Browsing by Author "Rodrigues, Teresa"
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- A 1-Ma record of sea surface temperature and extreme cooling events in the North Atlantic: A perspective from the Iberian MarginPublication . Rodrigues, Teresa; Alonso-Garcia, Montserrat; Hodell, D. A.; Rufino, MM; Naughton, F.; Grimalt, J. O.; H L Voelker, Antje; Abrantes, FatimaThe Iberian Margin is a sensitive area to track high and low latitude processes, and is a key location to understand major past climatic and oceanographic changes. Here we present new biomarker data from IODP Site U1385 ("Shackleton site") (1017-336 ka) that, when combined with existing data from Cores MD01-2443/4 (last 335 ka), allows us to assess the evolution of sea surface temperature (SST) and meltwater influx over the last 1 Ma at the Iberian Margin. Interglacial periods throughout the last 1 Ma show SST close to 20 degrees C, even during the so-called "luke-warm" interglacials that are marked by relatively low atmospheric CO2 concentrations. During glacial periods, extremely cold stadial events are recognized at the Iberian Margin, and are very likely related to meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. We subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials: 1) from 1017 to similar to 900 ka, only minor sporadic freshwater input occurred during deglaciations; 2) from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations, which results in abrupt deglacial SST shifts; 3) from 675 to 450 ka only a few, very short-lived events are recorded and seldom is there freshwater input at the Iberian Margin; 4) during the last 450 ka the extreme cold events occurred under full glacial conditions, with particularly severe events during MIS 6 and 8. We propose these mid -glacial events are associated with a strong discharges of European ice sheet (EIS). The fact that these extreme cold events do not coincide with deglaciations questions the role of European ice sheet discharges in triggering deglaciations. (C) 2017 Elsevier Ltd. All rights reserved.
- Combination of insolation and ice-sheet forcing drive enhanced humidity in northern subtropical regions during MIS 13Publication . Oliveira, Dulce; Desprat, Stéphanie; Yin, Qiuzhen; Rodrigues, Teresa; Naughton, Filipa; Trigo, Ricardo M.; Su, Qianqian; Grimalt, Joan O.; Alonso-Garcia, Montserrat; H L Voelker, Antje; Abrantes, Fatima; Sánchez Goñi, Maria FernandaMarine Isotope Stage (MIS) 13, similar to 533-478 ka, has received particular attention due to the unexpected enhancement of monsoon systems under a cool climate characterized by lower atmospheric CO2 and larger ice volume than many other interglacials. Key questions remain about its regional expression (intensity, climate variability, length), and underlying forcing factors, in particular at the mid-latitudes. Here we examine the SW Iberian vegetation, terrestrial climate and sea surface temperature (SST) variability during MIS 13 by combining pollen and biomarker data from IODP Site U1385 with climate-model experiments. We show, for the first time, that despite strong precessional forcing, MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model comparison reveal that MIS 13 orbitally driven SW Iberian climate and vegetation changes are modulated by the relatively strong ice-sheet forcing. We find that the Northern Hemisphere ice-sheets prescribed at the MIS 13 climate optimum reinforce the insolation effect by increasing the tree fraction and both winter and summer precipitation. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.
