A(n) ____ is a place where a tide meets a river current.? | Yahoo Answers
This is called the "mouth" of the river. A stretch of a river whose depth varies with the sea tides is called an estuary, and may contain brackish water or saltwater. When river water meets sea water, the lighter fresh water rises up and Tidal currents, which act independently of estuarine circulation, also. Citation: Bianchi, T. S. () Estuaries: Where the River Meets the Sea. Schematic showing important linkages between physical (e.g., tidal currents, river .
As a large volume of fresh water accumulated in the North Atlantic, major ocean currents were disrupted, diminishing the ocean's capacity to distribute heat around the entire planet.
An area where river currents and an ocean tide meet is called an
This disruption impacted world climate, which influenced glaciers' extent on land. The glacier's forming displaced the location of shorelines worldwide. Much of the coastal land area in the Northern Hemisphere went from being under water to above water and exposed the previously underwater continental shelf to the air.
Mud on the continental shelf, then exposed to the atmosphere, was eroded by winds increasing the concentration of particulate mater in the atmosphere. This disrupted the amount of sunlight reaching Earth's surface further impacting climate. Warm surface waters in the ocean also provide the energy source for tropical storms. As the surface waters of the ocean have warmed, so too has the energy source for storms.
This may also impact the severity and frequency of future storm systems. Although more storms may provide increased regional mixing of ocean water and, an increased supply of nutrients for marine organisms, human populations and infrastructure will likely be more adversely impacted.
Ecosystems Links for Teachers Links for Students Ecosystems that span several tidal zones include anchored plants, and animals, and ephemeral species that move with the daily tides or during some portion of their life cycle. Intertidal ecosystems can be found in estuarine environments and shallow water coastal communities. Organisms that live in intertidal zones must be able to live both above and below water depending on the tide.
Other organisms depend on currents for survival. Coral reefs are dependent on ocean currents to deliver their food to them zooplankton and disperse their larvae. Reefs located in shallow waters are most at risk from tidal emersions which can lead to bleaching and death. Without tides and currents these ecosystems would not exist. Estuaries Estuaries are bodies of water and their surrounding coastal habitats typically found where rivers meet the sea.
Estuaries harbor unique plant and animal communities because their waters are brackish—a mixture of fresh water draining from the land and salty seawater. Estuaries are some of the most productive ecosystems in the world.How to Survive An Undertow
Estuaries are often protected from severe ocean conditions but depend on the currents created by tributary streams, long shore currents, and tidal fluctuations to cycle nutrients and provide a transportation mechanism for organisms such as shellfish, eels, and turtles during some stages of their life cycles.
Many animal species rely on estuaries for food and as places to nest and breed.
One example is the blue crab. Their life cycle is dependent on estuarine habitats, and they have become one of the most recognizable icons of the Chesapeake Bay. Egg masses are produced in the warm salty water near the mouth of Chesapeake Bay where the newly hatched eggs can be swept out into the Atlantic by water currents.
After a few months in the ocean they are able to swim vertically and can be transported back to the grass beds in the lower Bay by tides and wind-blown surface currents. From there they migrate north into the Bay where their mating cycle can start again in brackish waters. For more information go to http: Intertidal Zones Intertidal zones are regions between the highest water line and the mean low tide level.
This area is exposed to the air at low tide and submerged at high tide and can include many different types of habitats, including steep rocky cliffs, sandy beaches or vast mudflats.
Organisms in the intertidal zone are adapted to harsh extremes. Water can be high due to tides, rain and run off, and this water can be very salty at one time and very fresh another. These areas can also become very dry when tides are low for extended periods of time, very hot with full sun or freezing in colder climates. Some examples of organisms that live in the intertidal zone include: Some shorelines have a rocky intertidal zone and harbor organisms that need a "rock solid" bottom for attachment.
Although the surface appears calm, the underwater intersection of fresh and salt water roils with turbulent eddies as strong as any in the ocean. The confusion of swirling water and suspended sediments disorients homeward-bound salmon, providing an easy feast for the sea lions. Not all rivers end as dramatically as the Fraser. But the mixing of freshwater streams and rivers with salty ocean tides in a partly enclosed body of water—natural scientists call it an estuary—fuels some of the most productive ecosystems on Earth, and also some of the most vulnerable.
Long before the advent of civilization, early humans recognized the bounty of the estuary and made these regions a focal point for human habitation. Unfortunately, overdevelopment, poor land use, and centuries of industrial contamination have taken a toll on most estuaries.
Yet there is hope. Estuaries are the borderlands between salt- and freshwater environments, and they are incredibly diverse both biologically and physically. The diversity and the high energy of the ecosystem make estuaries remarkably resilient. With a better understanding of these systems, we can reverse their decline and restore the ecological richness of these valuable, albeit muddy, environments.
How does an estuary work? When river water meets sea water, the lighter fresh water rises up and over the denser salt water.
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Sea water noses into the estuary beneath the outflowing river water, pushing its way upstream along the bottom. Often, as in the Fraser River, this occurs at an abrupt salt front.
Across such a front, the salt content salinity and density may change from oceanic to fresh in just a few tens of meters horizontally and as little as a meter vertically. Accompanying these strong salinity and density gradients are large vertical changes in current direction and strength. Pliny the Elder, the noted Roman naturalist, senator, and commander of the Imperial Fleet in the 1st century A.
But when the velocity difference reaches a certain threshold, vigorous turbulence results, and the salt and fresh water are mixed. Tidal currents, which act independently of estuarine circulation, also add to the turbulence, mixing the salt and fresh waters to produce brackish water in the estuary.
In the Fraser River, this circulation is confined to a very short and energetic frontal zone near the mouth, sometimes only several hundred meters long.
In other estuaries, such as San Francisco Bay, the Chesapeake Bay, or the Hudson River, the salt front and accompanying estuarine circulation extend inland for many miles.
The landward intrusion of salt is carefully monitored by engineers because of the potential consequences to water supplies if the salt intrusion extends too far. For instance, the city of Poughkeepsie, N. Roughly once per decade, drought conditions cause the salt intrusion to approach the Poughkeepsie freshwater intake.
The last time this happened, inextra water had to be spilled from dams upstream to keep the salt front from becoming a public health hazard.
The lifeblood of estuaries Estuarine circulation serves a valuable, ecological function.
Where the Rivers Meet the Sea
The continual bottom flow provides an effective ventilation system, drawing in new oceanic water and expelling brackish water. This circulation system leads to incredible ecological productivity. Nutrients and dissolved oxygen are continually resupplied from the ocean, and wastes are expelled in the surface waters. This teeming population of plankton provides a base for diverse and valuable food webs, fueling the growth of some of our most prized fish, birds, and mammals—salmon, striped bass, great blue heron, bald eagles, seals, and otters, to name a few.
The vigor of the circulation depends in part on the supply of river water to push the salt water back. The San Francisco Bay area has become a center of controversy in recent years because there are many interests competing for the fresh water flowing into the Bay—principally agriculture and urban water supplies extending to Southern California. Estuarine circulation is also affected by the tides; stronger tides generally enhance the exchange and improve the ecological function of the system.
Effects and Influences
The Hudson estuary, for example, is tidal for miles inland to Troy, N. Some are self-inflicted; some are caused by the abuses of human habitation. An estuary, with all of its dynamic stirrings, has one attribute that promotes its own destruction: When suspended mud and solids from a river enter the estuary, they encounter the salt front.
Unlike fresh water, which rides up and over the saline layer, the sediment falls out of the surface layer into the denser, saltier layer of water moving into the estuary.