Response of the ocean, climate and terrestrial carbon cycle to Holocene freshwater discharge after 8 kyr BP

The "green'' McGill Paleoclimate Model is run from 8 to 0 kyr BP under variable insolation ( Milankovitch forcing), Taylor Dome CO2 ( radiative forcing) and four prescribed meltwater scenarios ( freshwater forcing) due to the retreat of the Laurentide Ice Sheet ( LIS). For each scenario, we constrain the total volume of meltwater to be 1.62 x 10(15) m(3) ( sea level-equivalent of 4.62 m), which is obtained from the work of Paterson ( 1972) and the reconstructed sea level increase between 8 and 6 kyr BP. During each freshwater perturbation, the simulated maximum Atlantic meridional overturning circulation (MOC) intensity is reduced, by amounts of up to 8 Sv. During the time of a weakened MOC, the sea surface temperature is reduced in the high-latitude North Atlantic and increased in the Southern Ocean. Our model results indicate that the freshwater impact on the Holocene climate and terrestrial carbon cycle is likely negligible after the 8.2-kyr cold event. Only a large freshwater perturbation (> 0.1 Sv) has a significant impact on the Holocene climate and terrestrial carbon cycle; it results in an enhanced cooling of about 1 degrees C in the Northern Hemisphere (NH) and notable drops in the global net primary productivity ( 2 PgC/yr) and total land carbon storage ( 40 PgC)