SOUTHERN PEATLANDS: A NEW PERSPECTIVE ON LONG-TERM CARBON DYNAMICS

Patagonian peatlands have sequestered about 15 Gt of organic carbon (C) since the Last Glacial Maximum. Their resemblance to northern peatlands, at least in terms of vegetation, is striking, but Patagonian peatlands have developed under very different climate boundary conditions than their northern counterparts, mainly because of different orbital parameters as well as the influence of strong oceanic and atmospheric circulation patterns. Therefore, Patagonian peatlands provide a unique opportunity to study long-term peat-C dynamics under different climatic settings, allowing us to further test ongoing hypotheses and theories about peatland formation and climate sensitivity. Here we present 4 radiocarbon-dated Patagonian peat profiles and provide the first estimates of long-term peat-C accumulation rate and net carbon balance for these southern ecosystems.

All four sites are Sphagnum magellanicum peat bogs of less than 10,000 years in age, but they are influenced by different precipitation regimes (drier rain-shadow of the Andes vs. wetter coastal regions). They are characterized by deep (> 5m) peat deposits with a relatively low density of about 0.04-0.06 g cm^-3. Peat addition rate and decay for the entire profiles were derived from age-depth models and estimated using exponential decay curves (Clymo’s peat bog growth model). A proportional rate of decay of about 0.0002 yr^-1 and a constant peat addition rate of 1600 g C m^-2yr^-1 were found. While this rate of decay is within the range recorded for northern peatlands, the peat addition rate is one order of magnitude greater than what is typically found for peat in corresponding northern latitudes. Similar results were found by Smith and Clymo on the Falkland Islands for an herbaceous peat-forming community. Though the underlying cause for these unusually rapid peat addition rates remains uncertain, we speculate that very long growing seasons are the main factors controlling these ecosystems, and that decomposition only plays a second role. This is supported by our results, which indicate that even ‘drier’ peatlands (< 500 mm of rain annually) are sequestrating as much peat-carbon as their wetter counterparts. This southern perspective on the rate of peat formation could provide insights on long-term carbon dynamics in peatlands from around the world.