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Also See: CDC's Climate Glossaries and Weather Tools

A - B- C - D- E- F- G- H- I- J- K- L- M- N- O - P - R- S- T-U-Z
absolute dating
- Dating methods that determine time without ambiguity to a known level of accuracy. Most radioactive decay-based methods are considered absolute.

- Used in Paleoclimatology to describe the deposition of sediment or other material over time. Accumulation rates are usually measured as mass/time, volume/time, or mass/length2/time.

- A suspension of solid or liquid particles in a gas, for example sulfate molecules (SO4-) found in the earth atmosphere.

- The percentage of solar radiation that is reflected relative to the total incoming radiation.

- A substance which, when added to water, decreases the hydrogen-ion concentration; a solution containing a base, a substance that combines with a hydrogen ion in solution.

- A period of high temperature; a postglacial thermal optimum

- Single-celled, multi-celled or colonial marine or freshwater plants that contain chlorophyll; they don't have true roots, stems or leaves and also do not flower or contain seeds

- A high elevation plateau in southeastern Peru and western Bolivia, elevation about 3500 m.

- The flowering seed plants, as differentiated from gymnosperms, the non-flowering seed plants.

anthropogenic - Generated by the actions of humans.

aphelion- The point in the earth's orbit furthest away from the sun.

aquatic macrophytes - Aquatic plants that are found in the near-shore zone.

arid - Lacking moisture, especially having insufficient rainfall to support trees or woody plants.

atmosphere - The whole mass of gases surrounding the earth or other celestial bodies. Today's atmosphere is made up primarily of nitrogen (78%), free oxygen (21%) and greenhouse gases which can capture solar radiation: water vapor, which ranges from less than 1% in arid regions to over 3% in moist areas, carbon dioxide (0.035%) and methane (0.00018%). In the past the composition of the Earth's atmosphere has varied.

autotroph -Organisms that are able to produce their own food through processes such as photosynthesis.


basal sediments - Till carried at or deposited from the under surface of a glacier.

bedrock substrate - Solid, in place rock underlying unconsolidated sediments or other superficial material

benthic Foraminifera - Single-celled amimals that live near the sediment water interface and have calcium carbonate skeletons. The skeletons of benthic foraminifers are often preserved in ocean sediments, providing a rich fossil record of the environmental conditions of the lake.

Bergmann's Rule - An ecological theory that proposes there is an inverse relationship between environmental temperature and an organism's body size.

carbon dating
- A dating method that uses the disintegration of the 14C atom to determine the age of sample containing carbon. 14C is produced in the atmosphere by cosmic ray bombardment, and has a half-life of 5570 years, making it useful for dating samples in the range of 0-40,000 years.

celestial equator - The great circle on the celestial sphere midway between the celestial poles (the projection of the north and south pole onto the celestial sphere).

celestial sphere - An imaginary sphere of infinite radius, on which the stars appear to be placed.

calcium carbonate (CaCO3) - A molecule consisting of calcium, carbon and oxygen that is secreted by corals, forming their skeleton; it also secreted by mollusks (clams, oysters, etc.), forming their protective shells.

calcium concentrations - Concentration (units mass/mass) of the calcium ion (Ca+), often found in layers of ice, and derived from atmospheric transport of dust.

calving - To separate or break so that a part becomes detached.

- A general term for the age-depth relationship in ice, sediment, or another deposit. Ages are usually measured for discrete samples, and the ages of intermediate samples is interpolated between samples with measured ages.

Classic Collapse
- Collapse of the Maya civilization that occurred between 800 and 900 A.D.. Symptoms of the collapse included abandonment of the countryside and ceremonial centers as well as a cessation of cultural activities.

clast - Fragment of rock.

climate - Long term characteristics of weather.

climatic feedback mechanisms - A feedback is an enhancement (positive feedback) or a damping (negative feedback) of an initial change, in this case in the climate system. For example, when less energy reaches the earth, temperature decreases and the area covered by snow increases. The albedo of the planet increases, reflecting more solar energy back into space. Consequently less energy is absorbed at the surface, and temperature further decreases. The whole "cycle" from the initial cooling to the further cooling is a feedback. It is a positive feedback in this example.

clone - An individual, identical to the parent organism, created by the splitting or budding of cells from the parent organism.

continental processes - tectonic movements that relate to the continental land masses.

coral bleaching
- An environmental stress indicator for coral; if conditions for corals are not optimum, the corals will expel the algae that live among the living polyps, therefore giving the colony a bleached appearance.

