Ryan_MeltwaterDischarge_v2 - Lamont

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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
“Sr isotopes show two prominent
peaks between 18 and 16 ka BP cal
associated with meltwater from
disintegrating Eurasian ice sheets.”
Major et al., 2006. Quat. Sci. Rev, 25, 2031-2047
A distinct drop in d18O 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
Greenland Ice Core
Terrestrial organic tracers
branched and isoprenoid
tetraether (BIT) index
C25-alkane/total organic carbon
Ti/Ca ratio
Terrestrial inorganic tracers
Neodymium isotopes (eNd)
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 d18O by 1 o/oo
Red-brown meltwater deposit
(25 meters thick)
Left bank of Dnieper
submarine canyon
Deeply-incised mega-meander
valleys of the Dnieper and
Southern Bug Rivers
200 km
Post HS1 ice sheet
Lake Disna
LGM limit
Red till
and clay
17,500 to 15,500 years ago
200 km
ice sheet
Lake Missoula
deposit
15,000 to 13,000 years ago
Lake
Water Volume Deposit Volume
(km3)
(km3)
Missoula
2500
200
Disna
4000
15
Number
Events
40
4
Deposit
volume/event (km3)
5
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.
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