Compilation of geophysical, geochronological, and geochemical evidence indicates a rapid Mediterranean-derived submergence of the Black Sea's shelf and subsequent substantial salinification in the early Holocene (original) (raw)

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Highlights

• •
  Compilation of geochronological, geochemical, and geophysical data is used to reinterpret Black Sea-Lake level history.
• •
  The Black Sea-Lake remained fresh during deglaciation until the marine transgression at 9300
  calendar
  years
  BP.
• •
  Prior to the transgression, the Black Sea-Lake level was 120
  mbsl or lower.
• •
  The transgression was fast and took no longer than a couple of decades.
• •
  The salinification that followed took <~1500
  years.

Abstract

Our knowledge of rate and processes in which semi-enclosed environments alternate from lacustrine to marine is commonly limited because of the paucity of specific proxies for sea level and salinity. Here we investigate the timing, rate, and key mechanisms involved in the transformation of the previously isolated Black Sea-Lake to the modern partly-enclosed marine sea using a suite of geophysical, geochemical, and geochronological methods.

Cores were collected in transects across shelves of Ukraine, Romania, Bulgaria, and Turkey. Biogenic carbonate from these cores was analyzed for radiocarbon and strontium, oxygen, and carbon isotopes. Strontium results indicate that the submergence of the Black Sea shelf at 9300

calendar

years BP was caused by the ingress of Mediterranean water and was abrupt, taking <

40

years. The seismic reflection profiles show a uniform drape of subsequent sediment over aeolian dunes indicating a drowning with no time for erosion accompanying the submergence. Moisture measurements beneath the uniform drape indicate that the shelf was dry before submergence and the shoreline of the Preboreal lake may have regressed to beyond 120

mbsl. Mollusks colonized the newly submerged substrate of the inner shelf at the same time as they colonized the outer shelf. The succession of mollusk species with shells whose strontium isotope composition has a marine component indicates a rising salinity. The transformation of the lake to a sea is affirmed by increases in the shells' strontium and oxygen isotopic ratios towards the external ocean value.

Radiocarbon years are calibrated to calendar years by tuning the oxygen and carbon isotope composition of the mollusk record to that of the U/Th dated Sofular Cave stalagmites. The match shows a reduction of the lake's prior high reservoir age accompanying the inflow of the Mediterranean water. In 900

years the salinity reached a threshold that excluded all previous Black Sea lacustrine fauna. These results imply that any substantial postglacial submergence of the Black Sea shelves did not occur prior to entry of Mediterranean water.

Keywords

Black Sea transgression

Isotope geochemistry

Black Sea

Marine-lake connections

Reflection profiles

Paleoceanography

Paleosalinity

Lake transgression

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© 2016 The Authors. Published by Elsevier B.V.