ALBERT

Description: Rhodes et al. 2015 (doi:10.1126/science.1262005) The causal mechanisms responsible for the abrupt climate changes of the Last Glacial Period remain unclear. One major difficulty is dating ice rafted debris (IRD) deposits associated with Heinrich events: Extensive icebergs influxes into the North Atlantic Ocean, linked to global impacts on climate and biogeochemistry. In a new ice core record of atmospheric methane with ultra-high temporal resolution, we find abrupt methane increases within Heinrich stadials 1, 2, 4 and 5 that, uniquely, have no counterparts in Greenland temperature proxies. Using a heuristic model of tropical rainfall distribution, we propose that Hudson Strait Heinrich events caused rainfall intensification over Southern Hemisphere land areas, thereby producing excess methane in tropical wetlands. Our findings suggest that the climatic impacts of Heinrich events persisted for 740 to 1520 years. --- Rhodes et al. 2017 (doi:10.1002/2016GB005570) In order to understand atmospheric methane (CH_4) biogeochemistry now and in the future, we must apprehend its natural variability, without anthropogenic influence. Samples of ancient air trapped within ice cores provide the means to do this. Here we analyze the ultrahigh-resolution CH_4 record of the West Antarctic Ice Sheet Divide ice core 67.2-9.8 ka and find novel, atmospheric CH_4 variability at centennial time scales throughout the record. This signal is characterized by recurrence intervals within a broad 80-50 year range, but we find that age-scale uncertainties complicate the possible isolation of any periodic frequency. Lower signal amplitudes in the Last Glacial relative to the Holocene may be related to incongruent effects of firn-based signal smoothing processes. Within interstadial and stadial periods, the peak-to-peak signal amplitudes vary in proportion to the underlying millennial-scale oscillations in CH_4 concentration-the relative amplitude change is constant. We propose that the centennial CH_4 signal is related to tropical climate variability that influences predominantly low-latitude wetland CH_4 emissions.