Download The Oceans

The Oceans
Introduction
The increase in world population and the
continued rise of industrialization have resulted in a
need to further understand the world’s oceans.
One of the most important factors that
impact the biosphere is the condition of the world’s
oceans.
A basic understanding of the structure and
composition of the ocean and knowledge of how
life in the ocean affects life on land can increase the
extent to which we are able to protect this
important natural resource and the life that
depends on it.
Misconceptions
• The general understanding is that the ocean
surface has no actual relief of its own and
therefore is flat.
• Another misunderstanding that people often
have is that tides are caused by the action of
the wind. Actually, tides are not caused by the
wind, but by the gravitational pull of the moon
and sun on the Earth.
Misconceptions
• The ocean depths are devoid of life.
• The seafloor is flat and the same age as the
continents.
Regulating Mechanism
• What is the biological pump?
– Biologic activity, in particular primary productivity,
draws in CO2 from the surrounding water column.
– Dead organisms will sink in the water column.
Some of it will remineralize and some will
continue below the thermocline. That material
that makes it below the thermocline is effectively
segregated from the surface ocean, thereby
completing the “pumping” of atmospheric CO2
into the deep ocean.
Regulating Mechanism
What does the pump affect?
• Global climate (perhaps) and carbon flow
– Locally change CO2 levels
• Also alter CH4, N2O, and DMS
– 30 to 40% of fossil fuel CO2 goes into oceans
• Small perturbations to the system can have large
ramifications
Ocean Structure and Composition
• Atmospheric pressure at sea level is 14.7
pounds per square inch (also referred to as
"one atmosphere"), and pressure increases by
an additional atmosphere for every 10 meters
of descent under water.
Ocean Structure and Composition
Epipelagic Zone
The surface layer of the ocean is known as the
epipelagic zone and extends from the surface to
200 meters (656 feet). It is also known as the
sunlight zone because this is where most of the
visible light exists. With the light come heat. This
heat is responsible for the wide range of
temperatures that occur in this zone.
Mesopelagic Zone
Below the epipelagic zone is the mesopelagic
zone, extending from 200 meters (656 feet) to
1000 meters (3281 feet). The mesopelagic zone
is sometimes referred to as the twilight zone or
the midwater zone. The light that penetrates to
this depth is extremely faint. It is in this zone
that we begin to see the twinkling lights of
bioluminescent creatures. A great diversity of
strange and bizarre fishes can be found here
Bathypelagic Zone
The next layer is called the bathypelagic zone. It is
sometimes referred to as the midnight zone or the
dark zone. This zone extends from 1000 meters
(3281 feet) down to 4000 meters (13,124 feet).
Here the only visible light is that produced by the
creatures themselves. The water pressure at this
depth is immense, reaching 5,850 pounds per
square inch. In spite of the pressure, a surprisingly
large number of creatures can be found here.
Sperm whales can dive down to this level in search
of food. Most of the animals that live at these
depths are black or red in color due to the lack of
light.
Abyssopelagic Zone
The next layer is called the abyssopelagic zone, also
known as the abyssal zone or simply as the abyss. It
extends from 4000 meters (13,124 feet) to 6000
meters (19,686 feet). The name comes from a
Greek word meaning "no bottom". The water
temperature is near freezing, and there is no light at
all. Very few creatures can be found at these
crushing depths. Most of these are invertebrates
such as basket stars and tiny squids. Three-quarters
of the ocean floor lies within this zone. The deepest
fish ever discovered was found in the Puerto Rico
Trench at a depth of 27,460 feet (8,372 meters).
Hadalpelagic Zone
Beyond the abyssopelagic zone lies the forbidding
hadalpelagic zone. This layer extends from 6000 meters
(19,686 feet) to the bottom of the deepest parts of the
ocean. These areas are mostly found in deep water
trenches and canyons. The deepest point in the ocean is
located in the Mariana Trench off the coast of Japan at
35,797 feet (10,911 meters). The temperature of the
water is just above freezing, and the pressure is an
incredible eight tons per square inch. That is
approximately the weight of 48 Boeing 747 jets. In spite
of the pressure and temperature, life can still be found
here. Invertebrates such as starfish and tube worms can
thrive at these depths.
Ocean
Currents
Ocean Currents
• Ocean currents allow for mixing to occur. This
in turn provides for redistribution of heat from
low latitudes to high latitude, carry nutrients
from deep waters to the surface, and shape
the climates of coastal regions.
• There are three primary ways for mixing to
occur.
Ocean Currents
• Waves and surface currents are caused mainly
by winds.
• The Ekman transport causes mixing by
combining the effects of the wind and the
Coriolis effect – deflecting the current
approximately 45 to the direction of the wind
– going to the right in the Northern
hemisphere and left in the Southern
hemisphere.
