Carbon cycling and climate: the CO2 connection : Carbon cycling and climate: the CO2 connection Gasses in the ocean The carbonate system (and buffering in the ocean) Carbon dioxide and the climate connection.


Dissolution of gas in water: Dissolution of gas in water Dissolution for any gas is controlled by temperature: Gas dissolution increases with decreasing temperature: COLD water holds MORE gas.


Dissolved gasses in the ocean: Dissolved gasses in the ocean Gasses dissolve in the ocean in proportion to their amounts in the atmosphere (mostly…..)


Oxygen has a “local” source: Oxygen has a “local” source Photosynthesis can cause oxygen to be super saturated


Below the euphotic zone is the oxygen minimum : Below the euphotic zone is the oxygen minimum … but why is the concentration of oxygen in deeper waters more than in surface waters?


….Thermohaline circulation: ….Thermohaline circulation


Carbon dioxide concentration in the ocean : Carbon dioxide concentration in the ocean Is not just controlled by partial pressure and respiration…..


The carbonate system in the ocean: The carbonate system in the ocean Absorption of CO2 by the ocean involves 3 equilibria 1 CO2(aq) + H20 H2CO3(aq) (carbonic acid) 2 H2CO3(aq) H+(aq)+ HCO3-(aq)(bicarbonate ion) 3      HCO3-(aq) H+(aq)+ CO3-2(aq) (carbonate ion) 4 Ca++(aq)+ CO3-2(aq) CaCO3 (calcium carbonate mineral) Generally equation 4 is ignored, and one and 2 are shortened to: 5 CO3-2(aq) + CO2(aq) + H20 HCO3-(aq) + H+ …is a case of buffered acid-base chemistry……


Slide9: Carbonic acid titration…..


The buffering of the carbonate system: The buffering of the carbonate system To summarize these 3 equilibria; CO2(aq) H2CO3(aq) ) H+(aq)+ CO3-2(aq) …pushes these reactions to the center……


Slide11: The ocean is buffered


The ocean is buffered: The ocean is buffered Because the pH of the ocean is fixed at about 7.8 to 8 it pushes the reaction to bicarbonate: CO2(aq) 2HCO3-(aq)  CO3-2(aq) The reaction runs to the middle. Result: if CO2 increases so must CO3-2 and the source of carbonate is CaCO3 not CO2 Result: if carbon dioxide is added to the water calcium carbonate dissolves or is harder to precipitate.


Carbonate system equilibrium : Carbonate system equilibrium   K = [CO2(aq) ][ CO3-2] [HCO3- ]2 the governing equation: CO3-2 + CO2(aq) + H20 2HCO3- (aq) + H+ What does this mean practically? The more CO2 in the water , more CO3-2 is needed to balance it.


CO2 and the sediment connection : CO2 and the sediment connection CO2 in the water must be balanced by CO3-2 : the carbonate ion source is the sediments: CaCO3(s) + Ca +++ CO3-2(aq) (solid calcium carbonate) When CaCO3 is precipitated it creates CO2(aq) HCO3- + Ca ++ H2CO3(aq) CaCO3 + CO2 + H20 Counter intuitively, calicification “produces” carbon dioxide Conversely, dissolving CaCO3 sediments “uses” CO2 . Dissolution of CaCO3 counter acts the “acidity” of the CO2 in the ocean, Not calicfication. (more CO2 makes it harder to calicify) Counter intuitively – the practical result overall is: the more CO2 in the ocean the more it can hold.


Seltzer is not buffered…..: Seltzer is not buffered….. But lets look at the carbonate –carbon dioxide dissociation in a simple system


Carbon dioxide concentration in the ocean : Carbon dioxide concentration in the ocean The dissociation reaction allows the ocean to hold 50 times as much CO2 as the atmosphere


The carbon cycle: quantified: The carbon cycle: quantified


Slide18: Controls on the distribution of CO2 DIC DIC DIC DIC DIC DIC Corg Corg Corg Corg Corg Corg Corg Corg Corg Corg DIC DIC DIC DIC DIC DIC Water downwells: Low nutrients High O2 low CO2 content DIC content of Water increases with increasing age Carbonate Sediments are a source and sink of carbon, both Corg and CO2 CO2 CO2 CO2 CO2 CO2 CO2


The Atlantic Ocean is primarily a sink for CO2: The Atlantic Ocean is primarily a sink for CO2


The ocean takes up CO2….: The ocean takes up CO2…. …and releases it……… The numbers are fluxes, positive numbers are flux of CO2 into the ocean, negative are fluxes out


The ocean is both a source and sink for CO2….: The ocean is both a source and sink for CO2…. In different places and at different times…


CO2 levels in the atmosphere: CO2 levels in the atmosphere Where is the “missing” CO2??


The biological pump interacts with the excess CO2 we are putting into the atmosphere. : The biological pump interacts with the excess CO2 we are putting into the atmosphere. The marine system is taking up CO2 in surface waters and Putting it into the deep ocean. Because most of the deep ocean is “capped” by the thermocline, the CO2 remains there….. Until the water upwells…. Question: how long does water remain “deep”? And how long have we been putting CO2 into the atmosphere?


Record of CO2 in the atmosphere through time: Record of CO2 in the atmosphere through time The record of CO2 levels in the atmosphere measured in bubbles trapped in ice cores


The ocean is both a source and sink for CO2….: The ocean is both a source and sink for CO2…. In different places and at different times…


The vertical profile of 13C reflects the global thermohaline circulation : The vertical profile of 13C reflects the global thermohaline circulation