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- The climate of the Common Era off the Iberian PeninsulaPublication . Abrantes, Fatima; Rodrigues, Teresa; Rufino, Marta; Salgueiro, Emilia; Oliveira, Dulce; Gomes, Sandra; Oliveira, Paulo; Costa, Ana; Mil-Homens, Mario; Drago, Teresa; Naughton, FilipaThe Mediterranean region is a climate hot spot, sensitive not only to global warming but also to water availability. In this work we document major temperature and precipitation changes in the Iberian Peninsula and margin during the last 2000 years and propose an interplay of the North Atlantic internal variability with the three atmospheric circulation modes (ACMs), (North Atlantic Oscillation (NAO), east atlantic (EA) and Scandinavia (SCAND)) to explain the detected climate variability. We present reconstructions of sea surface temperature (SST derived from alkenones) and on-land precipitation (estimated from higher plant n-alkanes and pollen data) in sedimentary sequences recovered along the Iberian Margin between the south of Portugal (Algarve) and the northwest of Spain (Galiza) (36 to 42 degrees N). A clear long-term cooling trend, from 0 CE to the beginning of the 20th century, emerges in all SST records and is considered to be a reflection of the decrease in the Northern Hemisphere summer insolation that began after the Holocene optimum. Multi-decadal/centennial SST variability follows other records from Spain, Europe and the Northern Hemisphere. Warm SSTs throughout the first 1300 years encompass the Roman period (RP), the Dark Ages (DA) and the Medieval Climate Anomaly (MCA). A cooling initiated at 1300 CE leads to 4 centuries of colder SSTs contemporary with the Little Ice Age (LIA), while a climate warming at 1800 CE marks the beginning of the modern/Industrial Era. Novel results include two distinct phases in the MCA: an early period (900-1100 years) characterized by intense precipitation/flooding and warm winters but a cooler spring-fall season attributed to the interplay of internal oceanic variability with a positive phase in the three modes of atmospheric circulation (NAO, EA and SCAND). The late MCA is marked by cooler and relatively drier winters and a warmer spring-fall season consistent with a shift to a negative mode of the SCAND. The Industrial Era reveals a clear difference between the NW Iberia and the Algarve records. While off NW Iberia variability is low, the Algarve shows large-amplitude decadal variability with an inverse relationship between SST and river input. Such conditions suggest a shift in the EA mode, from negative between 1900 and 1970 CE to positive after 1970, while NAO and SCAND remain in a positive phase. The particularly noticeable rise in SST at the Algarve site by the mid-20th century (+/- 1970), provides evidence for a regional response to the ongoing climate warming. The reported findings have implications for decadal-scale predictions of future climate change in the Iberian Peninsula.
- The Late Pleistocene-Holocene sedimentary evolution of the Sines Contourite Drift (SW Portuguese Margin): A multiproxy approachPublication . Teixeira, Manuel; Terrinha, Pedro; Roque, Cristina; Voelker, Antje; Silva, Pedro; Salgueiro, Emilia; Abrantes, Fatima; Naughton, Filipa; Mena, Anxo; Ercilla, Gemma; Casas, DavidThe Sines Contourite Drift (SCD), located in the Alentejo margin, southwest Iberian continental margin, has been through many depositional phases in result of dimatic variations and bottom current oscillations, which determined a variable depositional pattern and an irregular sedimentary evolution since the Late Pleistocene. The SCD, being in the main path of the Mediterranean Outflow Water (MOW), which greatly constrains the sedimentary building of this drift, constitutes the distal part of the Gulf of Cadiz Contourite Depositional System and its sedimentary evolution therefore reflects the history of MOW variations. In order to investigate this, we report on a multiproxy analysis of grain-size, carbon content and physical, geochemical, and environmental-magnetic properties on the AMS C-14 dated 350-an long gravity core CO14-GC-07, retrieved in the SCD, at 1425 meters water depth (mwd). The main objective is to reconstruct the evolution of the sedimentary package of the SCD from >43 cal kyr BP to Present and bring new insights about the impact of bottom currents' activity on the morphosedimentary evolution of the margin. Results show the existence of four distinct depositional phases in response to climate variations and bottom current oscillations during the Late Pleistocene-Holocene. Phase 1 (350-322 cm: >42.9 cal kyr BP) occurred in Marine Isotope Stage (MIS) 3 and presents silty-muddy sediments with presence of shell fragments and moderate bioturbation. Phase 2 (322-176 cm: >42.9-similar to 30.5 cal kyr BP), which lasted from middle MIS 3 to the onset of MIS 2, reveals sediment coarsening towards the top limit, suggesting climate cooling and strong bottom current winnowing. Phase 3 (176-144 cm: similar to 30.5-17.1 cal kyr BP) covers most of MIS 2 prior to the last deglaciation and shows the sharpest variations on all sediment properties and the coarsest sediment facies, with Fe-rich layers associated with the increase of lerrigenous input and sea-level regression that coincide with the enhancement of MOW. Phase 4 (144-0 cm: <17.1 cal kyr BP) is associated with the degladal sea-level rise and represents a calmer depositional environment with finer sediments and increasing contributions of biogenic material. The MOW is the most prominent bottom current and the most active seabed shaping agent in the study area, whose vertical shifting during glacial (similar to 800-2200 mwd) and interglacial (600-1500 mwd) periods is coincident with the most active morphosedimentary sector of the area, contributing to the development of landslide scars and sediment waves. (C) 2020 Elsevier B.V. All rights reserved.
