North Atlantic influence on 19th–20th century rainfall in the Dead Sea watershed, teleconnections with the Sahel, and implication for Holocene climate fluctuations

The importance of understanding processes that govern the hydroclimate of the Mediterranean Basin is highlighted by the projected significant drying of the region in response to the increase in greenhouse gas concentrations. Here we study the long-term hydroclimatic variability of the central Levant region, situated in the eastern boundary of the Basin, as reveled by instrumental observations and the Holocene record of Dead Sea level variations. Observations of 19th and 20th century precipitation in the Dead Sea watershed region display a multidecadal, anti-phase relationship to North Atlantic (NAtl) sea surface temperature (SST) variability, such that when the NAtl is relatively cold, Jerusalem experiences higher than normal precipitation and vice versa. This association is underlined by a negative correlation to precipitation in the sub-Saharan Sahel and a positive correlation to precipitation in western North America, areas that are also affected by multidecadal NAtl SST variability. These observations are consistent with a broad range of Holocene hydroclimatic fluctuations from the epochal, to the millennial and centennial time scales, as displayed by the Dead Sea lake level, by lake levels in the Sahel, and by direct and indirect proxy indicators of NAtl SSTs. On the epochal time scale, the gradual cooling of NAtl SSTs throughout the Holocene in response to precession-driven reduction of summer insolation is associated with previously well-studied wet-to-dry transition in the Sahel and with a general increase in Dead Sea lake levels from low stands after the Younger Dryas to higher stands in the mid- to late-Holocene. On the millennial and centennial time scales there is also evidence for an anti-phase relationship between Holocene variations in the Dead Sea and Sahelian lake levels and with proxy indicators of NAtl SSTs. However the records are punctuated by abrupt lake-level drops, which appear to be in-phase and which occur during previously documented abrupt major cooling events in the Northern Hemisphere. We propose that the mechanisms by which NAtl SSTs affect precipitation in the central Levant is related to the tendency for high (low) pressure anomalies to persist over the eastern North Atlantic/Western Mediterranean region when the Basin is cold (warm). This, in turn, affects the likelihood of cold air outbreaks and cyclogenesis in the Eastern Mediterranean and, consequently, rainfall in the central Levant region. Depending on its phase, this natural mechanism can alleviate or exacerbate the anthropogenic impact on the regions' hydroclimatic future

Rock varnish evidence for a Younger Dryas wet period in the Dead Sea basin

Rock varnish from 14.6 to 13.2 ka recessional shorelines of late glacial Lake Lisan and fan delta surfaces between 280 and 365 m bmsl (meters below mean sea level) along the western margins of the Dead Sea contains replicable layering patterns, characterized by a low Mn and Ba orange/yellow surface layer and a high Mn and Ba dark basal layer. The deposition of the dark basal layers immediately after the lake recession represents a wet period coinciding with the Younger Dryas (YD) cooling (12.9–11.6 ka), manifesting the influence of midlatitude westerly winds in the eastern Mediterranean-central Levant (EM-CL). In contrast, varnish from the distal base of fan deltas contains only orange/yellow surface layers, diagnostic of the Holocene relatively dry climate. The absence of the dark basal layers in the varnish further indicates a YD high stand at ~365 m bmsl and a lake level rise of at least 100 m from its Bølling-Ållerød lowstand. This rise stands in contrast to the abrupt drop of the lake level during the Heinrich (H1) cold event, illustrating the opposite response of the EM-CL climate to changes in the North Atlantic climate. The YD wet event most likely reflects a southward shift of the Atlantic meridional overturning circulation-modulated midlatitude westerly wind belt in the EM-CL region

Dead Sea drawdown and monsoonal impacts in the Levant during the last interglacial

Sediment cores recovered by the Dead Sea Deep Drilling Project (DSDDP) from the deepest basin of the hypersaline, terminal Dead Sea (lake floor at ∼725 m below mean sea level) reveal the detailed climate history of the lake's watershed during the last interglacial period (Marine Isotope Stage 5; MIS5). The results document both a more intense aridity during MIS5 than during the Holocene, and the moderating impacts derived from the intense MIS5e African Monsoon. Early MIS5e (∼133–128 ka) was dominated by hyperarid conditions in the Eastern Mediterranean–Levant, indicated by thick halite deposition triggered by a lake-level drop. Halite deposition was interrupted however, during the MIS5e peak (∼128–122 ka) by sequences of flood deposits, which are coeval with the timing of the intense precession-forced African monsoon that generated Mediterranean sapropel S5. A subsequent weakening of this humidity source triggered extreme aridity in the Dead Sea watershed and resulting in the biggest known lake level drawdown in its history, reflected by the deposition of thick salt layers, and a capping pebble layer corresponding to a hiatus at ∼116–110 ka. The DSDDP core provides the first evidence for a direct association of the African monsoon with mid subtropical latitude climate systems effecting the Dead Sea watershed. Combined with coeval deposition of Arabia and southern Negev speleothems, Arava travertines, and calcification of Red Sea corals, the evidence points to a climatically wet corridor that could have facilitated homo sapiens migration “out of Africa” during the MIS5e peak. The hyperaridity documented during MIS5e may provide an important analogue for future warming of arid regions of the Eastern Mediterranean–Levant

