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Grammar and Style Guide

AGU Publications has updated its manuscript style, reflected in the below guide. Read about it in Eos Editors’ Vox. The updated style will be applied to manuscripts during the typesetting process. Please use the below updated guide as you prepare new submissions.

AGU follows American Psychological Association (APA) style on grammar, punctuation, table formatting, citations, and references. This full guide includes basic APA style (and exceptions) and AGU-specific style

For detailed information, see Publication Manual of the American Psychological Association, Sixth Edition.

In this Guide:
Reference Format
Examples of Common References
Quotation Marks
Colons and Semicolons
Italics and Boldface
Commonly Used Proper Names
Geographical Terms
Miscellaneous Geological and Scientific Terms
Table Formatting
Special Characters
Date and Time
Word List


This section explains and gives examples of in-text citations and reference list for different media.

AGU follows APA reference style as found in the Publication Manual of the APA, latest edition. Please note that all sources cited in text, tables, and figures must appear in the reference list, and all entries in the reference list must be cited in text. References that are only cited in supporting information should also be included in the reference list of the paper and cited in text. Data created, used from others, and supports findings should be included in the Availability Statement and cited in the References sections. Software specific to the research should also be included and cited. See Data and Software for Authors for further guidance.

Text citations. In-text should be cited using author surname(s) and the date of publication:

“in earlier studies (Johnson, 2009)” or “ given by Johnson and Smith (2008)” or “In 2012, Johnson and Smith’s study showed that”

Note that author names are not italicized and a comma follows the author name(s) if the reference is enclosed in parentheses. If a multiple-author citation is in the running text, use the word “and”; if in a parenthetical citation, use the ampersand:

Zhu and Zhang (2016) found that....

A subsequent study found that... (Zhu & Zhang, 2016).

For references by three or more authors, use “et al.” after the first author: (Zhang et al., 2005). Please note, this is a deviation from APA style which lists all author names in works by three to five authors in the first citation in text and “et al.” in subsequent citations.

  • If a parenthetical citation includes two or more papers, separate the citations with a semicolon and list alphabetically by first author name: (Forbes et al., 1999; Hausler & Wu, 2001).
    Exception: You may distinguish a major citation from others by inserting a phrase such as see also, before the remaining, which should be in alphabetical order: (Zimecki & Thomas, 2001; see also Jong, 1999; Rembrandt et al., 2007). You may also describe the seminal work outside of parentheses then include more minor contributions at the end of the sentence in parentheses in alpha order.

  • If two or more citations by the same author(s) are listed consecutively, they should be combined: (Jones, 1999, 2001; Jones & Tuller, 2003, 2004; Jones et al., 2006, 2008).

  • To distinguish two or more papers by the same author(s) published in the same year, add a, b, c, etc. after the year: (Park, 1995a,1995b; Park et al., 2001a, 2001b, 2001c); the corresponding letter should also appear with the date in the reference list.

  • If two or more references of more than three but less than six surnames with the same year, shorten to the same form (e.g., both Jones, Tuller, Park, & Wu, 2013, and Jones, Tuller, Park, Le Pinchon, & Johnson, 2013), shorten to cite the surnames of the first authors and of as many of the subsequent authors as necessary to distinguish the two references followed by a comma and “et al.”: Jones, Tuller, Park, and Wu (2013) and Jones, Tuller, Park, Le Pinchon, et al. (2013).

  • If two or more references from the same year contain the same first six or more authors, use a, b, c, and so on for the in-text citation and in the references list (e.g. Tuller et al., 2016a; Tuller et al., 2016b). This is the case even when the entire author lists are not identical. This is to avoid ambiguity in the in-text citation. See also References list, below.

  • If there are different first authors having the same last name, citations should always include the first initials to avoid ambiguity.

  • For citations that appear in parentheses, use commas to set off the publication year: (see Figure 3 of Zhu et al., 2013, for linear growth rates).

  • Avoid reference citations in the abstract unless dependent on or closely related to another paper (e.g., companion, comment, reply, or commentary on another paper(s)). If included, also include the DOI after the year: (Izett & Fennel, 2018, or Izett and Fennel (2018,

Reference list. Reference entries should be ordered alphabetically by the last name of the first author. Follow a strict letter-by-letter alphabetization of the entire last name, ignoring spaces in surnames with multiple words (Lefer before Le Pichon, Vander Linden before van Giessen). When alphabetizing surnames, consider that “nothing precedes something” e.g., Brown before Browning. Other examples: Sanders before St. Amant, MacMillian before McArthur—i.e., alphabetize them literally, not as if they were spelled out.

  • All authors’ initials and surnames are given in reverse order; include a comma between surname and initials. Include periods between initials.

  • For two to seven authors, use a comma then an ampersand before the final author.

  • For eight or more authors, include the first six author names, followed by “et al.”. E.g.: Yao, Q., Brown, P.M., Lui, S., Rocca, M.E., Trouet, V., Zheng, B., et al. (2017)..... Note: This represents an exception to APA reference style. AGU’s latex template and APA style in reference management software do not include this exception. You do not need to update your manuscript with this exception; it will be applied by the production vendor during the copy-editing process.

  • If two or more references from the same year contain the same first six or more authors, use a, b, c, etc. after the year. This is the case even when the entire author lists are not identical. This is to avoid ambiguity in the in-text citation. See Text Citations section, above, on how to cite in-text.

  • A publication date must be given for each reference.

  • Note the use of lowercase letters to allow differentiation of text citations of work published in the same year when at least the first six authors are the same.

  • The Digital Object Identifier (DOI) is a required part of the citation for AGU journal articles. When they are known, DOIs should be included for non-AGU publications.

List references by the same first author in the following order:

  1. First author alone, chronologically (earliest first):

Smith, R. (2000a). ....

Smith, R. (2000b). ....

Smith, R. (2003). ....

  1. With one coauthor, alphabetically by coauthor and then earliest first when identical author lists:

Smith, R., & Allen, F. A. (2001). ....

Smith, R., & Frank, L. A. (1998). ....

Smith, R., & Frank, L. A. (2001). ....

  1. With two or more coauthors, alphabetically by surname of the second author:. Arrange references with the same first author and different second or third authors alphabetically by the surname of the second author or, if the second author is the same, the surname of the third author, and so on. One-author entries precede multiple-author entries even when multiple-author work was published earlier:

Smith, R. (2016).

