2005 Lost City Expedition Towers of the Lost City FOCUS 500 ml glass beaker pH, buffers, and chemistry of the Lost City hydro- 2 - 1 liter beakers or Erlenmeyer flasks for mix- thermal chimneys ing solutions Plastic washbottle, 500 ml capacity GRADE LEVEL Glass stirring rod; one for each student group 7-8 (Physical Science/Earth Science) Sodium hydroxide pellets, approximately 50 grams (see Learning Procedure, Step 1) FOCUS QUESTION Solid citric acid (to neutralize sodium hydroxide What chemical processes are involved in forming spills); approximate 450 grams the Lost City hydrothermal chimneys? Distilled water; approximately 150 ml for each student group, plus 1.5 liters for making solu- LEARNING OBJECTIVES tions (see Learning Procedure, Step 1) Students will be able to define a buffer, and Artificial seawater; approximately 150 ml for explain in general terms the carbonate buffer sys- each student group, plus approximately 250 ml tem of seawater. for demonstration pH test paper, wide range; one roll for each Students will be able to define pH, and contrast student group the pH of hydrothermal vent fluids at Lost City Dilute acetic acid solution in dropper bottles; with those associated with “black smokers.” one bottle containing approximately 50 ml for each student group (see Learning Procedure, Students will be able to describe the process Step 1) through which hydrothermal chimneys are formed 0.1 M sodium hydroxide solution in dropper at Lost City, and identify the primary chemicals bottles; one bottle containing approximately involved in this process. 50 ml for each student group (see Learning Procedure, Step 1) MATERIALS (Optional) modeling clay, two colors (see Copies of the Buffer Properties of Seawater Learning Procedure, Step 6) Worksheet; one copy for each student group Protective goggles and gloves; one set for each AUDIO/VISUAL MATERIALS student and one for the teacher Marker board or overhead projector with trans- 100 ml glass beaker; one for each student group parencies 100 ml graduated cylinder; one cylinder may be shared by several student groups, but have TEACHING TIME separate cylinders for distilled water and sea- One or two 45-minute class periods water 1 2005 Lost City Expedition – Grades 7-8 (Physical Science/Earth Science) 2005 Lost City Expedition – Grades 7-8 (Physical Science/Earth Science) Focus: pH, buffers, and chemistry of the Lost City hydrothermal chimneys oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: pH, buffers, and chemistry of the Lost City hydrothermal chimneys SEATING ARRANGEMENT diverse food web that includes large tubeworms Groups of two to four students (vestimentiferans), clams, mussels, limpets, poly- chaete worms, shrimp, and crabs. MAXIMUM NUMBER OF STUDENTS 30 In 2000, a different sort of vent field was seren- dipitously discovered on an underwater mountain KEY WORDS called the Atlantis Massif near the Mid-Atlantic Lost City Ridge. This new field also had hot fluids venting Hydrothermal vent from rocky chimneys. But these chimneys towered Peridotite as much as 200 feet above the seafloor, much Buffer larger than chimneys found in other vent fields. pH In fact, the vent field was located 15 kilometers Calcium carbonate away from the spreading axis of the Mid-Atlantic Ridge and the chimneys looked so much like BACKGROUND INFORMATION towers and spires of a fantastic city that the new In 1977, scientists in the deep-diving submersible vent field was named “Lost City.” And the fluids Alvin made the first visit to an oceanic spread- emerging from the chimneys, as well as the sur- ing ridge near the Galapagos Islands, and made rounding biological communities, were unlike any one of the most exciting discoveries in 20th cen- other known hydrothermal system. Subsequent tury biology. In the middle of deep, cold ocean investigations have shown that the newly-discov- waters, they found hot springs and observed ered hydrothermal fields are not formed by sea- black smoke-like clouds billowing from chimneys water reacting with molten magma. Instead, these of rock; and nearby were communities of animals fields are formed when seawater reacts with solid that no one had ever seen before. mantle rocks. These rocks, called peridotites, are formed deep inside the Earth, but a unique type These hot springs came to be known as hydro- of faulting can bring them close to the seafloor. thermal vents, and since that first discovery, more Cracks in the seafloor can allow seawater to than 200 similar vent fields have been docu- percolate down to the up-lifted peridotites. When mented in the world’s ocean. These systems are this happens, numerous chemical reactions occur formed when seawater flowing through cracks in between seawater and minerals in the rock (a the seafloor crust enters magma-containing cham- process called serpentinization). These reactions bers beneath a spreading ridge. Intense heat produce a large amount of heat that causes the from the molten rock causes a variety of chemi- fluids to rise