Major
Candace O.
Major
Candace O.
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PreprintThe co-evolution of Black Sea level and composition through the last deglaciation and its paleoclimatic significance( 2006-01-28) Major, Candace O. ; Goldstein, Steven L. ; Ryan, William B. F. ; Lericolais, Gilles ; Piotrowski, Alexander M. ; Hajdas, IrkaThe strontium and oxygen isotopic compositions of carbonate shells are a measure of the water delivered to the Black Sea lake since the last glacial maximum. Commencing at ~18 ka BP cal with the arrival of substantial meltwater from the Alpine and northern European ice sheets and overflow via the Caspian Sea from the disintegrating Siberian ice cover, the 87Sr/86Sr ratio rose rapidly from a glacial minima around 0.7087 to reach a set of peaks near 0.7091 in layers of conspicuous reddish-brown clay with a mineralogy of Eurasian provenance. The 87Sr/86Sr ratio oscillates between high in the red-brown layers to low in interbedded gray clays with glacial era mineralogy, indicative that the meltwater came in pulses. On the other hand, the rise of the δ18O ratio from glacial low values of -7 per mil was delayed until15.2 ka BP cal, after the last meltwater pulse. The rising δ18O of the Black Sea lake corresponds with two episodes of calcite precipitation whose interruption corresponds to the Younger Dryas cold period. During each interval of calcite precipitation the δ18O increased a further 2 per mil, without variation in the 87Sr/86Sr composition. During cooling the 87Sr/86Sr ratio trended back toward its glacial value with little change in the δ18O. The disparity between the Sr and O isotope behavior demonstrates that δ18O is not simply a signal of end-member mixing, but instead the δ18O record reflects changes in atmospheric moisture delivered to the Black Sea watershed. At 9.4 ka BP cal the 87Sr/86Sr composition shifted to that of the global ocean and remained there to the present. Since lake water is significantly depleted in strontium relative to seawater, any earlier leakage from the Mediterranean should have left a corresponding signal.
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ArticleHydrology in the Sea of Marmara during the last 23 ka : implications for timing of Black Sea connections and sapropel deposition(American Geophysical Union, 2010-02-06) Vidal, L. ; Menot, Guillemette ; Joly, C. ; Bruneton, H. ; Rostek, F. ; Cagatay, M. Namik ; Major, Candace O. ; Bard, EdouardSediments deposited under lacustrine and marine conditions in the Sea of Marmara hold a Late Quaternary record for water exchange between the Black Sea and the Mediterranean Sea. Here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells, major and trace elements, and specific organic biomarker measurements, as well as a micropaleontological study from a 14C-dated sediment core retrieved from the Sea of Marmara. Pronounced changes occurred in δ18O and 87Sr/86Sr values at the fresh and marine water transition, providing additional information in relation to micropaleontological data. Organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n-alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event. When compared with the Black Sea record, the results suggest that the Black Sea was outflowing to the Sea of Marmara from the Last Glacial Maximum until the warmer Bølling-Allerød. The first marine incursion in the Sea of Marmara occurred at 14.7 cal ka B.P. However, salinification of the basin was gradual, indicating that Black Sea freshwaters were still contributing to the Marmara seawater budget. After the Younger Dryas (which is associated with a high input of organic matter of terrestrial origin) both basins were disconnected, resulting in a salinity increase in the Sea of Marmara. The deposition of organic-rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population.
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ArticleAbrupt changes of temperature and water chemistry in the late Pleistocene and early Holocene Black Sea(American Geophysical Union, 2008-01-12) Bahr, Andre ; Lamy, Frank ; Arz, Helge W. ; Major, Candace O. ; Kwiecien, Olga ; Wefer, GeroldNew 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 δ 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. 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 δ 18O record is less pronounced and would fit to an inflow lasting ∼100 a.