🌊Oceanography Unit 5 – Ocean Circulation and Surface Currents

Key Concepts and Definitions

• Ocean circulation movement of water in the world's oceans, driven by wind, tides, and differences in water density
• Surface currents horizontal movement of water at or near the ocean's surface, primarily driven by wind
• Deep ocean currents movement of water in the deep ocean, primarily driven by differences in water density
• Thermohaline circulation global-scale circulation driven by differences in temperature and salinity
• Coriolis effect apparent deflection of moving objects, such as ocean currents, due to Earth's rotation
• Ekman transport net movement of water perpendicular to the wind direction, caused by the Coriolis effect
• Geostrophic flow balance between the Coriolis effect and the pressure gradient force, resulting in currents that flow along lines of constant pressure
• Upwelling process by which deep, cold, nutrient-rich water is brought to the surface, often driven by wind

Ocean Circulation Basics

• Ocean circulation plays a crucial role in redistributing heat, nutrients, and dissolved gases throughout the world's oceans
• Driven by a combination of wind stress, differences in water density, tides, and Earth's rotation
• Surface currents are primarily wind-driven and extend to depths of about 100-200 meters
• Deep ocean currents are primarily driven by differences in water density, which is determined by temperature and salinity
• Thermohaline circulation is a global-scale circulation pattern that connects the ocean basins and is driven by differences in water density
• Upwelling and downwelling are important processes that influence nutrient distribution and biological productivity in the oceans
• Ocean circulation patterns can vary on different time scales, from daily tidal cycles to long-term climate oscillations (El Niño-Southern Oscillation)

Types of Surface Currents

• Gyres large, circular current systems that dominate ocean basins, such as the North Pacific Gyre and the North Atlantic Gyre
• Western boundary currents fast, narrow, and deep currents that flow along the western edges of ocean basins (Gulf Stream, Kuroshio Current)
  • Characterized by warm temperatures, high salinity, and high velocity
  • Play a significant role in poleward heat transport
• Eastern boundary currents slow, broad, and shallow currents that flow along the eastern edges of ocean basins (California Current, Canary Current)
  • Characterized by cool temperatures, low salinity, and nutrient-rich waters due to upwelling
• Equatorial currents flow westward near the equator, driven by the trade winds (North Equatorial Current, South Equatorial Current)
• Antarctic Circumpolar Current flows eastward around Antarctica, connecting the Atlantic, Pacific, and Indian Oceans
• Coastal currents flow parallel to coastlines and are influenced by local wind patterns, topography, and freshwater input (Alaska Coastal Current)

Factors Influencing Ocean Currents

• Wind stress the force exerted by wind on the ocean surface, which drives surface currents and creates Ekman transport
• Coriolis effect causes currents to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere
• Density differences in water, caused by variations in temperature and salinity, drive deep ocean circulation
• Bathymetry the shape and depth of the ocean floor, influences the path and intensity of currents
• Tides periodic rise and fall of sea level, caused by the gravitational pull of the moon and sun, can influence coastal currents
• Seasonal changes in wind patterns and solar radiation can affect the strength and direction of currents
• Climate oscillations (El Niño, La Niña) can alter global circulation patterns and influence regional current systems

Global Circulation Patterns

• Global conveyor belt a simplified model of the global thermohaline circulation, which connects the ocean basins and redistributes heat and nutrients
• Atlantic Meridional Overturning Circulation (AMOC) a major component of the global conveyor belt, characterized by northward flow of warm, saline water in the upper layers and southward flow of cold, dense water in the deep layers
• Antarctic Bottom Water (AABW) cold, dense water formed in the Southern Ocean that spreads northward along the bottom of the ocean basins
• North Atlantic Deep Water (NADW) dense water formed in the North Atlantic that flows southward at intermediate depths
• Indian Ocean Dipole (IOD) an irregular oscillation of sea surface temperatures in the Indian Ocean that affects regional circulation and climate
• Pacific Decadal Oscillation (PDO) a long-term climate oscillation that affects sea surface temperatures and circulation patterns in the Pacific Ocean

Impacts on Climate and Weather

• Ocean currents redistribute heat from the equator to the poles, moderating Earth's climate
• Western boundary currents (Gulf Stream, Kuroshio Current) transport warm water poleward, influencing regional climates and weather patterns
• Upwelling regions (Peru, California) are characterized by cool, nutrient-rich waters that support high biological productivity and influence local climate
• El Niño and La Niña events alter global circulation patterns, affecting temperature, precipitation, and storm activity worldwide
• Changes in thermohaline circulation can have long-term impacts on global climate, such as the Younger Dryas cold period during the last deglaciation
• Ocean circulation plays a crucial role in the carbon cycle by absorbing and redistributing atmospheric CO2, influencing global climate change

Tools and Techniques for Studying Currents

• Drifters floating devices that are released into the ocean to track surface currents and measure water properties (temperature, salinity)
• Acoustic Doppler Current Profilers (ADCPs) instruments that use sound waves to measure current velocity and direction at various depths
• Satellite altimetry measures sea surface height, which can be used to infer geostrophic currents and monitor large-scale circulation patterns
• Moored buoys anchored platforms that measure current velocity, temperature, salinity, and other water properties at fixed locations
• Argo floats autonomous underwater vehicles that drift with currents and measure temperature and salinity profiles in the upper 2,000 meters of the ocean
• Numerical models computer simulations that use mathematical equations to predict and study ocean circulation patterns and their interactions with the atmosphere and climate

Real-World Applications and Case Studies

• Oil spill tracking and response understanding ocean currents is crucial for predicting the movement and dispersal of oil spills (Deepwater Horizon, 2010)
• Search and rescue operations knowledge of local currents can aid in the planning and execution of search and rescue missions at sea
• Marine protected area design information on current patterns can inform the placement and design of marine protected areas to ensure connectivity and larval dispersal
• Fisheries management understanding the relationship between currents, upwelling, and biological productivity is essential for sustainable fisheries management (Peruvian anchovy fishery)
• Shipping and navigation accurate knowledge of ocean currents is important for optimizing shipping routes and ensuring safe navigation
• Climate change adaptation and mitigation studying changes in ocean circulation patterns can help predict and mitigate the impacts of climate change on marine ecosystems and human communities (coral reef conservation, coastal infrastructure planning)