Thoughts on the ocean, the environment, the universe and everything from nearly a mile high.

Panorama of The Grand Tetons From the top of Table Mountain, Wyoming © Alan Holyoak, 2011

Monday, November 19, 2012

Chasing Mavericks - Great movie and awesome wave


Chasing Mavericks is a fantastic movie!  It triggered a whole pile of memories and thoughts about waves, surfers, etc.

DISCLAIMER:  Though I lived in Santa Cruz 1987-1992 I do not pretend to be a surfer, because I am not one. I have, however, spent a lot of time in the water body surfing and body boarding (boogie boarding) in Hawaii and Santa Cruz. Plus as a marine biologist I have spent considerable amounts of time near, in, and on the ocean. With that being said...

"Chasing Mavericks" is probably the best surfing movie I have ever seen. This biopic of young Jay Moriarity and his reluctant mentor Frosty Hesson delves into the psyche of surfing better than any other surfing movie I've ever seen.

I've liked Gerard Butler in just about everything I've seen him in and once again he didn't disappoint.  He plays a sage surfer who reluctantly agrees to train a teenager to surf one of the most dangerous waves in the world - Mavericks.

To "get" this movie you have to understand this wave.

Mavericks is a surf break at the north end Half Moon Bay, CA.  It breaks big there only when waves are big enough and they come from the right direction.  This combination of factors produces waves that can be 20-80' feet tall, and is one of the most dangerous places in the world to surf.  There are only a few places in the world with waves in this size class. 

This Google Earth image shows the location of Mavericks in relation to San Francisco Bay and the central California coast.  Santa Cruz is BTW at the very bottom edge of the image.

This Google Earth image shows Pillar Point at the north end of Half Moon Bay, CA, where Mavericks breaks.

Most offshore breaks occur over reefs that are 20 feet deep or less (e.g., Pipeline, on the north shore of Oahu), but the reef at Mavericks is much deeper.  This means that it takes a truly huge wave to break there.  In addition to the deep reef at Mavericks, there is an unusual underwater rock formation that helps the big waves there set up and break. 

The image above shows a rocky ramp sloping upward toward a point SSW of Pillar Point.  This is where Mavericks breaks on big days.  Waves slow down as they move over increasingly shallow water.  As a wave slows it gets taller.  The part of the wave on either side of the rocky ramp, however, is deeper, so waves there don't  slow as quickly.  This focuses the power of the wave inside the box shown above.  (Image: Wikimedia Commons)

The photo above shows Pillar Point, at the north end of Half Moon Bay, CA.  The white water is inshore of where Maverick's breaks when it is big.  The rocks in the water are called the Bone Yard.  The Bone Yard is not where you want to be with the wave breaks big - or anytime, really. (Image: Wikimedia Commons)

The series of photos above shows Mavericks breaking on a big day.  A single wave at a time sets up over the deep reef and rocky point and breaks right and left.  The helicopter and boats give the wave a size perspective.  Mavericks is not only a tall wave, it is incredibly thick, releasing massive amounts of energy as it breaks.  

OK, back to the movie. Young Jay Moriarity, like just about every other surfer along the central California coast those days had heard rumors of a giant wave, but it was dismissed largely as myth. One day though, Jay discovers someone who rides that wave - Frosty Hesson - and Jay sees the wave and Frosty and his surfing partners riding at Mavericks. It takes some doing, but Frosty is finally convinced to train young Jay for Mavericks.

This movie is about what it takes to survive Mavericks when everything goes wrong, not how to ride it when everything goes right.  

There is a good dose of surfing in the movie, and while there is a strong mental and spiritual component to the movie, it does not come across as eclectic or preachy. it's just downright amazing!

The sheer force and presence and bone-shaking power of the wave is awe-inspiring, and the willingness and ability of a small handful of big-wave surfers who challenge and ride it are beyond impressive. What they do borders on the miraculous.

I've been held down by a a couple of waves in the 6-8' range in Hawaii, and that wasn't fun, so it's nearly impossible to imagine the amount of force in a wave the size of Mavericks.  It's a wave that you feel more than you hear or see it. Sheer power!

It's difficult to imagine the power that is in these waves.  I've been held down by much smaller waves in Hawaii, so it's nearly impossible to imagine the amount of force in a wave the size of Mavericks. It's a wave that you feel more than you hear or see it. Sheer power!

It's important to know when to get in the water and when it's time to sit on the shore and just drink in the power that is out there.

Wednesday, November 7, 2012

Understanding Climate Change - Glossary

This is the glossary for readings 1-7 for my course on climate change.

Understanding Climate Change - Glossary

(Alan Holyoak, PhD)

Absolute path (Coriolis effect) – The path of a moving object actually moves in a straight line even though the Earth is rotating under it.

Absolute reference frame (Coriolis effect) – The observer is stationary in space and the path of a moving object is in a straight line with the Earth rotating under it.

Absolute zero – This is zero degrees Kelvin (-273oC or -459oF), and indicates the complete absence of heat, i.e., when molecules stop vibrating.

