🏝️Earth Science Unit 6 – Earth's Oceans and Marine Ecosystems

Ocean Basics

• Oceans cover approximately 71% of the Earth's surface and contain about 97% of the planet's water
• The five major oceans are the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans
• Oceans play a crucial role in regulating the Earth's climate by absorbing and redistributing heat from the sun
• Marine life depends on the oceans for survival, with an estimated 50-80% of all life on Earth residing in the oceans
• Oceans are the source of many resources, including food (fish and seafood), minerals, and energy (oil and gas)
• The average depth of the oceans is about 3,688 meters (12,100 feet), with the deepest point being the Challenger Deep in the Mariana Trench at 10,994 meters (36,070 feet)
• Oceans are divided into various zones based on depth and light penetration, including the sunlight zone, twilight zone, and midnight zone

Physical Properties of Seawater

• Seawater is a complex solution of water, salts, and dissolved gases
• The average salinity of seawater is about 35 parts per thousand (ppt), which means that for every 1,000 grams of seawater, there are 35 grams of dissolved salts
  • The main dissolved salts in seawater are sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2)
• The density of seawater is higher than that of freshwater due to the dissolved salts, with an average density of about 1.025 g/cm³
• Seawater pH typically ranges from 7.5 to 8.4, making it slightly alkaline
  • Ocean acidification occurs when the pH of seawater decreases due to the absorption of excess atmospheric carbon dioxide (CO2)
• The temperature of seawater varies depending on factors such as latitude, season, and depth
  • Surface water temperatures range from about -2°C (28°F) in polar regions to over 30°C (86°F) in tropical regions
• Seawater has a high specific heat capacity, meaning it can absorb and store large amounts of heat energy without significant changes in temperature
• The color of seawater is influenced by factors such as the presence of dissolved organic matter, phytoplankton, and the scattering of light by water molecules

Ocean Currents and Circulation

• Ocean currents are continuous, directed movements of seawater driven by various forces, including wind, temperature, salinity, and the Earth's rotation (Coriolis effect)
• Surface currents are primarily driven by wind and affect the upper 400 meters (1,300 feet) of the ocean
  • Examples of surface currents include the Gulf Stream in the Atlantic Ocean and the Kuroshio Current in the Pacific Ocean
• Deep ocean currents, also known as thermohaline circulation, are driven by differences in water density caused by variations in temperature and salinity
  • The global conveyor belt is a simplified model of thermohaline circulation that depicts the interconnected flow of ocean currents worldwide
• Upwelling occurs when deep, nutrient-rich water is brought to the surface, often along coastlines, promoting high biological productivity
• Gyres are large, circular ocean current systems that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere
  • There are five major gyres: the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Ocean gyres
• Ocean currents play a vital role in redistributing heat, nutrients, and oxygen throughout the ocean, influencing global climate patterns and marine ecosystems
• The El Niño-Southern Oscillation (ENSO) is a periodic fluctuation in ocean temperatures and atmospheric pressure in the Pacific Ocean that can significantly impact global weather patterns

Marine Ecosystems and Biodiversity

• Marine ecosystems are communities of living organisms interacting with each other and their physical environment in the ocean
• Biodiversity refers to the variety of life forms within an ecosystem, including the diversity of species, genetic variation within species, and the range of ecosystems
• Primary producers, such as phytoplankton and seaweeds, form the foundation of marine food webs by converting sunlight into organic matter through photosynthesis
• Zooplankton, small drifting animals, consume phytoplankton and are in turn consumed by larger organisms like fish and whales
• Marine ecosystems are classified based on their physical characteristics, such as temperature, depth, and proximity to land
  • Examples include coral reefs, kelp forests, seagrass beds, mangrove forests, and deep-sea hydrothermal vents
• Coral reefs are among the most diverse and productive ecosystems on Earth, supporting an estimated 25% of all marine life
  • Coral bleaching occurs when corals expel their symbiotic algae due to stress factors like rising water temperatures, threatening the survival of coral reefs worldwide
• Marine biodiversity is threatened by various human activities, such as overfishing, pollution, habitat destruction, and climate change
• Marine protected areas (MPAs) are designated regions where human activities are restricted to conserve marine ecosystems and biodiversity

