Developing a Global Perspective on Dynamics of Riverine Transfer of Terrestrial Biospheric Carbon to the Ocean

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Over short timescales, small changes in the rate of exchange between large pools of "active" carbon such as soils and vegetation can significantly impact the size of the atmospheric CO2 reservoir. Therefore, to predict the ecological and biogeochemical consequences of the current atmospheric CO2 increase and concomitant global warming, we need to understand the natural processes of carbon exchange between these carbon reservoirs. A key aspect in this regard is the global-scale interaction between climate and the dynamics of terrestrial biospheric carbon cycling. In particular, we have only a very rudimentary understanding of the timescales over which carbon fixed by vascular plants on land is exported to the oceans - a crucial component of the carbon cycle. In this project, researchers at the Woods Hole Oceanographic Institution will begin to build a global database on the age of different terrestrial organic carbon (OC) constituents exported by rivers. The focus will be on terrestrial biospheric carbon exported within the particulate OC pool because it has a pivotal role in the global carbon cycle, is potentially the more sensitive to rapid perturbations such as climate change and anthropogenic activity, and leaves a legacy within continental margin sediment records that can be retrieved for paleoclimate reconstructions. The team will study the composition of terrestrial biospheric carbon discharged by rivers to the oceans by characterizing suspended sediments collected close to the terminus of the rivers, as well as deltaic deposits and inner shelf flood deposits. They will attempt to couple radiocarbon (14C) measurements at different levels - from bulk OC to specific molecules (biomarkers) - in order to constrain the age and relative proportion of the different constituents of the biospheric OC pool. They expect to derive a global picture of the dynamics of terrestrial biospheric OC export to the ocean by examining age characteristics of vascular plant-derived carbon discharged by a wide range of rivers that differ markedly in terms of drainage basin size, elevation, latitude, and materials flux. Specifically, they will (1) evaluate the robustness of the preliminary relationship observed between the age of riverine vascular plant-derived OC and the latitude of the river outlet, (2) more precisely define the nature of this relationship, (3) examine whether similar relationships holds for different components of the biospheric OC pool, and finally, (4) use these findings to explore the mechanisms controlling the age of the biospheric carbon discharged by rivers to the ocean at the global scale, and hence to derive insights into the interactions between OC cycling and regional and global climate. Broader impacts: This research initiative is fundamentally based on a collaborative approach that will utilize samples and knowledge shared by a large number of American, Chinese, and European colleagues who are involved in river studies all around the globe. The publications arising from this endeavor will reflect these collaborative partnerships. The project will provide a collaborative research, training and learning environment for a postdoctoral scientist at WHOI. Data emanating from the project will be contributed to a legacy database that is currently being compiled. The data will be shared with the community through publications, through a dedicated website, as well as by linking to other web-accessible community databases.