and eventually vent at the surface cal changes and many substances from the rocks of the seafloor. Mixing between the heated fluids become dissolved in the fluid. The heated fluid and cold surrounding seawater causes additional becomes less dense, rises upward, and emerges reactions that include precipitation of calcium onto the sea floor to form a hydrothermal vent. carbonate (limestone), which forms the towering When the heated fluid is cooled by cold water of chimneys of Lost City. Because the reactions of the deep ocean, many of the dissolved materials seawater with peridotites are essential to these precipitate, creating black clouds and chimneys formations, the Lost City is called a “peridotite- of rock-like deposits. The hydrothermal fluid hosted ecosystem.” emerging from the vents is rich in sulfide, which is used as an energy source by chemosynthetic In contrast to the abundant biological communi- bacteria to produce essential organic substances. ties of hydrothermal vents formed by volcanic These autotrophic bacteria are the base of a activity, the Lost City Hydrothermal Field (LCHF) 2 3 2005 Lost City Expedition – Grades 7-8 (Physical Science/Earth Science) 2005 Lost City Expedition – Grades 7-8 (Physical Science/Earth Science) Focus: pH, buffers, and chemistry of the Lost City hydrothermal chimneys oceanexplorer.noaa.gov oceanexplorer.noaa.gov Focus: pH, buffers, and chemistry of the Lost City hydrothermal chimneys initially appeared to be devoid of living organ- isms. But when scientists took a closer look at the (b) 0.1 M sodium hydroxide solution: Dilute surface of the chimneys (they actually vacuumed 25 ml of 4 M sodium hydroxide solution to the surface), they found large numbers of tiny a volume of 1 liter. Transfer the solution to shrimps and crabs. Because most of these animals dropper bottles, one bottle for each student are less than one centimeter in size, transparent group. or translucent, and tend to hide in small crevices, they were easily overlooked when the LCHF was [NOTE: Be careful! Concentrated sodium first discovered. While the total biomass around hydroxide is dangerous. Use goggles and pro- the LCHF vents appears to be less than at other tective rubber gloves when working with solid hydrothermal vents, scientists believe there is just chemicals and solutions, and be sure the surfaces as much diversity (variety of different species). of gloves and bottles are dry to avoid accidental Like previously discovered vent communities, the slippage when bottles are handled. Any chemi- LCHF ecosystem is based on microorganisms that cal that contacts the skin should be immediately are able to use chemicals in the vent fluids as an washed off with copious quantities of water. Then energy source for producing complex organic apply dilute vinegar solution to neutralize traces compounds that are used as food by other spe- of the alkali. Spills of alkalis should be diluted as cies (chemosynthesis). But again, the LCHF differs above before mopping up. For large spills, solid in that the fluids emerging from the chimneys has citric acid should be used as a neutralizer.] very little of the hydrogen sulfide and metals that are typical in hydrothermal fluids of other vent. (c) Dilute acetic acid solution: Transfer white Instead, LCHF vent fluids contain high concentra- vinegar to dropper bottles, one bottle for tions of methane and hydrogen, and these chemi- each student group. cals appear to provide the energy source for chemosynthetic microbes. (d) Artificial Seawater: Follow directions on package to prepare required quantity (see In this lesson, students will investigate some prop- Materials; typically, 1 liter will require erties of the ocean’s carbonate buffer system, and about two tablespoons of the dry powder). make inferences about the chemical reactions that form the towering chimneys at LCHF. 2. Briefly review the concepts of plate tecton- ics, being sure that students understand the LEARNING PROCEDURE processes that take place at convergent and 1. To prepare for this lesson: divergent boundaries, and why these boundar- • Visit the Lost City expedition’s Web pages ies are often the site of volcanic activity. Briefly (http://oceanexplorer.noaa.gov/explorations/05lostcity/ review the discovery of hydrothermal vents, and welcome.html; http://www.lostcity.washington.edu/; and describe the general appearance of hot fluids http://www.immersionpresents.org) for an overview of venting from chimneys or cracks in the seafloor. the expedition and background essays. You may want to show video clips from some of the sites referenced in Step 1 to supplement • Prepare solutions for student demonstration this discussion. Be sure students understand that and experiment: these vent communities were produced by sea- (a) 4 M sodium hydroxide solution: Dissolve water reacting with molten magma. 40 g NaOH in 100 mL water, then dilute to 250 ml. Transfer the solution to a plastic Tell students that in the year 2000 a differ- wash bottle.