Did North America Suffer Through Persistent La Niña Conditions During the Medieval Climate Anomaly/Warm Period?

Boreal peatland water table depth and carbon accumulation during the Holocene thermal maximum, Roman Warm Period, and Medieval Climate Anomaly

Authors:

Holmquist et al

Abstract:

The Boreal Shield and James Bay Lowland regions of Ontario have few Holocene reconstructions specific to surface moisture despite their potential importance to documenting the geographic patterns and teleconnections of Holocene pluvials and droughts, as well as their role in the global carbon cycle. We reconstructed water table depth using preserved testate amoebae in four stratigraphic peatland cores, supplemented with a literature review to investigate the effects of the Holocene Thermal Maximum (HTM) and Medieval Climate Anomaly (MCA) on surface moisture and long-term apparent carbon accumulation (LARCA) in the regions. A 7320 calendar years before AD 1950 (yrBP) length record registered a wet shift at 4600 yrBP in concert with the HTM and a later post-2550 yrBP shift towards wetter and more stable conditions, possibly related to the Roman Warm Period. During the late-Holocene the three most southern boreal records indicated a lack of droughts during the MCA. Medieval pluvials in boreal Ontario would be consistent with North American precipitation patterns under La Niña conditions. Of the three wet-warm periods identified (HTM, 2550 yrBP, MCA), the 2550 yrBP shift had the most consistent positive influence on LARCA regionally. Although past precipitation was positively correlated with temperature in the region, recent drying may be indicative of a fundamental change in evaporation-precipitation balance.

Evidence From Gulf of Mexico Deep Core Suggests Monsoonal Cycle was Intensified During Holocene Thermal Maximum

PALEOENVIRONMENTAL AND PALEOCLIMATIC IMPLICATIONS OF ENHANCED HOLOCENE DISCHARGE FROM THE MISSISSIPPI RIVER BASED ON THE SEDIMENTOLOGY AND GEOCHEMISTRY OF A DEEP CORE (JPC-26) FROM THE GULF OF MEXICO

Authors:

TRIPSANAS et al

Abstract:

Several meltwater floods initiated by the Laurentide Ice Sheet (LIS) drained to the Gulf of Mexico (GOM) through the Mississippi River during the last deglaciation (10–21 cal ka [calibrated kiloannum]). Such floods have been efficiently captured in the geochemical record of the Jumbo Piston Core 26 (JPC-26) from the northwestern GOM as distinct peaks in the content distribution of Si, Al, and Fe due to their common occurrence throughout North America. On the other hand, peaks in the content distribution of Ti, K, Zr, and V adequately describe the sediment source of each flooding event due to their clustered areal distribution in North America. The presence of three distinct peaks in the distribution of Si, Al, and Fe at 8.5, 5.2–7.6, and 2.9–3.5 cal ka indicates that events of enhanced Mississippi River discharge (EMRD) occurred during the Holocene as well. The geochemical signature of these flooding events suggests that their origin and sediment source is variable, depending on the retreating state of the LIS and the prevailing precipitation patterns in North America during these time periods. A comparison of the 8.5 and 2.9–3.5 cal ka EMRD events with the oxygen isotope and gas (CH4) records of the Greenland Ice Sheet Project 2 (GISP-2) ice core denotes that these events might be linked to short global warming episodes associated with periods of increased solar irradiance. The 5.2–7.6 cal ka EMRD event is associated with the Holocene Thermal Maximum, which resulted in the intensification of the North American monsoonal circulation.