Controls on the age of plant waxes in marine sediments - A global synthesis

Sedimentary high molecular weight (HMW) n-alkyl lipids derived from the waxes of terrestrial plants are common target compounds in biogeochemical and paleoenvironmental research. These plant waxes derive predominantly from the epicuticular cover of vascular plant leaves and their relative and absolute abundances and stable isotopic composition can be used as proxies to decipher, e.g., continental climate and land-ocean carbon transfer processes. In marine sediments, however, compound-specific radiocarbon analysis has revealed that plant waxes are often not syn-depositional, but instead are substantially C-14-depleted ('pre-aged') upon deposition. This C-14-depletion can be caused by various processes that either promote retention of plant waxes during transport from source to sink such as storage in soils or entrainment in deposition-resuspension loops in rivers and on continental shelves or, alternatively, by processes that add HMW n-alkyl lipids from other sources (e.g., petrogenic inputs). Here, we review the intrinsic and extrinsic processes affecting the sedimentary plant wax C-14 composition (ranging from chemical processes to continental-scale environmental conditions), how plant wax C-14 compositions translate into mean ages, and which processes control plant wax mean ages in marine sediments. Finally, we use a compilation of available and new compound-specific plant wax C-14 data to provide a synthesis and evaluate the major controls on plant wax mean ages in marine sediments at the global scale. (C) 2021 Elsevier Ltd. All rights reserved