Absorption – In terms of electromagnetic radiation, this occurs when photons of energy are taken up by matter.  When a photon is taken up, an electron becomes energized and moves to a higher energy state.  Energy is released when the energized electron releases the energy it absorbed and it then drops to a lower energy state.

Abyssal plain – A flat plain that makes up the majority of world’s seafloor 3-6 miles below the ocean surface.

Abyssalpelagic zone – Ocean depths from the 4oC depth mark to 6000 meters, and reaches all the way down to the abyssal plain.

Aerosols – Particulate matter and droplets of liquid small enough to remain suspended in the air for an extended period of time.

Albedo – The reflectivity of a surface as measured on a scale of 1.0 to 0.0.  A perfect white surface will reflect all radiation that strikes it and have a value of 1.0, while a perfect black surface will absorb all radiation that strikes it and have a value of 0.0.

Anoxic – A situation where there is no oxygen present.

Antarctic Circle – Line of latitude at 66.5oS that experiences one day each year where the sun does not rise above the horizon (that’s on the northern hemisphere summer solstice).

Anthropogenic – Produced or generated by humans.

Apparent path (Coriolis effect) – The path of an object moving over the Earth appears to deflect to the right in the northern hemisphere and to the left in the southern hemisphere, but only if the observer is on the surface of the rotating planet.

Arctic Circle – Line of latitude at 66.5oN that experiences one day each year where the sun does not rise above the horizon (that’s on the northern hemisphere winter solstice).

Autumnal equinox – The day between the northern hemisphere summer and fall when everywhere on the planet has equal day and night lengths, usually around Sept 22nd.

Bathypelagic zone – This layer in the ocean exists between the 10oC and the 4oC temperature layers.  This layer is in perpetual darkness.

The Big Experiment – The experiment involves the emission of increasing amounts of fossil carbon into the atmosphere, starting during the Industrial Revolution, that affects the amount of greenhouse gases there and the atmosphere’s greenhouse efficiency. 

The Boring Billion Years – The time period between about 1.8 – 0.8 billion years ago when the amount of oxygen in the atmosphere stayed at constant, low concentrations.

Calcium carbonate – A white compound made of one atom of calcium (Ca) and one carbonate ion (CO3-2).  This compound is extremely common, and can be made by organisms such as coral, snails, foraminiferans, etc.

Carbon cycle – The dynamic action of chemical, biological, and geological processes that release, take up, and store carbon on our planet.  

Carbon sink – Any process that removes carbon from the biosphere.

Carbon source – Any process that releases carbon into the biosphere.

Coal – Fossil fuel that was formed when ancient forests died, presumably in swamps, were covered by sedimentary rock, and under intense temperature and pressure became coal.  Coal contains carbon, hydrogen, and impurities like sulfur.

Continental shelf – Seafloor with a shallow slope that extends from the edge of a continent to the continental slope.

Continental slope – Seafloor that has a steep slope and drops from the outer edge of the continental shelf to the ocean’s abyssal plain.

Coral – Coral are animals related to sea anemones and jellyfish.  Some corals secrete calcium carbonate skeletons that form the framework for coral reefs. 

Coriolis effect – The apparent deflection of a moving object that is not attached to the earth, e.g., wind or water currents.  Coriolis effect causes moving objects to deflect to the right in the northern hemisphere and to the left in the southern hemisphere. 

Cyanobacteria – Also known as blue-green algae or blue-green bacteria.  These bacteria carry out photosynthesis, and are believed to be the first group of photosynthetic organisms that appeared on Earth. 

Deep-water currents – Ocean currents below the thermocline, existing all the way to the seafloor.  Thermohaline circulation forms and drives these currents.

Diffuse radiation – Scattered light that reaches the Earth’s surface.

Direct solar radiation – Solar radiation that passes through the atmosphere to the Earth’s surface without being scattered, absorbed, or reflected.

Eccentricity – Milankovitch cycle describing the oscillations of the shape of Earth’s orbit around the sun.

Ekman spiral –Surface waters move due to friction between it and surface winds.  The next layer of water down also moves, but due to Coriolis effect it moves in slightly different direction, and so on for each succeeding layer of deeper water.  This produces water moving in different directions at different depths.

Ekman transport – Surface waters move due to friction with surface winds.  Where Coriolis effect surface water to move away from the shore, deeper water is pulled to the surface, upwelling.

Electromagnetic spectrum of radiation – The range of all wavelengths of radiation from gamma rays at the shortest wavelength to long radio waves at the long end.

Energy budget – This is the balance between the amount and rate of energy entering a system and the amount and rate of energy leaving a system during a period of time.

Entropy – Entropy is used to indicate the efficiency of energy transformation.  The amount of energy available to do work before energy transformation equals the amount of energy able to do work after the energy transformation plus entropy.  Or, entropy represents waste heat no longer able to do work whenever energy transformation takes place.  The amount of entropy in a closed system increases or stays the same.

Epipelagic zone – This the top layer of the water column in the world’s oceans, and it extends from the surface to a depth where only about 1% of the light that strikes the surface has not been absorbed or scattered.  This is usually the top few hundred meters of the ocean, and is where photosynthesis occurs in the ocean.

