Earth and space science

Ocean Processes

La Nina

La Nina develops when the warmest region of the pacific shifts toward the western pacific. the strengthening temperature gradient increases pressure differences between the east and west, intensifying trade winds. these stronger winds enhances the westward movement of warm surface water causing the warm less dense water to accumulate in the western pacific deepening the thermocline in that region.

La Nina pt. 2

The thermocline is much shallower in the cooler eastern pacific. because the intensified trade winds pull surface water away from the south American coastline through friction, very strong upwelling occurs. cold nutrient rich water rises to the surface increasing biological productivity and supporting fisheries along the eastern pacific. Th e shift in ocean temperatures influence atmospheric circulation, creating wetter conditions in the western pacific and drier in the east.

El Nino

During El Nino events, the trade winds weaken or reverse. Warmer water that has built up in the west now moves back toward the east, assisted by gravity as it flows back down the gradient. The result is a flattening out of the sea level, causing warm waters to now pile up off the coast of South America. This increases the surface temps of the coastal waters. As warm water is less dense than cold water, it sits on top of the deeper, cooler water, pushing the thermocline down deeper.  

El Nino pt. 2

The depth of the thermocline prevents mixing of the surface and deep waters, so upper waters are now nutrient deficient bc no upwelling occurs so waters are less biologically productive and fisheries collapse as a result of mass fish die off. The east now experiences heavy rain and flooding, and Australia and Indonesia in the west experience droughts. Tropical cyclones also shift towards the central pacific.

The bioloigcal pump

The biological pump removes carbon dioxide from the surface waters, changing it into living matter and distributing it into the deeper water. 

The carbon dioxide in the atmosphere is in balance with the CO2 in the ocean. During photosynthesis, phytoplankton remove carbon dioxide from the seawater. 6CO2  + 6H2O + sunlight(in presence of chlorophyll) ---> C6H12O6 + 6O2.  

As some dissolved CO2 has been removed from the seawater, it allows the ocean to absorb additional CO2 from the atmosphere, therefore reducing atmospheric co2.

Plankton fix carbon in the form of organic molecules as well as into their skeletons or shells, platelets, in the form of calcium carbonate.  

Phytoplankton can also affect the CO2 levels in the oceans when they die. As they sink, zooplankton eat them and some are decomposed by bacteria, and as a result some carbon is returned to the ocean as CO2 through respiration.  

The CaCO3 platelets and shells sink to the seafloor where they join the sediments. As the layers build up, the calcium carbonate is buried turning into limestone, locking away the carbon for millions of years. 

The biological pump pt. 2

Warmer oceans – reduced number of phytoplankton 

Oceans heat up – thermocline more defined 

Separates warm less dense waters from cold dense waters beneath 

Reduced amount of upwelling occurs 

No mixing between layers 

Less nutrients will be upwelled 

If decrease in phytoplankton numbers 

Will decrease effectiveness of biological pump 

Less carbon able to be stored in ocean/sediment 

Increasing levels of atmospheric co2 

The physical pump

The physical pump is the movement of CO₂ from atmosphere into surface ocean. How much CO₂ dissolves depends on mixing, wind, and temperature. 

Cold, stormy waters hold more CO₂ because their particles have lower kinetic energy, which enables weak intermolecular interactions between water molecules and dissolved gas. This is why most carbon enters the ocean at high latitudes such as the Southern Ocean and the poles .  

As water cools and sinks, (pressure also increases CO2 solubility) more CO2 dissolves, increasing concentration of dissolved inorganic carbon.  

This acts to pump carbo from the atmosphere into the oceans depths.  

This dissolved CO2 then undergoes equilibrium reactions to form hydrogen carbonate and carbonate, reducing the dissolved CO2, allowing more CO2 to dissolve from the atmosphere. 

downwelling

The movement of surface water down into deep layer.  

Occurs at eastern continental coastlines as mounded up warm water pushed by trade winds piles up against the coast and pressure forces it under taking heat energy, carbon, nutrient and oxygen rich waters down to the deep ocean, allowing deep-sea organisms to survive. 

Also occurs near poles, where higher salinity and therefore denser water is cooled due to cool climate and becomes more dense so sinks below surface layer. Sequestering carbon through downwelling limits co2 in the atmosphere thus slowing greenhouse effect, although this eventually is released in upwelling regions. 

upwelling

Movement of colder denser water from the deep later to the surface driven by wind and the Coriolis effect.  

Occurs at the equator/ITCZ region when winds blow from northeast and south east and converge along the equator mounding up warm surface waters, which then flow away from the equator.  

The divergence of water allows colder denser nutrient rich water to be upwelled from below to replace it - increasing primary productivity and supporting large fisheries. 

 Upwelling regions are some of the most biologically productive areas in the world because the nutrient supply fuels phytoplankton growth, which supports higher trophic levels. 

The El Nino southern oscillation (ENSO)

A see-saw pattern of reversing surface air pressure between the eastern and western pacific regions. 

The albedo effect

Because ice is white, it reflects incoming radiation back into space at the surface.  

preventing radiation from heating up the surface of the ocean or land underneath the ice. 

 If the ice continues to melt away due to warming climate then more incoming solar radiation can be absorbed by the earths surface.  

This further increases land ice to melt establishing a positive feed back loop and further reduction in albedo.