Anthropogenic infilling of a Bermudian sinkhole and its impact on sedimentation and benthic foraminifera in the adjacent anchialine cave environment

Abstract

Abstract:In the mid-20 th century, an inland brackish pond from Bermuda, known as Eve's Pond, was filled with marine sediment from an adjacent coastal lagoon. At this time, an eyewitness reported "…sediment billowing out of the Green Bay Cave for days…", which is a marinedominated anchialine cave located proximal to the former location of Eve's Pond (~200 m). The purpose of this study was to evaluate the potential impact of this infilling event on cave sedimentation and benthic meiofaunal communities, as proxied by the unicellular protists foraminifera that remain preserved in the sediment record. Eight sediment cores were collected from an underwater passage in Green Bay Cave in a transect towards the location where Eve's Pond was surveyed in 1901 CE. The sediment cores were analyzed for visual and density changes (photography, X-radiography), textural variability, benthic foraminifera fauna and diversity, and radiocarbon dating. The recovered sediment cores mostly sampled a late Holocene carbonate mud facies that had been described during previous research in the cave, with benthic foraminiferal assemblages post-dating the onset of seawater circulating between the saline groundwater flooding the cave and the adjacent Harrington Sound ~1,900 years ago. However, two cores located further into the cave (cores 13 and 17) contain a carbonate sand layer with lagoon foraminifera that is anomalous with respect to the Holocene depositional history of the cave and is most likely related to the mid-20 th century infilling of Eve's Pond. Examination of these two cores showed that after the infilling event, the community of benthic foraminifera rapidly reverted to pre-impact assemblages with foraminiferal stygophiles (e.g., Spirophthalmidium emaciatum, Sigmoilina tenuis), which were not displaced by new colonizers introduced into the cave by the dredge spoils. We caution that the results cannot be extrapolated to the pelagic crustacean community, but the results suggest that this physical sedimentary disturbance only minimally impacted the benthic foraminifera community in the cave passages that were sampled.

Changes in Organic Matter Deposition Can Impact Benthic Marine Meiofauna in Karst Subterranean Estuaries

“…Aerolito Cave contains benthic foraminiferal taxa that are similar to flooded coastal caves in Bermuda (Cresswell et al, 2017;Cresswell and van Hengstum, 2021). However, the foraminiferal communities of Aerolito have a lower proportion of epifaunal taxa and increased infaunal taxa.…”

“…The environmental control of OM supply on benthic foraminiferal communities has been documented in a variety of coastal environments such as the Mediterranean (Dimiza et al, 2020) and the Bay of Biscay (Fontanier et al, 2002), as well as the deep sea (Corliss and Chen, 1988;Jorissen et al, 1995). OM effects on benthic foraminiferal microhabitats have been previously explored within the KSEs of Bermuda (van Hengstum and Cresswell et al, 2017;Little and van Hengstum, 2019;Cresswell and van Hengstum, 2021), where habitats with more increased terrestrial-based OM (depleted δ 13 C org values) are favored by certain taxa (e.g., Helenina, Bolivina, Rosalina).…”