Memory Effects in Salinity Profiles From Black Sea Sediments

Abstract

AbstractThe current saline state 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 128 and 65 Kyrs BP (Before Present). Our results argue that the down‐core salinity profiles of Black Sea Holocene sediments have been affected by upward diffusion of salt from the penultimate saline episode and possibly from residual salinity of the basin waters captured in the accumulating porewaters. Our retrodictions require that the Black Sea bottom waters be either fresh or weakly brackish (S ≤ 4), between 80 and 10 Kyrs BP. In addition, we find that the timing of the first deposition of the Holocene sapropel corresponds to the time when salty bottom waters first reached the surface waters, and we speculate that increased organic matter production was 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.