🌈Earth Systems Science Unit 7 – Ocean Circulation & Marine Ecosystems

Key Ocean Circulation Patterns

• Major surface currents form large circular patterns called gyres driven by wind patterns and Earth's rotation (Coriolis effect)
  • Five main gyres: North Pacific, South Pacific, North Atlantic, South Atlantic, Indian Ocean
• Thermohaline circulation is a global conveyor belt driven by density differences from temperature and salinity variations
  • Cold, salty water sinks in North Atlantic and Antarctic, travels along ocean floor, rises in Pacific and Indian Oceans
• Upwelling brings cold, nutrient-rich water from deep ocean to surface along certain coastlines (Peru, California)
  • Driven by winds blowing parallel to shore, Ekman transport moves surface water offshore
• Downwelling occurs when surface water converges and sinks, often in subtropical gyres
• Boundary currents are intense, narrow flows along continental margins (Gulf Stream, Kuroshio)
• Antarctic Circumpolar Current is the world's largest current, connecting Atlantic, Pacific, and Indian Oceans
• Eddies are smaller-scale circular currents that spin off from major currents, transporting heat and nutrients

Drivers of Ocean Currents

• Wind stress is the primary driver of surface currents, creating friction that moves water
  • Trade winds blow consistently from east to west near equator
  • Westerlies blow from west to east in mid-latitudes
• Earth's rotation causes the Coriolis effect, deflecting currents to the right in Northern Hemisphere and left in Southern Hemisphere
• Density differences from temperature and salinity variations drive thermohaline circulation
  • Cold, salty water is denser and sinks, while warm, fresher water is less dense and rises
• Tides are caused by gravitational pull of the moon and sun, creating regular changes in sea level and currents
• Topography of ocean basins and coastlines influences current patterns and creates local variations
• Seasonal changes in wind patterns and solar heating affect current strength and direction
• Climate oscillations like El Niño and the North Atlantic Oscillation can alter current patterns on interannual timescales

Marine Ecosystem Basics

• Marine ecosystems are characterized by complex interactions between organisms and their physical environment
• Primary producers like phytoplankton and algae form the base of marine food webs, converting sunlight into organic matter through photosynthesis
• Zooplankton are small animals that feed on phytoplankton and are a crucial link to higher trophic levels
• Marine food webs include a wide variety of consumers such as fish, marine mammals, seabirds, and invertebrates
  • Trophic cascades can occur when changes in one level of the food web affect multiple other levels
• Benthic ecosystems on the seafloor include diverse communities of organisms adapted to living on or in sediments
• Coral reefs are highly productive and diverse ecosystems found in shallow, tropical waters
  • Corals have a symbiotic relationship with algae called zooxanthellae that provide energy through photosynthesis
• Kelp forests are underwater forests that provide habitat and food for many species along temperate coastlines
• Hydrothermal vents support unique chemosynthetic communities fueled by chemicals from the Earth's interior instead of sunlight

Nutrient Cycling in Oceans

• Nutrients like nitrogen, phosphorus, and iron are essential for marine primary production
• The biological pump transfers carbon and nutrients from surface waters to the deep ocean through sinking of organic matter
  • Phytoplankton take up nutrients and carbon dioxide in surface waters, then sink as detritus or fecal pellets
• Upwelling brings nutrient-rich deep water to the surface, supporting high primary productivity in regions like the equatorial Pacific and coastal Peru
• Nitrogen fixation by cyanobacteria converts atmospheric nitrogen gas into biologically available forms
  • Trichodesmium is a common nitrogen-fixing cyanobacterium in tropical and subtropical oceans
• Denitrification by bacteria in low-oxygen zones converts nitrate back into nitrogen gas, removing it from the biologically available pool
• The microbial loop recycles nutrients and organic matter through bacterial decomposition and consumption by microzooplankton
• Atmospheric deposition of dust and volcanic ash can provide essential micronutrients like iron to surface waters
• Nutrient limitation can occur when one nutrient is in short supply relative to others, limiting primary production (Liebig's Law of the Minimum)

