# Module E Quiz — Question Bank **Source:** Canvas quiz, submitted Jul 29 at 11:51 a.m. (attempt took 7 minutes) **Score:** 1.9 / 2.0 — Question 6 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 — Least likely limiting factor in the tropical epipelagic ✅ Correct > In the tropical epipelagic, which of the following would LEAST likely be the limiting factor for most phytoplankton in the spring? - phosphate - **light** ✅ - nitrate - plankton predation - Cannot say as it depends on varying temporal and spatial factors. *Rationale: The tropics have a permanent shallow mixed layer and steady sunlight all year, so light is essentially never limiting. Tropical phytoplankton are nutrient limited year-round (usually nitrogen, sometimes phosphate or iron in HNLC zones), and grazing can also control them.* --- ## Question 2 — Liebig's Law in summer ✅ Correct > According to Liebig's Law of the Minimum, what mostly limits phytoplankton growth in most locations during the summer? - phosphate and nitrate - light and nutrients - nitrate and iron - **nitrate** ✅ - light and iron *Rationale: Liebig's Law says a single most-limiting resource controls growth. In summer there is plenty of light, but stratification blocks nutrient resupply — and nitrate is usually the first nutrient to run out (it is the most-needed nutrient after carbon).* --- ## Question 3 — Which ecosystem exports the most fecal carbon ✅ Correct > Which ecosystem will, on average, result with the most carbon exported by zooplankton fecal material annually? - Temperate coastal non upwelling zones - **Temperate coastal upwelling zones** ✅ - Tropical pelagic zones - Temperate open ocean pelagic zones (beyond the continental shelf) - Polar zones *Rationale: Upwelling sustains large diatoms and large herbivorous zooplankton for months (spring to early fall). Big cells and big fecal pellets sink fast, so carbon export is strongest. Polar blooms are intense but last only weeks; tropical/open-ocean systems use small cells that barely sink.* --- ## Question 4 — Which organisms create regenerated nutrients ✅ Correct > Which of the following organisms create regenerated nutrients in the water column? - Krill - **All organisms listed create regenerated nutrients.** ✅ - Dinoflagellates - Copepods - Great White Shark *Rationale: Regenerated (recycled) nutrients come from consumption, respiration, and excretion of organic matter. Every consumer — krill, copepods, mixotrophic/heterotrophic dinoflagellates, and sharks — releases nutrients back into the water.* --- ## Question 5 — Most trophic levels / least efficient ✅ Correct > In which of the following ecosystems will there be the most trophic levels (least efficient trophic transfer) between the top predators and the primary producers? - **Tropical pelagic ecosystem** ✅ - Antarctic ecosystem - Coastal temperate ecosystem - Upwelling ecosystem - Continental shelf ecosystem *Rationale: Nutrient-poor open ocean favors small phytoplankton (cyanobacteria), which forces a long food chain (~6 trophic levels, ~10% TTE). Upwelling has the shortest chain (3 levels, ~20%); continental shelf is intermediate (4 levels, ~15%).* --- ## Question 6 — What increases REGENERATED nutrients ❌ Incorrect (0 / 0.1) > Phytoplankton can receive an increased input of regenerated nutrients from which of the following processes? - **None of the processes listed will lead to an increase of regenerated nutrients.** ✅ (correct answer) - Shallowing of the mixed layer. - increased mixing with deeper waters. - All of the above - downwelling waters *Rationale: This question tests the "new" vs. "regenerated" distinction. **Regenerated** nutrients come only from decomposition of organic matter WITHIN the mixed layer. Mixing with deeper water supplies **new** nutrients, not regenerated ones — that is the trap. Downwelling pushes surface water (and its nutrients) down and away, and a shallowing mixed layer adds nothing (it can even strand recycled material below the new pycnocline). So none of the listed processes increases regenerated nutrients.* --- ## Question 7 — What limits the subarctic North Pacific spring bloom ✅ Correct > Typically in the subarctic North Pacific, what limits the spring bloom? - **Iron concentrations are low** ✅ - Nitrate concentrations are low - High grazing rates by coccolithophores - Light limitation due to a deep mixed layer - Silicate concentrations are low *Rationale: The subarctic North Pacific is an HNLC (high nitrate, low chlorophyll) region — nitrate and phosphate are abundant year-round, but iron (a micronutrient needed to use nitrate) limits growth. Other HNLC regions: equatorial Pacific and Southern Ocean (~20% of the ocean).