Smith, R., Allen, F. A., & Baker, T. L. (1999). ....

Smith, R., & Roberts, D. H. (2005). ....

Smith, R., Roberts, D. H., & Jones, J. (1998). ....

Smith, T. (1998). ....

  1. Alphabetize different first authors having the same last name according to the initials of their first names. In-text references should always include the first initials (even when year of publication is different) to avoid ambiguity.


The following explain elements, formatting, and provide examples of the most commonly cited reference types.

Article in journal

  • Authors, publication date, article title, journal, volume, and pages/citation number must be included. Note, there is no period after DOIs.

  • Article titles: Use sentence case for article titles, capitalizing the first word of the article title, subtitle, and proper nouns. Do not use quotation marks or italics.

  • Periodical/journal titles: Give the entire periodical title—do not abbreviate. Use title case, capitalizing major words and proper nouns. Italicize titles of periodicals.

Author, A. A., Author, B. B., & Author, C. C. (year). Title of article. Title of periodical, xx(x), pp-pp.

Deng, A., & Stauffer, D. R. (2006). On improving 4-km mesoscale model simulations. Journal of Applied Meteorology and Climatology, 45(3), 361–381.

Fang, X., Liemohn, M. W., Nagy, A. F., Luhmann, J. G., & Ma, Y. (2009). On the effect of the Martian crustal magnetic field on atmospheric erosion. Icarus. Advance online publication.

Wang, C. (2005). A modeling study of the response of tropical deep convection to the increase of cloud condensational nuclei concentration: 1. Dynamics and microphysics. Journal of Geophysical Research: Atmospheres, 110, D21211.

Yum, S. S., & Hudson, J. G. (2002). Maritime/continental microphysical contrasts in stratus. Tellus, Series B, 54, 61–73.

Book and reports

  • Authors, publication date, title, publisher’s location, and publisher must be included. Include the DOI if one is assigned.

  • Book and report titles: Use sentence case, capitalizing the first word of the article title, subtitle, and proper nouns.

  • Series titles: Use title case, capitalizing major words, e.g., Antarctic Research Series.

  • If location includes a U.S. state, do not use periods in state abbreviation.

  • To cite an entire edited volume, use the editors as the authors, as shown below.

  • If no authors, move the title to the author position. End title with a period.

  • Chapter or report titles within volume or series should use non-italics. Volume or series title should be in italics.

  • Include series and volume number when applicable.

de Marsily, G. (1986). Quantitative hydrogeology: Groundwater hydrology for engineers.San Diego, CA: Academic.

Klotz, S., & Johnson, N. L. (Eds.). (1983). Encyclopedia of statistical sciences, Hoboken, NJ: John Wiley.

Tape, W. (1994). Atmospheric halos. Antarctic Research Series. (Vol. 64). Washington, DC: American Geophysical Union.

Moridis, G. J. (1998). A set of semianalytical solutions for parameter estimation in diffusion cell experiments (Rep. LBNL-41857). Berkeley, CA: Lawrence Berkeley National Laboratory.

Trask, N. J. (1986). Size and spatial distribution of craters estimated from Ranger photographs. In Ranger 8 and 9 analyses and interpretation (Technical Report 32-800, pp. 251–260). Pasadena, CA: Jet Propulsion Laboratory.

U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute. (2003). Managing asthma: A guide for schools (NIH Publication No. 02-2650). Retrieved from

Chapter in book

  • Authors, publication date, chapter title, editors (preceded by “In”), book title, chapter pages, publisher’s location, and publisher.

  • If no authors, move the title to the author position. End the title with a period.

  • Chapter titles: Use sentence case, capitalizing the first word, first word of a subtitle, and proper nouns. Do not use quotation marks or italics.

  • Book or series title: Use title case, capitalizing major words. Use italics.

  • Include book series and volume number when applicable.

  • Editions, volume numbers, and page numbers should be placed in parentheses after the title.

  • If a work has many editors, they may be abbreviated with the first editor, then “et al..”

Langmuir, C. H., Klein, E. M., & Plank, T. (1992). Petrological systematics of mid-ocean ridge basalts: Constraints on melt generation beneath ocean ridges. In J. P. Morgan, D.K. Blackman, J.M. Sinton (Eds.), Mantle flow and melt generation at mid-ocean ridges,Geophysical Monograph Series (Vol. 71, pp. 183–280). Washington, DC: American Geophysical Union.

Tapley, B. D., & Kim, M.-C. (2001). Applications to geodesy. In L.-L. Fu & A. Cazenave (Eds.), Satellite altimetry and Earth sciences: A handbook of techniques and applications(pp. 371–406). San Diego, CA: Academic.

Moridis, G. J. (1998). A set of semianalytical solutions for parameter estimation in diffusion cell experiments. (Rep. LBNL-41857). Berkeley, CA: Lawrence Berkeley National Laboratory.

Trask, N. J. (1986). Size and spatial distribution of craters estimated from Ranger photographs. In Ranger 8 and 9 analyses and interpretation (Tech. Rep. 32-800, pp. 251–260). Pasadena, CA: Jet Propulsion Laboratory.


  • Authors, publication date, map title, publisher/sponsor, and publisher’s location must be included.

  • If no authors, move the title to the author position. End the title with a period.

  • If the map has a number or designator, it should be included (in italics).

  • If retrieved online, include the Web address.

Author, A. A. (1998). Title of work (Map No. xxx). Location: Publisher.

Bentor, Y., & Vroman, A. (1959). Arava Valley, with explanatory text. In The geological map of the Negev (rev. ed., Sheet 19, scale 1:1,000,000). Jerusalem: Government Printer.

Brown, R. J. E. (1967). Permafrost in Canada. (Map 1246A). Ottawa, ON: Geological Survey of Canada.


  • Authors, publication date, thesis title, degree, institution, and institution’s location must be included. If retrieved from an online repository, include name of database.

  • Use sentence case for the title, capitalizing the first word, first word of the subtitle, if any, and proper nouns.

Author, A. A. (2017). Title of doctoral dissertation or master’s thesis (Doctoral dissertation or master’s thesis). Retrieved from [Name of Database]. (Accession or Order No. or uri). Location: Institution.

Liu, X. (2017). Surface energy and mass balance model for Greenland Ice Sheet and future projections, (Doctoral dissertation). Retrieved from Deep Blue. ( Ann Arbor, MI: University of Michigan.

