Sm-Nd isotope and Mn/Ca ratios for cleaned Neogloboquadrina pachyderma from ODP Hole 105-647A (Table 1)

• Main Authors: Vance, Derek, Burton, Kevin W
• Format: Dataset
• Language: English
• Published: PANGAEA 1999
• Subjects: 105-647A; AGE; Calculated; DEPTH; sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Inductively coupled plasma - mass spectrometry (ICP-MS); Joides Resolution; Leg105; Manganese/Calcium ratio; Mass; Mass spectrometer Finnigan MAT 262; Neodymium; Neodymium/Calcium ratio; Neodymium-143/Neodymium-144 ratio; error; North Atlantic Ocean; Ocean Drilling Program; ODP; Samarium; Samarium-147/Neodymium-144; standard deviation; Samarium-147/Neodymium-144 ratio; Sample code/label; ε-Neodymium; Canada; Labrador Sea; Neogloboquadrina pachyderma; North Atlantic; Planktonic foraminifera
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.711374; https://doi.org/10.1594/PANGAEA.711374

The neodymium (Nd) isotope composition of ancient seawater is a potentially useful tracer of changes in continental inputs and ocean circulation on timescales of a few ka. Here we present the first Nd isotope record for seawater using sedimentary foraminifera cleaned using standard oxidative-reductive techniques. The data, along with Mn/Ca ratios, suggest that cleaned foraminifera provide a reliable record of Nd in seawater and hold out the prospect of using Nd in foraminifera to examine changes in seawater that accompany glacial-interglacial climatic cycles. The principal potential problem to be overcome with the use of forams as records of trace elements in ancient seawater is their diagenetic Fe-Mn coatings. These contain large amounts of Nd and other trace elements but can be cleaned off using highly reducing reagents. Mn(Ca ratios for the majority of the cleaned sedimentary foraminifera analysed here lie within the range (10-100 µmol/mol) that has yielded success in studies of transition elements in forams. Mass-balance modelling suggests that for residual Mn/Ca ratios <100 µmol/mol, Nd added to the foram in the coating will never shift the measured Nd isotope composition significantly away from the seawater value acquired by the foram test in the water column. Additionally, Nd concentrations measured in cleaned sedimentary foraminifera are comparable with those for a modern sample that has never encountered diagenetic fluids. Finally, core-top planktonic foraminifera for two sites have Nd isotope compositions that are identical to local surface seawater. The data we present here for Labrador Sea forams over the past 2.5 m.y. are interpreted in terms of changes in the seawater isotopic composition. The data show a pronounced shift from epsilon-Nd values of ~-12 to ~-19 in the period 2.5-1.5 Ma. This change is interpreted to result from the initiation of Northern Hemisphere glaciation and the increased derivation of Labrador Sea Nd via ice-rafting from Archaean terranes in central Canada. In combination ...