Inverse Modeling Of The Net Water Balance Of The Black Sea From The Last Glacial Maximum To The Present

The net freshwater balance plays a central role in the biological, chemical, geological and physical changes in the Black Sea since the Late Glacial Maximum (LGM), that is, 18-24,000 years BP. Past estimates of this balance vary widely. Here we solve inversely a water balance model coupled to two previously published Bosporus flow models, that is, flow rates controlled either by hydraulics with a critical height or by channel friction. We drive both models with two previously proposed Black Sea water-level histories, that is, a smooth transition to saltwater entry and the "flood" scenario. First, we find that flow control by channel friction is far more likely than control by critical-height hydraulics, as the latter does not allow Marmara Sea water to enter the Bosporus at any time in the past and predicts present-day outflows that are far greater than observed. Prior to intense glacial melting (12-14,000 years BP), all models retrodict net freshwater inflow far less than previously assumed, that is, on the order of -1 to +10 km(3) yr(-1), rather than +100 s km(3) yr(-1). Thus, our results explain the ease by which the Black Sea could switch from evaporative to water gain conditions, as implied by water-level records for that period. In addition, the channel friction model hindcasts glacial meltwater spikes during the transition from the LGM to the Holocene that are much smaller, that is, 100-250 km(3) yr(-1), than retrodicted by the hydraulic model or reported in the literature, that is, >1,000 km(3) yr(-1).