Climate Flashcards
Describe a La Niña condition.
- The atmospheric pressure difference between Tahiti (HIGH) and Darwin (LOW) is higher than usual
- Stronger trades
- More piling up of warm water
- Convective loop gets higher
- Thermocline deepens even further in the west,
and upwelling is more pronounced in the east

Describe a El Niño condition.
- The atmospheric pressure difference between Tahiti (HIGH) and Darwin (LOW) is lower than usual
- Weaker trades
- Less piling up of warm water
- Spreading of warm water
- Convective loop shifts eastwards
- Thermocline shallower in the west,
and deeper in the east (weaker/no upwelling)

What is thermohaline circulation?
Part of the ocean circulation that is driven by density differences (most of the ocean) dependent on temperature and salinity (mainly) and pressure.
- Warm seawater expands and is thus less dense than cold
- Saltier water is more dense than fresher water because dissolved salt fill interstices between water molecules
Overall a stable situation in the ocean is that less desnse water masses float over denser ones.
What is the main influence on ocean water temperature?
solar irradience
What does the T profile of the ocean look like?
- Surface T varies between -2-~36oC
- Upper ~200m: epipelagic/sunlight zone / mixed layer
- bio-pump action; tracers change in crazy dimensions t.f. surface oceans difficult to reconstruct
- Highest T gradient in upper water column
- 200-1000m = thermocline = area of steep T gradient
- Reletively stable below 1000m depth (~4oC in all ocean basins)

What are the main influences on the salinity of ocean waters?
- Evaporation = more saline
- Precipitation = fresher
- Freshwater input from rivers or melting ice (= fresher)
- Sea ice formation = more saline (sea ice has a salinity of almost zero)
What does salinity do to the freezing point of ocean water?
Lowers it from 0 to < -2oC
Which is the ocean has the fresher water?
The Pacific ocean is fresher than the Atlantic ocean and this influences how deep waters form
What is the equation of state?
- The equation of state expresses the relationship of T, S and P to density. And can be expressed as isopycnals on a T-S diagram.
- Isopycnal = line of equal density
- Rule of thumb: The colder or saltier a water mass, the denser it is.
- Water wasses which have the same density sit along the same isopycnal and so is helpful when infering ocean circulation.
- T and S combine to determine density
- Additional density increases with pressure (depth)

How do you form deep and bottom water?
- Dense surface water forms in winter at high latitudes in the Nordic and Labrador Seas in the N Atlantic
- When surface water becomes denser than the underlying water, the situation is unstable and the denser water sinks. It slides down an isopycnal into deep interior of the ocean forming NADW
- Sliding down density surfaces is easy - it requires no change of potential energy and takes no/little energy to achieve
- Deep water formation is called convection
One can trace the origin of deep water layers by matching them to similar density winter surface water
How is NADW formed?
As the Gulf stream travels northwards it gives out heat to the atmosphere, cools (+water is saline) and when surface water becomes denser than the underlying and surrounding waters we get deep water mass formation (convection) in the Nordic seas and intermediate water mass formation in Labrador sea. (Intermediate) Labrador sea water and overflows from the Nordic seas (bottom water) mix in the subpolar North Atlantic to form NADW - the major deep water mass of the global ocean.
What are the major water masses in the Atlantic ocean
Salinity outlines major water masses in the Atlantic ocean
- NADW
- AABW (Antarctic Bottom Water)
- AAIW (Antarctic Intermediate Water)
- Desnity not high enough to sink below ~1000m
- Fresh water and sinks when cold, particularly in winter
The Atlantic part of the global overturning circulation is called AMOC (Atlantic Meridional Overturning Circulation)

What are the major water masses in the Pacific ocean?
Salinity outlines the major water masses in the Pacific ocean
- NPIW (North Pacific Intermediate Water)
- PDW (Pacific Deep Water)
- AAIW (Antarctic Intermediate Water)
- AABW (Antarctic Bottom Water)
There is no deep water formation in the North Pacific, only NPIW is formed.
- The N Pacific is too fresh to form deep waters (ppt/evap balance)
PDW is the oldest water mass in the ocean (1200-1500 yrs old) because it forms as NADW in the Atlantic, travels through the southern ocean and then to the Pacific. PDW then upwells in a diffusive way to form surface currents that migrate towards the Indian ocean.

What part does the Southern Ocean have to play in ocean circulation?
The Southern Ocean connects/communicates bottom and surface waters from all 3 major ocean basins as there is no land barrier.