- Control mechanisms of primary productivity revealed by Calcareous Nannoplankton from marine isotope stages 12 to 9 at the Shackleton Site (IODP Site U1385)Publication . González‐Lanchas, A.; Flores, J.‐A.; Sierro, F. J.; Sánchez Goñi, M. F.; Rodrigues, Teresa; Ausín, B.; Oliveira, Dulce; Naughton, F.; Marino, M.; Maiorano, P.; Balestra, B.Nowadays, primary productivity variations at the SW Iberian Margin (IbM) are primarily controlled by wind-driven upwelling. Thus, major changes in atmospheric circulation and wind regimes between the Marine Isotope Stages (MIS) 12 and 9 could have driven substantial changes in phytoplankton productivity which remains poorly understood. We present a high-resolution calcareous nannofossil record from the Shackleton Site Integrated Ocean Discovery Program Site U1385 that allow the assessment of primary productivity and changing surface conditions on orbital and suborbital timescales over the SW IbM. These records are directly compared and integrated with terrestrial – Mediterranean forest pollen – and marine – benthic and planktic oxygen stable isotopes (δ18O), alkenone concentration [C37], Uk´37-Sea Surface Temperature and % C37:4 – proxy records from Site U1385. Our results indicate intra-interglacial increase in primary productivity together with intensification of the Azores anticyclonic high-pressure cell beyond the summer that suggests a two-phase upwelling behavior during the full interglacial MIS 11c (420–397ka), potentially drived by atmospheric NAO-like variability. Primary productivity is largely enhanced during the inception of glacial MIS 10 and the early MIS 10 (392–356ka), linked to intensified upwelling and associated processes during a period of strengthened atmospheric circulation. In agreement with the conditions observed during Heinrich events of the last glacial cycle, primary productivity reductions during abrupt cold episodes, including the Heinrich-type (Ht) events 4 to 1 (436, 392, 384 and 339ka) and the Terminations V and IV, seems to be the result of halocline formation induced by meltwater arrival, reducing the regional upward nutrient transference
- Coupled ocean and atmospheric changes during Greenland stadial 1 in southwestern EuropePublication . Naughton, F.; Costas, S.; Comes, S. D.; Desprat, S.; Rodrigues, Teresa; Goni, M. F. Sanchez; Renssen, H.; Trigo, R.; Bronk-Ramsey, C.; Oliveira, Dulce; Salgueiro, Emilia; Voelker, Antje H L; Abrantes, FatimaPaleoclimate reconstructions suggest that the complex variability within the Greenland stadial 1 (GS-1) over western Europe was governed by coupled ocean and atmospheric changes. However, few works from the North Atlantic mid-latitudes document both the GS-1 onset and its termination, which are often considered as single abrupt transition events. Here, we present a direct comparison between marine (alkenone-based sea surface temperatures) and terrestrial (pollen) data, at very high resolution (28 years mean), from the southwestern Iberian shelf record D13882. Our results reveal a rather complex climatic period with internally changing conditions. The GS-1 onset (GS-1a: 12890-12720 yr BP) is marked by a progressive cooling and drying GS-1b (12720-12390 yr BP) is the coldest and driest phase; GS-1c (12390-12030 yr BP) is marked by a progressive warming and increase in moisture conditions; GS-1 termination (GS-1d: 12030-11770 yr BP) is marked by rapid switches between cool wet, cold dry and cool wet conditions. Although hydroclimate response was very unsteady throughout the GS-1 and in particular during its termination phase, the persistence of an open temperate and Mediterranean forest in southwestern Iberia during the entire episode suggests that at least some moisture was delivered via the Westerlies. We propose coupled ocean and atmospheric mechanisms to reproduce these scenario. Changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) as well as variations in the North Atlantic sea-ice growth have favoured the displacement of the polar jet stream's latitudinal position and contributed to a complex spatial pattern and strength of the Westerlies across western Europe. (C) 2019 Elsevier Ltd. All rights reserved.
- delta O-18 and Mg/Ca thermometry in planktonic foraminifera: a multiproxy approach toward tracing oastal upwelling dynamicsPublication . Salgueiro, Emilia; H L Voelker, Antje; Martin, P. A.; Rodrigues, Teresa; Zuniga, D.; Frojan, M.; de la Granda, F.; Villacieros-Robineau, N.; Alonso-Perez, F.; Alberto, A.; Rebotim, A.; Gonzalez-Alvarez, R.; Castro, C. G.; Abrantes, FatimaPlanktonic foraminifera delta O-18 and Mg/Ca ratios are widely considered as a powerful proxy to reconstruct past seawater-column temperature. Due to the complex interpretation of planktonic foraminifera delta O-18 data in regard to past seawater temperatures, temperature determination based on the foraminifera shell Mg/Ca ratio is believed to be more accurate. Scarce Mg/Ca calibration data exists for coastal upwelling regions, resulting in incoherent results of past seawater reconstructions. The current study along the NW Iberia coastal upwelling system intends to define the best Mg/Ca temperature equation for the most representative species of this region (Neogloboquadrina incompta, Globigerina bulloides, and Globorotalia inflata). Seawater temperature from delta O-18 and Mg/Ca of these three planktonic foraminifera species was compared with the surface sediments alkenone derived SST and with the in situ temperatures measured at the depths where these foraminifera species currently live and calcify. The equations that better reflect each species calcification depth were selected as our regional equations for delta O-18 and Mg/Ca temperature reconstructions. The delta O-18-estimated temperatures for surface sediment specimens were comparable with in situ seawater-column temperature measurements, whereas the Mg/Ca derived temperatures seem to underestimate in situ values, in special for G. bulloides from samples affected by stronger coastal upwelling. The G. bulloides delta O-18 and Mg/Ca estimated temperatures from samples located offshore, further from coastal upwelling influence, are comparable to surface sediment alkenone derived temperatures. Our study shows that in upwelling areas, regional calibration of planktonic foraminifera Mg/Ca temperature equations is necessary for reliable interpretations of high-resolution past temperature variability in these important environments.
