The Sea Around Us Lecture 4: 21 January Water is The Wonder Substance: Physical & Chemical Properties Drown with Me Porcupine Tree. Ocean Breathes Salty Modest Mouse Water Cycle Jump! VV Brown, Shark In The Water Thanks to Rachel B., Zach R.

Lecture Review Questions:Lecture Review Questions: On-line Assignment 2 is due tonight by 11pm Homework 1 is available on Angel Cell Phone Recycling: Benefit Relay for Life and The Ocean! Book pics? (Angel dropbox) Questions (Angel) Read about The Sea Around Us Lecture notes and slides on the course web site Your book

The WONDER SUBSTANCE: Physical & Chemical Properties Ice is less dense than water. At 0°C, density of water is 1 gm/cc; Ice is gm/cc Ice has an open hexagonal structure Density of ice is about 91% of liquid water Water molecular structure Ice molecular structure

Density of Water Fresh water reaches maximum density at 3.98 °C Density= 1,000 kg/m 3 (1kg/liter) Density decreases as water is heated above 4°C At 20 °C, density of pure H 2 O is kg/m 3

Water: The Wonder Substance Low viscosity rapid flow to equalize pressure differences High surface tension allows wind energy to be transmitted to sea surface allows cells to hold shape --and life to form controls the behavior of water drops High heat capacity cools/warms slowly relative to land aids in heat retention & transport minimizes extremes in temperature helps to maintain uniform body temps High latent heat of evaporation very important in heat/water transfer in atmosphere

Latent Heat and Changes of State Latent heat of fusion (or melting) Heat to form or melt ice (liquid to solid phase) 333 kJ/kg (80 calories/gram) Latent heat of vaporization (or precipitation) Heat to vaporize (boil) a liquid or condense liquid from a gas phase 2260 kJ/kg (540 calories/gram) Evaporation of water from the surface can occur at any temperature. However, it takes more energy to evaporate at low T than to boil off vapor once water reaches 100°C

Heat capacity and phase changes: ice (solid) water (liquid) vapor or steam (gas) Latent Heat Heat needed to change phase (from solid to liquid, liquid to gas, liquid to solid, etc.)

Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Heat input (J/kg or cal/gram) Temperature (°C) Liquid water Rock & Soil Pepsi Let’s measure Heat Capacity

Heat input (J/kg or cal/gram) Temperature (°C) Rock & Soil Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Liquid water Let’s measure Heat Capacity

Heat input (J/kg or cal/gram) Temperature (°C) Rock & Soil Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Liquid water Let’s measure Heat Capacity

Heat input (J/kg or cal/gram) Temperature (°C) Rock & Soil Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Liquid water Let’s measure Heat Capacity

Heat input (J/kg or cal/gram) Temperature (°C) Rock & Soil Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Liquid water Let’s measure Heat Capacity

Heat input (J/kg or cal/gram) Temperature (°C) Rock & Soil Heat Capacity Heat required to change the temperature (by 1 °) of a given mass Liquid water Let’s measure Heat Capacity The green line is longer than the yellow line! If we add the same amount of heat to two materials, the one with lower heat capacity will warm up more!

Today is the first in-class iClicker exercise for credit A)Full credit if you answer 60% or more of the questions B) Bonus points if you get the correct answer for 80% of more of the questions C) If there are 10 questions and you answer at least 6 of them you’ll get full credit (100%) D) If there are 10 questions and you answer at least 8 of them correctly you’ll get a 5% bonus (105%) E) All of the above (this is the correct answer, choose E!)

Heat capacity and phase changes: ice (solid) water (liquid) vapor or steam (gas) Heat input (cal/gram) Temperature (°C) Liquid water Ice Vapor Latent Heat Heat needed to change phase (from solid to liquid, liquid to gas, liquid to solid, etc.) Latent heat of vaporization or condensation 540cal/gm Latent heat of fusion or melting 80cal/gm Ice + liquid vapor+ liquid

Seawater is essentially an NaCl solution Average seawater salinity is 35 ppt (35 g/kg), but it varies from place to place Why the Sea is Salty 37 ppt 30 ppt Surface water salinity

Why the Sea is Salty

And over the eons of time, the sea has grown ever more bitter with the salt of the continents

Was the Chemistry of the Ancient Oceans the Same as Today? Time (billions of yrs) Ocean Salinity 35 0/00 Surface water salinity ?

