Mozambique Core Brings Up 7 Million Years of Climate History
Read Sidney Hemming’s first post to learn more about the goals of her two-month research cruise off southern Africa and its focus on the Agulhas Current and collecting climate records for the past 5 million years.
We just completed coring at our northernmost Mozambique site. The sea is still. The weather is hot and muggy, but so still. This is how sediment coring should be. The stratigraphic correlators think they are having a dream. We have no gaps, beyond the absolute minimum from the coring process, and the variability in the physical properties makes correlating among the holes dead easy. And the variability looks like a fantastic, cyclic climate signal that is continuous back to 7 million years ago!
We are heading to the Zambezi site now. For our two river sites—offshore from the Zambezi and Limpopo Rivers—our big goal is making the most direct connection possible between what happened on land and in the oceans over the past ~2 million years. We’re only expecting about 2 million years because the accumulation rates are higher, but the nice thing about that is that we can get much more detail about the variability.
Among our science party, we have multiple tools to probe how the rainfall may have changed through time. We have organic biomarkers as well as several measures of terrigenous (land-derived) sediment sources, weathering intensity and fluxes. The Zambezi catchment is located at the very southern part of the annual shift in the Intertropical Convergence Zone (the so-called thermal equator), so there is a strong gradient to drier climate to the south. And that is one of the reasons having both the Zambezi and Limpopo is so exciting to think about. The “great grey-green greasy“ Limpopo catchment is much drier than the Zambezi.
We are going to be so busy. We have finished the coring, and yet more than half the cores are waiting to be processed for the various observations and measurements we have been making. We will get to the Zambezi site in less than two days, and the water depth is much shallower there, meaning the cores are going to come up every 20 minutes or so rather than every 45 minutes, as at the northern site. And then we only have about one more day to get to the Limpopo, where the same rate of coring is expected. So we are going to be buried in cores by the time we finish at Limpopo, and we’ll have about four days to finalize the data collection and reports before arriving at our final site, CAPE, off the tip of South Africa. More about CAPE later.
Sidney Hemming is a geochemist and professor of Earth and Environmental Sciences at Lamont-Doherty Earth Observatory. She uses the records in sediments and sedimentary rocks to document aspects of Earth’s history.