- Early Pleistocene calcareous nannofossil assemblages from the Gulf of Cadiz reveal glacial-interglacial and millennial-scale variabilityPublication . Trotta, Samanta; Marino, Maria; H L Voelker, Antje; Rodrigues, Teresa; Maiorano, Patrizia; Flores, José-Abel; Girone, Angela; Addante, Marina; Balestra, BarbaraCoccolithophore high resolution (300 years) quantitative analyses have been carried out on Early Pleistocene sediment samples from Integrated Ocean Drilling Program Site U1387 retrieved in the Gulf of Cadiz. The studied interval is well constrained by the delta 18O chronological frame and covers marine isotope stage (MIS) 48 to MIS 45, from 1465.9 ka to 1389.9 ka. The aim is to investigate paleoenvironmental changes during a poorly known interval of the "41 ky world" and understand how climate dynamics controlled coccolithophore abundance and variation at orbital up to millennial scale. Assemblage composition variation and Principal Component Analysis (PCA) indicate that temperature and nutrient availability are the main factors influencing coccolithophores. Precession forcing combined with hydrological and atmospheric dynamics affect changes in coccolithophore assemblage composition and abundance highlighting glacial-interglacial cycles and a millennial scale variability, which is more evident during glacials than during interglacials. Interglacial MIS 47 onset is more abrupt than MIS 45 inception in relation to a more prominent insolation maximum, which favors the sharp increase and highest abundance of warm water taxa in the early MIS 47. Short-term abundance peaks of C. pelagicus spp. pelagicus during glacials document polar-subpolar melting water influx into the Gulf of Cadiz and southward migration of the subpolar front during episodes of high volume ice-sheet in the north hemisphere and reduced Atlantic Meridional Overturning circulation. In late MIS 48 the lowest coccolithophore productivity, induced by colder and stratified surface waters, a terminal stadial has been inferred. Enhanced short-term glacial productivity is favored by higher mixing and nutrient content in surface water due to the strengthened westerly winds during symbolscript phases. This promotes arid condition and upwelling along the studied site. The interglacial short-term coccolithophore productivity increases are associated with insolation maxima and enhanced nutrients of land origin during more humid periods led by -NAO-like phases, which induce the southward position of the westerlies and higher precipitation in the Mediterranean region and North Africa, in agreement with the contemporary sapropel occurrences in Mediterranean Sea. Our data-set suggests a connection between climate dynamics in the Gulf of Cadiz and east of Gibraltar Strait during the Early Pleistocene as well as a relationship with the north hemisphere ice-sheet dynamics.
