Low terrestrial carbon storage at the Last Glacial Maximum: constraints from multi-proxy data
<p>Past changes in the inventory of carbon stored in vegetation and soils remain uncertain. Earlier studies inferred the increase in the land carbon inventory (<span class="inline-formula">Δ</span>land) between the Last Glacial Maximum (LGM) and the preindustrial period (...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/15/849/2019/cp-15-849-2019.pdf |
| Summary: | <p>Past changes in the inventory of carbon stored in vegetation and
soils remain uncertain. Earlier studies inferred the increase in the land
carbon inventory (<span class="inline-formula">Δ</span>land) between the Last Glacial Maximum (LGM) and
the preindustrial period (PI) based on marine and atmospheric stable carbon
isotope reconstructions, with recent estimates yielding 300–400 <span class="inline-formula">GtC</span>.
Surprisingly, however, earlier studies considered a mass balance for the
ocean–atmosphere–land biosphere system only. Notably, these studies neglect
carbon exchange with marine sediments, weathering–burial flux imbalances, and
the influence of the transient deglacial reorganization on the isotopic
budgets. We show this simplification to significantly reduce <span class="inline-formula">Δ</span>land in
simulations using the Bern3D Earth System Model of Intermediate Complexity
v.2.0s. We constrain <span class="inline-formula">Δ</span>land to <span class="inline-formula">∼850</span> <span class="inline-formula">GtC</span> (median estimate;
450 to 1250 <span class="inline-formula">GtC</span> <span class="inline-formula">±1</span>SD) by using reconstructed changes in
atmospheric <span class="inline-formula"><i>δ</i><sup>13</sup>C</span>, marine <span class="inline-formula"><i>δ</i><sup>13</sup>C</span>, deep Pacific
carbonate ion concentration, and atmospheric <span class="inline-formula">CO<sub>2</sub></span> as observational
targets in a Monte Carlo ensemble with half a million members. It is highly
unlikely that the land carbon inventory was larger at LGM than PI.
Sensitivities of the target variables to changes in individual deglacial
carbon cycle processes are established from transient factorial simulations
with the Bern3D model. These are used in the Monte Carlo ensemble and provide
forcing–response relationships for future model–model and model–data
comparisons. Our study demonstrates the importance of ocean–sediment
interactions and burial as well as weathering fluxes involving marine organic
matter to explain deglacial change and suggests a major upward revision of
earlier isotope-based estimates of <span class="inline-formula">Δ</span>land.</p> |
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| ISSN: | 1814-9324 1814-9332 |