Southward migrations of tropical rainfall during Heinrich Events: compelling evidence from δ18O of atmospheric O2

Multiple independent paleoclimate records from marine sediments, speleothems, and ice cores support the notion that the thermal equator and tropical rain belts abruptly shifted southward in response to northern high-latitude iceberg discharge during Heinrich Events (HEs). Here we present a composite, 50-ka record of δ18O of O2 (δ18Oatm) from the Siple Dome (SD) and WAIS Divide (WD) Antarctic ice cores which provides further evidence for this teleconnection from a globally integrated paleoclimate archive: atmospheric air bubbles. We introduce a simple mechanism by which changes in the global isotopic fractionation of atmospheric O2 (ΔɛLAND) record the centroid latitude of terrestrial oxygen production: the terrestrial oxygenesis equator (TOE). Drawing on modern seasonal records of terrestrial gross primary productivity (GPP) and δ18O of precipitation (δ18Op), we identify a strong negative correlation between TOE and GPP-weighted δ18Op. This relationship suggests that past increases in ΔɛLAND following HEs indicate southward displacements of terrestrial oxygen production, presumably due to southward displacements of the thermal equator and tropical rain belts. In the composite SD-WD record, local maxima in ΔɛLAND coincide (within dating uncertainty) with small, abrupt increases in atmospheric methane (measured in WD) within Heinrich Stadials 1, 2, 4 and 5. The composite ΔɛLAND record therefore adds strong support to the interpretation that these methane spikes indicate stimulation of southern hemisphere wetland emissions due to southward shifts of tropical rainfall in response to HEs.