Drought significantly affects the growth and physiological responses of Zagros forests, one of the most important natural habitats in Iran. The Brants oak (Quercus brantii Lindl), a widely distributed and dominant tree species in the Central Zagros Mountains of western Iran, serves as a valuable natural archive for studying historical climate variability and ecological changes. For climate-growth analysis, 30 Q. brantii trees cored from Lordegan area (1820 to 2280 m a.s.l.) in the southwest of Zagros forests of Iran. After preparing the samples, measuring the tree ring widths and cross-dating developed the tree ring chronology (1710-2023) using dplR. The relationships between tree-ring widths (TRW) and monthly mean temperature and precipitation values and the Standardized Precipitation Evapotranspiration Index (SPEI) were analyzed. The strongest climate signal of SPEI was found from previous September until April, representing the pre-growing and early-growing seasons. Among these reconstructions were acknowledged extremely narrow rings in 1870, 1923, 1960, 1964, and 2018, while extremely large rings were found in 1784, 1852, 1957, and 1976. Based on preliminary calculations showing a strong winter SPEI signal, this chronology could be used for climate reconstruction, but further analysis is required. These studies indicate the vulnerability of oak forests in the Zagros Mountains to ongoing climate change and a pressing need for sustainable forest management strategies to preserve these vital ecosystems.

 Keywords: Zagros forests, Iran, Quercus brantii, reconstruction, tree-ring widths

How to cite: Hatami, F., Klesse, S., Treydte, K., Verstege, A., Etemad, V., Pourtahmasi, K., Gessler, A., and Iranmanesh, Y.: Potential for a 300-year drought reconstruction in the Zagros Mountains, Iran based on the tree-ring width of Quercus brantii Lindl. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10067, https://doi.org/10.5194/egusphere-egu25-10067, 2025.

Powerful volcanic eruptions inject into the stratosphere sulphur and tephra that may be spread globally and affect the Earth’s climate. Over the last 2500 years, Sigl et al. (2015) made a synthesis of the polar ice core atmospheric sulphur record and climate anomalies from dendrochronological records. Aside from a few historical events, most large eruptions with a bipolar imprint and a significant climate anomaly are from the tropical latitudes, but their sources are unknown.

We analysed the micron-size crytotephra composition accompanying the (stratospheric) sulphate of the 1458 CE and 426 BCE volcanic events recorded in three Antarctic ice cores. The 1458 CE event occurred within a cool climate and was initially attributed to the Kuwae (Vanuatu) eruption. This link is however questioned by Hartman et al. (2019) from their study of a South Pole ice core. The 426 BCE event appears concomitant with a significant global climate cooling, but its source is unknown.

Within the sulphate peak, the particle size distribution, when available, helps documenting the dynamics of the arrival of the stratospheric plume. Cryptotephra are collected by filtration and after carbon-coating, analysed by an EPMA microprobe. We applied the analytical procedure of Narcisi et al. (2019) (who identified the 1257 CE Samalas eruption), adapted to the micron-size of the crytotephra.

For the 1458 CE event, a medium-K dacite to rhyolite composition is consistently observed from Vostok and Dome C ice core samples (218 values). The dacite patch (SiO2~68%) fits well the composition of proximal Kuwae deposits as well as that of an ash layer (~140 values) on Efate Island (Standberg et al, 2023). The rhyolite composition patch (SiO2~72%) is unlikely from a South American source, but appears discretely represented in proximal Kuwae deposits as well as in sediments in the nearby Epi Submarine zone. We suggest that rhyolite is a daughter product from dacite by evolving in the upper layers of the magmatic chamber, and it was spread out first and far away by the eruption.  

 For the 426 BCE event, the cryptotephra composition (220 values) is consistently found within the three ice cores (Vostok, Dome C, Talos Dome) and belongs to high-K rhyodacite. Coincidentally such composition is very close to Kuwae’s (except for higher K) suggesting it was issued from a very similar magmatic chamber. The 10 km wide Ambrym caldera located 50 km north of Kuwae, collapsed ~2000 years ago appears the best candidate. 