Equinox – Two days each year when the length of day and night are exactly the same everywhere on earth: Vernal (spring) equinox and Autumnal (fall) equinox.

Ferrel Cell – Air circulation pattern where air rises at 60oN & S and returns to the surface at 30oN & S.  This produces low pressure and higher amounts of rainfall at 60o, and high pressure and low precipitation at 30o. 

First law of thermodynamics – The total amount of energy in closed system will remain constant.  And energy (i.e., heat) will move from a location of high energy to low energy until the amount of energy is uniform throughout the closed system.

Foraminifera – One of the most abundant groups of marine plankton.  They are related to amoeba, and they secrete a calcium carbonate (CaCO3) shell.

Fossil carbon – Carbon that was once part of a living thing, but has been removed from the biosphere, embedded in the sediment and formed coal, oil, or natural gas.

Fossil fuel – Once living material, mainly algae, plankton, and trees, that become fossilized into coal, crude oil, and natural gas.

Freezing point depression – Water has to get colder to freeze when it contains lots of salt (solutes) compared to when it contains less salt (solutes).

Gigaton – 1015 grams (= 1000 trillion grams)

Global conveyor (a.k.a. Atlantic conveyor, conveyor belt) – Deep-ocean current established and driven by thermohaline circulation.  Water takes 100s-1000s of years to finish one complete cycle.

Global Warming Potential (GWP) – A measure of the ability of a single molecule of a substance to absorb infrared radiation.  Carbon dioxide is assigned a GWP of 1.0, and the GWP of all other greenhouse gases are based on the CO2 standard. 

Great Oxygenation Event – Time period between about 2.5 – 1.8 billion years ago when oxygen first accumulated in Earth’s atmosphere.

Greenhouse effect – Infrared radiation is released by the Earth’s surface and by molecules in the atmosphere.  That heat is absorbed by greenhouse gases in the atmosphere that then release the energy in random directions.  This slows the rate of heat loss back into space.
Greenhouse gas – Any gas that is able to capture infrared radiation and temporarily hold that energy.  Different greenhouse gases absorb different wavelengths of energy.

Gulf Stream – Ocean surface current originating in the Caribbean Sea that moves along the east coast of North America and then moves across the North Atlantic Ocean.

Hadalpelagic zone – Water in ocean trenches.

Hadley Cell – Air circulation pattern where air rises at the equator and returns to the surface at 30oN & S.  This produces low pressure and higher amounts of rainfall at the equator, and high pressure and low precipitation at 30o.

Heat sink – Matter or process that absorbs heat. 

Heat source – Matter or process that releases heat.

Heavy oxygen – An isotope of oxygen with a molecular weight of 18 (18O)

Henry’s Law – The amount of gas that can be dissolved in water is a function of temperature and pressure.  Water under high pressure and at low temperature can hold more gas in solution than water that is warm and under low pressure.

Incident solar radiation – Solar radiation that strikes the Earth/Atmosphere system.  This is the radiation that is subsequently reflected, scattered, or absorbed.

Industrial Revolution – A significant change between 1750-1850 where the mechanization of agriculture, industry, transportation, etc., caused profound changes in the way we live, work, produce goods, etc., made possible by the development of steam power and the use of fossil fuels.

Insolation – A measure of solar radiation received per some unit area, e.g., Watts per meter squared.

Intertidal zone – The narrow zone around ocean shorelines where seafloor is exposed to the air during low tides and covered by water during high tides.

Intertropical convergence zone (ITCZ) – Surface air flowing north and south converge at the equator, heats up, and rises.  A perpetual band of cloud cover indicates the latitude of the ITCZ.

Isotope – Variants of a chemical element.  All (isotopes) variants have the same number of protons but different variants (isotopes) have different numbers of neutrons. E.g., 12C 13C 14C

Jet stream – Narrow, fast-moving currents of air in the upper troposphere that form along the boundaries between Hadley, Ferrel, and Polar cells. 

Joule – Unit of measurement for energy used doing work.  One Joule is the same expending one Watt of energy per second.

Latent heat – Heat that is absorbed by something without that matter changing temperature.  For example, latent heat is released when water vapor changes into liquid water.  Latent heat is absorbed as ice melts, but the temperature of the ice does not change. 

Law of conservation of matter – The amount of matter in a closed system will remain constant.  Matter can be rearranged by location or undergo chemical change, but the total amount of matter does not change.

Light oxygen  - An isotope of oxygen with a molecular weight of 16 (16O)
The Little Ice Age – A period of cool climate between 1600-1700 when no sunspots were observed.  Also called the Maunder Minimum.

Mass extinction event – A time period where many species go extinct in a short period of time.  Extinction events are often associated with rapid climate change.

Maunder Minimum – A period of cooling climate between about 1600-1700 when no sunspots were observed.  Also called “The Little Ice Age”.

Mesopelagic zone – This zone extends from the bottom of the epipelagic zone down to several hundred meters to a depth where water temps cool to about 10oC.

Mesosphere – The layer of the atmosphere that extends from about 30-53 miles in altitude.  Meteorites usually burn up as shooting stars here.

