Feb/21/2017: Prof. Yi-Cheng, Teng’s Speech:
Title: Global patterns of carbon-to-phosphorous ratios of marine organic matter export
Abstract: The carbon-to-phosphorus (C:P) ratio is key to understanding the role of marine ecosystems in the Earth’s carbon cycle. Recent analysis of particulate C:P in the upper ocean has revealed variations with strong latitudinal patterns. If these variations, measured in plankton, are transferred to the exported organic matter that remineralizes in the thermocline, an imprint on the DIC and PO4 concentrations might be detectable. Previous study did not detect significant variations in the dissolved C:P ratio in the thermocline and suggest that the circulation homogenizes any such imprint. Here we show that an improved analysis method using a recently developed data-constrained ocean circulation model and a expanded global database of DIC and PO4 measurements does reveal the large-scale signature of spatially varying carbon-to-phosphorus organic matter export (C:P)exp. The inferred pattern of export is consistent with the C:P ratios measured directly in particles. Specifically, the analysis reveals elevated (C:P)exp ratios in the nutrient-depleted subtropical gyres (185:1) and depressed (C:P)exp ratios in the nutrient-rich high-latitude and upwelling regions (94:1). The spatial variation in (C:P)exp also has implications for the rate of biological carbon sequestration. Estimates of carbon export from variable (C:P)exp ratios suggests less geographic variability and brings predictions closer to the measurements.