Changes in opal fluxes along the northwest African margin during the last glacial period; linking high and low latitude patterns of productivity

Abstract:

Recent studies have proposed competing hypotheses to explain increased opal fluxes in high and low latitudes during the most recent deglaciation. Anderson et al. (2009) rely on increased wind-driven upwelling in the Southern Ocean to explain the increased availability of Si in both the Southern Ocean and tropical thermoclines, leading to increased opal fluxes in both regions coincident with the deglacial rise in CO₂. Meckler et al. (2013) suggest that a decrease in the presence of North Atlantic intermediate water (GNAIW) during the deglaciation allowed Si-rich southern-sourced waters to fill the tropical Atlantic leading to increased opal burial.

We attempt to distinguish between these two mechanisms by reconstructing opal fluxes and fluxes of windblown dust over the past ~65ka at four sites along the northwest African margin. The records include the deglaciation, including Heinrich Event 1 (H1) and the Younger Dryas (YD), as well as several earlier Heinrich events. We find that opal and dust fluxes increase simultaneously during the deglaciation, and more highly resolved cores record H1 and the YD as distinct peaks within the deglaciation. Furthermore, opal and dust fluxes scale approximately linearly with one another during these events. We observe opal peaks associated with most Heinrich Events through H6. Finally, we observe a strong similarity between patterns of opal flux in the Southern Ocean and along the African Margin. This suggests that the pattern of diatom productivity and opal flux along the African Margin reflects a combination of changes in wind strength due to shifting temperature gradients, and changes in the export of silica-rich water from the Southern Ocean, both as a result of the global scale climate changes associated with Heinrich Events.

Anderson, R. F., S. Ali, L. I. Bradtmiller, S. H. H. Nielsen, M. Q. Fleisher, B. E. Anderson and L. H. Burckle. Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2. Science, 323 (5920), 1443-1448, (2009).

Meckler, A. N., D. M. Sigman, K. A. Gibson, R. Francois, A. Martinez-Garcia, S. L. Jaccard, U. Röhl, L. C. Peterson, R. Tiedemann and G. H. Haug. Deglacial pulses of deep-ocean silicate into the subtropical North Atlantic Ocean, Nature, 495 (7442), 495-498, (2013).