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Density Current
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Third segment of the Ocean Odyssey describes how the salinity and temperature of water increases its density. The Density Current segment describes how the different densities of water in the ocean create currents.
Hi, I'm Dr. Martins. Glad you found me.
00:00:00
Hi, Dr. Martins. Dr. D told us that the density of water depends upon its temperature and salinity.
00:00:04
But how does temperature make the water more dense?
00:00:10
Cold water molecules are packed together more tightly than warm ones, making cold water denser.
00:00:13
So do the density currents form near the north and south poles?
00:00:18
Exactly. The cold air at the poles cools the surface water, making it denser and causing it to sink.
00:00:22
What about salinity?
00:00:27
When ice forms in polar waters, it leaves behind salt, which increases the salinity of surrounding water.
00:00:29
The higher salt content makes the polar water denser.
00:00:35
I learned that evaporation also makes water saltier.
00:00:38
That's right. In areas such as the Mediterranean Sea, where there's little rainfall and lots of heat,
00:00:41
evaporation removes fresh water and leaves extremely salty water.
00:00:46
Where does the denser water go?
00:00:50
The denser polar water sinks and creates the thermohaline circulation.
00:00:52
Thermohaline?
00:00:55
Thermal for temperature and haline for salinity.
00:00:57
The cold, salty water masses that create this circulation form in only two places.
00:01:00
The water mass sinking off Greenland is called the North Atlantic Deep Water, or NADW.
00:01:05
The water mass sinking off Antarctica is called the Antarctic Bottom Water, or AABW.
00:01:11
Where do these currents end up?
00:01:16
They both sink down several kilometers while spreading out horizontally and moving along the bottom of the Atlantic Ocean.
00:01:18
They eventually mix while circulating around Antarctica.
00:01:24
Then they move into the deep Indian Ocean and finally into the Pacific.
00:01:27
So the water from the poles may one day end up on a beach in Hawaii?
00:01:31
I guess you can look at it like that.
00:01:35
What goes down must come up.
00:01:37
It takes the average water molecule a thousand years to make the complete cycle.
00:01:39
Wow, that's a long time.
00:01:43
Yes, we call the cycle the Global Conveyor Belt, and it has a large impact on climate.
00:01:45
I went swimming once, and the water was really cold.
00:01:50
My mom said it was an upwelling, but what's that?
00:01:53
The coastal upwelling that you experienced is different from thermohaline circulation.
00:01:56
It only brings up cold water from a few hundred meters deep.
00:02:00
It's also not as cold as AABW or NADW.
00:02:03
Coastal upwelling is generally caused by wind.
00:02:07
Is upwelling important?
00:02:10
Good question.
00:02:11
Upwelling brings lots of nutrients up from deep water.
00:02:12
We are researching the impact of nitrogen, a crucial nutrient, on Florida Keys reefs.
00:02:15
How does upwelling affect the reef?
00:02:20
It appears that there have been major changes in the health and community structure of coral reefs here in the Keys and throughout the world.
00:02:22
By observing the nitrogen composition of sponges, we can determine the importance of different nitrogen sources.
00:02:28
Wow, you've given us a lot to think about.
00:02:34
Thanks, Dr. Martens.
00:02:36
You're welcome. Good luck on your project.
00:02:37
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- Idioma/s:
- Niveles educativos:
- ▼ Mostrar / ocultar niveles
- Nivel Intermedio
- Autor/es:
- NASA LaRC Office of Education
- Subido por:
- EducaMadrid
- Licencia:
- Reconocimiento - No comercial - Sin obra derivada
- Visualizaciones:
- 617
- Fecha:
- 28 de mayo de 2007 - 15:34
- Visibilidad:
- Público
- Enlace Relacionado:
- NASAs center for distance learning
- Duración:
- 02′ 40″
- Relación de aspecto:
- 4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
- Resolución:
- 480x360 píxeles
- Tamaño:
- 16.18 MBytes
