Oceanography Flashcards
what are some statistics about the global ocean?
> 97.5% of water on or near the Earth lies in ocean
- southern hemisphere = 81% ocean
- northern hemisphere = 61% ocean
- the largest feature is the pacific ocean
average depth - 4,000 - 5,000 m
average temp = 3.9degrees C
average salinity = 34,48 %o (parts per 1000)
what is phytoplankton?
> the first link between the physicl and the biological in the ocean
play a key role in the marine ecosystem
just like plants on land phytoplankton require
- light, water, carbon dioxide and nutrients to grow
Diameter concentration - 1000s to 1,000,000 per millilitre
global biomass -
how do we map and study the ocean floor?
> the mapping and study of ocean floor contours is called bathymetry
how did early scientists study the ocean floor?
> early bathymetric studies used a weighted line to measure the depth of the ocean floor
what are some advancements in Bathymetry study?
> echo sounding
multibeam systems
satellite Altimetry
LIDAR ( light detection and ranging)
What is echo sounding?
> method to measure seafloor depth using powerful sound pulses
- pulses of sound energy, or “pings”, spread out in a narrow cone as they travel from the ship
when depth is great, the sounds reflects from a large area of seabed
- measures over deep depressions often inaccurate
- because the first sound of the returning echo is used to sense depth
what is the multibeam system?
> provide more accurate measurements
collect data from as many as 121 beams to measure contours of ocean floor
cover 120 deg arc @ right angles to direction of travel, ping sent every 10 secs
measure swath at bottom ~ 3.4x as wide as water is deep
What is satellite altimetry?
> measures the sea surface height from orbit
- bounce 1,000 pulses of radar energy off ocean surface every second
measures sea surface levels accurately (~2.5cm)
shows sea surface disortions
how does satellite altimetry measure sea surface distortions?
> distortion above a seabed feature occurs when extra gravitational attraction “pulls” water toward it from the sides, forming a mound over the water itself
2m or so mound
other influences are wind, currents , tides
what is the bathymetry of the ocean floor?
> varies with location
1/2 of the Earth’s solid surface is at least 3,000 meters below sea level
average depth of the ocean is 3800m greater than the average elevation of the continents 840m
how is the ocean floor classified?
Continental Margins
- the submerged outer edge of a continent
Ocean Basin
- the deep seafloor beyond the continental margin
what are the two types of continental margins?
> passive margins
- face the edges of diverging tectonic plates
- little volcanic or earthquake activity associated
- atlantic-type
active margins
- located near the edges of converging tectonic plates
- sites of volcanic and earthquake activity
- pacific-type
continental margins - are they passive or active?
> facing edges of diverging plates are PASSIVE MARGINS
> near edges of converging plates (or where plates are spilling past eachother) are ACTIVE MARGINS
what can earthquakes cause?
Tsunamis
What is a tsunami?
> generated by vertical movement of earth along faults
- are seismic waves
caused by water displacement
are long-wavelength, progressive waves caused by the rapid displacement of ocean water
move at high speed - due to extremely long wavelengths
200m between the peaks of each wave.
what are the distinct components of the continental margins?
1) With a vertical exaggeration 50:1
>continental shelf = shallow, submerged edge of continent
> continental slope = transition between continental shelf and deep-ocean floor
> shelf break = abrupt transition from continental shelf to continental slope (200m)
> continental rise = accumulated sediment at base of continental slope
2) no vertical exaggeration
> depth steadily decreases to mean of 4000m
what are the components of a x-section from a typical ocean basin flanked by PASSIVE continental margins? (atlantic)
> Continental margin
- submerged outer edge of a continent
Ocean basin
- deep-sea floor beyond the continental margin
oceanic ridges
- where new sea floor develops e.g., mid atlantic ridge
*note transition between thick, less dense granite rock of continents and thinner, denser basalt of deep-sea floor
how is the continental shelf impacted by changing sea levels? ON GRAPH
> rise and fall of sea level due largely to periods of increased and decreased glaciation
- currently: rapid change due to climate change.
a) a low stand of -125m @ climax of last ice age ~18,000 yrs ago
b) a high stand of +6m during last interglacial period ~120,000 yrs ago
c) shows present sea level in accelerating period of global warming - these changes in sea level over last 250,00 years as traced by data from ocean-floor cores
discuss continental shelves in relation to the sea levels of the past and the future
> SE coast of USA 18,000 years ago, during the last ice age, florida is much greater in size in the western edge
the position of sloping SE coast has been as much as 200km seaward from the present shoreline, leaving much of the continental shelf exposed
as the ocean expands and polar ice caps melt due to global warming, sea level could easily rise 6m, driving the coast inland as much as 250km
what is the topology of deep-ocean basins ?
