Hydrological CycleHydrological CycleDissolved Gases/Ocean & Dissolved Gases/Ocean &

AtmosphereAtmosphere

Water budgetsWater budgets Water and heat intimately related Evaporation removes H2O and heat

– Latent heat of evaporation – heat released to atmosphere as vapor rises, cools, condenses and falls back to earth (rain or snow)

Amount of water on earth’s surface has remained relatively constant for billions of years so we can make a budget (see Fig.)

Reservoirs and fluxes– Reservoirs; a place where water resides; contains an average

amount over time; unit of mass or volume– Fluxes; water is always moving among reservoirs; volume per unit

time

Where is the waterWhere is the water Ocean is the primary reservoir for water on EarthOcean is the primary reservoir for water on Earth Small quantities on continents and in atmosphere Small quantities on continents and in atmosphere

can be considered to be in transit back t the oceancan be considered to be in transit back t the ocean

Hydrologic CycleHydrologic Cycle

Water cycles between oceans, atm, and land Water cycles between oceans, atm, and land – driven by solar energy– driven by solar energy

Bulk of water is in the oceansBulk of water is in the oceans Evaporation removes water from the oceansEvaporation removes water from the oceans

– FW phase is highly dependent on atm as a conduitFW phase is highly dependent on atm as a conduit

Water residence time in the oceans ~4000 yrWater residence time in the oceans ~4000 yr Large exchanges between land/oceans and Large exchanges between land/oceans and

atm – evaporation and precipitationatm – evaporation and precipitation

Fig. 4-24a

Hydrological Cycle

ReservoirsReservoirs

OceanOcean Glaciers and iceGlaciers and ice Groundwater & soilGroundwater & soil Rivers & lakesRivers & lakes AtmosphereAtmosphere

FluxesFluxes

Evaporation (from oceans and lakes)Evaporation (from oceans and lakes) Precipitation (over land and sea)Precipitation (over land and sea) Wind transport (from sea to land)Wind transport (from sea to land) Condensation (clouds and fog)Condensation (clouds and fog) Sublimation (from snow on land)Sublimation (from snow on land) Runoff (rivers, etc)Runoff (rivers, etc) Underground flowUnderground flow

Fig. 4-24b

Small netSmall nettransporttransport

(balanced by (balanced by runoff)runoff)

BalanceBalance

Overall balanceOverall balance Locally, may be net evaporation over ocean Locally, may be net evaporation over ocean

or net precipitation over land (but that would or net precipitation over land (but that would run of into the ocean to balance things run of into the ocean to balance things globally)globally)

Properties of climate zones are determined Properties of climate zones are determined mostly by earth’s surface temperature and mostly by earth’s surface temperature and evaporation/precipitation ratiosevaporation/precipitation ratios

Equatorial regionsEquatorial regions– Hot, moist rain forests; ppt >> evapHot, moist rain forests; ppt >> evap

Subtropical desertsSubtropical deserts– Hot, dry; evap >> pptHot, dry; evap >> ppt

Temperate zonesTemperate zones– Cool, moist; ppt >> evapCool, moist; ppt >> evap

Polar areasPolar areas– Cold, dry; evap & freezing >> pptCold, dry; evap & freezing >> ppt

Residence timeResidence time

Time water (or anything else) spends in any one Time water (or anything else) spends in any one reservoir on average.reservoir on average.– Units of time [volume/(volume/time)] or volume/fluxUnits of time [volume/(volume/time)] or volume/flux

Larger reservoirs often have longer residence Larger reservoirs often have longer residence timestimes– Residence time in the ocean is longResidence time in the ocean is long– Implications for dumping garbage in the ocean!Implications for dumping garbage in the ocean!

