Abstract
ABSTRACTWe discuss present and developing techniques for studying radiocarbon in marine organic carbon (C). Bulk DOC (dissolved organic C) Δ14C measurements reveal information about the cycling time and sources of DOC in the ocean, yet they are time consuming and need to be streamlined. To further elucidate the cycling of DOC, various fractions have been separated from bulk DOC, through solid phase extraction of DOC, and ultrafiltration of high and low molecular weight DOC. Research using 14C of DOC and particulate organic C separated into organic fractions revealed that the acid insoluble fraction is similar in 14C signature to that of the lipid fraction. Plans for utilizing this methodology are described. Studies using compound specific radiocarbon analyses to study the origin of biomarkers in the marine environment are reviewed and plans for the future are outlined. Development of ramped pyrolysis oxidation methods are discussed and scientific questions addressed. A modified elemental analysis (EA) combustion reactor is described that allows high particulate organic C sample throughput by direct coupling with the MIniCArbonDAtingSystem.
Highlights
Organic carbon (C) is reduced C whose molecular structure is formed on skeletons of C atoms
Research using 14C of dissolved organic C (DOC) and particulate organic C separated into organic fractions revealed that the acid insoluble fraction is similar in 14C signature to that of the lipid fraction
There are two pools of organic C in seawater, dissolved organic C (DOC) that passes a 0.2 to 1.0 micron filter, and particulate organic C (POC) that is retained on the filter (Figure 1)
Summary
Organic carbon (C) is reduced C whose molecular structure is formed on skeletons of C atoms. Methods for measuring bulk DOC Δ14C in seawater were developed in the 1960s that required collection of 400–500 L of water in Gerard barrels (Figure 2), UV oxidation in 60 L batches, and gas counting of 14C in the CO2 (Williams et al 1969).
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