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

A continuous and high-resolution record of the radiocarbon reservoir age (RA) has been recovered from the primary aragonites that were deposited from the last glacial Lake Lisan. The RA is calculated as the difference between the measured 14C “apparent” age in the aragonite and the atmospheric age at any particular time. The RA shows temporal decreases during the time interval of ~28 to ~18 ka cal BP. This behavior is attributed to a continuous addition of low RA-high bicarbonate freshwater into the high RA-Ca-chloride (low bicarbonate) brine solution filling the lake. The mixing of the brine with freshwater drives the precipitation of CaCO3 in the form of aragonite from the lake epilimnion (surface layer). The runoff-brine mixture in Lake Lisan is also reflected by the Sr/Ca ratios that are positively correlated with the RA. Nevertheless, the 14C content in the epilimnion did not drop at the same rate as the atmospheric value but rather remained nearly constant. We suggest that turbulent mixing with the much saltier hypolimnion (lower layer) across the hypolimnion/epilimnion interface at a depth of about 390 m below sea level, buffered the 14C content as well as the Sr and Ca concentrations in the aragonite precipitating solution. The RA-Sr/Ca related limnological model developed here opens the way to determine the reservoir-age-corrected atmospheric ages of Lisan Formation aragonites beyond 28 ka cal BP

Calibration of the 14C time scale to >40 ka by 234U–230Th dating of Lake Lisan sediments (last glacial Dead Sea)

A new comparison of 14C dates with 234U-230Th ages is presented of aragonites from Lake Lisan, the last Glacial Dead Sea, between ∼20–52 cal-ka-BP. The Lisan data are coincident with the coral based 14C-calendar age calibration through the continuous portion of the curve to 23.5 cal-ka-BP, and with the additional ‘checkpoints’ at ∼30 and ∼40 cal-ka-BP. The agreement with the corals provides evidence for the accuracy of the U-Th and 14C ages, and indicates that Lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric 14C variations through this crucial time interval. The Lisan data are compared with other records older than 25 cal-ka-BP from Lake Suigetsu, Japan, North Atlantic foraminifera, South African cave deposits and tufa from Spain. Over some age intervals the records show broad agreement, over other intervals they diverge. All agree that 14C ages were ∼2.5±0.5 ka younger than calendar ages between 20–32 cal-ka-BP. For ages >32 cal-ka-BP, the Lake Suigetsu data indicate small differences between 14C ages and calendar ages of less than 1.5 ka. The other records broadly agree that 14C ages are too young by ∼3±1 ka from 32–39 cal-ka-BP. At ∼40 cal-ka-BP, the foraminifera show equal 14C and calendar ages, while the corals, Lisan aragonites and the Spanish tufa indicate a large age difference of 4–5 ka. A recent paleomagnetic study of the Lisan Formation indicates that the high calendar-14C age difference at ∼40 cal-ka-BP may be associated with the Laschamp paleomagnetic excursion

Medieval Climate in the Eastern Mediterranean: Instability and Evidence of Solar Forcing

