Move Discussion from Wednesday to Friday Read for the discussion: ’Climate Change 2001: The Scientific Basis - Summary for Policy Makers’ You can download a pdf from

Crystal structure of ice looking down its ‘c-axis’ (axis of hexagonal symmetry)

Ice structure looking oblique to c-axis

Sea water Sea water is an aqueous solution; must add or subtract dissolved constituents by chemical means Cannot filter out dissolved constituents Dissolved constituents will not settle out Of 92 stable elements, 72 occur in sea water in measurable amounts Most abundant elements dissolved in sea water are the abundant in the earth’s crust, with two important exceptions –Si is abundant in crust but not in sea water –Cl is abundant in sea water but not in crust

Primary constituent ions in sea water total salinity = parts per thousand = PPT = per mil = ‰

Solute concentrations in sea water Composition of sea water is virtually constant worldwide –~35‰ salinity measured in all major oceans –The relative proportions of major solutes nearly constant, even where salinity is not 35‰ –Can use chloride concentration, e.g., to determine total salinity; salinity = x chlorinity Distinguish between –Conservative constituents, i.e. the major components of the dissolved solids, whose relative concentrations are effectively fixed (i.e. Na +1, Cl -1, or SO 4 -2 ) –Non-conservative constituents, i.e. minor elements whose concentrations are locally altered by biological activity, physical processes, etc. (i.e. NO 3 -1 or PO 4 -3 )

Changes in sea water salinity Salinity changes occur near edges of oceans –Where Amazon River flows into sea, find nearly fresh water 100 km off shore –In Persian Gulf, where shallow sea water evaporates & there is little precipitation or river recharge, salinity approaches 40‰ –Freezing sea water at high latitudes causes salinity to approach 38‰ Generally, however, sea water salinity is roughly constant, & it appears to have had this value for a long time

If sea water salinity has remained constant (oceans maintained a steady state), how is that accomplished?

What are the sources of the dissolved solids we see in the oceans?

Can river water be the source of the dissolved constituents in sea water? Hydrologic cycle - water evaporates from ocean, transported over land, falls as rain water, dissolves rock constituents, & carries them into ocean basins –When sea water evaporates, it takes some salts, but water vapor is effectively fresh water –When water condenses to form precipitation, it usually ends up with significant dissolved CO 2 & SO 2 –Rain water falling on continents is acidic –Acidic water dissolves the continents

Chemical constituents in river water Average river water salinity = 0.12‰ actual vs. (estimate of unpolluted value)

Most important dissolved constituents in sea water and river water Sea water River water 99% of dissolved components are –Cl -1 = ~ 55.1% –Na +1 = ~ 30.6% –SO 4 -2 = ~ 7.7% –Mg +2 = ~ 3.7% –Ca +2 = ~ 1.2% –K +1 = ~ 1.1% Salinity = ~35‰ 99% of dissolved components are –HCO 3 -1 = ~ 48.7% –Ca +2 = ~ 12.5% –SiO 2 = ~ 10.9% –SO 4 -2 = ~ 9.3% –Cl -1 = ~ 6.5% –Na +1 = ~ 5.2% –Mg +2 = ~ 3.4% –K +1 = ~ 1.1% Salinity = ~ 0.12‰

The total mass of dissolved solids added by rivers is great = ~4 x 10 9 tons, but cannot simply concentrate river water (by evaporation) & get sea water Some other chemical processes must occur to change concentrations of dissolved constituents

What other processes add or subtract dissolved constituents to sea water? What are the sources of & sinks for dissolved solids?

Biological activity Organisms are ubiquitous in surface waters; many have tests (shells or hard parts) Organisms consume chemical constituents to make tests After organisms die, their tests sink –Some sinking tests dissolve (remember CCD) –Others accumulate as oozes at the bottom of the ocean –Have calcareous & siliceous oozes –Remove 1-2 x 10 9 tons of Si +4, Ca +2, & CO 3 -2 as CaCO 3 & SiO 2

Degassing of ocean Dissolved gasses escape when bubbles move to the surface Bursting bubbles send small droplets of water into air Largest fall back to sea, but smallest remain in the air, carrying dissolved constituents Degassing may remove as much as 1-2 x 10 9 tons of all of the primary dissolved constituents, Na +1, Cl -1, Mg +2, SO 4 -2, HCO 3 -1, etc.

Formation of evaporites Move sea water to restricted basin, where there is little recharge Evaporate & concentrate dissolved solids to their solubility limits Form salt crystals, which collect in layers of minerals (called evaporites) Not important now, but was important in geologic past –Silurian Salina Group in Appalachians & Michigan Basin, Triassic Muschelcalk in Alps, Jurassic in the Gulf coast Evaporites remove masses of Na +1, Cl -1, Mg +2, SO 4 -2, HCO 3 -1 as halite (rock salt) & gypsum

Silicate clay flocculation Silicate clays are common weathering product, & are often carried into oceans by rivers Often clay minerals are missing cations in their structure Clays react chemically on encountering sea water, taking up Na +1 & K +1 Clay particles coagulate as a result of their sorption of Na +1 & K +1 & sink to the bottom Entire process = chemical reaction + coagulation + sinking = flocculation Flocculation removes masses of Na +1 & K +1

Hydrothermal vents at MOR (smokers), I At MOR, formation of new lithosphere fractures rock & brings magma to shallow depths Sea water percolates into rock along fractures, heats up, & rises through the oceanic crust to escape into sea water at hydrothermal vents Hot water is chemically active & metamorphoses basalt as it travels through crust Process also alters the types & concentrations of dissolved solids

Hydrothermal vents at MOR (smokers), II Circulation rates are high; one estimate has a volume equal to all the water in oceans moving through vent systems in 5-10 Ma Vent circulation probably removes masses of Na +1, Mg +2, SO 4 -2 from sea water & adds Ca +2, Si +4, and K +1 to it When hot water with high concentrations of dissolved solids enters the cold sea, minerals precipitate, causing water to look cloudy or smoky Leads to white & black smokers