Ocean Currents
• Thermohaline Circulation is responsible for
mixing the ocean at deeper levels.
• The density of water increases as it becomes
colder and saltier so it sinks at high latitudes
and is replaced by warm water flowing
northward from the tropics.
Ocean Currents
• When the Ekman Transport combines with the
Thermohaline Circulation, gyres are formed.
• Gyres rotate clockwise in the Northern
Hemisphere and counter-clockwise in the
Southern Hemisphere, driven by easterly
winds at low latitudes and westerly winds at
high latitudes.
The Ocean & the Earth’s Climate
• The oceans redistribute heat from high to low
latitudes by moving warm water from the
equator toward the poles.
• In areas where coastal upwelling brings cold
water up from the depths, cold currents have
the opposite effect.
• Because water warms and cools more slowly
than land, oceans tend to moderate climates
in many coastal areas.
Atmosphere / Ocean Cycle
Thermohaline Circulation
• Often referred to as the "global conveyor
belt“, it moves large volumes of water along a
course through the Atlantic, Pacific, and Indian
oceans.
• The thermohaline circulation is driven by
buoyancy differences in the upper ocean that
arise from temperature differences (thermal
forcing) and salinity differences (haline
forcing).
Thermohaline Circulation
Thermohaline Circulation
• Salinity differences are caused by evaporation,
precipitation, freshwater runoff, and sea ice
formation.
• When sea water freezes into ice, it ejects its
salt content into the surrounding water, so
waters near the surface become saltier and
dense enough to sink.
Driving Bodies of Water
• North Atlantic Deep Water (NADW), the
biggest water mass in the oceans, forms in the
North Atlantic and runs down the coast of
Canada, eastward into the Atlantic, and south
past the tip of South America.
• Antarctic Bottom Water (AABW), is the
densest water mass in the oceans.
– It forms when cold, salty water sinks in the seas
surrounding Antarctica and flows northward along
the sea floor underneath the North Atlantic Deep
Water.
Ocean Circulation and Climate Cycles
• Measuring the variables that signal switches in
climate cycles, such as changes in ocean
temperature and atmospheric pressure, is an
important research focus for ocean and
atmospheric scientists who are working to
make better predictions of climate and
weather cycles.
Ocean Circulation and Climate Cycles
Monsoon rain clouds near Nagercoil, India, August 2006
Ocean Circulation and Climate Cycles
• Monsoons are a well-known example of a
seasonal climate cycle.
– As land temperatures increase during summer
months, hot air masses rise over the land and
create low-pressure zones.
– At the surface, ocean winds blow toward land
carrying moist ocean air.
– When these winds flow over land and are lifted up
by mountains, their moisture condenses and
produces torrential rainfalls.
Ocean Circulation and Climate Cycles
• Hurricanes develop on an annual cycle
generated by atmospheric and ocean
conditions that occur from June through
November in the Atlantic and from May
through November in the eastern Pacific.
• The main requirements for hurricanes to
develop are warm ocean waters (at least
26.5°C/80°F), plenty of atmospheric moisture,
and weak easterly trade winds.
Ocean Circulation and Climate Cycles
• The best-known climate cycle is the El Niño Southern
Oscillation (ENSO), which is caused by changes in
atmospheric and ocean conditions over the Pacific
Ocean.
– Atmospheric pressure rises over Asia and falls over South
America, equatorial trade winds weaken, and warm water
moves eastward toward South and Central America and
California.
– Coastal upwelling in the eastern Pacific dwindles or stops.
• Warm, moist air rises over the west coasts of North
and South America, causing heavy rains and landslides
as droughts occur in Indonesia and other Asian
countries.
Ocean Circulation and Climate Cycles
• The Pacific Decadal Oscillation (PDO) is a 20- to
30-year cycle in the North Pacific Ocean.
– Positive PDO indices (warm phases) are characterized
by warm Sea Surface Temperature (SST) anomalies
along the Pacific coast and cool SST anomalies in the
central North Pacific.
– Negative PDO indices (cold phases) correspond to the
opposite anomalies along the coast and offshore.
• Cool PDO phases are well correlated with cooler and wetter
than average weather in the western United States.
• During the warm phase of the PDO, the western Pacific cools
and the eastern Pacific warms, producing weather that is
slightly warmer and drier than normal in the western states.
Ocean Circulation and Climate Cycles
• The North Atlantic Oscillation (NAO), another multi-decadal cycle, refers
to a low-pressure region south of Iceland and a high-pressure region near
the Azores.
• Positive NAO periods occur when the differences in Sea Level Pressures
(SLP) are greatest between these two regions. Under these conditions, the
westerly winds that pass from North America between the high and low
pressure regions and on to Europe are unusually strong, and the strength
of Northeast Trade Winds is also strengthened.
– This strong pressure differential produces warm, mild winters in the eastern
United States and warm, wet winters in Europe as storms crossing the Atlantic
are steered on a northerly path.
