The Ocean and Climate
We are not merely inhabitants
of a planet, adapting ourselves to it. Life has verily constructed
the planet. It would not behave as it does, even in its deep interior,
were it not for life. [Most of that life was in the ocean.]
(Oldroyd 1996: 297)
What is Climate
Traditionally, climate has been defined as the average
weather: temperature, precipitation, cloudiness, and how these variables
change throughout the year. Now, earth-system science leads to a much
For many, the term "climate" refers
to long-term weather statistics. However, more broadly and more
accurately, the definition of climate is a system consisting of
the atmosphere, hydrosphere, lithosphere, and biosphere. Physical,
chemical, and biological processes are involved in interactions
among the components of the climate system. Vegetation, soil moisture,
and glaciers, for example, are as much a part of the climate system
as are temperature and precipitation.
The Ocean and Ocean Life Strongly Influenced Earth's Climate
Over Billions of Years
Earth is totally different from what it would be if it had no ocean.
The ocean, and life in the ocean, have "constructed the planet." The
ocean is an important part of the Earth System, and it influences the
transformation of energy and materials important to the climate system.
On the most basic level, the ocean has shaped our atmosphere. Over millions
of years, the concentration of gases in the atmosphere is determined
by life. If life did not exist, especially life in the ocean, earth would
be very different. On a deeper level, oceanic microbes irreversibly altered
the geochemistry of earth and the biogeochemical cycles of H, C, N, O
Please note, there is only one ocean with many named parts. The largest
parts are the Atlantic, Indian, and Pacific Oceans. Earth would be much
different if there were several different, disconnected oceans.
The evolution of photosynthesis remade the
Archaean Earth. Before photosynthesis, the air and oceans were
anoxic. Now the air is a biological construction, a fifth
of which is free molecular oxygen, and the ocean can
sustain animal life even in the depths. The evolution,
first of anoxygenic [not
producing oxygen] and then of oxygenic [producing oxygen] photosynthesis,
sharply increased the productivity of the biosphere. Oxygenic photosynthesis
sustains free oxygen in the atmosphere. In the oceans, the beneficiaries
of the first photosynthetic prokaryotes [bacteria and archaea] today
range from cyanobacterial and algal plankton to large
kelp. Wearing plants as landsuits, from tiny mosses to
giant redwoods, cyanobacteria as chloroplasts have
occupied the land. The oxygen emitted has allowed the
evolution of animal life, to browse the plants and, in
turn, to respire the CO2 that sustains photosynthesis.
The management of the carbon cycle, by photosynthesis
coupled with respiration, had profound
consequences for the greenhouse setting of the surface
temperature. Photosynthetic productivity controls the
budgets of atmospheric carbon dioxide and, eventually,
methane too. This sets global temperatures, weather
patterns and may have even been a cause of the
great glacial events, where much of the Earth’s surface
Bendall et al (2008).
- Carbon dioxide, the most common gas on Venus is rare in earth's atmosphere
because oceanic animals have used carbon dioxide to make vast layers
of carbonates in the form of limestone, dolomite, and marble. Without
life, our atmosphere would be similar to that of Venus. Most sedimentary
rocks were laid down in the ocean.
El Capitan, Capitan Reef, Guadalupe Mountains National Park,
Texas. This is a coral reef is from the Permian. Photograph by
Mark Eberle, November 1999.
History of the Southwestern United States, a Fort Hayes State University
course taught by Mark Eberle.
- Free oxygen O2 which is not found in the atmosphere of
other planets, is produced by life. It is found in the atmosphere because
of production by photosynthesis and the deposition of organic carbon
on the the sea floor and the eventual inclusion of the organic carbon
into continental rocks by plate tectonics acting over many millions
of years (Falkowski and Godfrey, 2008). The organic carbon is stored
in sedimentary rocks on continents in the form of oil shales, coal,
oil, and natural gas.
