Download Earth Science 2.1 The World Ocean Presearch WO 3: Planet Ocean

Earth Science
2.1 The World Ocean
Presearch WO 3: Planet Ocean
At the equinox when the earth was veiled in a late rain,
wreathed with wet poppies, waiting spring,
The ocean swelled for a far storm and beat its boundary,
the ground-swell shook the beds of granite.
I gazing at the boundaries of granite and spray, the
established sea-marks, felt behind me
Mountain and plain, the immense breadth of the continent,
before me the mass and doubled stretch of water.
- Robinson Jeffers
from Continent’s End, 1924
“Water, water everywhere, nor any drop to drink.”
- Samuel Taylor Coleridge
from Rime of the Ancient Mariner, 1798
Themes: Systems, Flows of Energy, Cycles of Matter
Objectives:
1) Identify the names and locations of the world’s oceans.
2) Identify the names and locations of the primary ocean
currents.
3) Identify causes for movements of the world’s oceans.
Primary Questions:
1) What are the primary ocean currents, and how are they
caused?
2) What effect does differential heating have on ocean currents?
3) What effect does salinity have on ocean currents?
4) What effect does the Coriolis force have on ocean currents?
Illustration:
____ Compose a drawing to show the names and locations of the
world’s oceans.
____ Compose a drawing to show the names and locations of the
primary surface currents for the world’s oceans.
Reading:
____ “Introduction to the Oceans” from physicalgeography.net
Read the article actively. Briefly outline the characteristics of
each of the world’s oceans, as presented in the article.
Read the following actively, and outline the contents in 2-column
notes.
____ “The Global Conveyor”
from Life’s Matrix, by Phillip Ball
____ “Ocean Currents”
from Rise of the Ranges of Light, by David Scott Gilligan
____ “Earth’s Ocean Currents”
from Reading the Rocks, by Marcia Bjornerud
Read actively, and respond to the prompts attached:
____ “Salt Power
from Life’s Matrix, by Phillip Ball
Vocabulary:
____ Add the following to your interactive vocabulary:
gyre
circulation
salinity
dilution
thermohaline
Introduction to the Oceans
adapted from phyicalgeography.net
Seen from space, our planet’s surface appears to be dominated by the color blue.
The Earth appears blue because large bodies of saline water known as the
oceans dominate the surface. Oceans cover approximately 70.8% or 361 million square
kilometers (139 million square miles) of Earth’s surface (Table 1) with a volume of
about 1370 million cubic kilometers (329 million cubic miles). The average depth of
these extensive bodies of sea water is about 3.8 kilometers (2.4 miles). Maximum depths
can exceed 10 kilometers (6.2 miles) in a number of areas known as ocean trenches. The
oceans contain 97% of our planet's available water. The other 3% is found in atmosphere,
on the Earth's terrestrial surface, or in the Earth's lithosphere in various forms and stores.
The distribution of ocean regions and continents is unevenly arranged across the
Earth's surface. In the Northern Hemisphere, the ratio of land to ocean is about 1 to 1.5.
The ratio of land to ocean in the Southern Hemisphere is 1 to 4. This greater abundance
of ocean surface has some fascinating effects on the environment of the southern half of
our planet. For example, climate of Southern Hemisphere locations is often more
moderate when compared to similar places in the Northern Hemisphere. This fact is
primarily due to the presence of large amounts of heat energy stored in the oceans.
The International Hydrographic Organization has divided and named the
interconnected oceans of the world into five main regions: Atlantic Ocean, Arctic Ocean,
Indian Ocean, Pacific Ocean, and the Southern Ocean. Each one of these regions is
different from the others in some specific ways.
Table 1: Surface area of our planet covered by oceans and continents.
