Lecture 6 Geosc 040Chemistry of seaWater –Dissolved Gas & DensityAtmospheric Circulation & Ocean Circulation

Today’s music:

Behind the Sea- Panic! At the Disco

Thanks to Ashley K

Ocean Salinity Map

Home By the SeaGenesis

Bridgit Mendler – Hurricane

Thanks to Brenna M

Thanks to Justin A.

Read Chapter 6 and course web siteNote required reading: Greenhouse gasses and global warming

Homework 1 Due TodayQuiz 1, Feb 7

PSU 71 !!!OSU 70

Gases are dissolved in Seawater!

•Nitrogen (N2) 78.08•Oxygen (O2) 20.95•Carbon dioxide (CO2) 0.03 (365 ppm)•Argon, Helium, Neon (Ar, He, Ne) 0.95

% in atmosphere

What controls variations in oxygen and carbon dioxide with depth in the ocean?

Dissolved Gases in Seawater

Indicates:Oxygen production in

surface watersConsumption of

oxygen below surface waters

Indicates:CO2 consumption in

surface watersProduction of CO2 in

deep waters

Depth profiles of dissolved oxygen and dissolved carbon dioxide

Photosynthesis

Respiration

Density of Seawater

Recall that Oceans have about 35 grams salt per kg water (salinity = 35 ppt or 35 PSU) (PSU= Practical Salinity Units)

• Density of seawater increases as• Temperature drops• Salinity increases

• Maximum density and freezing point coincide for 24.7 ppt• Note that ppt = %O

• At higher salinities seawater reaches maximum density at freezing point

Seawater salinity:

Which is/are True?

A. The most abundant element dissolved in seawater is Cl

B. The element sodium is present in table salt and it is dissolved in seawater

C. We have a homework exercise due today and a quiz on Feb 7

D. All of the above

E. A and B

General Classification of Water Masses

• Why is ocean water stratified into these layers?• What are the characteristics of each of these regions?• Why do we care?

Zone of Light Penetration(the Photic Zone)

Shorter wavelengths of visible light (e.g. blue) penetrate deeper than longer wavelengths (e.g. red)

Zone of Light Penetration(the Photic Zone)

The Energy Cycle

Note that photosynthesis (and formation of plant organic matter) requires sunlight and nutrients

Organic matter is consumed by animals and plants (respiration), supporting their growth

Nutrients must be “recycled” (excreted by animals, “regenerated” by bacteria) to be reused by plants

Photosynthesis

Consumers

Consumers

nutrients

Hey, did younotice that blue light penetrates

deeper?

duh… anybody

knows that

Surface Zone (mixed layer)

Zone of rapid change with increasing depth

• Temperature and salinity vary considerably in the ocean• Because water has low viscosity and can flow, denser water

masses sinkwhile less dense water masses rise to the surface

• Deep water masses have a rather narrow range of T and S• Most T and S variability occurs in surface or near-surface waters• The ocean is density stratified (this is a stable configuration)

Density of Seawater & Stratification

Pycnocline is the zone of rapid density change with depth

Density of

Seawater

500 to 2000 years!

t =

What is the residence time of deep water in

the large ocean basins?

Ocean Surface Currents

Ocean Currents Are Driven by Seawater Density

Salinity (S) - Temperature (T) - Density Diagram• note dual effects of S & T• typical range of seawater S & T

Define Sigma t :

t = (Density-1.0) x 1000

For example: seawater with a density of 1.026

would have t = 26

We'll use this diagram to differentiate water masses

Increasing

Density

More complete Salinity- Temperature- Density Diagram for the normal range of salinity and temperature in the oceans. You should become familiar with this diagram.

t = 21

t = 24

t = 29

t = (Density-1.0) x 1000

Let’s look at this in a bit more detail.

1

2

What is the density of 1 vs. 2?

Which is more dense?Water masses 1 & 2 have same S (35 o/oo) But 2 (at 4°C) is colder than 1 (20°C)Therefore: Water mass 2 (t = 27.7) is more dense than water mass 1 (t = 24.8)

t: Salinity, temperature, density diagrams

A

C

D

B A. Which water mass is most like average deep water in the ocean?

B. Which water mass is most likely to be at the Ocean Surface?

C. Which water mass is most dense?

D. Which water mass has t of about 23?

Answer by entering the number (A, B, C or D) on your clicker

t: Salinity, temperature, density diagrams

A

C

D

B A. Which water mass is most like average deep water in the ocean?

B. Which water mass is most likely to be at the Ocean Surface?

C. Which water mass is most dense?

D. Which water mass has t of about 23?

Deep Water is Cold and Salty

A

C

D

B A. Which water mass is most like average deep water in the ocean?

