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
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 and S.
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 froze over.
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,
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 shale, 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.
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 tropical
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 circulation.
- Heat released
by rain in higher latitudes drives storms and winds.
- Heat released
by rain in hurricanes and thunderstorms drives these storms.
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
From Japan Meteorological Agency, Japanese
25-year Reanalysis (JRA-25) Atlas.
Left: Rain in the tropics warms
the atmosphere and drives the Hadley circulation.
Image from The Why Files.
Right: The Hadley cells (circulation) are a major part of the
climate system. Click on image for a zoom.
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 cycle.
- 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.
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 air.
- 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
Phytoplankton strongly influence cloud formation.
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.
Dimethylsulfide (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
From Wunsch (2005). The Total Meridional Heat
Flux and Its Oceanic and Atmospheric Partition. Journal of Climate,
- 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
- 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 page.
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 summer rains
from the North
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 zoom.
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 day.
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
far colder than the average temperature of our earth, which is 15°C
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
- 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 Center.
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, 2005).
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 University Press.
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
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
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,
21 December, 2012