Downwelling is the downward movement of a fluid parcel and its properties within a larger fluid. It is closely related to upwelling, the upward movement of fluid.
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll a.
In oceanography, a gyre is any large system of circulating ocean surface currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis effect; planetary vorticity, horizontal friction and vertical friction determine the circulatory patterns from the wind stress curl (torque).
The California Current is a cold water Pacific Ocean current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Sur. It is considered an Eastern boundary current due to the influence of the North American coastline on its course. It is also one of six major coastal currents affiliated with strong upwelling zones, the others being the Humboldt Current, the Canary Current, the Benguela Current, the Oyashio Current, and the Somali Current. The California Current is part of the North Pacific Gyre, a large swirling current that occupies the northern basin of the Pacific.
A pycnocline is the cline or layer where the density gradient is greatest within a body of water. An ocean current is generated by the forces such as breaking waves, temperature and salinity differences, wind, Coriolis effect, and tides caused by the gravitational pull of celestial bodies. In addition, the physical properties in a pycnocline driven by density gradients also affect the flows and vertical profiles in the ocean. These changes can be connected to the transport of heat, salt, and nutrients through the ocean, and the pycnocline diffusion controls upwelling.
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid behind the obstacle flows into the void creating a swirl of fluid on each edge of the obstacle, followed by a short reverse flow of fluid behind the obstacle flowing upstream, toward the back of the obstacle. This phenomenon is naturally observed behind large emergent rocks in swift-flowing rivers.
Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman transport is a component of wind-driven ocean current. Ekman transport occurs when ocean surface waters are influenced by the friction force acting on them via the wind. As the wind blows it casts a friction force on the ocean surface that drags the upper 10-100m of the water column with it. However, due to the influence of the Coriolis effect, the ocean water moves at a 90° angle from the direction of the surface wind. The direction of transport is dependent on the hemisphere: in the northern hemisphere, transport occurs at 90° clockwise from wind direction, while in the southern hemisphere it occurs at 90° anticlockwise. This phenomenon was first noted by Fridtjof Nansen, who recorded that ice transport appeared to occur at an angle to the wind direction during his Arctic expedition of the 1890s. Ekman transport has significant impacts on the biogeochemical properties of the world's oceans. This is because it leads to upwelling and downwelling in order to obey mass conservation laws. Mass conservation, in reference to Ekman transfer, requires that any water displaced within an area must be replenished. This can be done by either Ekman suction or Ekman pumping depending on wind patterns.
Thin layers are concentrated aggregations of phytoplankton and zooplankton in coastal and offshore waters that are vertically compressed to thicknesses ranging from several centimeters up to a few meters and are horizontally extensive, sometimes for kilometers. Generally, thin layers have three basic criteria: 1) they must be horizontally and temporally persistent; 2) they must not exceed a critical threshold of vertical thickness; and 3) they must exceed a critical threshold of maximum concentration. The precise values for critical thresholds of thin layers has been debated for a long time due to the vast diversity of plankton, instrumentation, and environmental conditions. Thin layers have distinct biological, chemical, optical, and acoustical signatures which are difficult to measure with traditional sampling techniques such as nets and bottles. However, there has been a surge in studies of thin layers within the past two decades due to major advances in technology and instrumentation. Phytoplankton are often measured by optical instruments that can detect fluorescence such as LIDAR, and zooplankton are often measured by acoustic instruments that can detect acoustic backscattering such as ABS. These extraordinary concentrations of plankton have important implications for many aspects of marine ecology, as well as for ocean optics and acoustics. Zooplankton thin layers are often found slightly under phytoplankton layers because many feed on them. Thin layers occur in a wide variety of ocean environments, including estuaries, coastal shelves, fjords, bays, and the open ocean, and they are often associated with some form of vertical structure in the water column, such as pycnoclines, and in zones of reduced flow.
In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface aligned with the wind. These circulations are developed when wind blows steadily over the sea surface. Irving Langmuir discovered this phenomenon after observing windrows of seaweed in the Sargasso Sea in 1927. Langmuir circulations circulate within the mixed layer; however, it is not yet so clear how strongly they can cause mixing at the base of the mixed layer.
The North Pacific Subtropical Gyre (NPSG) is the largest contiguous ecosystem on earth. In oceanography, a subtropical gyre is a ring-like system of ocean currents rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere caused by the Coriolis Effect. They generally form in large open ocean areas that lie between land masses.
The Somali Current is a warm ocean boundary current that runs along the coast of Somalia and Oman in the Western Indian Ocean and is analogous to the Gulf Stream in the Atlantic Ocean. This current is heavily influenced by the monsoons and is the only major upwelling system that occurs on a western boundary of an ocean. The water that is upwelled by the current merges with another upwelling system, creating one of the most productive ecosystems in the ocean.
Haida Eddies are episodic, clockwise rotating ocean eddies that form during the winter off the west coast of British Columbia's Haida Gwaii and Alaska's Alexander Archipelago. These eddies are notable for their large size, persistence, and frequent recurrence. Rivers flowing off the North American continent supply the continental shelf in the Hecate Strait with warmer, fresher, and nutrient-enriched water. Haida eddies are formed every winter when this rapid outflow of water through the strait wraps around Cape St. James at the southern tip of Haida Gwaii, and meets with the cooler waters of the Alaska Current. This forms a series of plumes which can merge into large eddies that are shed into the northeast Pacific Ocean by late winter, and may persist for up to two years.
