Earth, wind, flora sway Trinidad sulfur levels

A new study out of the University of Cincinnati suggests that coastal proximity, rain and prevailing wind direction can all influence the distribution of marine sulfur on land. While science has known for decades that sulfur is a useful method for tracking diet and mobility, UC researchers say the combined effects of wind and precipitation like rain and ocean spray hasn't been fully investigated before. 

Their results, also aligning closely with patterns reported for soils and precipitation in the Mediterranean and Pacific Islands, demonstrate that plants in coastal settings are utilizing marine-derived sulfur.

"What makes our study unique is that we were able to show quite clearly how the spatial distribution of sulfur isotopes in vegetation is related to not just coastal proximity, but also wind and rain," says Brooke Crowley, UC associate professor of geology and anthropology. "And we have shown that these spatial patterns are detectable in vegetation.

"This information may aid researchers in tracking not only the origin of human resources and the movement of animals but also sulfur emissions from human activities within the Caribbean." 

While sheep obvously travel more than plants, Sparks says the high content of marine-derived sulfur on inland sheep stems more from the environment than their movement. Unlike Trinidad's dense terrain, Ireland's lack of a diverse variety of plants, especially tall vegetation, and much stronger winds tend to carry the sulfur further inland in a very steady direction. This would enable the sea spray to travel farther without any windbreak.

The UC researchers’ results were more similar to patterns reported for soils and precipitation in Japan and Hawaii. Like Trinidad, these islands are peppered with a lot of diverse vegetation and mountains, and marine-derived sulfur is only found up to 16 kilometers inland, "so we were not completely unique," Sparks adds.

The results of this study, the researchers say, helped establish clear spatial patterns in the Carribbean because, although there have been other papers looking at sulfur isotopes in other parts of the planet, they may not be globally relevant. The researchers needed a baseline for what was going on regionally.

While focusing on wind direction and precipitation patterns across Trinidad's diverse terrain, they found differing oceanic sulfur signals between windward coasts blowing sea spray directly in from the ocean compared to coasts that are more leeward where wind is coming from across the island.

"If you travel from the east windward coast of Trinidad to the west coast there are obvious gradients. Within about 1.5 kilometers from the east coast, we see plant sulfur values that look just like marine sulfur," says Crowley. "The plants are using sulfur spray being blown in off the ocean, but there's also more rain there so we can't completely disentangle the influence of wind and rain — they work in concert.

"On the leeward west coast, we don't see that. Coastal plants resemble plants further inland."

Human activities may be affecting these patterns, specifically. Emissions from oil refineries and vehicles appear to have a measurable influence, they found.

“Sulfur isotope values of plants near busy roads or urban centers are clearly affected by modern human influences,” says Sparks. “Using these results and other modern datasets for reconstructions of the past, we need to acknowledge what sources would and would not have been present.”

"We hope our studies will be of use for future ecological and archaeological research, not only for Trinidad but for the Greater Caribbean and other coastal or island systems around the world."

Featured image at top: Strong winds help blow marine-dervied sulfur onto vegetation along the eastern, windward coast of Manzanilla, Trinidad. photo/Brooke Crowley