Vegetation and environment in Eastern North America during the Last Glacial Maximum

A paleotemperature record derived from dissolved noble gases in groundwater of the Aquia Aquifer (Maryland, USA)

“…Cold temperatures close to the margin of the Laurentide ice sheet and a steeper north-south temperature gradient are also indicated by paleoclimate reconstructions based on pollen, plant macrofossil, and midge larvae records in lake sediments Jackson et al, 2000;Levesque et al, 1997). With regard to our study site, the pollen-based reconstruction of Webb III et al (1998) suggests Ϸ15°C lower January temperatures and Ϸ5°C lower July temperatures than today.…”

“…In particular, our data suggest a somewhat weaker cooling than the recent synthesis of vegetation data of Jackson et al (2000). Weaknesses of both methods may explain the difference.…”

“…With regard to our study site, the pollen-based reconstruction of Webb III et al (1998) suggests Ϸ15°C lower January temperatures and Ϸ5°C lower July temperatures than today. The more recent analysis of Jackson et al (2000) indicates even colder January temperatures (Ϸ22°C lower than present). The paleoclimate simulations of Bartlein et al (1998) yield a similar pattern of Ϸ20°C lower January temperatures and Ϸ5°C lower July temperatures, with an annual mean LGM cooling for the entire southeastern US of 10°C.…”

“…Climate models indicate that the large ice sheets on the northern continents, and in North America in particular, had a profound effect on the distribution of surface temperatures (Manabe and Broccoli, 1985;COHMAP, 1988;Bartlein et al, 1998). Both models and pollen-based climate reconstructions indicate that sites close to the Laurentide ice sheets experienced a larger LGM-Holocene temperature difference than sites further south, although there are considerable differences between the results of the two approaches Jackson et al, 2000). Independent quantitative paleoclimate reconstructions are desirable to improve our view of the LGM climate in regions influenced by ice sheets.…”

Do Low CO2 Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO2 for Plant–Climate Interactions” by Cowling and Sykes

“…Partitioning the effect of CO 2 and low precipitation upon LGM community composition and pollen-based reconstructions requires modeling studies such as those performed by Cowling (1999) and Jolly and Haxeltine (1997). Pollen-based studies remain useful for showing past vegetation distributions (Jackson et al, 2000), and pollenderived climate estimates set a lower bound for the aridity of the LGM.…”