Was the Chemistry of the Ancient Oceans the Same as Today? Time (billions of yrs) Ocean Salinity 35 0/00 Surface water salinity

Note the attraction of oppositely charged ends of water molecules for one another

Cl -, Na +, S0 4 -2, Mg +2, Ca +2, K + >99% of salt in sea water HC0 3 -2, Br -, Sr -2, B +2, F - (with these, 99.99%) Seawater is essentially an NaCl solution (saltwater)

All other elements occur at very low concentrations (ppm to ppb: to ) Seawater is essentially an NaCl solution Average seawater salinity is 35 ppt or 35 g/kg. Relative abundance of ions in seawater, in rank order: Cl, Na, SO 4, Mg, Ca, K (these make up >99% of the salt in seawater) HCO3, Br, Sr, B, F (with these >99.99% of the salt in seawater)

Charges must balance, therefore: Charge associated with cations: Na +, Mg +2, Ca +2, K + Must equal charge associated with anions: Cl -, SO 4 -2 Major ions in seawater keep “constant proportion,” regardless of salinity Except near river outlets (near coastal regions) Salinity (o/oo) ~1.81 x Chlorinity (o/oo)

But rivers are not the only important input And in soils

Ocean Chemistry is influenced by Erosion and Weathering of the land

For example, exchange of Magnesium (Mg) in seawater for Ca in ocean crust supplies excess Calcium Difference in chemical compositions between rivers and ocean --reflects sedimentation (precipitation) processes --other inputs/exchanges, such as basalt-seawater reactions at midocean ridges Rivers vs. Other Sources

Oceans: Chemical Inputs -rivers (weathering) -volcanic gases: HCl, SO 2, CO 2 -interaction of seawater with seafloor, e.g., hot basalt associated with Hydrothermal Circulation, this is a source of Ca and K Note: A volume of water equal to the entire ocean is circulated through seafloor material (crust) ~ every 10 m.y.

Ocean Chemistry is influenced by: A.water interacting with rocks (Earth’s crust) at the mid-ocean ridges B.Evaporation of seawater C.River water D.Erosion and weathering of the land E.All of the above.

Seawater is essentially an NaCl solution Average seawater salinity is 35 ppt (35 g/kg), but it varies from place to place Why the Sea is Salty 37 ppt 30 ppt Surface water salinity

We’ve already examined why water is a powerful Solvent, now let’s look at the whole picture Can we explain ocean chemistry using the inputs of rivers alone? ocean rivers atmosphere rock weathering

Outputs compete with Inputs to shape the chemistry of seawater Ocean Chemistry and the Geochemical Cycle The Ocean has Both Inputs and Outputs Outputs include: 1--sea salt aerosols 2--biogenic sediments (biological processes); deposited on ocean floor (CaCO 3, SiO 2 ) 3--inorganic sediments (precipitates, evaporites; adsorption) 4--interaction of seawater with hot basalt (Mg and SO 4 "sink”)

Outputs: Seawater Evaporation in isolated basins. These sediments (“evaporites”) provide a record of seawater chemistry

Salt from the Sea Dead Sea Salt, Evaporation! At work

The Grand Geochemical Cycle: Residence time The average time that a substance remains dissolved in seawater We call this the “residence time” of an element or substance where Input rate= average concentration in rivers (kg/km 3 ) x river discharge (km 3 /yr) Let’s consider: We will see how this works: first for water, then for total salt, and, finally, for some individual elements. These calculations give us insights into how the system works Residence Time (yrs.) = Total amount in seawater (kg) Input rate (kg/yr)

How long does it take to cycle ocean water through rivers and back again? Residence time of water in the ocean Volume = 1.4 x 10 9 km 3 River Influx = 3.7 x 10 5 km 3 /yr t = Volume / Influx 1.4 x 10 9 km x 10 5 km 3 t = 4000 years t =

The Grand Geochemical Cycle How much time to make the ocean salty? about 5 x grams of dissolved solids in ocean rivers bring in about 2.5 x gm dissolved solids per year --think about it! Should only take about 2 x 10 7 years (20 million yrs.) to bring oceans to present salinity --but we know oceans are 3.8 billion yrs. old Assuming: rivers have kept approx. same input through time oceans have kept approx. same composition through time This confirms that there must be output of material from ocean!!

Cl 80 million yrs. SO 4 9 million yrs. Na 60 million yrs. Ca 1 million yrs. Mg 10 million yrs. PO thousand yrs. Typical Element Residence Times The Grand Geochemical Cycle Don’t worry too much about absolute numbers, but be able to explain why Cl residence time is so much longer than, say, that of phosphate

The Grand Geochemical Cycle Residence time is inversely related to extent of involvement in chemical reactions in the ocean Na and Cl primarily precipitate as evaporite deposits (infrequent events over geologic history). Bio-inert Ca used by organisms to make CaCO 3 (calcium carbonate) skeletons PO 4 used in biological cycle (organic matter production)--this is a nutrient element. Biolimiting

Was the Chemistry of the Ancient Oceans the Same as Today? We can use ancient evaporite deposits to tell us how ocean chemistry changed through time (different sequence of minerals precipitated) We also can use the chemistry of “brine” inclusions in the evaporites to constrain elemental ratios of major elements in seawater through time. New data suggest that ocean chemistry has changed a bit through time. Perhaps this reflects changes in ocean basin spreading rates and cycling of seawater through hydrothermal systems! We can use ancient evaporite deposits to tell us how ocean chemistry changed through time (different sequence of minerals precipitated) We also can use the chemistry of “brine” inclusions in the evaporites to constrain elemental ratios of major elements in seawater through time. New data suggest that ocean chemistry has changed a bit through time. Perhaps this reflects changes in ocean basin spreading rates and cycling of seawater through hydrothermal systems! Time (billions of yrs) Ocean Salinity 35 0/00