OCEANS Midterm 2

What is bathymetry?

Bathymetry is the measurement of ocean depth, typically done using sound (echo sounding).

What are the three main marine provinces based on bathymetry?

Continental margins, deep-ocean basins, and mid-ocean ridges.

What is the hypsometric curve?

It is a graph showing the distribution of Earth’s surface elevations (land vs. depth below sea level). It reveals that most of the Earth’s surface lies below sea level and that the ocean floor is mostly very flat.

Why does oceanic crust stay “afloat” in isostatic equilibrium?

Because of the balance between gravity (pulling the crust downward) and buoyancy (pushing it up), known as isostasy.

Why does the Atlantic Ocean have thicker sediment than the Pacific?

The Atlantic is smaller and has predominantly passive margins that allow sediments from rivers to accumulate over time. It also had more time to collect weathered material since Pangaea broke apart.

What is a passive margin? Give an example.

A passive margin is the transition between oceanic and continental crust that is not near a plate boundary. They have wide shelves, a continental slope, and a continental rise. An example is the East Coast of North America (Atlantic-type margin).

What is an active margin? Give an example.

An active margin is located at a plate boundary (convergent or transform), typically featuring a trench rather than a rise. They are tectonically active and have narrow shelves. An example is the West Coast of South America or the Juan de Fuca plate boundary off North America (Pacific-type margin).

What are some main features of deep-ocean basins?

Trenches, isolated volcanic peaks (seamounts), and vast abyssal plains.

What is an ion?

An ion is an atom or molecule with an electrical charge (positive = cation, negative = anion).

What makes water a polar molecule?

Water (H₂O) has a partial negative charge on the oxygen side and partial positive charges on the hydrogen ends, creating a dipole.

Why is water called the “universal solvent”?

Because the polarity of water molecules allows them to surround and separate many types of ions or molecules (e.g., dissolving salt).

What type of bond holds together the hydrogen and oxygen atoms within a single water molecule?

Covalent bonds (the atoms share electrons).

What is hydrogen bonding between water molecules?

A dipole-dipole attraction where the positively charged hydrogen of one molecule is attracted to the negatively charged oxygen of another.

How does hydrogen bonding lead to surface tension?

The strong attraction (cohesion) among water molecules at the surface creates a “skin-like” effect known as surface tension

What happens to salt (NaCl) when seawater evaporates or freezes?

Salt does not evaporate or freeze with water. In evaporation, only pure water vapor rises; when freezing, the ice is essentially freshwater while salts remain in the liquid phase.

What is heat capacity, and why is water’s heat capacity important?

Heat capacity is the amount of heat needed to raise 1 gram (or 1 cm³) of a substance by 1°C. Water has a very high heat capacity, meaning it heats and cools slowly, helping regulate Earth’s climate.

How do water’s three phases differ in terms of molecular arrangement?

Ice: Molecules locked in a structured lattice, less dense than liquid water.

Liquid Water: Molecules mostly connected by hydrogen bonds but also move freely.

Vapor: Molecules completely separate with no hydrogen bonding.

Why do coastlines have more moderate temperatures compared to inland areas?

Because water’s high heat capacity allows the ocean to absorb/release large amounts of heat with little temperature change, moderating the nearby air temperature (thermal inertia).

What is the average salinity of the ocean?

About 35 parts per thousand (3.5%).

How does temperature affect water density?

As temperature increases, density decreases (inverse relationship).

How does salinity affect water density?

As salinity increases, density increases (direct relationship).

Where in the oceans do we find the highest surface salinity and why?

Around 30° latitude (the “evaporation latitudes”) where dry conditions lead to higher evaporation rates, leaving salt behind.

Why is the Baltic Sea considered brackish?

It receives a lot of freshwater input from rivers, reducing its overall salinity compared to most seawater.

Why does the Dead Sea have such high salinity?

It is land-locked and located in an arid region, so evaporation concentrates the salt.

Name and describe the three main layers of the ocean by depth.

Surface Layer (Mixed Layer): Top ~200 m, warm and well-mixed by winds and currents.

Thermocline: ~200–1000 m, rapid decrease in temperature with depth.

Deep Zone: Below ~1000 m, cold, dark, very dense, and high pressure.

