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Title: Stable-Carbon Isotopes of U.S. Great Plains Soils and Climate Events during the Holocene.

Author
item LEAVITT, S - U OF AZ, TUCSON, AZ
item Follett, Ronald

Submitted to: Soil Science Society of America Special Publication Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/16/2007
Publication Date: 3/1/2009
Citation: Leavitt, S., Follett, R.F. 2009. Stable-Carbon Isotopes of U.S. Great Plains Soils and Climate Events during the Holocene. pp. 223-231 & Plates 14-1 to 14-4. In R. Lal and R.F. Follett (eds). SSSAJ Special Publication #57 (2nd Edition) 410p.

Interpretive Summary: The SOC Delta 13C profiles with radiocarbon dating control seem to capture general characteristics and changes of Holocene C3-C4 abundance. They also seem to capture some subtle changes that might be associated with climate events of the last 2000 years. However, their mapped distribution does not demonstrate any distinctive patterns corresponding to a specific zenith of the mid-Holocene Warm Period or with the abrupt cold event ca. 8200 years ago. Single ages were assigned to each event (e.g., Little Ice age 500 years ago and Medieval Warm Period 1000 years ago), but realistically these events persisted over intervals of hundreds of years. Therefore, C3-C4 distribution in other ages (e.g., 400 and 600 years ago for the beginning of the Little Ice Age) could be examined, but without the improvement in profile resolution limitations, it would probably not be very informative.

Technical Abstract: A suite of 12 soil profiles from the U.S. Great Plains and western Corn Belt were sampled to a depth of 2 m and radiocarbon dating control was established to investigate possible changes in stable-carbon isotope composition of SOC over space and time associated with major Holocene climate events. The investigation is based on the known influence of climate on the relative abundance of C3 and C4 grasses, and the input of carbon from vegetation into soil carbon pools to preserve a record of the plant abundance. Despite the complexity of the soil carbon system (e.g., sources, decomposition effects, organic carbon compounds), studies have successfully used depth profiles to infer temporal changes in vegetation. Here, “warm” periods 2000 and 1000 years ago seemed to show higher abundance of C4 grasses in the southern Great Plains than during the “cold” periods 1500 and 500 years ago. The period 8500 to 3500 years ago shows a progressive northeastward advance of C4 abundance, but no distinct' '13C configuration is present within the period attributable to a peak mid-Holocene “warm” period (or perhaps “cool and dry” period in parts of the Great Plains). Likewise, no distinguishing pattern of isotopic values appears in the interval from 9000 to 8000 years ago related to a cold event 8200 years ago. The numerous factors influencing soil carbon plus lag effects related to timing of climate and subsequent vegetation change decrease the potential for SOC '13C to identify specific, relatively ‘brief’ climate events, but higher resolution sampling of soil profiles for radiocarbon dating and Delta 13C analysis might improve such prospects. [GRACENet publication].