Sea surface alkalinity (from the GLODAP climatology)

Alkalinity or A_T is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. Alkalinity is closely related to the acid neutralizing capacity (ANC) of a solution and ANC is often incorrectly used to refer to alkalinity. However, the acid neutralizing capacity refers to the combination of the solution and solids present (e.g., suspended matter, or aquifer solids), and the contribution of solids can dominate the ANC (see carbonate minerals below). Image File history File links Size of this preview: 800 × 562 pixels Full resolution (1612 × 1133 pixel, file size: 273 KB, MIME type: image/png) Annual mean sea surface alkalinity from the Global Ocean Data Analysis Project climatology. ... Image File history File links Size of this preview: 800 × 562 pixels Full resolution (1612 × 1133 pixel, file size: 273 KB, MIME type: image/png) Annual mean sea surface alkalinity from the Global Ocean Data Analysis Project climatology. ... The Global Ocean Data Analysis Project (GLODAP) is a synthesis project bringing together oceanographic data collected during the 1990s by research cruises on the World Ocean Circulation Experiment (WOCE), Joint Global Ocean Flux Study (JGOFS) and Ocean-Atmosphere Exchange Study (OACES) programmes. ... Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time,[1] and is a branch of the atmospheric sciences. ... Equivalence point occurs during a chemical titration when equal amounts of acid and base have been reacted. ... Acid-neutralizing capacity or ANC in short is a measure for the overall buffering capacity against acidification for a solution, e. ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ...

The alkalinity is equal to the stoichiometric sum of the bases in solution. In the natural environment carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of carbon dioxide in the atmosphere. Other common natural components that can contribute to alkalinity include borate, hydroxide, phosphate, silicate, nitrate, dissolved ammonia, the conjugate bases of some organic acids and sulfide. Solutions produced in a laboratory may contain a virtually limitless number of bases that contribute to alkalinity. Alkalinity is usually given in the unit mEq/L (milliequivalent per liter). In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... Carbonate Alkalinity is a measure of the amount of carbonate and bicarbonate anions in solution. ... Ball-and-stick model of the carbonate ion, CO32− For other meanings, see Carbonate (disambiguation) In chemistry, a carbonate is a salt or ester of carbonic acid. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Borates in chemistry are chemical compounds containing boron bonded to three oxygen atoms written as B(OR)3. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... Trinitrate redirects here. ... For other uses, see Ammonia (disambiguation). ... An organic acid is an organic compound that is an acid. ... Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ...

Alkalinity is sometimes incorrectly used interchangeably with basicity. For example, the pH of a solution can be lowered by the addition of CO₂. This will reduce the basicity; however, the alkalinity will remain unchanged (see example below). Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In...

Theoretical treatment of alkalinity

In typical groundwater or seawater the measured alkalinity is set equal to: Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ... Annual mean sea surface salinity for the World Ocean. ...

A_T = [HCO₃⁻]_T + 2[CO₃⁻²]_T + [B(OH)₄⁻]_T + [OH⁻]_T + 2[PO₄⁻³]_T + [HPO₄⁻²]_T + [SiO(OH)₃⁻]_T − [H⁺]_sws − [HSO₄⁻]

(Subscript T indicates the total concentration of the species in the solution as measured. This is opposed to the free concentration, which takes into account the significant amount of ion pair interactions that occur in seawater.) In chemistry the ion pair concept (introduced by Saul Winstein) describes the interactions between a cation, anion and surrounding solvent molecules. ...

Alkalinity can be measured by a sample with a strong acid until all the buffering capacity of the aforementioned ions above the pH of bicarbonate or carbonate is consumed. This point is functionally set to pH 4.5. At this point, all the bases of interest have been protonated to the zero level species, hence they no longer cause alkalinity. For example, the following reactions take place during the addition of acid to a typical seawater solution:

HCO₃⁻ + H⁺ → CO₂ + H₂O

CO₃⁻² + 2H⁺ → CO₂ + H₂O

B(OH)₄⁻ + H⁺ → B(OH)₃ + H₂O

OH⁻ + H⁺ → H₂O

PO₄⁻³ + 2H⁺ → H₂PO₄⁻

HPO₄⁻² + H⁺ → H₂PO₄⁻

[SiO(OH)₃⁻] + H⁺ → [Si(OH)₄⁰]

It can be seen from the above protonation reactions that most bases consume one proton (H⁺) to become a neutral species, thus increasing alkalinity by one per equivalent. CO₃⁻² however, will consume two protons before becoming a zero level species (CO₂), thus it increases alkalinity by two per mole of CO₃⁻². [H⁺] and [HSO₄⁻] decrease alkalintiy, as they act as sources of protons. They are often represented collectively as [H⁺]_T.

Alkalinity is typically reported as mg/L as CaCO₃. This can be converted into milliEquivalents per Liter (mEq/L) by dividing by 50 (the approximate MW of CaCO₃/2).