oceanography physical processes

OceanographyPhysical processes

Guillaume Roullet

LOPS, roullet@univ-brest.fr

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Oultine

1/ Physical Properties

2/ Tide

3/ General Circulation

4/ Eddies

5/ Upwelling systems

6/ Mixing in the ocean

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Reference

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1/ Physical properties Pressure Temperature (in situ, potential) Mixed layer, thermocline Salinity Density and compressiblity Sound propagation Light propagation

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FIGURE 3.2

The relation between depth and pressure, using a station in the northwest Pacific at 41° 53’N, 146° 18’W.

TALLEY Copyright © 2011 Elsevier Inc. All rights reserved

Hydrostatic pressure

1dbar ~ 1m

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Temperature decreases from Eq to Pole.Why?

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Temperature decreases with depth. The bulk of the ocean is cold.Why?

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Incidentally the energy flux coming from the Sun is balanced by IR flux of equal intensity

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Thermocline

Temperature seasonal cycle

Mixed layer

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-

=

T January T July

Seasonal amplitude

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Salinity (1 psu ~ 1g.kg-1)

Salinity variations are small, but not negligible

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FIGURE 3.1

Values of density t (curved lines) and the loci of maximum density and freezing point (at atmospheric pressure) for seawater as functions of temperature and salinity. The full density is 1000 + t with units of kg/m3.

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Salinity (S) and Temperature (T) control the density (ρ) [kg.m-3]

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T-S determine « water masses »

(T,S) is a signature of the water origin, e.g. : Mediterranean Water (warm and salty)

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FIGURE 3.4

Increase in density with pressure for a water parcel of temperature 0°C and salinity 35.0 at the sea surface.

Sea water is compressible

Variation of in-situ density with depth for a given (T-S) = (0°C, 35psu) watermass

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Potential density removes the effect of pressure.

It can be referenced at the surface (or at any depth)

Potential density referenced at 10km

Potential density referenced at surface

Mariana Trench

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FIGURE 3.6

(a) Potential density and (b) Brunt-Väisälä frequency (cycles/h) and period (minutes) for a profile in the western North Pacific.

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Brunt Vaisala frequency (N) of vertical oscillations

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FIGURE 3.7

For station Papa in the Pacific Ocean at 39°N, 146°W, August, 1959: (a) temperature (°C) and salinity (psu) profiles, (b) corrections to sound speed due to salinity, temperature, and pressure, (c) resultant in situ sound-speed profile showing sound-speed minimum (SOFAR channel).

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Speed of sound ~ 1500 m/s

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FIGURE 3.8

Sound ray diagrams: (a) from a shallow source for a sound-speed profile initially increasing with depth in upper mixed layer to a shallow minimum and then decreasing, and (b) from a sound source near the speed minimum in the sound channel for a typical open ocean sound-speed profile.

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SOFAR channel(p50)

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Sea Mammal's Greatest hits

http://www.whoi.edu/science/B/people/kamaral/Sound/MammalHits.html

Sound in the Sea[truly amazing!!!]

https://dosits.org/

Intensity of Sound (dB)

I ~ log10

( p² )

Wave amplitude (pressure)

https://youtu.be/WabT1L-nN-E

Video shown in class (whale song) : https://www.youtube.com/watch?v=WabT1L-nN-E

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Incoming (light) – outgoing (IR) energy flux

Mean annual energy flux at the surface (in W.m-2) and the incoming spectrum (next page)

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« missing wavelengths » have been absorbed by certain air molecules (0

2 and H

20)

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Light is absorbed with depth

k=1/δ is the attenuation coefficient, it depends on the wavelength λ

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FIGURE 3.10

(a) Attenuation coefficient k, as a function of wavelength(m) for clearest ocean water (solid line) and turbid coastal water (dashed line). (b) Relative energy reaching 1, 10, and 50 mdepth for clearest ocean water and reaching 1 and 10 m for turbid coastal waters.

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attenuation coefficient =f(λ ; turbidity)

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Marine life impacts sea color

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https://landsat.visibleearth.nasa.gov/view.php?id=86449

On August 11, 2015, the Operational Land Imager (OLI) on Landsat 8 captured this false-color view of what appears to be a large bloom of cyanobacteria swirling in the Baltic Sea.

Cyanobacteria bloom in the Baltic Sea

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Questions for biologists Biodiversity at high pressure, cold water? Biodiversity in very salty water (bottom of Red

Sea)? Source of energy for deep ecosystems? What are the colors of abyssal species living in

the dark? Find your question !