Micrometer – 1/1000th of a millimeter. Designated by “μm”.

Mid-oceanic ridges – An interconnecting series of undersea mountain ranges, the longest in the world, formed where tectonic forces cause seafloor spreading and new oceanic crust is produced.

Milankovitch cycles – natural oscillations in the shape of Earth’s orbit, tilt of Earth’s axis, and the direction the axis is pointing relative to the sun.  See also eccentricity, obliquity, and precession.

Montreal Protocol – The official name is “The Montreal Protocol on Substances that Deplete the Ozone Layer.”  This is an international agreement to stop producing chlorine and bromine containing substances (such as CFCs) that were discovered to deplete the stratospheric ozone layer.  The agreement was signed in 1987 and implemented in 1989. 

Nanometer – 1/1,000,000th of a millimeter. Designated by “nm”.

Natural gas – Small molecules made of carbon and hydrogen are formed when crude oil and coal are also formed, and are gases under normal conditions.  E.g., Methane, propane, butane.

Neritic zone – The part of the ocean above the continental shelf.

Net radiation (Rnet) – This is used to indicate the net balance of energy entering and energy leaving a particular area of Earth’s surface.  This is greatly affected by latitude.

Non-renewable energy – Any energy source that is finite or that takes such a long time to replenish itself that it is essentially non-renewable.  E.g., Fossil fuels can be replenished, but it takes millions of years for that to happen so it is considered to be non-renewable.

Obliquity – Milankovitch cycle describing the oscillation of the angle of tilt of the Earth’s axis.

Oceanic carbon sink – CO2 diffuses into seawater from the atmosphere.  It or carbonates are then taken up by living things and incorporated into their bodies.  They die, and that carbon settles to the seafloor where it is covered by sediment.

Oceanic trenches – The deepest locations in the ocean, and exist where tectonic forces cause one plate to subduct under another plate.  Volcanoes are commonly formed and earthquakes occur regularly along trenches.

Oceanic zone – The part of the ocean over everything except the continental shelf.

Oil (crude oil, petroleum) – The remains of dead plankton and algae are covered by sediment, and under intense temperature and pressure becomes a mixture of carbon-containing molecules of different sizes that remain in a liquid state under normal conditions.  There is an immense amount of energy stored in these compounds that is released when it burns.

Ozone – A molecule made of three atoms of oxygen bonded to each other.  This is a harmful greenhouse gas when it is found in the troposphere, and it protects us from UV radiation when it is in the stratosphere.

Paleocene-Eocene Thermal Maximum (PETM) – A spike in global temperature that occurred about 55 million years ago, as indicated by proxy data from ocean sediment cores. 

Paleoclimatology – The study of climate changes throughout Earth’s history.

Pelagic zone – The part of the ocean where the seafloor is never uncovered by a low tide (everything other than the intertidal zone).

Petagram – Equal to one gigaton = 1015 grams (=1000 trillion grams, one liter of water = 103 grams)

Photosynthesis – The biochemical process where energy from light is used make glucose (a carbohydrate) from carbon dioxide and water. 

Plate margins – This is where the edges of tectonic plates meet.

Polar Cell – Air circulation pattern where air rises at 60oN & S and returns to the surface near the poles.  This produces low pressure and higher amounts of rainfall at 60oN and high pressure and low precipitation at the poles.

Polar jet stream – Jet stream that sometimes forms at the boundary between Ferrel and Polar cells.

Precession – Milankovitch cycle describing oscillation of the direction Earth’s axis points relative to the sun. 

Radiation – This is electromagnetic energy.  This is NOT the same as radioactivity/radioactive decay.

Radiometric dating – A method for determining the absolute age of a sample by measuring the rate of radioactive decay of radioactive atoms in it.

Rayleigh scattering – The phenomenon that produces yellows, oranges, and reds seen at dawn and dusk, and that makes the sky appear blue the rest of the time.  Most Rayleigh scattering is done by molecules in the atmosphere, and blue light scatters more than other colors.  This is what gives the sky it’s blue color.  At dawn and dusk light travels through more light to reach the surface, scattering all blue light and leaving only longer wavelength light – reds, oranges.  Air pollution can accentuate Rayleigh scattering since there are more particles in the air and light scatters more than otherwise.

Ridge (jet stream) - In the northern hemisphere where a jet stream swoops toward the north, and at the same time rises to a higher altitude.  A high-pressure cell forms at lower altitudes as air from a jet stream descends from a ridge toward a trough.

Relative reference frame (Coriolis Effect) – The observer is on the surface of the planet, and is thus changing position as the Earth rotates.  From this frame of reference the apparent path of an object deflects to the right in the northern hemisphere and to the left in the southern hemisphere.

Renewable energy – Energy that comes from natural sources that can be replenished in a short period of time by natural processes, e.g., wood, wind, hydroelectric, solar panels, tides, biofuels, etc.
Rotational motion – The amount of spin a body experiences as the Earth rotates.  A body experiences 100% rotational motion when it is at one of Earth’s poles, and 0% rotational motion when it is on the equator.

