Chemical Oceanography Lecture 3: 5/30/2014

Salinity Definition: weight of inorganic salts in one kg of seawater There are many ions and salts in seawater, but they are never the dominant mass

Inputs Outputs

Weathering: the physical & chemical processes that break down rock

A simplified biogeochemical cycle

Steady State and Equilibrium Draw on board

Acidity pH = -log[H + ] – Dissociated water molecule H 2 O = H + + OH - In 1L of water (55.6 moles) moles dissociated; therefore, moles/L of both H + and OH - (i.e. pH = 7, pOH = 7) pH 7 alkaline

Seawater Buffering, Alkalinity Alkalinity = measure of the amount of ions present that can react with, or neutralize, H + – Higher alkalinity of a solution  more difficult to produce a pH change by adding acid – Alkalinity measures acid buffering capacity Simple measure of Alkalinity (A) A = [HCO 3 - ] + 2[CO 3 - ] + [OH] - - [H + ] Assumes bicarbonate, carbonate, hydroxyl ions dominate seawater alkalinity

Seawater Buffering, Alkalinity More substances can react with [H + ] From Pilson 1998

Two important carbon reactions pertain to primary production: CO 2 + H 2 O  CH 2 O + O 2 (consumes acid) Ca +2 + HCO 3 -  CaCO 3 + H + (produces acid) CO 2 (g)  H 2 CO 3 (aq)  HCO 3 -  CO 3 -2   C org CaCO 3 Air Sea – photic zone Sea – aphotic zone ‘export’ Ecology influences the net effect of biology on the air-sea transfer! Seawater Carbonate Buffer System

Thermodynamic Constants K H = pCO 2 /{H 2 CO 3 } K 1 = {H + }{HCO 3 - }/{H 2 CO 3 } K 2 = {H + }{CO 3 -2 }/{HCO 3 - } ‘Apparent’ Constants K 1 ’ = K 1   H2CO3 /  HCO3- = {H + }[HCO 3 - ]/[H 2 CO 3 ]  o C, I=0.7) K 2 ’ = K 2   HCO3- /  CO3-2 = {H + }[CO 3 -2 ]/[HCO 3 - ]  o C, I=0.7) 3 Equations but, 5 unknowns! How can system be defined uniquely? pCO2 (open system) pH (≡ -log a H+ )  CO2 (mass balance) Alkalinity (acid-neutralizing capacity) H 2 CO 3 – a diprotic weak acid

mass balance constraint  CO 2 = [H 2 CO 3 ] + [HCO 3 - ] + [CO 3 -2 ] Respiration CH 2 O + O 2  CO 2 + H 2 O Dissolution CaCO 3 + H +  Ca +2 + HCO 3 - ~1%~90% ~9%  CO2 i.e. DIC

Total Dissolved Inorganic Carbon DIC, i.e.  CO2 (  mol/kg)

Total Alkalinity (  mol/kg)

Emiliania huxleyi, a coccolithorophorid Discospaera sp., another coccolithophorid planktonic foraminifera pteropods These organisms all make skeletal material from calcium carbonate – calcite in some cases, aragonite in others Both CaCO 3 bryozoa stalks sponge spicules

Centric diatoms – an alga Radiolarian – a protozoan Both make a skeleton based on the element Si – ‘biogenic silica’ or SiO 2

CaCO 3 (s)  Ca +2 (aq) + CO 3 -2 (aq) K sp * = [Ca +2 ] saturated + [CO 3 -2 ] saturated K sp * calcite (e.g., foraminifera, coccolithophorids):3.3 x aragonite (e.g., coral, pteropods):4.6 x Biogenic Silica (e.g. diatoms, radiolarian):2.0 x Q: What is more soluble – CaCO 3 or SiO 2 ? Q: Which form of calcium carbonate is more soluble? Solubility of Calcite versus Aragonite

Dissolution of biogenic particles Solubility also is a function of temperature and pressure In the deep ocean, CaCO 3 becomes very soluble – Carbonate Compensation Depth (CCD) Below CCD calcium carbonate is under- saturated (like SiO 2 ) – Decrease in pH also can increase calcium carbonate solubility – CCD is a dynamic depth (NOT fixed)

Nutrients In oceanography, “nutrient” refers to important and commonly measured element needed for growth of plants Includes the major nutrients (i.e. macronutrients): – Phosphorus – Nitrogen – Silicon