- Oxygen in the atmosphere led to the formation of earth's stratospheric
ozone layer which protects all life from solar ultraviolet radiation.
The Ocean Strongly Influence Earth's Present Climate
The ocean drives the atmospheric circulation
by heating the atmosphere, mostly in the tropics.
- Most of the sunlight absorbed by earth is absorbed at the top
of the tropical ocean. The atmosphere does not absorb much sunlight.
It is too transparent. Think of a cold, sunny, winter day at
your school. All day long, the sun shines on the outside, but
the air stays cold. But if you wear a black coat outside and
stand out of the wind, the sun will quickly warm up your coat.
Sunlight passes through the air and warms the surface of the
ocean, just as it warms the surface of your coat. Most of the
ocean is a deep navy blue, almost black. It absorbs 98% of the
solar radiation when the sun is high in the sky.
Heating of earth's surface by solar radiation, in W/m2,
calculated from the ECMWF 40-year reanalysis of atmospheric data.
Notice that most of the heat absorbed by earth goes into the
From Kallberg et al 2005.
- The ocean loses heat by evaporation (the technical term is
latent heat release). Think of this as the ocean sweating. Trade
winds carry the evaporated water vapor to the Inter-Tropical
Convergence Zone where it condenses as rain. Condensation
releases the latent heat and warms the air. Warm air rises, further
drawing in warm wet air, releasing more heat. Large areas of
the tropical ocean get more than 3 m (115 inches) of rain each
year (8 mm/day in the figure below).
- So much heat is released by rain in the Inter-Tropical
Convergence Zone that it drives much of the atmospheric
circulation. This circulation is called the Hadley
- Heat released by rain in higher latitudes drives storms
- Heat released by rain in hurricanes and thunderstorms drives
25-year average of rain rate.
From Japan Meteorological Agency, Japanese
25-year Reanalysis (JRA-25) Atlas.
25-year average of heating of the atmosphere. Notice the
high correlation with rain rate shown above. Rain and absorption
of infrared radiation heats the atmosphere, mostly in the
tropics. This heating drives the atmospheric circulation.
From Japan Meteorological Agency, Japanese
25-year Reanalysis (JRA-25) Atlas.
Left: Rain in the
tropics warms the atmosphere and drives the Hadley
Image from The
Right: The Hadley cells (circulation)
are a major part of the climate system. Click on image for
Image from NASA Earth Observatory.
- The ocean also loses heat by sending out infrared radiation
(energy), mostly in the tropics. The infrared radiation is absorbed
by water vapor in the tropical atmosphere, further heating the
- The winds drive ocean currents, and together they carry heat
from the tropics to the polar regions. See The Climate System
The ocean dominates earth's hydrological cycle.
- All but 3% of earth's water is in the ocean. See The
- The ocean supplies almost all the water that falls on land.
Watch moisture stream from the tropics into mid-latitudes where
it falls as rain in this visualization for January and
for August from
the Visualization Group at
the National Center for Atmospheric Research.
The ocean and ocean life control the amount
of carbon dioxide in the atmosphere, and they dominate earth's carbon
Carbon dioxide is a greenhouse gas. By absorbing infrared radiation
(energy) from the earth's surface, it helps keep the surface warm.
The amount of carbon dioxide in the air is increasing, partly because
we burn fossil fuels such as coal, natural gas, and oil. The increasing
amounts of carbon dioxide are causing earth to slowly warm up. To understand
the warming, we must understand how the ocean controls earth's carbon
- Most of the available carbon is in the ocean. The ocean holds
50 times more carbon than the atmosphere.
- About half of earth's primary production, the conversion of water,
carbon dioxide, sunlight, and inorganic nutrients into oxygen and
hydrocarbons, occurs in the ocean. Primary producers in
the ocean are the phytoplankton. They also produce oxygen as a
by product of this reaction.
- When the phytoplankton die and decay, or when they are eaten,
the hydrocarbons are converted back to carbon dioxide, using up
all the oxygen produced by the phytoplankton.
