Precessional forcing of tropical vegetation carbon storage

Since the Mid-Pleistocene Revolution, which occurred about one million years ago, global temperatures have fluctuated with a quasi-periodicity of ~100 thousand years (kyr). The pattern of past change in the extent of woodlands, and therefore by inference vegetation carbon storage, has been demonstrated to have a strong positive link with this global temperature change at high and mid latitudes. However, understanding of climate systems and ecosystem function indicates that the pattern of woodland change at low latitudes may follow a fundamentally different pattern. We present output from the intermediate complexity model GENIE-1, comprising a single transient simulation over the last 800 kyr and a 174-member ensemble of 130 kyr transient simulations over the last glacial cycle. These simulations suggest that whilst vegetation carbon storage in mid-high northern latitudes robustly follows the characteristic ~100 kyr cycle, this signal is not a robust feature of tropical vegetation which is subject to stronger direct forcing by the precessional (21 kyr) orbital cycle (albeit with a highly uncertain response). We conclude that the correlation of palaeoenvironmental records from low latitudes with global temperature change must be done with caution.