In April-May, 2001, just months before 9/11, a team of scientists led by Gerald Ganssen and I sailed aboard the Dutch-flagged R/V Pelagia from Dar es Salaam, Tanzania to Port Said, Egypt on the penultimate leg of a scientific circumnavigation of the African continent. This cruise sailed along the pirate-infested waters of the Somali coasts and the Gulf of Aden. With the vigilance of our captain and crew we safely navigated these waters and collected some new, extremely valuable, sediment cores and surface plankton tow and water samples from this geopolitically challenging region.
Pirate probability density function
One of these cores, P178-15P, was taken from a perched basin in the Tadjoura Trench from a site cored long ago (in 1947!) by the Swedish ship Albatross. Finding this site was a challenge as the position was only approximate (pre-GPS!), so we used the PDR depth finder to zero in on the known 869m depth location.
Jess Tierney came to Lamont in 2011 as a NOAA post-doc to work up the plant-wax biomolecular record for this core, specifically extracting the plant waxes from these sediments as fatty acid methyl esters; FAMEs) and analyzing their hydrogen isotopic composition by GC-IRMS in our new stable isotope mass spectrometry facility. The leaf wax D/H composition (δDwax) is a powerful proxy for regional aridity, as the plants record precipitation/evaporation balance and changes in regional convection.
The results were surprising in many ways. The amplitude of the D/H excursions over this 40 ka long record was remarkably large, reaching nearly 40-50 per mil. Also, because the sedimentation rate for this core was so high (32 cm/ka), it offers a high-fidelity and continuous record of the hydroclimate shifts in the region. To our surprise, the onset and termination of the African Humid Period (roughly 12-5 ka BP) were really abrupt, with each transition completed within a couple of centuries. It’s sobering to think that climate changes this large can occur so swiftly. As discussed in the Tierney and deMenocal (2013) Science paper, a similar history is found in sediment cores from East African Lakes, Turkana, Challa, and Tanganyika.
Tierney, J.E., deMenocal, P.B., Abrupt shifts in Horn of Africa hydroclimate since the Last Glacial Maximum. Science (2013). Tierney.deMenocal.2013.pdf