This paper examines the hydroclimate history of the Eastern Mediterranean (EM) region during the 10th to 14th centuries C.E., a period known as the Medieval Climate Anomaly (MCA), a time of significant historical turmoil and change in the region. The study assembles several regional hydroclimatic archives, primarily the Dead Sea reconstructed lake level curve together with the recently extracted deep-lake sediment record, the Soreq Cave speleothem record and its counterpart, the EM marine sediment record and the Cairo Nilometer record of annual maximum summer flood levels in lower Egypt. The Dead Sea record is a primary indicator of the intensity of the EM cold-season storm activity while the Nilometer reflects the intensity of the late summer monsoon rains over Ethiopia. These two climate systems control the annual rainfall amounts and water availability in the two regional breadbaskets of old, in Mesopotamia and Egypt. The paleoclimate archives portray a variable MCA in both the Levant and the Ethiopian Highlands with an overall dry, early-medieval climate that turned wetter in the 12th century C.E. However, the paleoclimatic records are markedly punctuated by episodes of extreme aridity. In particular, the Dead Sea displays extreme low lake levels and significant salt deposits starting as early as the 9th century C.E. and ending in the late 11th century. The Nile summer flood levels were particularly low during the 10th and 11th centuries, as is also recorded in a large number of historical chronicles that described a large cluster of droughts that led to dire human strife associated with famine, pestilence and conflict. During that time droughts and cold spells also affected the northeastern Middle East, in Persia and Mesopotamia. Seeking an explanation for the pronounced aridity and human consequences across the entire EM, we note that the 10th–11th century events coincide with the medieval Oort Grand Solar Minimum, which came at the height of an interval of relatively high solar irradiance. Bringing together other tropical and Northern Hemisphere paleoclimatic evidence, we argue for the role of long-term variations in solar irradiance in shaping the early MCA in the EM and highlight their relevance to the present and near-term future

Freshwater on the route of hominids out of Africa revealed by U-Th in Red Sea corals

A fundamental issue in the evolution of human culture concerns the route and conditions of anatomically modern hominids during the migration out of Africa. A particular question is, how could anatomically modern hominids cross the hyperarid Arabian deserts? Here we outline the evidence for significant presence of freshwater along the Red Sea shores during the last interglacial period. Freshwater caused an extensive recrystallization of coral reefs from aragonite to calcite, indicating uplift of the reefs through well-developed phreatic freshwater coastal aquifers. Applying novel open-system U-Th dating methodology to the calcitic corals, we dated the freshwater recrystallization to ca. 140 ka, consistent with other geological lines of evidence placing the migration of anatomically modern hominids out of Africa at the onset of the last interglacial

Dead Sea lake level for the last 260 ka

The rain regime of the Levant during the late Quaternary was controlled primarily by Mediterranean cyclonic systems associated with North Atlantic climate shifts. Lake levels in the Dead Sea basin have been robust recorders of the regional hydrology and generally indicate highstand (wet) conditions throughout glacial intervals and lowstands (dry) during interglacials. However, sporadic deposition of travertines and speleothems occurred in the Negev Desert and Arava Valley during past interglacials, suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid-latitude Red Sea synoptic troughs and/or low-latitude tropical plumes. The southerly incursions of wetness were superimposed on the long-term interglacial Levantine arid conditions, as reflected by the current prevailing hyperaridity, and could have had an important impact on human migra- tion through the Red Sea-Dead Sea corridor

Primary carbonates and Ca-chloride brines as monitors of a paleo-hydrological regime in the Dead Sea basin

Lakes Samra, Lisan and the Dead Sea occupied the Dead Sea basin during the Last Interglacial (not, vert, similar140–75 ka BP), last glacial (not, vert, similar70–14 ka BP) and Holocene periods, respectively. The age of Lake Lisan and Samra was determined by U–Th dating of primary aragonites comprising parts of the lacustrine sedimentary sequences. The lakes have periodically deposited sequences of layered calcitic marls (Lake Samra) or laminated primary aragonite (Lake Lisan). The deposition of aragonite as the primary carbonate phase reflects the contribution of the incoming freshwater (loaded with bi-carbonate) and high Mg-, Ca-chloride brine that originated from the subsurface vicinity of the Dead Sea basin. Deposition of calcitic marls suggests a minor effect of the brines. The Ca-chloride subsurface brine has been migrating in and out of the wall rocks of the Dead Sea basin, reflecting the regional hydrological conditions. During most of the last glacial period and during the late Holocene, sufficient precipitation above the Judea Mountains pushed the subsurface Ca-chloride brines into the lakes causing the deposition of aragonite. During the Last Interglacial period the rain that precipitated above the Judea Mountains was insufficient to induce brine flow toward Lake Samra. It appears that sporadic floods provided calcium, bicarbonate and detritus to produce the Samra calcitic marls. Travertines deposited at the Samra–Lisan boundary indicate the early stage in the resumption of groundwater (springs) activity that led to the resurgence of Ca-chloride brine and rise of Lake Lisan. Similar variations in the regional rain precipitation and hydrological activity probably characterized the long-term geochemical evolution of Pleistocene lacustrine water-bodies in the Dead Sea basin, enabling the use of the carbonates as paleo-hydrological monitors