Ocean Dynamics - Circulation Lecture PDF

OCEAN DYNAMICS - CIRCULATION Definition The dynamics of the ocean, also known as ocean dynamics, involve the study of the movement of ocean water and the forces that drive these movements. It encompasses a wide range of physical processes that govern the distribution and movement of ocean w...

OCEAN DYNAMICS - CIRCULATION Definition The dynamics of the ocean, also known as ocean dynamics, involve the study of the movement of ocean water and the forces that drive these movements. It encompasses a wide range of physical processes that govern the distribution and movement of ocean waters, including currents, waves, tides, and mixing processes. These dynamics are driven by various forces such as wind, temperature and salinity differences, the Earth's rotation, and gravitational interactions with the moon and sun. Ocean dynamics play a crucial role in regulating climate, supporting marine ecosystems, influencing weather patterns globally, and safety of the marine structures. World Ocean Circulation Importance of Ocean Dynamics? Understanding ocean dynamics is crucial for several reasons: ❖ Climate Regulation: Oceans absorb and redistribute heat, playing a vital role in regulating the Earth's climate. ❖ Marine Ecosystems: The movement of water and nutrients supports diverse marine life and ecosystems. ❖ Weather Prediction: Ocean conditions influence weather patterns and phenomena such as hurricanes and monsoons. ❖ Human Activities: Knowledge of ocean dynamics aids in navigation, fishing, coastal management, and environmental protection. ❖ Safety of the marine structures: Ocean dynamics play a vital role in the safety and stability of marine structures. Key Components of Ocean Dynamics 1. Ocean Circulation 2. Waves 3. Tides 4. Upwelling and Downwelling 5. Ocean-Atmosphere Interactions 6. Heat and Salt Transport 7. Ocean Mixing and Stratification Ocean Circulation Ocean circulation refers to the large-scale movement of water within the world’s oceans, driven by a combination of wind, temperature, salinity differences, and the Earth’s rotation. This circulation plays a critical role in regulating climate, distributing heat, and supporting marine ecosystems. There are three major types of Ocean circulation. ❖ Wind-driven circulation is caused by complex interactions among air-sea motions, the Coriolis effect, and gravity. ❖ Thermohaline circulation is caused by density differences among water masses (volume of water with identifiable physical and chemical characteristics). ❖ Tide-driven circulation refers to the movement of ocean water caused primarily by the gravitational forces exerted by the moon and the sun on the Earth's oceans. These tidal forces result in the rise and fall of sea levels, known as tides, which in turn generate currents. Tidal circulation plays a critical role in coastal and estuarine environments, influencing sediment transport, nutrient cycling, and marine ecosystems.  Wind-driven Circulation Wind-driven circulation refers to the movement of surface ocean waters primarily caused by the action of the wind. It plays a crucial role in the distribution of heat, nutrients, and other properties within the ocean. This type of circulation is responsible for the formation of large-scale ocean currents, gyres, and phenomena such as upwelling and downwelling. ▪ The difference in heating of the earth’s surface and subsequent development of atmospheric pressure systems cause global winds, which then transfer energy to the ocean’s surface layer. ▪ As the wind moves over the sea surface, it creates stress on the sea surface. ▪ This stress creates waves and other water movement. ▪ These winds are subject to the Coriolis Effect, which creates their motion based on the rotation of the earth. Wind-driven Circulation ▪ The direct effect of stress is confined to a layer beneath the surface (0 to 100m), called the Ekman layer. Wind-driven Circulation -Coriolis effect and Ekman transport The Coriolis effect is a phenomenon that results from the rotation of the Earth, causing moving fluids like air and water to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This effect is crucial for understanding the movement of large-scale ocean currents, wind patterns, and atmospheric circulation. ❖ Current speed is generally 2% of wind speed Ekman layer and transport ❖ Current is deflected by Coriolis effect ❖ In NH, the surface layer moves to the right of the wind ❖ Surface current imparts stress on the bottom layer ❖ Current velocity diminishes with depth ❖ The overall current will be 90° to the right of the wind ❖ The wind-driven water transport deflected by the Earth's rotation is called Ekman transport, named after the Swedish oceanographer Vagn Walfrid Ekman. Wind-driven Circulation – Upwelling and downwelling Upwelling ❑ Upwelling and downwelling are two important processes in oceanography that describe the vertical movement of water in the ocean. ❑ When the wind blows parallel to the coastline, the Coriolis effect causes the surface water to move away from the coast (Ekman transport). This movement of surface water is replaced by deeper cooler water rising to the surface (upwelling). ❑ Upwelling brings nutrients from the deep ocean to the surface, which supports high primary productivity and marine life. ❑ Coastal downwelling occurs when winds blow towards the coast. The Downwelling Coriolis effect causes surface water to move towards the coast and the excess water sinks. ❑ Downwelling transports oxygen-rich surface water to deeper layers, which is crucial for deep-sea ecosystems. Thermohaline circulation Thermohaline circulation, also known as the global conveyor belt, is a large-scale ocean circulation driven by differences in temperature (thermo) and salinity (haline). This circulation plays a crucial role in regulating the Earth's climate by redistributing heat and influencing patterns of climate and weather. Thermohaline circulation is driven by density differences in seawater, which are controlled by temperature and salinity. Colder and saltier water is denser