The distribution of sediment in the Kara Sea is controlled by the discharge of Western Siberia’s two largest rivers, the Yenisey and the Ob’. These two rivers have a combined annual fluid discharge of 942 cu km, ranking them fourth behind the Amazon, Congo, and Ganges-Brahmaputra rivers in total annual discharge. This discharge represents almost 1% of the total volume of the Kara Sea. The combined delta of the 2 rivers covers approximately 230,000 sq km at the 50-m isobath.
During the winter months, the rivers freeze and discharge approaches zero. A saltwater wedge must move far upstream. During spring breakup and flooding, the salt water is flushed out, and the major part of the annual discharge and sediment load flows into the Kara Sea. The finer sediments continue flowing seaward, toward the Arctic basin.
The genetic interrelation of river, delta, submarine canyon, and abyssal fan does not hold strictly for the Yenisey-Ob’ system. The northern Kara Sea contains 3 major physiographic provinces—the St. Ann and Voronin Troughs, separated by the Central Kara Plateau. Most of the sediment is carried to the Arctic basin along the eastern side of the longer, deeper St. Ann Trough, a sediment transport distance of approximately 600 km. The sediment may then go through a submarine canyon (no conclusive data available) to an abyssal fan (suggested on contour maps of the Arctic basin).
Sediment-distribution patterns in the St. Ann Trough reflect the transport of the distal deltaic sediments across the area. The sediment on the eastern side is fine silty clay, containing abundant illite, chlorite, and mica, with a high organic carbon and water content, and with a limited, dominantly arenaceous, foraminifer population. The sediments on the western side are much coarser, have smaller organic carbon and water contents, and contain an Arctic foraminifer population. In addition to some illite, the dominant clay mineral is locally derived kaolinite.
Abundance of the foraminifers appears to be directly proportional to bottom temperature and pH. The distribution is not a simple depth zonation. Globigerina pachyderma is the only planktonic species found.