Relationship between thermohaline and biochemical patterns in the levantine upper and intermediate water masses, Southeastern Mediterranean Sea (2013–2021)

The relationships between the interannual variations of the Levantine intermediate water (LIW) core properties and the corresponding biochemical variations in the euphotic zone were systematically studied in the Southeastern Mediterranean during 2013–2021 and since 2002 based on a previous study. Salinity and temperature interannual fluctuations in the LIW continue to follow the Adriatic–Ionian Bimodal Oscillating System (BiOS) mechanism, with salinity and temperature peaks in the years 2008–2010, 2014–2015, and 2018–2019 coinciding with periods of anticyclonic circulation of the North Ionian Gyre (NIG). During these anticyclonic periods, the transport of Atlantic Water into the Levant is reduced together with the transport of LIW out of the basin. These interannual fluctuations are superimposed on a long-term warming trend clearly evident from previous studies, showing a maximal temperature in 2018–2019, higher than the previously mentioned temperature peaks by ~0.7°C and ~0.4°C. The enhanced warming in 2018–2019 has caused a decrease in density (sigma) values of the LIW core, which gave way to the shallowest record of this water mass (~110-m depth), bringing it well within the lower photic zone. We suggest that a higher level of nutrients became available, supporting the observed long-term rise of the intergraded chlorophyll a (Chl.a) (0.89 mg m−2 year−1), with a maximum recorded during 2018–2019. The long-term record of the mixed layer depths shows no significant change; thus, the uplift of nutrients during winter mixing cannot support the trend and variations of the integrated Chl.a. Additional biological parameters of specific pico-phytoplankton populations and integrated bacterial production and abundance were measured in 2013–2021, but the measurements were too sparse to follow a clear interannual dynamics. Yet significantly higher average levels for integrated primary production and bacterial abundances were observed during the anticyclonic period (as for Chl.a). The combined impacts of the BiOS mechanism and global warming, and hence the increase in LIW residence time and buoyancy, may impact the primary producers’ biomass at the photic zone. This latter feedback may slightly counter the enhanced oligotrophication due to enhanced stratification

Strontium and Oxygen Isotope Analyses Reveal Late Cretaceous Shark Teeth in Iron Age Strata in the Southern Levant

Skeletal remains in archaeological strata are often assumed to be of similar ages. Here we show that combined Sr and O isotope analyses can serve as a powerful tool for assessing fish provenance and even for identifying fossil fish teeth in archaeological contexts. For this purpose, we established a reference Sr and O isotope dataset of extant fish teeth from major water bodies in the Southern Levant. Fossil shark teeth were identified within Iron Age cultural layers dating to 8–9th century BCE in the City of David, Jerusalem, although the reason for their presence remains unclear. Their enameloid 87Sr/86Sr and δ18OPO4 values [0.7075 ± 0.0001 (1 SD, n = 7) and 19.6 ± 0.9‰ (1 SD, n = 6), respectively], are both much lower than values typical for modern marine sharks from the Mediterranean Sea [0.7092 and 22.5–24.6‰ (n = 2), respectively]. The sharks’ 87Sr/86Sr are also lower than those of rain- and groundwater as well as the main soil types in central Israel (≥0.7079). This indicates that these fossil sharks incorporated Sr (87Sr/86Sr ≈ 0.7075) from a marine habitat with values typical for Late Cretaceous seawater. This scenario is in line with the low shark enameloid δ18OPO4 values reflecting tooth formation in the warm tropical seawater of the Tethys Ocean. Age estimates using 87Sr/86Sr stratigraphy place these fossil shark teeth at around 80-million-years-old. This was further supported by their taxonomy and the high dentine apatite crystallinity, low organic carbon, high U and Nd contents, characteristics that are typical for fossil specimens, and different from those of archaeological Gilthead seabream (Sparus aurata) teeth from the same cultural layers and another Chalcolithic site (Gilat). Chalcolithic and Iron Age seabream enameloid has seawater-like 87Sr/86Sr of 0.7091 ± 0.0001 (1 SD, n = 6), as expected for modern marine fish. Fossil shark and archaeological Gilthead seabream teeth both preserve original, distinct enameloid 87Sr/86Sr and δ18OPO4 signatures reflecting their different aquatic habitats. Fifty percent of the analysed Gilthead seabream teeth derive from hypersaline seawater, indicating that these seabreams were exported from the hypersaline Bardawil Lagoon in Sinai (Egypt) to the Southern Levant since the Iron Age period and possibly even earlier