and tends to sink, while warmer and less salty water is less dense and tends to rise. The densest water forms in polar regions where the temperature is very low and sea ice formation increases salinity by excluding salt. This dense water sinks to the ocean depths, initiating the global conveyor belt. Tide driven circulation ✓ Tidal circulation refers to the movement of ocean water caused primarily by the gravitational forces exerted by the moon and the sun on the Earth's oceans. These tidal forces result in the rise and fall of sea levels, known as tides, which in turn generate currents. Tidal circulation plays a critical role in coastal and estuarine environments, influencing sediment transport, nutrient cycling, and marine ecosystems. ✓ The moon’s gravitational pull is the primary force driving tides. The side of the Earth facing the moon experiences a strong gravitational attraction, causing the water to bulge outwards, creating a high tide. Simultaneously, Tide-driven circulation on the opposite side of the Earth, inertia causes another bulge, resulting in a second high tide. ✓ Flood Currents: These occur as the tide rises, bringing water into bays, estuaries, and coastal areas. Flood currents transport nutrients and sediments landward. ✓ Ebb Currents: These occur as the tide falls, moving water out of bays, estuaries, and coastal areas back to the ocean. Ebb currents carry sediments and nutrients seaward.  Ocean-Atmosphere Interactions- El Nino, La Nina o Ocean-atmosphere interactions refer to the dynamic exchanges of energy, El Nino and La Nina momentum, water, and gases between the ocean and the atmosphere. These interactions are crucial for regulating the Earth's climate, weather patterns, and biogeochemical cycles. o Wind blowing across the ocean surface exerts a stress that drives ocean currents. o These surface currents affect global climate and weather patterns (monsoons, El Nino, La Nina etc). o El Niño and La Niña are opposite phases of the El Niño-Southern Oscillation (ENSO) cycle, a climatic phenomenon that occurs in the tropical Pacific Ocean. These phases have significant impacts on global weather patterns, climate, and marine ecosystems. o El Niño is characterized by unusually warm sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean, leading to the weakened trade wind, and wetter conditions in the Americas, and drier conditions in Asia. o La Niña is characterized by unusually cool sea surface temperatures in the central and eastern equatorial Pacific Ocean leading to more rainfall in Asia and frequent floods. Ocean-Atmosphere Interactions- Monsoon o Monsoon: A seasonal change in the direction of the prevailing winds of a region, leading to drastic changes in precipitation. o Derived from the Arabic word "mausim," meaning "season. o Differential Heating: Monsoons are driven by the differential heating of land and sea. During the summer, landmasses heat up more quickly than the oceans, causing low pressure over the land and high pressure over the ocean. o Wind Reversal: This pressure difference causes winds to shift direction, blowing from the ocean towards the land in summer (wet season) and from the land towards the ocean in winter (dry season). Ocean-Atmosphere Interactions- Hurricanes, cyclones and typhoons Cyclones ❖ Hurricanes, cyclones and typhoons are powerful and complex weather systems that have significant impacts on the regions they affect. These terms refer to the same type of storm, but their names vary depending on their location. ❖ They form in an area of low pressure. This area of low pressure draws in surrounding winds. As the Earth rotates, it creates forces that cause the winds to swirl around the low pressure. This helps the cyclone start to spin. ❖ Hurricanes: These are tropical cyclones that occur in the Atlantic Ocean and the northeastern Pacific Ocean. ❖ Cyclones: This term is used for similar storms in the South Pacific and Indian Ocean. ❖ Typhoons: These are tropical cyclones occurring in the northwestern Pacific Ocean. ❖ Understanding their formation, structure, and impacts is crucial for effective preparedness and response. Ocean Dynamics and marine structures ❑ Ocean dynamics significantly impact marine structures, including offshore platforms, ships, submarines, coastal infrastructure, and underwater pipelines. ❑ The interaction between ocean dynamics and marine structures involves complex forces and responses that must be carefully analyzed and accounted for in design, construction, and maintenance. ❑ Ocean currents exert forces on marine structures, affecting their stability and integrity. ❑ Waves are a major dynamic force impacting marine structures, causing both short-term and long-term effects. ❑ Tidal movements cause fluctuations in water levels, influencing the design and operation of marine structures. ❑ Understanding these effects is crucial for designing, constructing, and maintaining resilient and efficient marine structures. ❑ Understanding wave action, currents, wind forces, and pressure variations is crucial for ensuring the stability and longevity of marine structures. ❑ Design Engineers must account for ocean dynamics in the design and maintenance of marine structures. ❑ By considering material selection, structural design, dynamic response analysis, and continuous monitoring, engineers can create resilient and durable structures capable of withstanding the challenging ocean environment. Summary and conclusion ❑ Ocean dynamics encompasses a wide range of physical and chemical processes that govern the behavior and movement of ocean waters. ❑ Understanding these components is crucial for predicting weather patterns, managing marine resources, and studying climate change. ❑ Ocean dynamics play a critical role in the stability and integrity of marine structures such as offshore platforms, pipelines, wind turbines, and coastal infrastructure. ❑ Understanding the interaction between ocean forces and marine structures is essential for designing, constructing, and maintaining these structures to ensure their safety and functionality.