Download Ocean Water Chemistry

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.
• 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.
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,
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.
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]
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
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
• 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
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
“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”)
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 ~ 3-4000 yrs