atoc 182 midterm exam

what is ocean topography

the study of the ocean floor

Mercator Projection Map

flat representation of the earth

molliweide projection map

round representation of the earth

what is the earth's axis of rotation?

23.5 degrees

latitude

Distance north or south of the equator

parallels

lines of latitude; imaginary lines parallel to the equator

longitude

Distance east or west of the standard meridian, measured in degrees

where is the standard meridian

Greenwich, England (0 degrees E or W)

meridians

intersection at earth's surface of a plane perpendicular to the equatorial plane and passing through earth's axis of rotation

what is the ocean's max depth

~8km

what is the average depth of the ocean

3-4km

what is the radius of the earth

6378 km

what are the layers of the earth

core (inner and outer), lower mantle, asthenosphere, lithosphere (comprises of oceanic and continental crusts)

explain what the earth being density stratified means

gravity sorts components by density "heaviness". densest components are closer to the center

Explain the continental drift theory

pangea and panthalassa (the ocean around it)- earth used to contain one super continent. over time, the continents slowly drifted away from one another and are still drifting away.

explain seafloor spreading theory

- new seafloor develops at mid ocean ridges (divergent plate boundaries) then spreads away from center

- the material forming the new sea floor comes from the asthenosphere in the form of magma

- cools down and gets denser

- seafloor gets deeper

- sediments accumulate

- continents are pushed aside likewise

- this theory explains why mid-ocean ridges are a heat source

How many lithospheric plates are there?

12

Explain the 3 plate Boundaries

- divergent: 2 plates move apart from each other

- convergent: 2 plates move towards each other and interact

- transverse: 2 plates slide laterally past each other

what happens at convergence zones

- ocean continent convergence zones: gives rise to subduction zones- ocean crust is denser and sinks below continental crust. this causes volcanoes and earthquakes

- continent-continent convergence: forms mountains

- ocean-oceann convergence forms deep trenches and island arcs in subduction zones (exmaple: Japan)

what is a continental margin

the submerged outer edge of a continent (continental shelf, continental slope, continental rise)

what is an ocean basin

The seafloor beyond the continental margin (abyssal plains, ridges, trenches, island arcs, ect)

what is the distribution of free water on earth

ocean: 97%

ice caps (greenland, antartica, glaciers): 2%

rivers, lakes, wetlands, groundwater: < 1 %

describe the hydrological cycle

water cycles continuously. this is powered by solar radiation. the average residence time of water in the ocean is 4100 years but only 9 days in the atmosphere

describe the properties of water

- cohesion: strong molecule-molecule connection because of hydrogen bonds. this gives H2O a high surface tension

- dissolution: is good at dissolving other molecules/compound into its elements (example salt)

- Adhesion: water sticks to other molecules well because of H bonds

- cohesion + adhesion = capillary action

heat vs temp

heat: energy produced by atoms or molecules moving

- action

- measured in joules

temperature: the response of an object to the removal of heat energy

bathtub = more heat

candle = more temperature

Explain heat capacity.

the measure of the heat required to raise the temp of 1 gram of a substance by 1 degrees Celsius. different substances have different heat capacities. water has a large heat capacity which means that it can absorb/release large amount of heat while changing little in temp

what is thermal inertia

Tendency of a substance to resist change in temperature with the gain or loss of heat energy.

- the ocean cools slower than the land because its thermal inertia is larger

- the ocean stores large amounts of heat during the day and released it at night

- the ocean reduces the daily and seasonal swings of temp on earth

what is salinity

a measure of the dissolved solids in seawater, usually expressed in g/kg or parts per thousand (0/00) by weight

what is seawater's salinity?

35 0/00, 3.5% of seawater contains dissolved substances, 3.5 grams of solid salt

- however salinity varies across the ocean from 33 0/00 to 37 0/00

what influences seawater's salinity?

evaporation, precipitation and fresh water runoffs from the continents

what is the relationship between dissolution of gases and temperature

dissolution of gases increases with cold temperature

what are the main dissolved gases in the ocean?