Surface
Percent
Area
of
Square
Earth’s Kilometers
Total
Surface
Area
Area
Square
Miles
Earth’s
Surface
Area
Covered
by Land
29.2%
148,940,000
Earth’s
Surface
Area
Covered
by
Water
70.8%
361,132,000 139,397,000
Pacific
Ocean
30.5%
155,557,000
60,045,000
Atlantic
Ocean
20.8%
76,762,000
29,630,000
Indian
Ocean
14.4%
68,556,000
26,463,000
Southern
Ocean
4.0%
20,327,000
7,846,000
Arctic
Ocean
2.8%
14,056,000
5,426,000
57,491,000
Atlantic Ocean
The Atlantic Ocean is a relatively narrow body of water that snakes between nearly
parallel continental masses covering about 21% of the Earth’s total surface area (Figure
1). This ocean body contains most of our planet’s shallow seas, but it has relatively few
islands. Some of the shallow seas found in the Atlantic Ocean include the Caribbean,
Mediterranean, Baltic, Black, North, Baltic, and the Gulf of Mexico. The average depth
of the Atlantic Ocean (including its adjacent seas) is about 3300 meters (10,800 feet). The
deepest point, 8605 meters (28,232 feet), occurs in the Puerto Rico Trench. The MidAtlantic Ridge, running roughly down the center of this ocean region, separates the
Atlantic Ocean into two large basins.
Many streams empty their fresh water discharge into the Atlantic Ocean. In fact, the
Atlantic Ocean receives more freshwater from terrestrial runoff than any other ocean
region. This ocean region also drains some of the Earth’s largest rivers including the
Amazon, Mississippi, St. Lawrence, and Congo. The surface area of the Atlantic Ocean is
about 1.6 times greater than the terrestrial area providing runoff.
Figure 8 1: Atlantic Ocean region
Arctic Ocean
The Arctic Ocean is the smallest of the world’s five ocean regions, covering about
3% of the Earth’s total surface area. Most of this nearly landlocked ocean region is
located north of the Arctic Circle (Figure 2). The Arctic Ocean is connected to the
Atlantic Ocean by the Greenland Sea, and the Pacific Ocean via the Bering Strait. The
Arctic Ocean is also the shallowest ocean region with an average depth of 1050 meters
(3450 feet). The center of the Arctic Ocean is covered by a drifting persistent icepack
that has an average thickness of about 3 meters (10 feet). During the winter months, this
sea ice covers much of the Arctic Ocean surface. Higher temperatures in the summer
months cause the icepack to seasonally shrink in extent by about 50%.
Figure 2: Arctic Ocean region
Indian Ocean
The Indian Ocean covers about 14% of the Earth’s surface area. This ocean region is
enclosed on three sides by the landmasses of Africa, Asia, and Australia (Figure 3). The
Indian Ocean’s southern border is open to water exchange with the much colder Southern
Ocean. Average depth of the Indian Ocean is 3900 meters (12,800 feet). The deepest
point in this ocean region occurs in the Java Trench with a depth of 7258 meters (23,812
feet) below sea level. The Indian Ocean region has relatively few islands. Continental
shelf areas tend to be quite narrow and not many shallow seas exist. Relative to the
Atlantic Ocean, only a small number of streams drain into the Indian Ocean.
Consequently, the surface area of the Indian Ocean is approximately 400% larger than the
land area supply runoff into it. Some of the major rivers flowing into the Indian Ocean
include the Zambezi, Arvandrud/Shatt-al-Arab, Indus, Ganges, Brahmaputra, and the
Irrawaddy. Sea water salinity ranges between 32 and 37 parts per 1000. Because much of
the Indian Ocean lies within the tropics, this basin has the warmest surface ocean
temperatures.
Figure 3: Indian Ocean region
Southern Ocean
The Southern Ocean surrounds Antarctica extending to the latitude 60° South (Figure 4).
