As global climate changes because of anthropogenic influences, it has become critical to better understand past climate and its various forcing mechanisms as a baseline for future comparison. To this end, we present a continental isotopic record from an 11.2-m-long wetland piston core sampled at 10–50 yr resolution; the core was taken in the heavily populated, economically vibrant northeastern United States (adjacent to Fayetteville Green Lake) and spans 14,600–3200 cal. yr B.P.
We use a historically based correlation between δ18Ocalcite obtained from individual varves in a box core from Fayetteville Green Lake and winter atmospheric circulation over the northeast United States to examine the way in which changes in winter circulation have influenced δ18O in precipitation from 14,600 to 3200 cal. yr B.P. Our correlation analysis suggests that in periods during which the circumpolar westerlies are expanded, storms track more frequently from the Gulf of Mexico region, delivering precipitation with relatively high δ18O values to the study site. By contrast, contracted westerlies result in more frequent low-δ18Oprecipitation cross-continental storms. By using this relationship we model winter-vortex latitudes over the northeast United States for the prehistoric oxygen isotope record, focusing on millennial-scale change, abrupt transitions, and multidecadal- to centennial-scale variability. The δ18Ocalcite and winter-vortex latitude records are characterized by a long-term asymmetric change interrupted by two notable, abrupt transitions at ca. 11,600 cal. yr B.P. and ca. 5200 cal. yr B.P. Several forcing mechanisms are considered including precession of the equinoxes (millennial-scale), ice-sheet-margin retreat (millennial-scale), thermohaline circulation (abrupt transitions), and ocean-atmosphere linkages (decadal to centennial scale).
Analysis of historical δ13Ccalcite values from a box core of varved Fayetteville Green Lake sediment and correlation of these values to early summer precipitation amounts reveal a relationship in which high δ13Ccalcite values (usually attributed to greater primary productivity) correspond with low annual precipitation amounts. From this relationship, we propose a climate- control hypothesis in which less early summer precipitation enhances productivity by increasing sunlight availability through reduced total cloud cover. We use this relationship to interpret early summer precipitation and cloud cover for the period from 14,600 to 3200 cal. yr B.P. The δ13Ccalcite, precipitation and cloud-cover data are characterized by fluctuations about a mean value with multiple abrupt transitions occurring throughout the length of the record; there is no obvious trend in the δ13Ccalcite data. Spectral analysis indicates that both the δ13Ccalcite and δ18Ocalcite data are characterized by a variety of time scales with the most significant periods in the multidecadal to centennial time frame, corroborating other research that has determined a strong multidecadal to centennial periodicity in late glacial–Holocene climate proxy records.