Large inert carbon pool in the terrestrial biosphere during the Last Glacial Maximum

Abstract

During each of the late Pleistocene glacial-interglacial transitions, atmospheric carbon dioxide concentrations rose by almost 100 ppm. The sources of this carbon are unclear, and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions. Here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon-cycle modelling to estimate terrestrial and oceanic gross primary productivity during the Last Glacial Maximum. We find that the rate of gross terrestrial primary production during the Last Glacial Maximum was about 40 +/- 10 Pg C yr(-1), half that of the pre-industrial Holocene. Despite the low levels of photosynthesis, we estimate that the late glacial terrestrial biosphere contained only 330 Pg less carbon than pre-industrial levels. We infer that the area covered by carbon-rich but unproductive biomes such as tundra and cold steppes was significantly larger during the Last Glacial Maximum, consistent with palaeoecological data. Our data also indicate the presence of an inert carbon pool of 2,300 Pg C, about 700 Pg larger than the inert carbon locked in permafrost today. We suggest that the disappearance of this carbon pool at the end of the Last Glacial Maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations

Transient simulations of the carbon and nitrogen dynamics in northern peatlands: from the Last Glacial Maximum to the 21st century

“…From the LGM to the pre-industrial period, LPX simulates a net increase in total northern peatland and global mineral soil C of 440 Pg C and global vegetation C of 100 Pg C. This is within the uncertainty of recent estimates (Ciais et al, 2012) and much less than in simulations with a previous version of the model (Joos et al, 2004). The attribution of the increase considerably changed since then as the model has undergone significant changes, such as the addition of permafrost, peatland and dynamic N cycle modules.…”

Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics

“…Prentice et al, 1993;Kaplan et al, 2002;Köh-ler and Fischer, 2004;Brovkin et al, 2012;O'ishi and AbeOuchi, 2013). The resulting range of carbon storage change estimates is from a few hundred to about 1000 PgC (Ciais et al, 2012). One could add to this changes in the weathering of soil minerals and hence CO 2 uptake from the atmosphere, as well as nutrient, particularly phosphate, supply to the ocean and hence changes in the ocean productivity.…”

“…Bradshaw et al, 2015;Claussen et al, 2006;Jahn et al, 2005;O'ishi and Abe-Ouchi, 2013;Shellito and Sloan, 2006) or biogeochemical impacts (e.g. Kaplan et al, 2002;Ciais et al, 2012) and the question of the overall feedback on climate rarely addressed, although Claussen (2009) argues that the net effect at the LGM is dominated by the biogeophysical effects.…”

Simulation of climate, ice sheets and CO<sub>2</sub> evolution during the last four glacial cycles with an Earth system model of intermediate complexity

“…Each of these four pools occupies the same fraction of grid cell as the respective vegetation type. Crichton et al (2014) in their version of permafrost carbon implementation in CLIMBER-2 have not changed the pool structure but modified turnover time, assuming that it is increasing under permafrost conditions. In the new version of the carbon cycle model which we use in the present work, we have introduced three new carbon pools: boreal peat, permafrost, and carbon buried under ice sheets.…”

“…Among them are changes in the ocean circulation (Watson et al, 2015) and an increase in Southern Ocean stratification (e.g. Kobayashi et al, 2015), increase in sea ice area in the Southern Ocean (Stephens and Keeling, 2000) and a shift in the westerlies (Toggweiler et al, 2006), increase in nutrient inventory or change in the marine biota stoichiometry (Sigman and Boyle, 2000;Wallmann et al, 2016), changes in coral reefs accumulation and dissolution (Opdyke and Walker, 1992), accumulation of carbon in the permafrost regions (Ciais et al, 2012;Brovkin et al, 2016), variable volcanic outgassing (Huybers and Langmuir, 2009), and several other mechanisms. Most of these processes are not directly related to ice sheet area or volume, and thus should be considered as amplifiers or modifiers of the direct response of CO 2 to ice sheets operating through the climate-carbon cycle feedbacks.…”