This ocean region occupies about 4% of the Earth’s surface or about 20,327,000 square
kilometers (7,846,000 square miles). Relative to the other ocean regions, the floor of the
Southern Ocean is quite deep ranging from 4000 to 5000 meters (13,100 to 16,400 feet)
below sea level over most of the area it occupies. Continental shelf areas are very limited
and are mainly found around Antarctica. But even these areas are quite deep with an
elevation between 400 to 800 meters (1300 to 2600 feet) below sea level. For
comparison, the average depth of the continental shelf for the entire planet is about 130
meters (425 feet). The Southern Ocean’s deepest point is in the South Sandwich Trench
at 7235 meters (23,737 feet) sea level. Seas adjacent to this ocean region include the
Amundsen Sea, Bellingshausen Sea, Ross Sea, Scotia Sea, and the Weddell Sea. By
about September of each year, a mobile icepack situated around Antarctic reaches its
greatest seasonal extent covering about 19 million square kilometers (7 million square
miles). This icepack shrinks by around 85% six months later in March.
Figure 4: Southern Ocean region
Pacific Ocean
The Pacific Ocean is the largest ocean region (Figure 5) covering about 30% of the
Earth’s surface area (about 15 times the size of the United States). The ocean floor of the
Pacific is quite uniform in depth having an average elevation of 4300 meters (14,100
feet) below sea level. This fact makes it the deepest ocean region on average. The Pacific
Ocean is also home to the lowest elevation on our planet. The deepest point in the
Mariana Trench lies some 10,911 meters (35,840 feet) below sea level as recorded by the
Japanese probe, Kaiko, on March 24, 1995. About 25,000 islands can be found in the
Pacific Ocean region. This is more than the number for the other four ocean regions
combined. Many of these islands are actually the tops of volcanic mountains created by
the release of molten rock from beneath the ocean floor.
Figure 5: Pacific Ocean region
Relative to the Atlantic Ocean, only a small number of rivers add terrestrial
freshwater runoff to the Pacific Ocean. In fact, the surface area of the Pacific is about
1000% greater than the land area that drains into it. Some of the major rivers flowing into
this ocean region include the Colorado, Columbia, Fraser, Mekong, Río Grande de
Santiago, San Joaquin, Shinano, Skeena, Stikine, Xi Jiang, and Yukon. Some of larger
adjacent seas connected to the Pacific are Celebes, Tasman, Coral, East China, Sulu,
South China, Yellow, and the Sea of Japan.
The Global Conveyor
adapted from
Life’s matrix: a Biography of Water, by Phillip Ball
What lies over the ocean’s rim? Since humans first took to the sea, this
question has been irresistible. The Phoenicians and Vikings crossed the Atlantic
long before Columbus and Magellan in the heyday of European seafaring, and
Chinese mariners reached the east coast of Africa in the fifteenth century, well
before Portuguese colonists. By 1700, maps of the Atlantic Ocean were almost as
accurate as today’s. But although dragons may have been banished from the
world’s end, it was largely the promise of distant lands (and resources), not the
allure of the blue waters, that stimulated these explorations. There was little
systematic effort to look at the seas for their own sake until the celebrated voyage
of the British research vessel H.M.S. Challenger, which circled the globe from 1972
to 1876 and took depth soundings and ocean-water samples in an attempt to look
at the oceans as part of the planet’s geography, rather than as a highway to
foreign exploitation.
What we have learned since then is sobering. Around half of the Earth’s
solid surface is between 1.8 and 3.6 miles below sea level: the places where we
live are like the tips of icebergs. The deepest parts of the ocean—the trenches—
can plummet about seven miles, well over a mile deeper than Mount Everest is
high. The floors of the great oceans are scarred down their middle by rugged
submerged ridges several miles high. These mid-ocean ridges mark the borders
of tectonic plates; here magma wells up from the mantle, cooling at the seabed to
solidify into fresh ocean floor, while the plates move apart on either side.
