The Salinity-Temperature-Depth Relationship in the World OceansThe Salinity-Temperature-Depth

Relationship in the World Oceans

Part One – Depth Profiles

October 29, 2009

Part One – Depth Profiles

October 29, 2009

Seawater – General Trends

• Temperature and salinity determine the density of seawater.– Colder water is more dense; therefore, it sinks.– Saltier water is more dense; therefore, it sinks.

• Which is more variable on the earth? Temperature or salinity?

• Which would have a greater effect on the density of seawater? Temperature or salinity?

Global Sea Surface Temperature

• This image shows the temperature of the ocean water at the surface. Measurements were taken from August 6-11, 2001. The temperature scale is in Celsius. Cold temperatures are shown in pink to purple, moderate temperatures in aqua to green and warm temperatures in yellow to red.

• This particular data set was taken by the NOAA-16 satellite. NOAA-16 is part of the TIROS series of polar-orbiting, environmental satellites. Image courtesy of The National Oceanic and Atmospheric Administration (NOAA)

Biogeographical Zones

• Based on sea surface temperature, four major biogeographical zones emerge:– Polar

– Cold temperate

– Warm temperate (subtropical)

– Tropical (equatorial)

Global Sea Surface Salinity

Depth Profiles

• Graph that shows a specific ocean variable plotted against depth.

– Usually drawn “upside down” with increasing depth on the Y-axis and the variable across a top X-axis so that the graph represents an “ocean profile.”

– For any specific location, a depth profile can be understood as a vertical ‘snapshot’ of a column of water or water column.

Increasing variable 0

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Depth ProfilesWhich one represents temperature? salinity?

© 2000-06 National Oceanic and Atmospheric Association (NOAA)

Depth ProfilesHow do temperature and salinity contribute to density?

© 2000-06 National Oceanic and Atmospheric Association (NOAA)

Salinity-Temperature-Depth Profile

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Thermocline – the depth zone of the most rapid temperature decline

Halocline – the depth zone of the most rapid salinity change

Pycnocline – the depth zone of rapid density change

Other Profiles

• What might the depth profile look like for the following variables?– Dissolved oxygen– Transparency of light– Pressure

Light Transparency

This diagram offers a basic illustration of the depth at which different colors of light penetrate ocean waters. Water absorbs warm colors like reds and oranges (known as long wavelength light) and scatters the cooler colors (known as short wavelength light). Image courtesy of Kyle Carothers, NOAA-OE

Light Transparency

Sunlight is composed of colors with different wavelengths

• RROOYY GG BBIIVV

• Longer wavelengths (red/orange) have lower energy than shorter wavelengths (violet/indigo)

– E = hc/λ – where E = energy, h = Planck’s constant, c = speed of light, and λ = wavelength

Light Transparency

General trends:• Longer wavelengths are absorbed at the

surface. Shorter wavelengths can penetrate to depths of approximately 1000m in clearest waters.

• Extent of light attenuation defines photic zone

– Euphotic zone – surface to approx. 200m max. – sufficient sunlight for photosynthesis

– Disphotic zone – variable 50-1000m, usually 200-600m – insufficient sunlight for photosynthesis (less than 1% of sunlight penetrates)

– Aphotic zone – below disphotic zone – no light

• Pattern can vary with suspended/dissolved substances. – More suspended/dissolved substances less light penetration

Dissolved Oxygen

0

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0 1 2 3 4 5 6Oxygen (ml per L)

Dep

th (

m)

Change in dissolved oxygen with depth in eastern tropical Pacific Ocean (red line) and the tropical Atlantic Ocean (orange line). Modified from Oceanography: An Introduction, D.E. Ingmanson & W.J. Wallace, ©1973.

Oxygen• non-conservative• low solubility in seawater

• only 5.4 ml/L at 35 ppt and 20ºC (8 ml/L at 0ºC)• more soluble in colder water• less soluble in saltier water

• oxygen minimum zone – usually 500 to 1000m depth

Dissolved Oxygen

Oxygen Minimum Zone• depth in open ocean waters at which oxygen

concentration approaches zero• usually between 200 and 1000m• Why there?Why there?

• Inputs of O2 to the oceans – wave action, storms, surface mixing, photosynthesis

• Depletion of O2 from the oceans – respiration, decomposition

At this depth, consumption of O2 by organisms for respiration consumes all of the oxygen, without suitable replacement by photosynthesis or surface mixing.

Pressure

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Pressure (atm)

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Surface • 1 atmosphere of air (1kg/cm3 or 14.7 lbs./in.2 or ≈ 1 bar) pushing down at sea level

With Depth• water more dense than air• each 10m of depth increases pressure by an additional atmosphere• linear relationship

What is significance for marine organisms?

What is significance for marine research and exploration?

ReferencesCastro, Peter, and Michael E. Huber. Marine Biology. 5th. Boston: McGraw Hill Higher Education, 2005.

Davidson, M.A., Abramowitz, M., Olympus America, Inc., and Florida State University, (2003 Aug 1). Optical Microscopy Primer. Retrieved February 21, 2007, from Molecular Expressions Web site: http://micro.magnet.fsu.edu/primer/lightandcolor/lightsourcesintro.html

Enchanted Learning.com, (2007). Twilight Ocean (Disphotic) Zone Animal Printouts. Retrieved February 21, 2007, from Biomes-Habitats Web site: http://www.zoomschool.com/biomes/ocean/twilight/

Naik, Naomi. "Plot the Temperature Profile." Climate Kids Corner. Lamont-Doherty Earth Observatory. 19 Feb 2007

National Oceanic and Atmospheric Association (NOAA) (2007 Feb 12). Deep Light. Retrieved February 21, 2007, from Ocean Explorer Web site: http://oceanexplorer.noaa.gov/explorations/04deepscope/background/deeplight/deeplight.html

National Oceanic and Atmospheric Association (NOAA). "NOAA/NESDIS Edge Image Display." Windows to the Universe. 2000-06. LUniversity Corporation for Atmospheric Research (UCAR). 19 Feb 2007 <http://www.windows.ucar.edu/tour/link=/earth/Water/images/ocean_temp.html&edu=high>.

Nybakken, James W., and Mark D. Bertness. Marine Biology: An Ecological Approach. 6th. San Francisco: Pearson Education, Inc., 2005.

photic zone. (2007). In Encyclopædia Britannica. Retrieved February 20, 2007, from Encyclopædia Britannica Online: http://www.britannica.com/eb/article-9059790