Salinity – The salt content of water.

Scattering (of light) – The redirection of a ray of solar energy resulting from contact with aerosols.

Second law of thermodynamics – The amount of energy able to do work decreases whenever energy is transformed.  Every time energy is transformed entropy is produced and released as waste heat.

Sediment core – A cylindrical a sample of the sediment removed from the bottom of the ocean or a lake by using a plug or a drill. 

Solar faculae – Brighter, hotter areas on the surface of the sun that form when sunspots are also present. 

Specific heat – The amount of heat needed to change a substance’s temperature.  E.g., A substance with a high specific heat absorbs lots of heat before its temperature will change very much.  Water has the highest specific heat of any common substance.

Speleotherm – Stalactites, stalagmites, and other formations are formed when ions and other materials are dissolved by water as it percolates through rock layers, and that material is deposited when that water drips into a cave.

Stalagmite – A speleotherm that rises from the floor of a cave/cavern.

Stratosphere – The layer of the atmosphere that extends from 7-30 miles above the Earth’s surface.  This is where the ozone layer exists that protects us from harmful UV radiation.

Subduction/Subducted – A tectonic process where one crust plate is pushed underneath another crust plate. 

Subtropical jet stream – Jet stream that sometimes forms at the boundary between Hadley and Ferrel cells.

Summer solstice – The longest day of the year in the northern hemisphere, around June 22nd.

Sunspot – A markedly darker and cooler area on the surface of the sun than surrounding sun surface.

Supercontinent – Two or more major continental plates that are temporarily fused together to form a larger landmass, e.g., Pangea.

Surface currents (ocean) – Movement of surface waters to 100s of meters deep that are formed and driven by surface winds and deflected by Coriolis effect.

Thermocline – Narrow depth separating warm surface waters from deep cold water; a narrow depth of rapid temperature change indicates it. 

Thermohaline circulation – The circulation of ocean waters driven by a combination of temperature and salinity factors that causes seawater to become dense enough to sink.  Major centers of thermohaline circulation are the North Atlantic and the waters surrounding Antarctica.

Thermosphere – The layer of the atmosphere that extends from 53-90 miles in altitude.  This is the top layer of Earth’s atmosphere.

Translational motion - The degree to which a body changes position as the Earth rotates.  A body experiences 0% motion when it is at one of Earth’s poles (it spins, but doesn’t change position), and 100% rotational motion when it is on the equator (it moves, but doesn’t spin at all).

Tree ring – Trees that experience seasonal growth produce one wide ring and one narrow ring of wood.  Together these rings represent one year’s worth of growth.  A tree’s age and annual growing conditions can be inferred from these rings.

Tropic of Cancer – A line of latitude 23.5oN, the farthest north you can go and have the sun directly overhead for only one day a year (on the summer solstice).

Tropic of Capricorn – A line of latitude 23.5oS, the farthest south you can go and have the sun directly overhead for only one day a year (on the winter solstice).

Troposphere – The layer of the atmosphere closest to the Earth’s surface, extending to an altitude of 3-12 miles.  This is where the vast majority of Earth’s weather events take place.

Trough (jet stream) – In the northern hemisphere where a jet stream dips toward the south, and at the same time dips to a lower altitude.  A low pressure cell forms in lower altitudes as a jet stream rises from a trough toward a ridge.

Upwelling – When deep, cool, nutrient-rich water is pulled up to the surface, usually by Ekman transport or offshore winds.

Ultraviolet (UV) radiation – Electromagnetic radiation with a wavelength of 10-400nm.  Exposure to shorter wavelength UV radiation can produce skin cancer and cataracts.

Vernal equinox – The day between the northern hemisphere winter and spring when everywhere on the planet has equal day and night lengths, usually around March 22nd.

Visible light –The wavelengths of radiation we can detect with our eyes, between 380-740nm.

Watt – Unit used to express the expenditure of energy. One Watt = 1.0 Joule/second.  When used in climate science Watts are usually used to refer to the amount of energy per unit area, e.g., Watts/m2.

Wavelength – The distance between two peaks or crests of a wave.

Winter solstice – The shortest day of the year in the northern hemisphere.  Usually around December 22nd.

Monday, November 5, 2012

Understanding Climate Change Part 7 - Oxygen Signals and Paleoclimates

Oxygen Signals and Paleoclimates

(Reading #7 for my course on Climate Change, Alan Holyoak, PhD)

Note: This is the last reading in this series.  This set of 7 readings is designed to help college general education students gain the the foundational background they need to understand the contents of the book "The Climate Crisis" by Archer and Rahmstorf, which I use as a course textbook.  

Daily Objectives
1.     Be able describe the differences between heavy and light oxygen isotopes. 
2.     Be able to explain why ice cores from polar glaciers contain meaningful climate records.
3.     Be able to explain why speleotherms, wood, and coral contain meaningful climate records.
4.     Be able to explain why paleoclimatologists probably get excited when they find skeletons of foraminiferans in their sediment samples.
5.     Be able to comment on the general pattern of global temperature change over billions, millions, and hundreds of thousands of years.