Phosphorus Cycle: global Ruttenberg, 2001 (Encyclopedia of Ocean Sciences)

Phosphorus Forms of occurrence in seawater – Inorganic phosphate (i.e. orthophosphate) No major redox state differences Nearly all dissolved phosphorus present in deep sea – Organic phosphorus Phospho- … -lipids, -proteins, -carbohydrates Nucleic acids & nucleotides Phosphonic acid derivatives – Polyphosphates Wide variety of straight-chain, branched and cyclic polymeric forms Sorption affects bioavailability – Fe oxy-hydroxides, Carbonate-mineral sorption Redox sensitivity – Low Dissolved oxygen induces phosphate release from sediments (VERY IMPORTANT IN Gulf of Mexico and adjacent estuaries)

Distribution of Dissolved organic phosphorus (DOP) and Soluble Reactive Phosphorus (SRP)

Nitrogen in the marine environment Gruber (Ch 1) in Nitrogen in the Marine Environment 2 nd Ed (2008)

Nitrogen acquisition Chemical forms of nitrogen and their major characteristics Chemical Form Nitrate (NO 3 - ) Nitrite (NO 2 - ) Nitrous oxide (N 2 O) Nitrogen gas (N 2 ) Ammonia (NH 4 + ) Amines (-NH 2 ) Oxidation State Used by plants Yes NoYes OxidizedReduced

Major Chemical forms/transformations Gruber (Ch 1) in Nitrogen in the Marine Environment 2 nd Ed (2008)

Global Mean Profiles Gruber (Ch 1) in Nitrogen in the Marine Environment 2 nd Ed (2008)

Behold … the world’s most awesome element

Silicon Second most abundant element in earth’s crust – 25.5% of crust by weight (Oxygen is 49%) – Si-O chemical bond one of most abundant In seawater Si is relatively scarce ~ atom% In diatoms (a phytoplankton group beloved by your instructor) = 5.0 atom % Some vertebrates = atom%

Current view of the marine Si cycle Tréguer and De La Rocha Annu. Rev. Mar. Sci NOTE: No major gas phase No major organic Si pool UNITS: Tmols Si year -1

Dissolved silicate At seawater pH – >97% Si(OH) 4 (orthosilicic acid) Dominant form transported by diatom (Del Amo and Brzezinski 1999, Journal of Phycology) pH – 14-23% ionic (Si(OH) 3 - May be transported across the membrane but typically much lower rates (Reidel et al Journal of Phycology)

Ocean Chemical Tracers Tracer conservation equations establish the relationship between the time rate of change of tracer concentration at a given point and the processes that can change that concentration (Sarmiento and Gruber 2006) – Processes include: Physical transport (advection, mixing) Sources and sinks (biological and chemical transformation) Examples: chemical ocean tracers – AOU = apparent oxygen utilization – Chlorofluorocarbons (CFC) – Carbon 14

AOU Apparent Oxygen Utilization – AOU = [O 2 ] saturated – [O 2 ] measured Difference between measured oxygen and what equilibrium saturation (as a function of the physical/chemical characteristics) – From biological activity – Oxygen increased by primary production – Oxygen used by respiration

Apparent Oxygen Utilization AOU = [O 2 ] saturated – [O 2 ] measured Which locations have the highest AOU at depth? Lowest? Why?

Preformed nutrients: those initially present at the time of downwelling = total nutrient – regenerated nutrient - Calculated using AOU Characteristic of waters originating from different regions – Hence use as tracer AOU and Preformed Nutrients ‘Preformed’ Nutrient AOU Phosphate

From Broecker et al Preformed P (top) & Preformed N (bottom) From Sarmiento & Gruber 2006

CFC

Manmade compounds (where are highest values?) High radiative forcing (relative to CO 2 ) 12,400x higher for CFC-11 15,800x higher for CFC-12 Useful as ocean tracers (i.e. only manmade source is from atmosphere)

Natural vs Anthropogenic 14 C Production Industrial Revolution Burning 14 C-dead Coal! “Suess Effect” Tree Ring Records Coral Records Nuclear Weapons Testing! Test Ban Treaty – 1963! 14 C now decreasing -

surface waters (-50‰) contain more 14 C than deep waters deep waters in the Atlantic contain more 14 C than those in the Pacific while those in the Indian Ocean and Antarctic have intermediate values.

Radiocarbon age – do trends look familiar?