Atrotorquata lineata as a proxy for Juncus roemerianus, Part II: Tracking changes in positions of Juncus roemerianus marshes through time by use of the fungal proxy Atrotorquata lineata

摘要

Juncus roemerianus is a species that occurs at the upper reaches of salt water influence in marshes from Delaware to Texas. As such, J. roemerianus is a good marker for sea level, defined for this study as mean highest high water; thus, being able to track its positions over time should enable one to track past changes in relative sea level. In 2006, a palynomorphic fingerprint to identify surface sediment from J. roemerianus marshes was discovered in a South Carolina study (Marsh 2006, Marsh & Cohen 2008). Further study (Marsh & Cohen 2016) showed that one component of this fingerprint, the spore of the fungus Atrotorquata lineata, was so omnipresent in surface sediment from J. roemerianus marshes that the fungus, by itself, can be considered a proxy for J. roemerianus marshes. In this study we investigated the potential to use Atrotorquata lineata to track past positions of Juncus roemerianus marshes. First we investigated whether A. lineata is preserved beneath the surface. Cores from South Carolina, North Carolina and Florida were found to contain A. lineata, including one from the Harney River area of southwestern Florida in which we had previously found A. lineata at ca 250 cm depth at a level that had been radiocarbon-dated to ca 3200 years BP (Cohen 1968, Cohen & Spackman 1972, 1977, Spackman & Cohen 1976, Marsh & Cohen 2016). Building upon that discovery, we then investigated the possibility of tracking changes in the size and position of J. roemerianus marshes over time. Additional sets of cores clearly revealed evidence of expansion and contraction of J. roemerianus patches over time and further suggested recent past fluctuations in sea level that were both higher and lower than at present but contained within an overall transgressive sequence.