Centennial-scale variations in the carbon cycle enhanced by high obliquity

Abstract

Centennial-scale increases of atmospheric carbon dioxide, known as carbon dioxide jumps, are identified during deglacial, glacial and interglacial periods and linked to the Northern Hemisphere abrupt climate variations. However, the limited number of identified carbon dioxide jumps prevents investigating the role of orbital background conditions on the different components of the global carbon cycle that may lead to such rapid atmospheric carbon dioxide releases. Here we present a high-resolution carbon dioxide record measured on an Antarctic ice core between 260,000 and 190,000 years ago, which reveals seven additional carbon dioxide Jumps. Eighteen of the 22 jumps identified over the past 500,000 years occurred under a context of high obliquity. Simulations performed with an Earth system model of intermediate complexity point towards both the Southern Ocean and the continental biosphere as the two main carbon sources during carbon dioxide jumps connected to Heinrich ice rafting events. Notably, the continental biosphere appears as the obliquity-dependent carbon dioxide source for these abrupt events. We demonstrate that the orbital-scale external forcing directly impacts past abrupt atmospheric carbon dioxide changes. Centennial-scale releases of atmospheric CO2 occurred during periods of high obliquity over the past 500,000, suggesting a link between external forcing and atmospheric CO2 variations, according to a record from an Antarctic ice core.