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- Oxygen and hydrogen isotope signatures of Northeast Atlantic water massesPublication . Voelker, Antje; Colman, Alber; Olack, Gerard; Waniek, Joanna J.; Hodell, DavidOnly 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 (0-100 m) and central (100-500 m) 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) 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 50 m. 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.
- A southern Portuguese Margin Perspective of Marine Isotope Stage 47—An interglacial in the 41 kyr WorldPublication . Voelker, Antje; Rodrigues, Teresa; Trotta, Samanta; Marino, Maria; Kuhnert, HenningIn order to better understand interglacial climate variability within the 41 kyr world, we produced high-resolution climate records for interglacial Marine Isotope Stage (MIS) 47 (1424-1452 ka) at IODP Site U1387 (36 degrees 48 ' N, 7 degrees 43 ' W) on the southern Portuguese margin. Using benthic and planktonic foraminifera stable isotope records, U-37(k') sea-surface temperature (SST), and plankton assemblage data we investigated Mediterranean Outflow Water (MOW) and surface water conditions. The MOW-level records indicate a poorly ventilated and sluggish bottom current during the MIS 48/MIS 47 transition in association with the insolation maximum, whereas a well-ventilated MOW formed a contourite layer during the second insolation maximum. The benthic delta O-18 record shows a fairly abrupt change during the deglaciation of MIS 48, while the surface waters experienced a terminal stadial event that was associated with initial cooling and freshening followed by stepwise warming until interglacial SST was reached at 1450 ka. Interglacial conditions with SST of 24 degrees C or higher persisted until 1427 ka, although warm SST prevailed into MIS 46. The persistent and prolonged warmth is attributed to a northward expansion of the subtropical gyre during MIS 47 as reflected by the dominance of subtropical-tropical planktonic foraminifera species and the presence of warm water coccolithophores taxa.
- The GEOTRACES Intermediate Data Product 2014Publication . Mawji, Edward; Schlitzer, Reiner; Dodas, Elena Masferrer; Abadie, Cyril; Abouchami, Wafa; Anderson, Robert F.; Baars, Oliver; Bakker, Karel; Baskaran, Mark; Bates, Nicholas R.; Bluhm, Katrin; Kretschmer, Sven; Kumamoto, Yuichiro; Laan, Patrick; Labatut, Marie; Lacan, Francois; Lam, Phoebe J. Lam; Lannuzel, Delphine; le Moigne, Frederique; Lechtenfeld, Oliver J.; Lohan, Maeve C.; Saito, Mak A.; Lu, Yanbin; Masqué, Pere; McClain, Charles R.; Measures, Christopher; Middag, Rob; Moffett, James; Navidad, Alicia; Nishioka, Jun; Noble, Abigail; Obata, Hajime; Roshan, Saeed; Ohnemus, Daniel C.; Owens, Stephanie; Planchon, Frédéri; Pradoux, Catherine; Puigcorbé, Viena; Quay, Paul; Radic, Amandine; Obata; Rehkämper, Mark; Remenyi, Tomas; Salt, Lesley; Rijkenberg, Micha J. A.; Rintoul, Stephen; Robinson, Laura F.; Roeske, Tobias; Rosenberg, Mark; van der Loeff, Michiel Rutgers; Ryabenko, Evgenia; Sarthou, Géraldine; Schauer, Ursula; Scott, Peter; Sedwick, Peter N.; Sha, Lijuan; Shiller, Alan M.; Sigman, Daniel M.; Bowie, Andrew; Smethie, William; Smith, Geoffrey J; Sohrin, Yoshiki; Speich, Sabrina; Stichel, Torben; Stutsman, Johnny; Swif, James H; Tagliabue, Alessandro; Thomas, Alexander; Tsunogai, Urumu; Bown, Johann; Twining, Benjamin S.; van Aken, Hendrik M.; van Heuven, Steven; van Ooijen, Jan; van Weerlee, Evaline; Venchiarutti, Celia; Voelker, Antje; Wake, Bronwyn; Warner, Mark J.; Woodward, E. Malcolm S. W; Boye, Marie; Wu, Jingfeng Wu; Wyatt, Neil; Yoshikawa, Hisayuki; Zheng, Xin-Yuan; Xue, Zichen; Zieringer, Moritz; Zimmer, Louise A.; Boyle, Edward A.; Branellec, Pierre; Bruland, Kenneth W.; Brzezinski, Mark A.; Bucciarelli, Eva; Buesseler, Ken; Butler, Edward; Cai, Pinghe; Cardinal, Damien; Casciotti, Karen; Chaves, Joaquin; Cheng, Hai; Chever, Fanny; Church, Thomas