Explain how AABW is formed?
Antarctic bottom water is formed in the Weddell and Ross Seas from surface water cooling due cold surface wind blowing off the Antarctic continent and is also formed below the ice shelf. The winds are stronger during the winter months and thus AABW formation is more pronounced during the Antarctic winter season. Surface water is enriched in salt from sea ice formation. Due to its increased density, it flows down the Antarctic continental margin and continues north along the bottom.
It is the densest water in the free ocean, and underlies other bottom and intermediate waters throughout most of the southern hemisphere. AABW is very abundant everywhere but the North Atlantic. AABW drops to >4000m water depth.
What are the main mechanisms of transporting carbon in the Ocean?
- Carbon pumps
- Solubility pump
- Biological pump
- Organic carbon pump (soft tissue pump)
- CaCO3 counter pump
How does the solubulity pump work?
The solubility pump is resticted to surface waters and is to do with the exchange equilibria between the atmosphere and surface ocean.
Solubility of gases such as CO2 is higher in colder, fresher waters (although the salinity gradient is not that great across oceans) and under higher pressures deep in the ocean. So more CO2 is dissolved in cold waters at higher latitudes (compared to lower latitudes) and is transported by ocean circulation into the deep ocean where it can be sequestered.
In carbonate chemistry, what relates the amount of CO2 in the oceans and the atmosphere?
Henry’s Law
Under equilibrium condition, the concentration of CO2 in the surface ocean is related to the fugacity (or partial pressure) of CO2 in the atmosphere.
CO2 (g) = CO2 (aq)
Where do we see uptake of CO2 and degassing in the oceans?
The CO2 flux is determined by ocean circulation.
- Uptake where there is sinking cold water (NADW, AAIW, NPIM)
- Pressure relief and degassing and subsequent realease of CO2 in major upwelling areas (e.g. east Pacific, part of ENSO system)

Why can the ocean store so much more CO2 than the atmosphere?
Dissolved Inorganic Carbon (DIC) can be present as 4 different species in the oceans:
- H2CO3 (carbonic acid)
- HCO3- (bicarbonate ion)
- CO2 (aq)
- CO32- (carbonate ion)
And the carbonate ions are related thusly when dissolved:
CO2 (aq) + H2O = H2CO3 (put CO2 in ocean)
Carbonic acid is unstable so it dissociates soon after formation in two steps:
H2CO3 = HCO3- + H+ (K1 - 1st dissociation constant)
HCO3- = CO32- + H+ (K2 - 2nd dissociation constant)
K1 and K2 (and therefore the carbonate sp. formed) are dependent on T, salinity (S) and P.
Why are the oceans typically dominated by HCO3-?
Partitioning of DIC between CO2, HCO3- and CO32- in the ocean is a function of pH.
The modern surface sea water in the ocean has a pH of just above 8. This correlates to ~90% HCO3, ~9% CO32- and <1% CO2.
There is an anticorrelation between the carbonate ion (CO32-) and CO2 and HCO3- acts as the buffer in the reaction. As the pH is lowered, CO2 is favoured and thus waters get more acidic.

What is the Biological Pump?
The combined biological processes which transfer organic matter to depth.
It quickly removes carbon from surface ocean and atmosphere and puts it in the deep ocean.
Turning off the biological pump would lead to a 200ppm increase in atmospheric CO2 i.e. the biological pump locks away the equivalent of 200ppm of CO2 in organic carbon.
How does the organic carbon or soft tissue pump work?
- Small algae called phytoplankton that live in the euphotic zone of surface ocean waters comsume CO2 by photosynthesis and form organic matter as tissue (carbohydrate) and release oxygen. These tiny particles cannot sink and so cannot transport carbon deeper into the ocean.
- Phytoplankton is at the bottom of the food chain and so are grazed upon by zooplankton. The excretion produced by zooplankton contains millions of phytoplankton and has now accumulated into denser aggregate called marine snow. Marine snow is heavy/dense enough to start sinking.
- As the aggregate sinks deeper into the ocean it gets acted upon by bacteria. Under the uptake of 1 mole of oxygen, the organic C is decomposed, freeing 1 mole of dissolved CO2 which is then physically mixed and recycled.
- This carbon flux takes place in the ocean mixed layer (top 100m)
In modern oceans only 1% of Corg gets deposited on the sea floor before respiration takes place, but there were times in Earth history when black shales were getting deposited.
The amount of Corg getting deposited obviosly effects the climate balance and controls deep water ocean chemistry of O2, inorganic carbon, and nutrients (the elements marine organisms need for life = C, N, P, Si, Cd, Fe etc.)

What is the organic carbon or soft tissue pump?
The ‘organic carbon or soft tissue pump’ is the part of the biological pump that takes CO2 from the atmosphere, converts it to organic C, and carries it to the deeper ocean, where it gets remineralised again (i.e. decomposition).