- The early–middle pleistocene transition in the gulf of Cadiz (NE Atlantic) – an interplay between subtropical gyre and extremely cold surface watersPublication . Mega, Aline; Rodrigues, Teresa; Salgueiro, Emilia; Padilha, Mária; Kuhnert, Henning; Voelker, AntjeBesides the shift in dominant orbital cyclicity depicted in paleoclimate proxy records, the Mid-Pleistocene Transition or Early-Middle Pleistocene Transition (EMPT) was linked to a change in the deep thermohaline circulation. Those changes contributed to more intense and longer-lasting glacial periods and cooler sea surface temperatures (SSTs) during glacials. Within the Atlantic Ocean, the Iberian Margin is considered a key location to study climatic variations influenced by both high- and low-latitude processes. In this study we focus on IODP Site U1387 on the southern Portuguese margin to reconstruct surface water circulation changes and related plankton foraminifera ecosystems during the interval of Marine Isotope Stage (MIS) 28 to MIS 18 (1006-750 ka). Our planktonic foraminifera assemblages and SST reconstructions (foraminifera assemblages and U-37(K ') alkenone index) demonstrate warm, relative stable SST conditions during much of the interval due to persistent influence of subtropical gyre waters as indicated by the tropical-subtropical and Azores Current-related foraminifera species and the periods with dominant sinistral coiling direction of the species Globorotalia truncatulinoides. Maximum interglacial SSTs were up to 2 degrees C warmer than at present in both summer and winter, with the exception of interglacial MIS 23 with SSTs similar to 1.5 degrees C colder than in the other interglacials. Subsequent to the respective glacial inception, the relatively warm conditions were periodically interrupted by millennial-scale extreme cold events when polar species Neogloboquadrina pachyderma became abundant (> 30 %), and the SSTs, reconstructed from the foraminifera assemblage data, dropped below 10 degrees C in summer and 5 degrees C in winter, although some of those values might be overestimated. The most pronounced event, considering the amplitude of cooling and duration, occurred between 870 and 864 ka, marking the terminal stadial event of the MIS 22-MIS 21 transition (Termination X). Extreme cold events, always associated with the incursion of subpolar waters into the Gulf of Cadiz, mark all the terminal stadial events from Terminations XII to IX and the millennial-scale variability during the transitions to full glacial conditions, although the duration of the cooling varied greatly. The extreme cooling was only possible through migration of the subarctic front into the lower mid-latitudes as a consequence of cooling and freshening in the higher latitudes and the associated extreme reduction in the Atlantic Meridional Overturning Circulation. The amplitude of cooling, duration, and frequency of subpolar water incursions during MIS 24 to MIS 22 stands out, providing further evidence for the "900 ka event" being a key feature of the EMPT.
- High-frequency glacial climate instability during the early pleistocene: insights from IODP site U1387 (Gulf of Cadiz)Publication . Trotta, Samanta; Duque Castaño, Monica Liliana; Rodrigues, Teresa; Voelker, Antje; Maiorano, Patrizia; Balestra, Barbara; Flores, José-Abel; Siniscalchi, Agata; Addante, Marina; Marino, MariaWe provide new high-resolution data on alkenone-derived sea surface temperature (SST) and calcareous plankton key taxa in temporally well constrained, high resolution benthic and planktonic oxygen isotope records at Integrated Ocean Drilling Program site U1387 in the Gulf of Cadiz. The investigated time interval encompasses the Early Pleistocene marine isotope stages (MIS) 48 to MIS 43. The aim is to evidence millennial climate variability during glacial phases of the “41 kyr world” and understand the impact of North Atlantic climate dynamics on the southern Portuguese margin. Neogloboquadrina pachyderma and Coccolithus pelagicus ssp. pelagicus record prominent, short-term abundance peaks concurrent with short-term SST minima and heavier values of ™18O in late MIS 48 and in the middle of MIS 46 and MIS 44. Superimposed on the obliquity and precession forcing, the wavelet analysis carried out on selected proxies (planktonic ™18O, N. pachyderma, C. pelagicus ssp. pelagicus, alkenone derived sea surface temperature) highlighted the occurrence of a higher frequency climate variability.