- Climate changes in south western Iberia and Mediterranean Outflow variations during two contrasting cycles of the last 1 Myrs: MIS 31-MIS 30 and MIS 12-MIS 11Publication . Goni, Maria F. Sanchez; Llave, E.; Oliveira, D.; Naughton, F.; Desprat, S.; Ducassou, E.; Hodell, D. A.; Hernandez-Molina, Francisco J.Grain size analysis and physical properties of Sites U1388, U1389 and TJ1390 collected in the Contourite Depositional System of the Gulf of Cadiz during the Integrated Ocean Drilling Program (IODP) Expedition 339 "Mediterranean Outflow" reveal relative changes in bottom current strength, a tracer of the dynamics of the Mediterranean Outflow Water (MOW), before and after the Middle Pleistocene Transition (MPT). The comparison of MOW behavior with climate changes identified by the pollen analysis and 8180 benthic foraminifera measurements of Site U1385, the Shackleton Site, collected in the south western Iberian margin shows that the interval MIS 31-MIS 30,similar to 1.1-1.05 million years ago (Ma), before the MPT, was marked by wetter climate and weaker bottom current than the interval MIS 12-MIS 11 (0.47-0.39 Ma), after the MPT. Similarly, the increase in fine particles from these glacials to interglacials and in coarse fraction from interglacials to glacials was coeval with forest and semi-desert expansions, respectively, indicating the lowering/enhancement of MOW strength during periods of regional increase/decrease of moisture. While these findings may not necessarily apply to all glacial/interglacial cycles, they nonetheless serve as excellent supporting examples of the hypothesis that aridification can serve as a good tracer for MOW intensity. The strongest regional aridity during MIS 12 coincides with a remarkable increase of coarse grain size deposition and distribution that we interpret as a maximum in MOW strength. This MOW intensification may have pre-conditioned the North Atlantic by increasing salinity, thereby triggering the strong resumption of the Meridional Overturning Circulation that could contribute to the great warmth that characterizes the MIS 11c super-interglacial. (C) 2015 Elsevier B.V. All rights reserved.