- But, sometimes phytoplankton and other life in the sea die
and sink to the sea floor before they can decay. When they
are buried in the sediments, they leave behind the oxygen produced
by the phytoplankton. Over millions of years this produced
the oxygen in the atmosphere. It also produced the oil, gas,
and coal we now use to make electricity, heat our homes, and
run our cars and trucks. We call this process the biological
pump that takes carbon dioxide out of the air.
- Almost exactly half of the carbon dioxide put into the air by
our burning of fossil fuels is absorbed by the ocean. Carbon dioxide
dissolves in cold water near the Arctic and Antarctic. When the
cold water sinks deep into the ocean in winter, it carries the
carbon dioxide away from the atmosphere. Many years later, the
water is gradually pulled closer to the sea surface by mixing in
the ocean. When it gets to the surface in warm areas it releases
the carbon dioxide back to the air. This process allows the ocean
to store great quantities of carbon dioxide for many centuries.
We call this the physical pump that takes carbon dioxide out of
- The biosphere expands and contracts on a 450,000 year cycle in
response to changes in insolation (incoming sunlight at different
latitudes). The long period is due to long-term storage of carbon
in the ocean and the dissolving of carbonate on the sea floor.
influence cloud formation and climate.
Clouds influence the reflection sunlight from earth, which influences
earth's temperature (Meskhidze and Nenes (2006). The phytoplankton
release great quantities of a sulfurous gas called dimethyl
sulfide which changes the way clouds are formed in the atmosphere.
First, sunlight causes chemical reactions that change the gas to sulfate
aerosols (microscopic particles in the air). The tiny aerosol particles
cause water vapor to condense to form cloud drops. Because about one-third
of the sunlight reaching earth is reflected back to space by clouds,
any process that influences cloudiness also influences the amount of
sunlight that is absorbed by earth.
Phytoplankton in the ocean produce dimethyl sulfide (DMS) that is converted
to sulfate aerosols (SO4), which influence the amount of
sunlight reflected by clouds.
Dimethyl sulfide (DMS) and Climate by the Atmospheric
Chemistry Program at the National Oceanic and Atmospheric Administration's
Pacific Marine Environmental Laboratory.
The ocean stores and transports heat.
Temperature in the atmosphere, even global changes in temperature are
slowed by the exchange of heat with the ocean. Thus, 18 times more
heat has been stored in the ocean since the mid 1950s due to global
warming than has been stored in the atmosphere. Most of the heat
trapped by greenhouse gases has gone into the ocean, not the atmosphere.
Earth's climate is the result of the uneven distribution of the temperature
at the surface. The difference in temperature between the poles and
the tropics eventually leads to winds and ocean currents that carry
heat heat from the tropics to the polar regions. The ocean carries
heat out of the tropics, and the winds carry heat to higher latitudes.
- The tropics are warm because they receive so much sunlight.
- The poles are cold because they receive much
less sunlight, and because the polar atmosphere is transparent
to infrared radiation. They radiate away much more heat than they
receive from the sun.
Zonal average of heat gained from the sun (red line) and lost to
space by emitted infrared radiation (green line).
Image from Lyndon State College Survey of Meteorology course by Nolan Atkins.
This plot shows the zonal average of heat transported by the atmosphere
and the ocean in units of petawatts (PW = 1015 Watts)
(solid black line), by the ocean (red dashed line), and by the
atmosphere (blue dashed line), averaged along lines of constant
latitude. The ocean is important for carrying heat out of the tropics,
and the atmosphere is important at latitudes greater than 20°.
From Wunsch (2005). The Total Meridional Heat
Flux and Its Oceanic
- The transport of heat is influenced by many other parts of the
- Continents interrupt or deflect winds and currents.
- Life on earth has changed the composition of the atmosphere,
which has changed the way heat gets from earth's surface to space.
- Water vapor in the atmosphere also influences the way heat
gets from earth's surface to space. Water vapor is the most
important greenhouse gas.
