OCEANOGRAPHY 1080 EXAM 2

Iowa State University

What is a hydrogen bond?

Weak electrostatic attraction between hydrogen atom covalenty bonded to highly electronegeative atom → Positive end of one molecule attracted to the negative end of another/ adjacent molecule

How does hydrogen bonding relate to temperature and density?

• More hydrogen bonds in warm water than cold water 

• As we decrease temperature, more hydrogen bonds, expands volume 

  • Increase in temperature means increase in density 

• Due to competing effects, many have a maximum density at a specific temperature (4 degrees), below this density decreases since hydrogen bonds become more prominent

How does the density of freshwater relate to temperature?

• Density is highest at 4 degrees. Water is densiest when just above freezing, and is less dense than the water below it

• Heated - water molecules spread apart, decreasing density

• Colder - contracts until it crystalline structure as ice making it less dense than liquid water

What is latent heat?

The heat required to convert a substance into a different phase (gas-solid, solid-liquid)

Describe water’s heat capacity.

High resistance to temperature change requiring lots of energy to heat it up and releasing large amounts of heat as it cools

What is the definition of salinity? What is the average salinity of the ocean?

The amount of dissolved salts in a body of water

35 parts per trillion (ppt

What ions comprise the majority of ocean salts? Does the proportion of these ions change with salinity?

• Chlorine, sodium

• No the proportions do not change with salinity

Where do the majority of these ions come from?

Weathered rocks on land, volcanic activity and hydrothermal vents on seafloor

How are salts added to and removed from oceans?

1. INPUT:  by river input (from rock weathering) and volcanoes and hydrothermal vents

2. REMOVED:  by salt spray, recycling though hydrothermal vents, biogenetic sediments (hard parts, fecal pellets) and evaporites

Which ocean, the Atlantic or the Pacific is more salty? Why?

Atlantic because of atmospheric circulation patterns, drier air, lots of evaporated moisture → i.e higher evaporation rates and less freshwater input

What is meant by “steady state” of the ocean? How does this relate to the principle of constant proportions?

1. Salinity in a constant state through time. The amount of salts going in = the amount of salts coming out 

2. Relates while overall salinity may change in different locations the ratios of the ions remain nearly constant everywhenre in the open ocean

What is a residence time? What are the relative residence times of ions in seawater? (ie. long? short?) How does the reactivity of an ion influence its residence time?

Average length of time a substance remains dissolved in sweater

1. Unreactive = longer residence time - higher concentration in sweater

2. Reactive = shorter residence time - smaller concentration in seawater 

Does ocean salinity change from region to region? What affects these changes?

• Yes, it is changed by adding or removing water (not adding/removing salts)

  • Decreases salinity by precipitation (rain/snow), river runoff, melting snow

  • Increased salinity by evaporation, formation of sea ice

How does salinity vary latitudinally? Longitudinally?

Latitude:

• Polar regions = salinity is lower → lots of tan/snow and runoff

• Mid-latitudes = salinity is high → high rate of evaporation

• Equator = salinity is lower, lots of rain

Longitude: driven by balance between precipitation and evaporation

• Equator = salinity is low, high precipitation rates outweigh effects of high temperatures and potential evaporation

• Polar regions = salinity lowest in high latitiued, low evaporation, melting of sea ice and snow

• Mid-latitudes = salinity decreases as precipitation increases and evaporation decreases

• Subtropical - salinity reaches its max, high evaporation rates, minimal precipitation

How does salinity affect water’s physical properties?

• Increasing salinity:

  • increases heat capacity

  • Decreases freezing point

  • Increases density

  • Decreases the temperature of maximum density

How does salinity relate to temperature? Density? Pressure?

• Temperature: as salinity increases the freezing point decreases.    

• Density: as salinity increases, density increases. Same volume, bigger mass

• Pressure: increases density, less significant than temperature

What is the density of salt water? How does salt water density relate to temperature?

• Density of salt water is around 1.025, ~1.03 g/cm^3

• As temperature increases, density decreases. As temperature decreases, density increases

What is meant by the temperature of maximum density? How does it differ between fresh and salt water and why?

