Abrupt changes of temperature and water chemistry in the late Pleistocene and early Holocene Black Sea

Abstract

New Mg/Ca, Sr/Ca, and published stable oxygen isotope and 87Sr/86Sr data obtained on ostracods from gravity cores located on the northwestern Black Sea slope were used to infer changes in the Black Sea hydrology and water chemistry for the period between 30 to 8 ka B.P. (calibrated radiocarbon years). The period prior to 16.5 ka B.P. was characterized by stable conditions in all records until a distinct drop in δ18O 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. While the Mg/Ca and Sr/Ca records remained rather unaffected by this inflow; they show an abrupt rise with the onset of the Bølling/Allerød warm period. This rise was caused by calcite precipitation in the surface water, which led to a sudden increase of the Sr/Ca and Mg/Ca ratios of the Black Sea water. The stable oxygen isotopes also start to increase around 15 ka B.P., although in a more gradual manner, due to isotopically enriched meteoric precipitation. While Sr/Ca remains constant during the following interval of the Younger Dryas cold period, a decrease in the Mg/Ca ratio implies that the intermediate water masses of the Black Sea temporarily cooled by 1–2°C during the Younger Dryas. The 87Sr/86Sr values drop after the cessation of the water inflow at 15 ka B.P. to a lower level until the Younger Dryas, where they reach values similar to those observed during the Last Glacial Maximum. This might point to a potential outflow to the Mediterranean Sea via the Sea of Marmara during this period. The inflow of Mediterranean water started around 9.3 ka B.P., which is clearly detectable in the abruptly increasing Mg/Ca, Sr/Ca, and 87Sr/86Sr values. The accompanying increase in the δ18O record is less pronounced and would fit to an inflow lasting ∼100 a.

Black Sea temperature response to glacial millennial‐scale climate variability

“…Our TEX 86 and Mg/Ca ostracods records suggest that HE and non-HE stadials cooled to about 5.5°C, with no significant difference between them. Variations in Mg/Ca ostracods , which closely resemble the TEX 86 surface temperature record during MIS 3 (Figure 1a), correspond to temperature changes of roughly 2-4°C [Bahr et al, 2008] at this intermediate water depth and confirm the DO-related temperature changes, although we cannot provide absolute temperature values due to the absence of an appropriate calibration for the formerly limnic Black Sea. The magnitude of the temperature variability for the bottom water is therefore comparable to the amplitudes of the TEX 86 surface temperature and suggested a generally well mixed water column at the coring site during the last glacial period and especially during MIS 3 (Figure 1a).…”

“…Precision (2.2%) and accuracy (1.4%) were checked every five samples by comparison with the international reference material ECRM 752-1 (BAS). The Mg/Ca ratios of benthic ostracod carbonate shells (Mg/Ca ostracods ) document the mean annual changes in bottom water temperatures [Bahr et al, 2008;Wegwerth et al, 2014]. The methods for the total inorganic carbon (TIC) and IRD C analyses are described in Nowaczyk et al [2012].…”

“…(a) Greenland temperature [Kindler et al, 2014] (NGRIP); TEX 86 -based mean annual lake surface temperature (LST). The variability in bottom water temperature was estimated from the Mg/Ca of benthic ostracods, with ΔT reflecting a minimum estimate of the temperature changes [Bahr et al, 2008]. Total inorganic carbon (TIC) served as a proxy for phytoplankton productivity.…”

Abrupt drainage cycles of the Fennoscandian Ice Sheet

“…Additionally, to the south, the hydrology of the BS was also strongly affected by the cyclic drainage of Lake Disna. The increase in runoff due to repeated seasonal floods over four successive periods of ∼220 y raised the BS water level by around 100 m, until the sill of the Bosphorus Strait was reached (12,13,16,44,45), leading to the flooding of the vast northwestern shelf of the BS basin and the attendant drastic retreat of the coastline (SI Text). The resulting outflow of BS waters into the northeastern Mediterranean basins altered the hydrology of both the Marmara Sea (45) and the Aegean Sea (46,47).…”

Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey

“…18 O between$16.5 and 14.8 kyr BP due to enhanced inflow of isotopically depleted melt water [Bahr et al, 2008], the subdued nature of GI 1 (BA) and the continuous increase in d…”