DOI: 10.25921/vdpp-dh37
title: NOAA/WDS Paleoclimatology - Deep Pond, Massachusetts 12KYr LOI Data and Moisture Balance Reconstructions

description: A decline of hemlock (Tsuga) populations at ca 5.5 ka (thousands of calibrated radiocarbon years before 1950 AD) stands out as the most abrupt vegetation change of the Holocene in North America, but remains poorly understood after decades of study. Recent analyses of fossil pollen have revealed a concurrent, abrupt oak (Quercus) decline and increases in the abundance of beech (Fagus) and pine (Pinus) on Cape Cod in eastern Massachusetts, but the replacement of drought-tolerant oaks by moisture-sensitive beeches appears inconsistent with low lake levels in the region at the same time. The oak and beech changes are also limited to coastal areas, and the coastal-inland differences require an explanation. Here, we develop a new lake-level reconstruction from Deep Pond, Cape Cod by using a transect of sediment cores and ground-penetrating radar (GPR) profiles to constrain the past elevations of the sandy, littoral zone of the pond. The reconstruction shows that a series of multi-century episodes of low water coincide with the abrupt hemlock and oak declines, and interrupt subsequent phases of hemlock recovery. The lake-level variations equal precipitation deficits of ~100 mm superimposed on a Holocene long moisture increase of >400 mm. However, because moisture deficits do not easily explain the oak and beech changes, we also evaluate how the climate preferences of the regional vegetation changed over time by matching the fossil pollen assemblages from Deep Pond with their modern equivalents. Reconstructions of the precipitation requirements of the vegetation correlate well even in detail with the lake-level record (r = 0.88 at Deep Pond), and indicate close tracking of effective moisture (precipitation minus evapotranspiration) by the vegetation despite the abrupt species declines, which could have decoupled climate and vegetation trends. Reconstructions of the temperature preferences of the vegetation indicate that coastal sites may have cooled by 0.5-2.5 C after ca 5.5 ka, while inland sites warmed by 0.5-1 C. The change in coastal temperature preferences agrees with sea surface cooling in the western Atlantic Ocean of >1 C. Consequently, the persistence of low hemlock abundance after 5.5 ka in the northeast U.S. may have resulted from oceanic changes that produced multi-century droughts and thus delayed the post-decline recovery of hemlock populations.
description: Sediment loss-on-ignition (LOI) values and moisture balance (lake-level and DeltaP-E, 
Precipitation minus Evaporation) reconstructions for Deep Pond, Massachusetts. 
Also included are facies thresholds for differentiating littoral and sub-littoral lake sediment facies 
based on the raw core data, for use in the iterative lake-level reconstruction process. The reconstruction 
process iteratively applies each set of thresholds in R to produce an ensemble of reconstructions. The code for 
generating the lake-level reconstruction according to the process described in Pribyl and Shuman (2014) is provided.
Also included are the ensemble mean lake-level reconstruction and its uncertainty per 50-yr interval for the length 
of the record, and the individual ensemble members for each time step (but without the ages for the steps).
R script MoistureBalance is the code for the simple moisture-budget calculation based on the lake-level reconstruction. 
Again this follows Pribyl and Shuman (2014).  PErecon contains the median P-E reconstruction as an anomaly from modern 
 for each 50-yr interval, as well as the 1-sigma and 25% and 75% quantiles of the reconstruction uncertainty.
Data and R code are included in original contributor files: Deep_cores.csv, Deep_Iterations_012414.csv, 
Deep_LLrecon_012414.csv, Deep_PErecon_012414.csv, Deep_R_Script_LLRecon_012414.txt, 
Deep_R_Script_MoistureBalance_011414.txt, and FaciesThresholds_Deep.csv, plus WDC Paleo formatted text files deep2013loi.txt,
deep2013ll.txt, and deep2013p-e.txt.