GEOL 3070 Lecture 22: Ocean Carbon and Acidification

2 Pages
Unlock Document

Geological Sciences
GEOL 3070
Thomas Marchitto

Ocean Carbon and Acidification Thursday, March 23, 2017 10:59 AM 1. Carbon and pH A. Carbon in seawater • One of the 7 major elements in seawater • Basic building block of organic molecules • Occurs in seawater in several forms: ○ ~2% dissolved organic carbon (DOC) ○ ~98% dissolved inorganic carbon (DIC) ▪ ~1% carbon dioxide gas (CO ) 2 - ▪ ~90% bicarbonate (HCO ) 3 ▪ ~10% carbonate (CO ) 32- ○ Relative abundance of DIC species is related to pH B. pH + - Pure Water: a tiny fraction of H 2 dissociates into hydrogen (H ) and hydroxide (OH ) • Since H O 2s the only source of these ions in pure water, their abundances must be equal ○ E.G. [H ] = [OH ] = 10 mol/kg + • pH= -log[H ] = 7 for pure water (neutral) + - Seawater: [H ] & [OH ] are imbalanced because of the presence of numerous other ions that consumer or release [H ] or [OH ] - • [H ] is less abundant and [OH] is more abundant • Seawater pH is slightly basic --> pH ~7.5-8.5 **Presence of Hydrogen (H ) makes things more basic & vice versa** C. pH is affected by CO (Nat2ral & Anthropogenic) If DIC is naturally removed from the surface ocean • C0 +2H O -2> H CO -2> H 3 HCO + 3- and added to the deep ocean (as CO ),2what is your + • C0 a2dition: most (but not all) C0 bec2mes carbonic acid which dissociates into H prediction for the pH change with depth? & HCO 3- • Higher pH at the surface, lower pH at depth + 2- - • Most (but not all) of the H combines with the C0 3 to form HC0 3 • Basic at surface, Acidic at depth • NET RESULT: Higher [C0 lower p2],and lower [C0 ] (acidific3tion) + 2- • Because most of the H gets consumed by [C0 ] we sa3 that seawater is buffered • C0 removal reverses this (raises pH and [C0 ]) 2- 2 3 D. DIC speciation varies with pH • CO ad2ition changed the pH and the DIC speciation--> high carbon is more acidic??? II. Oceanic Carbon Cycling (natural) A. DIC distribution • Low at the sea surface and high in the deep ocean • Removed by photosynthesis and added by respiration B. CaCO diss3lution and pH • Dissolves under high pressure, low temperature, low pH • Preserved in shallower regions like snow on mountains • At a given temperature and pressure, seawater is saturated with respect to CaCO 3 once [Ca ][CO ] r3aches a certain value 2- • Since the deep ocean has lower pH due to CO addit2on, it's [CO ] is l3wer and it is therefore more under-saturated A. Air-sea exchange of CO 2 Of the three forms of DIC, only CO ca2 enter the atmosphere • At equilibrium, the partitioning of CO be2ween the atmosphere and ocean is d
More Less

Related notes for GEOL 3070

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.