Constraints in the application of the Branched and Isoprenoid Tetraether index as a terrestrial input proxy

Determination of the relative inputs of aquatic autochthonous and terrestrial allochthonous organic matter into marine and lacustrine environments is essential to understanding the global carbon budget. A variety of proxies are used for this purpose, including the Branched and Isoprenoid Tetraether...

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Bibliographic Details
Published in:Journal of Geophysical Research 2011-10, Vol.116 (C10), p.n/a, Article C10032
Main Authors: Fietz, Susanne, Martínez-Garcia, Alfredo, Huguet, Carme, Rueda, Gemma, Rosell-Melé, Antoni
Format: Article
Language:English
Subjects:
BIT index
branched GDGTs
crenarchaeol
Earth sciences
Earth, ocean, space
Exact sciences and technology
Geochemistry
Geophysics
Marine
Organic matter
Sedimentary geology
Soil organic matter
Terrestrial environments
Water column
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Summary:Determination of the relative inputs of aquatic autochthonous and terrestrial allochthonous organic matter into marine and lacustrine environments is essential to understanding the global carbon budget. A variety of proxies are used for this purpose, including the Branched and Isoprenoid Tetraether (BIT) index. This is calculated from the concentrations of branched glycerol dialkyl glycerol tetraethers (GDGTs), derived from unidentified terrestrial bacteria, and crenarchaeol, a marker for aquatic mesophile Thaumarchaeota (Crenarchaeota group I). As the index is a ratio, its value depends on both the crenarchaeol aquatic in situ production and the soil‐derived branched GDGT input. Therefore, the BIT index reflects not only changes in the input of terrestrial or soil organic matter but also relative variations in aquatic Thaumarchaeota abundance in the water column. In fact, we show that in oceanic and lacustrine settings, the BIT index can be dominated by the aquatic end‐member of the ratio. Consequently, the BIT index by itself can be an unreliable proxy to compare the input of terrestrial matter between sites and over time, and we propose that the quantification of branched GDGT fluxes or concentrations may instead be a better indicator of soil terrestrial inputs. Key Points The BIT is often uncorrelated to other terrestrial organic matter input proxies Paleorecords reveal that the aquatic end‐member dominates the BIT Branched GDGTs give a better estimate of the terrestrial organic matter input
ISSN:0148-0227
2169-9275
2156-2202
2169-9291
DOI:10.1029/2011JC007062