A late Quaternary palaeolimnological record from Jamaica based on trace-element chemistry of ostracod shells

The trace-element chemistry of ostracod shells provides one of the most promising methods for palaeolinmological reconstruction. In this paper, molar Sr/Ca and Mg/Ca ratios in shells of the ostracod Cypretta brevisaepta Furtos, 1934 were used to reconstruct the late Quaternary palaeolimnology of Wallywash Great Pond, a small freshwater coastal lake in Jamaica. Analyses of modern Jamaican ostracods were undertaken to establish molar distribution coefficients (KDDMs) for this species (KDSr = 0.306±0.069; KDMg=0.0142±0.0088). These values were used to reconstruct past levels of (Sr/Ca)water and (Mg/ Ca)water for a 9.23-m lake-sediment core from Wallywash Great Pond. The results were coupled with previously-published stable-isotope (δ18O and δ13C) determinations on fine-grained calcite, to reconstruct the salinity, palaeohydrology and palaeoproductivity of the lake over the last 125 ka B.P. (103 calendar years before present). Three major highstands with slightly elevated salinity occurred during marine isotope stage 5, under elevated sea level and a humid climate. The lake dried out ∼ 93.5 ka B.P. as sea level felll and the climate became drier. It refilled around 10.7 ka B.P. Three separate highstands during the Holocene were sustained by humid conditions and high relative sea level. Although there were small increases in salinity during the Holocene when sea level was close to the deepest part of the lake, significant saltwater intrusion appears to have been prevented by freshwater discharge from inland. Throughout the late Quaternary, the salinity of the Great Pond showed low absolute variations, from ∼ 0.3 to ∼ 0.6%o. The long-term trends in lake level reflect both orbitally-induced changes in insolation and eustatic sea level. Water-level fluctuations during the Holocene, however, reflect climatic changes on the millennial timescale rather than orbital forcing or sea-level change.