Oceanography Exam #2

structure of the water molecule

• 2 hydrogen atoms

• 1 oxygen atom

shape “mickey mouse”

how is the water molecule held together?

strong covalent bonds — electrons shared between atoms

how is the electrical charge distributed in a water molecule? what is this structure called?

asymmetrical distribution of electrical charge — H end more positive, O end more negative

dipolar structure

what is responsible for the many properties of water?

dipolar structure of the water molecule & formation of hydrogen bonds between molecules

hydrogen bonds

relatively weak electrostatic forces between oppositely charged ends of adjacent water molecules

3 states of water

• solid (ice)

  • less dense crystalline structure

• liquid (water)

  • more dense than ice; surface tension

• gas (vapor)

  • high energy molecules w/ few h-bonds

properties of water

• occurs in 3 states

• high surface tension

• good solvent

  • dipolar structure weakens attraction between other molecules

• high heat capacity

  • absorbs and releases considerable amt of heat (sensible heat and latent heat) w/ little change in temperature

sensible heat

vibration of water molecules, the temperature measured with a thermometer

how is heat measured?

calories

1 cal = amt needed to raise temp of 1g water by 1deg Celsius

latent heat

the heat/energy required to change water phase without a change of temperature

extra head involved in phase change due to breaking or forming h-bonds

what is required to break hydrogen bonds when ice melts and when water evaporates? how much?

heat energy

ice melting — 80cal/g

water evaporating — 540cal/g

hydrologic cycle

(evaporation-precipitation) redistributes heat around the planet by cycling water due to evaporation and precipitation

a process of the troposphere

how does the earth stay habitable?

hydrologic cycle → heat removed from the ocean in one area and released into the atmosphere somewhere else keeps earth habitable and more evenly warmed

evaporation

latent heat removed from the ocean

condensation and precipitation

latent heat released to the atmosphere

sublimation

phase change from solid to vapor

deposition

phase change directly from vapor to solid

why are tropical cyclones “mother nature’s safety valve?”

redistribute excess heat out that builds up in the tropics and subtropics to the higher latitudes

substances dissolved in seawater

1. gases (like o2 and Co2)

2. nutrients (like nitrates, phosphates, trace elements, vitamins)

3. organic molecules

4. mineral salts (like Cl^-, Na⁺, SO₄²-, Mg²⁺)

salinity

total dissolved solids

average ocean salinity

35‰ (units = parts per thousand → 3.5%

how does ocean salinity vary depending on environmental factors?

• lower in areas of high precipitation (P>E) or high river runoff from the land

• higher in areas of high evaporation (E>P) → subtropics; desert

how many naturally occurring elements are dissolved in seawater?

all of them: 6 ions account for 99.4% of all dissolved solids in seawater (Cl^-, Na⁺, SO₄²-, Mg²⁺, Ca²⁺, and K⁺); Cl^- & Na⁺ account for ~85%

methods to measure salinity

• measure chlorinity by titration

• measure electrical conductivity using conductivity/salinometer

• evaporate a known volume of seawater and measure mass of salts (solids) left behind

where do the dissolved “salts” in seawater come from? (input)

1. chemical weathering of rocks, runoff from the land

2. volcanic emissions

3. hydrothermal activity on the seafloor (e.g. at spreading centers)

4. fluids generated at subduction zones/accretionary prisms (above trenches)

has the chemical composition of the ocean remained constant over time? why?

yes; because input = output

biogeochemical and geochemical cycles are very important in maintaining ocean chemistry steady state! important for the evolution of life

sink for “salts” (output)

1. biological recycling (skeletons & shells, plus biological productivity) marine sediments

2. burial in sediments

3. ionic exchange between superheated seawater & oceanic crust at the spreading centers

4. subduction (recycling of crust & sediments)

4 major types of marine sediments

1. terrigenous

2. abyssal red clay & authigenic deposits

3. calcareous ooze

4. siliceous

terrigenous sediments

(sand, mud) derived from the erosion & weathering of the land, transported to the sea by rivers, ice, and wind. masks other sediment types because of high accumulation rates

• continental margins — high accumulation rates of sand and mud (mask other sediment types); turbidity currents move sediment

• abyssal plains — slow accumulation of red clay; may be associated with authigenic iron-manganese (poly-metallic) nodules.

red clay

wind-blown dust & current transported clays

accumulates very slowly on the abyssal plains

funneled to deep sea with submarine canyons

calcareous ooze

derived from plankton with calcium carbonate shells (CaCO3) e.g. coccolithophorids and foraminifera

accumulates on bathymetric highs above the carbonate compensation depth/CCD (ridges, rises, flanks of volcanoes away from continental margins).

siliceous ooze

derived from plankton with siliceous hard parts (SiO2), e.g., diatoms and radiolarians.

