The sedimentary response to a rapid change in lake level in Lake Tanganyika

We present records of sedimentary organic carbon, nitrogen, and carbonate, and stable isotope records of organic material and carbonate from a series of sediment cores that straddle the permanent chemocline in Lake Tanganyika. Sedimentation rates for these cores are consistent among the sites (~0.05-0.1cm y^-1), and all records show an increase in sedimentary carbonate (aragonite) content centered at ~1879. The mid-19th century coincides with a major (~10m) lake level transgression. Throughout the period of lake level transgression and subsequent regression, the organic matter δ¹³C and δ¹⁵N records develop a prominent and coincident negative excursion followed by a return to values similar to those prior to the lake level transgression. This negative excursion in δ¹⁵N and δ¹³C is also coincident with an increase in carbonate-corrected organic carbon. We interpret the δ¹³C results as a decline in primary production during the transgression with the δ¹⁵N results signaling a concomitant increase in the reliance on nitrogen fixation as the nitrogen source. The coincident peak in organic carbon is interpreted as being a result of enhanced preservation driven by the precipitation and burial of aragonite.