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Study of surface sediment samples collected in Bermuda subtropical environments reveals foraminifera assemblages from lagoons, reefs, caves, mangroves, and ponds that are sufficiently different to serve in paleoenvironmental reconstructions. These assemblages are based on species diversity, suborder percentages, characteristic species and associations, and sediment types. Some subenvironments can even be recognized, such as outer/lagoonal reefs, open/semi- protected/protected lagoons, mangrove swamps/fringing mangroves, non-tidal marine landlocked ponds/mangroves and other ponds. The main factors controlling foraminifera distribution in Bermuda are salinity, sediment type, pH, water energy, oxygen content, and light penetration. Presence of phytal substrate is also very important but was not investigated in this more geological study of sediment assemblages.

Bermuda recent sediment hosts a benthic foraminifera fauna as diverse as in other subtropical and tropical areas, and the general trends of foraminifera distribution and morphology are similar despite some differences.

In Bermuda mangrove swamps, foraminifera distribution shows a zonation relative to higher high water level, that can be used in accurate paleosea-level reconstructions. The present work includes the first detailed measured transects carried out in mangrove swamps for foraminiferal studies. Study of vibracore and Davis core samples permitted the construction of a late Holocene sea-level curve for Bermuda. This curve shows a lowstand between 2,000 y BP and 1,000 y BP, and a relative sea level (RSL) acceleration in rise since about 500 y BP that preceded the onset of modern global warming. The lowstand occurred also in Connecticut and South Florida, but not in other areas, and coincided with a cool period (Early Medieval Ice Advances) also detected elsewhere, and possibly also with a displacement of the Bermuda High over Bermuda. This curve illustrates the high variability of late Holocene sea level and climate.

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Pages: 646
Supervisor: David Scott