References

Hartman et al. (2019). Nature Sci. Rep. 9. https://doi.org/10.1038/s41598-019-50939-x.

Narcisi, B. et al., 2019. Quat. Sci. Rev. 210, 164-174 https://doi.org/10.1016/j.quascirev.2019.03.005.

Sigl, M., et al. Nature 523, 543–549 (2015). https://doi.org/10.1038/nature14565

Strandberg NA et al., (2023). Front. Ecol. Evol. 11: 1087577.doi: 10.3389/fevo.2023.1087577

How to cite: Petit, J.-R., Savarino, J., Delmonte, B., Gautier, E., Ginot, P., and Batanova, V.: Cryptotephra fingerprinting of 1458 CE and 426 BCE volcanic events in East Antarctic ice cores, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2329, https://doi.org/10.5194/egusphere-egu25-2329, 2025.

Aeolian mineral dust and diatom influxes at the summit of Roosevelt Island (79.364°S, 161.706°W, 550 m a.s.l.) were investigated over the last 2 kyrs from the RICE ice core (Bertler et al., 2018). Mineral dust at the site is mainly related to large-scale atmospheric circulation patterns within the Eastern Ross and Amundsen Seas, while aeolian diatoms, mainly consisting of Fragilariopsis spp. (F. nana , F. cylindrus, , F. curta), depend on the local oceanic influence of air masses from the marine boundary layer. Thus, the complementarity of these proxies allows appreciating climatic and atmospheric changes experienced at Roosevelt Island over the last 2000 years, in response to some major forcing factors such as ENSO. During the 550-1470 CE period, when higher/less depleted stable water isotope values are observed, the increased importance of blocking ridges in the Amundsen Sea and a weakened Amundsen Sea Low promoted dust-rich air mass advection to RICE. This pattern was accompanied by an increasing trend in snow accumulation and reduced sea ice in the Eastern Ross and Amundsen Seas. At about 1300 CE, the maximum expression of the Ross Sea dipole is reached, with enhanced katabatic outflow in the Western Ross Sea and reactivation of the Ross Sea polynya. At the same time,  the Eastern part of the Ross Sea was still under the influence of blocking ridges promoting maritime air mass advection to RICE and southward shift of the South Westerly Winds. After 1470 CE, unprecedented peaks of aeolian diatom concentration suggest a rapid reorganization of local atmospheric circulation, that probably occurred in relation to the eastward enlargement of the Ross Sea polynya culminating with the opening of the  Roosevelt Island polynya.
For the RICE site, we suggest that several drivers contribute to the long-term dust, sea-ice and polynya variability, but ENSO-driven teleconnections are particularly prominent. On a longer (multidecadal) timescale it seems that El Niño-dominating conditions promoted the establishment of the Ross Sea dipole, while La Niña conditions favored a deeper Amundsen Sea Low and an eastward expansion of the polynya. 

How to cite: Delmonte, B., Lagorio, S., Tetzner, D., Malinverno, E., and Bertler, N.: Aeolian dust and diatoms at Roosevelt Island (Ross Sea, Antarctica) over the last two millennia reveal the local expression of climate changes and the history of the Ross Sea polynya., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8574, https://doi.org/10.5194/egusphere-egu25-8574, 2025.