Where is the thermocline strongest, and why?

It is strongest in tropical regions due to the greatest surface heating and warm upper layers, creating a sharp temperature gradient.

Why does cold, salty water sink at high latitudes?

Because it has a higher density. This sinking process is called downwelling and drives deep ocean currents (thermohaline circulation).

What three factors primarily drive weather on Earth?

The sun (solar energy), the oceans (source of water vapor), and the atmosphere (transport and distribution).

What role does Earth’s rotation play in weather patterns?

It affects wind and ocean current directions (Coriolis effect), distributing heat and moisture around the globe.

What is the hydrologic cycle, and why is it considered one of the simplest cycles on Earth?

The hydrologic cycle describes how water continuously moves between the oceans, atmosphere, and land. It’s considered “simplest” because it involves straightforward processes of evaporation, condensation, precipitation, and runoff, all driven primarily by the sun’s energy.

What are the main processes of the hydrologic cycle?

Evaporation (liquid water turning into vapor, mainly from the ocean’s surface)

Condensation (water vapor cooling and turning into liquid droplets)

Precipitation (water falling from the atmosphere back to land or the ocean)

Runoff (water flowing over land back to the ocean)

What is runoff?

It is any water moving from the land back into the ocean, usually through rivers, streams, and groundwater flow.

Why does evaporation cool the surface of the ocean?

During evaporation, water molecules absorb heat energy as they transition from liquid to gas, removing heat from the ocean’s surface and leaving it slightly cooler.

What happens during condensation, and how does it affect the atmosphere?

Condensation is when water vapor turns back into liquid. As this occurs, the water vapor releases the heat it absorbed during evaporation, warming the surrounding atmosphere.

Why is evaporation considered an energy-intensive process?

Because it takes a substantial amount of heat to overcome the hydrogen bonds between water molecules, allowing them to escape the liquid phase and become vapor.

How does precipitation fit into the hydrologic cycle?

Precipitation (rain, snow, etc.) returns water from the atmosphere to Earth’s surface (land or ocean). Once on land, that water can either infiltrate the soil or become runoff flowing back to the ocean.

How do the oceans supply moisture to the atmosphere in this cycle?

Through evaporation from the ocean surface. The sun’s energy causes surface water to vaporize, feeding moisture into the atmosphere for condensation and precipitation.

How are weather and the hydrologic cycle connected?

The ocean provides the majority of Earth’s evaporated water, which fuels cloud formation and ultimately precipitation. Meanwhile, the sun’s heat and Earth’s rotation distribute this moisture around the globe, driving weather patterns.

What is the significance of water vapor transport in global climate?

Water vapor is a powerful greenhouse gas; it transports latent heat as it moves through the atmosphere, influencing regional and global temperature and precipitation patterns.

Why do equatorial regions receive more concentrated solar energy than polar regions?

At the equator, the sun’s rays hit at a higher angle, concentrating heat in a smaller area. Near the poles, the sun’s rays strike at a lower angle, spreading energy over a larger area.

What is albedo, and how does it differ between ice and oceans?

Albedo is the reflectivity of a surface. Ice has a high albedo (reflects much sunlight), while the ocean has a low albedo (absorbs more sunlight).

Why do polar regions lose heat while equatorial regions gain heat?

Polar regions receive sunlight at a low angle and have reflective ice surfaces, leading to less absorption of solar energy. Equatorial regions absorb more energy because of direct sunlight and low-albedo ocean surfaces.

Why don’t oceans at the equator simply keep heating up until they boil?

Ocean currents and atmospheric circulation distribute heat away from the equator, preventing the oceans from continually warming in one place.

What role do ocean currents play in global temperature regulation?

They move warm water from low latitudes (equator) to higher latitudes and vice versa, balancing the planet’s heat distribution.

What are the four main gases in Earth’s atmosphere and their approximate percentages?

Nitrogen (N₂): 78%

Oxygen (O₂): 21%

Argon (Ar): ~0.9%

Carbon dioxide (CO₂): ~0.04%

Why is CO₂ content crucial for life, despite its low percentage?

CO₂ is a greenhouse gas that helps regulate Earth’s temperature. Small changes in its concentration can significantly impact climate and life.

