SHALLOW WATER (<4 M) FORAMINIFERA AND SEDIMENT IN TWO BERMUDIAN ANCHIALINE CAVES: IMPLICATIONS FOR RECONSTRUCTING CAVE PALEO ENVIRONMENTS

Benthic foraminifera are useful proxies of long-term environmental change because of their sensitivity to local environmental change and high preservation potential in the sediment record. Recently, benthic foraminifera have become increasingly used to reconstruct paleoenvironmental change in underwater caves on carbonate platforms. However, it is unknown if the chosen microfossil processing technique (≥45 µm vs ≥63 µm mesh sieve size) may bias resultant foraminiferal assemblages, given that many cave organisms have evolved a diminutive size. In shallow water pools (<4 m) two Bermudian anchialine caves (Deep Blue, Cow Cave) provide a modern analog for the potential of benthic foraminifera to colonize coastal underwater caves when inundated by groundwater-level rise as caves switch from being in the vadose versus phreatic zone. These cave systems were investigated for their morphological similarities with shallow, benthic areas that progressively deepen (<4 m) further into the cave, but different sediment texture (coarser detrital sediment vs. micrite). Benthic fauna in each cave likely differ with variation in sunlight exposure, environmental exposure and subsequent influx of terrestrial organic material and rainwater. In Cow Cave and Deep Blue, Q-mode cluster analysis revealed two benthic assemblages: a Shallow-water Assemblage (<1 m) and a Saline Groundwater Assemblage (>1 m). Sieve size had little impact on (a) the resultant assemblages identified through cluster analysis, (b) the dominant taxa in the assemblages, (c) foraminiferal diversity, or (d) the proportion of foraminifera wall structure. However, faunal density increased with the inclusion of the 45-63 µm size fraction, likely due to an increased representation of juveniles or microspheric individuals also present in the >63 µm size fraction. This study demonstrates that future work in anchialine cave systems utilizing benthic foraminifera as paleoenvironmental proxies can save time by using just the >63 µm sediment size fraction.