Massive meltwater discharge into the Black Sea Euxine Lake

Massive meltwater discharge into the Black Sea Euxine Lake

William B. F. Ryan, Anastasia Yanchilina, Elizabeth Matamoros and Timothy Kenna

Lamont-Doherty Earth Observatory of Columbia University

1975 Glomar Challenger at DSDP Site 380

“Core 1: Black mud on top 2 meters. The bottom 7 meters consists mainly of greenish gray calcareous mud, with dark greenish gray sandy silt interbeds, and a few intercalations of light brown carbonate-rich mud and clay.”

D. Ross, Yu. Neprochnov et al., 1978

1998 BLASON 1 Expedition on the R/V Suroit Cores BLKS9809 and BLKS9810

“Two intervals of brown muds rich in illite and kaolinite. The appearance of the northern provenance brown muds ~15,000 and 13,400 yr (uncalibrated) suggests a linkage with the collapse of the Scandinavian and Alpine glacial ice and perhaps the melting of the permafrost.”

Major et al., 2002. Marine Geology 190, 19-34

Major et al., 2006. Quat. Sci. Rev, 25, 2031-2047

“Sr isotopes show two prominent peaks between 18 and 16 ka BP cal associated with meltwater from disintegrating Eurasian ice sheets.”

A distinct drop in 18O values combined with a sharp increase in 87Sr/86Sr occurred between 16.5 and 14.8 ka B.P. This event is attributed to an increased runoff from the northern drainage area of the Black Sea between Heinrich Event 1 and the onset of the Bølling warm period.

Bahr et al., 2008. G3 AGU v9, #1

“The 87Sr/86Sr record by Major et al. [2006] is tuned to the new stratigraphy using the red layer interval and the Ca peaks as an independent time marker”

Bahr et al., 2008. G3 AGU v9, #1

2009 - 2011 Collecting cores on transects across the Bulgarian margin with R/V Akademik, Petko Dimitrov, chief scientist

nine successive graded beds of red-brown clay with silty and sandy bases on the distal Danube deep-sea fan

Matamorous et al., 2012

branched and isoprenoidtetraether (BIT) index

Greenland Ice Core

C25-alkane/total organic carbon

Neodymium isotopes Nd)

Ti/Ca ratio

Terrestrial organic tracers

Terrestrial inorganic tracers

Soulet et al., 2013. PNAS

Titanium enrichment

Area of deposit = ~75,000 km2

Volume of deposit = ~40 km3 Flood water volume = 20,000 km3

Decreased Lake water 18O by 1 o/oo

Red-brown meltwater deposit(25 meters thick)

Left bank of Dniepersubmarine canyon

Deeply-incised mega-meander valleys of the Dnieper and Southern Bug Rivers

Lake Disna

Post HS1 ice sheet

LGM limit

17,500 to 15,500 years ago

200 km

Red tilland clayRed till

and clay

Lake Missoula

ice sheet

deposit

200 km

15,000 to 13,000 years ago

Lake Water Volume (km3)

Deposit Volume (km3)

Number Events

Deposit volume/event (km3)

Missoula 2500 200 40 5Disna 4000 15 4 3.75

Summary

•The Black Sea’s ice-age lake experienced massive floods during Heinrich Stadial 1 derived from proglacial lakes at the southern edge of the Fennoscandian Ice sheet.

•These discharges are comparable to the cataclysmic floods that swept periodically across eastern state of Washington (USA) at the end of the ice age.

•The magnitudes of the shifts in strontium and oxygen isotopes suggests that total amount of meltwater might have exceeded a quarter of the volume of the Black Sea’s Euxine Lake.

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 reddish-brown 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.