Conference paper

  • Authors, meeting date, title of paper presented, name of meeting (preceded by “paper presented at”), meeting sponsor, and location of meeting are required.

  • Conference proceedings published as books or in journals should be formatted as those types.

Khain, A., Pokrovsky, A., Blahak, U., & Rosenfeld, D. (2008). Is the dependence of warm and ice precipitation on the aerosol concentration monotonic? Paper presented at 15th International Conference on Clouds and Precipitation, Cancun, Mexico.

Smith, E. A., Haddad, Z. S., Tanelli, S., & Tripoli, G. J. (2008). Advancements in NEXRAD in Space (NIS). Paper presented at 28th Conference on Hurricanes and Tropical Meteorology, American Meteorological Society, Orlando, FL.

Indigenous Oral Teachings

Cardinal, D. Goodfish Lake Cree Nation. Treaty 6. Lives in Edmonton. Oral teaching. personal communication. April 4, 2004


See Data and Software for Authors - Data and Software Citation.


Compound words can be open as two words, combined as a solid word, or hyphenated. Hyphenation follows APA grammar rules. If an applicable rule is not listed below, consult the dictionary and AGU’s Word List at the end of this document, then follow hyphenation and compound word usage of your scientific discipline. See also Words formed with Prefixes section in this guide.

Attributive Adjectives

Always hyphenate:





Noun + present or past participle

English-speaking people
U-shaped tube
sulfate-containing aerosols
e-folding layer
sediment-filled streams
hand-drawn graphs
V-shaped weir

AGU will follow author if the noun in the combination is modified. For example, if “field-aligned” appears in the paper, it is author choice to hyphenate “magnetic-field-aligned irregularity.”

Adjective + present
or past participle (except compass directions)

straight-sided vessel
coarse-textured grain
lunar-orbiting satellite

Do not hyphenate if the adjective is modified by an adverb, as in: more coarse textured grain, very fine grained

+ preposition or adverb (unless closed up or opened in dictionary)


Consult dictionary for closed or opened:

Closed: secondhand, crosstown, groundwater

Opened: full moon, real estate

“Well,” “ill,” or “little”
+ past participle

well-known theorem
ill-defined term
little-known derivation

Do not hyphenate if the combination is being used as a predicate adjective or if well (ill, little) is modified by an adverb:

The model is well known.
very well known model
less well defined terms

Preposition + noun or adjective

near-surface reaction
behind-arc spreading
near-normal wave mode

Close up “nearshore” and others that appear closed in the dictionary in AGU’s Word List

“Quasi” + adjective or adverb. Check the dictionary for closed forms.

quasi-2-D convection
quasi-linear expression
quasiperiodic wave

When quasi is used with a two-part adjective, quasi should stand by itself to avoid ambiguity:
quasi steady state system
quasi self-consistent model

“Self,” “cross,” “all,”
and “no” compounds

self-sustaining reaction
cross-L sweep
cross-section(al) diagram
cross-correlation function
all-salt deposit
no-flow boundaries

Also hyphenate as a predicate adjective. Check the dictionary for approved closed forms.

Fractions and
temporary compounds formed by adjective + noun indicating number, dimension, or

two-thirds majority
zero-base budgeting
one-dimensional figure
k-dimensional model
two-fluid response
single-chain reaction
multiple-layer model
high-energy particles
middle-latitude stations
low-P region
low-Mg samples
lowest-latitude sample

Do not hyphenate if adjective is modified by an adverb: very high frequency signals.

There may be instances of a temporary compound that is modified by an adverb and another that is not, such as “high-frequency waves” and “very high frequency waves”; do not treat them similarly (i.e., do not hyphenate both or leave both open). The presence of the adverb in the second combination makes the difference.

Colors in combination

bluish-green overlay
blue-gray particle

Attributive adjectives formed by a noun + one of the following or similar words:
type, soluble, specific, (in)dependent, rich,
only, free, wide (check dictionary for solid words), scale, odd, synchronous,
variable, invariant, inclusive, perpendicular, parallel

pH-dependent finding
Fe-rich deposit (very Fe-rich deposit; very is modifying
Fe rich, not just Fe)
C- and N-rich deposits (but do not use C-rich and -poor

Words with equal weight: Usually, they are connected because they have an “either-or,” “from-to,” or “between-and” relationship

wave-particle interaction
noon-midnight value
plant-soil system
air-sea interface
north-south range
time-space plot

Phrases that act as adjectives and precede the term they

month-by-month computation
order-of-magnitude change



In general, new compound nouns are spelled with two words and without hyphens. Check dictionary (Merriam-Webster’s Collegiate Dictionary (2005)) for permanent closed and opened forms. If word is not in the dictionary, is not described below, and does not appear in AGU’s Word List, use community standard, employing hyphens if clarity is needed.





“Self” compounds


Verb + preposition (unless closed up in the dictionary)




Do not hyphenate



Quasi + noun (unless closed in the dictionary)

quasi response
quasi steady state
quasi self-help

Noun + gerund

problem solving
data logging


one half
two thirds

“Fold,” “glow” and “side” compounds should be closed up


Use numeral and hyphen if a hyphenated number would precede fold: 125-fold


Words Formed With Prefixes

Spell all words formed with prefixes closed with exceptions explained below. Some common prefixes are listed below. Check dictionary for other prefixes and closed forms:
pre-, post-, un-, non-, re-, after-, intra-, extra-, inter-, semi-, multi-, micro-, macro-, bi- sub-, super-, supra-, mini-, maxi-, mid- (but mid-ocean), mega-, over-, under-, fore-, anti-, infra-, ultra-, counter-, pro-, anti-, co-

Spell all words formed with the above prefixes closed unless:

  • The prefix precedes a capitalized word or a numeral (mid-Cretaceous, post-1950)

  • Compound can be misread (recover versus re-cover; remark versus re-mark, un-ionized vs unionized)

  • The same vowel would be repeated (intra-aggregate, semi-infinite), except co-, de-, pre-, pro-, and re- may be set closed even when a double vowel forms (preexist); but hyphenate if triple vowel results.

Use an en dash if the second element is a proper noun or proper adjective consisting of more than one word (pre–World War II, post–Civil War period).

Use two hyphens if the second element consists of more than one word (hyphenated) (non-time-homogeneous equation, non-English-speaking people).

