Department of Earth System Science

Radiocarbon (Δ¹⁴C) and stable carbon isotopes (δ¹³C) were measured for total amino acids, carbohydrates, lipids and acid-insoluble organic fractions separated from sinking particulate organic matter (POM_sink), detrital aggregates, sediment floe and sediments collected from the deep Northeast Pacific Ocean. The results show distinct Δ¹⁴C signatures among these organic compound classes. Bomb ¹⁴C, produced 3–4 decades ago in the atmosphere, was present in all organic fractions in the POM_sink in the deep sea. Δ¹⁴C values decrease with depth, from the sediment trap POM_sink (3450 m) to the sediment (4100 m), with rapid changes occurring at the sediment-water interface. Total lipid had much ‘older’ Δ¹⁴C values than those of amino acid and carbohydrate fractions in detrital aggregates, sediment floe and sediments. These data demonstrate that two processes may be occurring: 1) preferential decomposition of organic matter at the sediment-water interface, and 2) incorporation of ‘old’ organic carbon into POM and sediment. The alteration of carbon found in these organic compound classes suggests that differences in decomposition and chemical behavior exist for each of these compound classes in the deep ocean.