The Oceans. Introduction The increase in world population and the continued rise of...
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The Oceans. Introduction The increase in world population and the continued rise of industrialization have resulted in a need to further understand the
Introduction The increase in world population and the continued
rise of industrialization have resulted in a need to further
understand the worlds oceans. One of the most important factors
that impact the biosphere is the condition of the worlds 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.
Slide 3
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.
Slide 4
Misconceptions The ocean depths are devoid of life. The
seafloor is flat and the same age as the continents.
Slide 5
Regulating Mechanism What is the biological pump? Biologic
activity, in particular primary productivity, draws in CO 2 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 CO 2 into the deep
ocean.
Slide 6
Regulating Mechanism What does the pump affect? Global climate
(perhaps) and carbon flow Locally change CO 2 levels Also alter CH
4, N 2 O, and DMS 30 to 40% of fossil fuel CO 2 goes into oceans
Small perturbations to the system can have large ramifications
Slide 7
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.
Slide 8
Ocean Structure and Composition
Slide 9
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.
Slide 10
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
bioluminescent
Slide 11
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.
Slide 12
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).
Slide 13
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.
Slide 14
Ocean Currents
Slide 15
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.
Slide 16
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.
Slide 17
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.
Slide 18
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.
Slide 19
The Ocean & the Earths 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.
Slide 20
Atmosphere / Ocean Cycle
Slide 21
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).
Slide 22
Thermohaline Circulation
Slide 23
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.
Slide 24
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.
Slide 25
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.
Slide 26
Ocean Circulation and Climate Cycles Monsoon rain clouds near
Nagercoil, India, August 2006
Slide 27
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.
Slide 28
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 26.5C/80F),
plenty of atmospheric moisture, and weak easterly trade winds.
Slide 29
Ocean Circulation and Climate Cycles The best-known climate
cycle is the El Nio Southern Oscillation (ENSO), which is caused by
changes in atmospheric and ocean conditions over the Pacific
Ocean.El Nio Southern Oscillation (ENSO) 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.
Slide 30
Ocean Circulation and Climate Cycles The Pacific Decadal
Oscillation (PDO) is a 20- to 30-year cycle in the North Pacific
Ocean.Pacific Decadal Oscillation (PDO) 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.
Slide 31
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.North Atlantic Oscillation (NAO) 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.
Slide 32
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.
Slide 33
Biological Activity in the Upper Ocean
Slide 34
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 chalk-
coated coccolithophores.dinoflagellates,green
algae,coccolithophores.
Slide 35
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.
Slide 36
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.
Slide 37
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.)MODIS
Slide 38
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.
Slide 39
Biological Activity in the Upper Ocean Climate cycles can have
major impacts on biological productivity in the oceans. An El Nio
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.
Slide 40
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.
Slide 41
The "Biological Pump"
Slide 42
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 CO 2, 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.
Slide 43
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.
Slide 44
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 CO 2 as organic carbon
during photosynthesis and form shells from calcium carbonate (CaCO
3 ). 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.
Slide 45
The "Biological Pump" Without this mechanism, concentrations of
CO 2 in 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.
Slide 46
Resources http://people.duke.edu/~ts24/ENSO/ - El Nino video
http://people.duke.edu/~ts24/ENSO/
http://www.nasa.gov/vision/earth/lookingate arth/plankton.html -
chlorophyll productivity map
http://www.nasa.gov/vision/earth/lookingate arth/plankton.html
http://earthobservatory.nasa.gov/Features/Ph ytoplankton/ -
phytoplankton information
http://earthobservatory.nasa.gov/Features/Ph ytoplankton/