ESTABLISHING THE EFFECT OF SEA SPRAY ON SULFUR ISOTOPE VALUES IN VEGETATION ON THE ISLAND OF TRINIDAD

Sea spray can affect the sulfur isotope (δ³⁴S) values in vegetation in coastal settings. However, the relative impact of sea spray on small tropical islands is unknown. It is possible that sea spray only impacts coastal areas. Alternatively, it may uniformly affect all island vegetation. Trinidad, which lies 12 km off the coast of Venezuela, can be used as a model for sea spray effects on other Caribbean islands.

The predominant winds on Trinidad are driven by the northeasterly trade winds, which is similar to other Caribbean islands. If wind is the primary factor that determines the distribution of sea spray, then we would expect the influence of sea spray to be greater (and therefore vegetation δ³⁴S values are highest) along the eastern coast of the island. Sulfur isotope values for marine water are typically around 21‰ while terrestrial sources can range from -22‰ to +22‰. The majority of isotopic variability among terrestrial sources is accounted for by bedrock geology. With the exception of some ores and evaporites, most lithologies have δ³⁴S values that are considerably lower than marine water. Assuming the fractionation during sulfur assimilation into plant biomass is small (~ 1‰), the incorporation of marine sulfur in most terrestrial environments should be clear.

We present isotopic data for foliage samples that were collected along a transect from Trinidad’s windblown east coast to the calm west coast. Surface geology along this transect is primarily Miocene sandstones and clays. We find that δ³⁴S values for plants from the east coast resemble marine water. In contrast, δ³⁴S values for interior and west coast plants are dramatically lower. As expected, these data suggest a strong gradient in δ³⁴S values with increasing distance from the windward coast. Establishing this modern baseline of marine sea spray inputs to terrestrial vegetation provides context for investigating spatial and temporal patterns in the resources used by prehistoric people on Trinidad.