CIMAR Associated Laboratory

Porto, Portugal

CIMAR Associated Laboratory

Porto, Portugal
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Voelker A.H.L.,Instituto Portugues do Mar e da Atmosfera IPMA | Voelker A.H.L.,CIMAR Associated Laboratory | Colman A.,University of Chicago | Olack G.,University of Chicago | And 2 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 δ18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, δD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0-100m) and central (100-500m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5‰ for δ18O and 0 to 2‰ for δD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high δ18O (0.5-1.1‰) and δD (3-6‰) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (δ18O: -0.1 to 0.5‰ δD: -1 to 4‰) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed δ18O-salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0.46 described previously by Pierre et al. (1994, J. Mar. Syst. 5 (2), 159-170.) for the tropical to subtropical Northeast Atlantic. This slope decreases to 0.46 for the subtropical North Atlantic Central Water (NACW) and the MOW and to 0.32 for the surface waters of the upper 50m. The δD-salinity mixing lines have estimated slopes of 3.01 for the complete data, 1.26 for the MOW, 3.47 for the NACW, and 2.63 for the surface waters. The slopes of the δ18O-δD relationship are significantly lower than the one for the Global Meteoric Water Line with 5.6 for the complete data set, 2.30 for the MOW, 4.79 for the NACW, and 3.99 for the surface waters. The lower slopes in all the relationships clearly reflect the impact of the evaporation surplus in the subtropics. © 2015 Elsevier Ltd.

Bartels-Jonsdottir H.B.,National Laboratory of Energy and Geology | Bartels-Jonsdottir H.B.,University of Aarhus | Voelker A.H.L.,National Laboratory of Energy and Geology | Voelker A.H.L.,CIMAR Associated Laboratory | And 7 more authors.
Marine Micropaleontology | Year: 2015

A high-resolution sedimentary sequence recovered from the Tagus prodelta has been studied with the objective to reconstruct multi-decadal to centennial-scale climate variability on the western Iberian Margin and to discuss the observations in a wider oceanographic and climatic context. Between ca. 100BC and AD400 the foraminiferal fauna and high abundance of Globorotalia inflata indicate advection of subtropical waters via the Azores Current and the winter-time warm Portugal Coastal Current. Between ca. AD400 and 1350, encompassing the Medieval Climate Anomaly (MCA), enhanced upwelling is indicated by the planktonic foraminiferal fauna, in particular by the high abundance of upwelling indicator species Globigerina bulloides. Relatively light δ18O values and high sea surface temperature (SST) (reconstructed from foraminiferal assemblages) point to upwelling of subtropical Eastern North Atlantic Central Water. Between ca. AD1350 and 1750, i.e. most of the Little Ice Age, relatively heavy δ18O values and low reconstructed SST, as well as high abundances of Neogloboquadrina incompta, indicate the advection of cold subpolar waters to the area and a southward deflection of the subpolar front in the North Atlantic, as well as changes in the mode of the North Atlantic Oscillation. In addition, the assemblage composition together with the other proxy data reveals less upwelling and stronger river input than during the MCA. Stronger Azores Current influence on the Iberian Margin and strong anthropogenic effect on the climate after AD1750 is indicated by the foraminiferal fauna. The foraminiferal assemblage shows a significant change in surface water conditions at ca. AD1900, including enhanced river runoff, a rapid increase in temperature and increased influence of the Azores Current. The Tagus record displays a high degree of similarity to other North Atlantic records, indicating that the site is influenced by atmospheric-oceanic processes operating throughout the North Atlantic, as well as by local changes. © 2015 Elsevier B.V.

Palumbo E.,University of Sannio | Flores J.A.,University of Salamanca | Perugia C.,University of Sannio | Emanuele D.,University of Sannio | And 4 more authors.
Journal of Quaternary Science | Year: 2013

A high-resolution coccolithophore study allowed reconstructing sea surface conditions during the last 24ka BP off the Iberian Margin. Variations in nannoplankton accumulation rate, cold-water species, Florisphaera profunda, Umbilicosphaera sibogae and Coccolithus pelagicus ssp. azorinus trends suggest the occurrence of substantial changes in surface water dynamics. Palaeoproductivity shows changes during the glacial and the interglacial transition from intense glacial upwelling to persistent interglacial stratification. A drastic productivity decline occurred between ∼18 and 13ka BP related to the arrival of subpolar waters indicated by the presence of the subarctic subspecies C. pelagicus pelagicus and increased percentages of tetra-unsaturated alkenones. Abrupt variability at core MD03-2699 during the last 24 ka BP was observed in palaeoproductivity and sea surface temperatures proxies. Increases of reworked species fluxes were observed during the Last Glacial Maximum and during the transition to the Holocene, likely connected to turbidity currents and/or contourites formed by Mediterranean outflow intensification. In addition, C. pelagicus ssp. pelagicus presence, Gephyrocapsa muellerae and tetra-alkenone percentages reveal rapid coolings coeval with the Holocene Bond cycles and rapid climate coolings recognized for the Northern Hemisphere between 11.02 and 1.7 ka BP and associated with subpolar water arrival at the site. © 2013 John Wiley & Sons, Ltd.

