Ocean Circulation Concepts

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Questions and Answers

What characterizes the equatorial Walker circulation during normal conditions in the tropical Pacific?

East-West sea surface temperature gradient driving circulation (correct)

Intense drought conditions in the eastern Pacific

High pressure over the western Pacific and low pressure over the eastern Pacific

Uniform sea surface temperatures across the equator

How does the El Nino phenomenon primarily affect global temperature?

It leads to an increase in global surface temperatures. (correct)

It stabilizes global temperatures at a consistent level.

It has no significant impact on global temperatures.

It decreases global temperatures significantly.

What is a significant consequence of El Nino on rainfall patterns?

Increased rainfall in Indonesia and surrounding regions

Dry conditions in Indonesia with higher occurrence of drought and fires (correct)

Global rainfall becomes entirely predictable

Consistent rainfall distribution across all regions

Which phenomenon is characterized by unusual cooling patterns following El Nino?

La Nina Signup and view all the answers

What role does atmospheric circulation play during El Nino events?

It becomes disrupted, leading to widespread climate impacts. Signup and view all the answers

What happens to anthropogenic carbon emissions during El Nino events?

A larger fraction remains in the atmosphere. Signup and view all the answers

Which of the following is a known impact of El Nino on Southeast Asia?

Increased fire and atmospheric haze pollution Signup and view all the answers

What describes the El Nino-Southern Oscillation (ENSO)?

It represents the conjunction of oceanic and atmospheric phenomena with varying phases. Signup and view all the answers

How does NPP vary during the El Niño and La Niña phases?

NPP is larger during La Niña and smaller during El Niño Signup and view all the answers

Which factor is primarily responsible for seawater density?

Salinity and temperature Signup and view all the answers

What primarily drives surface ocean currents?

Wind patterns Signup and view all the answers

What effect does the Coriolis effect have on subtropical gyres?

It results in westward intensification Signup and view all the answers

What is the main driver of deep-ocean overturning thermohaline circulation?

Density differences Signup and view all the answers

Which phenomenon is considered the most significant climate fluctuation over year-to-year timescales?

El Niño-Southern Oscillation (ENSO) Signup and view all the answers

Which cycles should be focused on in relation to human impacts as per the assigned reading?

C, N, P, and S cycles Signup and view all the answers

How are biogeochemical cycles connected to climate control?

They exert strong control on climate through various interactions Signup and view all the answers

What primarily drives the ocean surface currents?

Winds in the lowermost atmosphere Signup and view all the answers

Which process leads to higher sea levels in gyre centers?

Ekman transport Signup and view all the answers

What effect does the Coriolis effect have on ocean currents in the Northern Hemisphere?

Currents are deflected to the right Signup and view all the answers

What contributes to the formation of deep ocean currents?

The sinking of dense water masses Signup and view all the answers

In terms of ocean circulation, what is the role of upwelling?

It causes nutrient recycling from deeper waters Signup and view all the answers

What is the term for the global oceanic circulation driven by density differences?

Thermohaline circulation Signup and view all the answers

What primarily determines the structure of ocean gyres?

Wind patterns and basin shape Signup and view all the answers

Which water mass forms predominantly in the North Atlantic region?

North Atlantic Deep Water (NADW) Signup and view all the answers

What effect does basin shape have on ocean currents?

It modifies current flow and intensity Signup and view all the answers

Which of the following is NOT a characteristic of Ekman transport?

Uniform direction at all depths Signup and view all the answers

How does temperature influence deep ocean currents?

Cold water density drives sinking Signup and view all the answers

What nutrient cycle is associated with upwelling zones?

Nutrient recycling Signup and view all the answers

What happens to currents as they deepen in the ocean?

They weaken and are further deflected Signup and view all the answers

Study Notes

Surface Ocean Circulation

Driven primarily by surface winds in the lower atmosphere
Density differences (dense water sinking) drive deep ocean circulation (thermohaline)
Friction between ocean layers creates Ekman spirals
Coriolis effect deflects currents relative to surface winds
Bathymetry (ocean floor shape) and basin shape significantly impact currents, though these are mostly fixed now but were different in the past due to plate tectonics.

Surface Currents - Schematic

Largely driven by surface winds
Warm currents transport heat poleward (moving energy)
Basin-scale patterns are called "gyres"
Illustrated with global map showing various ocean currents and gyres (e.g., North Pacific Gyre, South Pacific Gyre, etc.)