* --- ## Question 8 — Where deposit feeders concentrate ✅ Correct > Where are you most likely to find the largest concentration of deposit feeders in the ocean? - **On the benthos under a productive upwelling system.** ✅ - Top of the mesopelagic - Between the mesopelagic and the abyssalpelagic - Above the benthos under an HNLC region - On the surface in the subtropical Pacific *Rationale: Deposit feeders need organic-rich SEDIMENT, which only exists on the bottom. A strong upwelling drives a strong biological pump, delivering the most POC to the benthos below it. (There are no deposit feeders in the epipelagic — no substrate.)* --- ## Question 9 — What limits growth in temperate/polar regions ✅ Correct > Which of the following will limit phytoplankton growth (either short or long term scales) in temperate and polar regions? - **All choices limit light to phytoplankton.** ✅ - Occurrence of a hurricane - Season change from summer to fall - Onset of night - Increased phytoplankton cells in the epipelagic due to a bloom. *Rationale: Every option works through light: hurricanes bring cloud cover, fall shortens the days, night removes light entirely, and a dense bloom causes **self-shading** for cells deeper in the photic zone.* --- ## Question 10 — When and where cyanobacteria dominate ✅ Correct > Looking at the figure of typical cycles of phytoplankton in the Northern Hemisphere, which time and location would most likely favor cyanobacteria as the dominant phytoplankton? > *(Figure: total PP yearly.jpg)* - Fall peak in the temperate zone in late September - August through October in a Polar zone. - Peak of the temperate bloom (~April) - **Tropics in February** ✅ - Peak of the polar bloom (June/July) *Rationale: Cyanobacteria are small cells with high SA/V and low nutrient demand, so they dominate warm, stratified, nutrient-poor water — the tropics year-round (February included). Bloom peaks in temperate and polar zones favor large, fast-dividing diatoms; the temperate fall peak is fed by new storm-mixed nutrients.* --- ## Question 11 — Why the oxygen minimum zone exists ✅ Correct > Why is oxygen at a minimum at the oxygen minimum zone in the water column (~1000 m)? - **Respiration from heterotrophy of marine snow and other sinking POC.** ✅ - Mixing of shallow and deeper water. - Decreased photosynthesis due to nutrient limitation. - Seawater temperature - High concentrations of predatory fish just above the OMZ *Rationale: Heterotrophic bacteria decompose sinking organic matter and consume oxygen at all depths. Maximum breakdown coincides with the OMZ at ~1,000 m (which is also where nutrients peak). Below the OMZ, oxygen rises again via mixing with cold, oxygen-rich deep water formed at the poles.* --- ## Question 12 — Why cold water holds more nutrients ✅ Correct > Colder seawater temperatures are often associated with higher nutrient concentrations. Which of the following best explains why? - River runoff is generally due to glacier melt and will have higher nutrient concentrations. - Colder water has a higher carrying capacity for nutrients than warmer water. - Deeper water (below the epipelagic) has higher nutrients. - Surface water nearer the poles have higher nutrient concentrations. - **All answers are correct.** ✅ *Rationale: Each statement supports the association: cold polar surface waters are nutrient-rich (little uptake in the dark season), cold deep water accumulates regenerated nutrients below the pycnocline, and continental runoff (including glacial melt) adds nutrients to cold coastal water.* --- ## Question 13 — The downwelling statement (True/False) ✅ Correct > Coastal downwelling can be an important contributor to global primary productivity. In areas where the seasonal wind blows in the correct direction, surface water is moved offshore and is replaced by colder, nutrient-rich water from below. This supplies nutrients required for diatom blooms. - True - **False** ✅ *Rationale: The process described is coastal UPWELLING (Ekman transport moves surface water offshore; deep nutrient-rich water replaces it). Downwelling is the opposite: surface water is pushed TOWARD the coast, piles up, and sinks — keeping surface waters low in nutrients.* --- ## Question 14 — El Niño: upwelling vs. non-upwelling production ✅ Correct > During an El Niño year off the coast of British Columbia, which of the following is most likely true when comparing coastal upwelling zones with coastal temperate (non upwelling) locations? - Rates of production for both locations will be close to zero. - Coastal upwelling rate of production will be LESS THAN than the coastal temperate sea rate of production. - **Coastal upwelling rate of production will roughly equal coastal temperate sea rate of production.