Brief Guide to AGU Style and Grammar

AGU Publications has updated its manuscript style, reflected in the below guide. Read about the change 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.

This brief guide summarizes the major instructions from AGU’s detailed Grammar and Style Guide. AGU follows American Psychological Association (APA) style on grammar, punctuation, table formatting, citations, and references. For detailed information, see Publication Manual of the American Psychological Association, Sixth Edition.

The brief guide contains guidance on:

Reference Format
Examples of Common References
Italics and Boldface
Date and Time
Table Formatting
Word List

For additional rules and complete explanations, and examples, see the full Grammar and Style Guide.

Reference Format

AGU follows APA reference style as found in the Publication Manual of the APA, Sixth 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 sets that are not newly reported as part of this research should also be cited in the references.

Text citations. In-text should be cited using author surname(s) and the date of publication: “in earlier studies (Johnson & Smith, 2009)” or “…as given by Johnson and Smith (2008)” or “In 2012, Johnson and Smith’s study showed that….” Note:

  • Author names are not italicized.
  • Comma follows the author name(s) if the reference is enclosed in parentheses.
  • If a two-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, abbreviate citation using “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). 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 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 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.
  • 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,

See complete Grammar and Style Guide for additional citation guidelines.

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, and consider that “nothing precedes something.” Examples: Lefer before Le Pichon, Vander Linden before van Giessen, Brown before Browning, Sanders before St. Amant, MacMillian before McArthur. 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 identical authors, use a, b, c, etc. after the year.
  • 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 when shortened to form the in the in-text citation. See Text Citations section, above, on how to cite in-text.
  • Use DOI for AGU articles; use DOI for non-AGU journal articles if known.

See complete Grammar and Style Guide for additional instructions.

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). ….

2. 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). ….

3. 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.


Elements and Examples of Common References

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.



Hyphenation rules can be found in the full Grammar and Style Guide. Below find examples of hyphened and non-hyphenated words and phrases.

Use hyphens Do not use hyphens
sulfate-containing aerosols
sediment-filled streams
lunar-orbiting satellite
little-known derivation
near-normal wave mode
self-sustaining reaction
cross-correlation function
all-salt deposit
no-flow boundaries
zero-base budgeting
k-dimensional model
two-fluid response
nth-order equation
single-chain reaction
multiple-layer model
high-energy particles
middle-latitude stations
low-P region
low-Mg samples
higher-energy particles
lowest-latitude sample
pH-dependent finding
wave-particle interaction
noon-midnight value
plant-soil system
air-sea interface
less known derivation
a priori solution
per mille basis
in situ technique
slowly flowing stream
ferric oxide layer
north central Utah
upper right corner
northeast trending
south directed
westward moving currents
plasma flow region
wake surface potential
solar wind
electric field
magnetic field
ion cyclotron
cosmic ray
pitch angle
steady state
atomic oxygen
sporadic E
molecular oxygen
F region
γ ray
x component
P wave
2 cm pipe
1 km wide trench
5 year old record
6 mm diameter tube
9 year old pine plantation
6 mile wide highway
10 to 20 km wide area
ramp-up (when used as noun)
data logging
problem solving
one half
two thirds

Words Formed With Prefixes

Spell all words formed with prefixes closed with exceptions below. Check dictionary for other prefixes and closed forms.

Common prefixes: 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-


  • 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).

See also AGU’s Word List in the full Grammar and Style Guide.


See full Grammar and Style Guide for detailed punctuation rules. Notable examples are below.


Use periods: 

  • 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 periods:

  • 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


Use commas: 

  • Serial comma: “Only density, pressure, and speed had any effect on the results.”
  • Numerals with four or more digits (see exceptions to the right)
  • With parameters are optional: temperature T; temperature, T,; temperature (T) are all acceptable

Do not use commas:

  • Page numbers: page 3457
  • Binary digits: 00101110
  • Serial numbers
  • Degrees of temperature
  • Acoustic frequency designations

Examples of comma usage can be found in the full Grammar and Style Guide.

