The Effect of Temperature on Microbially-Mediated Organic Carbon Decomposition from a Global Survey of Scientific Ocean Drilling Data

Abstract:

The burial of particulate organic carbon (POC) in marine sediments is an important process in the Earth’s carbon cycle. While some POC is buried for the long term, a substantial fraction is decomposed within the sediment, fueling subseafloor microbial life. The fundamental controls on the rate of POC decomposition are not well understood at present. Temperature has been proposed as an important factor, because at higher temperatures reaction rates are expected to be faster (as in the Arrhenius equation). To test the effect of temperature on POC decomposition, we assembled from the global scientific ocean drilling archive (DSDP, ODP, and IODP) a large data set of POC content in Cenozoic marine sediments. We concentrated on sites that are in regions of high POC deposition (continental margins and upwelling areas), have a reliable age model, and had in situ measurements of sediment temperature. Using the age and temperature data, we selected two sets of sites where sediments experienced either relatively high- or low-temperature histories that should have resulted in different rates of POC decomposition. We then compared average POC contents versus age in the high-T and low-T sets of sites. The POC content versus age in the low-T set (82 sites) follows a pattern similar to that of all the sites with an age model (419 sites): POC content (dry sediment weight fraction) starts around 1% at the seafloor, reaches a maximum of 1.2-1.3% at ~1.5 Ma, and then slowly decreases with increasing age to a nearly constant value of 0.6-0.7% at ages > 5 Ma. In the high-T set (83 sites), the average POC content shows a stronger decrease from a maximum of ~1.5% around 1 Ma to a low constant value of 0.4% at ages > 5 Ma. The more pronounced decrease in POC content and the lower amount remaining at ages > 5 Ma suggest that higher temperatures result in a greater extent of POC decomposition.