When did oxygen become a major component of Earth’s atmosphere?

After the “oxygen revolution,” driven by photosynthetic organisms that released oxygen over billions of years.

In which layer of the atmosphere does almost all weather occur?

The troposphere (the lowest ~12 km).

How does temperature change as you go higher in the troposphere?

Temperature generally decreases with altitude.

What is the tropopause, and why do airplanes often cruise at this altitude?

The tropopause is the boundary between the troposphere and stratosphere. Airplanes fly here because it is relatively free of weather disturbances.

How is the atmosphere stratified by density?

Warmer, more humid air (less dense) rises, while colder, drier air (denser) sinks. Overall, air density decreases with altitude.

Why is warm, humid air the least dense air mass?

Water vapor is lighter than the nitrogen and oxygen it displaces, and warmth increases the volume of the air, making it less dense.

What is atmospheric pressure?

It is the weight of the air column pressing down on Earth’s surface.

What distinguishes a low-pressure system from a high-pressure system?

Low-pressure system: Air is rising and the column of air above is lighter.

High-pressure system: Air is sinking, creating a heavier column of air pressing downward.

Where are low-pressure systems commonly found, and what weather do they bring?

Low-pressure systems are common around the equator (0°) and around 60° latitudes; they bring cloud formation and rainfall (instability).

Where are high-pressure systems commonly found, and what weather do they bring?

High-pressure systems are common at around 30° latitudes and the poles, bringing clear, dry, and stable weather.

Why do rainforests tend to be near the equator, while deserts are often near 30° latitudes?

The equator has rising, humid air (low pressure and heavy rainfall), whereas 30° latitudes have sinking, dry air (high pressure and arid conditions).

What is convection in the atmosphere?

Convection is the vertical movement of air due to density differences (warm, moist air rising and cooler, drier air sinking).

Why does rising air at the equator cool and form clouds?

As air rises, it expands in the lower pressure environment and cools. Cooling causes water vapor to condense into clouds.

What are Hadley cells, and where are they found?

Hadley cells are circulation cells between the equator (0°) and 30° latitudes. Warm air rises at the equator and sinks around 30°, driving major weather patterns in the tropics/subtropics.

What happens to air between 30° and 60° latitudes?

Rising air near 60° meets cold polar air, creating frontal storms. This region often experiences westerly winds and more frequent weather changes.

What is the Coriolis effect?

It is the apparent deflection of moving objects (wind, water) due to Earth’s rotation, causing paths to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Why is there essentially no Coriolis effect at the equator?

The Coriolis effect weakens to zero at the equator because the component of Earth’s rotation that can cause deflection is minimal at that latitude.

How does the Coriolis effect influence global wind patterns?

It bends the flow of air, creating prevailing wind belts such as the trade winds (easterlies) and westerlies.

Which winds are called “trade winds” (easterlies), and where do they blow?

Trade winds blow from the northeast to the southwest in the Northern Hemisphere between 0° and 30° latitudes (and from southeast to northwest in the Southern Hemisphere).

What are the westerlies, and where do they occur?

Westerlies blow from the southwest to the northeast in the Northern Hemisphere between 30° and 60° latitudes (and northwest to southeast in the Southern Hemisphere).

How are winds named?

Winds are named for the direction from which they originate (e.g., a “northeasterly” wind blows from the northeast).

What is a hurricane?

A hurricane is a large, rotating low-pressure storm system that forms over warm ocean waters in the tropics.

Why don’t hurricanes form on land or in cold oceans?

They need warm, moist air from the ocean as their energy source; when separated from warm water, they lose strength

Where are hurricanes (tropical cyclones) commonly found on Earth?

In tropical regions around 30° latitude, including the North Atlantic, West Pacific (typhoons), and Indian Ocean (cyclones).

What are the regional names for tropical cyclones?

Hurricanes: Americas, North Atlantic

Typhoons: West Pacific

Cyclones: Indian Ocean

Does the same storm type go by different names in different ocean basins?

Yes; they are structurally the same storms, just called by different names depending on location.

How do hurricanes move differently in the Northern vs. Southern Hemispheres?

Northern Hemisphere: Generally move east to west (pushed by trade winds) and spin counterclockwise.