            A way tool to gain insight into current patterns of climate change is to learn as much as possible about Earth’s climate history.  This field of study is called paleoclimatology.   Paleoclimatologists collect data from as many sources as possible to help them develop a picture of what Earth’s climate was like in the past.  These observations range from glacial erratics and glacial striations that you have already learned about to oxygen and carbon isotope ratios in ice, water, and sediments, among other things.  In this reading you will learn about the data that paleoclimatologists collect to investigate Earth’s climate history.  One important thing to keep in mind is that the farther we look back in time, the greater the range of uncertainty there is in the data.

Climate Clues

            Just like a detective, paleoclimatologists are good observers and creative thinkers.  This helps them identify and make sense of the climate clues that exist in Earth’s historical record.  You already learned how boulders and rocks that seemed out of place and strange scratches on rock faces led to Louis Aggasiz’s 1837 Ice Age Theory.  Similarly, other good observers discovered other ways to tease more clues about Earth’s climate history from sources such as ice, wood, ocean sediments, and even stalagmites. 

Climate and oxygen isotopes

            All isotopes of an element have the same number of protons, but different numbers of neutrons.  This difference in neutron number gives each isotope a unique atomic mass.  There are three isotopes of oxygen, 16O, 17O, and 18O.  These isotopes are not radioactive so their global concentrations are stable.  Their characteristics are listed in Table 1.

Table 1. Characteristics of isotopes of oxygen

Oxygen Isotope
Number of Protons
Number of Neutrons
Proportion of all oxygen atoms
Oxygen-16 (16O)
Oxygen-17 (17O)
Oxygen-18 (18O)

            Paleoclimatologists are interested in finding light oxygen (16O), and heavy oxygen (18O) in compounds in samples they collect.  They use the ratio between 18O and 16O atoms in oxygen-containing compounds as proxy data for temperatures of past time periods.  Fortunately these kinds of compounds are found in ice, sediments, fossils, and other long-lived substances.  The heavy to light oxygen ratio is calibrated against a standard of heavy to light oxygen isotopes in seawater 200-500 meters deep in our ocean today.  The ratio between light and heavy oxygen-containing compounds at this depth correlates extremely well with average surface seawater temperature.  It therefore stands to reason that whenever we find oxygen ratios similar to those in today’ oceans and associated seawater temperatures, the same oxygen-ratio/seawater temperature relationship should have existed in oceans throughout history.
            The vast majority of water molecules are made with light oxygen, but the rest contain heavy oxygen (Table 1).  Scientists discovered that the rates of evaporation and condensation of water with high and heavy oxygen are not identical; water with light oxygen evaporates slightly more readily than water with heavy oxygen, and water with heavy oxygen tends to condense and fall as precipitation before most of the water vapor that is made of light oxygen (Fig. 1). 

Figure 1. Relationship between temperature and heavy oxygen (18O) concentration in precipitation.  These data show the percent divergence from the standard 16O:18O ratio in the ocean.  Negative values mean there is less 18O present than in the ocean standard. (Image: NASA)

            When air cools water vapor condenses and falls as precipitation. 18O has a greater mass than 16O and water made with heavy oxygen therefore has a greater mass, and as subject to a greater gravitational force than something that has a lower mass.  As a result, water made with 18O falls more readily than water made with 16O.  Water vapor left in the atmosphere at this point is partially 18O-depleted.  This depletion happens faster when temperatures are low than when they are high.  Therefore, when the Earth is in a cool phase most of the 18O-water precipitates out before water vapor reaches the poles, leaving mostly 16O water to fall as snow to form ice layers there.  Conversely, when the Earth is in a warm phase 18O-water stays in the air longer, and more 18O reaches the poles than when the Earth is cool.  This produces a 16O to 18O ratio in polar ice that contains elevated levels of 18O when the Earth is warm (Fig. 2).  Scientists have measured the ratios of oxygen isotopes in ice layers from polar ice caps to produce accurate records of climate change going back as far as the ice record.  These data currently go back 800,000 years. Fortunately, we can look even farther back using other kinds of data, because oxygen isotope ratios go only so far back using ice alone. 

Figure 2. Water rich in both heavy and light oxygen evaporates at the equator, but as air moves away from the equator it cools, and heavy oxygen water falls as rain at a faster rate than light oxygen water.  During an ice age polar ice there will be significantly less 18O in the ice than when the Earth is in a warm phase.  (Image: NASA)

Before we look at other things that contain oxygen ratio data, however, there is something else of interest that oxygen ratios in water can tell us.  These ratios can tell us whether a particular time period was wet or dry.  This is the case because most of the heavy oxygen tends to condense first and fall as precipitation over oceans, leaving mostly light oxygen water to move onshore to fall as rain over continents.  So, if sediments in a region of ocean have increased amounts of 16O in it, this is almost certainly the result of freshwater runoff from continents.  When this is observed we conclude that Earth was experiencing a wet climate. 