> it differs from that of the continental margin
some features are:
- Oceanic Ridges
- Trenches
- hydrothermal Vents
- Abyssal plains
- Seamounts - important, birds focus around these
what is an oceanic ridge? refer to map
> a mountainous chain of young, basaltic rock at an actively-spreading centre of the ocean
the oceanic ridge system stretches 65,000km around Earth
East pacific rise typically spreads ~6x faster than mid-Atlantic rise
What are trenches? refer to map
> form in subduction zones
are arc-shaped depressions in the ocean floor caused by the subduction of a converging ocean plate
mostly around the edges of the active Pacific
are the deepest places in the Earth’s crust - 3-6km deeper than adjacent basin floor
the Mariana Trench is 11,022m deep
describe the hydrologic cycle
> water circulates in a continuous cycle between the ocean, the atmosphere and reservoirs of freshwater
what is the difference between heat and temperature
> heat is energy produced by the random vibrations of atoms or molecules
temperature is the object’s response
what is heat capacity?
> heat capacity is a measure of heat (calories) required to raise the temperature of 1g of a substance by 1 degrees celsius
not all substances have the same heat capacity
water has a high heat capacity
it resists changing temp when heat is added or removed
due to the strength of H bonds between water molecules, water can gain or lose large amount of heat with little change in temperature
this thermal inertia moderates temperatures globally
how does temperature affect density?
> the relationship between temperature and density for pure water is unusual
refer to diagram
what are the implications of water’s heat capacity?
> this along with the ability of ice to float are vital to maintaining Earths moderate surface temperature
water also has the highest latent heat of vapourisation of any known substance (540cal/gram)
describe the cycle of temperature versus heat?
> must add 80 calories of energy to change a gram of ice to liquid water
once melted, 1 calorie of heat is needed to raise each gram of water by 1 degree celsius
but 540 calories must be added to each g of water to vaporise it!
approx. 1m of water evaporates from ocean surface/ yr (334,00km3)
when 1 g of ocean vapour condenses, it releases 540 calories
these calories power thunder, storms, currents, wind and waves
describe the average surface temp and salinity for the world
> as expected, temperatures lowest in polar regions and highest near the equator
heavy rainfall in the equatorial regions “freshens” the ocean near the equator
hot and dry conditions near the tropic lines, salinity in the equatorial regions vs near the tropic lines: heavy rainfall vs hot and dry conditions
what allows for massive amounts of heat to be moved very efficiently?
> lots of latent heat is used to evaporate water in the tropics and is released when vapour is carried towards the poles and reprecipitated.
oceans currents carry heat from the tropical to polar regions
there is a much larger variation in the latent heat and specific heat capacity of land than in water, i.e, water is a moderator
what are the constituents of seawater?
> by weight, seawater = 96.5% water and 3.5% dissolved substances
if oceans evaporated completely, a salt layer of 45m thick would result
what is salinity?
> the measure of total dissolved inorganic solids in 1kg of seawater
by mass, salinity varies from 3.3-3.7% in the ocean (33-37ppt)
what are the most abundent components of sea water?
>chloride > sodium > sulfate > magnesium > bicarbonate > calcium > potassium > other
where do salts come from?
> processes that regulate major constituents in seawater
- ions added: rivers, volcanic activity, hydrothermal vents, decay of once living organisms
- ions removed: mid-ocean ridge systems, uptake by livign organisms, incorporation into sediments, and ultimately subduction
components of ocean salinity are modified by Earth’s crust
how do scientists determine the salinity of seawter?
by measuring the chlorinity of the sample
> salinity in%o = 1.80655 x chlorinity in %o
> ratio of major salts in ocean is constant but salinity might vary in seawater from different locations
> ocean is in chemical equilibrium
what is residence time?
the average length of time an element spends in the ocean
> residence time of ocean water is 4,100 years
> residence for water in atmosphere is 9 days
> ocean mixing occurs over a period of 1,600yrs by currents
wht are the percentages of gases in surface seawater?
> nitrogen - 48% > oxygen - 36% - vital for many animals - source from photosynthesis and dissolved from atmosphere > carbon dioxide - 15% - used in photosynthesis - 60x more in ocean than in atmosphere
what are the different gas concentrations at different depths?
> refer to diagram
- O2 concentration is higher near the surface because photosynthesis of plants occurs here
below sunlight layer [O2] decreases because of respiration and oxygen consumed by decay as organisms slowly sink
as it gets even deeper, the [CO2] increases
at the surface plants use CO2, but at depth, CO2 builds up as photosynthesis cannot occur in the dark
CO2 also increases with depth because its solubility increases as pressure increases and temperature decreases
what is the pH of seawater?
> mildly alkaline with a natural pH of about 8
however, the ocean is becoming more acidic as it absorbs additional carbon dioxide from the atmosphere
a less alkaline environment is making it difficult for organisms to build hard structures containing calcium (shells, coral, etc)
warmer
viruses are evolving rapidly
