Memory Effects in Salinity Profiles From Black Sea Sediments

The current saline state of the Black Sea is only the latest of a series of freshening-salinization episodes that have affected that body of water during past glacial-interglacial cycles. Here, we model the salinity history of the basin and its sedimentary porewaters since the end of the penultimate saline period, variously thought to have occurred in the period between similar to 128 and similar to 65 Kyr BP. Our model results argue that the down-core salinity profiles of Black Sea Holocene sediments have been affected by the diffusion of salt from the penultimate saline episode. Retrodiction of these porewater profiles also requires that the Black Sea bottom waters be either fresh, or very weakly brackish (S <= 1), between similar to 50 and similar to 10 Kyr BP. In addition, we find that the timing of the first deposition of the well-known Holocene sapropel corresponds to the time when salty bottom waters first reached the surface waters, and we speculate that increased organic matter production could have been caused by the release of nutrients stored in the saline bottom water. Finally, using current salinity proxy data, we find that the porewater salinity profiles generated from these proxies do not match the observed interstitial profiles.