Controls on the Radiocarbon Reservoir Ages in the Modern Dead Sea Drainage System and in the Last Glacial Lake Lisan

Abstract

ABSTRACT. Carbon isotopic and chemical compositions of freshwaters feeding the Dead Sea and the Sea of Galilee (i.e. perennial streams and floods along their stream profiles) were used to constrain the factors that dictate the reservoir ages (RA) of these lakes and the last glacial Lake Lisan. Runoff waters are characterized by high Ca 2+ , Mg 2+ , alkalinity, and radiocarbon contents (67-108 pMC), suggesting a major role for ,4 C atmospheric exchange reactions (carbonate rock dissolution alone will result in lower pMC values). These exchange, processes were corroborated by dissolved inorganic carbon (DIC) and Ô 13 C trends throughout the flood profile. During the evolution from rain to incipient runoff, the 14 C DIC of the water increases and is accompanied by a DIC increase and Ô 13 C DIC decrease, suggesting an addition of soil C0 2 , which is characterized by light ô ,3 C and high 14 C content. When incipient runoffs evolve to floods, the opposite trends are observed.It appears that the Sea of Galilee, the Dead Sea, and its last glacial precursor, Lake Lisan, maintained uniform but specific RAs of 0.8 ±0.1, 2.3 ±0.1, and 1.6 ± 0.3 kyr, respectively. However, applying the 14 C contents of modern Dead Sea water sources to the water mass balance of Lake Lisan reveals that the RA of Lake Lisan is higher than that predicted by the mass balance. This discrepancy may reflect enhanced dissolution of carbonatic dust, changes in the amount of 14 C exchanged in Judean Desert floods, or variations in the contribution of brine and saline springs. Furthermore, the small fluctuations in the Lisan RA (1.6 ± 0.3 kyr) may reflect small, short-term changes in the relative contributions of these sources.

Radiocarbon Reservoir Ages as Freshwater-Brine Monitors in Lake Lisan, Dead Sea System

“…The continuous and the annual mode of deposition of primary aragonite from the epilimnion, and the possibility to obtain U-Th ages on the aragonites, make the Lisan aragonite a potential highresolution archive for atmospheric 14 C calibration (Schramm et al 2000;Haase-Schramm et al 2004;Torfstein et al 2013). Yet, the 14 C of the dissolved inorganic carbon content of the lake solution, from which the primary aragonite precipitates, is a mixture of 3 reservoirs: dissolved atmospheric CO 2 supplied mainly through runoff entering the lake (Belmaker et al 2007); "dead carbon" ( 14 C-depleted) dissolved from the surrounding Phanerozoic carbonate terrains (e.g. the Cretaceous Judean Mountain wall-rocks of the Dead Sea basin); and 14 C provided by saline springs that underwent water-rock interaction and 14 C "aging" within the aquifers (e.g.…”

“…the Cretaceous Judean Mountain wall-rocks of the Dead Sea basin); and 14 C provided by saline springs that underwent water-rock interaction and 14 C "aging" within the aquifers (e.g. Belmaker et al 2007). Thus, the fresh and saline solutions that enter the lake are characterized by different amounts of 14 C reflecting their primary source, dissolution processes, and exchange processes with the atmosphere.…”

“…Bard et al 1998;Fairbanks et al 2005), but is often complicated in the case of speleothems and laminated lake sediments (cf. Schramm et al 2000;Beck et al 2001;Belmaker et al 2007).…”

Characterization and Dating of Saline Groundwater in the Dead Sea Area

“…14 C in the DS is affected by CO 2 exchange with the atmosphere and by 14 C DIC contributions from the Jordan River, rain, groundwater, and mountain floods from both sides of the DS. The main processes that affect these components were estimated to be water-rock interaction and the exchange of 14 CO 2 between the water and atmosphere (Belmaker et al 2007). Chemical and stable isotope investigations of groundwater brines in the DS area were conducted by Bentor (1961), Gat et al (1969), Starinsky (1974), Fleischer et al (1977), Vengosh et al (1991), Yechieli et al (1996), Stein et al (1997), and Gavrieli and Stein (2006).…”

“…This range could be the outcome of mixing between 2 freshwater components with different 14 C DIC values, one being old groundwater from the Cretaceous aquifer, owing to relatively low 14 C DIC , and the other, recent rain and flood water that penetrated into the aquifer. The flood water is characterized by high 14 C DIC values, determined by the extent of CO 2 exchange with the atmosphere (Belmaker et al 2007). Due to the relatively high DIC values of the spring water compared to those of the DS values, the relative contribution of this end-member is higher, causing the expected mixing line to be lowered a little and not linear.…”