But, residence times vary depending on fluxesBut, residence times vary depending on fluxes– Implications for water quality and planningImplications for water quality and planning

Ice is second largest reservoir for waterIce is second largest reservoir for water

High altitudes on major mountain chainsHigh altitudes on major mountain chains High latitudes, e.g., Greenland and Antarctica are High latitudes, e.g., Greenland and Antarctica are

capped by glaciers. Antarctica is surrounded by ice. capped by glaciers. Antarctica is surrounded by ice. Arctic always ice-covered. Arctic always ice-covered.

10% of earth’s surface covered by ice (freshwater).10% of earth’s surface covered by ice (freshwater). Life cycle of a glacier – accumulation of snow, Life cycle of a glacier – accumulation of snow,

compaction, “flow” down slope under their own compaction, “flow” down slope under their own weight, melting and evaporationweight, melting and evaporation

Ice that makes it to sea can break off and form Ice that makes it to sea can break off and form icebergs in a process called calving.icebergs in a process called calving.

Ice-covered continentsIce-covered continents

Ice cap extends over edge of landIce cap extends over edge of land Breaks off to form icebergsBreaks off to form icebergs Largest iceberg ever found was in the Ross Sea Largest iceberg ever found was in the Ross Sea

(near Antarctica) and measured 100 by 350 km (near Antarctica) and measured 100 by 350 km (twice the size of Connecticut).(twice the size of Connecticut).

Properties of waterProperties of water

High heat capacityHigh heat capacity High dissolving powerHigh dissolving power Exists in all 3 phases at Earth surface conditionsExists in all 3 phases at Earth surface conditions Ice floats in waterIce floats in water

WaterWater Unique properties – important for understanding Unique properties – important for understanding

interaction between ocean & atmosphereinteraction between ocean & atmosphere– ClimateClimate

Dissolved constituents can affect water’s Dissolved constituents can affect water’s propertiesproperties

What is WaterWhat is Water HH22OO

Covalent & hydrogen bondingCovalent & hydrogen bonding Water as a solventWater as a solvent DensityDensity Heat Capacity and specific heatHeat Capacity and specific heat Salinity (next time)Salinity (next time)

A covalent bond exists when two electrons are shared by two non-metallic atoms. Dipolar.

**Electron density higher around oxygen, giving that end a partial negative charge.

•Oxygen has 6 electrons, and wants 2 more electrons for stability. •Hydrogen has 1 electron and wants 1 more electron for stability.

104.5°

Electrons and “charge” not distributed evenly so moleculebecomes polar.

Hydrogen bond is a weak bond formed when a charged part of a molecule having polar covalent bonds forms an electrostatic (charge, as in positive

attracted to negative) interaction with a substance of opposite charge. The weak bonds are easily and rapidly formed and broken under normal biological conditions. They are extremely important in biological systems and Their

presence explains many of the properties of water.

H-bonding impartsadhesion and cohesion of water.

Creates surface tensionand wetting ability

Water cohesion (imparted by the H-bonding between water Water cohesion (imparted by the H-bonding between water molecules) causes surface tension & capillary action. molecules) causes surface tension & capillary action. Adhesion allows water molecules to “stick” to other things or Adhesion allows water molecules to “stick” to other things or get wet.get wet.

Water is a powerful solvent

Ethanol dissolveswell in water becauseit is polar.

On the other hand, oil is repelled by water because it is non-polar, and thus does not dissolve well in water.

Ionic molecules dissolve well in water.

Water & heatWater & heat

Temperature – how rapidly molecules are vibratingTemperature – how rapidly molecules are vibrating– Response to addition and removal of heatResponse to addition and removal of heat

Heat capacityHeat capacity– Amount of heat required to change the temperature of a Amount of heat required to change the temperature of a

substance (raise or lower)substance (raise or lower)– Calorie is the amount of heat required to raise Calorie is the amount of heat required to raise

temperature of 1 gram water by 1 temperature of 1 gram water by 1 ooCC– Heat capacity of water is among the highest of all known Heat capacity of water is among the highest of all known

substancessubstances– This high heat capacity is a result of water’s structure This high heat capacity is a result of water’s structure