Palumbo E.,University of Sannio | Flores J.A.,University of Salamanca | Perugia C.,University of Sannio | Petrillo Z.,Italian National Institute of Geophysics and Volcanology | And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

A high resolution coccolithophore study was carried out in order to improve the understanding of the paleoceanographic evolution and changes in paleoproductivity occurring off the Iberian Margin (IM) between 445 and 360. ka, i.e. during late Marine Isotope Stage 12 to 11. Coccolithophore assemblages allowed reconstructing surface water changes characterized by millennial-scale oscillations (~. 1.5. kyr cycles) involving Portugal or Iberian Poleward Currents (PC and IPC) prevalence. Changes in paleoproductivity, possibly related to the upwelling of Eastern North Atlantic Central Waters (ENACW) - of sub-tropical (ENACWst) or sub-polar origin (ENACWsp) - were also recognized. This study also permitted detecting abrupt events (stadial/interstadial-type oscillations) and revealed that changes in paleoproductivity are related to opposite dynamics during glacial and interglacial stages, with the reversed setting being established during the deglaciation. Furthermore, a possible control of half and fourth precessional cycle components, on the occurrence of abrupt changes within the assemblages' structure, during the deglaciation, is proposed on the basis of wavelet analysis results applied to selected taxa. © 2013 Elsevier B.V.

Amore F.O.,University of Sannio | Flores J.A.,University of Salamanca | Voelker A.H.L.,National Laboratory of Energy and Geology | Voelker A.H.L.,CIMAR Associated Laboratory | And 3 more authors.
Marine Micropaleontology | Year: 2012

Changes in paleoclimate and paleoproductivity patterns have been identified by analysing, in conjunction with other available proxy data, the coccolithophore assemblages from core MD03-2699, located in the Portuguese margin in the time interval from the Marine Isotope Stage (MIS) 13/14 boundary to MIS 9 (535 to 300. ka). During the Mid-Brunhes event, the assemblages associated with the eccentricity minima are characterised by higher nannoplankton accumulation rate (NAR) values and by the blooming of the opportunistic genus Gephyrocapsa. Changes in coccolithophore abundance are also related to glacial-interglacial cycles. Higher NAR and numbers of coccoliths/g mainly occurred during the interglacial periods, while these values decreased during the glacial periods. Superimposed on the glacial/interglacial cycles, climatic and paleoceanographic variability has been observed on precessional timescales. The structure of the assemblages highlights the prevailing long-term influence of the Portugal (PC) and Iberian Poleward (IPC) Currents, following half and full precession harmonics, related to the migration of the Azores High (AH) Pressure System. Small Gephyrocapsa and Coccolithus pelagicus braarudii are regarded as good indicators for periods of prevailing PC influence. Gephyrocapsa caribbeanica, Syracosphaera spp. ., Rhabdosphaera spp. and Umbilicosphaera sibogae denote periods of IPC influence. Our data also highlights the increased percentages of Coccolithus pelagicus pelagicus during the occurrence of episodes of very cold and low salinity surface water, probably related to abrupt climatic events and millennial-scale oscillations of the AH/Icelandic Low (IL) System. © 2012 Elsevier B.V..

Marino M.,University of Bari | Maiorano P.,University of Bari | Tarantino F.,University of Bari | Voelker A.,Instituto Portugues Do Mar e da Atmosfera | And 6 more authors.
Paleoceanography | Year: 2014

Quantitative coccolithophore analyses were performed in core MD01-2446, located in the midlatitude North Atlantic, to reconstruct climatically induced sea surface water conditions throughout Marine Isotope Stages (MIS) 14-9. The data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby North Atlantic records that support the coccolithophore signature at glacial-interglacial to millennial climate scale. Total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations. Coccolithophore warm water taxa (wwt) indicate that MIS11c and MIS9e experienced warmer and more stable conditions throughout the whole photic zone compared to MIS13. MIS11 was a long-lasting warmer and stable interglacial characterized by a climate optimum during MIS11c when a more prominent influence of the subtropical front at the site is inferred. The wwt pattern also suggests distinct interstadial and stadial events lasting about 4-10 kyr. The glacial increases of Gephyrocapsa margereli-G. muellerae 3-4μm along with higher values of Corg, additionally supported by the total alkenone abundance at Site U1313, indicate more productive surface waters, likely reflecting the migration of the polar front into the midlatitude North Atlantic. Distinctive peaks of G. margereli-muellerae (>4μm), C. pelagicus pelagicus, Neogloboquadrina pachyderma left coiling, and reworked nannofossils, combined with minima in total nannofossil accumulation rate, are tracers of Heinrich-type events during MIS12 and MIS10. Additional Heinrich-type events are suggested during MIS12 and MIS14 based on biotic proxies, and we discuss possible iceberg sources at these times. Our results improve the understanding of mid-Brunhes paleoclimate and the impact on phytoplankton diversity in the midlatitude North Atlantic region. ©2014. American Geophysical Union. All Rights Reserved.

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