- The timing of the deglaciation in the Atlantic Iberian mountains: Insights from the stratigraphic analysis of a lake sequence in Serra da Estrela (Portugal)Publication . Hernández, Armand; Sáez, Alberto; Santos, Ricardo N.; Rodrigues, Teresa; Martin‐Puertas, Celia; Gil‐Romera, Graciela; Abbott, Mark; Carballeira, Rafael; Costa, Pedro; Giralt, Santiago; Gomes, Sandra D.; Griffore, Melissa; Ibañez‐Insa, Jordi; Leira, Manel; Moreno, João; Naughton, Filipa; Oliveira, Dulce; Raposeiro, Pedro M.; Trigo, Ricardo M.; Vieira, Gonçalo; Ramos, Alexandre M.Understanding the environmental response to the last glacial termination in regions located in transitional climate zones such as the Atlantic Iberian mountains is crucial to estimate potential changes in regions affected by current glacial melting. We present an 8.5 m-long, solid last deglaciation and Holocene chronostratigraphic record including detailed sediment analysis from Lake Peixao, a pro-glacial lake in the Serra da Estrela (Central Portugal). The age-depth model relies on a Bayesian approach that includes 16 AMS C-14 dates and Pb-210-(CS)-C-137 measurements, robustly dating the lake formation at 14.7 +/- 0.32 cal. ka BP. This chronological reconstruction shows an average sedimentation rate of ca. 0.07 cm yr(-1) (15 yr cm(-1)), enabling proxy analyses at decadal timescales. The sediment sequence is composed of five lithological units: (U1) coarse and unsorted fluvioglacial lacustrine deposits; (U2) massive fluvioglacial lacustrine deposits (863-790 cm below surface [bsf]; 14.7 +/- 0.32-13.8 +/- 0.12 cal. ka BP); (U3) water current fluvioglacial lacustrine deposits (790-766 cm bsf; 13.8 +/- 0.12-12.9 +/- 0.29 cal. ka BP); (U4) laminated/banded lacustrine deposits characterized by terrigenous deposits from ice-covered lake periods and episodic events of ice and snow melting (766-752 cm bsf; 12.9 +/- 0.29-11.7 +/- 0.15 cal. ka BP); and (U5) massive muddy lacustrine deposits (752-0 cm bsf; 11.7 +/- 0.15 cal. ka BP-present). The occurrence of U2 to U4 deposits defines the transition from glacial cold (U1) to net warm postglacial conditions (U5). These climate transitions are marked by changes in sediments and the presence of very low sedimentation rate periods, possibly related to the Intra-Allerod Cold Period and the coldest phase of the Younger Dryas. Our results support the previously proposed timing of the retreat of the Serra da Estrela glaciers ca. 13.8 +/- 0.12 cal. ka BP. The robust chronology of Lake Peixao highlights the potential of Iberian pro-glacial lakes for dating deglaciation processes and will lead to unprecedented decadal-to-centennial timescale palaeoclimate reconstructions in this region since the last glacial-interglacial transition.
- Identifying imprints of externally derived dust and halogens in the sedimentary record of an Iberian alpine lake for the past ∼13,500 years – Lake Peixão, Serra da Estrela (Central Portugal)Publication . Moreno, J.; Ramos, A. M.; Raposeiro, P. M.; Santos, R. N.; Rodrigues, T.; Naughton, F.; Moreno, F.; Trigo, R. M.; Ibañez-Insa, J.; Ludwig, P.; Shi, X.; Hernández, A.Iberian lacustrine sediments are a valuable archive to document environmental changes since the last glacial termination, seen as key for anticipating future climate/environmental changes and their far-reaching implica -tions for generations to come. Herein, multi-proxy-based indicators of a mountain lake record from Serra da Estrela were used to reconstruct atmospheric (in)fluxes and associated climatic/environmental changes over the last similar to 13.5 ka. Depositions of long-range transported dust (likely from the Sahara) and halogens (primarily derived from seawater) were higher for the pre-Holocene, particularly in the late Bolling-Allerod-Younger Dryas period, compared to the Holocene. This synchronous increase could be related to a recognized dust-laden at-mosphere, along with the combined effect of (i) an earlier proposed effective transport of Sahara dust for higher latitudes during cold periods and (ii) the progressive Polar Front expansion southwards, with the amplification of halogen activation reactions in lower latitudes due to greater closeness to snow/sea ice (halide-laden) surfaces. Additionally, the orographic blocking of Serra da Estrela may have played a critical role in increasing precipi-tation of Atlantic origin at higher altitudes, with the presence of snow prompting physical and chemical processes involving halogen species. In the Late Holocene, the dust proxy records highlighted two periods of enhanced input to Lake Peixao, the first (similar to 3.5-2.7 ka BP) after the end of the last African Humid Period and the second, from the 19th century onwards, agreeing with the advent of commercial agriculture, and human contribution to land degradation and dust emission in the Sahara/Sahel region. The oceanic imprints throughout the Holocene matched well with North Atlantic rapid climatic changes that, in turn, coincided with ice-rafted debris or Bond events and other records of increased storminess for the European coasts. Positive parallel peaks in halogens were found in recent times, probably connected to fire extinction by halogenated alkanes and roadway de-icing.
