10,000 years of climate and environmental changes in Jamaica, a biodiverse tropical island

Methods

Summary

We will collect and analyze a sediment core from Wallywash Great Pond which is located in southwestern Jamaica, and is the island’s largest lake. We will then examine the sedimentary record of pollen, charcoal, ostracod δ¹⁸O, and Sporormiella at Wallywash Great Pond to develop a high resolution paleoenvironmental history of vegetation, fire, climate, and human impacts in Jamaica spanning > 10 ka.

· Δ¹⁸O values measured from ostracod shells reflect the precipitation-evaporation regime of lakes, because ostracods incorporate oxygen from their host lake waters during growth. The lighter oxygen isotope (¹⁶O) preferentially evaporates during periods of high evaporation; therefore, changes in the isotopic composition of ostracod shells in lake sediments can tell us about relative moisture availability in the surrounding lake area.

Pollen, Sporormiella, and charcoal preserved in lake sediments will be identified and quantified in the laboratory using a microscope.

· The type and relative abundances of pollen found in sediment cores provide information about changes in the vegetation community of the surrounding lake area over time. For example, an abrupt decline in tree pollen along with increases in pollen from crops and weeds may indicate agricultural land clearance.

· The dung fungus Sporormiella produces characteristic spores that are well-preserved in sediments, and can be used as a proxy for local herbivore densities or herbivore presence. Peaks in Sporormiella abundances in our sediment core may indicate periods of enhanced grazing activity associated with the introduction of domesticated livestock to Jamaica by European settlers. 

· The amount of charcoal found in our sediment core will tell us about the intensity and frequency of fire events on the island. Furthermore, sharp increases in charcoal in sediment cores can be used to detect landscape burning associated with human arrival on islands.

Challenges

In order to infer the presence of different climates from sedimentary pollen records, the preserved pollen grains must be identified taxonomically. For example, a shift of pollen from moisture-adapted species to drought-tolerant species would indicate a transition from wet to more arid climatic conditions. We will use published pollen reference guides in conjunction with prepared pollen slides to aid the proper identification of pollen contained in our sediment samples.

Pre Analysis Plan

The date of first human arrival in Jamaica will be determined using three criteria:

(1) A sharp increase in sedimentary charcoal particles in excess of background charcoal levels, indicative of increased anthropogenic firing of the landscape,

(2) The appearance of pollen from non-native food crops such as maize and sweet potato in the sedimentary record,

(3) An abrupt increase in pollen from fast-colonizing weeds, characteristic of landscape disturbance.

The concomitant fulfillment of multiple criteria before the established date for first human settlement of the island would strongly suggest that this date should be revised.