Last interglacial (MIS 5e) and Holocene paleohydrology and paleovegetation of midcontinental North America from Gulf of Mexico sediments

Abstract

Marine Isotope Stage (MIS) 5e experienced slightly higher insolation and lower global ice volume compared to the pre-industrial climate, however, how climate and vegetation differ regionally during MIS 5e is poorly known. Here, we examined MIS 5e hydrologic and vegetation conditions in the Mississippi River Basin (MRB) in North America (NA) and compared this to the Holocene. To do this, we reconstructed paleohydrology and paleovegetation conditions during the last 150 kyr using plant waxes (n-alkanes) and their carbon (δ13Calk) and hydrogen (δ2Halk) isotopic compositions preserved in ODP 625B core from the northwestern Gulf of Mexico (GOM) near the MRB discharge area. In the early MIS 5e, the jet stream may have been located in its northern most position over the last 150 kyr indicated by the highest δ2Halk values resulting in high warm and moist air mass contribution from the GOM and tropical Atlantic to the MRB. This is likely caused by northern expansion of the Atlantic Warm Pool and a northward shift of the ITCZ with increased warming. The climate may have become drier towards late MIS 5e with precipitation concentrated in summer expanding the C4 grassland distribution, which persisted through the MIS 5b. We speculate that this may be due to prolonged warming and drying from early to mid MIS 5. There were notable increases in plant wax export from western dry grasslands during deglaciation (13.5 ka) and the mid-Holocene (5.3 ka). In contrast, plant wax delivery was low during the MIS 5e without significant source changes. Such contrast between the two interglacials is due to the earlier completion of the LIS retreat in late MIS 6 and an onset of a full interglacial climate during the MIS 5e compared to the Last Glacial and Holocene transition. This study presents timing and mechanisms of precipitation source and vegetation composition changes over the NA as a result of slight changes in insolation and rates of deglaciation. These results provide a baseline for understanding the sensitivity of regional hydrologic and vegetation conditions to slight changes in global climate.