Climate-Ocean Interactions

• Oceans play a crucial role in regulating Earth's climate by absorbing and redistributing heat and carbon dioxide
• The high heat capacity of water allows oceans to store vast amounts of thermal energy, moderating temperature fluctuations
• Ocean currents transport heat from the equator to the poles, influencing regional climates
  • The Gulf Stream brings warm water from the Caribbean to the North Atlantic, warming Europe's climate
• Sea surface temperature patterns like El Niño and La Niña can have far-reaching effects on global weather patterns
  • El Niño events occur when warm water pools in the eastern equatorial Pacific, altering atmospheric circulation
• Ocean-atmosphere coupling through evaporation and precipitation helps drive the global water cycle
• The ocean's biological pump removes carbon dioxide from the atmosphere and stores it in deep waters and sediments
• Ocean acidification occurs as the ocean absorbs excess carbon dioxide from the atmosphere, lowering pH and affecting marine life
• Sea level rise from thermal expansion and melting of land-based ice can impact coastal communities and ecosystems
• Changes in ocean circulation patterns can affect regional climates and marine productivity

Human Impacts on Marine Systems

• Overfishing has depleted many fish stocks worldwide, altering marine food webs and ecosystems
  • Bycatch of non-target species in fishing gear is a major threat to marine life like sea turtles and dolphins
• Pollution from land-based sources like agricultural runoff, sewage, and plastic waste harms marine life and degrades water quality
  • Eutrophication from excess nutrients can lead to harmful algal blooms and oxygen-depleted "dead zones"
• Coastal development and habitat destruction, such as dredging and filling of wetlands, reduces biodiversity and ecosystem services
• Shipping and recreational boating can introduce invasive species through ballast water discharge and hull fouling
  • The lionfish invasion in the Atlantic has disrupted coral reef ecosystems
• Underwater noise pollution from shipping, sonar, and seismic surveys can disrupt marine mammal communication and behavior
• Climate change impacts like ocean warming, acidification, and deoxygenation put stress on marine organisms and ecosystems
  • Coral bleaching occurs when warm water causes corals to expel their symbiotic algae, often leading to coral death
• Exploitation of deep-sea resources like oil, gas, and minerals can damage poorly understood ecosystems

Ocean Health and Conservation

• Marine protected areas (MPAs) are designated regions where human activities are restricted to conserve biodiversity and ecosystem functions
  • The Great Barrier Reef Marine Park in Australia is a well-known example of a large, multiple-use MPA
• Ecosystem-based management considers the complex interactions within marine ecosystems and the cumulative impacts of human activities
• Sustainable fisheries management aims to maintain fish populations and ecosystem health through tools like catch limits, gear restrictions, and seasonal closures
  • Rights-based approaches like individual transferable quotas (ITQs) can provide incentives for sustainable practices
• Habitat restoration efforts seek to restore degraded ecosystems like oyster reefs, seagrass beds, and mangroves
• Reducing land-based pollution through improved waste management, agricultural practices, and stormwater treatment can benefit coastal waters
• International agreements and cooperation are essential for addressing transboundary issues like migratory species conservation and high seas governance
  • The United Nations Convention on the Law of the Sea (UNCLOS) provides a legal framework for ocean management
• Citizen science and community-based conservation engage the public in monitoring and protecting marine resources
• Sustainable aquaculture practices can help meet growing seafood demand while reducing pressure on wild fish stocks

Future Trends and Research

• Climate change adaptation strategies are needed to help marine ecosystems and coastal communities cope with impacts like sea level rise and ocean acidification
  • Nature-based solutions like living shorelines and coral reef restoration can enhance coastal resilience
• Improved ocean observation systems using satellites, drones, and autonomous vehicles will provide better data for understanding and managing marine systems
• Advances in remote sensing and machine learning will enable more efficient monitoring of illegal fishing, pollution, and other threats
• Genetic tools like eDNA metabarcoding can help assess biodiversity and detect invasive species or rare organisms
• Research on marine microbiomes is revealing the crucial roles of bacteria, archaea, and viruses in ocean biogeochemistry and ecosystem functioning
• Exploration of the deep sea and polar regions is uncovering new species, habitats, and resources
  • The NEPTUNE cabled observatory network enables real-time monitoring of the Juan de Fuca tectonic plate
• Interdisciplinary approaches that integrate natural and social sciences are needed to address complex ocean challenges
• Innovative technologies like marine renewable energy, sustainable aquaculture feeds, and biodegradable plastics offer opportunities for more sustainable ocean use
• Increased public awareness and engagement through education, media, and policy advocacy can build support for ocean conservation and sustainability