Ocean Zones and Habitats

• The ocean is divided into distinct zones based on depth, light penetration, temperature, and pressure
• The epipelagic zone, also known as the sunlight zone, extends from the surface to about 200 meters (660 feet) and receives enough light for photosynthesis
  • This zone is home to a diverse array of marine life, including phytoplankton, zooplankton, fish, and marine mammals
• The mesopelagic zone, or twilight zone, extends from 200 to 1,000 meters (3,300 feet) and receives minimal sunlight
  • Many organisms in this zone are bioluminescent, producing their own light to communicate, find prey, or avoid predators
• The bathypelagic zone, or midnight zone, extends from 1,000 to 4,000 meters (13,100 feet) and is characterized by complete darkness, high pressure, and cold temperatures
  • Life in this zone is sparse and includes species adapted to extreme conditions, such as anglerfish and giant squid
• The abyssopelagic zone extends from 4,000 to 6,000 meters (19,700 feet) and is characterized by extremely high pressure and near-freezing temperatures
• The hadopelagic zone, or hadal zone, includes the deepest parts of the ocean, such as trenches, and extends from 6,000 meters to the ocean floor
  • The Mariana Trench, the deepest known part of the ocean, reaches depths of over 11,000 meters (36,000 feet)
• Benthic habitats are those on or near the seafloor and include environments such as continental shelves, slopes, and abyssal plains
  • Benthic organisms, such as clams, crabs, and bottom-dwelling fish, play essential roles in nutrient cycling and food web dynamics

Human Impact on Oceans

• Overfishing has led to the depletion of many fish stocks worldwide, disrupting marine food webs and threatening the livelihoods of coastal communities
  • Bycatch, the unintentional capture of non-target species, is a significant problem associated with certain fishing practices like bottom trawling
• Pollution, including plastic debris, oil spills, and agricultural runoff, can have detrimental effects on marine life and ecosystems
  • Microplastics, tiny plastic particles less than 5 mm in size, are ingested by marine organisms and can accumulate in food chains
• Coastal development, such as the construction of ports, harbors, and tourist facilities, can lead to the destruction of critical habitats like wetlands and mangrove forests
• Climate change, driven by human activities that increase greenhouse gas emissions, is causing ocean warming, acidification, and sea-level rise
  • Rising ocean temperatures can lead to coral bleaching, shifts in species distributions, and changes in ocean circulation patterns
• Invasive species, often introduced through human activities like shipping and aquaculture, can disrupt native ecosystems and cause significant economic damage
• Underwater noise pollution from sources like shipping, seismic surveys, and sonar can interfere with marine mammal communication and navigation
• The cumulative impact of human activities on the oceans is leading to a decline in marine biodiversity and the degradation of essential ecosystem services

Ocean Conservation Efforts

• International agreements, such as the United Nations Convention on the Law of the Sea (UNCLOS), provide a framework for the conservation and sustainable use of ocean resources
• Marine protected areas (MPAs) are established to safeguard marine ecosystems, preserve biodiversity, and support sustainable fisheries
  • Examples of MPAs include the Great Barrier Reef Marine Park in Australia and the Papahānaumokuākea Marine National Monument in the United States
• Sustainable fisheries management practices, such as catch limits, gear restrictions, and seasonal closures, aim to maintain fish populations and minimize the environmental impact of fishing
• Efforts to reduce marine pollution include bans on single-use plastics, improved waste management infrastructure, and the development of biodegradable alternatives
• Coastal habitat restoration projects, such as the replanting of mangrove forests and the creation of artificial reefs, help to restore degraded ecosystems and enhance marine biodiversity
• Public awareness campaigns and educational initiatives promote the importance of ocean conservation and encourage individuals to adopt sustainable practices
• Scientific research plays a crucial role in understanding marine ecosystems, monitoring environmental changes, and informing conservation strategies
  • Examples include satellite monitoring of ocean temperature and color, underwater surveys using remotely operated vehicles (ROVs), and genetic studies of marine organisms

Key Takeaways and Future Outlook

• Oceans are vital to the Earth's climate, biodiversity, and human well-being, providing numerous ecosystem services and resources
• The physical properties of seawater, such as salinity, temperature, and density, influence ocean circulation patterns and the distribution of marine life
• Ocean currents play a critical role in redistributing heat, nutrients, and oxygen, shaping global climate patterns and marine ecosystems
• Marine ecosystems are incredibly diverse, with a wide range of habitats and species adapted to various conditions
• Human activities, such as overfishing, pollution, coastal development, and climate change, are having significant impacts on the health and resilience of marine ecosystems
• Ocean conservation efforts, including international agreements, marine protected areas, sustainable fisheries management, and habitat restoration, are essential for safeguarding the future of our oceans
• Addressing the challenges facing our oceans requires a multi-faceted approach that involves governments, industries, scientists, and individuals working together to promote sustainable practices and mitigate the impacts of human activities
• As our understanding of marine ecosystems grows, it is crucial to integrate this knowledge into decision-making processes and develop innovative solutions to the pressing issues facing our oceans
• The future outlook for our oceans depends on our collective ability to balance human needs with the conservation and sustainable use of marine resources, ensuring that these vital ecosystems continue to support life on Earth for generations to come