Speaker: Prof. Samar Khatiwala (Columbia University, Lamont-Doherty Earth Observatory)
Abstract: The release of fossil fuel CO2 to the atmosphere by human activity has been implicated as the predominant cause of global climate change. The ocean plays a crucial role in mitigating the effects of this perturbation to the climate system, sequestering 20 to 35% of anthropogenic CO2 emissions from the atmosphere. While much progress has been made in recent years in understanding and quantifying this sink, considerable uncertainty remains as to the distribution of anthropogenic CO2 in the ocean, its rate of uptake over the industrial era, and the partitioning of fossil fuel CO2 between the ocean and land biosphere.

In this talk, I will present the first observationally-based reconstruction of the 3-dimensional, time-evolving history of anthropogenic carbon in the ocean over the industrial era. The reconstruction is based on a novel inverse method that allows us to deconvolve the ocean's transport Green function from oceanographic data. We show that ocean uptake of anthropogenic CO2 has increased sharply since the 1950s and is currently at 2.5+/-0.6 PgC/y, with a total inventory of 150+/-26 PgC. The Southern Ocean is the primary conduit by which this CO2 enters the ocean. Our results also suggest that the terrestrial biosphere was a source of CO2 until the 1940s, subsequently turning into a sink. To better understand the effectiveness of the ocean as a long term sink of CO2 emission, I will also describe model simulations of the path density, a diagnostic of advective-diffusive flows that allows us to track surface-to-surface transport of water and tracers, and thus quantify the time scales and pathways between uptake of CO2 and subsequent re-exposure to the atmosphere