All the oceans of the world are interconnected. Yet the lumbering
continents and the high points of the ocean floor moderate the degree of
connection, enabling us to define distinct water masses, in “basins” separated by
shallow shelves. Once mariners considered that there were seven seas to sail: the
Atlantic, Pacific, Indian, and Arctic oceans, the Mediterranean and Caribbean
seas, and the Gulf of Mexico. Today we recognize only three different ocean
basins—the Atlantic, Pacific, and Indian—although the southernmost portions of
these three, encircling Antarctica itself, are loosely considered a fourth ocean, the
Southern or Antarctic. The world’s seas, including the Mediterranean, the North
Sea, the Red Sea, the Arabian Sea, and the East and South China Seas, are large
bodies of water that lie on the margins of the oceans and are typically separated
by narrow gaps or straits, such as the Strait of Gibraltar, or by high ridges on the
seabed.
The waters in these oceans do not simply sit there bobbing up and down;
they are constantly passing in masses from one place to another, both vertically
and horizontally, like shoppers riding the escalators in a crowded multistory
department store. It is a stately procession, a sluggish reflection of the jets,
streams, fronts, and vortices of the ever-active atmosphere. But unlike
movements of air masses, the circulation of water between the oceans is
constrained by the arbitrary distribution of the continents. These have found
their way to their present positions through continental drift, the movement of
the tectonic plates driven by the even more sluggish convective motion of the
Earth’s mantle. There is thus a poetic recurrence of movement here in the
classical elements of air, water, and earth, at a successively slower pace. We
might with only a little poetic license find the sequence completed with the
overturning of “fire”—molten iron—in the Earth’s core.
Because the tectonic plates go right on drifting and colliding, there is
nothing fixed about the pattern of the oceans. About 170 million years ago, there
were only two major oceans. The Panthalassa Ocean occupied virtually the
whole planet between longitudes 30 degrees W (now the mid-Atlantic) and what
is now the International Dateline (mid-Pacific), and the Tethys Ocean stretched
between latitudes 30 degrees N (level with North Africa today) and 30 degrees S
(which now passes through southern Australia) in the eastern part of the globe.
The Panthalassa became the Pacific, while the Tethys was gradually squeezed
out of existence as the Indian continent collided with Asia to throw up the
Himalayas.
Today there is a strong asymmetry in the distribution of land and sea
between the north and south hemispheres. Almost two-thirds of the global ocean
is in the Southern Hemisphere, and a remarkable 95 percent of all land points
have antipodes—equivalent points in the opposite hemisphere—on the sea. Only
in the Southern Ocean can one sail around a complete line of latitude without
encountering land.
The ocean’s surface currents, which shift the top three hundred feet or so
of water, are driven mainly by winds. They propel the sea surface just as blown
air will create currents on the surface of a cup of coffee. So these ocean-surface
currents, which are crucial to the distribution of fish and other marine organisms
and to the transport of heat around the globe, are at the mercy of the atmosphere.
A confusing practice has developed whereby ocean currents are named
for the directions they are going, while air currents—winds—are named for the
directions from which they come. So westerly wind drives an eastward oceansurface current, both moving in the same direction. Westerly winds prevail
between latitudes 30 degrees and 60 degrees in both hemispheres. Closer to the
Equator, down to latitudes of 15 degrees, the easterly trade winds drive
westward currents. Around the Equator itself the winds are weak—the
Doldrums—and predominantly eastward.
This almost symmetrical driving of ocean-surface currents is modified by
two factors: the continents get in the way, and the Earth is spinning. Except in
the Southern Ocean, the currents are hemmed in by landmasses to the east and
west, and so are deflected northward and southward close to the coasts to trace
out huge closed loops called “gyres” (Figure 1). This gyration is accentuated and
modified by the effect of the Earth’s rotation, through an influence called the
Coriolis force. Named after the nineteenth century French engineer Gaspard
Coriolis, this force acts on an object that moves within a rotating system. You can
feel this force if you try to walk in a straight line out toward the edge of a
rotating platform: the Coriolis force makes you veer away from the line. On
Earth, this force causes a current to curve away from its initial course, toward the
right in the Northern Hemisphere, and toward the left in the Southern
Hemisphere.
