The large Amazonian peatland carbon sink in the subsiding Pastaza‐Marañón foreland basin, Peru

The carbon ( C ) dynamics of tropical peatlands can be of global importance, because, particularly in S outheast A sia, they are the source of considerable amounts of C released to the atmosphere as a result of land‐use change and fire. In contrast, the existence of tropical peatlands in A mazonia has been documented only recently. According to a recent study, the 120 000 km 2 subsiding P astaza‐ M arañón foreland basin in P eruvian A mazonia harbours previously unstudied and up to 7.5 m thick peat deposits. We studied the role of these peat deposits as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 5–13 sites. The basal ages varied from 1975 to 8870 cal yr bp , peat accumulation rates from 0.46 to 9.31 mm yr −1 and C accumulation rates from 28 to 108 g m −2 yr −1 . The total peatland area and current peat C stock within the area of two studied satellite images were 21 929 km 2 and 3.116 Gt (with a range of 0.837–9.461 Gt). The C stock is 32% (with a range of 8.7–98%) of the best estimate of the S outh A merican tropical peatland C stock and 3.5% (with a range of 0.9–10.7%) of the best estimate of the global tropical peatland C stock. The whole P astaza‐ M arañón basin probably supports about twice this peatland area and peat C stock. In addition to their contemporary geographical extent, these peatlands probably also have a large historical (vertical) extension because of their location in a foreland basin characterized by extensive river sedimentation, peat burial and subsidence for most of the Q uaternary period. Burial of peat layers in deposits of up to 1 km thick Q uaternary river sediments removes C from the short‐term C cycle between the biosphere and atmosphere, generating a long‐term C sink.