Oceanography & Climate: Tides, Currents, and Marine Ecosystems

El Niño

Warmer than normal sea surface temperature in the central & eastern Pacific.

La Niña

Cooler than normal sea surface temperature in the central & eastern Pacific.

Trade Winds

Weaken during El Niño and strengthen during La Niña.

Upwelling

Deep, cold, nutrient-rich water rises to the surface, feeding phytoplankton and supporting fisheries & biodiversity.

Downwelling

Surface water sinks due to convergence or density, moving oxygen to the deep ocean and driving thermohaline circulation.

Thermohaline Circulation

Driven by differences in temperature and salinity, redistributes heat globally and stabilizes long-term climate.

Gulf Stream

Warm current moving north along U.S. East Coast, warming Western Europe.

Equatorial Currents

Warm, westward currents near the equator that fuel tropical weather systems.

Ocean Temperatures

Warm oceans lead to stronger storms (hurricanes, cyclones) while cooler oceans lead to weaker storms.

Coriolis Effect

Earth's rotation deflects moving fluids to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Coral Reefs

Highly temperature-sensitive; warmer oceans cause coral bleaching, leading to reef decline and biodiversity loss.

Seabirds & El Niño

Depend on fish supported by upwelling; El Niño causes food shortages and mass die-offs.

Gulf Stream Weakening

Results in colder Northern/Western Europe and potential heating of the tropics, disrupting global weather systems.

Precipitation Patterns during El Niño

Increased rainfall and flooding in the Eastern Pacific (Peru/Ecuador) and drier conditions in the Western Pacific (Australia/Indonesia).

Underwater Features & Currents

Seamounts and ridges deflect currents, create eddies, and support diverse ecosystems and migratory pathways.

Impact of Warm Currents

Bring moisture and heat, resulting in warmer, wetter coasts.

Impact of Cold Currents

Bring cool, dry conditions, resulting in deserts and less rainfall.

South America's Coasts: Climate Contrast

Cold Peru (Humboldt) Current leads to cool, dry coastal deserts on the West Coast (e.g., Atacama Desert), while the Warm Brazil Current leads to humid, tropical conditions on the East Coast.

Marine Life during El Niño

Declines due to fewer nutrients from decreased upwelling.

Marine Life during La Niña

Improves due to nutrient-rich waters from increased upwelling.

Tidal range

The difference between the highest high tide and the lowest low tide, calculated as tidal range = (high tide height) − (low tide height).

Neap tide

A period of the smallest tidal range, often occurring when the Moon is in the first or third quarter.

Flood tide

A phase where the water level is rising, indicated by an upward curve on a tidal chart.

Ebb tide

A phase where the water level is falling, indicated by a downward curve on a tidal chart.

Slack tide

A phase where the water level shows little change, indicated by a flat curve at the top (near high) or bottom (near low) of a tidal chart.

Lunar cycles

The phases of the Moon, which influence the occurrence of spring tides at the new moon and full moon.

Spring tides

Tides that occur at the new moon and full moon when the Sun, Moon, and Earth are aligned, resulting in the largest tidal ranges.

Gravitational forces

The forces exerted by the Earth, Moon, and Sun that interact to create tidal movements.

Tidal forces

The gravitational effects of the Moon and Sun on Earth's oceans that cause tides.

Intertidal organisms

Marine life that relies on regular exposure and submersion, affected by tidal ranges.

Coastal navigation

The practice of navigating coastal waters, which is influenced by tidal ranges affecting water depth and safe passage timings.

Currents

The flow of water that can be affected by tidal phases, influencing activities like fishing and boating.

Nutrient transport

The movement of nutrients into estuaries, which can be enhanced by flood tides.

Larval transport

The movement of larval marine organisms, which can be influenced by tidal ranges.

Habitat availability

The accessibility of habitats for marine life, which can be affected by changes in tidal ranges.

Docking

The process of bringing a boat to a dock, which can be made harder by strong flood currents.

Shoals and mudflats

Shallow areas that can be exposed during ebb tides, affecting navigation and marine life.

Fishing methods

Techniques used in fishing that may be less effective during slack tides due to minimal current.

Earth's rotation

The spinning of the Earth that carries shorelines through tidal bulges, producing cyclic tidal movements.

Tidal chart

A graphical representation of tidal heights and times, used to identify tidal phases.

Tidal forcing

The influence of celestial bodies on the ocean's tides.

Semidiurnal tide

A tidal pattern with two high tides and two low tides roughly every 24 hours.

Diurnal tide

A tidal regime with one high tide and one low tide each lunar day (~24 hours 50 minutes).

Coastal flooding risk

Increased likelihood of flooding in coastal areas during storms or onshore winds.

Tidal currents

The flow of water caused by the rise and fall of tides, which can change sediment transport and erosion patterns.

Intertidal feeding zones

Areas that are exposed at low tide and submerged at high tide, providing feeding opportunities for certain species.

Tidal range calculation

To calculate tidal range, subtract the low tide height from the high tide height (e.g., high - low).

Boating impacts from tidal range

Large tidal ranges can change channel depths dramatically, requiring careful timing for safe entry and exit.

Fishing impacts from tidal range

Species distribution and feeding windows shift with tidal depth and current strength, affecting fishing success.

Intertidal harvesting

The collection of resources from areas that are exposed during low tide.

Beach access

The ability to reach the beach, which can depend on the expected tidal range.

Coastal construction

Building activities along the coast that must consider tidal range for planning and safety.

High tide occurrence

If high tide occurs every ~12 hours, it indicates a semidiurnal tide.

Diurnal vs. Semidiurnal impacts

Semidiurnal tides provide more frequent changes in water level, while diurnal tides have longer exposure cycles.

High tide height example

An example high tide height could be 3.2 m.

Low tide height example

An example low tide height could be 0.6 m.

Tidal cycle duration

In a diurnal tidal area, low tide occurs once every ~24 hours.