1. Key Concepts in Physical Oceanography
Meteorology background early
How I joined the Navy
Navy career
Oceanography switch over
CDR Shawn Gallaher
Maury Project
10 July 2017
CDR Shawn Gallaher
Oceanography Department
29 Jan 2015

2. Specialties within Oceanography
Chemical
Biological
Geological
Boundary Layer
Physical
Arctic
Estuarine
Many disciplines in Oceanography (go through them); however, they revolve around the physical characteristics of the water.
For example, I don’t have training in biological or chemical oceanography, but our biological and chemical oceanographer have had extensive training on physical oceanography.
Nearshore
Coastal
The physical properties and characteristics of seawater.

3. So, where did it all come from?
Ocean Stats
Covers ~70% of the Earth’s surface
Contains ~97% of the Earth’s water
Averages 4000 m depth
Volume of 1.33 billion km3
Weighs 1.45 x 1018 tons
~7% of the Earth’s mass (mantle to surface)
Ocean Stats
Several Theories:
Leading theory seems to be from asteroid impacts
Water or at least oxygen was organic to the Earth from the beginning and combined with Hydrogen in the Earth’s atmosphere.
So, where did it all come from?

4. Water – A Remarkable Substance
Phase temperatures
Energy for phase changes
Facilitates hydrological cycle
High heat capacity
Density of solid phase
Absorption of long-wave radiation in gas phase
High surface tension (Hydrogen bond structure)
Good Solvent (Polar molecule)
High temperature for liquid and gas phase and coverage large range (comfortable for life).
Harder to break H bonds than to build them, therefore, latent heat of evaporation is about 7 times that of latent heat of fusion (keep water liquid and helps with human cooling).
Heat capacity ten times that of iron – reduces Earth’s temperature fluctuations (Mars +70 F to -100 F).
Ice formation permitting a reflective surface in ice on surface.
Absorbs LW radiation to further mitigate temperature changes (water vapor more effective than CO2 or CH4 as greenhouse gas).
High surface tension – form water droplets (clouds), decreases evaporation, permits momentum transfer from air to ocean.
Good solvent – see law of constant proportions.
No life on Earth without it!

5. Law of Constant Proportions
Dittmar, 1884
The composition of seawater ions does not vary much from place to place.

6. Seawater Properties - Salinity
~85% of seawater is comprised of the ions Na+ and Cl- to form salt.
Source of ions are from eroded rocks
Heavier than freshwater (1000 kg/m3 vs kg/m3)
Density (ρ) and salinity are proportionally related (↑S↑ρ)
Archimedes Principle and the Law of Buoyancy
Molecular weight of H2O = 18 g/mol vs. NaCl = 59 g/mol
Na and Cl ions are the most abundant and least used by biological life; therefore, levels have built up over time.

7. Seawater Properties - Salinity
Function of semi-permanent atmospheric systems and basin orientation.
Evaporation vs. Precipitation
WHOI
Varies widely from 5 psu in the Bay to 38 psu in the Mediterranean Sea
Driven by Basin shape and semi-permanent high pressure belts around 30 N/S. Precipitation belts along the ITCZ and mid-lats, lack of evaporation at high latitudes.

8. Measuring Salinity Over the Years
Knudsen method (1902) - Salinity defined as the weight in grams of all dissolved constituents (inorganic) in one kilogram of seawater. But some complications: Must replace all the Br and I by the equivalent amount of Cl, convert all carbonate to oxide; and all organic material is burned off at 480 degrees C (units ppt).
Chlorinity method - Measure the total mass of halogen ions in seawater (F, Cl, Br, I). Salinity (ppt) = * Chlorinity (units ppt).
Electrical conductivity method - It is the method used today and is fast, easy, cheap, and very accurate. Units migrated from practical salinity units (psu) to no units.
Talk about CTD on YP-686.

9. Conductivity puts the “C” in CTD
Talk about CTD on YP-686.

10. Seawater Properties - Temperature
Density (ρ) and temperature have inverse relationships (↑T↓ρ)
Primary source of heating – shortwave (SW) radiative forcing
85% of the solar absorption occurs in the top 10 meters of the ocean
Ocean heat storage results from an imbalance between incoming (SW & longwave (LW) radiation) and outgoing energy (LW, sensible, latent).
90% of the Earth’s energy imbalance is stored in the oceans.
NOAA Ocean Explorer
Ocean’s heat capacity has mitigated much of the recent warming. Water can absorb a 1000 times more heat than air per cubic meter.
High heat capacity of water mitigates warming (& cooling) events.

11. Seawater Properties - Temperature
Primarily a function of latitude
Redistribution by poleward and equatorward currents
Different than salinity distribution (function of latitude primarily).

