MARS 3450 – Exam #1 Study GuideESSAY QUESTIONS1. Why does the pycnocline look like the mirror image of the thermocline? What role does salinity play?The pycnocline represents the rapid change in density over a short vertical distance, while thethermocline represents the rapid change in temperature over the same distance. As you go deeper inthe water, the water temperature decreases and the density increases. So, essentially, temperatureand density are directly related, meaning that when one factor increases, the other factor decreases;this relationship creates the “mirror image” effect in depth profiles. The density increases as you godeeper because seawater becomes more dense as its temperature decreases; therefore, density relieson temperature. Density also relies on salinity. Seawater becomes more dense as its salinity increases.The most saline water is present at the bottom of the ocean because salinity increases as depthincreases. While salinity plays a smaller role than temperature, it still contributes to density increasingwith depth, and, therefore, contributes to the “mirror image” of the thermocline that the pycnoclineappears to be.2. Global warming is increasing the temperature of surface waters in the polar regions and melting theglaciers. Predict the effect this will have on deep ocean circulation and explain the basis for yourprediction.Deep ocean circulation is the pattern of water flow around the globe that cycles water and replenishesnutrients. In the deep water circulation pattern, water sinks at the poles; this is because low levels oflight and glaciers cool the surface waters, causing them to sink beneath the warmer waters below andcreating the cycling of ocean water. Global warming is melting the glaciers, which will gradually reduceand potentially even halt the cycling of ocean water. Without glaciers to cool the surface waters, deepocean water will not be circulated because the surface waters will not cool and sink beneath thewarmer deep waters. My prediction is based on the fact that warm water rises and cool water sinks.Without glaciers, water will no longer sink at the poles and deep water circulation will cease to exist.3. Marine members of the phylum Mollusca exhibit a range of strategies for locomotion/motility. Usingexamples, discuss the types of motility found within this group.Marine members in three classes of the phylum Mollusca exhibit various locomotive strategies.Organisms in the class Gastropoda (including snails, slugs, limpits, abalones, and nudibranchs) movearound on a foot, which essentially suctions them to a hard surface. Organisms in the class Bivalvia(including mussels, clams, oysters, and scallops) have a foot adapted to burrowing and move around inseveral different ways. Mussels have byssal threads that allow them to hang from different surfaces,while oysters are sessile, cemented to a surface. Clams crawl with a foot similar to that of Gastropods,while scallops move by clapping their shell, which forces water out and propels them forward.Organisms in the class Cephalopoda (including the octopus, squid, cuttlefish, and nautilis) all move bypushing water behind them using their tentacles, which propels them forward.4. Fish species that move fast and frequently change position vertically in the water column often don’thave swim bladders. Why is this the case? What other strategies can these fish use instead?Since the point of having a swim bladder is to maintain a certain depth without having to waste energyto swim and maintain that depth, fish that do not wish to maintain the same depth do not develop aswim bladder. Fish without swim bladders use other strategies to move around. Some organisms,such as sharks, mackerels, and tuna, develop oversized livers that keep them from sinking. Otherorganisms constantly swim around because their fins provide lift. Mostly Cnidaria (but also a few otherorganisms) use the ion replacement method, which entails expelling heavy ions (like Ca and Mg) andmaintaining lighter-weight ions (like NH4+). All of these methods have evolved to be just as effective asswim bladders.1MARS 3450 – Exam #1 Study Guide5. What is the compensation depth? How might you expect it to vary over a 24-hour cycle? How mightyou expect it to vary between coastal and open ocean water?The compensation depth is when the rate of respiration of photosynthetic organisms is equal to therate of photosynthesis. Since photosynthesis depends on light from the sun, it would be expected forthe compensation depth to be shallower at night and deeper during the day. This expectation is basedon the fact that the rate of respiration will exceed the rate of photosynthesis in more of the watercolumn at night (when the sun is not present) than during the day, while the rate of photosynthesis willexceed the rate of respiration in more of the water column during the day (when the sun is present)than at night. The compensation depth is deeper in clear, open ocean waters and shallower in costalwaters, where a large number of particles cloud the water.6. Although net plankton can be an important component of the plankton, if you only sampled with a net,you might miss many organisms. Describe what the problem is and what groups of organisms you’dlikely miss (hint: be sure to think about both phyto- and zooplankton).The problem with using nets to catch organisms begins with net size. Nets with large meshes (largeholes) must be used to catch the large zooplankton. If those same large nets were used to catchphytoplankton, then none would be caught because those organisms are so small that they would flowthrew the holes; therefore, nets with small meshes (small holes) must be used to catch phytoplanktonlike microplankton. While microplankton (most commonly diatoms and dinoflagellates) can be caughtwith a net, other types of phytoplankton, like nanoplankton and picoplankton, are too small to becaught with a net. A net that could catch the tiny nanoplankton and picoplankton with have to havesuch tiny holes that water would not be able to pass through the mesh; therefore, nanoplankton andpicoplankton are the most likely organisms to be missed in a net plankton catch.7. Describe the annual cycle of phytoplankton and zooplankton in the temperate North Pacific (make sureyou explain the micrograzer hypothesis as part of your