(H-bonding)(H-bonding)

Many metals have low heat capacities(change temperaturewith small changesin heat content)

Significance of heat capacitySignificance of heat capacity

Water is a good buffer for heatWater is a good buffer for heat Land temperatures change more easily and Land temperatures change more easily and

rapidly than waterrapidly than water– Compare daily changes on land and in the seaCompare daily changes on land and in the sea– Compare land near the coast with inlandCompare land near the coast with inland

Heat transferHeat transfer

Latent heatLatent heat

Latent heat does not cause temperature Latent heat does not cause temperature changechange

Much higher for vaporization than for fusionMuch higher for vaporization than for fusion Must break H bonds for vaporizationMust break H bonds for vaporization Evaporation has a cooling effect because Evaporation has a cooling effect because

heat is removed from waterheat is removed from water Evaporation is a huge source of heat flow Evaporation is a huge source of heat flow

between the atmosphere and the oceanbetween the atmosphere and the ocean

4 J ≈ 1 calories (kg)

Sensible heat versus latent heat

Water and densityWater and density

Density is mass per unit volumeDensity is mass per unit volume Density curve is NOT linearDensity curve is NOT linear

– Normally, as you heat something, molecules move Normally, as you heat something, molecules move faster and then density decreases and vice versafaster and then density decreases and vice versa

Density and state (liquid, gas, solid)Density and state (liquid, gas, solid) Solid ice is less dense than liquid waterSolid ice is less dense than liquid water

– Changes bond angle between oxygen and hydrogen Changes bond angle between oxygen and hydrogen atoms in water (from 104.5 to 109atoms in water (from 104.5 to 109oo) allowing lattice ) allowing lattice structurestructure

Maximum density of water is about 4oC

Normal substances

Water3-D

Implications of densityImplications of density

Ice floatsIce floats Density differences drive thermohaline Density differences drive thermohaline

circulationcirculation Salt increases density of water (fresh water Salt increases density of water (fresh water

should float on salty water)should float on salty water) Water column stable when density stratified Water column stable when density stratified

(less dense water rises and denser water (less dense water rises and denser water sinks)sinks)

Salt and properties of waterSalt and properties of water

Salt water is 96.5% water and 3.5% Salt water is 96.5% water and 3.5% dissolved solids and gasesdissolved solids and gases

Salt changes water’s densitySalt changes water’s density Salt changes water’s freezing behaviorSalt changes water’s freezing behavior Maximum density of seawater is about –2Maximum density of seawater is about –2ooCC Why does ice that forms from seawater still Why does ice that forms from seawater still

float? (salts don’t freeze!)float? (salts don’t freeze!) We’ll talk more about salinity next time.We’ll talk more about salinity next time.

Properties of waterProperties of water

High heat capacity and dissolving powerHigh heat capacity and dissolving power– Storage and transport of heatStorage and transport of heat– Transport of massTransport of mass

Water can exist in all three phases on EarthWater can exist in all three phases on Earth– Water involved in biogeochemical processesWater involved in biogeochemical processes

Hydrogen bonding – max density at 4 deg CHydrogen bonding – max density at 4 deg C Ice is less dense than waterIce is less dense than water Water transports heat (energy and matter) Water transports heat (energy and matter)

among Earth’s system components.among Earth’s system components.

Heat transportHeat transport

Along with circulation, water cycle Along with circulation, water cycle redistributes heatredistributes heat

Weather and climate are the response of the Weather and climate are the response of the atm to unequal latitudnal distribution of atm to unequal latitudnal distribution of energyenergy

Fig. 5-15 Poleward heat transport in the Northern Hemisphere.

