Sample collection and preparation
Samples were identified as subglacial in origin, sampled asseptically by sterile stainless steel spatula into new Whirlpack. 
Bulk samples were freeze-dried, sieved to remove >2 mm particles, and ground using a mixer mill (MM 400, Retsch, Germany). 
Sub-samples were taken for individual analyses. See details in the original journal article.

Instruments used for analyses
- Radiocarbon Date -- analysed using accelerator mass spectroscopy (AMS); Geochemical d14C was normalized to to Δ14C; 
Calendar ages (cal BP) were retrieved from radiocarbon ages BP by a calibration within OxCal v4.2.4 using the IntCal13 calibration curve 
and are given in the 2σ range (95% confidence level).
- Inorganic and Organic Carbon (IC, OC) contents -- ELTRA CS 530, ELTRA CS 500 TIC analysers (ELTRA, Germany). Detection limit was 100 mg/kg. 
The content of organic carbon (OC) was calculated by subtracting IC from TC.
- Contents of Total Nitrogen (TN) and Total Sulphur (TS) -- Elementary Analyzer Flash 2000 NCS (Thermo Scientific, UK). Detection limit of 10 mg/kg. 
- Elemental composition (XRF) -- X-ray Fluorescence spectrometer (PERFORM’X, Thermo Scientific ARL, Switzerland), 
range from 1 mg/kg to 100 %; following standard-less quantitative analysis in the program UniQuant (Thermo Fisher Scientific, UK). 
All elements were standardized to 100 %.
- Phosphorus (P) was extracted using six-step sequential extraction -- content of P in each of the extracts was determined by inductively coupled 
plasma optical emission spectrometry (ICP-OES; Agilent 720, Agilent Technologies Inc., USA); content of PO43- was determined by ion-exchange chromatography 
with suppressed conductivity [ICS 1600 (Dionex, USA) equipped with an IonPac AS11-HC (Dionex, USA)], guard and analytical columns. 
Organic P (OP) was calculated by subtraction of PO43- from phosphorus content. Detection limits were 3 mg/kg for loose P, labile P and Fe/Al P, 
9 mg/kg for OM/min P fractions, and 3 mg/kg for residual P.
- Aliphatic Lipids & Lignin-derived phenols -- extracted using solvent extraction and copper (II) oxide [CuO] oxidation; extracts analyzed using
Agilent model 6890N GC coupled with an Agilent model 5973N quadrupole mass selective detector (Agilent Technologies, USA)

NOTES
See details regarding methodology in the original journal article and cite your resources!

* na - not analyzed; bd - below detection