FINGER-PRINTING SALT POOLS IN THE STRATIGRAPHIC RECORD: IMPLICATIONS FOR UNDERSTANDING MORPHOLOGICAL CHANGE IN NORTH-TEMPERATE SALT MARSH SYSTEMS

Salt pools are shallow, water-filled depressions common to north-temperate salt marshes. Interest in these features arose from studies in the Mid-Atlantic and Gulf Coast regions that observed increases in pool area and accompanying marsh loss in response to rising sea levels. Until recently, however, little work characterized salt pools in the geologic record and pools were often confused with other marsh microhabitats like tidal creeks and mudflats. This work uses geochemical, isotopic, and biological tracers to characterize pools in the stratigraphic record from five salt marshes distributed S-N along Maine’s coast (Ogunquit, Brunswick, Gouldsboro, Addison, and Lubec). Our work indicates that most pools in Maine are secondary and dynamic features (84% of cored pools; n = 19), rather than primary, relict landforms. Salt pool sediment is characterized by dark gray muddy material with high water content, unique micro- and macro-fossils (e.g., Ruppia maritima drupes, Quercus leaf fragments, and Hydrobia totteni gastropods), low C:N ratios, and is clearly identifiable in the paleo-record. In addition, time-series of aerial photographs indicate that many pools alter their shape and size over decadal time periods and that the dynamic exchange between pools and tidal creeks is one mechanism resulting in substantial transformations of the marsh surface. Isotope analyses (²¹⁰Pb and ¹³⁷Cs) of paired cores in high-marsh and re-vegetated pools indicate that pools may drain, rapidly in-fill, and re-vegetate. Our results demonstrate how a suite of tracers may be used to better understand surficial processes of north-temperate salt marshes. Recognition that pool dynamics are preserved in the geologic record improves our interpretations of salt marsh peat records, including previous work that reports rapid sea-level fluctuations derived from these same records. Likely, this variation captures pool dynamics, which may be independent of changes in relative sea level.