1-5 The effect of temperature on the marine environment (PDF)

Chemical reactions and their impact on water quality 1−5 Lesson 1-5 The effect of temperature on the marine environment Have you ever wondered how temperature affects marine organisms? Or why do the oceans stay warm even after the sun goes down? And why, on a h...

Chemical reactions and their impact on water quality 1−5 Lesson 1-5 The effect of temperature on the marine environment Have you ever wondered how temperature affects marine organisms? Or why do the oceans stay warm even after the sun goes down? And why, on a hot summer day, does the air around you feel hotter quickly, while the water in lakes and rivers stays cooler? Heat and temperature In everyday conversation, some people confuse the concepts of “amount of heat” and “temperature.” Although they are related, there is a difference in their meaning in physics. Any object or system is made up of an enormous number of particles that are spaced apart and in constant motion. The sum of the potential energy due to the position of the particles relative to each other and the kinetic energy due to the motion of the particles is called the internal energy of the object or system The concept of the amount of heat refers to the energy transferred from, to, or through an object when there is a temperature difference, and the amount of heat is measured in Joules (Joule) Temperature is a quantitative description of how hot or cold an object or system is. It represents the average kinetic energy of the particles of that object or system, and its international unit is the Kelvin (K). To find the value of temperature in kelvin corresponding to its value in degree Celsius, the relation used is: (TK = t °C + 273), knowing that an increase in temperature by one degree Celsius (°C) is equivalent to an increase in temperature by one Kelvin (K) When an object or system gains thermal energy, the amplitude of vibration of the molecules, as well as their kinetic energy, increases, and so its temperature rises. Does a unit of mass (1 kg) of different substances require the same amount of heat for their respective temperatures to rise by one kelvin? The specific heat of some substances Substance Specific heat (J/kg.K) Substance Specific heat (J/kg.K) Zinc 388 Lead 130 Liquid mercury 140 copper 385 Aluminum 897 Methanol 2450 Glass 840 Water vapor 2020 Carbon 710 Water 4180 iron 450 Ice 2060 23 Chapter 1 Aquatic ecosystem Specific heat of matter (c) The amount of heat gained by 1 kg of a substance that causes its temperature to rise by 1 K is called the specific heat of this substance, and its measuring unit is J/kg. K. The higher the specific heat of a substance, the more thermal energy a given mass of this substance takes to raise its temperature by 1 K if compared with an equal mass of another substance with a lower specific heat. The opposite table lists the specific heat of some substances. The amount of heat gained or lost by an object (Qth) can be calculated from the relationship: 𝐐𝐭𝐡 = 𝐦 𝐜 ∆𝐭 Where m: the body mass , ∆t: the amount of change in body temperature Example Calculate the amount of heat required to raise the temperature of 0.3 kg of copper from 20 degrees Celsius to 70 degrees Celsius given that the specific heat of copper = 385 J/kg. K. solution Qth = m c ∆t = 0.3 × 385 ×(70−20) = 5775 J ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ Example A piece of aluminum with a mass of 200g and a temperature of 80 °C is dropped into a quantity of water at room temperature. If the final temperature of the system is 40 °C, calculate the amount of heat gained by the amount of water. The specific heat of aluminum is 897 J/kg. K solution Based on the law of conservation of energy, the amount of heat gained by the water is equal to the amount of heat lost by the aluminum piece, assuming no thermal energy leaked or lost from the system. (Use international units.) QAl = mAl⋅cAl⋅ΔTAl QAl = (0.2 kg). 897 J/kg. K) ⋅ (40°C - 80°C) QAl = -7176 J The negative sign here indicates that the aluminum piece has lost heat to the water sample, so the amount of heat transferred to the water is 7176 J ‫ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ‬ The importance of the high specific heat of water: The specific heat of water is high compared to other substances and is roughly equal to 4200 J/kg. K due to the presence of hydrogen bonds between its molecules, making it partially responsible for the mild climate near large bodies of water. The temperature of a large body of water during the summer is low compared to the temperature of beach sand and rocks. Air over land heats up, becomes less dense, and rises upward. Cooler air from above the surface of the water moves landward, and is called the sea breeze, to replace the hot air that has risen upward, as shown in the figure. 