Figure 1: Major ocean-surface currents, driven by winds. The obstruction by the
continents and the force generated by the Earth’s rotation mold the currents into
circulating “gyres.” The circulation in the Indian Ocean reverses direction between
winter and summer, owing to seasonal changes in the Asian monsoon winds.
To see what effect this has on ocean currents, consider the north Pacific
gyre. The easterly trade winds drive a westward current (around 15 degrees N),
while the westerlies at around 30 degrees N generate an eastward current at that
latitude. But as the current is deflected to the right by the Coriolis force, it
becomes squashed up against the Asian coast to the west, but stretched out and
broadened as it proceeds toward the North American coast. What this means is
that the western part of the gyre becomes a very intense northward flow, called
the Kuroshio, while the southward edge of the gyre off California is much more
dispersed. In the Kuroshio Current, the speed of the flow can reach up to three
feet per second, which is three to ten times faster than currents typically
observed elsewhere in the ocean.
This same phenomenon occurs in the North Atlantic, where an intense
northeasterly flow from the Gulf of Mexico and the Florida Straits along the
eastern coast of North America forms the Gulf Stream. This narrow flow
becomes a more diffuse northeasterly current, the North Atlantic Current, which
travels toward the British Isles and Norway, bringing warm water and a milder
climate to western Europe than is experienced at similar latitudes on the North
American continent. A similar focusing of subtropical gyres occurs in the
Southern Hemisphere, creating the Brazil Current in the South Pacific and the
Agulhas Current off southeastern Africa in the south Indian Ocean.
All of this is generalization, however, that describes the averaged annual
flows. Only the easterly trade winds are steady throughout the year. The
inconsistency of the oceans is illustrated most strikingly in the Indian Ocean,
where the surface currents rotate in different directions at different times of the
year, in response to changes in the Asian monsoon winds.
Ball, Philip. Life’s Matrix: A Biography of Water. Berkeley, CA: University of California
Press, 2001.
Ocean Currents
adapted from
Rise of the Ranges of Light, by David Scott Gilligan
Although new land is what they sought, the explorers and geographers of
the golden age were first and foremost sailors. Their realm to roam was the sea,
and it was here that some of their most important contributions to science were
made. From the earliest times, those who focused their attention on the sea took
note of massive ocean currents, for their success at sea depended upon intimate
knowledge of these. After enough shipwreck stories passed down through the
years, sailors could hit the water with a certain degree of confidence of where the
ocean wanted to take them. In short, the ocean basins were like giant washtubs,
with their waters moving in a predictable fashion.
As we now know, the waters of the North Pacific and North Atlantic both
circulate in a clockwise fashion. In the Atlantic, warm equatorial waters are
drawn west from the coast of Africa. These waters then move north along the
Antilles and the Bahamas, continuing up along the coastline of the southern
United States before diverging from the continent and heading northeast directly
toward Ireland, Great Britain, and Scandinavia. The warm waters delivered by
the North Atlantic Current moderate the climate of whatever lands they contact,
thus simulating the climactic conditions of lower latitudes. Bermuda, at a latitude
comparable to the Carolinas, has a tropical climate. Great Britain, at the same
latitude as Labrador, rarely sees snow and has a lengthy growing season. Palm
trees planted along the west coast of Scotland grow and thrive. Northern
Norway, at the same latitude as the ice caps of central Greenland and Baffin
Island, supports vast forests of birch and alder, though far above the Arctic
Circle.
Eventually the ocean waters do cool, circulating back down the west coast
of Europe towards Africa, where again the water is warmed and the cycle begins
anew.