Diversity of Oxygen Records

Ice was pointed out in the previous section as an extremely important source of climate data.  Why is this the case?  Scientists drill cores of ice from polar glaciers (e.g., Antarctica and Greenland) and collect date-specific data from water and other materials trapped in ice (Fig. 3).  The cores from this drilling show distinctive layers that are produced annually (Fig. 4 & 5).  Scientists take samples from each layer, analyze the ice for oxygen isotope ratios and other materials trapped in the ice, and can thereby determine the temperature of the Earth when the ice was formed.

Figure 3. Drilling ice cores from polar ice caps.  (Image courtesy of NASA.)
Figure 4. This photograph was taken when scientists in Antarctica dug a trench, but left a thin wall of snow between the two halves of the trench.  Light illuminating the wall clearly shows the annual layering of snow, which eventually gets compacted into ice layers. The stuffed animal is included for scale. (Image courtesy of NASA.)

Figure 5. These images show ice cores from different depths within a polar ice cap.  The upper image clearly shows layers of ice in the exposed side of an ice sheet.  The lower image shows layers of ice from ice cores, and that they can be quite distinctive, depending on their depth and age, as well as anything else that is trapped in the ice. (Images: NASA.)

            Oxygen isotopes are found in more materials than just ice.  It is also stored in wood, shells, bone, coral, and some kinds of rocks.  One extremely important source of temperature data is stored in the microscopic skeletons of tiny organisms called foraminiferans.  These small organisms are related to amoeba, but they produce calcium carbonate (CaCO3) shells.  The shell of each species of foraminifera has its own unique shape and sculpturing (Fig. 6).  This means that whenever a scientist spots foraminiferan shells, they can know what species of foraminiferan they are looking at, and whether those foraminifera were warm-water or cold-water species.  Looking for the presence of warm and cold-water species, and the oxygen isotope ratios in their shells in sediment layers provide important clues about paleoclimates.  This is one of the reasons why climatologists drill sediment cores as well as ice cores (Fig. 7).

Figure 6. Scanning electron photograph of shells of foraminiferans. 

Figure 7. Drilling ships like the one above are used to collect sediment cores for analysis.  Scientists slice the sediment cores, do chemical analyses of each layer, and look for foraminifera and other evidence of climate change. (Image: NASA.)

            Paleoclimate records also exist in stalagmites that are formed in caves and caverns (Fig. 8).  These kinds of climate data are called speleotherms.  How can speleotherms contain meaningful climate information?  Structures in caves are largely isolated from the surface and do not experience processes of erosion like rocks on the surface do, so once materials are deposited there they remain there indefinitely. 

Figure 8.  Giant stalagmites in Carlsbad Caverns, New Mexico. (Photo: Wikimedia Commons.)

Stalagmites are produced by water that trickles through the soil and rock layers above the cave.  As water moves through the soil some materials, like CaCO3 dissolve in it.  When water drips into caves and then evaporates, the CaCO3 is left behind.  A new layer of CaCO3 is added to a stalagmite each year, so if you slice through a stalagmite and polish the cut edge the individual layers are visible (Fig. 9).  Just like tree rings, the rings in speleotherms are wider during wet years and narrower during dry years, and samples can be taken from each layer for analysis.  But, how can we know the ages of the layers of a stalagmite?  Again, think back to FDSCI 101 and your discussions on radiometric dating.  That works here too!
            As indicated in the text below Fig. 9, Uranium-Thorium radiometric dating can be carried out on a sample from each layer of a speleotherm.  Uranium readily dissolves in water and is deposited along with CaCO3 then the water evaporates.  Thorium, however, does not dissolve as readily in water, so all Thorium in a layer is the result of Uranium decay, and can be used to calculate an accurate age for each layer.  Pretty slick, huh?
Figure 9. This is a photograph of a cross-section cut through a small stalagmite.  Each band represents one year of deposition of chemicals from water dripping from above.  Samples from each section can be used to measure oxygen isotope ratios and to carry out radiometric dating, as indicated in the text below the photo.  (Image courtesy of NASA.)  

            Climate is, of course, more than just temperature.  It is also includes the pattern of precipitation area experiences.  Figure 10 shows the relative precipitation record for the region around Carlsbad Cavern, NM, based on speleotherm data.

 Figure 10.  A record of stalagmite ring thicknesses from Carlsbad Caverns, NM.  The ring thickness provides a record of relative amounts of rainfall in that area over the past 450 years. It is typical for any natural system to exhibit variability around the overall trend. (Image courtesy of NASA.)

            Scientists can also use tree core data to decipher recent climate changes.  As mentioned about in relation to speleotherms, trees in temperate and Polar Regions produce a pair of rings of wood each year.  In years when conditions promote abundant growth trees produce a thick tree ring.  In years when conditions limit growth trees produce a narrow ring (Fig. 11).  By producing overlapping tree ring records scientists have produced climate records extending back thousands of years.  Bristlecone pines are among the known longest living trees, and a climate record using their tree rings has been produced that goes back over 5,000 years (Fig. 12).

