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Title: POTENTIAL USE OF SOIL C ISOTOPE ANALYSES TO EVALUATE PALEOCLIMATE

Author
item Follett, Ronald
item KIMBLE, JOHN - USDA-NRCS, LINCOLN ,NE
item LEAVITT, S - U OF AZ, TREE RING RES
item Pruessner, Elizabeth

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2004
Publication Date: 7/15/2004
Citation: Follett, R.F., Kimble, J., Leavitt, S., Pruessner, E.G. 2004. The potential use of soil c isotope analyses to evaluate paleoclimate. Soil Science. pp. 471-488.

Interpretive Summary: We evaluated the potential to relate 14C dating of SOC along with its observed its 13C/12C isotope ratios (expressed as Delta 13C as per mil -- 0/00) in soil horizons from native sites extending from South to North in the US Great Plains and Western Corn Belt to existing paleoclimatic literature. The purpose was to determine whether these data support existing literature and if additional information could be obtained about climate changes within this region during the Holocene. Our data support the occurrence of major aeolian soil movement at some sites, often coincidental with reports of drought. Soil profiles provided only low-resolution records of wetter and dryer climatic periods. Our measurements of SOC age and Delta 13C signature in soil horizons can be related to pre-boreal warming during entry into the Holocene. An important question our data raises is the timing of the peak of the Medieval Warm Period (MWP) prior to the start of the Little Ice Age (LIA). Our data indicate a change to increased C3 plant dominance (indicating cooler temperature) at ~1500 yr BP, several hundred years prior the reported start of the LIA (~600 yr BP), from Greenland ice cores, but nearer to other reports. Our approach holds promise as an additional method to evaluate climate back thousands of yrs, but additional measurements besides those from the isotopes of C are often needed.

Technical Abstract: This study evaluated use of the naturally occurring isotopic carbon (C) in soil organic matter to help assess paleoclimate in the Central United States. Sampling sites were on major geomorphic units with similar slope and aspect in major soil temperature and moisture regimes in the historic US grasslands. Soil samples were collected from approximate 0-5 and 5-10 cm (A1 and A2 profile) and by genetic soil horizon thereafter to ~2 m depth. Bulk density and soil texture were determined. Sieved, handpicked, and delimed sub-samples each horizon were analyzed for total soil organic carbon (SOC) and Delta 13C and 14C dated. Data from some sites support that major aeolian movement of soil occurred during the Holocene, often coincidental with long periods of drought. The SOC age and ÿ13C signature in soil horizons was related to pre-boreal warming during entry into the Holocene. Our data but requiring raised question of the timing of the peak of the Medieval Warm Period (MWP) reported to have occurred prior to climate cooling associated with the Little Ice Age (LIA). Based on Delta 13C our data indicate a change from C4 plants to increasing C3 plant dominance (representing cooler temperature) at ~1500 yr BP, whereas the reported start of the LIA is ~600 yr BP. The approach we used holds promise as an additional proxy for evaluating prior climate back thousands of yrs, but additional measurements besides those from the isotopes of C will be needed.