- The complexity of millennial-scale variability in southwestern Europe during MIS 11Publication . Oliveira, Dulce; Desprat, Stephanie; Rodrigues, Teresa; Naughton, Filipa; Hodell, David; Trigo, Ricardo; Rufino, Marta; Lopes, Cristina; Abrantes, Fatima; Sanchez Goni, Maria FernandaClimatic variability of Marine Isotope Stage (MIS) 11 is examined using a new high-resolution direct land sea comparison from the SW Iberian margin Site U1385. This study, based on pollen and biomarker analyses, documents regional vegetation, terrestrial climate and sea surface temperature (SST) variability. Suborbital climate variability is revealed by a series of forest decline events suggesting repeated cooling and drying episodes in SW Iberia throughout MIS 11. Only the most severe events on land are coeval with SST decreases, under larger ice volume conditions. Our study shows that the diverse expression (magnitude, character and duration) of the millennial-scale cooling events in SW Europe relies on atmospheric and oceanic processes whose predominant role likely depends on baseline climate states. Repeated atmospheric shifts recalling the positive North Atlantic Oscillation mode, inducing dryness in SW Iberia without systematical SST changes, would prevail during low ice volume conditions. In contrast, disruption of the Atlantic meridional overturning circulation (AMOC), related to iceberg discharges, colder SST and increased hydrological regime, would be responsible for the coldest and driest episodes of prolonged duration in SW Europe. (C) 2016 University of Washington. Published by Elsevier Inc. All rights reserved.
- Pollen in marine sedimentary archives, a key for climate studies: the example of past warm periodsPublication . Desprat, Stephanie; Oliveira, Dulce; Naughton, Filipa; Sanchez Goni, Maria FernandaThe interglacials of the last 800,000 years are all warm periods comparable to the current interglacial, called the Holocene. However, their intensity, duration, variability and regional expression are different as the result of different astronomical and greenhouse gases forcing. The work presented here focuses on the regional expression of these interglacials in southwestern Europe, and it is based on recent studies using pollen from Iberian margin sedimentary sequences that enables a direct comparison of atmospheric and marine processes. This work highlights the diversity of these interglacials in southwestern Europe in terms of duration as well as vegetation and climatic variability, in particular in southwestern Iberia where changes in precipitation play an important role. This work additionally allows discussing mechanisms involved in glacial inception during orbital analogs of the current interglacial (i.e. marine isotopic stages 19c and 11c).
- Insights of Pb isotopic signature into the historical evolution and sources of Pb contamination in a sediment core of the southwestern Iberian Atlantic shelfPublication . Mil-Homens, Mario; Vale, Carlos; Brito, Pedro; Naughton, Filipa; Drago, Teresa; Raimundo, Joana; Anes, Barbara; Schmidt, Sabine; Caetano, MiguelStable Pb isotopic ratios and concentrations of Al, Cu and Pb were measured in a 5 m long sediment core (VC2B) retrieved at 96 m water depth in the southwestern Iberian Atlantic shelf. Five phases during the last 9.5 kyrs were identified, two of them (Roman Period and modern mining) marked by a decrease of Pb-206/Pb-207 ratios reflecting additional inputs of Pb derived from mining activities. The Roman Period was also characterized by high Pb-208/Pb-206 ratios suggesting the exploitation of the outcropping portion of the orebody intensely weathered when compared with the other formations later mined. The shift of Pb-208/Pb-206 ratios towards linearity took approximately 1.0 kyrs, which may mirror the time of environmental recovery from the impact of Roman mining activities. The application of a mixing model allowed the quantification of the contribution associated with anthropogenic mining activities to the shelf sediments. The maximum values of Pb contamination occurred in the 20th century. This study gives direct evidence of Pb and Cu exploitation over the last 2000 years. The stable Pb isotopic signatures point to legacy of mining activities that are still the prevailing metal source recorded in the southwestern Iberian Atlantic shelf sediments. (C) 2017 Elsevier B.V. All rights reserved.
