Radiogenic Nd Isotope Labeling of the Northern NE Atlantic During MIS 2

Supplementary material

Radiogenic Nd isotope labeling of the northern NE Atlantic during MIS 2

Natalie L. Roberts and Alexander M. Piotrowski

Figures

Figure S1. Temperature and salinity cross plots for each of the BOFS core sites using the closest available station data taken from the World Ocean Database 2013 and plotted using Ocean Data View. The map shows coloured circles indicating the stations used, whereby purple is closest to BOFS 5K, black BOFS 8K, blue BOFS 10K, red BOFS 11K and green BOFS 17K, and the cross plot shows coloured circles indicating the depth of each core site. The Temperature and salinity data are only shown for ~1 – 4km depth. Except for BOFS 17K, which is bathed by slightly more saline water, all of the other BOFS core sites are bathed by water < 35 PSU. Grey regions of the cross plot highlight literature values for watermass properties in this area (McGrath et al., 2012 and references therein). BOFS 17K is primarily bathed by Wyville-Thomson overflow water (WTOW), while the deeper cores are bathed by a mixture of Labrador seawater (LSW), Iceland-Scotland overflow water (ISOW), WTOW and a component of Antarctic bottom water (AABW), which is most apparent at BOFS 8K.

Figure S2. Nd isotope composition measured on unclean foraminifera (filled symbols), leachates (open symbols) and fish debris (grey symbols) for cores BOFS 17K (green), 11K (red), 10K (blue) and 8K (black), displayed with 2σ error bars. The similarity in Nd isotope composition between leachates and foraminifera supports observations made by Wilson et al. (2013), whereby < 50 hours decarbonation results in identical εNd values, due to insufficient removal of carbonate and minimal attack of volcanic phases. However, it is still safer to use foraminifera than to leach, in order to best avoid detrital contamination. The close match between fish debris εNd, from which 100% of the detrital material can be removed, and foraminifera εNd, confirms there is no laboratory contamination of foraminifera samples during the dissolution step.

Figure S3. Comparison between volcanic IRD concentrations and unclean foraminifera Nd isotope composition for each core. The shallowest cores, BOFS 17K and BOFS 11K, exhibit the highest R2 values, relating to low sedimentation rates and high bioturbation smearing the volcanic IRD concentration through the cores compared with the deeper, higher sedimentation rate cores.

Figure S4. Uncleaned planktonic foraminifera rare earth element ratios for HREE/LREE (Tm + Yb + Lu)/(La + Pr + Nd) and MREE/MREE* (Gd + Tb + Dy/ average of HREE and LREE) have been added to a figure produced by Martin et al. (2010) based on data collected from several studies (filled grey symbols are from Martin et al. (2010), open grey symbols are from references within). All foraminifera data (coloured diamonds) fall within the area produced by other authigenic phases and show no indication of detrital contamination.

Figure S5. Redox sensitive element concentrations measured in unclean planktonic foraminifera and converted to mass per mass of CaCO3a. manganese, b. iron, c. uranium for cores BOFS 11K (red), 10K (blue) and 8K (black). The grey bar highlights the period of highest radiogenic Nd composition and demonstrates a lack of coherent redox changes between cores over this interval.

Methods

For measurement of rare earth element and Mn concentrations in foraminifera, using a Perkin-Elmer SCIEX DRC II quadrupole inductively coupled mass spectrometer, a suite of calibration standards were prepared gravimetrically using single element solutions obtained from CPI International. Each element solution was tested for contaminating elements. The only significant contamination was found on 144Nd, by 3% addition from 144Sm, and the Nd standard concentration was corrected accordingly. The calibration standards were then checked for accuracy by using them to measure element concentrations of know reference materials. For a basalt rock powder, BCR-2 diluted 49117× and spiked with a pure Ca solution to 100 ppm Ca, our standards reproduced the mean literature values within 5%, well within the range of literature values available. For a surface water sample, SPS-SW2 diluted 10× and spiked with a pure Ca solution to 100 ppm Ca, our standards reproduced the mean literature values within 10%.

For measurement of B, Fe and U in foraminifera, using an Element XR inductively coupled mass spectrometer, a suite of calibration standards were prepared gravimetrically using single element solutions. These standards were checked for accuracy by using them to measure element concentrations of a powdered giant clam, JCt-1, recently used in an inter-laboratory calibration study (Hathorne et al., 2013). Based on 46 runs of JCt-1 during 2014 our laboratory measured mean B/Ca = 214.1 ± 3.0 μmol/mol 2SD, mean U/Ca = 24.1 ± 0.8 nmol/mol 2SD and Fe/Ca ~ 0.01 mmol/mol (which is too low to be meaningful). Our B/Ca and U/Ca values are in agreement with Hathorne et al. (2013).

References:

Hathorne, E.C., Gagnon, A., Felis, T., Adkins, J., Asami, R., Boer, W., Caillon, N., Case, D., Cobb, K.M., Douville, E., 2013. Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements. Geochemistry, Geophysics, Geosystems 14, 3730-3750.

Martin, E.E., Blair, S.W., Kamenov, G.D., Scher, H.D., Bourbon, E., Basak, C., Newkirk, D.N., 2010. Extraction of Nd isotopes from bulk deep sea sediments for paleoceanographic studies on Cenozoic time scales. Chemical Geology 269, 414-431.

McGrath, T., Nolan, G., McGovern, E., 2012. Chemical characteristics of water masses in the Rockall Trough. Deep Sea Research Part I: Oceanographic Research Papers 61, 57-73.

Wilson, D.J., Piotrowski, A.M., Galy, A., Clegg, J.A., 2013. Reactivity of neodymium carriers in deep sea sediments: Implications for boundary exchange and paleoceanography. Geochimica et Cosmochimica Acta 109, 197-221.