# Module C Quiz — Question Bank **Source:** Canvas quiz, submitted Jun 22 at 10:25 a.m. (attempt took 10 minutes) **Score:** 1.6 / 2.0 — Questions 1, 2, 6, and 8 answered incorrectly; all others correct. **Note:** Correct answers are marked with ✅. For multiple-choice questions the student's selection was not captured in the paste; correct answers are identified from course content. --- ## Question 1 — Why CO₂ rises and falls each year ❌ Incorrect (0 / 0.1) > The Mauna Loa Observatory has measured CO₂ concentrations from 1958 until the present. Data over each single year shows a rise and fall in the CO₂ concentration data. What is the most likely reason? - Anthropogenic (human caused) CO₂ production is higher in the winter. - Anthropogenic (human caused) CO₂ production is higher in the summer. - **Photosynthesis in the Northern Hemisphere is lower in the winter and higher in the summer.** ✅ (correct answer) - Scientists are not completely sure of the reason. - Respiration in the Northern Hemisphere is higher in the summer. *Rationale: The yearly sawtooth in the Keeling Curve comes from the seasonal cycle of productivity (photosynthesis draws down CO₂ in summer; respiration and decomposition release it in winter), dominated by the Northern Hemisphere.* --- ## Question 2 — What scientists can directly measure at sea ❌ Incorrect (0 / 0.1) > Which of the following can be DIRECTLY MEASURED by scientists at sea? Please select the best answer. - critical depth - photosynthesis depth - respiration depth - **compensation depth** ✅ (correct answer) - all of the answers provided are directly measurable. *Rationale: The **compensation depth** can be measured experimentally (e.g., bottle incubations where photosynthesis = respiration). The **critical depth** cannot be measured directly — it is calculated (derived from compensation depth and light measurements) because it describes the whole mixed population. Note: the lesson adds that even the compensation depth is often inferred from radiometer data using models, but it is the only one of these depths described as experimentally measurable.* --- ## Question 3 — Where marine snow is found ✅ Correct > Which of the following zones are you likely to find marine snow? - mesopelagic - epipelagic - **You can find marine snow in all zones listed here.** ✅ - abyssalpelagic - hadalpelagic *Rationale: Marine snow forms in the productive surface ocean but sinks continuously, so it is found at every depth — and it is the main food supply for deep benthic communities.* --- ## Question 4 — Life entirely in the water column ✅ Correct > An organism that spends its entire life cycle in the water column without ever contacting the seafloor is inhabiting which specific realm? - The Epipelagic realm; defined strictly as the area below the depth of 1% light penetration. - **The Pelagic realm** ✅ - The Neritic realm; limited to the area beyond the continental shelf. - The Benthic realm; similar to a bird that must return to land for reproduction. - The Hadalpelagic realm; characterized by shallow water habitats near the coastline. *Rationale: Pelagic = the whole water column, never touching bottom. Neritic is only the part over the continental shelf; epipelagic is only the sunlit surface layer.* --- ## Question 5 — The nutricline ✅ Correct > What is the 'nutricline', and where is it typically located in the water column? - A layer of high nutrient uptake by phytoplankton; found at the compensation depth. - The region where oxygen is produced by decomposition; found in the aphotic zone. - **The location where nutrients rapidly increase with depth; usually found just below the mixed layer.** ✅ - A depth where nutrients are depleted to zero; found at the very surface. - The boundary between the neritic and oceanic zones. *Rationale: The nutricline sits just below the mixed layer, where light becomes too weak for phytoplankton uptake. It often coincides with the pycnocline/thermocline.* --- ## Question 6 — Warmest period in the past 600 million years ❌ Incorrect (0 / 0.1) > Approximately, over the past 600 million years, when did the Earth have the highest average temperatures? - 15 million years ago - 220 million years ago - 0.15 million years ago - 2021 (last year) - **540 million years ago** ✅ (correct answer) *Rationale: On the Phanerozoic temperature record (Figure 12, Lesson 3.5), the early part of the eon (~540 mya) shows the highest average temperatures of the choices listed. Today's warming is rapid and unusual, but not the highest absolute temperature of the past 600 million years.