Increased North African Dust Fluxes and Higher Productivity in the Eastern Equatorial Atlantic Ocean Linked to Stronger Trade Winds From About 2.7 Million Years ago

Abstract

For at least the last 11 million years, the North African landscape has repeatedly oscillated on astronomical timescales between the dry dusty conditions of today and more humid, vegetated conditions such as those documented for the mid-Holocene. These changes were primarily driven by expansion and contraction of the tropical rainbelt in response to changes in summer insolation. However, other mechanisms are needed to explain temporal variability in the sensitivity of African humidity to this rhythmic forcing. A main interval of observed change is the Pliocene-Pleistocene transition (∼3.5–2.4 Ma) when Africa is widely (but not universally) suggested to have become drier and dustier. Here we present new suborbitally resolved records of surface ocean temperature, foraminiferal stable isotopes and export productivity from the Northwest African margin and the eastern equatorial Atlantic Ocean and compare them to published records. We find strong coupling at astronomical timescales between productivity and dust fluxes throughout our study interval, indicating the sustained influence of the northeast trade winds on dust transport, upwelling strength and perhaps dust-driven ocean fertilization. We attribute observed increases in dust fluxes delivered to the NW African margin and eastern equatorial Atlantic to strengthening of the trade winds driven by the steepening latitudinal temperature gradients associated with the intensification of Northern Hemisphere glaciation. Taken together with published evidence of increased strength in the mid-latitude westerlies at this time, our results point to invigoration of large-scale atmospheric circulation globally during intensified glacial periods of the Pliocene-Pleistocene transition.