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Eastern Mediterranean hydroclimate reconstruction over the last 3600 years based on sedimentary n-alkanes, their carbon and hydrogen isotope composition and XRF data from the Gialova Lagoon, SW Greece
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Navarino Environmental Observatory (NEO), Greece.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
Vise andre og tillknytning
Rekke forfattare: 82018 (engelsk)Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 194, s. 77-93Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Understanding past hydroclimate variability and related drivers is essential to improve climate forecasting capabilities especially in areas with high climatic sensitivity, such as the Mediterranean. This can be achieved by using a broad spectrum of high resolution, multiple proxy records which can also allow us to assess linkages between regional hydroclimate variability and shifts in the large-scale atmospheric patterns. Here, we present a multiproxy reconstruction of the central-eastern Mediterranean hydro climate changes over the last 3600 years based on a sediment core from the Gialova Lagoon, a shallow coastal ecosystem in SW Peloponnese, Greece. Our combined dataset consists of the distribution and compound-specific carbon and hydrogen isotope (delta C-13 and 8D) composition of n-alkanes, bulk organic matter properties and X-ray fluorescence (XRF) core scanning data. This approach was complemented with a semi-quantitative analysis of plant remains in the core. The results indicate a high contribution of local aquatic vegetation to organic matter. Large delta C-13 variations in predominantly aquatic plant-derived mid-chain alkanes (C23-23) mainly reflect changes in the aquatic plant abundance and their carbon source. Our data suggest that higher delta C-13(23-25) values (up to 19 parts per thousand) largely correspond to expansion of aquatic vegetation during wet and/or cold periods causing carbon-limiting conditions in the water and assimilation of isotopically-enriched bicarbonate by the plants. The 8D records of the individual n-alkanes (C-17 to C-31) exhibit a nearly identical pattern to each other, which implies that they all reflect changes in the source water isotope composition, driven by hydroclimate variability. In addition, the 8D profiles are consistent with the XRF data with both proxies being driven by a common hydroclimate signal. We observe two major shifts from dry and/or warm periods at ca 3600-3000 cal BP and ca 17001300 cal BP to wet and/or cold episodes at ca 3000-2700 cal BP and ca 1300-900 cal BP. The period ca 700-200 cal BP is the wettest and/or coldest in our record and coeval with the Little Ice Age. The climatic fluctuation reported in this study can be explained by the relative dominance of high-latitude (e.g. North Atlantic Oscillation during winters) and the low-latitude atmospheric patterns (Intertropical convergence zone, Subtropical High and the effects of Asian monsoons during summers) which suggests an Atlantic-Mediterranean-Monsoon climate link in this area for the late Holocene.

sted, utgiver, år, opplag, sider
2018. Vol. 194, s. 77-93
Emneord [en]
n-alkanes, Biomarkers, Stable isotopes, Paleoclimate, Macrophytes, Late Holocene
HSV kategori
Forskningsprogram
naturgeografi
Identifikatorer
URN: urn:nbn:se:su:diva-160104DOI: 10.1016/j.quascirev.2018.07.008ISI: 000441487700007OAI: oai:DiVA.org:su-160104DiVA, id: diva2:1249499
Tilgjengelig fra: 2018-09-19 Laget: 2018-09-19 Sist oppdatert: 2019-04-25bibliografisk kontrollert
Inngår i avhandling
1. Holocene environmental changes and climate variability in the Eastern Mediterranean: Multiproxy sediment records from the Peloponnese peninsula, SW Greece
Åpne denne publikasjonen i ny fane eller vindu >>Holocene environmental changes and climate variability in the Eastern Mediterranean: Multiproxy sediment records from the Peloponnese peninsula, SW Greece
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: Department of Physical Geography, Stockholm University, 2019. s. 49
Serie
Dissertations in Physical Geography, ISSN 2003-2358 ; 2
Emneord
Mediterranean, Greece, Peloponnese, Holocene, sediments, diatoms, n-alkanes, stable isotopes, tectonics, climate variability, monsoons, NAO, NCP
HSV kategori
Forskningsprogram
naturgeografi
Identifikatorer
urn:nbn:se:su:diva-167747 (URN)978-91-7797-664-6 (ISBN)978-91-7797-665-3 (ISBN)
Disputas
2019-06-14, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2019-05-22 Laget: 2019-04-02 Sist oppdatert: 2019-05-23bibliografisk kontrollert

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