- The procedure of matching and synchronizing ring-width variations and other structural characteristics among trees that have grown in nearby areas, allowing the identification of the exact year in which the ring was formed.

cryosphere - The portion of the world's climate system which consists of snow and ice deposits

Dansgaard-Oeschger cycles - Climate oscillations averaging a few thousand years in duration that dominate Greenland ice-core records.

debris slide - Downward movement of unconsolidated mass of mud, sediment, and rock.

dendrochronology - A science based on the exact calendar dating of annual growth rings in wood.

dendroclimatology - A subfield of dendrochronology, which investigates the climatic effect on tree growth, and uses dated tree rings to reconstruct and study past and present climate.

density - The mass per unit volume of a substance under specified conditions of pressure and temperature.

detrital carbonate
- Crystalline calcium carbonate found in ocean sediments, usually derived from continental weathering of carbonate rock. Detrital carbonate is more resistant to dissolution compared to the calcium carbonate produced by plankton that falls directly to the seafloor.

diatom - Single celled phytoplankton that produce silica skeletons. Diatoms are one of the most abundant, widely distributed primary producers in the ocean. Different species of diatoms living in ocean and lakes have affinities for different environmental conditions such as alkalinity, available nutrients, salinity and acidity.

Diluvian Theory - Theory that attributed most geological features of the earth to the great flood described in the Bible.

diurnal cycle - Mean solar day occurring as Earth rotates from east to west on its axis.

dolomite - Mineral consisting of calcium, magnesium carbonate found in crystals, and in extensive beds as a compact limestone -- CaMg(CO3)2.

Dreizack seamounts
- A chain of extinct underwater volcanoes rising 1000m or higher above the sea floor, either flat-topped or peaked and located in the eastern North Atlantic.

- The portion of the annual ring produced early in the growing season, characterized by large, thin-walled cells. Earlywood is more porous than latewood, and often lighter in color. Also known as springwood.

eccentricity - The amount that the earth's revolution deviates from a circular path; the variation of an ellipse from a circle, where a circle has an eccentricity of 0.

ecliptic - The apparent path of the sun on the celestial sphere, also used for the plane in which the motion of the earth around the sun takes place.

ecosystem - Relationships between and among living organisms and their non-living environment.

El Niño - The appearance of unusually warm waters in the eastern Pacific; termed the "Christ child," because of the time of year it effects the South American coastline.

ENSO - An acronym for El Niño Southern Oscillation

epidermis - The outermost layer of skin cells.

equinox - Either of two points on the celestial sphere where the celestial equator intersects the ecliptic; either of the two times each year when the sun crosses the equator, and day and night are of equal length (spring equinox, fall equinox).

erratics - Large boulders displaced from their natural geologic location by glaciers.

evolutionary change - Either phenotypic or genetic changes that occur in an organism from generation to generation through the exchange of genes.

exine - The outer wall layer of a spore or pollen grain.

false ring
- A change in cell structure within an annual growth layer, which resembles the boundary of a true annual ring, making it appear to be two or more growth layers instead of one. Also known as a double ring or an intra-annual ring.

fault depression - Basin formed by the downward movement of the earth's crust at a geological fault.

fault line- A brittle fracture across which relative movement of rocks has occurred.

firn - Granular, partially consolidated snow that has passed through one summer melt season but is not yet glacial ice. Also called old snow.

fossil air
- A sample of air that preserves the composition of the environment at the time it was deposited. Bubbles found in ice cores are one example of fossil air that records the atmospheric composition of the atmosphere at the time the ice was formed.

- Egg or sperm cell that combines with a gamete of the opposite sex to form a zygote cell.

gastropods - Class of mollusks that includes snails.

glacier - River of ice that under pressure can deform and flow plastically.

geologic time scale - Relative time scale based onstratigraphic position and correlation, and many different types of chronologic evidence. Geologic time is broken down into eons, eras, periods and epochs.