N, O, C

what is water's pH

7.8 (slightly alkaline)

sea water's density

- has a greater density than fresh water

list and describe the factors that effect density

- density decreases as temperature increases

- density increases with salinity

- density increases with pressure (deep depths)

what temperature does seawater freeze at

-2 degrees celsius

what is sensible heat

heat exchanged accompanied by a change in temp. is detectable by a thermometer

what is latent heat

heat exchanged without a change in temperature (a change in state)

latent heat of fusion

heat removed from a liquid during freezing (or added to a solid during thawing) that produces a change in state but not a change in temp

how much of the ocean is covered by ice at all times?

~15%

every year, how much of the ocean evaporated

the top 1m of the ocean

what is light

a form of electromagnetic radiation that travels as waves through space, air and water

what is reflection

the change in direction of light at an interface between 2 different media

- light is reflected by the clouds and sea surface

what is scattering

the dispersion (or "bounce") of light waves when they strike particles suspended in water or air

- light is scattered/absorbed by atmospheric gases and particles

what is light absorption

light energy into heat

- in the ocean, water rapidly absorbs all light. the top mete3rs of the ocean absorb nearly everything

- the energy of some colours of light is absorbed nearer to the surface that others

- violet, green and blue wavelengths are able to travel deeper down into the water column

different zones in the ocean column

photic zone: where light is visible (top 50 m photosynthesis is able to happen, until up to 600 m light is found). most of the ocean's life is here

aphotic zone

no light is here. deep, not much marine life

sound

is a mechanical wave. a form of energy transmitted by rapid pressure changes in an elastic medium (gas, solid, liquid)

how does sound work in the ocean

- sound intensity decreases as it travels through the ocean because of spreading, scattering and absorption

- unlike light, sound travels through water very efficiently

- average speed is 1500m/s

- the speed of sound increases with temp and pressure (this creates competition between the 2)

- minimum sound velocity found at ~1000 m

what is refraction

bending of light and sound waves through as they move through different optical or acoustal densities. due to the wave not travelling at the same speed in different media or same media of ≠ densities

SOFAR layer

layer of minimum sound velocity where sound transmission over long distances is actually quite efficient due to refraction

SONAR

(sound navigation and ranging)

Active Sonar: sends short pulses (pings) of high frequency sounds and analyzes the returning echoes to gain info of geological, biological or military importance

echo sounder: used to determine the depth of the water

What is the cryosphere?

the frozen water on the surface of the earth

the saltier the water the ___ the freezing point

lower

brine

droplets of highly saline water. formed due to salt accumulation in small pockets as ice crystals form

brine rejection

the process of brine being rejected back into the ocean

- raises the salinity of the near surface water, increasing density

- over time, brine drains out so sea ice salinity decreases

early stages of sea ice growth: frazil

small needle like ice crystals, typically 3 to 4 mm in diameter, suspended in water

→ Calm ocean: frazil crystals develop into smooth sheets of sea ice

→ Rough ocean: frazil crystals accumulate into slushy circular disks, called pancakes

interactions between sea ice sheets: rafting

currents or winds push around thin ice so they slide over each other

interactions between sea ice sheets: ridging

sea ice is pushed around into piles that then form small mountains above the sea ice surface

new ice

less than 10cm thick

young ice

10-30 cm thick

first year ice

thicker than 30cm but has not survived a summer melt season

multi year ice

Ice that persists over at least one complete summer melt season

leads

long, linear areas of open water ranging from a few meters to over a kilometer in width, and tens of kilometers long. they develop as ice diverges

Polynyas

irregularly shaped areas of persistent open water

melt ponds

pools of melted snow and ice on the sea ice surface created during the summer melt

What is thermodynamics?

