Marine Carbonate System & Marine Vert. Tagging Flashcards
p/s & decomposition
(decomposition is reverse of p/s & uses up same amount of oxygen)
- carbon cycle & water regulate temperature on Earth
- bi-product is that it also regulates CO2 in the atm
importance of carbon & water
- carbon is basis of all life on Earth eg. we are 18-19% carbon
- carbon cycle & water regulate temperature & climate on Earth
- bi-product is that it also regulates CO2 in atmosphere (CO2 is a trace gas) with higher amounts of oxygen.
- Earth holds a lot of carbon, but v little is airborne
why does exchange occur?
Fluid systems (atmosphere & ocean) are attempting to reach some sort of equilibrium (ie they are attempting to reach a state of maximum entropy)
types of exchange
- momentum energy (eg wind)
- mass (eg rain and dust)
- heat (latent and sensible)
- gases (eg CO2, O2).
- combos of all (and they are all interlinked)
-> 2-way exchange / movement (flux) can occur… eg. gases from ocean to atmosphere & vice versa / momentum energy from water to air
-> Exchange occurs at interface, but once exchanged it can influence throughout both systems & become mixed & circulated
Impact of atmosphere-ocean heat fluxes
- water has a much higher specific heat capacity than the atmosphere
- heat capacity of water is 4,200 J kg-1 K-1). ie it takes 4,200 J to raise temperature of 1 kg of water by 1 K (or °C).
- BUT specific heat capacity of air is 1,000 J kg-1 K-1
- consequently, ocean has absorbed > 90% of all anthropogenic heat (think about gradient across the atm-ocean interface)
Impact of atmosphere-ocean momentum fluxes
- energy continually exchanged between the two fluids.
- atmosphere has largest impact on ocean eg. atmospheric storms changing sea state
- to a lesser extent, the ocean can still exert momentum energy back onto atmosphere eg. in regions of ocean currents, upwelling & waves, frontal systems
- energy interactions (from both fluids) control turbulent exchange at interface of matter, gases & heat (ie. at surface water & atmospheric marine boundary layer)
Impact of atmosphere-ocean CO2 gas fluxes
- pre 1750 (pre industrial revolution), ocean was a source of CO2.
- post 1750, ocean has become sink of atmospheric CO2. ie. anthropogenic emissions are forcing the system (think about the gradient across the atmosphere-ocean interface).
- long-term absorption is fundamentally altering the chemistry in the oceans
ocean carbonate system
- oceanic carbonate system can be understood and probed through 4 key parameters: total alkalinity (AT), total dissolved inorganic carbon (DIC or CT), basity (pH), and fugacity or partial pressure of CO2 (fCO2 or pCO2)
- knowledge of any 2 of these parameters is sufficient to solve the carbonate system equations along with temperature and pressure (due to thermodynamics). Salinity effects carbonate system calculation coefficients.
- some pairs are more optimal than others
- relationship between different carbonate parameters is fundamentally driven by thermodynamics.
AT: The ability for the ocean to buffer and acid.
CT: Total dissolved inorganic carbonate chemical species.
pH: Number of hydrogen ions.
pCO2: The amount of gaseous CO2 in solution.
why are DIC and TA the preferred variables for tracers in numerical models (and for in situ monitoring of carbonate system)?
- DIC and TA are conservative quantities, i.e. their concentrations measured in gravimetric units (mol kg-1) are unaffected by changes in pressure or temperature, for instance, and they obey the linear mixing law.
- so they are often the preferred variables for tracers in numerical models of the ocean’s carbon cycle and for in situ monitoring of the carbonate system
due to chemical buffering…
- CO2 enters water and forms carbonic acid, H2CO3
- acids release free protons, H+, into the water, lowering the pH
- the additional hydrogen ions released by carbonic acid bind to carbonate (CO32-) to form bicarbonate (HCO3–), decreasing the amount of carbonate in the water
- so coupled pH reactions help to stabilise the CO2 concentration (buffers) and in doing so this changes the pH of the water.
- this combination of reactions together form the chemical buffer system that controls the pHof the water and enables it to hold for CO2 than would otherwise be possible
chemical buffering happens, therefore…
- absorption of CO2 fundamentally alters the chemistry of the water
- the gradual and long‐term lowering of pH and carbonate ion concentration – termed ocean acidification – is measurable on decadal timescales
- this lowering of pH and carbonate ion, CO32-, concentrations can, and is, having catastrophic impacts on marine life and ecosystems. eg harder to grow calcareous shells
Calcium carbonate (CaCO3) saturation state
Ω -> level of calcium carbonate saturation in seawater
negative impacts to marine life
- reducing carbonate ions (CO32- ) means less material for animals to grow.
- Calcium carbonate (CaCO3) saturation state, Ω
- ocean acidification is steadily reducing the amount of water that is supersaturated. ie the depth and places within which some animals, that need CaCO3, can live and grow is reducing. eg lobsters, shellfish, calcifying plankton.
- potential devastating impacts on marine food webs.
conclusions
- CO2 entering the ocean goes into solution and then splits into different carbonate species.
- relationship between different carbonate parameters is fundamentally driven by thermodynamics.
- carbonate system can be monitored through just 2 carbonate system parameters along with temperature and pressure.
- chemical buffering enables the ocean to hold more CO2 than would be possible otherwise.
- long-term absorption of CO2 is leading to ocean acidification and this is having widespread impacts.
