Multidisciplinary study Of Continental/ocean Climate dynamics using High-resolution records from the eastern mediterraneAn
Final Report Abstract
To obtain insight in the character of the causes and effects of high temporal resolution climatic variability in the eastern Mediterranean, we have investigated the organic-geochemical and marine palynological content of surface and down-core sediments from the Adriatic Sea and Gulf of Taranto. Organic-geochemical and palynological proxy calibration on surface sediments from the Po-river discharge plume and surrounding area reveal that the proxy results are highly dependent on the physical and climatical characteristics of the research area. The physical conditions are, in turn, strongly influenced by the extent and characteristics of the discharge waters of the Po-river and of eastern Italian river systems draining the Apennine Mountains as well as from weather induced changes in water column characteristics such as mixing of the upper water column and temperature changes. The dinoflagellate cyst association in surface sediments reflects both upper and bottom water conditions. Four specific associations can be distinguished that are characteristic for the major oceanographic settings in the region. (1) River discharge association (2) Warm water association (3) Oxygenated bottom water association and (4) Golfo di Taranto association. Core-top calibration of the lipid the UK’37 and TEX86 temperature proxies shows that the the UK’37 primarily reflects winter temperatures. Offshore, the TEX86 reflects summer temperatures whereas at near-coastal sites the TEX86 is low which is explained a by different timing of archaeal production due to particle-rich surface waters and prevailing higher nutrient contents (no oligotrophic conditions) and/or terrestrial input leading to a cold-biased TEX86 signal. The stable hydrogen and carbon isotopic composition of plant wax derived n-alkanes and their molecular distribution in terrestrial, coastal and offshore surface sediments shows a southward δD enrichment of plant waxes relative to the δD enrichment of precipitation. It reflect the more negative water balance in southern Italy compared to northern Italy. Regional differences in the δ 13C-δD of plant waxes enable quantification of plant wax supply from the N Adriatic Sea by the Western Adriatic Current to the offshore sediments of the Gulf of Manfredonia. South of this Gulf, plant waxes are largely delivered by regional sources. The establishment of detailed reconstructions of palaeoceanographic conditions in the Gulf of Manfredonia and Gulf of Taranto on tri-annual scale of the last 400 years based on dinoflagellate cyst associations reveals that previous to 1880 natural forcing factors dominantly influence the environmental conditions. Our studies imply that changes in precipitation and temperature have a cyclic character that can be related to solar insolation changes. Synchronous to the start of the industrial revolution in Italy around 1880, a combination of both natural and anthropogenic influences on the system have been reconstructed. Whereas total cyst production rates appear to reflect natural induced variability in river discharge, changes in the cyst association reflects agricultural development related changes in the trophic state of the upper waters. Increase in abundance of nutrient indicators Lingulodinium machaerophorum and Stelladinium stellatum around 1920 reflect the first chemical production and dispersion of ammonia in and throughout Europe. After 1955 increased abundances of these species as well as Polykrikos schwarzii, Brigantedinium spp. and Pentapharsodinium dalei correspond to agricultural induced change to hypotrophic conditions. A slight improvement of the water quality can be observed rom 1987 onward. We also studied the changes in the lipid distribution and in the stable carbon and oxygen isotopic composition of foraminifera as recorded in the sediments of the Gulf of Taranto since 1500 AD. On the basis of the earlier regional proxy calibration studies and the associated careful evaluation of the ecology of the source organisms for the alkenone (UK'37), archaeal lipid (TEXH86 ) and planktic foraminifera (δ18O of G. ruber (white)) based SST proxies made we could now infer how changes in the atmospheric circulation pattern (e.g. NAO) influenced the stratification and coastal water-mass contribution and water balance in the region during the last 500 years. We show that during the Maunder Minimum seasonal contrast was stronger than during the remainder of the studied interval. At about 1880 AD a steady increase is inferred in eutrophication and terrestrial input (based on the BIT index, increasing concentrations of alkenones, crenarchaeol and n-alkanes as well as 13C of the benthic foraminifer U. mediterranea) in the coastal environment. These changes are attributed to an increasing human impact on the region. To obtain insight into character and potential forcing of short term climatic and oceanographic variability in the southern Italian region during the „Medieval Classical Period“ (MCP) (800-1200 AD) and “Roman Classical Period” (60 BC - 200 AD), detailed high temporal resolution climatic and environmental reconstructions based on a dinoflagelate cyst record from Gulf of Taranto cores located at the distal end of the Po-river discharge plume have been established. We show that reconstructed strong SST fluctuations characterised the Medieval Period. For this time interval mean SST is reconstructed to have been colder compared to that of last 100 years whereas for the Roman Warm Period slightly warmer temperatures are suggested. Both upper water temperature and precipitation related river discharge changes show a strong cyclic character in these time intervals. This can be related to changes in solar insolation. Apart from this several non-cyclic environmental changes are observed that can be subscribed to (global) volcanic activity in both time periods and wind-driven dust transport fluctuations in Medieval times. Our reconstructions of a relatively warm stable climatic in the „Roman Classical Period“ corresponds to times of the “Pax Romana”. Conflicts between Roman and neighbouring cultures became more frequently along with the subsequent Roman decline about 100 years after which we show the start of a cooling trend, suggesting that there might be a link between climate and the Roman history that is worth to be investigated in more detail in future.
Publications
- (2009). Environmental significance of dinoflagellate cysts from the proximal part of the Po-river discharge plume (off southern Italy, Eastern Mediterranean). Journal of Sea Research 62, 189-213
Zonneveld, K.A.F., Chen, L., Möbius, J. and Mahmoud, M.S.
- (2010). Core top calibration of the lipidbased UK’37 and TEX86 temperature proxies on the southern Italian shelf (SW Adriatic Sea, Gulf of Taranto). Earth and Planetary Science Letters 300, 112-124
Leider A., Hinrichs K.-U., Mollenhauer G. and Versteegh, G. J. M.