Italics and boldface

Use italics:

  • To define ranges of a scale (“Respondent could choose any value from 0 (not important) to 10 (very important).”)
  • To introduce a technical or key term. After it has been used once, do not continue to italicize it.
  • For emphasis or definition; do not use boldface or all capitals.

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


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 the full Guide.


See full Grammar and Style Guide for detailed capitalization rules. Below find notable cases and examples.

Capitalize Do not capitalize
  • Major words in article title.
  • Nouns followed by numbers or letters that denote specific place in numbered series: Experiment 2, Site 17.
  • Major words in article headings and subheadings and references to titles of sections.
  • References to titles of sections within the same paper.
  • Conjunctions and articles in article title.
  • Titles of articles and books in references list.
  • Major words in headings and figure captions (capitalize first word only).

See full Grammar and Style Guide for capitalization of geographical terms (e.g., lakes, mountains, rivers, valleys, countries, seas, oceans, etc.).

Stratigraphic Divisions

Refer to NACSN’s Stratigraphic Code.

Date and Time Formatting

  • 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. Other examples of proper usage for date range can be found in the complete Guide.
  • Never use: 1/3/80, 010380, 1-3-80, or the 1st of March
  • Use CE (Common Era) instead of AD and BCE (Before Common Era) instead of BC.
  • 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 billion/million years”) or use abbreviation Myr, Gry, Kyr, or yr (for years).


Use Arabic numerals: Write out: Use Roman numerals:
  • 10 or higher.
  • 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 from a non-AGU source).
  • When implying an arithmetical manipulation: a factor of 7, 4 orders of magnitude, magnification of 50 (50X, use capital “ex” closed up to number), 5 times the height; use either 2 or two standard deviations (follow usage but be consistent).
  • For one through nine except as indicated to the left.
  • At the beginning of a sentence, a head, or a title 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. For plurals: tens, not 10s. Exception: Allow a sentence to begin with a numeral if that numeral is in superscript, such as 14C or 228Th.
  • Numbers that directly precede 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 (first, second, third, etc.) unless hyphenated,(e.g., twenty-first, use 21st) in text. If non-hyphenated 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 only if a part of an established terminology, name, or title.
  • Do not use in names of artificial satellites, rockets, etc.: Explorer 8, Vanguard 3, Surveyor 1 (the standard is Arabic numerals)
  • Do not use for figure or table numbers.

Additional miscellaneous style for numbers and special characters can be found in the full Grammar and Style Guide.

Table Formatting

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

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

Test Method Log permeability – literature Log permeability – data set
Min Max Min Mean Max Observations
[m2] [m2]
Measurement Based Aquifer Scale Modele -20 -10 -16.5 -14.7 -13.2 37
Discrete Tunnel Inflow Measurementa, k -20 -8 -21.8 -15.7 -8.7 2870
(Induced) Seismicityg -16 -7p -16.0 -15.3 -14.9 3
Cross-Borehole Tracer Testl -15 -8 -17.9 -10.9 -6.9 119
Open Hole Pumping/Slug Testl,n -14 to -13 -8 -17.7 -12.7 -9.9 687
Single Packer Testc,f,h,i,l,n -21 to -14 -13 to -8 -20.9 -14.8 -7.1 773
Multi-Packer Testb,c,f,h,i,n -21 to -18 -13 to -8 -21.6 -15.5 -7.7 13877
Drill Stem Testb,d,f,h,i,l -17 to -14 -13 to -11 -18.3 -17.0 -16.1 5
Borehole Lugeon/WD Testd,f,l,m -18 to -15 -12 to -8 -18.0 -13.6 -9.1 334
Difference Flow Logsj -18 -13 -17 -15.1 -9.9 4635
Pneumatic Testo -21 -8 -21 -14.9 -13.0 64
Pressure Tunnel Test ?p ?p -15.7 -14.3 -12.9 14
Hydrofrac Testb,c,f,h,i,n -21 to -18 -13 to -8 -18.5 -16.7 -14.2 45

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.

Word List

See the full Grammar and Style Guide for a word list of commonly occurring terms in AGU papers and their treatment (hyphenation, spelling, capitalization, etc.).