- Greenland Ice Sheet Project 2, the second phase of an effort by a group of scientists to produce long records of climate by drilling into the Greenland Ice Sheet from the surface to bedrock.

global warming
- an increase in temperature that occurs globally such as the interglacial warming period the earth experienced after the last Ice Age, or that predicted to result from human increases in greenhouse gases.

greenhouse gases - Any one of the gases found in the atmosphere (including CO2, H2O, CH4) that act to allow short wave radiation from the sun to reach the earth, but which absorbs outgoing long wave radiation from the earth surface.

"greenhouse effect"
- The process by which the equilibrium temperature of the earth is increased due to presence of gases in the atmosphere that absorb outgoing longwave radiation.

growth band - The secretion of CaCO3 by coral forms yearly growth bands; one yearly growth band contains two smaller bands representing winter growth and summer growth.

gymnosperms - The non-flowering seed plants, as differentiated from angiosperms, the flowering seed plants.

- Location where a plant or animal species naturally lives and grows.

half-life - The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.

hemipelagic sediments
- Deep-sea sediment in which more than 25% of the fraction coarser than 5 microns is of terrigenous, volcanogenic, and/or neritic origin. Such deposits usually accumulate near the continental margin.

- Organisms that are unable to produce their own food, therefore they consume other organisms (plants or animals) to obtain energy.

Holocene epoch - An epoch of the Quaternary period dating from the end of the Pleistocene approximately 11,000 years ago until the present.

hominid - Any of a family (Hominidae) of erect bipedal primate mammals comprising recent humans together with extinct ancestral and related forms

Ice Age - Period during which polar ice extends to much lower latitudes than normal.

ice rafted detritus
- Continental material transport within a matrix of ice and deposited in marine sediments when the ice matrix melts.

ice sheet margin
- Edge of the ice sheet where melting and calving of icebergs occurs.

ice streams - Rapidly flowing ice generally in the bottom of an ice sheet and flowing from the middle to the ice sheet margin.

increment borer - A manual tool used to bore and extract a thin cylinder of wood from tree stems.

Indonesian Low - The low pressure, or cyclonic air circulation, normally found in the western tropical Pacific and Indonesia, associated with a large, deep layer of warm ocean water.

insolation - Amount of solar radiation received on a given body or in a given area.

Intertropical Convergence Zone - The region that circles the Earth, near the equator, where the trade winds of the Northern and Southern Hemispheres come together.

ion - Atoms that have either a positive or negative charge.

isotope - A form of a specific element that has the same number of protons, but differs in the number of neutrons; forms of the same element that have different mass numbers.

Jurassic period
- The second period of the Mesozoic era, thought to have covered the span of time between 190 and 135 million years ago.

karstic - Comprised of limestone.

keystone species - A species that exerts a major influence on the composition and dynamics of the community in which it lives.

latewood - Dense, often dark, and heavily lignified wood produced in the annual ring during the later part of the growing season, characterized by small, thick-walled cells. Also known as summerwood.

littoral zone - Area of shore between mean high water and mean low water.

lithic - Made of rock.

locally absent ring
- A growth ring that is discontinuous around the stem so that it is absent along certain radii; also referred to as a partial ring or missing ring.

loess - A wind-deposited sediment consisting mostly of silt, the silt commonly derived from finely ground rock washed out of continental glaciers.

meltwater plume
- Body of fresh water derived from the melting of glacial ice that floats in large bodies of salt water.

Mesoamerica - Continental North America south of Mexico that is usually considered to comprise the present day countries of Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama.

methane (CH4) - An odorless, colorless, flammable gas, the major constituent of natural gas, and produced by a variety of natural sources.

