Publication Date:
2019-07-16
Description:
The processes that control past monsoon
variability in the East African Tropics during the Holocene are poorly
understood. Especially the role of Sea Surface Temperatures (SST)
controlling East African Rainfall on millennial timescales, as it is
observed on decadal timescales, is currently intensely debated. In
addition, it has been suggested recently that the longitudinal
migration of the Congo Air Boundary (CAB) modulates East African precipitation on a regional scale as well [Tierney et al., 2011].
Here, we present a high-resolution marine sediment record for the
past 12 kyrs from offshore Tanzania, close to the Rufiji River delta,
to contribute to the current debate from a marine point of view. We
reconstructed past SST and !18Oseawater, derived from planktic
foraminiferal Mg/Ca and !18O, and past Sea Surface Salinity (SSS)
variations, derived from planktic foraminiferal Ba/Ca-ratios. In the
vicinity of river deltas, Ba/Ca-ratios have potential to record
precipitation changes in the rivers’ catchment area.
Our records show that East African precipitation, derived from
Ba/Ca-ratios, roughly varies in concert with Indian Ocean SST,
suggesting higher Indian Ocean SST to be an important prerequisite
for stronger precipitation, and hence an intense monsoon episode in
East Africa. We calculated the difference ("SST) between our
record of Indian Ocean SST and SST of the tropical Atlantic
[Weldeab et al., 2005], showing that "SST variability resembles the
isotopic pattern of the Kilimanjaro ice core record [Thompson et al.,
2002]. We suggest this to be the consequence of a longitudinal
movement of the CAB over the African Continent, changing the
trajectory of Indian Ocean moisture into the continent and therefore
affecting the !18O of the East African rainout.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Conference
,
notRev
Format:
application/pdf