In the Pacific, the story is much the same, with warm waters moderating
southeastern China and Japan, veer off towards Alaska, and cool waters
circulating down the west coast of North America. South of the equator the
situation is reversed, and the oceans circulate in a counterclockwise fashion. A
quick look at a map of ocean currents will show that in the Southern Hemisphere
things are much as they are in the north. Warm waters moderate the east coasts
at lower latitudes and eventually diverge and head east. The west coasts at
higher latitudes are moderated by these warm ocean currents. Eventually the
waters cool down, and these waters circulate along the west coasts back towards
the equatorial regions.
Gilligan, David Scott. Rise of the Ranges of Light. Berkeley, CA: Heyday Press, 2100.
Earth’s Ocean Currents
adapted from
Reading the Rocks by Marcia Bjornerud
Earth’s ocean currents are the planet's heat distribution system, equalizing
differences in the amount of solar radiation received at different latitudes. Large
currents like the Gulf Stream transport warm water from the tropics toward the
polar regions. Without this source of imported heat, Britain and northern
Europe, which lie at the same latitudes as do Alaska and northern Canada,
would be far less habitable. Growing seasons would be so short that agriculture
would not be possible. As the Gulf Stream water moves northward and lends its
heat to the surrounding lands, the water not only cools but also becomes saltier,
owing to repeated cycles of evaporation during its journey. Ultimately, in the
Norwegian-Greenland Sea, the water becomes so dense that it sinks again. From
this point, it begins an epic journey back to the south, snaking deep below the
surface as bottom water, eventually reaching the Indian Ocean, where, now
warmed, the water may rise and meet the atmosphere again.
This thermohaline ocean circulation is driven by convection. Like the muchlonger-term convection in Earth’s mantle, thermohaline (“heat-salt”) circulation
requires a critical balance of variables. If the salinity of the water in the North
Atlantic did not reach the critical value for sinking, the entire conveyor could
stop, just as a single stalled car on a highway can back up traffic for miles.
Late in the last Ice Age, as the continental glaciers covering North America
and Europe were rapidly disintegrating, huge amounts of fresh meltwater likely
flooded the North Atlantic. Vast glacial lakes in North Dakota and Manitoba,
larger than all the modern Great Lakes combined, may have spilled out
catastrophically into the Hudson Bay and the Saint Lawrence Seaway.
The fresh meltwater would have diluted waters coming up from the south
to the point where the resulting, less saline water had no inclination to sink. The
oceanic currents--the equivalent of a thousand Mississippis--would have been
jammed for decades or longer as more and more meltwater came streaming off
the land. Cut off from its source of warmed water, the North Atlantic and
surrounding land areas would have become colder and colder, triggering a brief
return to glacial conditions. This in turn would have allowed the Gulf Stream to
reestablish itself, warming the north again, and finally pulling the Earth out of
the Ice Age.
These ideas, intoned by Dennis Quaid, made it to Hollywood in the 2004
thriller The Day After Tomorrow. The premise of the film is that human
greenhouse emissions have triggered rapid melting of the ice masses, causing the
sudden freshening of the North Atlantic and the shutdown of the thermohaline
conveyor. Extreme weather ensues over a period of about a week, and when the
snow settles, the Statue of Liberty is up to her armpits in ice.
The film’s timescale is absurdly compressed, but the underlying science is
sound. We should start imagining climate change in our own lifetimes.
Bjorerud, Marcia. Reading the Rocks. New York, NY: Westview Books, 2005.
Salt Power
adapted from
Life’s Matrix: a Biography of Water, by Philip Ball
Winds can’t drive ocean circulation at depths much below three hundred
feet. Deep circulation has another origin: it is driven largely by differences in
water temperature. This churning, at depths of between one half and three miles,
carries warm water into colder seas, and so redistributes heat around the planet.
Deep-water circulation forms a conveyor belt flow which links all three of the
world’s oceans via the Southern Ocean (Figure 1). To see how this flow works,
let’s pick up a ride at the sea surface in the equatorial Atlantic Ocean. The upper
part of the conveyor belt here is traveling northward, and consists of water that
has been warmed in the tropics. As it travels poleward, this water mass cools and
becomes more dense. At the same time, evaporation from the sea’s surface leaves
the surface water more salty, since the escaping vapor does not take the salt with
it. This increased salinity (saltiness) also increases the density of the sea water. So
as the current progresses toward the pole it becomes heavier than the water
below, and it sinks in the vicinity of the Labrador Sea, south of Greenland.
