[M-IS10] Paleoclimatology and paleoceanography

[MIS10-29] CO₂ controls on land vegetation in the Northern Hemisphere during the last glacial

*Osamu Seki¹, Naomi Harada², Igarashi Yaeko³ (1.Institute of Low Temperature Science, Hokkaido University, 2.JAMSTEC, 3.Institute for Paleoenvironment of Northern Regions)

Keywords:Climate system, carbon cycle, Negative feedback, boreal vegetation, Last Glacial

It is a key to understand the controlling mechanism of the carbon cycle in the earth’s surface to better understand the whole climate system. Previous studies revealed strong coupling of the climate and carbon cycle. Interesting feature of the past CO₂ record is that CO₂ level has never drewdown below around 190 ppm in glacial periods, suggesting that there is limit to atmospheric CO₂ on the geologically short timescale of glacial cycles. This feature is evident in the glacial-interglacial cycles in the late Pleistocene, implying an operation of the strong negative feedback, which directly respond to CO₂ change in timescale of <1,000 years. Vegetation feedback (the change in the biomass in response to CO₂ change) has been proposed as the negative feedback. However, this hypothesis has not demonstrated yet due to a difficulty of direct comparison of a vegetation record derived from sediment with the ice core CO₂. In this study, we reconstruct vegetation change (broadleaf tree vs grass) over the past 85 kyrs based on high-resolution analyses of plant biomarker (n-alkane C₂₉/C₃₁ ratio) and pollen in Okhotsk Sea sediment core (XP07-C9), which allow us direct comparison of sedimentary record with ice core. Surprisingly, comparison of the vegetation and CO₂ records revealed that millennial scale vegetation change tightly coupled with CO₂ change rather than Dansgaard-Oeschgar cycle, which significantly exerted on millennial scale climate changes in the Northern Hemisphere during the last glacial period. This correspondence suggests that land biomass change even in high latitude region of the Northern Hemisphere is primary controlled by CO₂ changes during the last glacial period and vegetation plays an important role in climate system as a negative feedback which contribute to prescribe the lower limit of CO₂.