Accumulates under areas of upwelling and high biological productivity (equator, around Antarctica and the Arctic)

turbidity currents

rip down submarine canyons creating huge submarine fans at base of continental slope; continental rise = thick wedge of sediments

authigenic deposits

precipitate directly from seawater under specific biochemical conditions (e.g. FeMn nodules)

hydrothermal activity at spreading centers “black smokers” → a major source of dissolved source of metal oxides

lower latitudes and solar radiation

tropical/subtropical areas receive a net gain of incoming solar radiation (insolation)

more solar radiation is received during daylight hours than is radiated back into space at night

high latitude and solar radiation

polar/subpolar regions experience net loss of mean annual insolation

experience months of total darkness or low sun angles → heat absorbed by the ocean and atmosphere is less than energy radiated back to space

how much redistribution of heat do the atmosphere and ocean share? due to what?

atmosphere — via hydrologic cycle: evaporation-precipitation (latent heat) and winds/weather) and ocean (via large ocean currents: subtropical gyres) share about equally in redistribution of heat from the low latitudes to the high latitudes

greenhouse effect

natural process where gases in Earth’s atmosphere trap heat from the sun, keeping the planet warm enough to support life/makes earth habitable for life

global warming. why?

magnitude of the warming and the rising rate of warming are of critical concern

due to ever increasing levels of anthropogenic greenhouse gas emissions

why does earth have seasons?

earth tilted at 23.5 degree angle relative to revolution around the sun

sun directly over tropic of cancer on N.H. summer solstice (earth tilted toward sun → more insolation)

sun directly over tropic of Capricorn on N.H. winter solstice (earth tilted away from sun → lower insolation)

equinox

occurs twice a year when everywhere on the planet receives 12 hours of daylight and 12 hours of darkness

fall and spring

what shape is earth’s orbit

nearly a circle; only slightly elliptical

how does the ocean transport heat? subtropical gyres?

by large surface currents

subtropical gyres are large circulation cells

• warm waters move poleward along western sides of ocean basins

• cool waters move equatorward along eastern sides of ocean basins

gulf stream

transports warm waters north and east

how does the atmosphere transport heat?

transports heat by way of hydrologic cycle

h-bonds broken during evaporation of water (latent heat removed from ocean 540 cal/g) → moisture rich air masses cool → condensation causes cloud formation and precipitation as h-bonds form (latent heat released to atmosphere)

highest noontime sun in Amherst (42.5 degN) at summer and winter solstice?

Highest noontime sun at summer solstice = 71deg above the horizon

highest noontime sun at winter solstice = 24deg

weather

day-to-day changes in the atmosphere

climate

seasonal progression of weather in a particular region and its year-to-year characteristics (including interannual variability)

relationship between atmospheric pressure and air masses?

low atmospheric = rising air masses

high = sinking air masses

prevailing winds. what directions do they blow?

Westerlies = west to east

Trade winds = east to west

polar easterlies

bands/zones on earth and relation to cloud formation

clouds = greater precipitation; P>E

• precipitation → air masses rising → low atmospheric pressure

alternating with other zones displaying less clouds and greater precipitation = greater evaporation; E>P

• evaporation → air masses sinking → high atmospheric pressure

what direction do hurricanes and typhoons travel and in what zones in the northern hemisphere? what causes this movement?

they move east to west in the tropics and then hook north and east as they move out

Coriolis effect — they come from east to west by the trade winds then hook around move west to east due to the westerlies

ITCZ (intertropical convergence zone)

where the winds come together and rise to form clouds in the tropics

marks the convergence of the NE trade winds and the SE trade winds

how many atmospheric circulation cells in each hemisphere? what are they? what move along the edges of the cells? how often do boundaries shift?