24 Chemical reactions and their impact on water quality 1−5 Lesson Analytical activity: Analyze the data in the table and then answer the following questions: 1) What are the factors that affect the specific heat of matter? 2) Which of the three states of water has the greatest value of specific heat? The matter Its temperature The Physical state Specific heat J/kg. K(C) air 25°C Gas 1003.5 lead 25°C Solid 129 Pure water 25°C Liquid 4181.3 Water vapor 100°C Gas 2020 ice 0°C solid 2090 The effect of temperature changes on marine organisms: Temperature changes in the oceans affect the distribution of marine organisms. Organisms that live in warm surface waters may be unable to survive in colder depths. For example, coral reefs need specific temperatures to survive, and a change in temperature due to climate change may lead to their death. The high specific heat of water plays a large role in the relative stability of water temperature in seas and oceans as water can absorb a large amount of heat without a significant change in its temperature This makes the oceans and lakes huge thermal reservoirs, because during the day the water absorbs large amounts of solar energy without getting too hot, and then slowly releases this energy at night, helping to maintain stable temperatures in the surrounding marine environment. This thermal balance is very important for the sustainability of marine life. This property protects marine organisms from rapid changes in temperature, especially cold- blooded creatures (Poikilotherms), whose body temperature depends on the temperature of the surrounding environment. For this reason, we often find these organisms in the deep seas and oceans where the temperature is stable. Probe and investigation (activities) Use different sources to find out how to measure the specific heat of water using Joule calorimeter. Check your understanding 1.Given the different specific heats of land and seawater, explain the phenomenon of the sea breeze. 2.Explain why the specific heat of water is a critical factor in the sustainability of marine life. 3. What are the factors that affect the amount of heat lost or gained by a substance when its temperature changes? 25 Chapter 1 Aquatic ecosystem 1-6 The effect of light and solar radiation on aquatic environments Imagine you are diving into the sea, and you observe how the intensity of light changes as you dive deeper into the water. You may wonder: How does this affect the organisms that live in the depths? How does light in different layers of water affect photosynthesis? and what role does solar radiation play in maintaining the ecological balance in the oceans? Solar radiation refers to the energy produced by the sun, some of which reaches the Earth. It serves as the primary source of energy for most processes in the atmosphere, hydrosphere, and biosphere. Solar radiation can be converted into other forms of energy, such as heat and electricity, using various technologies. The technical and economic feasibility of these technologies depends on the available resources of solar radiation. Visible light is a part of the electromagnetic spectrum, which propagates as electromagnetic waves that differ in their wavelengths (λ) and frequency (ν). Visible light represents only a small portion of this spectrum and is composed of different wavelengths, known as the colors of the visible spectrum (these colours are red, orange, yellow, green, blue, indigo, and violet). 26 Chemical reactions and their impact on water quality 1−6 Lesson Solar radiation reaching Earth can be classified into two categories: Direct solar radiation: This is the radiation that reaches the Earth's surface without scattering. Indirect solar radiation: This is the light which scattered while passing through the atmosphere. The amount of solar radiation reaching a specific location or a certain object on Earth's surface depends on several factors such as geographic location, season, time of day, cloud cover, and altitude. Solar radiation and its effect on water: Solar radiation is the primary source of energy on Earth, and it directly affects the various layers of water. When sunlight penetrates the water’s surface, part of it is absorbed by water, suspended matter, and aquatic plants, while the other part scatters in the depths. light zones in water: As water depth increases, the intensity of light gradually decreases. This light gradient defines different zones in the oceans, such as the euphotic (sunlit) zone, the twilight (mesopelagic) zone, and the aphotic (deep) zone. Marine organisms inhabit these zones according to their ability to adapt with the available light. When sunlight hits the ocean surface, part of it is reflected