Figure 11. This photograph shows part of the cross section of a trunk from a tree.  The tree rings vary in width depending on local climate conditions; wide rings indicate favorable growth years, and narrow rings indicate years in which growth was limited. (Image: NASA)

Figure 12. Precipitation record from overlapping Bristlecone Pine tree ring data (blue line) compared to the average precipitation from the 20th Century (tan line).  Scientists apply knowledge about the relationship between precipitation, temperature, soil quality, and other factors and tree ring thicknesses in living trees to reach conclusions about past climate conditions.  (Image: NASA)

While speleotherms and tree rings are useful for reconstructing terrestrial climate conditions, they do not help us understand how climate changes affect conditions in the ocean.  Fortunately, while trees produce annual tree rings, corals also produce records of annual growth that is recorded in their CaCO3 (Fig. 13).  The CaCO3 secreted by corals occurs in the upper levels of the ocean, so we can analyze each layer of coral skeletons to discover the 16O and 18O ratios to see how climates changed in the tropics during recent history (Fig. 14).

Figure 13. This x-ray of a cross section through a coral colony’s skeleton exposes the annual layers of growth.  The heavy and light oxygen ratios in the CaCO3 that makes up each layer provides a signal that can be used to generate a climate record extending back as far as the age of the colony.  Some colonies are known to have lived well over 1000 years. (Image courtesy of NASA.)

Figure 14.  Oxygen isotope ratios were used to generate a temperature profile for ~1890-1950 (lower graph).  These data are compared to periodic ENSO (El Nino Southern Oscillation) oscillations that occur in the tropical Pacific Ocean to see if correlations exist (upper graph).  Red areas represent temperatures above the long-term average, and blue areas show cooler temperatures.  Dark gray vertical bars represent strong El Nino events, and light gray bars represent weak El Nino events. (Image: NASA.)

Climate Patterns in Deep Time

            Paleoclimatologists use data from sediment cores, ice cores, speleotherms, tree rings, coral growth layers, and other data, to reconstruct Earth’s climate history.  Several groups of climatologists, working independently, generated climate models using available data to provide estimates of past climates throughout Earth’s history.  While these models represent the best science on this topic, the farther we go back in time, the less precise the scenarios tend to be. Earth history with only a relative indication of temperature extremes.  The reconstruction of Earth’s climate history is shown in Fig. 15.  This figure is based on sea level change, proxy data of CO2 concentrations in the atmosphere, and other proxy data from the geologic record.  Figure 16 shows a model of CO2 levels from 400 Ma (million years ago) compared to proxy temperature data.

Figure 15. This figure shows a deep time reconstruction of Earth climate history.  Earth has oscillated between cold and warm periods throughout its history.  Cold periods are indicated in blue and warm periods in…peach J? Observe that the time scale on the left side of the figure is not linear.  It is roughly logarithmic, with older time periods being allocated less space than recent time periods.  This is appropriate since we have much better data for recent time periods than for more ancient times, but if one is unaware of this it can give someone a skewed view of earth’s climate history.  (Image from WW Norton, adapted from Kump et al. 1999.)

Figure 16. Model of paleo-CO2 levels, comparing the model to other predictors of climate.  (Image from Archer and Rahmstorf.)

            Climate reconstructions from deep geologic time are helpful in showing general trends, but if we hope to identify current climate trends and make sense of what is happening now, we must compare what is happening today with more recent climate histories.  For example, by using oxygen isotope data from ocean sediments we can generate a relatively precise record of climate from 65 Ma.  This reconstruction is shown in Fig. 17.  Many climatologists who have studied the Paleocene-Eocene Thermal Maximum (PETM) have suggested that evidence of events before and during this thermal maximum around 55 Ma are similar in some respects to trends we are experiencing today.

Figure 17. Reconstruction of past climate using evidence from the deep ocean, including oxygen isotope ratios and other evidence from sediment cores. (Image from Archer and Rahmstorf.)

            As shown in Fig. 17, Earth has, with a few ups and downs in global temperature, undergone gradual cooling over the past 65Ma.  As we look at progressively shorter time intervals we see that over the 400,000 years that Earth has experienced a temperature equilibrium including oscillations between cool and warm periods, i.e., glacial and interglacial periods. 

Figure 18. The past 400,000 years of Earth’s temperature variability.  Four prolonged glacial periods are indicated in blue, and warm interglacial periods are shown in red. (Image adapted by ARH from a figure courtesy of NASA.)

            The bottom line when it comes to Earth’s climate history is that climate has changed in the past, it’s changing today, and it will continue to change in the future.  This conclusion is evidenced by the fact that we have seen periods of Earth’s history where it was probably a lot like a giant ice ball, and other times when it was like a giant hot house.  Geologically speaking, recently Earth has experienced a more or less stable climate cycle of warm and cool periods.  So, when we begin to consider the current state of the climate, this recent trend is the most meaningful baseline we have for comparison to what we see today.  Deviations from Earth’s recent past stable climate conditions deserve to be investigated.  Those are, of course, topics for other class discussions, and we will address them later in the semester. 

Source material

Archer, D., and S. Rahmstorf. 2010. The Climate Crisis. Cambridge University Press.

Riebeck, H. 2005. Paleoclimatology. NASA Earth Observatory Program.