Massive meltwater discharge into the Black Sea Euxine Lake
Wiliam B. F. RYAN1, Anastasia YANCHILINA1, Elizabeth MATAMOROS2, and Timothy
KENNA1
1Lamont-Doherty
Earth Observatory of Columbia University, Palisades, NY, USA,
billr@ldeo.columbia.edu, nyanchil@ldeo.columbia.edu, tkenna@ldeo.columbia.edu
2Department
of Earth and Planetary Sciences, Harvard University, Cambridge, MA,
USA, elizabethmatamoros@college.harvard.edu
An abrupt shift in the color and composition of the Black Sea lacustrine sediment
occurs at the end of the last glacial period. The change is from gray mud rich in
smectite and manganese to reddish-brown mud with illite, kaolinite, iron and
titanium. The compositions indicate a switch in watershed from Anatolia to Eurasia,
and timing corresponds to the collapse of the Eurasian lobe of the Fennoscandian
Ice Sheet (Major et al., 2002; Ryan et al., 2003). The reddish-brown sediment is
present in >30 cores in the western Black Sea. This mud occurs in beds of finely
laminated silt and clay (Bahr et al., 2006; Soulet et al, 2011; 2013). Strontium
isotopes reveal an excursion to more radiogenic values in each reddish-brown bed
(Major et al., 2006). The layers are thickest on the outer shelf and slope and thinner
on the basin floor. Titanium enrichment is attributed to abundant ilmenite and
rutile in placer deposits within the Dnieper watershed. The area covered by the
muds exceeds 60,000 km2 and is equivalent to >20% of the total seafloor. The
volume approaches 100 km3. Dilution to the density of sediment-laden river water
requires >50,000 km3 of water delivered through the Dnieper watershed in
repetitive flooding events. The strontium isotopic excursions also imply that a
substantial portion of the Euxine Lake was replaced with meltwater derived from
pro-glacial lakes as suggested by similarity between the neodymium isotope
composition of the mud and the Ukrainian Shield (Soulet et al., 2013). The reddishbrown mud appears at 18,000 cal years BP (Bahr et al., 2006; Ryan, 2007, Soulet et
al., 2011). Wiggle-matching of isotopic variations in Black Sea cores to the
Greenland GRIP ice core (Ryan, 2007) and Hula Cave stalagmites (Soulet et al.,
2011) indicates that the 14C reservoir age of the Euxine Lake water dropped from
1600 years in the dark gray glacial muds below the reddish-brown mud to 200
years at the top. This decrease implies a vast volume of melt water with dissolved
14C equilibrated with the atmosphere. The eastern Black Sea floor does not contain
the reddish-brown mud.
References:
Bahr, A., Arz, H.W., Lamy, F., Wefer, G., 2006. Late glacial to Holocene
paleoenvironmental evolution of the Black Sea, reconstructed with stable oxygen
isotope records obtained on ostracod shells, Earth Planet. Sci. Lett., 241, 863-875.
Major, C., Ryan, W., Lericolais, G., Hajadas, I., 2002. Constraints on Black Sea outflow
to the Sea of Marmara during the last glacial-interglacial transition, Mar. Geol., 190,
19-34.
Major, C.A., Goldstein, S.L., Ryan, W.B.F., Lericolais, G., Piotrowski, A., Hajadas, I.,
2006. The co-evolution of Black Sea level and composition through the last
deglaciation and its paleoclimatic significance, Quat. Sci. Rev., 25, 2031-2047.
Ryan, W.B.F., Major, C.O., Lericolais, G., Goldstein, S.L., 2003, Catastrophic flooding of
the Black Sea, Annu. Rev. Earth Planet. Sci., 31, 525–54.
Ryan, W.B.F., 2007. Status of the Black Sea Flood, in The Black Sea Flood Question,
Yanko-Hombach et al, Eds, Springer, 63-68.
Soulet, G., Ménot, G., Garreta, V. Rostek, F. Zaragosi, S., Lericolais, G., Bard, E., 2011.
Black Sea “Lake” reservoir age evolution since the Last Glacial — Hydrologic and
climatic implications, Earth Planet. Sci. Lett., 308, 245-258.
Soulet, G., Ménot, G., Bayon, G., Rostek, F., Ponzevera, E., Toucanne, S., Lericolais, G. ,
Bard, E., 2013. Abrupt drainage cycles of the Fennoscandian Ice Sheet, PNAS, 110,
#17, 6682-6687.