If the second element contains more than one word and is a combination that we never hyphenate, match the solution to the type of prefix:

  • Post-, pseudo-, and mid- can stand alone if necessary (i.e., can function as adjectives or adverbs); therefore, use: pseudo magnetic field, post cosmic ray event

  • Other prefixes are in the dictionary only as combined forms and cannot stand alone (e.g., non-, pre-).

In some cases, the meaning will permit the prefix to be attached to the first word of the second element: nonsteady state

In other cases, use an en dash or rephrase: pre-solar wind or before the solar wind, non-fully persistent (“non” applies to “fully persistent,” not just “fully”).

When multiple prefixes precede the same base word, the prefixes should not stand alone; e.g., use preseismic and postseismic, not pre- and postseismic. Change mid- and high-latitude (as adjectives) to midlatitude and high-latitude or middle- and high-latitude.


Include a single space after words, sentences, and periods following initials of names (T. K. Singh).


In addition to ending a complete sentence, notable uses of periods are:

  • Initials of names (T. K. Singh)

  • Abbreviation of United States when used as an adjective: U.S. Army

  • Latin abbreviations: a.m., cf., i.e., and vs.

  • Reference abbreviations: Vol., Eds., etc.

Do not use in the following situations:

  • For state names: New York, NY, Washington DC, etc.

  • Capitalized abbreviations and acronyms

  • At the end of a URL or DOI in the References. In text, include in parentheses or rewrite sentence so that it doesn’t end in a URL.

  • Metric and non-metric measurements except “inch” is “in.” so that it’s not misinterpreted


This section lists correct usage examples and APA style around comma usage. See APA’s Publication Manual for additional rules.

Serial Comma: Use a serial comma; in a list of three or more, use a comma before a conjunction: “Only density, pressure, and speed had any effect on the results.”

Nonrestrictive clauses: Use commas to set off nonessential information from sentences that would retain their meaning if the set off text were removed: “The sites in this study, which were all above sea level, were selected for their.... “

With Parameters: It is not necessary to set off variables in text with commas (or parentheses) if they directly follow the parameter for which they stand: “The modeling equations can be closed by specifying the constitutive equations for the stress tensor T of gas and solids, drag D, and heat transfer Q.”

However, if a phrase separates the variable and the parameter, then retain enclosures (either commas or parentheses but be consistent within a paper): “The enthalpy (h), the thermal conductivity (k), and the volumetric heat transfer coefficient for the exchange of heat between the gas and pyroclasts (Q)....”

Follow community standard usage with parameters, even if inconsistent. That is, any of the following are acceptable:

  • temperature T

  • temperature, T,

  • temperature (T)

Commas in Numbers: Use a comma only in numerals with four or more digits. Exceptions are:

  • Page numbers: page 3457

  • Binary digits: 00101110

  • Serial numbers

  • Degrees of temperature

  • Acoustic frequency designations

Jr. and III: Do not use commas around or before Jr., Sr., or III except in reference list for authors in inverted order: “House, J. H., Jr., &....”

Do not use a comma:

  • Before a restrictive clause: “The multiyear plan that was signed by both governments...” (restricting the meaning to this specific plan)

  • Between two parts of a compound predicate: “The research team extracted and analyzed the samples.” Not “The research team extracted, and analyzed the samples.”

Examples of Correct Comma Usage

Use a comma:

  • After the results were computed, we made a log plot of the data. (introductory adverb clause)

  • Using the data, we constructed a graph. (participial phrase)

  • To confirm the results, a second experiment was planned. (infinitive phrase)

  • The results being in question, the experiment was repeated. (nominative absolute)

  • In general, the results from the two studies are in agreement. (sentence modifier)

  • Initially, the current meters produced ambiguous data. (adverb ending in -ly)

  • In the references above, the reader may find further details of the methodology used here. (could be misread)

  • After reweighing, the samples were subjected to further tests. (ends in verb form)

  • We performed the experiment at room temperature, but the results were not as good. (compound sentence)

  • In the cool, humid climate the plants thrived. (a series of adjectives)

  • The samples were collected in a glass beaker, which had been washed, dried, and weighed. (nonrestrictive)

  • The data, the number of echo soundings per second, were entered into the computer. (nonrestrictive appositive)

  • The distance per unit time, or velocity, is important to this calculation. (nonrestrictive appositive)

  • While a few were sandstone, the rocks were mostly granite. (introductory subordinate clause)

  • Papers based on data from Pioneers 10 and 11 conclude that a magnetic field decreases, while papers based on the data from Voyagers 1 and 2 are consistent with the Parker model. (nonrestrictive clause)

  • At the mountaintop, where the air is thin, it is necessary to wear oxygen masks. (nonrestrictive)

  • The altitudes above 120 km, where O3(ν) fluorescence was too weak to be observed, provided data considered irrelevant for this study. (nonrestrictive)

  • This follows the theory of Smith & Ames (1980), who solved the full MHD equations. (nonrestrictive phrase)

  • The expedition was a joint effort of American, Canadian, and French scientific societies. (series)

  • Thus, although the temperature is lowered, it did not affect the results. (Thus followed by introductory phrase)

  • If the lava flow were emplaced in this 550 year period, it would also have been entirely submarine. (If, then)

Do not use a comma:

  • Nappes therefore appear to have common history.

  • We dismissed data having high or low values and plotted the remaining data on a TS grid. (compound verb)

  • An examination of Figure 4 indicates that the midlatitude values are relatively low for this parameter and that high-latitude values are quite divergent. (parallel dependent clause)

  • In the area where O3 molecules are densest, damage by aerosols was the greatest. (restrictive phrase)

  • It was understood that given the above constraints, agreement would be tenuous. (after “that”)

  • These migmatites remained within the field long enough to deform while they were partially molten. (“while” meaning “at the same time”)

  • We did not perform the experiment because the specimen was contaminated. (before a restrictive subordinate clause at end of sentence)

  • Virtually all the Mauna Loa lavas encountered are interpreted to be subaerially emplaced. (exception to after -ly)


Use quotation marks to:

  • Quote material directly from a cited source.

  • Identify a word or phrase used as an ironic comment, slang, inverted/coined expression. Use quotations only once for a particular phrase; thereafter, do not use quotation marks.

  • Set off title of an article or chapter in a periodical or book when mentioned in the text.

  • Periods and commas go inside closing quotes; semicolons and colons go outside.


