A 6500-YR PALEOENVIRONMENTAL RECONSTRUCTION OF NO MAN’S LAND SINK, ABACO ISLAND, A LARGE INLAND LAKE IN THE NORTHERN BAHAMAS

No Man’s Land Sink is one of the largest inland lakes on the Little Bahama Bank in the northern Bahamas, so its paleoenvironmental history may provide important insight into how the regional hydroclimate and groundwater systems developed over the Holocene. In its modern state, the site is shallow (3 m deep), brackish (20.6 psu), 170 m in diameter, ~700 m from the coastline, and it is currently a flooded sinkhole. Prior to 6400 cal yrs BP, the deposition of only terrestrial peat (no ostracods, foraminifera, aquatic mollusks) indicates that the site was a terrestrial ecosystem. However, the site transitioned into a subaqueous freshwater environment from 6400 to 3200 cal yrs BP, with widespread palustrine-lacustrine carbonate deposition and appearance of freshwater microfossils (charophytes, ostracods: Candona annae, Cypridopsis vidua, mollusks: Planorbis, Hydrobia). A slight salinity increase at 4200 cal yrs BP is inferred from the appearance of the ostracod Cyprideis americana and deposition of laminated microbial mats. Thereafter, an organic-rich, algal sapropel unit (54% bulk organic matter) devoid of any microfossils or mollusks, yet enriched in d¹⁵N, was deposited. This unit suggests that the lake hosted a stratified water column, where eutrophic surface waters enriched the dissolved stable nitrogen isotopic composition and corrosive or anoxic bottom water conditions hampered microfossil growth or precluded their preservation. The transition to the modern environment (~20 psu) is characterized by diversification of brackish ostracods (Aurila floridana, Dolerocypria inopinata), foraminifera (Elphidium, Ammonia beccarii, Quinqueloculina) and mollusks (Anomalcardia, Cerithidea). Over the middle to late Holocene, No Man’s Land has experienced abrupt salinity increases that are likely driven by southern migration of the intertropical convergence zone, and shoreline migration and groundwater-level rise in response to Holocene sea-level rise.