The Canary Islands, located in the central North Atlantic, provide an exceptional setting for investigating long-term climate dynamics within the Macaronesian region. This study presents sedimentary records from volcanic lacustrine basins across Tenerife, La Gomera and La Palma, analyzed using a multi-proxy approach including magnetic susceptibility, XRF geochemistry, elemental composition (TOC, TN, TS), mineralogy, lipid biomarkers, and updated age models. Preliminary age models suggest that the sequences of La Vega Lagunera (northern Tenerife) extend back up to 400,000 years, and El Malpaís de La Rasca (southern Tenerife), Garajonay (La Gomera), and Playa de Taburiente (La Palma) span the Holocene.
Preliminary results from La Vega Lagunera, a Pleistocene clastic lake, indicate colder conditions during MIS 2 and MIS 4, warmer conditions during the Holocene, MIS 3, and MIS 5, and millennial-scale cycles during MIS 3 and MIS 4. Climate during the Last Glacial Maximum (MIS 2) was notably drier, resembling mid-latitude records. 
Holocene records from paleolacustrine deposits of two closed-drainage basins located in two volcanic craters (La Gomera and Malpaís de La Rasca) and the lacustrine-marsh system of Playa de Taburiente showed coherent patterns of Holocene regional climate variability, with increased fluvial and alluvial activity during the Greenlandian (11.7 to 8.2 ka), a decline during the Northgrippian (8.2 to 4.2 ka), and reduced clastic input during the Meghalayan (last ~4.2 ka). These trends suggest increasing aridity throughout the Holocene. 
These new sedimentary sequences from Tenerife, La Gomera, and La Palma provide further evidence of rapid climate dynamics during glacial and interglacial intervals. Improved age models (OSL, 14C) are still being developed to characterize the cyclic patterns better, while multi-proxy analyses are enhancing our understanding of past climate dynamics. Further research is needed to clarify the roles of regional climate and local factors.
This work is supported by TED2021-129695A-I00 project funded by MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR; PALEOMOL (2915/2022) and IVRIPARC (2779/2021), both funded by the Spanish National Parks Organism, and IMPACT (2022CLISA04, Fundación CajaCanarias and Fundación La Caixa).

How to cite: Ocón-Bermúdez, C., Galofre-Penacho, M., Valero-Garcés, B., Armenteros-Armenteros, I., Herrera-Herrera, A., Égüez, N., Martín-Luis, M. C., Casillas Ruiz, R., Vegas, J., Castellano-Rotger, L., Diez-Herrero, A., Casado-Vara, R., and Jambrina-Enríquez, M.: A Multi-Proxy Approach to Reconstructing Long-Term Climate and Environmental Dynamics in the Canary Islands: Inter-Island Comparisons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12407, https://doi.org/10.5194/egusphere-egu25-12407, 2025.

The unique mass-occurrence of tiny heteromorph ammonites found in a single layer in the Mt. Cipollara locality of Cerreto d'Esi (Maiolica Formation, Umbro-Marchean Basin, Italy) provides critical insights into the depositional environments of the Cretaceous upper Maiolica Formation. The mechanisms behind the formation and preservation of these ammonite assemblages within black shales remain poorly understood. To solve this knowledge gap, we constrained by means of biostratigraphy and stable Carbon isotopes the whole sections hosting the ammonites-rich layer. The latter was then subjected a high-resolution paleoecological analyses. Samples were collected systematically across multiple stratigraphic levels to ensure comprehensive coverage. The ammonite assemblages were documented, focusing on their morphology, abundance, and associated sedimentary structures. Additionally, sedimentological petrographic examinations were conducted to elucidate depositional processes. Our results reveal a rich assemblage dominated by the family Leptoceratoididae, exhibiting relatively good preservation within a predominantly dysoxic low-energy environment at the bottom. Calcareous nannofossils data suggest the presence of a well-stratified water column, with a low salinity water cap. The multidisciplinary analyses indicates that these black shales served not only as a repository for ammonite remains but also reflected localized paleoecological conditions characterized by reduced turbulence and increased organic deposition. This unique sedimentary context suggests that the deposition of these assemblages could have been influenced by both regional sea-level fluctuations and local hydrographic conditions. In conclusion, the study of the Mt. Cipollara heteromorph ammonites underscores the complexity of Cretaceous paleoenvironments and provides an enhanced understanding of the occurrence of black shales within the Maiolica Formation.

How to cite: Conti, C., Faraoni, P., Mancini, A. M., Luca, M., and Negri, A.: Unusual mass-occurrence of small, uncoiled ammonites in a black shale of the Maiolica Formation in the Umbria-Marche Basin (Central Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3477, https://doi.org/10.5194/egusphere-egu25-3477, 2025.