- Pollen from the deep-sea: A breakthrough in the mystery of the ice agesPublication . Goni, Maria F. Sanchez; Desprat, Stephanie; Fletcher, William J.; Morales-Molino, Cesar; Naughton, Filipa; Oliveira, Dulce; Urrego, Dunia H.; Zorzi, CoraliePollen from deep-sea sedimentary sequences provides an integrated regional reconstruction of vegetation and climate (temperature, precipitation, and seasonality) on the adjacent continent. More importantly, the direct correlation of pollen, marine and ice indicators allows comparison of the atmospheric climatic changes that have affected the continent with the response of the Earth's other reservoirs, i.e., the oceans and cryosphere, without any chronological uncertainty. The study of long continuous pollen records from the European margin has revealed a changing and complex interplay between European climate, North Atlantic sea surface temperatures (SSTs), ice growth and decay, and high-and low-latitude forcing at orbital and millennial timescales. These records have shown that the amplitude of the last five terrestrial interglacials was similar above 40 degrees N, while below 40 degrees N their magnitude differed due to precession-modulated changes in seasonality and, particularly, winter precipitation. These records also showed that vegetation response was in dynamic equilibrium with rapid climate changes such as the Dangaard-Oeschger (D-O) cycles and Heinrich events, similar in magnitude and velocity to the ongoing global warming. However, the magnitude of the millennial-scale warming events of the last glacial period was regionally-specific. Precession seems to have imprinted regions below 40 degrees N while obliquity, which controls average annual temperature, probably mediated the impact of D-O warming events above 40 degrees N. A decoupling between high-and low-latitude climate was also observed within last glacial warm (Greenland interstadials) and cold phases (Greenland stadials). The synchronous response of western European vegetation/climate and eastern North Atlantic SSTs to D-O cycles was not a pervasive feature throughout the Quaternary. During periods of ice growth such as MIS 5a/4, MIS 11c/b and MIS 19c/b, repeated millennial-scale cold-air/warm-sea decoupling events occurred on the European margin superimposed to a long-term air-sea decoupling trend. Strong air-sea thermal contrasts promoted the production of water vapor that was then transported northward by the westerlies and fed ice sheets. This interaction between long-term and shorter timescale climatic variability may have amplified insolation decreases and thus explain the Ice Ages. This hypothesis should be tested by the integration of stochastic processes in Earth models of intermediate complexity.
- Footprint of roman and modern mining activities in a sediment core from the southwestern Iberian Atlantic shelfPublication . Mil-Homens, Mário; Vale, Carlos; Naughton, Filipa; Brito, Pedro; Drago, Teresa; Anes, Bárbara; Raimundo, Joana; Schmidt, Sabine; Caetano, MiguelA 5-m long sediment core (VC2B), retrieved in the Southwestem Iberian Atlantic shelf, at 96 m water depth, was used to assess major changes in climate and human activities during the last 9.7 kyrs. Analytical measurements included sedimentological (mean grain size, and the contents of sand, silt and day), geochemical (major, minor, trace and rare earth elements; REEs) and chronological (Pb-210 and C-14) parameters. Two episodes of increment of fine-grained particles, occurring at 3050 BCE and 1350 CE, suggest the retreat of the coast line to the present level and the beginning of a wetter phase associated with the "Little Ice Age". The North American Shale Composite (NASC)-normalized REE-pattern detected in the shelf is similar to that found in the Guadiana estuarine sediments. The possibility of this estuary as a contributor to the sediment load deposited in the adjacent coastal zone was indicated. Trace elements were significantly correlated with Al until 1850 CE, pointing that grain-size rules its distribution in sediments. The depth variation of As, Cu and Pb enrichment factors relative to background values shows two periods of intense human activity that can be mainly linked to mining: (i) across the Roman Period, marked by low enrichments; and (ii) starting on the second half of the 19th century until nowadays with significantly increased enrichments, especially of Pb and Cu. In addition to As, Cu and Pb, this period is also marked by high enrichments of Hg and Zn. Despite the decrease/closure of sulphide massive deposits mining exploitation (e.g., Sao Domingos, Las Herrerias) during the second half of the 20th century, results showed ongoing input of Pb,Cu, As, Hg and Zn to coastal sediments. Thus, the legacy of contamination by these elements, mainly from leaching of slags and tailings, and remobilization/reworking of contaminated estuarine sediments, is still recorded in marine sediments. (C) 2016 Elsevier B.V. All rights reserved.
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