- Water evaporated from the ocean carries heat into the atmosphere,
and it warms the atmosphere when it condenses as precipitation.
Most of the heating occurs in the tropical rain belts.
Variations in the ocean's circulation have
been implicated in abrupt climate change during the last 400,000
See Abrupt Climate Change web
The Ocean Influences Regional Climate
- The difference in temperature between the land
and the ocean drives monsoons. During the winter, the center of a continent
is much colder than the surrounding ocean. This causes cold air to
flow out of the continent. During the summer, the center of continent
is much hotter than the ocean. This draws moist air into the continent
bring much needed summer rains. Monsoon winds are especially important
for Asia and North America. Arizona, and the American southwest get
from the North
India gets rain during the Asian
Arizona thunderstorm. Such storms in the American west are common in
summer due to the North American monsoon. Click on the image for a
From the National Weather Service Forecast Office Flagstaff Arizona's
article on the monsoon.
- Cities along coasts benefit from the sea
breeze. It too is due to the difference in temperature between
the land and the ocean. During the night the land is cooler, and
during the day it is warmer. The contrast in temperature causes winds
to blow toward the ocean at night, and toward the land during the
Influence of Greenhouse Gases Especially Water Vapor
Let's look at how greenhouse gases influence the climate system, and
how they might cause climate change. The ideas below come from George
Philander's book, Our Affair With El Niño,
chapter 7: Constructing a Model of Earth's Climate, page 105.
- Earth with no atmosphere
If earth had no atmosphere, if it had a land surface that reflected
some sunlight like the real earth, and if it were in equilibrium
with solar heating, the average surface temperature of earth would
be -18°C (0°F), far colder than the average temperature of
our earth, which is 15°C (59°F). Worse, the surface would
cool down to around -160°C (-250°F) soon after the sun set
because the surface would radiate heat to space very quickly, just
as the moon's surface cools rapidly as soon as the sun sets on the
- Earth with a static atmosphere and no ocean
If the earth had a static atmosphere with the same gases it has now,
but with little water vapor and no ocean, the average surface temperature
of earth would be 67°C (153°F). This is much warmer than
our earth. The planet would be so hot because greenhouse gases in
the atmosphere help keep heat near the surface, and because there
is no convection, and no transport of heat by winds. Adding winds
cools the planet a little, but not enough.
- Earth with an atmosphere and ocean
Earth has an atmosphere and ocean, and the average surface temperature
is a comfortable 15°C (59°F). Water evaporates from the ocean
and land, cooling the surface. Winds carry the water vapor to other
latitudes, and sometimes high up into the air, where heat is released
when the vapor condenses to water.
This very large thunderstorm was photographed
by astronauts flying over the Indian Ocean, east of Madagascar (25.0N,
56.0E). The storm is about 65 nautical miles on a side and has a
top that reaches into the stratosphere at 45,000 to 50,000 ft. and
casts long shadows in the low sun. Such storms carry heat from the
tropical seas high into the atmosphere, cooling the surface.
Image from Camex-4 Program,
NASA Marshall Space Flight Center. Original from NASA Johnson Space
Everything Is Connected
From this simple discussion of the climate system, we can conclude that
we must understand how earth, with its atmosphere, greenhouse gases,
ocean, life, winds, and currents all interact to produce our climate.
The ocean is one big part of the earth system. The ocean, atmosphere,and
land are connected through the climate system. Changes in one area cause
changes everywhere else. Everything is connected, and everything influences
For example, rain heats the atmosphere. The warm air rises, creating
wind. Wind drives ocean currents. Currents help determine where phytoplankton
live. Phytoplankton help determine where clouds are formed. Clouds influences
where the atmosphere is heated. Heating determines where the ocean evaporates,
and the amount of evaporation.
There are many interacting parts in the earth system.
As a result of these connections:
- Earth has a surface temperature that is just right for life. Water
vapor from the ocean is essential for setting the earth's temperature.
