The composition of pore fluids trapped in the bottom sediments of the Black Sea provides information on geochemical and paleohydrologic aspects of the Black Sea during the Holocene and late Pleistocene Epochs.

Most piston cores show a decrease in interstitial chlorinity and salinity with depth. Calculations suggest that, during isolation of the Black Sea in the last glacial maximum (Neoeuxinian), the Black Sea had a relatively homogeneous chlorinity of about 3.5 g/kg Cl, compared with more than 12 g/kg Cl in present bottom water.

Accumulation of riverborne salts during isolation probably contributed only a relatively small proportion of total chloride (0.2 g/kg), but a large calcium increment (0.5 g/kg), possibly equal to or greater than present calcium concentrations.

Submarine discharge of fresh to brackish groundwaters is occurring in several areas of the Black Sea, especially off the western shelf of the Crimean peninsula and the southeastern Caucasus coast. In addition, there is a saltier subsediment input near the Bosporus channel, possibly as a result of upward diffusion of salts from evaporites or continental brines.

Diagenetic reactions between pore fluids and sediments result in (1) strong uptake of interstitial potassium and magnesium in nonexchangeable positions in the sediments and (2) loss of sulfate by bacterial reduction. Calcium, bicarbonate alkalinity, silica, and ammonia are added to the pore fluids and tend to diffuse into overlying bottom waters of the deep basin. After initial increase, bicarbonate alkalinity decreases with depth in cores, suggesting that both carbonate precipitation and dissolution occur in the deeper sediments.

Interstitial waters are the main source of iron, manganese, and phosphorus for iron-manganese concretions on the oxygenated Crimean shelf. Supply from this source corresponds to a growth rate of 5 mm/1,000 years.