- Leaf wax biomarkers of a high-mountain lake area in western iberia—Implications for environmental reconstructionsPublication . Santos, Ricardo N.; Schefuß, Enno; Cordeiro, Lívia; Oliveira, Dulce; Hernández, Armand; Ramos, Alexandre M.; Rodrigues, TeresaLeaf wax n-alkane biomarkers are widely used to infer past vegetation dynamics and hydroclimate changes. The use of these compounds strongly relies on the characterization of modern plants. However, few studies have explored leaf waxes of modern plants and their application to reconstructing climate and environmental changes in the Iberian Peninsula, a region known for its high vulnerability to climate change. In this study, we characterize the distributions and compound-specific isotopic compositions of the leaf waxes of dominant plants in the vegetation cover, soil, and surface sediment of the Lake Peixao area, a high-mountain glacial lake in Serra da Estrela (central Portugal). Our results show that the modern oro-Mediterranean (subalpine) vegetation of the study area is dominated by C-3 grasses/herbs and shrubs that preferentially produce long-chain leaf waxes (& GE;C-27). The C-31 n-alkane display the overall highest concentration, produced by some grasses and shrubs, but especially Erica sp (heather), which is highlighted as a major source for the total n-alkane pool in the lake sediments. C-29 is the second-most abundant and the most equally produced n-alkane of the vegetation cover; C-25 and C-27 homologs are mainly associated with aquatic-related grasses/herbs, while C-33 and C-35 are particularly linked to cold-drought tolerant Juniperus sp. shrubs. Shrubs show higher but proportional values than grasses/herbs in the isotopic space, suggesting a directly proportional physiological adaptation of the two ecological forms to the prevailing climatic and environmental factors of the study area. C-29 is pointed as the most representative (or less plant-biased) leaf wax n-alkane in the lake sediments. Thus, delta D of C-29 n-alkane is interpreted as a robust terrestrial hydrological indicator (delta D-terr), which signal is believed to be strongly influenced by the mean air temperature and/or precipitation amount. Despite the sparse vegetation and small catchment area, the apparent hydrogen fractionation factor, determined from delta D-terr of the lake surface sediment, is in line with the modeled global mean values for the latitude of the study area. The different molecular and compound-specific signatures of the studied oro-Mediterranean species have the potential to support future interpretations of leaf wax biomarkers in the Iberian Peninsula.
- Marine Isotope Stage 4 (71–57 ka) on the Western European margin: insights to the drainage and dynamics of the Western European Ice SheetPublication . Toucanne, Samuel; Rodrigues, Teresa; Menot, Guillemette; Soulet, Guillaume; Cheron, Sandrine; Billy, Isabelle; Eynaud, Frederique; Antoine, Pierre; Sinninghe Damste, Jaap S.; Bard, Edouard; Sanchez Goñi, Maria-FernandaMarine Isotope Stage (MIS) 4 (ca. 71–57 ka; within the Middle Weichselian Substage) is considered a significant Pleistocene glaciation, but it remains poorly constrained in comparison to that of the Late Weichselian Last Glacial Maximum (LGM; ca. 29–19 ka, during MIS 2), or even the Late Saalian MIS 6 (ca. 190–130 ka). Most MIS 4 glacial landforms in Europe were erased by the more extensive LGM ice advance, precluding a robust recon struction of its extent and dynamic through time. Marine sedimentary archives, in preserving the source-to-sink sediment transfer signals of ice-sheet and glacier processes, help to bridge this gap. Here, the signals west of the European Ice Sheet (EIS) are tracked for MIS 4 from the deep Bay of Biscay (NE Atlantic), which was the outlet for Fennoscandian Ice Sheet (FIS) sediment-laden meltwater during extensive glaciations, specifically when the British-Irish Ice Sheet (BIIS) and the FIS coalesced into the North Sea (as during MIS 6 and the LGM). Sedi mentological, geochemical, and mineralogical proxies reveal the absence of FIS-derived material in Bay of Biscay sediment throughout MIS 4, which indicates that FIS meltwater and huge river systems from the North European Plain never drained into the Bay of Biscay at that time. This suggests that contrary to MIS 6 and the LGM, the BIIS and FIS were not likely large enough to coalesce and form a (grounded) ice bridge onto the North Sea, thus confirming geomorphic evidence for a significant, but relatively limited, glaciation in Europe during MIS 4. Closer to the Bay of Biscay, ice-marginal fluctuations of the BIIS are identified in the Celtic-Irish Sea region from the deep-sea record. More specifically, our findings suggest an early retreat of the Irish Sea Ice Stream as soon as ca. 68–65 ka, a few millennia before the demise of the EIS, and the Northern Hemisphere ice sheets as a whole, during Heinrich Stadial (HS) 6. This pattern is similar to that already recorded during MIS 2. Finally, this study reveals that the MIS 4 period in Western Europe corresponds, as for MIS 2, to a complex combination of general ice advance interspersed by preliminary-to-final EIS demises highlighted by HS conditions.
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