- The tropical ocean supplies almost all the water that falls on land.
- The ocean absorbs half of the carbon dioxide released by our burning
of fossil fuels. This reduces global warming caused by carbon dioxide.
- So much heat is absorbed by the oceans, that the the warming of
earth's surface by greenhouse gases is slowed down. 84% of the energy
available to warm earth's surface has gone into the ocean during the
48 years from 1955 to 2003; 5% has gone into the land; 4% has gone
into the atmosphere; and the remainder has gone into melting ice. (Levitus,
Conversion factors for temperature
- 0 degrees Celsius = 273.15 Kelvin
- Degrees Fahrenheit = 9/5 Celsius + 32
- So, zero degrees Celsius = 32 degrees Fahrenheit
Bendall, D. S., C. J. Howe, et al. (2008). Introduction. Photosynthetic
and atmospheric evolution. Philosophical Transactions
of the Royal Society B: Biological Sciences 363(1504): 2625-2628.
Oldroyd, D. R. (1996). Thinking About the Earth:
A History of Ideas in Geology. Cambridge Massachusetts, Harvard
Falkowski, P. G. and L. V. Godfrey (2008). Electrons,
life and the evolution of Earth's oxygen cycle. Philosophical
Transactions of the Royal Society B: Biological Sciences 363 (1504):
The biogeochemical cycles of H, C, N, O and
S are coupled via biologically catalysed electron transfer (redox)
reactions. The metabolic processes responsible for maintaining these
cycles evolved over the first ca 2.3 Ga of Earth's history in prokaryotes
and, through a sequence of events, led to the production of oxygen
via the photobiologically catalysed oxidation of water. However,
geochemical evidence suggests that there was a delay of several hundred
million years before oxygen accumulated in Earth's atmosphere related
to changes in the burial efficiency of organic matter and fundamental
alterations in the nitrogen cycle. In the latter case, the presence
of free molecular oxygen allowed ammonium to be oxidized to nitrate
and subsequently denitrified. The interaction between the oxygen
and nitrogen cycles in particular led to a negative feedback, in
which increased production of oxygen led to decreased fixed inorganic
nitrogen in the oceans. This feedback, which is supported by isotopic
analyses of fixed nitrogen in sedimentary rocks from the Late Archaean,
continues to the present. However, once sufficient oxygen accumulated
in Earth's atmosphere to allow nitrification to out-compete denitrification,
a new stable electron 'market' emerged
in which oxygenic photosynthesis and aerobic respiration ultimately
spread via endosymbiotic events and massive lateral gene transfer
to eukaryotic host cells, allowing the evolution of complex (i.e.
animal) life forms. The resulting network of electron transfers led
a gas composition of Earth's atmosphere that is far from thermodynamic
equilibrium (i.e. it is an emergent property), yet is relatively
stable on geological time scales. The early coevolution of the C,
N and O cycles, and the resulting non-equilibrium gaseous by-products
can be used as a guide to search for the presence of life on terrestrial
planets outside of our Solar System.
Meskhidze, N. and A. Nenes (2006). Phytoplankton and Cloudiness in
the Southern Ocean. Science 314 (5804):
Kallberg P., P. Berrisford, et al. (2005). ERA-40
Atlas. European Centre for Medium Range Weather Forecasts.
Levitus, S., J. Antonov, et al. (2005). Warming of the world ocean. Geophysical
Research Letters 32 (1).
Palike, H., R. D. Norris, et al. (2006). The Heartbeat of the Oligocene
Climate System. Science 314 (5807): 1894-1898.
Philander, S. G. (2004). Our Affair With El
Niño, Princeton University Press.
Pielke Sr, R. A. (2008). A broader view of the role of humans in the
climate system. Physics Today 61 (11):
Wunsch (2005). The Total Meridional Heat Flux and Its Oceanic and Atmospheric
Partition. Journal of Climate, 18: 2374–2380.
21 December, 2012