The effect of river freshwater discharge on the carbon cycling of the US Eastern continental shelf: Results from a three-dimensional total dissolved organic matter model study

Jianhong Xue, Virginia Institute of Marine Science, jxue@vims.edu
Marjorie Friedrichs, Virginia Institute of Marine Science, marjy@vims.edu (Presenter)
Antonio Mannino, NASA GSFC, antonio.mannino@nasa.gov
Bronwyn Cahill, IMCS, Rutgers University, bronwyn@marine.rutgers.edu
John Wilkin, IMCS, Rutgers University, john wilkin
Cindy Lee, Stony Brook University, cindy.lee@sunysb.edu
Katja Fennel, Dalhousie University, katja.fennel@dal.ca
Eileen Hofmann, Old Dominion University, hofmann@ccpo.odu.edu
Raymond Najjar, The Pennsylvania State University, najjar@meteo.psu.edu
Kimberly Hyde, NOAA, kimberly.hyde@noaa.gov

On a global scale, rivers export roughly 39,000 km3/year of freshwater and 48 Tg/yr of nitrogen to coastal waters. These exports have significant effects on both the physical and biogeochemical character of continental shelf waters, especially near the mouths of major river discharge regions. Recent studies have shown that discharges of most of the world’s largest rivers have undergone significant changes in the past half century, and are likely to undergo more changes in future decades. In this study, we used a coupled biogeochemical-circulation model of the U.S. eastern continental shelf to examine the effect of changes in riverine freshwater discharge, nitrate and dissolved organic carbon on the coastal carbon fluxes in this region. Sensitivity experiments were conducted in which freshwater discharge and nutrient fluxes were independently and simultaneously doubled and halved. Our results show that changes in river discharge most significantly affect carbon burial and air-sea CO2 exchange, with a doubling of river discharge resulting in increases of up to 20-30% in the magnitude of these fluxes. These anomalies occur mostly in the summer months, and are greatest in the surface waters within the mid-Atlantic Bight coastal area. These changes result from two mechanisms: increased nutrient input to the coastal zone increases productivity, carbon burial and air-sea CO2 flux, whereas increased freshwater input enhances stratification and air-sea CO2 flux, but lowers productivity. As a result, the overall effect of increased river discharge is minor in terms of changes in productivity, but significant in terms of its effect on air-sea CO2 exchange.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Friedrichs, Marjy: Impacts of Changing Climate and Land Use on Carbon Cycling and Budgets of the Coastal Ocean Margin: Observations, Analysis, and Modeling ...details

Poster Location ID: 20