Grading Criteria: Student sketch must show sequential order from coast to basin: shallow, gently sloped Shelf → steep drop-off Slope → gradual sediment accumulation at Rise → flat, vast Abyssal Plain.
Bathymetric Maps & Contour Line Spacing:
3 Points
Definition: Bathymetric maps are topographic maps of the ocean floor that illustrate underwater depths and seafloor features using contour lines (isobaths) connecting points of equal depth.
Contour Spacing: Closely spaced lines represent a very steep slope (rapid depth change over short horizontal distance). Widely spaced lines represent a very gentle or nearly flat slope (such as a shelf or abyssal plain).
Thermal Properties & Water Structure Solutions
Phase Change Temperatures (°C):
2 Points
Liquid water becomes solid (ice): 0 °C
Liquid water becomes gas (steam/vapor): 100 °C
*Note: Seawater freezes at approx. -1.8 °C to -2.0 °C due to dissolved salt freezing point depression.
Volume & Density Responses to Temperature:
3 Points
A) Warms up:
Molecules vibrate faster & push apart. Volume increases; Density decreases.
B) Cools off (to 4°C):
Molecules slow & pack closer. Volume decreases; Density increases (max at 3.98°C).
C) Freezes (into ice):
Forms hexagonal crystal lattice. Volume expands ~9%; Density decreases.
Molecular Hydrogen Bonding in Ice:
3 Points
In liquid water, hydrogen bonds constantly break and re-form dynamically. As temperature drops to 0°C, thermal motion diminishes and each water molecule forms four stable, rigid hydrogen bonds with its neighbors. This locks the molecules into an open hexagonal crystal lattice, holding molecules farther apart than in liquid form and making solid ice less dense than liquid water.
Unit Review • Teacher Answer Key & Scoring Guide Page 2 of 6
Part 3: Ocean Salinity, Density & Buoyancy
4 Ocean Surface Temperature Regions:
4 Points
Region 1 Polar (< 2 °C)
Region 2 Cold-Temperate (~5–12 °C)
Region 3 Warm-Temperate (~12–22 °C)
Region 4 Tropical (~25–30 °C)
Thermal Stratification of Seawater:
3 Points
Sunlight heats surface water, making it warm, expanded, and less dense. This warm layer floats at the surface (surface mixed zone). Cold water is denser and sinks toward the seabed (deep ocean zone). Because warm and cold water do not readily mix without turbulent energy, stable horizontal density layers form, preventing vertical mixing.
Comprehensive Salinity Definition:
6 Points
Salinity is the total amount of solid dissolved matter or solute—primarily sodium chloride alongside other salts (magnesium, sulfate, calcium)—dissolved in the liquid solvent (pure water) within seawater, quantitatively measured and expressed in parts per thousand (ppt).
Measured Salinities:
2 Points
A) Open Ocean Average: 35 ppt (or 33–37 ppt)
B) The Dead Sea: ~330–350 ppt (~33–35%)
Salinity Stratification & Halocline:
3 Points
High-salinity water has more mass per unit volume and is denser, sinking below fresher water. The ocean zone where salinity changes sharply with depth is the halocline. In regions with precipitation or ice melt, a buoyant, lower-salinity lens rests on saltier deep water.
3 Reasons Icebergs Float:
3 Pts
Lower density of ice (~0.92 g/cm³) vs liquid water.
Dissolved salt increases fluid density. Under Archimedes' Principle, buoyant force equals displaced fluid weight. Because salty water weighs more per volume, less volume is displaced, allowing objects to float noticeably higher.
Unit Review • Teacher Answer Key & Scoring Guide Page 3 of 6
Part 4: Ocean Thermoclines, Latitude Profiles & Upwelling
Thermocline Definition:
2 Pts
A distinct transition layer in the water column characterized by a rapid drop in temperature with increasing depth.
Layer of Thermocline:
2 Pts
Located in the intermediate layer (pycnocline/mesopelagic zone), typically extending between roughly 200 m and 1,000 m depth.
3 Layers on Low-Latitude Temperature Profile:
4 Points
• Surface Mixed Layer (0–200 m): Warm (~22–28 °C) and nearly vertical (isothermal) line on the graph due to wind and wave mixing.
• Intermediate Layer (200–1,000 m): Permanent thermocline; shows a steep diagonal line where temperature plunges from >20 °C to ~4 °C.
• Deep Layer (1,000 m to bottom): Cold (~1–4 °C) and nearly vertical line; receives no sunlight and remains uniformly cold to the abyss.
Comparing Low vs. High Latitude Profiles:
3 Points
Low Latitudes (Tropics): Intense year-round sun warms the surface (~25°C) over cold deep water (~2°C), creating a sharp permanent thermocline curve.
High Latitudes (Poles): Surface water is freezing or near-freezing (~0°C to -1.8°C), identical to deep water. Thus, polar profiles are isothermal with no thermocline.
Seasonal Thermocline:
3 Pts
The surface mixed layer (upper 50–100 m) in temperate zones. In summer, solar warming forms a shallow thermocline; winter cooling and wind storms erase it.
