TRACING SHIFTS IN LAKE TANGANYIKA'S OXYCLINE USING MODERN AND RECENT SEDIMENTS: A CASE STUDY FROM NKAMBA BAY (ZAMBIA)

Lake Tanganyika is a very important modern geological setting for understanding the depositional processes of carbonaceous sediments in a tropical rift basin. This is because Lake Tanganyika combines several key characteristics thought to be necessary for carbonaceous sedimentation, which include: (1) a warm tropical climate that promotes high primary productivity, (2) a morphology that hinders vertical mixing because of deep subsidence and tectonic relief, and (3) seasonally shifting winds, promoting localized seasonal upwelling.

The limnogeology of southern Lake Tanganyika in Zambia remains understudied. To help narrow the knowledge gap around carbonaceous sedimentation in this area, we use new lake floor grab samples (n=81 samples) and short sediment cores (n = 12 cores) collected from Nkamba and Kasaba Bays in Lake Tanganyika. The hypothesis being tested in this study is that sediment composition can be used to detect the oxycline and track changes in its position over time. The presence/absence of lake floor oxygen is evaluated using total organic carbon (TOC) and total nitrogen concentrations, redox-sensitive metals (Fe, Mn), and benthic fossil (mollusks, ostracods) content. Short cores were collected in a depth transect exceeding 44 to 267 m, whereas the catalog of grab samples is from water depths < 100 m deep.

Preliminary results from the grab samples show that modern lake floor sediments display TOC values ranging from 0.12 to 4.55 wt.%, with high concentrations recorded in samples collected from ~ 50-80 m, and in samples with finer particle sizes. Sediment core analysis is ongoing, and ²¹⁰Pb will be used to elucidate sediment accumulation rates in Nkamba and Kasaba Bays. In addition to new limnogeological information, the results of this study will provide insights into understanding the consequences of climate change on lake function and fisheries conservation.