Ekman Transport

Wind-driven surface currents are deflected by the Coriolis effect (right in the Northern Hemisphere).
Currents weaken with depth due to friction.
Further deflection with depth by the Coriolis effect.
Net Ekman transport is perpendicular to surface wind stress.
Contributes to convergence and higher sea levels at gyre centers.

Surface Currents - Gyres

Prevailing winds, basin shape, and geostrophic balance, working together, create gyre structures.
Net Ekman transport is perpendicular to surface wind stress.
Leads to convergence and higher sea levels in gyre centers.
Resulting pressure gradient force is balanced via Coriolis effect. Surface flow is geostrophic.
A weaker Coriolis effect near the equator results in narrow, strong western boundary currents.

Upwelling

Diverging surface currents cause upwelling along certain coasts (often in the Southern Hemisphere).
Upwelling brings nutrient-rich water from deeper depths to the surface.
Associated with high biological productivity due to the increased nutrients.

Past Surface Ocean Currents

Bathymetry and basin shapes significantly impact ocean currents.
Maps showing current patterns during the Late Jurassic (150-200 million years ago) and Early Tertiary (~50 million years ago) are provided.
Changes in map patterns demonstrates the shifting continents.

Deep Ocean Circulation

Not discussed in detail in the provided images.

Surface Density

Dense, cold, and salty water sinks.
Dense waters significantly contribute to deep ocean overturning circulation

Thermohaline Circulation (THC)

Driven by deep water formation (density-driven).
Connected to temperature(thermo) and salinity (haline)
Arctic deep waters enter the global ocean in the North Atlantic.
Two key deep water masses formed: North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW).
NADW mainly forms in the North Atlantic, Norwegian, and Greenland Sea regions.
AABW forms around Antarctica.

THC in Ocean Properties

Graphs illustrating temperature and salinity variations are provided with depth in the Atlantic Ocean.
NADW and AABW deep water locations indicated and shown as features of the THC.

The Thermohaline Circulation - Globally

Circulation patterns are shown on a global map, emphasizing deep and surface currents.
Deep water masses (NADW, AABW), form and flow throughout the globe.

El Niño Phenomenon

Characterized by unusual warming in the central and/or eastern Pacific Ocean.
This impacts the ENSO (El Niño-Southern Oscillation) system.
This impacts global atmospheric circulation patterns.

Tropical Pacific - Normal Conditions

East-West sea surface temperature (SST) gradient drives equatorial Walker circulation.
Trade winds blow westwards.
Warm surface water piles up in the western Pacific.
Cold water upwells in the eastern Pacific.
A coupled ocean-atmosphere system.

El Niño Impacts

Global surface temperature increase.
Rainfall anomalies (e.g., droughts in Indonesia).
Increased fire risk in areas with dry conditions.
Reduced land sink for atmospheric carbon (meaning more CO2 in the atmosphere).
Impact on global temperatures are demonstrated by data (like charts).

El Niño and Rainfall Anomalies

"Tele-connections" in atmospheric circulation are important.
Maps show rainfall anomalies associated with El Niño events in various locations.

El Niño and Southeast Asian "Haze"

Lower rainfall combined with land use change leads to fires.
Atmospheric pollution (haze) increases in Southeast Asia during El Niño events.
Visibility Reduction data presented in various geographical areas and given for specific times.

ENSO and Carbon Uptake by Land

ENSO affects Net Primary Production (NPP) in certain regions.
NPP (larger) during El Niño, and (larger) during La Niña.

The Oceans - Summary

Ocean density is determined by temp. and salinity.
Surface currents are driven by wind.
Westward intensification of subtropical gyres is influenced by Coriolis Effect.
Deep-ocean overturning thermohaline circulation is density-driven.
Ocean-atmosphere connections strongly influence climate.

Before the next class

Students should watch a recording about biogeochemical cycles and outlines the C and N cycles
Read article "Planetary Boundaries" (Steffen et al. 2015)
Notes are needed on how human activity impacts C, N, P, and S cycles.

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Description

Explore the fundamental concepts of surface ocean circulation, including the roles of wind, density differences, and the Coriolis effect. This quiz covers key terms such as Ekman transport, ocean currents, and the impact of bathymetry. Test your understanding of how these elements shape our oceans.