In addition to APA standard colon and semicolon usage:

  • Do not use colons after forms of the verb “to be,” after prepositions, or to separate a verb from its object. Colons may be used after forms of “to follow.” If you want to retain the colon for any of the above cases, insert “as follows” or “in the following” or “for the following.”

  • Use a semicolon, not a comma, before “hence” when it introduces an independent clause: “The results were uncertain; hence, we did not use them.”


Italics may be used for emphasis, but sparingly. Do not use in long phrases, as a complete sentence, or as whole paragraphs. Use italics to:

  • Define ranges of a scale (“Respondent could choose any value from 0 (not important) to 10 (very important).”)

  • Introduce a technical or key term. After it has been used once, do not continue to italicize it.

  • Do not use boldface or all capitals for emphasis or definition; use italics instead.

  • Note: Latin phrases are not italicized except genus and species names.


Singular vs plural with certain nouns:

  • Number: “A,” as in “a number of..” takes plural verb: “A significant number of points are in large disagreement with (2) and (3).”

  • “The” takes singular verb: “From Table 3 it is apparent that the number of points over which averages are taken varies considerably between data divisions.”

  • Set and group (collective nouns) should take singular verb unless the individuals of the group are to be emphasized: “A set of points, such that N and X are both ... are defined as feasible designs for satisfying the information demand of the nth parameter.” And “Furthermore, the set of nonzero Lagrange multipliers represents the set of trade-off ratios between the principal objective and each of the constraining objectives.”

  • “Data” must take the plural verb; however, “geodetic datum” is singular, and “geodetic datums” is plural.

  • “Series” can take singular verb if individuals in series are not emphasized: “A series of models have been constructed that approximate the measured horizontal disturbance at the Earth’s surface derived by Langel (1973).” And “The series that we used helps to identify the position of the vector.”

  • “The” percentage always takes a singular verb. “A” percentage can take either a plural or singular verb depending on object of preposition: “A substantial percentage of these individuals are quite sure that they have made the best decision.”

  • Percent can take either plural or singular verb depending on object of preposition: “Roughly 8% of all proton velocities were contoured.” And “About 9% of the field was rejected.”

  • Total takes a singular verb: “A total of 98 field stations was established with an elevation range from 4400 to 9000 m.”

  • Chain takes a singular verb: “The changes in neutral composition trigger a complex chain of events, which affects not only the distributions but also the emission rates.”

  • Proportion can take either plural or singular verb depending on object of preposition: “A relatively larger proportion of bound H2 molecules emerge and flow from the hotter dayside to the cooler nightside.”

  • Sequence takes a singular verb: “The following sequence of boundary conditions is therefore obtained for the free surface geometry.”

  • Part (determine singular or plural sense): “Part of the results of the simple model are compared with magnetic field mappings of IMP and Mariner 5.” And “The part that we used was not properly verified.”

  • Fraction (determine singular or plural sense): “A large fraction of the reports available are clustered over the continent.” And “A fraction will be chosen that is indicative of the actual cost per person.”

  • “None” may take either plural or singular depending on emphasis: “None of the outliers are from earlier parts of the records.”


Spelling should conform to American English as in Merriam-Webster’s Collegiate Dictionary (2005). If the dictionary gives a choice, use the first spelling listed. See also AGU’s Word List at the end of this guide.

  • Do not use double final consonants before endings (use “equaled” not “equalled”). Drop the vowel when adding suffixes “-ment” and “-able” (use “judgment” not “judgement.” If both forms are given in the dictionary, use the spelling listed first: Equaled, not equalled (but controlling); focuses, biases, not focusses, biasses; focused, biased not focussed, biassed; pluses, not plusses; modeling, not modelling; judgment, not judgement; acknowledgment, not acknowledgement, sizable, not sizeable (but noticeable).


See APA Publication Manual for basic capitalization rules. Please note the different capitalization rules between titles in-text and those in the reference list. Notable rules:

  • Capitalize major words in the article’s title, but not conjunctions and articles (“title case”).

  • Use title case for other titles appearing in the text of the article.

    • Capitalize verbs, nouns, adjectives, adverbs, pronouns, and all words with four or more letters.

    • Capitalize both words in hyphenated compounds and the first word after a colon or dash including table titles and figure legends.

  • In references, titles of articles and books use “sentence case,” where only the first word, first word after a colon or em dash, and proper nouns are capitalized.

  • In references, titles of journals and periodicals use “title case,” where the major words, but not conjunctions and articles, are capitalized.

  • In table headings and figure captions, capitalize only the first word and proper nouns (sentence case).

  • Capitalize nouns followed by numerals or letters that denote a specific place in a numbered series. E.g., Experiment 2, Site 17, Table 6.

  • Capitalize adjectives derived from proper names: Kelvin, Martian, Lambertian, Stokes.

  • In text, capitalize Figure 2 and Table 1 but lowercase model 1, section 1, and equation (2).

  • Capitalize nouns followed by numerals or letters that denote a specific place in a numbered series such as Region 1, Model 3, Experiment A-3, Batch 5, Run 12. Site 43, Hole 128, and Leg 26.

  • Protected trademarks are capitalized (Teflon, Plexiglas, Pyrex, Freon, etc.). When a trademark is used, do not capitalize the common noun portion (Pyrex beaker).

  • Lowercase law, such as Snell’s law.

  • Lowercase spelled out words in an abbreviation unless words are proper nouns. E.g. Upper Colorado River Basin (UCRB), but spatially referenced regression on watershed attributes (SPARROW).

  • For mixed case abbreviations, such as for programs and missions, follow original capitalization of sponsoring organization. For example, NASA’s overview of MAVEN shows “Mars Atmosphere and Volatile EvolutioN (MAVEN).”


The following is a list of commonly used proper names with unusual spellings or accented letters. If community standard is not to use accents or umlauts, you may choose not to use them, but be consistent throughout the paper.

Avé Lallemant (author)
Bénard (associated with cells or convection)
Bouguer (gravity anomaly)
Chappuis (band)
Debye (theory, constants) (in combination with Scherrer)
Grüneisen (parameter – gamma)
Kolmogorov-Smirnov (goodness of fit test)
Lagrange (constant)
Lamé (constant)
Mohorovičić (Moho, no accents with “discontinuity”)
Murnaghan (as in Birch-Murnaghan equation)
Poisson (ratio, sigma)
Rayleigh (wave, number)
Savonius (rotor)
von Kármán
Crank-Nicolson (no “h”)


The following is a list of spellings used by Webster’s and the State Department for the Baltic States and the Republics that were formerly part of the Soviet Union. Change to these spellings.