The temperature at which liquid reaches its highest possible density 

• As freshwater cools from higher temperatures, it becomes densier until it reaches max density at 4 degrees. Below this temperature volume increases and density decreases

• As saltwater cools, density continues to increase until it reaches its freezing point below 0 degrees. At around 42.7 psu, temperature of maximum density and freezing point coincide (-1.332 degrees C)

Describe why freshwater freezes before salt water (not just because freshwater has a higher freezing temperature than salt water).

• Normal seawater does not reach its maximum density before it freezes and then becomes less dense 

• The dissolved salt ions disrupt the water molecules ability to form ice.

Define the following: thermocline, halocline, and pycnocline.

• Thermocline = layer where temperature changes rapidly with depth

• Halocline = layer where salinity changes rapidly with depth

• Pycnocline = layer where water density increases sharply with depth

How does the pycnocline vary with latitude? How does the pycnocline influence mixing water surface and deep waters?

• Strongest at mid-latitudes due to temperature and salinity differences between surface and deep water. Absent at higher latitudes where water is uniform

• Acts as a barrier to mixing between surface and deep waters, prevents vertical currents and influences ocean circulation by separating low density warmer surface layer from colder denser deep ocean

What is air comprised of?

• Nitrogen (70%), oxygen, carbon dioxide, argon gasses and other gasses 

How does the density of air vary with altitude?

• As you leave the earth’s surface the density of air decreases 

• Density decreases exponentially with increasing altitude - less air above it to compress it.

How do atmospheric pressure and temperature relate to the density of air?

• High pressure means increased density 

• Higher temperature decreases density 

  • Less dense air will rise until it reaches altitude where air around it is same density → why warm air rises

What happens to the temperature of an air mass when it rises? Why?

• Decreasing pressure causes an air mass to cool due to decreasing atmospheric pressure. Expansion requires air to use internal energy causing a drop in temperature

• Increasing pressure causes an air mass to warm which makes it rise

How is solar radiation distributed across the globe? Why?

• Unequal because it is concentrated at the equator and decreased towards the poles because of the earth’s spherical shape 

• Angle of suns rays is most direct near the equator focusing the energy on smaller areas, at poles rays hit at a slant spreading the same amount of energy over a larger area

Why are the poles not constantly cooling down and the equator constantly heating up (as the balance of ingoing and outgoing radiation would indicate should be happening)?

Global ‘heat engine’ caused oceanic currents and atmospheric circulation that redistributes heat. Warm water and air from equator to poles, cooler air and water from the poles toward the equator 

What is the Coriolis Effect? What factors influence it?

The apparent deflection of a moving object to the Earth’s rotation

• Latitude and speed of the objects motion and speed of Earth’s rotation  

How do objects appear to move in the northern hemisphere? Southern hemisphere?

• Curve to the right in Northern hemisphere, south (left) in Southern Hemisphere → due to fact that at different parts of the earth move at different speeds → equator moves faster 

How does atmospheric pressure relate to the formation of atmospheric circulation cells?

• atmospheric circulation cells are formed due to pressure differences caused by earth’s uneven heating 

• Pressure gradient drives air to flow from high pressure to low pressure areas

How do winds form? How do wind patterns vary latitudinally and in the northern and southern hemisphere?

• From pressure gradient force pushing air from high to low pressure areas (influenced by Coriolis effect from earths rotation) causing a deflection to the right in the Northern Hemisphere, and to the left in the Souther Hemisphere.

• Trade winds near equator, westerlies mid-latitude, and polar Easterlies near the poles

What is the major factor controlling near-surface ocean currents? Describe how.

• Surface winds: movement of the air directly impacts the movement of ocean currents due to frictional drag 

What two factors drive Ekman transport?

Wind stress and Coriolis effect

How does Ekman transport water in the northern hemisphere? Southern hemisphere?

• 90 degrees to the right of wind direction in Northern

• 90 degrees to the left of wind direction in Southern

What is an ocean gyre? How do they behave in the northern hemisphere? Southern hemisphere?

Large rotating system of ocean currents driven by earth rotation and wind

• In Northern hemisphere they rotate clockwise

• Southern hemisphere they rotate counter-clockwise

How do ocean gyres form?

• Combinatoon of global wind patterns, coriolis effect and boundary of continents, Ekmans

• Winds push surface water while earths rotation causes coriolis effect to deflect cirrents creating circular motion. Continents act as boundaries forcing current into large rotating systems

What is geostrophic flow? How does it relate to the pressure gradient force?