M.; Colman, Albert S.; Conway, Tim M.; Croot, Peter L.; Cutter, Gregory A.; de Baar, Hein J.W.; Souza, Gregory F. de; Dehairs, Frank; Deng, Feifei; Thi Dieu, Huong; Dulaquais, Gabriel; Echegoyen-Sanz, Yolanda; Edwards, R. Lawrence; Fahrbach, Eberhard; Fitzsimmons, Jessica; Martin, Fleisher; Frank, Martin; Friedrich, Jana; Fripiat, François; Galer, Stephen J. G.; Gamo, Toshitaka; Solsona, Ester Garcia; Gerringa, Loes J. A.; Godoy, José Marcus; Gonzalez, Santiago; Grossteffan, Emilie; Hatta, Mariko; Hayes, Christopher T.; Heller, Maija Iris; Henderson, Gideon Henderson; Huang, Kuo-Fang; Jeandel, Catherine; Jenkins, William J.; Seth, John; Kenna, Timothy C.; Klunder, MaartenThe GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes.
- Data report: IODP Site U1387: the revised splice between Sections U1387B-18X-3 and U1387C-8R-3 (>171.6 mcd)Publication . Voelker, Antje; Jimenez-Espejo, F. J.; Bahr, A.; Rebotim, Andreia; Cavaleiro, Catarina; Salgueiro, Emilia; Röhl, U.; Stow, Dorrik A. V.; Hernández-Molina, F. J.; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsThe Expedition 339 shipboard splice of Integrated Ocean Drilling Program (IODP) Site U1387 deeper than ~155 meters composite depth (mcd) is based on a composite of the magnetic susceptibility and natural gamma radiation data. When generating high-resolution paleoceanographic reconstructions for the Mid-Pleistocene Transition and early Pleistocene sections of Site U1387, it quickly became obvious that proxy data misfits existed at several splice transitions. Thus, a revised splice was generated for Site U1387 below Core 339-U1387B-18X based on X-ray fluorescence– derived element records (e.g., ln[Fe/Ca]) and the stable isotope records obtained for planktonic and benthic foraminifers. Corrections were needed at most of the splice transitions below Core 339-U1387A-19X, with adjustments ranging from a few centimeters to several meters. In addition, Core 339-U1387A-33X and sections of Core 36X were integrated into the revised splice to replace Core 339-U1387C-2R and sections of Core 5R, respectively. The replacement of Core 339-U1387C-2R with Core 339-U1387A33X is an option for the intended paleoceanographic research and not essential for lower resolution studies. The splice tie point table, therefore, also includes an option for a splice that retains Core 339-U1387C-2R. The extensive revision of the shipboard splice reveals that making a splice for sediment sequences rich in contourite layers and coring disturbances (biscuiting in the extended core barrel cores) can be tricky and that data misfits at splice transitions are not necessarily a data problem but could indicate a splice problem.
- Mediterranean outflow conditions during the early to middle Pleistocene linked to precession forcingPublication . Voelker, Antje; Salgueiro, Emilia; Henning, KuhnertThe Mediterranean Outflow Water (MOW) is an important intermediate depth water mass in the North Atlantic. Here we reconstruct changes in the MOW during the early Pleistocene interval from 630 to 1760 ky, encompassing the Mid-Pleistocene Transition (MPT), which marks an important change in orbital climate forcing. Neither MOW ventilation nor MOW flow strength reveal changes related to the MPT, but incorporate variations related to precession (insolation) forcing. The MPT related change to higher glacial benthic δ O values occurs earlier at Site U1387 than in most deep-sea records, i.e. with MIS 26 instead of the MIS 24 to MIS 22 interval
- Variations in mid-latitude North Atlantic surface water properties during the mid-Brunhes (MIS 9-14) and their implications for the thermohaline circulationPublication . Voelker, Antje; Rodrigues, T.; Billups, K.; Oppo, D.; McManus, J.; Stein, R.; Hefter, J.; Grimalt, J.O.Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9-14 (300-540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north - south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.