LACUSTRINE SEDIMENTS OF GRENADA – TOWARD A RECORD OF HOLOCENE PRECIPITATION VARIABILITY IN THE NORTHERN EQUATORIAL ATLANTIC

We recently obtained three cores from Grand Etang (GE) and Lake Antoine (LA), both on the Caribbean island of Grenada in the northern equatorial Atlantic. GE (N12°05’48.6”, W61°41’46.4”, 530 masl) is within the island’s wet central mountainous region. LA (N12°11’02.9”, W61°36’41.1”, 16 masl) is on the drier northeast coast. Sedimentologic records of both ~6 m-deep lakes record Holocene tropical precipitation changes, likely related to SST variations and latitudinal shifts in the trade winds.

Lithologic descriptions, magnetic susceptibility logs, and initial radiocarbon dates have been completed on all cores. Grain size analysis, total inorganic and organic carbon analyses, diatom analysis, oxygen and nitrogen isotope analyses and additional ¹⁴C dating are underway. The preserved paleoclimatic record extends through the YD; in a shallow-water (1.4 m) GE core, organic-rich strata directly above an ash-bearing unit at 6.11 m subbottom, yielded an age of 12,550 +/- 110 ¹⁴C yrs BP. These strata are part of a 3-m-thick basal unit of clayey gyttja with silty and ashy laminations that lies beneath a lithologically distinct unconformity. Black to brown, coarse detrital gyttja lies above the unconformity. A deeper-water (5.95 m) GE core is dominated by brown clayey gyttja with rare ashes. Organic-rich sediment at 3.53 m in these strata yielded an age of 3240 +/-90 ¹⁴C yrs BP. The LA core (from the deepest part of the lake) is characterized by algal-rich, clayey detrital gyttja, thin ash beds, and local carbonate-bearing laminations. Radiocarbon dates from 4.83 m and 5.51 m in this core yielded ages of 3825 +/-90 and 5810 +/-100 ¹⁴C yrs BP, respectively. Sedimentation rates of ~1m/1000 yrs are recorded in the deep parts of each lake. However, changes in sedimentation – as suggested by silty strata throughout the cores – reflect changes in runoff into the lake basins and changes in local (and regional) precipitation.

Continued analysis of these terrestrial records and comparison with nearby paleo-SST records will aid in our understanding of atmospheric responses to oceanic forcings throughout the Holocene and lead to a better understanding of the teleconnections between the northern Atlantic, the tropics, and adjacent land masses in both the northern and southern hemispheres.