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Biomarker hydrogen isotope composition (D) as proxy for Holocene hydroclimatic change and seismic activity in SW Peloponnese, Greece
Stockholm University, Faculty of Science, Department of Geological Sciences. Navarino Environmental Observatory, Greece.
Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
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Number of Authors: 62018 (English)In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 33, no 5, p. 563-574Article in journal (Refereed) Published
Abstract [en]

We present a 6000-year-long record tracing hydroclimate changes in SW Greece, based on hydrogen isotope composition of aquatic plant-derived n-C-23 alkanes (D-C23) in a sediment core from the Messenian plain, Peloponnese. The D-C23 record co-varies with other eastern Mediterranean records, suggesting relatively wetter conditions c. 6-4.5ka, followed by progressively drier conditions leading up to maximum aridity c. 2.8 ka. This arid phase was interrupted by a shift in D-C23 between 3.3 and 3.1ka inferring wetter conditions and/or tentative responses to anthropogenic water regulating activities during the Late Bronze Age. After 2.7ka, a return to more humid conditions was followed by increased dryness and stronger seasonality contrasts from c. 2.0ka. The D-C23 record shows three short-lived excursions (5.7, 5.3, 2.8ka), where isotope values dropped by >20 parts per thousand and immediately stabilized again. The events were paralleled by abrupt increases in sedimentation rates. We hypothesize that the isotopic shifts represent a response to mixing of ground water systems during tectonic events, followed by sealing of seismically derived cracks in the active fault. The outcome of the study is promising for future expansion of isotope-based proxies on sediments in the region, to reconstruct both hydroclimate and past seismic activity.

Place, publisher, year, edition, pages
2018. Vol. 33, no 5, p. 563-574
Keywords [en]
biomarkers, n-alkanes, paleoclimate, Peloponnese, Greece, seismicity, stable hydrogen isotopes
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-158360DOI: 10.1002/jqs.3036ISI: 000437134000009OAI: oai:DiVA.org:su-158360DiVA, id: diva2:1238402
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2019-04-25Bibliographically 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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