Memory Effects in Salinity Profiles From Black Sea Sediments. Issue 6 (20th June 2022)

• Record Type: Journal Article
• Authors: Boudreau, Bernard P.; Calvert, Stephen; Kienast, Markus
• Is Part Of: Paleoceanography and paleoclimatology. Volume 37:Issue 6(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-06-20
• Subjects: Black Sea -- salinization -- porewaters -- salt balance -- salinity model -- sapropel -- salinity proxies; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2022PA004466
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The 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. Plain Language Summary: The Black Sea has changed from a freshwater or mildly brackish lake to a salty inland sea over the past 10, 000 years, as Mediterranean Sea water invaded, starting at about that time. Those salinity changes are recorded in the porewaters preserved in the accumulating sediments at the bottom of that sea. However, past attempts with models to explain the changes in salinity with depth in those sediments have not accounted for the freshwater‐to‐saltwater history of the Black Sea. There was a previous saline period between about 128 and 65, 000 years ago (BP), which is preserved deeper in the sediment. That porewater salt is slowly leaking back into the more recent saline porewaters via diffusion and that has not been taken into account by previous models. When that history is included, the available data can be predicted. Key Points: We present and solve models for the evolution of the salinity of the Black Sea and its sediments from the Eemian to the Holocene The correspondence between available data and our model results from inclusion of memory of the previous Eemian‐post‐Eemian salinization Available porewater data do not appear to be consistent with hindcasts from available salinity proxies