Source(s) and cycling of the nonhydrolyzable organic fraction of oceanic particles

Jeomshik Hwang,Ellen R.M Druffel,Timothy I Eglinton,Daniel J Repeta

doi:10.1016/j.gca.2006.07.020

Abstract

A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using 13C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. 13C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments.

Highlights

Understanding the fluxes, transformations, and fate of particulate organic carbon (POC) is a major focus of oceanic carbon cycle research
The nonhydrolyzable fractions account for 37% and 44% of sinking POC and sedimentary organic carbon (SOC) samples, respectively (Table 1)
Considering potential losses during sample processing, we suspect the actual percentage of the nonhydrolyzable fraction is larger than these values

Summary

Introduction

Understanding the fluxes, transformations, and fate of particulate organic carbon (POC) is a major focus of oceanic carbon cycle research. Less than half of sinking POC and sedimentary organic carbon (SOC) has been molecularly characterized (Wakeham et al, 1997), and the molecularly uncharacterized component [MUC, (Hedges et al, 2000; Lee et al, 2004)] accounts for an increasing fraction of sinking POC with increasing water depth. A major reason why the majority of POC remains uncharacterized is because it can neither be extracted with organic solvents nor be hydrolyzed with strong non-oxidizing acids or bases for further analysis. Only a fraction of the extracted or hydrolyzed organic matter can be characterized by chromatographic and/or mass spectrometric analyses.

Methods

Results

Conclusion