Climate Change Ocean & Marine Systems 2 — Questions and Answers
Question 1: Which coastal ecosystems are recognized as the most effective stores of 'blue carbon'?
- Rocky intertidal zones and coral reefs
- Mangroves, seagrasses, and salt marshes (Correct answer)
- Open-ocean phytoplankton blooms and kelp forests
- Sandy beaches and tidal estuaries
Correct answer: Mangroves, seagrasses, and salt marshes
Mangroves, seagrasses, and salt marshes sequester carbon at rates far exceeding most terrestrial ecosystems per unit area and store it for centuries in their soils.
Question 2: What are the two primary physical mechanisms driving global sea level rise in a warming climate?
- Groundwater depletion and increased river sediment discharge
- Thermal expansion of seawater and melting of land-based ice sheets and glaciers (Correct answer)
- Increased ocean precipitation and reduced evaporation rates
- Shifting ocean currents and tectonic plate subsidence
Correct answer: Thermal expansion of seawater and melting of land-based ice sheets and glaciers
Sea level rises because warming seawater expands (thermal expansion) and because melting glaciers and ice sheets transfer previously land-locked water into the ocean.
Question 3: Marine heatwaves are formally defined as periods when sea surface temperatures exceed what threshold?
- The monthly seasonal average for that location
- The 90th percentile of local climatological temperatures for at least 5 consecutive days (Correct answer)
- An absolute threshold of 30°C (86°F) for more than 14 days
- 2°C above the long-term monthly mean for any duration
Correct answer: The 90th percentile of local climatological temperatures for at least 5 consecutive days
The scientific definition requires temperatures above the local 90th percentile climatological threshold for at least 5 consecutive days, ensuring comparisons are relative to local baseline conditions.
Question 4: Which major Atlantic circulation system is considered most vulnerable to weakening as Arctic ice melts add freshwater to the North Atlantic?
- El Niño–Southern Oscillation (ENSO)
- Atlantic Meridional Overturning Circulation (AMOC) (Correct answer)
- Antarctic Circumpolar Current (ACC)
- Pacific Decadal Oscillation (PDO)
Correct answer: Atlantic Meridional Overturning Circulation (AMOC)
AMOC is driven by the sinking of cold, salty water in the North Atlantic; freshwater input from melting ice reduces salinity and density, potentially slowing or disrupting this circulation.
Question 5: What is ocean deoxygenation and why does climate change accelerate it?
- The widespread loss of dissolved oxygen driven by warming reducing gas solubility and increased stratification limiting replenishment (Correct answer)
- The process by which marine plants release oxygen during photosynthesis in warmer conditions
- The seasonal depletion of surface oxygen during colder winter months globally
- A deep-ocean chemical reaction that consumes oxygen near hydrothermal vents
Correct answer: The widespread loss of dissolved oxygen driven by warming reducing gas solubility and increased stratification limiting replenishment
Warmer water holds less dissolved gas (lower oxygen solubility), and stronger stratification prevents oxygen-rich surface waters from mixing into the deeper ocean.
Question 6: How does climate change most directly affect the geographic distribution of marine species?
- Species remain in traditional ranges due to strong evolutionary habitat fidelity
- Many species shift poleward or to deeper, cooler waters to track their preferred temperature range (Correct answer)
- Tropical species aggressively outcompete and replace temperate species at mid-latitudes
- Marine species distributions are largely unaffected because oceans buffer temperature changes well
Correct answer: Many species shift poleward or to deeper, cooler waters to track their preferred temperature range
As ocean temperatures rise, many species—from fish to zooplankton—are tracking thermal gradients by moving toward cooler polar regions or deeper waters.
Question 7: Mass coral bleaching events on the Great Barrier Reef are primarily triggered by which climate-related factor?
- Increased UV radiation from stratospheric ozone depletion over Australia
- Elevated sea surface temperatures during warming events amplified by global climate change (Correct answer)
- Ocean acidification dissolving the calcium carbonate reef framework directly
- Increased sediment runoff following more intense rainfall events
Correct answer: Elevated sea surface temperatures during warming events amplified by global climate change
Even 1–2°C above the typical summer maximum for several weeks triggers bleaching; global warming is making such thermal stress events more frequent and severe on the reef.
Climate Change Ocean & Marine Systems 2
Which coastal ecosystems are recognized as the most effective stores of 'blue carbon'?