Bio-carbonates from Well NK1 were sampled from every chip using a micro-drill. Twenty-four chips were drilled twice and the duplicate samples were used for quality control. Sub-samples of 50 mg were firstly leached with 0.3 N acetic acid and Milli-Q water for 30 min to remove absorbed salt. Rinsed samples were placed in 1.5 ml of 1.0 N acetic acid and sonicated for 2 hrs. Elemental compositions of the carbonate phase were firstly measured on the ICP-MS using 0.5 mL of supernatant. Elemental concentrations and 87Sr/86Sr isotope of insoluble residue from one sample (NK1-Nd-73 at 721.85 m) were measured. Insoluble residue of this sample was digested using a mixture of HNO3 (0.2 ml) and HF (0.8 ml). Following a modified procedure by Deniel and Pin (2001), one-half milliliter of supernatant was loaded to the preconditioned Sr-Spec columns to separate strontium. Strontium-isotope ratios were measured on a Nu Plasma high-resolution (HR) multi-collector ICP-MS at the Radiogenic Isotope Facility, University of Queensland. The standard deviation of triple measurements is 0.000009 on average. During the course of measurements, analyses of NBS SRM987 yield a mean 87Sr/86Sr ratio of 0.710222 ± 20 (2σ). All data are normalized to 86Sr/88Sr = 0.1194 and the 87Sr/86Sr are corrected to SRM987 =0.710249 ± 28 (2σ) to reflect the long-term drift.

Median standard deviations for triple measurements.*Median standard deviation incorporating the external SRM987 errors with measurement errors of samples and the standard.