3 atmospheric circulation cells in each hemisphere defined by alternating low and high atmospheric pressure

1. polar cell

   1. high latitudes; polar easterlies

2. Ferrel cell

   1. mid latitudes; westerlies

3. hadley cell

   1. low latitudes; NE trades

fast moving jets move along the edges of the circulation cells

boundaries shift daily and seasonally

the polar vortex

a rotating mass of cold arctic air. polar jet stream separates cold polar air (polar easterlies) from warm subtropical and temperate air (westerlies)

is the jet stream a straight line?

no; the jet stream is wavy and dynamic; big southward dips called troughs and northward waves called ridges

Coriolis effect

the deflection of air masses, water masses, airplanes, or missiles due to the rotation of the earth underneath

direction of Coriolis effect for northern and southern hemisphere

to the right in the northern hemisphere; deflection to the left in the southern hemisphere

where is the Coriolis effect strongest, and where is it weaker? why?

strongest at the poles and diminishes toward the equator where it changes sign from right to left

due to differences in the velocity of the Earth’s spherical surface as it rotates in space

where do air masses rise, and where do they fall?

air masses rise near the equator (L) and sink in the sub tropics (H)

near surface air masses are drawn south toward the equator but due to the rotation of the Earth, these air masses are deflected to the right in the N. Hem. (left in the S. Hem.) giving rise to the NE Trade Winds (SE Trade Winds).

what direction do storms turn in the northern hemisphere vs the southern hemisphere?

northern hemisphere → counterclockwise

southern hemisphere → clockwise

Coriolis effect in relation to the equator

no Coriolis effect at equator bc that’s where it changes signs. bc of this the air masses just rise, so there are no swirly clouds like there are in the mid-latitudes, just tall puffy ones

ocean salinity in relation to region/latitude

higher ocean salinity in subtropics and lower salinity in tropics and temperate regions (mid latitudes)

natural climate variability

seasonality

1. tropical cyclones

2. extra-tropical cyclones

3. monsoons

interannual variability

• el nino southern oscillation (ENSO)

• ocean heat waves

  • more frequent and longer lasting

el nino southern oscillation (ENSO)

• triggered by a change in H to L pressure gradient across tropical pacific → affects the stregnth of the trade winds

• normally strong trade winds pine up warmer water in western pacific. trade winds slacken?

  • → warm pool slides east causing drought in SE Asia, heavy rain in Peru (and california), reduced upwelling off south america and affecting global climate patterns

• el nino yrs = low biological productivity

monsoons

causes by seasonal movement of ICTZ and seasonal reversal of the winds resulting in dry season and wet season in affected tropical regions

effects of continued global warming on weather

greater extremes

• increased precipitation in wet places and increased aridification — desertification — in dry places (deserts expanding)

  • west coast wildfires

ocean heat waves

becoming more frequent and warmer and have significant impact on marine ecosystems

rising surface temps breeding more intense hurricanes and typhoons

temp ranges depending on latitude

• polar (high latitudes) — cold to very cold

• temperate (mid-latitudes) — cool to warm

• tropics (low latitudes) — warm to very warm

what heats ocean surface. what does this create?

solar energy heats surface waters in low to mid latitudes; net solar gain in tropics and subtropics

creates warm less dense surface layer over very cold and dense deep waters

permanent thermocline

the depth interval through which temperature decreases rapidly with increasing water depth

the step from warm surface waters to cold deep waters; the intervals of change

how can you measure the permanent thermocline?

CTD deployments

measure conductivity (salinity); how well electricity travels through water depends on the amt of ions in it. travel faster? → more ions → 85% seawater NaCl

mixed layer

surface-most part of ocean where temperature is vertical; thickness can vary by season

depth of the mixed layer

a function of mixing (homogenization) of the warmed surface waters by the day-to-day winds and storms, waves and surface currents

presence of permanent thermocline by latitude

• polar waters (high latitudes) → very weak/no permanent thermocline

• temperate waters (mid latitudes) → permanent thermocline present, w/ seasonal thermocline

• tropical waters (low latitudes) → strong thermocline present

how is the world ocean structured? why?

well-stratified (layered) in the low-to-mid latitudes due to solar heating of surface waters and formation of permanent thermocline

• permanent thermocline separates warm (less dense) surface waters from icy cold (denser) deep waters

seawater density controlled by?

seawater density is a function of temperature and salinity

pycnocline

layer of water in the ocean where seawater density increases rapidly by depth

presence of pycnocline by latitude

• polar waters (high latitudes) → very weak/no permanent pycnocline

• temperate waters (mid latitudes) → pycnocline present

• tropical waters (low latitudes) → strong pycnocline

how does water become more dense?

cooling , sea-ice formation, evaporation

depth of the permanent thermocline?

100-1000 m deep. below 1000m is all icy cold

why are deep waters denser than surface waters?

• deep waters originate on the surface, they just sink

• they become more dense (in order to sink) by:

  • adding salt

  • cooling — the water molecules become more densely packed