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[1] 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.

Citation for published item:pietzD F nd ruguetD gF nd fendleD tFeF nd islD wF nd qllherD gF nd rerfortD vF nd tmiesonD F nd wrt¡ %nezEqriD eF nd wglymontD iFvF nd ekD FvF nd rhlD pFqF nd ossiD F nd uedD qF nd nsonEfrrerD eF nd osellEwel¡ eD eF @PHIPA 9goEvrition of renrheol nd rnhed qhqs in glollyEdistriuted mrine nd freshwter sedimentry rhivesF9D qlol nd plnetry hngeFD WPEWQ F ppF PUSEPVSF Further information on publisher's website: httpXGGdxFdoiForgGIHFIHITGjFgloplhFPHIPFHSFHPH Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Global and planetary change. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Global and planetary change, 92-93, 2012Global and planetary change, 92-93, , http://dx.doi.org/10.1016Global and planetary change, 92-93, /j.gloplacha.2012 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. findings from this large-scale data set suggest that a common or mixed source for both 56GDGT types is actually commonplace in lacustrine and marine settings.

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