Miocene epoch
- An epoch of the early Tertiary period, found in-between the Oligocene and the Pliocene eras.

morphology - The scientific study of organic form, including both its development and its function.

natural climate record
- A record of climatic events found by examining the natural environment (tree rings, coral growth bands, layers of ice in glaciers).

nepheloid layer
- Layer of seawater containing a high concentration of suspended sediment that may reach heights of several hundred meters above the ocean floor.

nitric acid (HNO3) - A highly reactive oxidizing agent obtained by distilling a nitrate with sulfuric acid.

normal faulting
- A fault in which the hanging wall moves downward relative to the footwall, in response to extensional stress.

obliquity - The angle between the planes of the celestial equator and the ecliptic, currently the earth has a 23.4 degree obliquity cycle.

orbital forcing - Theory that proposes large scale climate changes are due in part to the variations in precession, eccentricity and obliquity that affects the amount of solar radiation received by the earth.

ostracods - Marine and fresh-water crustaceans that have their body enclosed in a bi-valved shell.

oxygen isotopes - Oxygen atoms having the same atomic number (protons) but different mass numbers (and different numbers of neutrons). The two stable isotopes of oxygen are 16O and 18O.

- Relative loss of electrons in a chemical reaction; usually associated with the liberation of energy.

oxygen isotope ratio (d18O) - An expression for the ratio of the 18O to 16O atoms in a sample relative to a standard, defined as:D18O= (18O/16Osample - 18O/16Ostandard)/ 18O/16Ostandard

pack rat middens
- Remains of food and other materials left in caves inhabited by pack rats which are preserved and serve as a "time capsule" of the vegetation of the time and, by extension, the climate.

- Past or ancient climates.

paleoclimatologist - One who studies ancient (paleo-) climate.

paleoenvironmental proxy - An environmental remnant of the past (pollen grains, tree rings, lake sediments, pack rat middens, ice cores, coral skeletons) that assist researchers in deciphering past climate conditions through the use of scientifically proven dating techniques.

Paleozoic - An era of geological history which extends from the beginning of the Cambrian to the close of the Permian and is marked by the culmination of nearly all classes of invertebrates except the insects and in the later epochs of which seed-bearing plants, amphibians, and reptiles first appeared.

palynology - The study of pollen analysis; used to determine past environmental conditions.

particulate - Material made up of small pieces.

PCR (polymerase chain reaction) - A technique used to rapidly reproduce millions of copies of a particular stretch of DNA.

pelagic - Primary division of the sea that includes the whole mass of water subdivided into neritic and oceanic zones.

pharynx - The section of the digestive system that extends from the mouth and nasal cavities to the larynx, where it becomes continuous with the esophagus.

phenotypic plasticity - The ability of an organism to adapt to a changing environment through the manipulation of its phenotype, without the alteration of its genotype.

phloem - In trees, the region containing food-conducting tissue in the bark.

- The process in green plants and certain other organisms by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source.
Carbon dioxide (CO2 ) and water (H2 O) are combined in the presence of sunlight and the green pigment chlorophyll, to produce food (C6 H12 O6 ) and oxygen (O2 ).

plankton - Small or microscopic organisms, including algae and protozoan, that float or drift in great numbers in fresh or salt water, especially at or near the surface, and serve as food for fish and other larger organisms.

planktonic Foraminifera - Marine zooplankton that passively float or weakly swim, and have calcium carbonate skeletons that are present in large numbers on the surface of the ocean. The skeletons of planktonic foraminifers are preserved in large numbers in deep-sea sediments, providing a rich fossil record of the environmental conditions of the upper ocean. The size of the shells is typically from 50 to 100 microns.

Pleistocene epoch - An interval of the Quaternary period, from 1.8 million years before present to 10 thousand years before present.

Pliocene - An epoch of the late Neogene period, from 5.3 to 1.8 million years before present.

pluvial pharynx - The part of the gut between the mouth and the esophagus, the throat.

polyp - The fleshy, living portion of coral; they are permanently fixed to the reef in which they are attached.

pollen - Pollen grains that are made up of microspores containing a mature or immature male gametophyte.

precession (of the equinoxes) - A measure of the slow clockwise motion of the equinoxes along the ecliptic due to the motion of the earth's axis of rotation around the pole of the ecliptic; the angular movement of the spin axis of an object around an axis fixed in space.

proxy signals - A general term for paleoclimate evidence that can be used to indirectly infer or estimate some aspect of the environment such as precipitation or temperature.