B. Which water mass is most likely to be at the Ocean Surface?

C. Which water mass is most dense?

D. Which water mass has t of about 23?

t: Salinity, temperature, density diagrams

Answer by entering the number (A, B, C or D) on your clicker

A

C

D

B A. Which water mass is most like average deep water in the ocean?

B. Which water mass is most likely to be at the Ocean Surface?

C. Which water mass is most dense?

D. Which water mass has t of about 23?

t: Salinity, temperature, density diagrams

Answer by entering the number (A, B, C or D) on your clicker

t: Salinity, temperature, density diagrams (in class) 1

3

4

2 This plot shows four water masses.

Which of the following is/are true:

A) 2 has lower density than 1

B) 4 has the lowest densityC) 2 has t (sigma_t) of 28D) the ocean’s deepwater is

most like 1E) none of the above

The concentration of dissolved oxygen in seawater is, in part, determined by:

A. The water temperature

B. The water salinity

C. The relative amount of respiration

D. The relative amount of photosynthesis

E. All of the above

Energy from the Sun!

Is that the end of the story?

Did you know?

Earth’s average surface temperature is 15°C

The moon’s average surface temperature is more than 30°C colder than Earth’s.

Why?

http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/

It’s all about the Atmosphere

The Role of the Atmosphere in Earth’s Temperature

The “greenhouse effect” is the higher temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap and re-radiate energy. Without these gases, heat (long-wave radiation) would escape back into space and Earth’s average temperature would be about 33ºC colder. These gases are loosely referred to as “greenhouse” gases.

http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/

Go to this website to see an animation that illustrates the “greenhouse effect.” Ignore, for a moment the pronouncements at the end of the animation--we’ll get to that later.

Average Sea Surface Temperatures

What Causes this Temperature Pattern?

Hot tropics

Cold near the poles

Strong Temperature gradient

-2° C 30° CSea Surface Temperature

Wind and Ocean Currents are driven by heat imbalance

Radiation Balance for the Earth

Fig. 6.12

The Sun heats Earth more at the equator than at the poles!

N. Pole

S. Pole

equator

Sun’s energy (solar heat) is radiated to Earth and received unevenly

Solar energy received at any location on Earth varies with latitude, because the sun angle changes with latitude.

It’s easier to get a tan at the equator than at the north pole!

Sun angle varies with seasons because Earth’s axis of rotation is tilted relative to the plane of our orbit around Sun.

Sun’s energy (solar heat) is radiated to Earth and received unevenly

EARTH’s ORBIT (elliptical)

SEASONALITY

Effects of Earth’sAxial Tilt--A. Northern Hemisphere summer(solstice) occurs when tilt is towards the sun.

Systematic variation in solar energy receipt on a yearly basis is produced by Earth’s axial tilt and orbit around the sun.

Elliptical orbit causes about 3.5% variation too.

The Earth is actually closer to the sun in January

Earth’s radiation balance is approximately at “Steady state,” which means that it doesn’t change much from one year to the next

A Balanced Budget means:Outgoing Radiation is approx. equal to Incoming Radiation

If the radiation budget were not balanced, Earth would either warm up or cool off over long periods of time!

This indicates that Earth must re-radiate energy equal to the amount that it receives from the sun.

Radiation balance for Earth

The Earth radiates energy in the form of infrared (long-wave) radiation, which is emitted in proportion to the Earth’s surface temperature

The previous slides provided a global summary of Earth’s radiation budget.

But solar energy input is not evenly distributed across the Earth’s surface.

At high latitude outgoing longwave rad. exceeds incoming solar (see figure)

This creates zones of surplus and deficiency

Question: Why don’t the tropics boil and the poles freeze over?

Answer:Heat Transfer -from the tropics to the poles!

Because a temperature gradient is created from low (warmer) to high (colder) latitude, heat must be transferred to compensate for the high-latitude thermal deficit.

But how is this heat transfer accomplished?

The Ocean-Atmosphere Connection, Winds & Surface Currents

Which of the following are correct associations

A) salinity and thermocline, density and pycnocline, and temperature and halocline

B) salinity and halocline, density and thermocline, and temperature and pycnocline

C) salinity and pycnocline, density and thermocline, and temperature and halocline

D) salinity and halocline, density and pycnocline, and temperature and thermocline

E) none of the above

GLOBAL ATMOSPHERIC CIRCULATION (WINDS)Large Scale Winds Transfer Heat, Note Air Pressure Zones

Average Sea Surface Temperatures

So, the Temperature Pattern is Determined by Solar Energy Receipt

but Must be Modified by Heat Transport\

Hot tropics

Cold poles

Strong Temperature gradient

The Pattern of Surface Water Ocean CirculationOcean Currents Transfer Heat