Enhanced East Pacific Rise hydrothermal activity during the last two glacial terminations

Abstract

Tables S1 to S5 as Excel files 2 Materials and Methods Age modelsAge control for the EPR cores is provided by stable isotope and radiocarbon analyses of planktonic foraminifera (G. ruber, > 250 m size fraction). Ages for the long cores at 11ºS (Y71-07-47 and Y71-07-53) were determined by correlation of their planktonic 18 O stratigraphy to the global benthic 18 O stack of ref. 30 (Table S2). We followed a similar approach for KLH068 and KLH093 at 1ºN (12 (Table S1) and as a result these points were excluded from the age model. Metal concentrationsMetal analyses of samples for cores Y71-09-115 and Y71-07-47 were performed using a Bruker Pioneer S4 XRF at Michigan State University (MSU) (34). The relative standard deviation for major elements in external standards USGS BHVO-1 and RGM-1 is <0.3%. Analyses of Y71-09-104, Y71-09-106, Y71-07-49, and Y71-07-51 were performed using laser ablation and a Thermo-Fisher ICAP Q ICP-MS at MSU. Relative standard deviations and accuracy for major elements are ~3%. The calibration for As 4 was obtained using NIST 612 and GSD-1G, JB1a, and JA3 standards, with accuracy within ±5% of accepted values. The GSE-1G standard was run as an unknown for quality control; the mean of 4 measurements on 4 separate analytical sessions was within 5% of accepted value, with a relative standard deviation of <5%. Arsenic relative standard deviation among sample replicates was 2-10%, depending on absolute As concentrations. ICP-MS data for Y71-07-53 were reported in (16) and assigned ages based on the 18 O stratigraphy developed for this work.Fe and Mn concentrations were corrected for detrital inputs using Ti and the average Flux estimatesFluxes of hydrothermal components were estimated using both mass accumulation rates (MAR) and the 3 He normalization method. MAR's were determined using the drybulk density (DBD) of each sample, estimated using %CaCO3 (37), and the sedimentation rate. Because sedimentation rates are based on the assigned age model, MAR's are sensitive to age uncertainty. We assume an age error of ±20% between 5 successive metal analyses, larger than either the DBD uncertainty (±3%) or the error associated with the metal analyses (typically 5% or less). The age uncertainty is the primary contributor to the metal flux errors depicted in Figures 2 and 3. Prior to combining the short and long records at 11ºS into a continuous time series (Figure 4), we normalized each record by subtracting the mean flux and dividing by the standard deviation. This was necessary because the shorter records are closer to the ridge crest ( Figure 1) and as a result have higher mean metal concentrations and fluxes. For both the western and eastern flank records in Figure 4, the 0-40 kyr BP interval is based on data from the shorter gravity cores while the interval prior to 40 kyr BP is based on data from the longer piston cores.We also estimated sediment flux for two cores (Y71-07-49 and Y71-09-106) using the 3 He normalization method. The primary benefit of this approach is that: 1) it is insensitive t...

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