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Climate changes in the Eastern Mediterranean over the last 5000 years and their links to the high-latitude atmospheric patterns and Asian monsoons
Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory (NEO), Greece.
Stockholm University, Faculty of Science, Department of Geological Sciences. Navarino Environmental Observatory (NEO), Greece.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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2019 (English)In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 175, p. 36-51Article in journal (Refereed) Published
Abstract [en]

This research aims to improve the knowledge of the mid to late Holocene climate changes and the underlying drivers in the eastern Mediterranean. We focus on the Peloponnese peninsula, SW Greece, characterized by a W-E rainfall/temperature gradient and a strong climate-sensitivity to shifts in the large-scale atmospheric patterns. A radiocarbon-dated sediment core, taken from the ancient Lake Lerna, a former lake in NE Peloponnese, was analyzed for distribution and hydrogen isotope (δD) composition of n-alkanes and bulk organic geochemistry (δ13C, TOC). The predominantly macrophyte (submerged/floating)-derived δD23 profile exhibits the largest long-term fluctuation in the record and co-varies with δD of long-chain n-alkanes providing evidence for precipitation and temperature changes over the last 5000 years. The Lerna δD23 signal is sometimes in agreement with other n-alkane δD records from SW Peloponnese indicating wetter conditions in the peninsula at ca 5000–4600, ca 4500–4100, ca 3000–2600 (more unstable in SW) and after ca 700 cal BP with drier periods at ca 4100–3900 and ca 1000–700 cal BP. Conversely, a NE-SW climate see-saw is revealed at ca 4600–4500, ca 3200, ca 2600–1800, and ca 1200–1000 cal BP when the δD23 Lerna exhibits more positive trends (drier in NE) with a reversal at ca 3900–3300, ca 3200–3000 and ca 1800–1300 cal BP. These opposing and sometimes similar signals between NE and SW Peloponnese can be explained by the relative dominance of high-latitude atmospheric patterns over the peninsula. A similar signal would be expected when the North Atlantic Oscillation (NAO) exerts the main control with NAO (+) creating conditions of reduced moisture. The dipole pattern is likely driven by shifts in North Sea–Caspian Atmospheric pattern (NCP), which account for the present-day regional climate variability with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The Asian monsoonal system likely has an additional impact on the δD variabilities through influencing the summer temperatures. There is a consistency between the Peloponnesian δD signals and monsoonal records after ca 4000 cal BP confirming the actualistic models. Strong monsoonal periods coincide with cooler summers (lower δD values) in Lerna, due to the northerly winds, the Etesians. On the contrary, SW Peloponnese is dominated by warmer conditions during the same periods as the area is located on the lee side of the mountain and highly influenced by the adiabatic warming associated with the subsidence over the Eastern Mediterranean.

Place, publisher, year, edition, pages
2019. Vol. 175, p. 36-51
Keywords [en]
Biomarkers, Hydrogen isotope, Paleoclimate, Holocene, Monsoons, NAO, NCP, Mediterranean
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-167739DOI: 10.1016/j.gloplacha.2019.02.001ISI: 000463982700004OAI: oai:DiVA.org:su-167739DiVA, id: diva2:1301643
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-04-29Bibliographically approved
In thesis
1. Holocene environmental changes and climate variability in the Eastern Mediterranean: Multiproxy sediment records from the Peloponnese peninsula, SW Greece
Open this publication in new window or tab >>Holocene environmental changes and climate variability in the Eastern Mediterranean: Multiproxy sediment records from the Peloponnese peninsula, SW Greece
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents multiproxy reconstructions of the mid to late Holocene climate and environmental changes in the Peloponnese peninsula, SW Greece. The combined dataset consists of diatom, biomarker and X-ray fluorescence spectrometry (XRF) elemental data in radiocarbon-dated sediment cores taken from the Agios Floros fen and the Gialova Lagoon in SW Peloponnese and the Ancient Lake Lerna in NE Peloponnese. Overall, the results highlight the complex interaction between climate, tectonics and human activities in the landscape development and further reveal changes in the W-E precipitation/temperature gradient over the peninsula connected to shifts in the large-scale atmospheric circulation patterns.

The Agios Floros study provides a 6000-year hydrological record based on diatoms and hydrogen isotopic (δD) analysis of aquatic plant-derived n-C23 alkanes. The records indicate two decadal-long periods of deep water conditions at ca 5700 and 5300 cal BP, largely attributed to local tectonic processes and the hydrological anomalies of the nearby karst springs. A period of intermediate water level at ca 4600 cal BP is dominated by the new fossil species Cyclotella paradistinguenda described in this thesis. The gradual development of a fen at ca 4500 cal BP is attributed to a combination of human activities and drier conditions, the latter culminating in SW Peloponnese mainly after ca 4100 cal BP. From ca 2800 cal BP and onwards, there is evidence for flooding events probably related to marked rainfall seasonality.

The n-alkane δD profiles and XRF data analyzed in the Gialova core co-vary with each other indicating a common climate signal during the last 3600 years, which resembles the Agios Floros record. The n-alkane δ13C values show high contribution of aquatic vegetation to sedimentary organic matter during wet/cold periods. The n-alkane δD signals from the Lake Lerna also exhibit a similar pattern to each other providing further evidence for precipitation/temperature changes over the last 5000 years.

Comparison of the δD records reveals sometimes similar and sometimes opposing signals between NE and SW Peloponnese, which can be attributed to the relative dominance of high latitude and low latitude atmospheric patterns over the peninsula. The records show wet conditions at ca 5000-4600 cal BP likely associated with the weakening of the Hadley circulation. High humidity is also evident at ca 4500-4100, ca 3000-2600 (more unstable in SW) and after ca 700 cal BP with drier conditions at ca 4100-3900 and ca 1000-700 cal BP. These periods correspond to regional climate changes, when the North Atlantic Oscillation (NAO) likely exerted the main control with NAO (+) creating conditions of reduced moisture. A NE-SW climate see-saw with drier conditions in NE Peloponnese is evident at ca 4600-4500, ca 3200, ca 2600-1800 and ca 1200-1000 cal BP and a reversal at ca 3900-3300 ca 3200-3000 and ca 1800-1300 cal BP. The dipole pattern is likely driven by shifts in the North Sea–Caspian Atmospheric pattern (NCP), with NCP (+) leading to wetter and colder conditions in NE Peloponnese. The opposing signal can also be explained by changes in summer temperatures driven by the Asian monsoon intensity. Strong monsoonal periods coincide with cool summers in Lerna, due to the northerly winds (Etesians), in contrast to SW Peloponnese, located on the lee side of the mountain and most affected by the large-scale air subsidence.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2019. p. 49
Series
Dissertations in Physical Geography, ISSN 2003-2358 ; 2
Keywords
Mediterranean, Greece, Peloponnese, Holocene, sediments, diatoms, n-alkanes, stable isotopes, tectonics, climate variability, monsoons, NAO, NCP
National Category
Climate Research
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-167747 (URN)978-91-7797-664-6 (ISBN)978-91-7797-665-3 (ISBN)
Public defence
2019-06-14, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
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Available from: 2019-05-22 Created: 2019-04-02 Last updated: 2019-05-23Bibliographically approved

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Katrantsiotis, ChristosNorström, ElinSmittenberg, Rienk H.Hättestrand, MartinaWastegård, Stefan
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