High-resolution paleosalinity reconstruction from Laguna de la Leche, north coastal Cuba, using Sr, O, and C isotopes

Isotopes of Sr, O, and C were studied from a 227-cm long sediment core in order to develop a high-resolution paleosalinity record to investigate the paleohydrology of Laguna de la Leche, north coastal Cuba, during the Middle to Late Holocene. Palynological, plant macrofossil, foraminiferal, ostracode, gastropod, and charophyte data from predominantly euryhaline taxa, coupled with a radiocarbon-based chronology, indicate that the wetland evolved through four phases: (1) an oligohaline (0.5-5 parts per thousand) lake existed from similar to 6200 to similar to 4800 cal yr B.P.; (2) water level in the lake increased and the system freshened from similar to 4800 to similar to 4200 cal yr B.P.; (3) a mesohaline (5-18 parts per thousand) lagoon replaced the lake similar to 4200 cal yr B.P.; and (4) mangroves enclosed the lagoon beginning similar to 1700 cal yr B.P., forming a mesohaline lake. Isotopic ratios were measured on specimens of the euryhaline foraminifer Ammonia beccarii, although several measurements were also made on other calcareous microfossils in order to identify potential taphonomic and/or vital effects. The Sr-87/Sr-86 results show that the average salinity of Laguna de la Leche was similar to 1.7 parts per thousand during the early lake phase and similar to 8 parts per thousand during the lagoon phase - a change driven by relative sea level rise. The delta O-18 results do not record the salinity increase seen in the Sr-87/Sr-86 data, but instead indicate high evaporation from the lake surface; this in turn suggests that the value of similar to 1.7 parts per thousand may slightly underestimate the average salinity of the wetland, at least for the period prior to - 4800 cal yr B.P. Variability in delta C-13 was controlled by plant productivity, episodic marine incursions, and vegetation community change. There is some evidence for seasonal effect and the lateral transport of microfossils prior to burial. The isotopic data independently confirm the hydrological interpretations made using the euryhaline indicators and have permitted the reconstruction of a significantly higher resolution paleosalinity record than would be possible using the paleoecological data. However, our results show that Sr isotopes, while often cited as a powerful paleosalinity tool, must be used in conjunction with other indicators when investigating paleosalinity trends; relying solely on any single isotopic or ecological indicator can lead to inaccurate results, especially in semi-enclosed and closed hydrological systems. (c) 2006 Elsevier B.V, All rights reserved.