Human-induced carbon emissions are altering the modern climate, with severe repercussions on ecosystems. Among others, anthropogenic pressure is causing deoxygenation of the bottom water, with the widespread establishment of hypoxic zones in several Mediterranean areas. The geological archives allow the investigation of past deoxygenation dynamics (sapropel events) and their impact on marine ecosystems. Here, we compare the causes and the evolution of deoxygenation dynamics that occurred during two different time periods (Messinian and Holocene) in different paleoceanographic settings based on their micropaleontological content. The Messinian sapropel events are the result of increased export productivity during a relatively cold and arid context, triggering bottom anoxic conditions. The Holocene sapropel formed in response to weakening/stopping of the thermohaline circulation due to increasing temperature and freshwater input. Our results suggest that the deoxygenation dynamics in the Mediterranean in the near future will not follow the trend characteristic of the Holocene deep-sea sapropel because of the predicted drying trend. Differently, the paleoceanographic setting triggering the Messinian shallow-sea sapropels is comparable with the modern situation in different Mediterranean areas, where human-induced eutrophication is promoting deoxygenation. Based on these results, we suggest that the patchy deoxygenation trend in the Mediterranean Sea caused by climate warming may lead to a drastic change in the ecosystem services which would likely impact human activities.

How to cite: Lozar, F., Mancini, A. M., Morigi, C., Gennari, R., and Negri, A.: Past analogues of deoxygenation events in the Mediterranean Sea: Comparison between shallow and deep settings , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15403, https://doi.org/10.5194/egusphere-egu25-15403, 2025.

Feedback mechanisms linked to ocean circulation, ice sheets, and the carbon cycle are key drivers of Quaternary climate variability, especially during glacial periods and transitions. These processes provide critical insights into potential future climate dynamics under ocean warming. This study focuses on two intervals: 410-490 ka (including MIS 12, ~428-468 ka) and 600-700 ka (among MIS 16, ~624-678 ka). We aim to investigate changes in ocean circulation during major glacial periods (MIS 12 and MIS 16) and explore the East-West thermal gradient in the subtropical Atlantic, and its impact on Subtropical Gyre (STG) dynamics within the broader context of global climate systems, by reconstructing sea surface temperatures (SSTs) for these key periods. Samples were taken from cores U1058B and U1058C (2984 meters below sea level) from Ocean Drilling Program (ODP) Site 1058 on the Blake Outer Ridge (BOR), under the strong influence of the Gulf Stream, affecting SSTs. A total of 185 samples were processed using alkenone-based analysis to reconstruct SSTs. Alkenones were extracted from 2.5-2.6 g of sediment, identified, and SSTs were reconstructed using the alkenone U^k'₃₇ index, applying the calibration equation of Müller et al. (1998). Our results reveal a significant SST decrease during the inception to the glacial (~23°C to ~18°C and ~23.5°C to ~19.5°C, at the onset of MIS 12 and MIS 16, respectively). The long term, SST variability displays a cyclicity of around 20-23 ka, with relatively warm/cold episodes that parallel changes in the precessional signal. The glacial-interglacial transitions (Termination V ~428 ka and VII ~624 ka) show contrasting signals: a rapid SST rise during Termination V (~18°C to ~22.5°C), driven by strong increase / maximum precession and obliquity signal, and a more gradual warming during Termination VII (~20°C to ~23.5°C), following obliquity signal. These findings provide valuable insights into Subtropical Gyre dynamics during MIS 12 and 16, enhancing our understanding of past ocean circulation.

This work, part of the Hydroshifts project (PTDC/CTA-CLI/4297/2021) funded by the Foundation for Science and Technology (FCT), used samples from ODP Expedition Leg 172.

How to cite: Martins, M., Rodrigues, T., and Naughton, F.: Glacial-Interglacial climate variability in the Subtropical Atlantic: Evidence from alkenone-based SST records at ODP Site 1058, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6258, https://doi.org/10.5194/egusphere-egu25-6258, 2025.