Assessing vermetid reefs as indicators of past sea levels in the Mediterranean

The endemic Mediterranean reef building vermetid gastropods Dendropoma petraeum complex (Dendropoma spp) and Vermetus triquetrus develop bio-constructions (rims) on rocky shorelines at about Mean Sea Level (MSL) and are therefore commonly used as relative sea-level (RSL) markers. In this study, we use elevations and age data of vermetid reefs to (1) re-assess the vertical uncertainties of these biological RSL indicators, and (2) evaluate the vertical growth rates along a Mediterranean east-west transect, in attempt to explain the differences found in both growth rates and uncertainties. In Israel, Differential Global Positioning System (DGPS) and laser measurements relative to the local datum show that the reef surfaces mainly occupy the upper intertidal zone with variations in elevation from +0.51 ± 0.07 m to +0.13 ± 0.05 m along the coast. However, in specific sites the vertical uncertainty exceeds the tidal range. In some places the local vermetid species D. anguliferum and V. triquetrus appear to alternate along the vertical rim profiles. This study documents a spatial variability of vertical growth rates, ranging from ~1 mm yr−1 in Israel and Crete, to ~0.1–0.2 mm yr−1 in NW Sicily and Spain. The order of magnitude of the difference in growth rates correlates with the east-west spatial thermal gradient of Sea-Surface Temperature (SST). Preferential skeleton deposition of D. petraeum and V. triquetrus measured by growth axis δ18O analysis shows that most calcification occurs at SST above the mean annual value. These findings indicate that vermetid reefs are a site-specific RSL indicator, displaying various vertical uncertainties and inner-structure complexities. Local data on the indicative range of vermetids are required when reconstructing relative sea-level changes using fossil vermetids

Seasonal patterns of coccolithophores in the ultra-oligotrophic South-East Levantine Basin, Eastern Mediterranean Sea

Coccolithophore seasonality was examined in the southeastern Mediterranean Sea, both at the edge of the coastal shelf and in the open sea offshore Israel during 2018–2019. Oceanographic conditions varied seasonally between markedly stratified and ultra-oligotrophic from April to September and water column-mixing with relatively higher nitrate levels from October to February. Coccolithophores were quantified during the early (April), mid (July) and late (October) stratification period and in the mixing period (January). During stratification, cell densities progressively declined to <1.5 × 104 cells L−1, while both diversity and vertical differentiation of communities markedly increased. Emiliania huxleyi, Umbellosphaera spp., Syracosphaeraceae and Rhabdosphaeraceae as well as holococcolithophores were prevalent in the upper and mid-water layers. Florisphaera profunda characterized deeper sub-euphotic layers. During winter, mixing eroded the vertical zonation of species and coccolithophore density increased up to ~3.5 × 104 cells L−1. Communities became largely dominated by E. huxleyi, coincident with higher nutrient availability. The observed composition of coccolithophore assemblages and succession patterns support previous descriptions that the eastern Mediterranean largely resembles oceanic gyre systems. At the shelf station, the presence of higher fractions of r-selected species, and the rarity of oligotrophic coccolithophores (namely Umbellosphaera irregularis and holococcolithophores), suggest a somewhat greater influence of nutrients towards the shore. Finally, cells from different life-cycle phases were identified for a variety of species, highlighting the clear ecological divergence between coccolithophore life-phases. These data represent important baseline values for this area of the global ocean which is affected by major climate and environmental changes

Eastern Mediterranean sea levels through the last interglacial from a coastal-marine sequence in northern Israel

A last interglacial (Marine Isotope Stage, MIS5e) marine-coastal sequence has been identified along the Galilee coast of Israel, with the type section located at Rosh Hanikra (RH). The microtidal regime and tectonic stability, along with the detailed stratigraphy of the RH shore, make the study region ideally suited for determining relative sea level (RSL) through the MIS5e interval in the eastern Mediterranean. The sequence contains fossilized microtidal subunits at a few meters above the current sea level. Unfortunately, all fossils were found to be altered, so that U-Th datings cannot be considered to represent initial deposition. We contend that U-Th dating of Strombus bubonius shells (recrystallized to calcite) suffices to indicate a lower limit of ?110 ± 8 ka for the time sea level dropped below the RH sedimentary sequence. The RH-section comprises three main subunits of a previously determined member (the Yasaf Member): (a) a gravelly unit containing the diagnostic gastropod Strombus bubonius Lamarck (Persististrombus latus), which was deposited in the intertidal to super-tidal stormy zone; (b) Vermetidae reef domes indicating a shallow-water depositional environment; and (c) coarse to medium-sized, bioclastic sandstone, probably deposited in the shallow sub-tidal zone. The sequence overlies three abrasion platforms that are cut by tidal channels at elevations of +0.8 m, +2.6 m and +3.4 m, and which are filled with MIS5e sediments. We present a detailed study of the sequence, with emphasis on stratigraphic, sedimentological, and palaeontological characteristics that indicate sea-level changes. Although without precise absolute dating, the stratigraphic sequence of RH through MIS5e allows us to identify a time-series of RSL positions, using the elevations of three stratigraphic subunits. Reconstructed RSL values range from +1.0 m to +7 m (with uncertainly < 1 m), and most fall within a narrow range of +1.0 to +3.3 m. Toward the end of MIS5e, RSL exceeded about +7 m. Glacial isostatic adjustment (GIA) modelling using multiple ice histories suggests that GIA corrections range between about ?1.8 m and +5.4 m. This implies that global mean sea level resided between ?0.8 m and +8.7 m during most of MIS5e. The absolute GIA correction would not be constant through the interglacial, and reduces to a range of ?1.2 m to+ 2.4 m towards the end of the interglacial