Black Carbon (BC) and the Global Carbon Cycle: Assessing BC Inventories in Coastal Seawater and Burial in Margin Sediments off the Northeastern USA

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Black carbon (BC), the product of incomplete combustion of fossil fuels and biomass, has been increasingly formed and released to the environment for the last century. Presently, it is not possible to quantify (a) the rate of BC burial in the oceanic margin sediments (where most of the OC is buried), (b) the size of the BC reservoir in seawater, nor (c) riverine fluxes of BC to the sea. Consequently, it is not possible to ascertain how important BC is to the global carbon cycle. Under this award, the PIs address the following questions: (1)What is the contribution of BC burial relative to the organic carbon burial in the Gulf of Maine? (2) How has the input flux of BC to the region's bed sediments changed in the past century? (3) What is the inventory of BC in coastal seawater off the Northeast United States and what temporal and spatial variability does this reservoir exhibit? (4) What are riverine inputs of BC to the Gulf of Maine and how do they vary seasonally? (5) Can we identify the major sources of BC (e.g., fossil fuel combustion-produced soots, biomass-derived chars) for coastal seawater and sediment of the Gulf of Maine? In addition to measurement of the abundance of BC in various samples, the approach taken includes field sampling of water and sediments, and a variety of analytical measurements including: 234Th/238U disequilibria in water and unsupported 210Pb in sediments, carbon isotopes in BC and specific compounds as well as with key marker compounds (PAHs), and BC analyses in radiometrically dated sediment cores collected from within and beyond the Gulf of Maine.