Open AccessDeep in the Sierra Nevada critical zone: saprock represents a large terrestrial organic carbon stock
Author(s) -
Kimber Moreland,
Zhiyuan Tian,
Asmeret Asefaw Berhe,
K. J. McFarlane,
Peter Hartsough,
Stephen C. Hart,
Roger C. Bales,
A. T. O’Geen
Publication year - 2021
Publication title -
environmental research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.37
H-Index - 124
ISSN - 1748-9326
DOI - 10.1088/1748-9326/ac3bfe
Subject(s) - radiocarbon dating , weathering , total organic carbon , bedrock , organic matter , soil carbon , environmental science , soil organic matter , geology , carbon cycle , regolith , soil water , soil science , environmental chemistry , geochemistry , geomorphology , chemistry , ecosystem , ecology , paleontology , physics , organic chemistry , biology , astrobiology
Large uncertainty remains in the spatial distribution of deep soil organic carbon (OC) storage and how climate controls belowground OC. This research aims to quantify OC stocks, characterize soil OC age and chemical composition, and evaluate climatic impacts on OC storage from the soil surface through the deep critical zone to bedrock. These objectives were carried out at four sites along a bio-climosequence in the Sierra Nevada, California. On average, 74% of OC was stored below the A horizon, and up to 30% of OC was stored in saprock (friable weakly weathered bedrock). Radiocarbon, spectroscopic, and isotopic analyses revealed the coexistence of very old organic matter (OM) (mean radiocarbon age = 20 300 years) with relatively recent OM (mean radiocarbon age = 4800 years) and highly decomposed organic compounds with relatively less decomposed material in deep soil and saprock. This co-mingling of OM suggests OC is prone to both active cycling and long-term protection from degradation. In addition to having direct effects on OC cycling, climate indirectly controls deep OC storage through its impact on the degree of regolith weathering (e.g. thickening). Although deep OC concentrations are low relative to soil, thick saprock represents a large, previously unrealized OC pool.