process that reflects the growth and melt of sea ice

albedo

a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy

- value of 0 means that the surface is a perfect absorber

- value of 1 means that the surface is a perfect reflector

- sea ice has high albedo (0.5 to 0.7)

- the ocean is almost a perfect absorber because it has an albedo of 0.06

Describe the ice-albedo feedback

increases in temperature-> sea ice melts revealing pockets of sea water -> sea water has a lower albedo (level of reflectance is reduced)-> increased absorption of solar radiation-> increases in temperature

seasonal cycle of sea ice

- autumn: ocean begins to freeze and sea ice grows

- winter: sea ice begins to growth and gets thicker

- spring: sea ice begins to melt

- summer: sea ice completely melted

fast ice

sea ice that is immobile and anchored to the shore or ocean bottom

what are the principle forces acting on sea ice

- wind

- ocean currents

- Coriolis force

- internal ice stress

- earth tilt

describe the movement of sea ice in the artic

→ Sea ice trapped in the Beaufort Gyre may circulate around the Arctic for several years

→ Sea ice trapped in the Transpolar Drift Stream generally leaves the Arctic through the Atlantic in one to two years

describe the movement of sea ice in the Antartic

- sea ice gradually moves to the northern edge after it is formed

- moves in a clockwise direction around Antartica

how does sea ice play a role on the climate?

- on the global temperature: sea ice absorbs less solar energy due to its high albedo, therefore it keeps the surface cooler

- on global ocean circulation: dense waters from sea ice affect global ocean circulation

- on gas exchange: sea ice acts as a lid on the ocean's surface which prevents gas exchange (ex. CO2)

antartic vs artic sea ice

arctic is a frozen ocean Antarctic is a continent surrounded by ocean. Antarctic: 98% of the continent covered by ice, 90% of global freshwater content

- artic has thicker sea ice than the Antarctic

- Antarctic essentially all marine life and arctic essentially all terrestrial life

what are the recent trends in the sea ice in the artic and the Antarctic

overall trend in a decline in sea ice

- arctic: fast decline in sea ice in summer/fall that has accelerated in late 1990s

- Antarctic: only a strong collapse in the past 3 years

how do scientists study sea ice

Observations through field camps, drifting buoys, automated weather stations, cruises with icebreakers, satellites*

what do satellite observations do

provide a continuous, nearly complete record of sea ice cover (since 1979). temp, roughness, thickness of sea ice can be derived from satellite obervations

how do satellites work

they observe the microwaves emitted from sea ice. observations are processed into pixels 25km x 25km big. scientists look at pixels to see how much sea ice coverage there is in one region (concentration). they also use laser/radar beams to detect sea ice.

how many oceans are there? what are their names?

5 oceans if including the Southern Ocean. Atlantic, Pacific, Indian, Arctic

list and describe the 3 density zones in the water column

- mixed layer: top layer of the ocean. temperature and salinity are relatively constant with depth (because well "mixed"). note that the depth of the mixed layer varies with space and time

- pycnocline: middle zone of the ocean where density increases rapidly with depth

- deep zone: below the pycnocline. little change in density with depth. contains around 80% of the ocean's water

thermocline

the layer in the ocean where temperature decreases rapidly with depth (except for in the arctic where it increases with depth)

halocline

the layer in the ocean where salinity increases rapidly with depth

differences in stratification across latitudes

- tropical regions: strong thermocline and halocline, hence strong stratification. in tropical regions, temp is going to explain most of the changes we see

- temperate regions: weak to strong thermocline (depends of the seasons), hence moderate stratification. in temperate regions, temp plays less of a role in determining stratification

