Tropical Atlantic Variability through the Holocene from Individual Foraminifera

The tropical oceans are major drivers of global climate variability. The equatorial Atlantic Ocean is home to the Atlantic Equatorial Mode (AEM) or "Atlantic Niño", the dominant mode of Atlantic inter-annual variability. The AEM exhibits similarities to the El Niño Southern Oscillation (ENSO), the largest source of inter-annual climate variability on Earth. Both ENSO and the AEM are coupled air-sea interactions that produce anomalous sea surface temperatures, affect hydroclimate, and alter the atmospheric Walker circulation. On both historical and geologic timescales, tropical Atlantic SST variations have impacted African hydroclimate including changes in the West African Monsoon system, a key control on precipitation across the northern portion of the African continent. We explore the relationship between Mid-Holocene African hydroclimate and SST variability in the context of an individual-foraminifera δ¹⁸O reconstruction of tropical Atlantic variability from deep sea sediment cores. Core-top calibration of the proxy using the planktic foraminifer Globigerinoides ruberindicate that intra-core shell δ¹⁸O variance closely tracks modern oceanographic SST values and seasonal variance. Downcore, we observe reductions in δ¹⁸O variance during the mid-Holocene between 4-6 ka BP during the drying of the "Green Sahara". The changes we observe in δ¹⁸O are similar in timing and amplitude to shifts observed in tropical Pacific SST variability reconstructions. We explore the relationship between tropical Atlantic variability and shifts in African hydroclimate and examine hypotheses of the role of land feedbacks in the climatic changes observed in the mid-Holocene, and investigate possible teleconnections between tropical Pacific ENSO variability via alterations of the Walker circulation.