Quantifying the impact of chemicals on stable carbon and oxygen isotope values of raw pollen

Carolina Müller,Gerhard Helle,Frank Riedel,Julian Hennig

doi:10.1002/jqs.3300

Abstract

ABSTRACTPurification protocols to extract pollen from lake sediments contain chemicals that alter the carbon and oxygen pollen‐isotope values according to pollen characteristics and family affiliation. Modern (raw) pollen of broad‐leaved (Alnus glutinosa, Betula pendula, Carpinus betulus, Corylus avellana, Fagus sylvatica and Quercus robur) and coniferous tree species (Picea abies and Pinus sylvestris) were treated with potassium hydroxide (KOH), hydrofluoric acid (HF), sodium hypochlorite (NaClO) and sulphuric acid (H2SO4) to test the impact on δ13Cpollen and δ18Opollen and assess the applicability in purification protocols. Pollen of broad‐leaved and coniferous trees reacted differently to chemical exposure, but response patterns are generally alike. Alterations of δ13Cpollen values vary between + 1.0‰ (B. pendula, NaClO‐treatment) and −5.0‰ (P. sylvestris, H2SO4‐treatment). The δ13Cpollen values of raw and chemically treated samples seem to be related after treatments with KOH, NaClO and HF, whereas the application of H2SO4 led to inconsistent changes among species. The impact of chemicals on δ18Opollen are more diverse and offsets range between +1.1‰ (C. avellana, NaClO‐treatment) and −17.9‰ (P. sylvestris, H2SO4‐treatment). In general, the use of isotope‐altering chemicals in purification protocols should be brought to a minimum, but the application of KOH and NaClO seems mostly unproblematic before δ13Cpollen and δ18Opollen analysis.

Highlights

Modern pollen can function as reference material to interpret fossil pollen‐isotope values
It is already known that chemical application alters the pollen‐isotope values (Amundson et al, 1997), but the single effect of certain chemicals on pollen‐isotope values of different species with variable pollen characteristics are unknown
Raw pollen differ from fossilized pollen, because decomposition of structurally weak pollen wall components and pollen wall coatings leaves only the sporopollenin layer of fossil pollen intact (Loader and Hemming, 2000)

Summary

Introduction

Modern (raw) pollen can function as reference material to interpret fossil pollen‐isotope values. The application of certain chemicals on raw pollen imitates a fossilization process to enhance comparability, but chemical substances are used to purify fossil pollen from organic and inorganic remains of a sample. Raw pollen differ from fossilized pollen, because decomposition of structurally weak pollen wall components and pollen wall coatings leaves only the sporopollenin layer of fossil pollen intact (Loader and Hemming, 2000). Sporopollenin, the main component of a pollen wall, is a highly resistant biopolymer approximately consisting of C90H150O33 (Brooks and Shaw, 1978; Loader and Hemming, 2004; Fraser et al, 2014; Li et al, 2019; Mikhael et al, 2019) and the proportion of sporopollenin within raw pollen of different species ranges between 55 and 85% (Nelson, 2012).

Objectives

Methods

Conclusion