to each other, with the Earth as the pivot point .

-Neap tides occur during the first- and third-quarter moon phases. During this time, the Sun and Moon are pulling the ocean in opposite directions , creating a smaller than average ocean bulge.

neap tide (first quarter moon)

Sun, earth at pivot point , and moon under then earth at a right angle

Neap tide (last quarter moon)

Sun, earth at pivot point, and moon over the sun

Coriolis Effect definition

A force that acts on the Earths rotation that causes objects or particles in motion to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

The higher the salinity the _____ the density.

higher

Currents

-currents are a continuous directional movement of seawater caused by wind, salinity, temperature and density, coriolis effect and shape of the seabed .

- Currents carry nutrients, dissolved gas, heat and even organisms with them.

- Currents have impacts on ecosystems and global climate.

What are surface currents?

-driven by the wind.

-steady and dependable of global wind patterns caused by an uneven heating of the Earth's surface by the Sun-

What are surface currents caused by?

the wind and the Coriolis effect.

Surface currents process

-Areas with large amounts of solar radiation (the equator) have excess heat energy

-causes air to rise in the atmosphere

-As air rises it transfers away some of its heat energy until it begins to sink in areas with less radiation and cooler temperatures

-movement of air in convection currents forms predictable winds

-this leads to constant surface sea currents at different latitudes

Coriolis Effect and surface currents

-Northern Hemisphere surface currents have clockwise spiral

- Southern Hemisphere they have a counter-clockwise spiral

-When an object moves across Earth, the object swerves to the left/right not in a straight line

-when wind blows the seawater across the ocean surface the rotation of the Earth actually deflects the water at a (45°) angle

-That is why wind and currents have spiral patterns away from the equator in both hemispheres.

Deep currents definition

movements of ocean water far below the surface

Deep currents

-Driven by differences in density caused by differences in temperature and salinity

-happen along the ocean floor and cannot be detected by satellite imagery the way surface currents can

-movement of these currents over the planet is called the global ocean conveyor belt .

What is the global ocean conveyor belt and why is it important?

The global ocean conveyor belt is a deep-water current system driven by temperature and salinity differences (thermohaline circulation). It moves cold, salty water from the Arctic through the Atlantic, Indian, and Pacific Oceans, rising and warming as it circulates. This system helps regulate global climate by distributing heat and nutrients around the world.

Thermohaline Circulation

large-scale ocean circulation caused by density differences due to temperature and salinity changes in the worlds ocean.

Down-swelling

The downward movement of water in the sea due to density differences

Cause: Occurs when surface water becomes denser (due to cooling or increased salinity) and sinks.

Effect: Moves oxygen-rich water to the deep ocean; important for deep-sea ecosystems.

Upswelling

The movement of deep, cold, nutrient-rich water from deep in the ocean to the surface.

*The process of upwelling as a result of surface winds.

Cause: Happens when surface water is pushed away (often by wind), and denser water from below rises to replace it.

Effect: Brings nutrients to the surface, supporting rich marine life and fisheries.

What does ENSO stand for?

El Niño Southern Oscilation

ENSO (El Niño Southern Oscillation) is a natural climate pattern that occurs every 3-5 years in the Pacific Ocean. Involves changes in ocean temperatures, winds, and rainfall. It has two main phases: El Niño, when warm water builds up near South America causing heavy rain there and drought in Australia and Asia, and La Niña, which causes the opposite—cooler water in the east and more rain in the west. Changes ocean currents.

What are the normal conditions in the equatorial Pacific Ocean?

Currents flowing north along the west coast of South America bring cold, nutrient-rich water towards the equator. As strong south-westerly winds blow water away from the coast, the cold water moves toward the surface, causing upwelling and high productivity. This supports small fish like anchovies, seabirds, and large marine consumers. Westerly winds push warm water toward Australia and Asia, where it evaporates, forming storm clouds and heavy rain. The eastern Pacific stays fairly dry.

What happens during El Niño conditions in the equatorial Pacific Ocean? PRT.1

Prevailing trade winds that normally blow from east to west weaken/stop. This prevents warm water and moist air from moving west, causing warm water to build up along the coast of South America. This stops the upwelling that usually occurs when the Humboldt Current brings cold water to the surface. As a result, Indonesia and Australia experience drought due to reduced rainfall, while Peru and the eastern Pacific experience increased rainfall.

EL Niño PRT.2

Without upwelling off the South American coast, there is no fresh supply of nutrients or colder water to reduce surface temperatures. Many cold-water species die, and primary productivity declines steeply due to lack of nutrients. This impacts all levels of the local food web, causing ecosystems and fishing industries to fail. Peruvian fishermen first noticed this change when warm waters in December stopped fish catches, allowing them to stay home for Christmas. The phenomenon was named El Niño, Spanish for "the boy child," in honor of the baby Jesus.

La Niña

La Niña, meaning "the girl" in Spanish, is a cooling phase that usually follows an El Niño event and shows the opposite pattern. It happens when stronger-than-average trade winds push cold water from the Humboldt Current up to the ocean surface off the coast of Peru, lowering sea surface temperatures by 3-5 °C for at least three months. This brings extra nutrients to the surface, boosting the growth of phytoplankton and increasing ocean productivity. La Niña impacts weather worldwide, especially causing more hurricane activity in the Atlantic Ocean and cooler, wetter conditions in parts of North America.

why does ENSO happen?

Its not proven but people speculate that climate change alters these conditions.

Major El Niño Events

Scientists use the Oceanic Niño Index (ONI) to detect El Niño events by tracking average sea-surface temperatures in the central equatorial Pacific in overlapping 3-month periods. An El Niño is declared when temperatures stay +0.5 °C or higher for five consecutive periods.

Notable strong El Niño events include:

1982-83: Temperatures rose to +2.1 °C, causing massive flooding along the eastern Pacific.

1997-98: Strongest on record, with temperatures reaching +2.3 °C, causing global weather disruptions.

2015-16: Matched the 1997-98 event at +2.3 °C, leading to 16 tropical cyclones in the Pacific and extreme weather worldwide.

El Niño events can cause floods, droughts, and disruptions to marine life and fisheries due to changes in ocean temperature and currents.

Humboldt Current

A cold water curren with low salinity levels that flows north along THR wedtern coast of South America ; also called the Peru current