* --- ## Question 7 — Thermal expansion and sea level rise ✅ Correct > How does 'Thermal Expansion' contribute to sea level rise? - It causes the seafloor to rise toward the surface. - It speeds up the Gulf Stream, which 'piles up' water at the equator. - **Warmer water molecules have more energy, forcing them further apart and increasing the total volume of water.** ✅ - It increases the salt content of the ocean, making it denser. - As water heats up, ice cubes in the ocean take up more space. *Rationale: Sea level rises from glacier melt PLUS thermal expansion of the water already in the ocean.* --- ## Question 8 — Carbon transfer in an upwelling food pyramid ❌ Incorrect (0 / 0.1) > In a coastal upwelling system, the transfer of carbon between trophic levels is more efficient than the average. Assuming there is 250,000 tonnes of carbon contained in the phytoplankton in that ecosystem, how many tonnes of the secondary consumer is possible assuming they only fed as shown in the food pyramid? > *(Figure: Module C food web.jpg — not included in paste)* - 5625 grams carbon - 2500 grams carbon - Impossible to tell from the information. - **10000 grams carbon** ✅ (correct answer) - 560 grams carbon *Rationale: The question cues "upwelling... more efficient than average," which maps to the ~20% trophic transfer efficiency of upwelling systems (vs. the ~10% average). The secondary consumer is two steps above the phytoplankton: 250,000 × 0.20 = 50,000 (primary consumer); 50,000 × 0.20 = 10,000 (secondary consumer). Note the quiz mixes units (tonnes in the question, grams in the options) — the intended number is 10,000. The 2,500 option is the trap for using the 10% average; 5,625 is the trap for 15%; 560 for an extra trophic step.* --- ## Question 9 — Redfield ratio calculation (N → P) ✅ Correct > If you analyzed a sample of healthy phytoplankton and found they contained 48 atoms (or units) of Nitrogen, according to the Redfield Ratio, how many atoms of Phosphorus should you expect to find? - 318 - 106 - 1 - **3** ✅ - 16 *Rationale: Redfield ratio = 106 C : 16 N : 1 P. 48 N ÷ 16 = 3, so phosphorus = 3 × 1 = 3.* --- ## Question 10 — The ocean region that cooled ✅ Correct > Since the mid 1990's, average ocean temperatures have been above average. From that time to the present, which region of the ocean has actually experienced, on average, areas with a reduction of heat content (cooling)? Select the general region that gives the best answer. - South Atlantic - North Pacific - South Pacific - **North Atlantic** ✅ - Equator *Rationale: The ocean heat-content trend map (1993–2020, Lesson 3.5 Figure 17) shows the main cooling patch (blue) in the North Atlantic — the well-known "warming hole" south of Greenland.* --- ## Question 11 — Where nutrient concentration is highest ✅ Correct > Which location will probably have the HIGHEST nutrient concentration at any given location? - above the nutricline - in the nutricline - All answers are correct. - **just below the nutricline** ✅ - above the thermocline *Rationale: The nutricline is the zone of rapid increase. Above it, phytoplankton keep nutrients depleted. Just below it, nutrients accumulate (sinking organic matter + no uptake), so concentrations are highest there.* --- ## Question 12 — Mechanism of ocean acidification ✅ Correct > What is the primary mechanism driving ocean acidification, and how does it affect marine life? - **Increased CO₂ absorption by oceans lowers pH, making it harder for organisms like corals and shellfish to form calcium carbonate shells.** ✅ - Increased photosynthesis by phytoplankton raises ocean acidity, affecting primary productivity. - Ocean acidification is due to reduced oxygen levels, which increase the acidity of seawater and harm fish. - Ocean acidification is caused by volcanic activity, which reduces ocean pH and disrupts marine ecosystems. *Rationale: Absorbed CO₂ reacts with water and releases H⁺ ions, lowering pH. Lower pH dissolves CaCO₃ and makes shell/skeleton formation costlier (corals, clams, coccolithophores, etc.).* --- ## Question 13 — Piscivores and carnivores (True/False) ✅ Correct > Many piscivore are carnivores. - **True** ✅ - False *Rationale: A piscivore eats fish, and fish are heterotrophs — so piscivores are carnivores by definition.* --- ## Question 14 — Microbial loop and the biological pump ✅ Correct > How does the 'Microbial Loop' contribute to the 'Biological Pump'? - By preventing phytoplankton from photosynthesizing. - **By converting DOM into bacterial biomass, which is then eaten and eventually sinks as larger particles (detritus).