into the atmosphere. The amount of energy that penetrates the water’s surface depends on the angle of the sun's rays. A greater amount of light penetrates the water when the sun's rays are perpendicular to the surface, while less light penetrates when the rays are inclined or tilted. Water absorbs nearly all infrared energy from sunlight within the top 10 centimeters of the surface. Depth not only affects the absorption of light colors but also the light intensity. The light intensity decreases gradually as it travels through the water. At a depth of 10 meters, more than 50% of visible light energy is absorbed. Even in clear tropical waters, only about 1% of visible light—mostly in the blue spectrum—reaches a depth of 100 meters. This diagram illustrates the difference in light penetration in shallow coastal waters and the open ocean. When different colors of the light spectrum penetrate ocean waters, warmer colors, like red and orange (with longer wavelengths), are absorbed, while cooler colors (with shorter wavelengths) are scattered. 27 Chapter 1 Aquatic ecosystem Photosynthesis in the aquatic environments: Many autotrophic organisms, such as aquatic plants, algae, and phytoplankton, rely on photosynthesis to convert solar energy into chemical energy which is used to produce organic compounds necessary for growth and survival. This process heavily depends on light availability and, therefore, mainly occurs in the surface layers of water bodies where light can reach these organisms. Solar radiation and ecological Balance: Solar radiation is a vital factor in maintaining ecological balance in aquatic environments. It does not only affect photosynthesis—an essential process for marine life—but also directly influences water temperature and the distribution of marine organisms. The Effect of Solar Radiation on Ecological Balance in Aquatic Environments: The role of solar radiation in the distribution of marine organisms: Marine organisms are unevenly distributed in water depending on their light and energy needs. Organisms that rely on photosynthesis, such as algae and phytoplankton, are abundant in the surface layers where solar radiation is plentiful. For example, coral reefs thrive in warm shallow waters near the equator, where solar radiation is available all year round. This radiation stimulates the growth of symbiotic algae living within coral tissues, providing the coral with nourishment. The effect of solar radiation on water temperatures: Solar radiation directly impacts water temperatures, which in turn affects the distribution of marine organisms. Warm waters resulting from solar radiation in tropical regions attract specific types of fish and marine animals that require certain temperatures to survive and reproduce. For instance, tropical fish such as tuna and barracuda live in warm waters, while other species like cod prefer colder waters found farther from the equator. Changes in solar radiation intensity: Variations in solar radiation intensity due to seasonal changes or climate changes can lead to disruptions in ecological balance. For example, in polar regions, where solar radiation is low or absent during the winter, photosynthesis rates drop significantly, affecting the food availability for marine organisms. This can lead to a decline in the numbers of organisms that rely on photosynthesis, thus impacting the entire food chain. On the other hand, global warming causes rise in water temperatures, leading to the death of coral reefs, which significantly affects the marine organisms’ dependence on coral reefs. The effect of solar radiation on ocean currents: Solar radiation also contributes to the formation of ocean currents, which play a crucial role in distributing heat and nutrients throughout the oceans. These currents influence the distribution of marine life and make certain areas rich in food resources. For example, the Gulf Stream carries warm waters from the equator to the North Atlantic, moderating the climate in regions like Western Europe and enhancing marine biodiversity. 28 Chemical reactions and their impact on water quality 1−6 Lesson Research and investigation (activities) Activity 1: Measuring light intensity in water aim: The student tests the light intensity of water at different depths. Tools: Light intensity meter, large basin of water, different light sources, ruler. Steps: 1.Place the light source above the aquarium. 2.Use the light meter to measure the intensity of light at different depths. 3.Record the results and discuss the effect of depth on light intensity. Check your understanding 1) How does the light gradient affect the distribution of marine organisms in the deep ocean? 2) Why is photosynthesis important for maintaining ecological balance in the oceans? 29