Ocean Water Chemistry

Water sets 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)

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

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)

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

Salinity Average in oceans is 3.5% or 35 ppt (written as 35 0 / 00 ) 1-20 ppt “brackish” (hyposaline) water - common in estuaries ppt “transitional marine” – coastal areas near fluvial runoff point source 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.

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)

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]

Principle of Constant Proportion (principle of constant composition) Forschammer/Ditmar –Works only with the major elements Na, Cl, SO 4, Mg, Ca, K The formula: x chlorinity 0 / 00 = salinity 0 / 00 or: x 18.98* = / 00 * average chlorinity of seawater By using Forschammer’s principle, it is possible to determine salinity very accurately by measuring only one element.

Ocean Salinity Major elements Na, Cl, SO 4, Mg, Ca, K (>99%) Minor elements HCO 3, Br, H 3 BO 3, 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 (CO 2, O 2, N 2, Ar, H 2, 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]

CCD and Ocean Temperature CCD=Calcium Carbonate Compensation Depth Actually is top of the AABW- below the CCD water is extremely cold and CaCO 3 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

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

Stable Isotopes O 18 is stable O 18 1/8 heavier than O 16 During evaporation O 18 is left behind and O 16 evaporated O 16 enriched water is locked up on land as glacial ice during an ice age. During an ice age, ocean waters are enriched with O 18 in animals shells/skeletons – silica (SiO 2 ) or lime (CaCO 3 ) will reflect increased O 18 Can read paleotemperature directly from ratio of O 18 in shell/skeleton

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

“Old Carbon” expression of how fast an ocean is recycling Pacific – yrs (large ocean, very slow) Atlantic – yrs (smaller ocean, more rapid recycling) Indian yrs (“middle child”)

Residence Time recycling 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 ~ yrs