Southern Hemisphere: Generally move west to east and spin clockwise.

Which global winds typically push hurricanes along their paths?

The trade winds (easterlies) near the equator push storms from east to west in the Northern Hemisphere.

How are hurricanes classified by strength?

Hurricanes are ranked from Category 1 to Category 5 based on wind speed. Below hurricane strength, storms are called tropical storms or tropical depressions depending on wind speed.

Where do the strongest hurricanes (highest categories) most commonly occur?

In the West Pacific, where ocean waters are very warm and can fuel more powerful storms.

When do most hurricanes typically form, and why?

In late summer to fall, when sea-surface temperatures have reached their peak due to high heat capacity (oceans retain summer heat).

Why are hurricanes more common in the Northern Hemisphere?

Northern tropical oceans often have warmer waters (especially in the west Pacific), plus large expanses of warm seas without the cooling influence of large ice sheets (like Antarctica in the south).

What fuels hurricanes, making them so powerful?

Warm, humid air evaporating from the ocean transfers massive amounts of heat energy into the atmosphere, driving the storm

What is special about the eye of a hurricane?

It is a region of calm, relatively clear skies and a small high-pressure system where air descends in the center of the storm.

What is found in the eye wall?

The most intense weather—strong winds, heavy rain—because rising warm air condenses, releasing even more energy.

What temperature must the ocean surface be for hurricane formation?

Around 26°C (80°F) or warmer.

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Besides warm water, what else is needed for a hurricane to develop?

Warm, moist (humid) air

Weak upper-level wind shear (so the storm can build vertically)

A pre-existing low-pressure area (helps air start to spiral)

Why is low wind shear important for hurricane growth?

Strong wind shear would disrupt the storm’s vertical structure, preventing it from intensifying.

What is a storm surge, and how does it form?

A storm surge is a rise in sea level accompanying a hurricane, caused by strong winds pushing ocean water onshore and the low-pressure system “pulling” the water surface upward.

Why can a storm surge be especially destructive during high tide?

Because the water level is already elevated at high tide, combining with the surge to flood coastal areas more severely.

Why can saltwater inundation from a storm surge be so damaging to agriculture?

Saltwater can contaminate soil, harming crops and reducing agricultural productivity long after the storm.

Why was Hurricane Katrina (2005) so catastrophic for New Orleans?

Much of New Orleans lies below sea level.

Levees were breached, causing massive flooding (about 80% of the city).

Storm surge traveled up man-made canals, overwhelming flood defenses.

What geographic feature contributes to New Orleans’ vulnerability?

It sits on the Mississippi River delta, a low-lying region prone to flooding and wetland loss.

How are hurricanes named each year?

They are given human names (alphabetical) based on popular baby names or an established rotating name list. Once a storm is especially deadly/costly, its name is retired.

Which global winds primarily drive surface ocean currents?

Surface ocean currents are primarily driven by easterlies (trade winds) and westerlies, which push the water and set the currents in motion.

Why do continents play an important role in shaping ocean currents?

When currents meet continental coastlines, they must change direction (north or south), which helps form or redirect the flow of gyres.

Name the two main types of surface currents in the ocean basins.

Western Boundary Currents (WBCs) and Eastern Boundary Currents (EBCs).

What are Western Boundary Currents (WBCs), and where do they originate?

WBCs are warm currents that flow on the western sides of ocean basins. They originate at equatorial/tropical latitudes and are deflected poleward, typically driven by the easterlies.

Give an example of a Western Boundary Current.

The Gulf Stream off the east coast of the United States is a classic example of a WBC.

What are Eastern Boundary Currents (EBCs), and where do they originate?

EBCs are cold currents that flow on the eastern sides of ocean basins. They originate at polar/high latitudes and are deflected equatorward, typically driven by the westerlies.

Give an example of an Eastern Boundary Current.

The California Current off the west coast of the United States is a classic example of an EBC.

What primarily drives deep ocean currents?

Deep ocean currents are driven by density differences (convection), often due to variations in temperature and salinity.

How do warm and cold currents affect coastal climates?

Warm currents (like WBCs) can make coastal regions more humid and warm.

Cold currents (like EBCs) can make coastal regions drier and cooler.