干旱区生态环境知识资源中心

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 Ca2+, Mg2+, alkalinity, and radiocarbon contents (67-108 pMC), suggesting a major role for C-14 atmospheric exchange reactions (carbonate rock dissolution alone will result in lower pMC values). These exchange processes were corroborated by dissolved inorganic carbon (DIC) and delta C-13 trends throughout the flood profile. During the evolution from rain to incipient runoff, the C-14(DIC) of the water increases and is accompanied by a DIC increase and delta C-13(DIC) decrease, suggesting an addition of soil CO2, which is characterized by light delta C-13 and high C-14 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 C-14 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 C-14 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.