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      Holocene forest dynamics in central and western Mediterranean: periodicity, spatio-temporal patterns and climate influence

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          Abstract

          It is well-known that the Holocene exhibits a millennial-scale climate variability. However, its periodicity, spatio-temporal patterns and underlying processes are not fully deciphered yet. Here we focus on the central and western Mediterranean. We show that recurrent forest declines from the Gulf of Gaeta (central Tyrrhenian Sea) reveal a 1860-yr periodicity, consistent with a ca. 1800-yr climate fluctuation induced by large-scale changes in climate modes, linked to solar activity and/or AMOC intensity. We show that recurrent forest declines and dry events are also recorded in several pollen and palaeohydrological proxy-records in the south-central Mediterranean. We found coeval events also in several palaeohydrological records from the south-western Mediterranean, which however show generally wet climate conditions, indicating a spatio-temporal hydrological pattern opposite to the south-central Mediterranean and suggesting that different expressions of climate modes occurred in the two regions at the same time. We propose that these opposite hydroclimate regimes point to a complex interplay of the prevailing or predominant phases of NAO-like circulation, East Atlantic pattern, and extension and location of the North African anticyclone. At a larger geographical scale, displacements of the ITCZ, modulated by solar activity and/or AMOC intensity, may have also indirectly influenced the observed pattern.

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          North Atlantic climate variability: phenomena, impacts and mechanisms

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            North Atlantic oscillation influence on precipitation, river flow and water resources in the Iberian Peninsula

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              Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic.

              The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch ( approximately 11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity ( approximately 3.5 degrees C and approximately 1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes, although the inflow can compensate on decadal timescales by becoming more saline. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change.
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                Author and article information

                Contributors
                federico.dirita@uniroma1.it
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                12 June 2018
                12 June 2018
                2018
                : 8
                : 8929
                Affiliations
                [1 ]GRID grid.7841.a, Department of Environmental Biology, , Sapienza University of Rome, ; Piazzale Aldo Moro, 5, 00185 Roma, Italy
                [2 ]ISNI 0000000121662407, GRID grid.5379.8, Department of Geography, , School of Environment, Education and Development, The University of Manchester, ; Oxford Road, Manchester, M13 9PL UK
                [3 ]ISNI 0000000121671098, GRID grid.11480.3c, Department of Geography, Prehistory and Archaeology, , University of the Basque Country, ; C/Tomás y Valiente s/n, 01006 Vitoria-Gasteiz, Spain
                [4 ]ISNI 0000 0001 1940 4177, GRID grid.5326.2, Istituto per l’Ambiente Marino Costiero (IAMC), , Consiglio Nazionale delle Ricerche, Calata Porta di Massa, Interno Porto di Napoli, ; 80133 Napoli, Italy
                Author information
                http://orcid.org/0000-0001-8918-0690
                Article
                27056
                10.1038/s41598-018-27056-2
                5997640
                29895868
                0cd93c72-4229-4ac3-bfb5-6385e03e039e
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 23 January 2018
                : 25 May 2018
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