The Papagayo jet, also referred to as the Papagayo Wind or the Papagayo Wind Jet, are strong intermittent winds that blow approximately 70 km north of the Gulf of Papagayo, after which they are named. The jet winds travel southwest from the Caribbean and the Gulf of Mexico to the Pacific Ocean through a pass in the Cordillera mountains at Lake Nicaragua. The jet follows the same path as the northeast trade winds in this region; however, due to a unique combination of synoptic scale meteorology and orographic phenomena, the jet winds can reach much greater speeds than their trade wind counterparts. That is to say, the winds occur when cold high-pressure systems from the North American continent meet warm moist air over the Caribbean and Gulf of Mexico, generating winds that are then funneled through a mountain pass in the Cordillera. The Papagayo jet is also not unique to this region. There are two other breaks in the Cordillera where this same phenomenon occurs, one at the Chivela Pass in México and another at the Panama Canal, producing the Tehuano (Tehuantepecer) and the Panama jets respectively.
The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) was a five-year scientific research program that investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols, clouds, and climate. The study focused on the sub-arctic region of the North Atlantic Ocean, which is the site of one of Earth's largest recurring phytoplankton blooms. The long history of research in this location, as well as relative ease of accessibility, made the North Atlantic an ideal location to test prevailing scientific hypotheses in an effort to better understand the role of phytoplankton aerosol emissions on Earth's energy budget.
Stratification in water is the formation in a body of water of relatively distinct and stable layers by density. It occurs in all water bodies where there is stable density variation with depth. Stratification is a barrier to the vertical mixing of water, which affects the exchange of heat, carbon, oxygen and nutrients. Wind-driven upwelling and downwelling of open water can induce mixing of different layers through the stratification, and force the rise of denser cold, nutrient-rich, or saline water and the sinking of lighter warm or fresher water, respectively. Layers are based on water density: denser water remains below less dense water in stable stratification in the absence of forced mixing.
A Wind generated current is a flow in a body of water that is generated by wind friction on its surface. Wind can generate surface currents on water bodies of any size. The depth and strength of the current depend on the wind strength and duration, and on friction and viscosity losses, but are limited to about 400 m depth by the mechanism, and to lesser depths where the water is shallower. The direction of flow is influenced by the Coriolis effect, and is offset to the right of the wind direction in the Northern Hemisphere, and to the left in the Southern Hemisphere. A wind current can induce secondary water flow in the form of upwelling and downwelling, geostrophic flow, and western boundary currents.
A baroclinic instability is a fluid dynamical instability of fundamental importance in the atmosphere and ocean. It can lead to the formation of transient mesoscale eddies, with a horizontal scale of 10-100 km. In contrast, flows on the largest scale in the ocean are described as ocean currents, the largest scale eddies are mostly created by shearing of two ocean currents and static mesoscale eddies are formed by the flow around an obstacle (as seen in the animation on eddy. Mesoscale eddies are circular currents with swirling motion and account for approximately 90% of the ocean's total kinetic energy. Therefore, they are key in mixing and transport of for example heat, salt and nutrients.
The Kuroshio Current is a northward flowing Western Boundary Current (WBC) in the Pacific Ocean. It is a bifurcation arm of the North Equatorial Current and consists of northwestern Pacific Ocean water. The other arm is the southward flowing Mindanao Current. The Kuroshio Current flows along the eastern Philippine coast, up to 13.7 Sv... of it leaking into the Luzon Strait - the gap between the Philippines and Taiwan - before continuing along the Japanese coast. Some of the leaked water manages to intrude into the South China Sea (SCS). This affects the heat and salt budgets and circulation and eddy generation mechanisms in the SCS. There are various theories about possible intrusion paths and what mechanisms initiate them.
Low-nutrient, low-chlorophyll (LNLC)regions are aquatic zones that are low in nutrients and consequently have low rate of primary production, as indicated by low chlorophyll concentrations. These regions can be described as oligotrophic, and about 75% of the world's oceans encompass LNLC regions. A majority of LNLC regions are associated with subtropical gyres but are also present in areas of the Mediterranean Sea, and some inland lakes. Physical processes limit nutrient availability in LNLC regions, which favors nutrient recycling in the photic zone and selects for smaller phytoplankton species. LNLC regions are generally not found near coasts, since coastal areas receive more nutrients from terrestrial sources and upwelling. In marine systems, seasonal and decadal variability of primary productivity in LNLC regions is driven in part by large-scale climatic regimes leading to important effects on the global carbon cycle and the oceanic carbon cycle.
The Lofoten Vortex, also called Lofoten Basin Vortex or Lofoten Basin Eddy, is a permanent oceanic anticyclonic eddy, located in the northern part of the Norwegian Sea, off the coast of the Lofoten archipelago. It was documented for the first time in the 1970s.
![Phytoplankton Bloom in the North Atlantic due to eddy upwelling. [We acknowledge the use of imagery provided by services from NASA's Global Imagery Browse Services (GIBS), part of NASA's Earth Observing System Data and Information System (EOSDIS).] Phytoplankton Bloom in the North Atlantic.jpg](http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Phytoplankton_Bloom_in_the_North_Atlantic.jpg/300px-Phytoplankton_Bloom_in_the_North_Atlantic.jpg)