- polar regions: thermocline almost absent and moderate halocline, hence weak stratification. in polar regions, salinity is all what determines stratification

stratification

how different layers are. mixing is the breakdown of stratification. example: oil and water. if an ocean has a strong pycnocline then it has strong stratification. weak stratification (waters being easy to mix) means that rain, gases from atmosphere, etc can descend down the water column easier

what is density a function of

temperature, salinity and pressure

how is temperature in the ocean often measured

with sensors using thermistors- resistance varies with temperature

how is salinity often measured

by measuring how well electricity travels through the water (conductivity). the more salt dissolved in the water, the higher the conductivity

explain the CTD probe and rosette

CTD stands for conductivity, temp and depth. is an acquisition of electronics placed in a pressure-protected case connected to a variety of sensors.

a rosette is a metal frame bolding water-sampling bottles.

the CTD is often attached to the Rosette

niskin bottles

bottles opened at both ends used to collect water samples. bottle closed by a "messenger" at a given depth

autonomous floats- Argo floats

drift with currents and measures temp, salinity and pressure. can stay in the ocean for several years, anywhere from the surface to 2km deep. Send profiles by satellite to a data treatment center upon arrival at the surface

autonomous floats- gliders

robotic underwater vehicles which are telecommanded. sampling water up to 1500 m depth. Equipped with a GPS that gives their position when they are on the surface. Can measure temperature, salinity, oxygen, chlorophyll, etc

autonomous floats: sail drones

- Wind-powered unmanned surface vehicles sampling at the surface of the ocean

- Carry a suite of science-grade sensors to collect meteorological and oceanographic data

- Designed for long-term ocean deployments, up to 12 months

- Powered exclusively by the wind for propulsion and solar energy to power the onboard instruments

animal-borne instruments

seals and turtles are equipped with conductivity-temperature-depth sensors (glued to their forehead). Data are transmitted through satellite-relay data loggers when seals pop up at the surface

satellite observations

- surface temp given by infrared sensors

- sea salinity measured by microwave emission

- disadvantage: only gives surface info

characteristics of the Atlantic Ocean

- second largest ocean

- north atlantic is the most studied ocean in the world

- Saltiest of the major oceans (influence of Mediterranean Sea, evaporation and bridge with Pacific)

- Formation of dense waters in the North Atlantic (important for global thermohaline circulation)

- Equatorial Counter Current separates the North from the South Atlantic

- Gulf Stream: transport warm waters to the North

- Brazil Current: transport warm waters to the South

characteristics of the arctic ocean

- smallest and shallowest

- enclosed by land

- Large part of the Arctic Ocean covered with sea ice in Winter → large seasonal variability

- Salinity is the lowest on average of the five major oceans (due to low evaporation, river inflow)

- Low temperature at the surface, higher temperature at the subsurface

- Transpolar Current: dominant current transporting large volumes of freshwater

- Beaufort Gyre: huge circular current driven by strong winds

- North Atlantic Current : transport warm, more salty surface water from the Atlantic into the Arctic

characteristics of the pacific ocean

- Most extensive (12,000 km) and deepest (4,200 m on average) of all the oceans (40% of global ocean)

- Connected to the Arctic Ocean through the narrow (85 km) and shallow (55 m) Bering Strait

- Largely open to the south to the Southern Ocean

- Connected with the Indian Ocean through the Indonesian Sea

- High temperature in the western Pacific and low temperatures in the eastern Pacific

- Salinity is lower in the North Pacific than in the North Atlantic (more precipitation and fresh water transfer from other regions)

- No formation of dense water (due to lower salinity, hence more stratification)

- Intense exchanges with the atmosphere in the equatorial zone

- Equatorial Counter Current separates the North from the South Pacific

- Kuroshio: intense warm western boundary current

- Alaska and California Currents: cold coastal currents

characteristics of the Indian Ocean

- Highest ocean surface temperatures on the planet (along with the western Pacific)

- Bay of Bengal: low salinity (due to fresh-water inflows from large rivers and precipitation)

- Arabian Sea: high salinity (due to strong evaporation)

- Strongest climatic seasonal variability of the planet

- Leeuwin Current: warm south flowing Eastern boundary current (unique)

- Agulhas Current: warm western boundary current