A monsoon index for the Turkana Basin: A predictive and retrodictive method for understanding climate change
It has been suggested that human evolution in East Africa was a consequence of dynamic and variable climates, such as the periods of extreme drought and increased moisture occurring in the Turkana Basin of northern Kenya. If this hypothesis is true, the current state of climate change is expected to produce an even larger impact. The effects of global warming in Turkana are dismal: the temperature and aridity of the Sahel environment are increasing at a faster rate (+2.5 ℃) than the global average (+0.8℃), and rainy seasons have become highly unpredictable. For the approximately 800,000 people living around the Turkana Basin, this scenario is potentially disastrous as they rely on the consistency of the seasonal cyclicity and of water and land availability to support their pastoralist, nomadic existence. Additionally, this area, like other parts of Africa, has been historically marginalized, poor, resource-starved, and climatically under-studied. Studies of organic-rich sediments (sapropels) over timescales of 3 million years in the Mediterranean Sea show that the African monsoon results from a complex combination of meteorological and astronomical parameters, and that the monsoon drives the climate in East Africa. Similar evidence is found in outcrop in the Kibish Formation in Ethiopia (196 Ma ± 5 ka). Melissa Boyd’s research on a 2 million-year-old lacustrine drill core from the Kaitio Member of the Nachukui Formation in the western part of the basin also provides comparable evidence. Her upcoming fieldwork in both West and East Turkana will seek further evidence in the sediments there.
The method Melissa will use in her research employs a multi-variate equation that considers numerous factors—such as latitude, astronomical parameters (insolation, precession, and eccentricity), and changes in insolation gradient—in order to derive a “monsoon index” for the region. As Melissa explains it, “Values above the monsoon threshold indicate times of enhanced monsoon precipitation and subsequently, geological evidence including sapropels, highstand deposits, or flooding surfaces. Application of the index to the core has been encouraging, and my objective is to use its predictive power to support my hypothesis in outcrop.” Melissa’s ultimate goal is to be able to use the monsoon index to better understand all of the deposits in the Turkana Basin. The utility of this monsoon index is threefold. First, it can be used by climate scientists and human rights organizations in the present to understand how the orbital parameters of the Earth are working in concert with global warming to affect monsoon strength. We know that global warming is negatively affecting the already hot and dry Turkana Basin, but this index can be used to calculate the degree to which global warming is having an effect. Second, it also can be used to predict monsoon strength in the future, as the orbital parameters of the Earth are cyclical, and the orbital solutions have been projected for ± 50 million years. Finally, it can be used by paleoscientists to better understand climate dynamics of the past and thus possibly discern how those dynamics shaped our hominin ancestors’ evolution in East Africa. Using this approach, scientists will be able to make comparisons during any time period to understand how the climate affected the environment and evolution of fauna and flora in this area.