12. Worthington’s Peak Can anyone guess why?
Most of the world ocean salinity and temperature fall around 34.7 and 2 ̊C.
(Worthington, 1970)
Val Worthington was a research physical oceanographer for WHOI
Answer to question: Deep water formation that fills the abyssal bathtub. Refer to Salinity and Temperature Global maps to illustrate the relationship between salinities in Labrador, Greenland, and Weddell Seas is ~34.7.
Can anyone guess why?

13. Comparing Global Salinity and Temperature with Depth
I thought you said salty water was heavy?
Salinity (S) and Temperature (T) figures of the Atlantic shows how it is the combined effects of S and T in the equation of state that determine the vertical resting place of water.

14. Basic Laws of Oceanography
Equation of State
ρ = ρ(S, T, P)
Temperature, salinity and pressure determine the density of sea-water.
Pressure is only a factor in deep water (hard to compress)
Full equation of state is non-linear and has over 40 terms in the equation.
Linear approximation
90% of the ocean

15. Linear Equation of State
For many applications it is possible to approximate the equation of state as:
– linear equation of state
coefficient of saline contraction
coefficient of thermal expansion
Reference temperature, salinity and density:

16. Why Evaluate Ocean Density
To identify the Halocline, thermocline, and resulting pycnocline.
Defines vertical (and horizontal – more later) stability/stratification.
Mixed Layer
Discuss the mixed layer as well.
Invitation to Oceanography (Pinet)
Is this stable or unstable?

17. Unstable Case – Seawater Freezing
Stability of a stratified one-component non-rotating fluid at rest
Salty
(brine rejection)
In winter, seawater freezes in the Arctic ocean leaving relatively fresh ice and rejecting brine (salt). Leads to denser surface waters and parcel sinking (static instability).
Fresher water
Arctic seawater density almost entirely a function of salinity!
See slope of density curve on S & T diagram

18. Effects of Pressure in Deep Water
Pressure is the force per unit area.
It has two effects on a parcel of seawater:
Compresses the seawater increasing density
Heats the seawater due to adiabatic warming
Oceanographers prefer to analyze the in situ (local) properties of seawater without the effects of compression:
Potential temperature (θ)
Potential density (ρθ) or sigma theta (σθ where σθ = ρθ kg/m3)
P = -ρ g z
8 tons per square inch is like having a 22 foot Penske truck sitting on each square inch.
Pressure is 8 tons per square inch in the Mariana Trench

19. Pressure Units
The SI unit for pressure is the K Pa = 10 3 pascals. Previous unit was the Bar. 1 bar = 1 standard atmospheric pressure (sea-level) where a standard Atmospheric pressure = Kpa = bars = mb = 760 mm Hg.
Important to note: 1 decibar = 10 Kpa = pressure due to 1 meter depth of seawater.

20. Problems that can arise from compression
Nature Education

21. Basic Laws of Oceanography Mass Conservation
For most applications, the ocean is considered incompressible leading to continuity of mass:
Baseball fans: Pablo Sandoval example.

22. Basic Laws of Oceanography Salinity and Temperature Conservation
Conservation of Salinity mass
Conservation of Energy
Double diffusion
Advective-Diffusive Equations
Describe salt fingering; temperature diffuses 100 times faster than salt creating instabilities at the molecular level as deep cold water diffuses with the shallow salty water causing it to sink (EOS). Vice-versa for the shallow warm water which diffuses with the deep fresher water causing it to rise (EOS).
Hilgersom et al. 2016

23. Momentum equations Coriolis** gravity* friction** pressure*
– Newton’s Second Law
Coriolis**
gravity*
friction**
pressure*
* Primary Force
** Forces that requires motion first

24. Basic Laws of Oceanography Equations of Motion
Local acceleration in x
Advective acceleration in x
Coriolis acceleration in x
Pressure Gradient acceleration in x
Frictional acceleration in x =
Local acceleration in y
Advective acceleration in y
Coriolis acceleration in y
Pressure Gradient acceleration in y
Frictional acceleration in y =
Local acceleration in z
Advective acceleration in z
Pressure Gradient acceleration in z
Gravitational acceleration
Frictional acceleration in z =

25. Result: Processes that span 9 orders of magnitude
Capillary Waves up to Thermohaline Circulations.
Capillary waves

26. Physical Oceanography Application
So why does Physical Oceanography matter – enables the applied Ocean Science fields to do their jobs based on the properties and forces associated with Physical Oceanography.
Applied Ocean Fields
Marine Fisheries
Resource Exploration
Ocean Engineering
Marine
Archaeology
Climate Modeling
Marine Pharmaceuticals