Ocean Water Chemistry

1. Ocean Water Chemistry

2. Watersets Earth apart from other planets On Earth, 71% of surface is water (hydrosphere); only 29% is land 97% of earth’s water is oceanic (salty) 2% is ice (cryosphere) in valley & continental glaciers .5% is ground water <.1% is all else (atmosphere, lakes, rivers, soil moisture)

3. How did all that water get here? • 2 major sources Volcanic outgassing water from within the Earth Comets Water from outside the Earth

4. The Water Molecule and Water • Exists as gas, liquid, & solid on Earth’s surface • Remarkably high heat capacity (specific heat) makes it slow to heat and slow to cool • Very high solvent power (dissolves everything!) • Molecule is “dipolar” (hydrogen[+], oxygen [-]) • Expands when freezes (ice floats, role in erosion) • Water density increases as temperature decreases (inverse relationship like air)

5. Salinity in Steady State Equilibrium • Even though salts are continually washed into the sea, the average salinity has remained the same for the last billion yrs. • Several mechanisms exist to remove salt: • Salt spray on land and into air • Salts precipitating along coastlines and marginal ocean basins • Marine organisms use salt ions to build shells, then die and are incorporated into sediments

6. Salinity • Average in oceans is 3.5% or 35 ppt (written as 35 0/00) • 1-20 ppt “brackish” (hyposaline) water - common in estuaries. • 20-30 ppt “transitional marine” – coastal areas near fluvial runoff point source • 40-50 ppt “restricted lagoon” – water enclosed, strong sunlight • >50 ppt “hypersaline” high evaporation – rare Because brackish water is so common & hypersaline water is so rare, most organisms adapt to the former and die in the latter.

7. Salinity • 5 different ways to measure salinity • Three ways to examine salinity in the ocean • Surface salinity (isohalines) • At one site from surface to ocean floor (halocline) • Looking at an ocean in profile N-S ………... And fifty ways to leave your lover (Paul Simon)

8. Salinity Measurement • Simple evaporation (gasses are lost) • Hydrometer (direct ratio) density • Salinometer (direct ratio) electrical conductivity of sea water • Refractometer (direct ratio) refraction (bending) of light • Chlorinity (titration) extremely accurate [Forschammer/Ditmar]

9. Principle of Constant Proportion(principle of constant composition) • Forschammer/Ditmar • Works only with the major elements Na, Cl, SO4, Mg, Ca, K The formula: • 1.80655 x chlorinity 0/00 = salinity 0/00 or: 1.80655 x 18.98* = 34.2 0/00 * average chlorinity of seawater By using Forschammer’s principle, it is possible to determine salinity very accurately by measuring only one element.

10. Ocean Salinity • Major elements Na, Cl, SO4, Mg, Ca, K (>99%) • Minor elements HCO3, Br, H3BO3, Sr, F [both major and minor are 99.99%] • Trace elements Li, I, Mo, Zn, Fe, Al, Cu, Mn, Co, Pb, Hg, Au • Nutrients P, N, Si, Fe, Zn & their compounds (critical for plant growth) • Organic compounds (lipid, proteins carbohydrates, hormones, vitamins) • Dissolved gasses (CO2, O2, N2, Ar, H2, Ne, He) • Particulates • Inorganic-clay, dust, ash • Organic-plants, & animals in the sea • [Grant Gross refers to seawater as “a dilute, dirty, living organic soup]

11. CCD and Ocean Temperature • CCD=Calcium Carbonate Compensation Depth • Actually is top of the AABW- below the CCD water is extremely cold and CaCO3 dissolves easily • During glacial/interglacial flux the volume of AABW waxes and wanes- So does CCD level • Undergoes “excursions” – rises during glaciation and lowers during interglacial periods • During excursions the amount of chalky limestone getting to the sea floor is in flux • Oceanographers use limestone incidence as an accurate measure of paleotemperature

12. Isotopes in Oceanography • All matter is made from atoms • Atoms have two types of particles in nucleus that have mass (weight) – protons and neutrons • The # of protons defines the element (ex. Carbon always has 6 protons, oxygen 8) • The # of neutrons can differ • Isotope- like an atom but # protons & neutrons not equal • Isotopes heavier or lighter than atoms & may be either stable or unstable

13. Stable Isotopes • O18 is stable • O18 1/8 heavier than O16 • During evaporation O18 is left behind and O16 evaporated • O16 enriched water is locked up on land as glacial ice during an ice age. • During an ice age, ocean waters are enriched with O18 in animals shells/skeletons – silica (SiO2) or lime (CaCO3) will reflect increased O18 • Can read paleotemperature directly from ratio of O18 in shell/skeleton

14. Unstable (Radioactive) Isotopes • Carbon 12 (C12) has an isotope Carbon 14 (C14) made from N in upper atmosphere • C14 changes back into Nitrogen (N) • Half-life- it takes 5500 yrs for half of the C14 to change into N • We measure the ratio of C14 to C12 to determine age

15. “Old Carbon”expression of how fast an ocean is recycling • Pacific – 1000-1600 yrs (large ocean, very slow) • Atlantic – 500-800 yrs (smaller ocean, more rapid recycling) • Indian - 700-1200 yrs (“middle child”)

16. Residence Timerecycling of chemicals in and out of the sea • Short residence time: Si (8,000 yrs), Mn (700 yrs), Fe (140 yrs), Al (100 yrs) • Chemically reactive (Al), rare (Mn), critical to biological systems (Fe, Si) • Long residence time Cl (80 m.y.), Ca (1 m.y.), K (11 m.y.), Na (210 m.y.) Mg (12 m.y.) • Not reactive, extremely abundant or not used in biology • Water has residence time of ~ 3-4000 yrs