** ✅ - The microbial loop actually stops the biological pump by keeping all carbon at the surface. - By increasing the temperature of the surface ocean. - By consuming all the oxygen in the aphotic zone. *Rationale: Heterotrophic bacteria turn non-sinking DOM into particulate biomass (POM). Grazers then package it into larger, sinking particles, which exports carbon to the deep ocean.* --- ## Question 15 — Redfield limitation problem ✅ Correct > You are out to sea in the summer as an oceanographer. You measure the nutrients in the water and find that there are 1060 units of carbon, 160 units of nitrate and 10 units of phosphate. Assuming that the phytoplankton are not limited by light, which nutrient will become limiting first (assume there are no other input of nutrients)? - phosphate - carbon - **all will run out at about the same time** ✅ - impossible to tell from the given information - nitrate - none of these are limiting, there is enough of all nutrients *Rationale: 1060 : 160 : 10 is exactly 10× the Redfield ratio (106 : 16 : 1). The nutrients are in perfect proportion, so they run out together.* --- ## Question 16 — Why the epipelagic shoals near coasts ✅ Correct > In the open ocean where productivity is low, the epipelagic zone typically extends to roughly 200 m. Why does this depth decrease as one approaches a coastline? - High nutrient levels at the coast absorb ultraviolet radiation before it can reach depth. - The mixed layer is always deeper at the coast due to storm activity. - **Increased concentrations of phytoplankton and sediment scatter and absorb light more rapidly.** ✅ - Because coastal water is colder, which slows down light waves. - Because the continental shelf physically blocks the light from going deeper. *Rationale: Productive coastal water holds more plankton cells and suspended particles, so light is absorbed and scattered faster (shading). The photic zone can shrink to only ~1 m in the murkiest coastal water.* --- ## Question 17 — Compensation depth vs. critical depth ✅ Correct > What is the fundamental difference between the 'compensation depth' and the 'critical depth'? - **Compensation depth is where P=R at a specific depth; Critical depth is where total integrated P=R for the entire mixed population.** ✅ - Critical depth is always shallower than the compensation depth. - Compensation depth refers to the entire water column, while critical depth refers to a specific fixed location. - There is no difference; the two terms are used interchangeably in physical oceanography. - Compensation depth is determined by nutrients, while critical depth is determined by light. *Rationale: Compensation depth treats phytoplankton as if held at one depth. Critical depth integrates photosynthesis and respiration over the whole mixed layer from the surface down. A bloom needs the mixed layer to be shallower than the critical depth.* --- ## Question 18 — Why food webs beat food chains ✅ Correct > Why are food webs considered a more realistic representation of ecosystems than food chains? - Only food webs include the microbial loop. - Because food chains only include autotrophs, while food webs include heterotrophs. - **Because species can change their feeding habits as they mature and may consume prey from multiple trophic levels.** ✅ - Food chains do not account for sunlight, whereas food webs do. - Food webs are easier to draw and understand for beginners. *Rationale: Real feeding is not linear. One species feeds across trophic levels (e.g., filter feeders eating phytoplankton, zooplankton, and detritus) and changes diet with life stage (e.g., salmon fry vs. adults).* --- ## Question 19 — Dim light: predators yes, photosynthesis no ✅ Correct > Which of the following zones would require visual predators but would NOT support phytoplankton growth? - epipelagic - **mesopelagic** ✅ - euphotic zone - aphotic zone - hadalpelagic zone *Rationale: The mesopelagic (dysphotic "twilight zone," 200–1000 m) has enough light to see by — so visual predators work and camouflage matters — but less than the 1% surface light needed for photosynthesis.* --- ## Question 20 — Fluorinated gases ✅ Correct > What are 'Fluorinated gases' (F-gases), and what is their origin? - Gases found inside the shells of foraminifera. - Natural gases from volcanoes; used for ancient fire protection. - Gases released by phytoplankton during a bloom. - Byproducts of the Redfield ratio in deep ocean trenches. - **Synthetic compounds developed to replace ozone-depleting substances; they are exceptionally potent heat-trappers.** ✅ *Rationale: F-gases (HFCs, PFCs, SF₆) are entirely human-made, used in refrigeration, air conditioning, insulation, and aerosols. Per molecule they trap thousands of times more heat than CO₂.*