Reconstructions of surface paleoceanographic conditions of the western tropical Atlantic and past climates of the Amazon basin were undertaken by analyzing sediments from a long piston core KNR197-3-11CDH (7°40’N, 53°49’W, water depth 550 m) recovered from the Demerara Rise. Previous studies on marine sediment cores recovered from between 4°S and the equator have documented surface ocean warming with pulses of terrigenous sediment recording increased precipitation and weathering on the Brazilian Nordeste associated with Heinrich events (North Atlantic cold events). We worked on core 11CDH located farther north along the South American continental slope, where modern sediment derives from the Amazon River basin and is transported by the North Brazilian Current. The record is dated by radiocarbon analysis and oxygen isotopic stratigraphy of near-surface-dwelling planktonic Globigerinoides ruber sensu stricto (white) foraminifers and spans from approximately 25 to 65 kyrs. Within the limits of dating accuracy, stable oxygen isotopic values (δ18O) of G. ruber s.s. increase during Heinrich events, indicating sea surface cooling. High-resolution XRF analysis shows no peaks in terrestrial elements compared to marine elements over time. Surface ocean cooling at our site and surface ocean warming at southern tropical sites is consistent with southward movement of tropical rainfall to the relatively warmer hemisphere during Heinrich events.


Wilson, Mark




Other Earth Sciences


Paleoclimate, Amazon, North Brazilian Current, Heinrich events

Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis



© Copyright 2017 Sarah M. McGrath