Armenia (Hayastan, use Armenia)




















Bishkek (formerly Frunze)









Chisinau (formerly Kishinev)












Kyyiv (Kiev)





Prefectures of Japan With Their Capitals






































































































The following may be either capitalized or lowercase except as indicated below: anticline, arc, bank, basin, butte, channel, crater (e.g., on Earth, the Moon, or Mars), fault, fold, formation, geyser, glacier, mount, plate, plateau, ridge, rill, strait, syncline, trench, trough, volcano. Be consistent throughout the paper.

Since terms such as convergence, divergence, currents, swells, water masses, and jets (air currents) have varying degrees of importance to different types of authors (biologists, chemists, geologists), follow the community standard.

The following is AGU style for commonly occurring geographical terms. This is not an inclusive list. Check atlas for recognized geographic features. AGU journals and books follow the United Nations for recognized geographic names: United Nations Bibliographic Information System. Alternative names should not be used in text, figures, and tables.

Note that generic terms such as lake, mountain, river, or valley are capitalized when used with a proper name no matter how they are listed in an atlas or gazetteer, except if “the/a river” precedes the proper name: the river Elbe. Also, Hudson River valley.

Capitalize plural geographic features when part of a single name (e.g., Hawaiian Islands) and when used with two or more names, regardless of whether the geographic feature precedes or follows the proper names (e.g., Mounts Washington and Rainier, the Illinois and the Chicago Rivers).

Africa, North, East, West, but central (south except country)
Alps, Southern, Eastern, and Western, but northern and central; also Southern Alps for New Zealand
Andes, sub-Andes, central Andes, inter-Andean
Arctic Ocean
Asia, South, Southeast, central, southeastern, East
Atlantic Ocean, North, South, but northern, southern, central
Caspian Sea (not divided, east, west, north, south)
China, south
Coastal Plain (US)
Earth (as planet rather than substance), but earthward and terrestrial
East Africa
East Antarctica
East Antarctic Ice Sheet
East China Sea
East Coast (referring to the eastern United States)
Eastern Hemisphere (Earth only)
eastern Mediterranean Sea
east Greenland
East Sea, change to Sea of Japan (East Sea)
East Siberian Sea
equator, equatorial
Europe, central, eastern, and western (capitalize Eastern and Western Europe only in political sense, rare)
Faeroe Islands (or Färoe)
Gobi desert
the Hawaiian Islands; the island of Hawaii (or Hawai‘i) (follow au for accent; when referring to the state of Hawaii, do not accent)
the Himalayas (or the Himalaya), Outer, Greater, Lesser, but central, middle, lower
Iceland-Greenland-Norwegian Seas (order may vary)
Jupiter, Jovian, Jovicentric, Jovigraphic
Mars, Martian
Mediterranean Sea
Mediterranean, western/eastern, but Arctic mediterranean seas (mediterranean in this case is generic in meaning, i.e., land-locked or mostly land-locked, here referring to several seas within the Arctic as a group)
Middle East (or Mideast)
Mojave Desert
the Moon, but lunar
Negev (desert, if used, is lowercased)
New York City (but follow author for adding “City”)
Nordic seas
Northern Hemisphere (Earth only)
North Pole (Earth’s only)
North Sea
open ocean
Pacific Northwest (but northwest Pacific)
Pacific Ocean, North, South, but northern, southern
plate (follow author within paper for capitalization):
African, Antarctic, Arabian, Australian, Caribbean, Cocos, Eurasian, Farallon, Indian, Juan de Fuca, Nazca, North American, Pacific, Philippine, Scotia
Northern California
Sahara (desert, if used, is lowercased)
San Francisco Bay Area or Bay Area
Sea of Japan (preferred), or Japan Sea
solar system
Southern Hemisphere (Earth only)
south China
South China Sea
Southeast Asia, but southeastern Asia
Southern California
Southern Ocean
South Indian Ocean
South Pole (and South Pole Station) (Earth’s only)
South Shetland Islands
the Southwest (only when referring to southwestern United States)
sub-Sahara, subalpine, sub-Andean
the Sun, but sunward and solar
Takla Makan, use Taklimakan
Taklimakan desert
Tibetan Plateau or Plateau of Tibet (aka
Qinghai-Xizang Plateau) but not Tibet Plateau
Venus, Venusian, Venus’s
Victoria Land
the West (of US), the North, the South, the East, and West Coast
West Africa
West Antarctica
west Australia
West Coast (referring to the western United States)
Western Australia (if state meant)
Western Hemisphere (Earth only)
western Siberia
west Greenland
world ocean


  • Use the following for both nouns and adjectives: Arctic and Antarctic (however, arctic may be lowercase in papers that do not use Antarctic).

  • Use subarctic and subantarctic as adjectives, but sub-Arctic and sub-Antarctic as nouns. Note that Antarctica is the continent and Antarctic is the region.

  • Use state of Washington, but use Washington State.


Follow usage for rock names. Both capital and lowercase may be used for the same rock within a paper, as they have different connotations. For example, Westerly Granite is a granite with a specific chemical composition, whereas Westerly granite is a more generic term. Use accepted community standard for Groups and Members.

Explosions are initial cap only, e.g., Cowboy, Salmon, Sterling.

Capitalize Hurricane/Typhoon when used with a specific name: Hurricane Andrew, Typhoon June.

Lowercase “earthquake”: western Tottori earthquake.

Stratigraphic Divisions: Refer to NACSN’s Stratigraphic Code.

Capitalize the attributive adjective (e.g., early, lower) only if it appears here as an officially recognized subdivision; otherwise, use lowercase: late Cenozoic, early Paleozoic, early Pleistocene, Late Jurassic, Upper Permian.


Cardinal numbers/arabic numerals

Use numerals:

  • For 10 or higher; write out under 10, except as indicated below.

  • With units of measure (abbreviate units if possible).

  • To make numbers under 10 consistent with larger numbers in a series: “We used data from 6 experiments in the first graph and from 12 to 14 experiments in the second and third graphs, respectively.”

  • With divisions (part, paragraph, section, rule, model): model 1, section 2, log 1, case 1 (do not change from roman to Arabic if roman numerals are used in figures or if from a non-AGU source).