This cool, salty, dense water mass becomes North American Deep Water,
which plunges to depths of more than half a mile and is then carried in a return
flow along the lower part of the conveyor belt back toward the equator. It passes
from north to south across the entire Atlantic Ocean before reaching the Southern
Ocean, where it rises toward the margins of the Antarctic continent. During the
Antarctic winter, a portion of this water mass freezes as sea ice in the Weddell
Sea, leaving behind even colder and saltier water (since freezing, like
evaporation, removes relatively pure water: the ice excludes the salt). This dense
water sinks right to the ocean floor as Antarctic Bottom Water, the densest water
in the oceans. But most of the deep current coming into the Southern Ocean from
the Atlantic is carried eastward as a salty flow called Antarctic Circumpolar
Water before turning northward into the Pacific Ocean off Australia. Here it
warms up as it flows into the tropical Pacific Ocean, and the warmer, less dense
Figure 1: The global conveyor. Circulation in the deep oceans bears warm, less-salty
water along its upper belt, and cold, salty water on the lower belt.
water rises in the central North Pacific Ocean on the ascending branch of the
conveyor belt, there to be carried back westward toward the Atlantic Ocean.
These differences in temperature and salinity mean that the deep oceans are
not simply one uniform mass of water--they can be divided into distinct
reservoirs, which follow different pathways and mix rather little. The global
conveyor belt of deep circulation is called thermohaline circulation, since it is
driven by changes in heat (Greek: thermos) and salinity (halos). The North Atlantic
limb of the conveyor belt carries huge amounts of heat poleward in the warmer
surface flow, which is released at high latitudes as the water cools and sinks. The
heat delivered to the high-latitude North Atlantic Ocean in this way is about a
quarter to a third of that delivered by direct sunshine. So the themohaline
circulation has a strong influence on climate. During the ice ages, it is believed
that the circulation was far weaker, because the temperature difference between
the tropics and high latitudes was less pronounced than it is today.
As the last ice age was coming to an end and the global climate was
warming, around twelve to ten thousand years ago, there was a sudden
reversion to glacial conditions. This shift in climate seems to have been mindbogglingly rapid: some estimates indicate that the global climate reverted from
something like present-day conditions to those of the ice age in around fifty
years. Some oceanographers believe the shift may have been caused by a partial
shutting down of the thermohaline circulation as the extensive northern ice
sheets melted and flushed fresh water into the ocean. This dilution of the salty
surface waters in the North Atlantic Ocean would have made them less dense
and less susceptible to sinking, and so the conveyor belt might have ground
almost to a halt. The message is sobering, and is reinforced by similar rapid
climate shifts that have shown up in climate records from the still more distant
past: the deep circulation of the oceans may be a sensitive switch that could
plunge the world into a deep freeze if disturbed.
Ball, Philip. Life’s Matrix: A Biography of Water. Berkeley, CA: University of California
Press, 2001.
Earth Science
Response to Non-fiction:
“Salt Power” from Life’s Matrix: a Biography of Water
by Philip Ball, 2001
Compose responses to the following prompts. Your work
should be done on loose-leaf and attached to this cover.
1) How are deep-water ocean currents different from surface
currents? How are they similar?
2) What factors affect the density of ocean waters? Explain
how changes in density contribute to ocean currents?
3) Where are the densest ocean waters located? Why?
4) Explain how deep water currents work to distribute heat
around the planet.
5) Compose a caption that explains Figure 1 in detail.
6) Explain how warming of Earth’s climate can affect the
salinity of ocean water. Explain what effect(s) a change
in salinity might have on Earth’s climate.