Polar ~0°C at Depth:
2 Pts
Freezing polar surface water forms sea ice, leaving behind ultra-dense, cold brine. This water sinks to the seafloor (thermohaline circulation) and spreads into the global deep ocean.
Upwelling & Biological Productivity:
4 Points
Mechanism: Upwelling occurs when winds blowing along coastlines combined with the Coriolis effect (Ekman transport) push warm surface water offshore, drawing deep, cold, nutrient-rich water up to the sunlit surface.
Ecological Impact: Dissolved nutrients (nitrates, phosphates, silicates) trigger massive phytoplankton blooms, nourishing dense populations of zooplankton, schooling fish (anchovies, sardines), marine mammals, and seabirds.
Unit Review • Teacher Answer Key & Scoring Guide Page 4 of 6
Part 5: Ocean Optics: Light Penetration, Color & Vision
3 Light Zones & Key Biological Process:
4 Points
1. Euphotic (Photic) Zone:
0 to ~200 m depth. Receives abundant sunlight sufficient to power photosynthesis; contains 90% of ocean life.
2. Disphotic (Twilight) Zone:
~200 to 1,000 m. Dim, faint light. Animals can see, but sunlight is insufficient for net photosynthesis.
3. Aphotic (Midnight) Zone:
>1,000 m to bottom. Total, perpetual darkness; zero solar light. Organisms rely on bioluminescence & marine snow.
Biological Process Enabled by Transparency: Photosynthesis by marine phytoplankton, microscopic algae, and submerged macroalgae, forming the base of the marine food web.
Electromagnetic Waves:
2 Points
Waves of synchronized electric and magnetic fields traveling at light speed. They are defined by their wavelength (crest-to-crest distance) and carry energy that increases as wavelength shortens.
Detectable Wavelength Range:
2 Points
Human eyes detect wavelengths between 380 to 750 nanometers (nm) (or ~400–700 nm). This narrow band of the EM spectrum is designated the Visible Light Spectrum.
Why Leaves Appear Green:
3 Points
Plant cells contain the photosynthetic pigment chlorophyll. Chlorophyll strongly absorbs blue and red wavelengths of white sunlight to fuel chemical reactions, while green wavelengths are not absorbed and are reflected into our eyes, causing us to perceive the foliage as green.
Color Penetration Depth & Physics:
4 Points
• Penetrates Farthest: Blue / Blue-green light (~450–490 nm). Blue light has a higher frequency and higher photon energy, allowing it to penetrate through water molecules up to 200+ meters in clear open ocean.
• Penetrates Least: Red light (~650–700 nm). Red light has a longer wavelength, lower frequency, and lower energy; water molecules quickly absorb it as heat within the top 5 to 10 meters.
Red/Orange Organisms at Depth:
3 Points
Advantage: Since red light is absorbed at the surface, no red light exists at depth to reflect. Thus, red animals (e.g., deep-sea shrimp) appear pitch black and invisible to predators.
Disadvantage: In shallow water, their red color makes them highly visible and vulnerable to predators.
Broadest Vision:
2 Pts
Mantis Shrimp (Stomatopod)
Has 12–16 distinct color photoreceptors, detects UV, infrared, and polarized light!
Unit Review • Teacher Answer Key & Scoring Guide Page 5 of 6
Part 6: Hydrostatic Pressure, Diving Physiology & Adaptations
Rate of Pressure Change:
2 Points
Hydrostatic pressure increases by 1 atmosphere (atm) for every 10 meters (33 feet) of ocean depth.
Pressure Unit & Meaning:
2 Points
Atmosphere (atm) or psi. 1 atm is the standard force exerted by Earth's atmosphere at sea level (14.7 pounds per square inch / 101.3 kPa).
Hydrostatic Pressure Calculation at 99 Feet:
4 Points
Surface Atmosphere: 1.0 atm
Water Added at 99 ft (99 / 33): 3.0 atm
Total Ambient Pressure: 4.0 atm (58.8 psi)
Step-by-Step Calculation: Every 33 feet of seawater adds 1 atm. \(\frac{99\text{ ft}}{33\text{ ft/atm}} = 3.0\text{ atm of water pressure}\). Adding the 1.0 atm of air pressing down at the surface yields: \(1.0\text{ atm (air)} + 3.0\text{ atm (water)} = \mathbf{4.0\text{ atm total}}\) (or \(4.0 \times 14.7\text{ psi} = \mathbf{58.8\text{ psi}}\)).
Compressible Air-Filled Human Organs / Structures:
Swim Bladder (Gas Bladder): An internal gas-filled organ found in bony fish that regulates buoyancy. By diffusing oxygen and other gases in or out of the bladder via the bloodstream and gas gland (rete mirabile), the fish counteracts water pressure changes (Boyle's Law) to maintain neutral buoyancy at variable depths without sinking or floating.
Grading Scale & Point Distribution Summary
TOTAL: 100 POINTS
Part 1 19 Pts
Part 2 16 Pts
Part 3 21 Pts
Part 4 18 Pts
Part 5 15 Pts
Part 6 11 Pts
Unit Review • Teacher Answer Key & Scoring Guide Page 6 of 6
