CLIMATE, HYDROLOGY, AND PROXY RECORDS OF CLIMATE

In order to investigate how lake and wetland hydrologic processes act as filters of climate signals recorded in sediments, we have been monitoring two nearly identical wetlands in close proximity (< 50 m). Both wetlands reside under the same climate, terrain, and the bulk of their water is received from snowmelt and spring rains, but they have different interactions with the groundwater.  One wetland (P8) currently functions as a through-flow basin; recharging and discharging the groundwater on opposite ends.  The second wetland (P1) receives a small amount of groundwater and primarily loses water through evaporation and secondarily to groundwater. P1 and P8 exhibit different water d¹⁸O, DIC d¹³C, and ostracode species assemblages. The d¹⁸O and DIC d¹³C are higher for P1 (d¹⁸O -3.5‰ vs -6.1‰ for P8, DIC d¹³C -4.6‰ vs -9.6‰ for P8) because of the longer residence time and the cumulative effect of photosynthetic activity. Ostracodes are small invertebrates sensitive to temperature, alkalinity/Ca ratio, and physical hydrology. Species such as Cypridopsis vidua and Potamocypris unicaudata are common to both P1 and P8, but Candona decora, Candona distincta and Notrodromas monicha, the species that prefer groundwater discharge sites, are only found abundantly in P8.  Thus even in these small wetlands with their simple hydrology relative to larger systems, hydrologic processes are modifying the climate signal as measured by proxies such as ostracode shell d¹⁸O and species assemblage before they are stored in the sediment. Such modification may not be easily discernible in a sedimentary paleoclimate record.