Remember

Annual changes in air temperature depending on air movement

Ocean breezes buffer heat by causingevaporation that takes up heat

Water Vapor – High heat loss in tropics due to evaporation

Annual changes in sea ice in Antarctica

Over 18,000 km3 of polar ice thaws and refreezes each year -- high seasonal latent heat movement

Land shows greater extremes in temperature near polesLand shows greater extremes in temperature near poles

Ocean and air currentsOcean and air currents

Ocean and air currents result from unequal solar Ocean and air currents result from unequal solar heating (more on these later)heating (more on these later)

Transport heats from equator to polesTransport heats from equator to poles Gulf stream is about 10Gulf stream is about 10ooC warmer than water C warmer than water

moving south to replace itmoving south to replace it Half the solar radiation entering the water results in Half the solar radiation entering the water results in

evaporationevaporation Condensation is usually removed from where Condensation is usually removed from where

evaporation is occurringevaporation is occurring Air moves about 2/3 of heat and ocean currents the Air moves about 2/3 of heat and ocean currents the

other 1/3.other 1/3.

Global climatesGlobal climates

Water cycle at regional scalesWater cycle at regional scales Big differences regionallyBig differences regionally Evaporation higher in tropics due to radiation imbalance – evap Evaporation higher in tropics due to radiation imbalance – evap

> ppt> ppt Water vapor and heat transport equator to polesWater vapor and heat transport equator to poles Energy transportEnergy transport

– Ocean currents move sensible heatOcean currents move sensible heat Oceans a heat reservoirOceans a heat reservoir Warm surface currents flow toward poles carrying heatWarm surface currents flow toward poles carrying heat

– Atm moves latent heat and sensible heatAtm moves latent heat and sensible heat Change of phase requires heatChange of phase requires heat Energy driving annual evap cycle ~23% of annual solar inputEnergy driving annual evap cycle ~23% of annual solar input

Sources of water for ppt at a Sources of water for ppt at a regional scaleregional scale

Also varyAlso vary Rainfall over oceans comes from oceansRainfall over oceans comes from oceans Rainfall over coastal areas largely from oceansRainfall over coastal areas largely from oceans Tropical rainforests rainfall derived largely from Tropical rainforests rainfall derived largely from

evapotranspiration (~75%)evapotranspiration (~75%)– Loss of water through plantsLoss of water through plants

Deforestation decreases regional rainforest water cycleDeforestation decreases regional rainforest water cycle– Decreases evap and pptDecreases evap and ppt– Loss of soil moisture which increases tempLoss of soil moisture which increases temp

Changes in hydrological cycle Changes in hydrological cycle over timeover time

Driven by changes in sea levelDriven by changes in sea level Glacial cycles increase amount of water stored in Glacial cycles increase amount of water stored in

continental glacierscontinental glaciers Changes in tectonic activityChanges in tectonic activity

– Increase/decrease of sea floor spreadingIncrease/decrease of sea floor spreading– Change in volume of oceans/cooling rate of crustChange in volume of oceans/cooling rate of crust– Increase CO2 flux from mantle/crustIncrease CO2 flux from mantle/crust– Change in greenhouse warming/coolingChange in greenhouse warming/cooling

NASA reconstruction of the Earth at the height of the last ice age

NASA reconstruction of a fully unglaciated Earth

ImplicationsImplications

Global warmingGlobal warming– More vigorous hydrologic cycle?More vigorous hydrologic cycle?– Freshening of N Atlantic and higher salinity in tropics?Freshening of N Atlantic and higher salinity in tropics?

Thermohaline circulation – shut down Thermohaline circulation – shut down conveyer belt?conveyer belt?

Now let’s think about the oceanNow let’s think about the ocean

Distribution of temperature and heat with Distribution of temperature and heat with latitudelatitude

Distribution of temperature and heat with Distribution of temperature and heat with depthdepth

Thermostatic effectsThermostatic effects

Ice and vapor - distributionsIce and vapor - distributions Water and air movementWater and air movement

– Because of the higher latent heat of Because of the higher latent heat of vaporization, atmosphere transfers more heat vaporization, atmosphere transfers more heat per unit mass than liquid water.per unit mass than liquid water.