  • When implying an arithmetical manipulation: a factor of 7, 4 orders of magnitude, magnification of 50 (50X, use capital “X” closed up to number), 5 times the height; use either 2 or two standard deviations (follow usage but be consistent).

Write out:

  • For one through nine except as indicated above.

  • At the beginning of a sentence, a head, or a title (if followed by a unit of measure, spell it out too: Ten kilometers...; or rephrase so that the number (and its unit of measure) does not begin the sentence, head, or title). If necessary to write out, hyphenate (both as noun and adjective) cardinal and ordinal numbers if compound: e.g., twenty-one, twenty-first. However, one hundred is not hyphenated (see number table in the dictionary). Exception: Allow a sentence to begin with a numeral if that numeral is superscripted, such as 14C or 228Th.

  • For plurals, e.g., tens, not 10s.

  • Write out a number that directly precedes or follows a numeral: ten 2 m strips; 136 two hour lectures.

  • In text, spell out fractions. Use “two thirds of the people” (noun form) and “two-thirds portion” (attributive adjective).

Ordinal numbers

  • Spell out ordinal numbers (first, second, third, etc.) unless hyphenated (e.g., twenty-first, use 21st) in text.

  • If nonhyphenated form used in conjunction with hyphenated, use numbers for all: 21st, 50th, 92nd.

  • Use the numeral and suffix form (1st, 2nd, 3rd, etc.) in references (e.g., 1st ed.).

  • Use nth, (n – 1)th, etc. (i.e., “th” is on line and not italic).

  • Use first, second, third, not firstly, secondly, thirdly, etc.

Roman numerals

  • Use roman numbers only if a part of an established terminology, name, or title.

  • Do not use roman numerals in names of artificial satellites, rockets, etc.: Explorer 8, Vanguard 3, Surveyor 1, OGO 3. (The standard is Arabic.)

  • Do not use roman numerals for figure numbers or table numbers: Figure 5 and Table 2.

Miscellaneous style for numbers

  • Give full ranges for pages or years; for example, use 801–806, not 801–6. Use 1979–1980 not 1979–80.

  • Mixed forms are permissible for very large numbers: 5 million; 2.3 billion. If units of measure are included, use scientific notation: e.g., 5 × 106 m3; 2.3 × 109 L.

  • Use a zero before the decimal point in a numeral less than unity: 0.002, not .002. However, do not add a zero after decimal point (e.g., 20.), but do retain decimal; adding a zero would change the degree of precision of the measurement.

  • You may use “number(s),” “no(s).,” or “#” as long as it makes sense, e.g., run number 5, well no. 4, #3 grit.

  • You may use an abbreviated format for scientific notation,e., 1.365E-3 in text instead of 1.365 × 10–3.


Each entry in a table should appear in a new cell. Avoid tables created with the tab key and embedded objects. Tables with pictures, color, or embedded objects must be submitted as figures. Notes, bold, italics, and bold-italics is preferred over color in a table. Tables must be editable and must not be embedded as pictures.

Table numbering

Cite each table in numerical order in the text. Tables in the main body of the text should be numbered consecutively, not by section. Include a table number using Arabic numbers. Do not use table parts (1a, 1b, etc.). Do not use other numeral types such as Roman.

Appendix tables should be numbered separately from the body and should begin with the letter of the appendix (e.g., Table A1 for the first table in Appendix A). Each table must be cited in text.

Table formatting

  1. Table title: Capitalize major elements (title case). Set in italics. Make the title concise. Longer table notes (including table caption text) should be set as a note.

  2. Column headings should only capitalize first word.

  3. When including citations in the table body, use ampersand; when including citations in the table notes, use “and.” Follow APA citation style.

  4. Table notes can include “Note,” superscript letters, and asterisks and other symbols. Use periods between footnotes.

    • Use “Note.” for general notes applicable to the entire table, including original table source. Use a Note instead of a long table title/caption.

    • Use superscript lowercase letters for specific notes to clarify a specific element in the table.

Table 1
Hydraulic Test Types Contributing to the Database of this Study


Test Method

Log permeability – literature

Log permeability – dataset









Measurement Based Aquifer Scale Modele







Discrete Tunnel Inflow Measurementa, k







(Induced) Seismicityg







Cross-Borehole Tracer Testl







Open Hole Pumping/Slug Testl,n

-14 to -13






Single Packer Testc,f,h,i,l,n

-21 to -14

-13 to -8





Multi-Packer Testb,c,f,h,i,n

-21 to -18

-13 to -8





Drill Stem Testb,d,f,h,i,l

-17 to -14

-13 to -11





Borehole Lugeon/WD Testd,f,l,m

-18 to -15

-12 to -8





Difference Flow Logsj







Pneumatic Testo







Pressure Tunnel Test







Hydrofrac Testb,c,f,h,i,n

-21 to -18

-13 to -8






Note. A minimum of about 100 observations is regarded as being representative for a given property, and measurement methods with fewer observations have been removed from the analyses.
aAchtziger-Zupančič et al. (2017). bAlmén et al. (1986). cClauser (1991). dDenzel et al. (1997). eGleeson et al. (2011). fHeitfeld et al. (1998). gIngebritsen and Manning (2010). hLee et al. (1982). iLeech et al. (1984). jLudvigson et al. (2002). kMasset and Loew (2010). lPrinz and Strauß (2012). mSievänen (2001). nSteiner et al. (2006). oAuthors’ experience. pUncertain/unknown.


  • Do not begin sentences with lowercase Roman or Greek letters or numerals. Enclosures are ok, e.g., [, +, (, as are capital Greek letters, e.g., Δ, Φ.
  • Always use degree sign with N, S, E, W: 24°N not 24N.
  • Write out N, S, E, and W when used alone (N-S, E-W okay). Okay to use NNW, etc. (do not change to N-NW; see the dictionary), e.g., air masses from the east, SE, and NW; also N20°E okay.

Units: The metric system should be used throughout. American measurements will be changed to International System of Units.


Use international date format: D Month YYYY, e.g., 1 March 1980. Also acceptable:

  • 1–3 March 1980

  • between 1 and 3 March 1980, we observed...

  • 1 March to 1 April (not 1 March–1 April)

  • March 1980 to August 1981

  • March–April 1991

  • En dashes should be used only between like things: 1–12 March 1983; but change 1 March–10 April to 1 March to 10 April.

