Dx500

We use ion data from DF1 and DF2 cores after and before 300,000 BP, respectively¹⁴ . Na⁺, Ca²⁺, Mg²⁺, NO₃⁻, and SO₄²⁻ were measured from both cores using ion chromatography. In addition, K⁺ was measured from DF2 core. For DF1 core, we use previously published data⁵⁰ after re-examination and removal of some data points because of large measurement errors. Fifty-nine samples were newly cut from DF1 core, re-measured, and the new data were added to the earlier dataset. Measurement errors were generally less than 10% but may be higher for low concentrations. For DF2 core, 10-cm-long samples were cut every 0.5 m and measured on two Dionex DX-500 ion chromatographs: one for anions and the other for cations. Measurement errors were estimated to be less than 3%. Sea salt (ss) Na⁺ and non-sea-salt (nss) Ca²⁺ concentrations were calculated from Na⁺ and Ca²⁺ concentration data using the weight ratios of Ca²⁺/Na⁺ for seawater (0.038) and average crust (1.78), as described in previous studies^{7 (link)–9 (link),16 (link),51 (link)}. The nssSO₄²⁻ concentrations were calculated assuming a sea ice source^{7 (link),8 (link)} of ssNa⁺. Similar values are obtained if we assume an open ocean source^{7 (link),8 (link)} of ssNa⁺. Fluxes of nssCa²⁺ and nssSO₄²⁻ were calculated by multiplying concentrations by estimated accumulation rates¹⁴ .

Sulfate content in the samples was quantified by high-performance anion-exchange chromatography (HPAEC) using a Dionex DX-500 (Dionex, Sunnyvale, CA, USA), as previously described by Chopin et al. [20 (link)].

High-Performance Anion-Exchange Chromatography (HPAEC) was used to quantify the linked ester sulphate group content in the native GY785 EPS and its derivatives, as previously described by Chopin et al. [44 (link)]. HPAEC analyses were carried out with a Dionex DX-500 ion chromatographic instrument controlled using Chromeleon^® software.

General soil analysis for the soil type used in the first part of the experiments (Section 2.1) was performed using ASTM standards for sieving, gravimetric water content (GWC), soil porosity, and bulk density determination prior to the experimental setup. A Dionex DX 500 ion chromatograph with PeakNet software was used for extractable ionic nitrogen species analysis at the end of the experiment to determine nutrient utilization (Section 3.3). Additional analyses for nitrogen and carbon concentration were done using an elemental combustion system (Costech Instruments).

Toluene concentration was measured using a GC-FID (Agilent HP7890, USA) equipped with a 30 m x 320 μm x 5 μm film thickness Agilent DB-MTBE column. The analytical setup was according to Martinez-Lavanchy et al. [30 (link)].
Nitrate (NO₃^-) and nitrite (NO₂^-) concentrations were measured using ion chromatography (DX 500, Dionex, USA). The column used for the analysis was an IonPac AG4A-SC (4x50 mm and AS4A-SC 4x2501).

The linked ester sulfate groups were quantified by High-Performance Anion-Exchange Chromatography (HPAEC) using Dionex DX-500 ion chromatographic instrument controlled with Chromeleon^® software (Dionex, Sunnyvale, CA, USA), as previously described by Chopin et al. [50 (link)].