** ✅ - Coastal upwelling rate of production will be GREATER than the coastal temperate sea rate of production. *Rationale: El Niño thickens the warm surface layer, so "upwelling" only pulls up warm, nutrient-poor water. The upwelling zone loses its nutrient advantage, and its production drops to roughly the level of a normal coastal temperate sea. (Off Peru the effect is even stronger — the fishery collapses.)* --- ## Question 15 — Nitrogen supply in the Gulf of Maine ✅ Correct > What process supplies more nitrogen to the surface waters of the Gulf of Maine? - downwelling - yearly river input - upwelling - **whale pump** ✅ - microbial loop *Rationale: Whales feed at depth and release fecal plumes (nitrogen, phosphorus, iron) at the surface. In the Gulf of Maine, this whale pump delivers more usable nitrogen to surface waters than all the rivers in the area combined.* --- ## Question 16 — Do zooplankton and phytoplankton bloom together? (True/False) ✅ Correct > Zooplankton blooms and phytoplankton blooms initiate at the same time in the spring/summer in most temperate locations. - True - **False** ✅ *Rationale: The zooplankton increase lags the phytoplankton bloom. Zooplankton cannot divide as fast as phytoplankton and must wait for cues from the bloom before their numbers rise (see Lesson 5-5, Figure 15).* --- ## Question 17 — Reading the nitrate profile ✅ Correct > Which of the following statements can be inferred/deduced based on the profile of nitrate concentration in the surface waters (0 to 200 m) shown in the figure? > *(Figure: nitrate.jpg — the June continental-shelf nitrate profile off Vancouver Island, Lesson 5-2 Figure 2)* - The water sampled is typical of surface water in a temperate location in the winter. - All of the mixed layer is phosphate limited. - The nutricline is deeper than the pycnocline. - The phytoplankton are mixed too deep to grow. - **The mixed layer ends at 20 m.** ✅ *Rationale: The figure shows nitrate near zero for the first ~20 m, then increasing — the mixed layer (uniform, nutrient-depleted by uptake) ends at ~20 m, and the nutricline begins there. It is a summer profile (winter surface water is nutrient-RICH from mixing), the depletion indicates nitrate (not phosphate) limitation, and a 20 m mixed layer is shallow, so the phytoplankton are not light limited.* --- ## Question 18 — Why oxygen starts to drop below the epipelagic ✅ Correct > Which of the following best explains why oxygen starts to decrease just below the epipelagic (top of the mesopelagic)? - Increased heterotrophic respiration - **No photosynthesis and no atmospheric oxygen input** ✅ - Swtich to smaller cyanobacteria for photosynthesis - Increased marine snow - Increased predator prey interactions *Rationale: Below the mixed layer there is no light for photosynthesis and no contact with the atmosphere, so no oxygen is produced or added — while respiration and decomposition keep consuming it. (Compare Q11: the respiration of sinking POC sets where the minimum falls.)* --- ## Question 19 — Most common regenerated nitrogen in the epipelagic ✅ Correct > What is the most common form of usable regenerated nitrogen created in the epipelagic? - Nitrate - **Ammonium** ✅ - Organic nitrogen - Nitrate - Regenerated nitrogen is generally not produced in the epipelagic. *Rationale: Regenerated nitrogen is released mainly as ammonium (NH₄⁺), and phytoplankton take it up immediately — which is why it can sustain low-level growth (e.g., in the tropics) but never trigger a bloom. Blooms need new nitrate from mixing or upwelling. (Note the quiz lists "Nitrate" twice as a distractor.)* --- ## Question 20 — What sinks in the biological pump ✅ Correct > (Following the concept of the biological pump) In the open ocean, which form of organic carbon sinks from the eutrophic zone to the deep ocean in the largest amount (select the best answer)? > *(Figure: biological pump.jpg)* - **POC** ✅ - Herbivore fecal pellets - Most organic carbon would no longer be in the form of fecal pellets, keeping most of the organic material in the mixed layer. - Large living phytoplankton - DOC - Migrating zooplankton *Rationale: Only **particulate** organic carbon (POC — dead cells, fecal pellets, marine snow) sinks out of the mixed layer. Fecal pellets are just one component of POC. DOC is dissolved and does not sink — it moves with currents. Large living phytoplankton and migrating zooplankton are too small a fraction to carry the largest amount.*