• Balance between the Coriolis force and horizontal pressure gradient force in the atmosphere and/or ocean

• PGF pushes fluid from high to low pressure while Coriolis effect deflects the fluid’s path

What is western intensification? Why does it occur (general explanation)?

Phenomenon where western boundary currents of subtropical gyres are narrower, faster and deeper than the eastern boundary currents

• Occurs due to Coriolis effect, wind - Coriolis force is stronger at high latitudes, deflecting eastward flowing currents and concentrates the flow against wester boundaries of ocean basins

How would you characterize a Western boundary current? What is an example of a well-known western boundary current?

• Narrow, deep fast flowing current transporting warm water from tropics towards the poles of the western edge of ocean basin. Strong currents and high speeds

• Gulf Stream in Atlantic Ocean

Describe coastal Ekman upwelling and downwelling. Where do these occur around the globe?

• Ekman transport moves seawater offshore. Water moves up to replace surface water → upwelling (eastern boundary currents)

• Ekman transport moves seawater towards shore. Water moves down at coastline → downwelling (southern hemisphere)

What is the equatorial counter current? Why does it form?

• Eastward-flowing ocean current located between the westward-flowing North and South Equitiral Currents near the equator 

• Forms because of prevailing trade winds push surface water westward causing it to pile up on western sides of the ocean basins

What is the equatorial undercurrent? Why does it form?

• Strong narrow eastward flowing water beneath the surface of the equatorial Pacific Ocean 

• exists in part because water piles up in the western Pacific Ocean and that water needs to be moved back over the eastern Pacific

What are coastal geostrophic currents? Why do they form?

• Large scale ocean currents that flow parallel to a coastline

• Form when winds or freshwater runoff pile up water against the coast creating a pressure gradient that drives water downhill – while Coriolis deflects this flow to the right and left

What is thermohaline circulation? What drives thermohaline circulation? What are its main transports?

• Ocean current system (large scale) driven by differences in water temperature and salinity 

• Driven by density changes, mainly the sinking of cold, salty water in polar regions which then travels the oceans

• Main transports: heat, nutrients and gasses, carbon dioxide, freshwater 

What is a polynya? How do polynyas relate to deep water formation?

• Area of open water surrounded by sea ice 

• The process of sea ice forming in open water releases salt, making the water denser

How is deep water formed? Where is deep water formed?

• When surface water becomes cold and salty enough to become dense enough to sink - cooling, sea ice formation, evaporation

• North Atlantic, Southern Ocean (Antarctic)

What are the different deep water masses?

• Antarctica Bottom Water

• North Atlantic Deep Water

• Antarctic Intermediate Water

How do the different deep water masses compare to each other (density, temperature, salinity, position in the water column)?

• Antarctica Bottom Water (AABW) - deepest layer, the floor of all major ocean basins. Denser than all other water masses, very cold, relatively fresh (due to formation in Weddell Sea)

• North Atlantic Deep Water (NADW) - flows beneath the surface layer but above AABW. Denser than surface water but less dense than AABW, cold, slatier than most deep water masses (due to evaporation in the North Atlantic)

• Antarctic Intermediate Water - intermediate depths between 700 -1200 meters. Less dense than NADW but denser than surface water, cold (3-7 degrees), relatively fresh (formation in the Antarctic Polar Front zone), with a unique salinity minimum

How do ocean gyres influence ocean circulation patterns (both surface currents and ocean upwelling/downwelling)?

• Upwelling: occurs in subpolar regions, wind pushes surface water away from coastline or where surface currents diverge. Resulting void filled with cold nutrient rich water from deep ocean

• Downwelling: occurs in subtropical where wind driven surface currents converge at the center. Drives warmer oxygen rich surface water downward taking oxygen to the deep ocean

What is Ionic and Covalent bonding? 

• Ionic Bonding → electron is given away, preferred for both atoms - both have full shells 

• Covalent Bonding → share of electrons, to both have stable/full shells

  • H₂O, CO₂, CH₄

What is true of a water molecule?

• polar molecule

• high heat capacity

• high latent heat

• great solvent

• high surface tension

What are the characteristics of deep ocean circulation?

• Slow global movement of water driven by density differences from temperature and salinity variations.

• Sinking of cold, dense water in polar regions and slow horizontal movement of deep water masses across globe before eventually rising to the surface