  • Use 1980s for decades (not 1980’s or 80s).

  • Use CE (Common Era) instead of AD and BCE (Before Common Era) instead of BC.

  • For time, use the accepted time standard among your scientific community.

Never use:

  • 1/3/80, 010380

  • 1-3-80

  • the 1st of March

For age, use abbreviation from Latin (preferred): Ma (mega-annum), Ga (giga-annum), ka (kilo-annum), where “ago” is implied. Or write out: “xx billion/million years ago,” when context is needed.

For duration/lengths of time, write out (“x million years”) or use abbreviation Myr, Gry, Kyr, or yr (for years).


The following is a list of words and phrases commonly occurring in AGU papers and their treatment (hyphenation, spelling, open or closed up, italics, trademarkss). This list does not include words and phrases appearing in Merriam Webster dictionary unless treatment is different. Please consult Hyphenation section of the AGU style guide for hyphenation rules. Consult also the Merriam Webster dictionary.

acoustic-gravity wave
advection-dispersion (n)
advective-dipersive (adj)
all-sky (adj)
along track (n), along-track (adj)
ash flow
aspect angle
atomic nitrogen
atomic oxygen
backarc (n, adj) back-arc (adj)
back azimuth
backprojection (time), back projection (space)
back slip
back thrust (n)
back thrusting (adj)
back trajectory
band-pass (adj), band pass (n)
bankfull or bank-full (adj)base flow or baseflow (n)
beam width
bench mark or benchmark (see dictionary)
best fit (adj)
bottom hole (n), bottom-hole (adj)
boundary element (adj)
burn-out (adj)
calc-alkaline (adj)
centroid depth
centroid moment
check shot
chi-square (not “squared”)
clear-sky (adj)
cloud top
cold-core (adj) (also warm-core)
computer programing
convection-diffusion (n)
convective-dispersive (adj)
core hole
cross correlation (n), cross-correlation (adj)
cross track (n), cross-track (adj)
dark field (n), darkfield (adj)
data logger
data pool
data processing
data set
date line or dateline (n) (dependent on meaning), dateline (v)
deep water (n),deepwater or deep water (adj) (dependent on meaning)
Digisonde (instrument, cap)
double couple (n)
double-couple (adj)
downgoing (adj)
drill hole
dropoff (n, adj), drop off (v)
dry land (n, adj), dry-land (adj) or dryland (adj) (dependent on meaning)
earth-atmosphere (adj)
electric field
end point or endpoint (dependent on meaning)
en echelon (adj, adv) (not italic)
far-field (adj)
far side or farside (dependent on meaning)
fast spreading (adj)
fault trench
field of view (n, adj), field-of-view (adj)
finite element
fission track
flow field
flow path
flow rate
foot points
forearc (n, adj), fore-arc (adj)
free air (n) free-air (adj)
F region
frequency domain
F test
γ ray (gamma ray)
Geodimeter (trademark) (hyphenate as Geo-dim-eter)
Geodolite (trademark)
gradient drift
gravel bed
gravity-capillary wave
gray scale (n), grayscale (adj)
grid point
ground track
half width (n), half-width (adj)
H alpha, use H α
head wave
heat flow
ice core
ice stream
in-phase (adj) (inphase, adj, electrical only)
in-place (adj)
in situ (not italic)
intermediate-depth (adj)
Invar (trademark)
ion cyclotron
Kapton (protected trademark)
k-means (always hyphenated, always plural)
lab frame
land use (adj)
least squares (not “square”)
left-lateral (adj)
line of sight (n, adj), line-of-sight (adj)
line source
log conductivity
log likelihood
log linear
log-periodic (antenna)(adj)
log transmissivity
longwave or long wave (n), longwave or long-wave (adj)
loss cone
main shock or mainshock
mass balance
mass transfer
Matlav (trademark)
mean square
melt-rock (adj)
molecular nitrogen
molecular oxygen
moveout (n, adj), move out (v)
narrow band (n)
near-field (adj)
non-ice (adj)
nonsteady state
nowcast (n) nowcasting (v)
Octol (trademark)
paddy land
path length
path loss
pitch angle
plasma sheet
power law
pseudo 3-D (n), pseudo-3-D (adj)
P wave
quick flow
quiet time
radio decay
radio echo
radio physics
rain flag
rain forest
rain splash
reefal (adj) (don’t use reef)
resource management
rest frame
ridge-perpendicular (adj)
right-lateral (adj)
ring beam
ring current
ring width
river flow
rock mass
rollover (adj), roll over (v)
Rossby-gravity wave
runout (n, adj), run out (v)
salt water (n)
sandshale (adj)
saw cut, sawtoothed (adj)
scale length
SeaMARC I and II
sea-salt (adj)
seismic reflection
shallow mixing layer
shear hole
ship track
short-period (adj)
shortwave(n, adj.)
side-looking (adj)
side scan
side scatter
signal-to-noise ratio
sine taper
slack-water (adj, v)
slow spreading (adj)
snow cover
soft water
solar-terrestrial (adj)
source time
spacecraft (sing, pl)
sporadic E
stage-by-stage (adj)
stage-discharge (adj)
state space (adj)
step over
stick-slip (n., adj)
storm time
storm water
straight line (n), straight-line (adj)
strain rate
stream bank
stream function
stream sediment
stream water
strike slip (n), strike-slip (adj)
strong motion
Sun photometer
S wave
takeoff (n, adj), take off (v)
terrain, terrane (see dictionary)
thin sheet
tie line (or tie-line for phone lines)
time delay
time domain
time-lapse photography
time period
timescale (historic, geologic, cosmic), time scale (otherwise)
time step
track line
trade-off (n, adj), trade off (v)
traveltime (geologic), travel time (otherwise)
t test
turn-on (n), turn on (v)
tweeks (space physics)
ultralow-temperature (adj)
ultraslow spreading (adj)
Umkehr (return reversal effect)
upscale (n, adj, v)
V notch
velocity-depth (adj)
velocity space
water mass
wave group
wave mode
wave path
wave power
wave speed
wave vector
wellhole (n), well-hole (adj)
well-known (adj), well known (otherwise)
well water
whistler mode
whole rock (n), whole-rock (adj)
wind field
wind forcing (adj)
wind speed
wind stress
wind-wave or wind wave (adj)
x, y, z (axis coordinates)
zeros (plural n), zeroes (v)