• In the negative phase, pressure weakens in the subtropics, so winter
storms cross the Atlantic on a more direct route from west to east.
– Both the eastern United States and Europe experience colder winters, but
temperatures are milder in Greenland because less cold air reaches its
latitude.
Biological Activity in the Upper Ocean
• Most life in the ocean does not have fins or
flippers.
• Single celled organisms called phytoplankton
far outnumber the sum of all the marine
organisms most of us think of first.
• They convert huge quantities of carbon
dioxide (CO2) into living matter.
– In that process they release a major percentage of
the world's oxygen into the atmosphere.
Biological Activity in the Upper Ocean
Biological Activity in the Upper Ocean
• Derived from the Greek words phyto (plant)
and plankton (made to wander or drift), phytoplankton
are microscopic organisms that live in watery
environments, both salty and fresh.
• Some phytoplankton are bacteria, some are protists,
and most are single-celled plants. Among the common
kinds are cyanobacteria, silica-encased
diatoms, dinoflagellates, green algae, and chalkcoated coccolithophores.
Biological Activity in the Upper Ocean
• Like land plants, phytoplankton have
chlorophyll to capture sunlight, and they use
photosynthesis to turn it into chemical energy.
They consume carbon dioxide, and release
oxygen.
• Phytoplankton, like land plants, require
nutrients such as nitrate, phosphate, silicate,
and calcium at various levels depending on
the species.
Biological Activity in the Upper Ocean
• Other factors influence phytoplankton growth
rates, including water temperature and
salinity, water depth, wind, and what kinds of
predators are grazing on them.
• When conditions are right, phytoplankton
populations can grow explosively, a
phenomenon known as a bloom.
Biological Activity in the Upper Ocean
Phytoplankton can
grow explosively over
a few days or weeks.
This pair of satellite
images shows a
bloom that formed
east of New Zealand
between October 11
and October 25,
2009. (NASA images
by Robert Simmon
and Jesse Allen,
based
on MODIS data.)
Biological Activity in the Upper Ocean
• Many of these events are not harmful in
themselves, but they deplete oxygen in the water
when the organisms die and decompose.
– Some types of phytoplankton algae produce
neurotoxins, so blooms of these varieties are
dangerous to swimmers and consumers of fish or
shellfish from the affected area.
• Most plankton blooms are beneficial to ocean life
because they increase the availability of organic
material.
Biological Activity in the Upper Ocean
• Climate cycles can have major impacts on
biological productivity in the oceans.
– An El Niño event – reduction of phytoplankton
results in no sardines and anchovies  reduces
food for large predators like tuna, sea lions, and
seabirds
– A PDO event – results in reduction of salmon,
several ground fish, albacore, seabirds, and
marine mammals in the North Pacific.
The "Biological Pump"
• Deep waters provide nutrients that plankton
need for primary production in the upper
ocean, but how do these nutrients get to the
ocean depths?
• They are carried down from the surface in a
rain of particles often referred to as marine
snow, which includes fecal pellets from
zooplankton, shells from dead plankton, and
other bits of organic material from dead or
dying microorganisms.
The "Biological Pump"
The "Biological Pump"
• When marine snow reaches deep waters,
some is consumed by bottom-dwellers and
microbes who depend on it as a food source.
• Some is oxidized, releasing CO2, nitrate, and
phosphate and recycling nutrients into deep
waters.
• The remainder is buried in sediments and is
the source of today's offshore oil and gas
deposits.
The
"Biological
Pump"
Three sediment trap designs.
The original funnel design uses
a large collection area to
sample marine snow that falls
to great depths. Surface waters
contain enough sediment that
traps there don't require
funnels. Neutrally buoyant,
drifting sediment traps catch
falling material instead of
letting it sweep past in the
current.
The "Biological Pump"
• This flow of particles to ocean depths is a critical
link in the global carbon cycle.
• Plankton take up carbon from the atmosphere in
two ways: they fix CO2 as organic carbon during
photosynthesis and form shells from calcium
carbonate (CaCO3).
• Marine snow carries both of these forms of
carbon away from the atmosphere and surface
waters to reservoirs in the deep oceans and
ocean sediments, where it remains stored for
centuries.
The "Biological Pump"
• Without this mechanism, concentrations of
CO2in the atmosphere would be substantially
higher.
• The overall efficiency of the biological pump
depends on a combination of physical and
biogeochemical factors.
– Both light and nutrients must be available in
sufficient quantities for plankton to package more
energy than they consume.
Resources
• http://people.duke.edu/~ts24/ENSO/ - El Nino
video
• http://www.nasa.gov/vision/earth/lookingate
arth/plankton.html - chlorophyll productivity
map
• http://earthobservatory.nasa.gov/Features/Ph
ytoplankton/ - phytoplankton information