Quaternary period
- The second period of the Cenozoic era containing the Pleistocene epoch and the Holocene epoch and dating from 1.8 million years to the present.

radiocarbon age - The age of plant or animal remains determined by measuring the remaining activity of the 14C atoms in the sample: A=A0e-ltwhere A is the measured activity, A0 is the initial activity, l is the decay constant, and t is the sample age.

radiocarbon time
- The use of the regular known rates of radiocarbon decay to determine the exact ages of carbon-based life.

relative dating
- Dating methods that determine time with respect to stratigraphic position, for example deeper layers being older, or with respect to some changing quantity or property, such as magnetic polarity.

rock varnish
- A dark, manganese coating that forms on top of rocks, usually paper-thin. The amount of moisture affects the amount of manganese, so the thicker the varnish the wetter the climate was.

sea surface temperatures
- Temperature of the ocean's surface used in collaboration with other data to predict an El Nino occurrence.

seismic profile - A two dimensional picture of the geophysical properties of layers of the earth reflecting differences in arrival time of energy waves as they propagate through the earth.

shelf break - The transition between the gently sloping continental shelf and the much steeper continental slope that descend to ocean depths.

skeleton plot - A graphical representation of ring width patterns, used in crossdating.

solar variability - changes in the sun's radiation due to the sun's internal dynamics.

Southern Oscillation (ENSO) - Shifting of pressure zones in the Pacific during an El Nino event.

spring tide - Tide that occurs when the sun, moon and earth are aligned either at a new moon or a full moon; these tides have the greatest range from low to high tide.

stable isotope - Different species of an element that have the same atomic number, but different atomic mass, that are not affected by radioactive decay.

standardization - The removal of growth trends due to the effects of increasing tree age and circumference. Standardized ring width time series are designed to have a stationary mean and variance.

stomata - A minute opening bordered by guard cells in the epidermis of leaves and stems through which gases pass.

striations - Small-scale grooves cut into rock by the rasping action of rock-laden glaciers.

symbiosis - A relationship between two organisms in which one or both of the organisms benefit from the other.

- Ripples of change that occur far away from the source; wildfires in the Australian Outback and flooding in the Peruvian Andes are teleconnections caused by El Nino.

tentacles - Structures located at the opposite end of the attached coral, used for capturing and swallowing their prey.

thermohaline circulation (THC)- Density-driven circulation system for the world's oceans. Warm Atlantic water moves northward along the axis of the Gulf Stream, evaporation makes the water more and more dense while releasing heat to the colder atmosphere in the North Atlantic. Once dense enough, the water sinks into the deep ocean, forming a downward limb of a giant conveyor-like circulation that extends around the world's oceans.

tracheid - In gymnosperms, dead, vertically oriented tubular cells that make up the xylem.

tradewinds - A system of low-level winds occurring in the tropics; the tradewinds blow from the northeast to the equator in the Northern Hemisphere and from the southeast to the equator in the Southern Hemisphere.

tree-ring chronology - The averaged standardized ring-width indices from a number of trees sampled from a particular site that can be used for crossdating and estimating past climate.

tree-ring indices - Dimensionless values, generated through the process of standardization, that represent annual departures in tree growth compared to mean growth at the site over time.

- A fast moving sediment-rich density current. The resulting sediment deposits are characterized by graded bedding, moderate sorting, and well-developed primary structures, especially laminations.

- Rising of cold, nutrient-rich water towards the surface.

varves - Lake or ocean annual layers of finer and coarser silt/clay that represent the annual cycles of deposition in that lake or ocean.

vascular cambium - The thin living sheath of meristematic tissue between the wood and the bark which differentiates into xylem on the inside and phloem on the outside and produces the annual ring.

vessel - Large, tube-like water-conducting element in the wood of angiosperms.

visual stratigraphy
- The process of identifying different layers in ice, rock, sediment, or another paleo deposit, based on visually apparent distinctions such as color or other properties. The identified stratigraphic layers are usually assigned different ages or age intervals.

weather - Temperature, precipitation and wind speed and direction that occur on a daily basis.

xylem - The water-conducting tissue of plants, which makes up the wood cylinder of a tree, located inside the vascular cambium and surrounding the pith.

zooxanthellae - Microscopic phytoplankton that have a symbiotic relationship with coral; they are also responsible for giving coral their slightly brown color.

Also See: CDC's Climate Glossaries and Weather Tools

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