Holocene carbon flux histories of the world’s peatlands

Abstract

This paper proposes a novel approach using basal peat ages and carbon (C) accumulation profiles from the world’s major peatland regions to decompose C flux terms from time-dependent C pool data observed from peat cores. Our peat-data syntheses show that the total peat C pools are 547 GtC, 50 GtC, and 15 GtC for northern, tropical and southern peatlands, respectively. The modeled net C balance (NCB) has a mean value of 41.8 TgC/yr for northern peatlands during the Holocene, ranging from 83.1 TgC/yr in the early Holocene around 9 ka (1 ka = 1000 cal. yr BP) to 21.5 TgC/yr around 2 ka, a temporal pattern mostly owing to the delayed effect of long-term decay of previously accumulated peat C. NCB from tropical and southern peatlands represents much smaller terms, mostly less than 10 TgC/yr. Northern peatlands represent about 90% of global total peatland C pool of 612 GtC and >90% of global peatland NCB. Our bottom-up global peatland synthesis indicates a decrease in rates of peatland area expansion and reduced CH4 emissions during the late Holocene, thus lending support for an anthropogenic source of late-Holocene CH4 rise. The C balance analysis of global peatland data indicates a cumulative net C uptake of 272 GtC in the early Holocene (11–7 ka), 151 GtC at 7–4 ka, and 116 GtC after 4 ka. The large cumulative fluxes and significant variations throughout the Holocene could greatly contribute to the observed atmospheric CO2 and δ13CO2 patterns derived from Antarctic ice cores. Thus, global mass-balance calculations or climate–carbon cycle simulations have to consider these large net C uptake terms from global peatlands and their variations over the Holocene.