DOI: 10.5285/b27e608b-47f6-40bd-8fcf-bd83085c77ca
title: Complementary Geochemical, mineralogical and microbiological analyses of materials collected on the Greenland Ice Sheet

description: This dataset comprises of geochemical, mineralogical and microbiological analyses of material collected on the southwestern margin of the Greenland Ice Sheet in 2016 and 2017. Stream water, melted ice and snow samples were collected and analysed for carbon, nitrogen, phosphorus, cation and anion concentrations, pH, conductivity, total dissolved solids (TDS), mineral phase and class abundances and Rare Earth Elements (REE). Microbial community composition was also analysed. In addition, the results of a nutrient incubation experiment are also presented.The data were collected as part of a project investigating drivers of glacial ice algal growth on the Greenland Ice Sheet. 

We acknowledge funding from UK Natural Environment Research Council Consortium Grant, Black and Bloom (NE/M020770/1, NE/M021025/1 and NE/S001670/1). LGB and SL acknowledge funding from the German Helmholtz Recruiting Initiative (award number: I-044-16-01). LGB, AMA, and MT were also supported through an ERC Synergy Grant (ʻDeep Purpleʼ grant # 856416) from the European Research Council (ERC)
description: Surface snow and ice samples were collected along a transect across the ablation zone of the southwestern margin of the Greenland Ice Sheet during the 2016 (July 27-August 17) and 2017 (June 1-28) melt seasons. Targeted surface habitats included clean ice (CI; free of macroscopically visible LAP), high algal biomass (Hbio) ice, Hbio snow, dispersed cryoconite (DCC) ice, cryoconite holes (CCH), a floating biofilm, and supraglacial stream water. The collected samples were classed into the following categories based on macroscopically visible characteristics: clean snow (n = 1), clean surface ice (CI, n = 4), high algal biomass ice (Hbio; n =19), high algal biomass snow (n = 2), and dispersed cryoconite ice (DCC; n = 5). In addition, supraglacial stream water (n = 2), a sample of cryoconite hole (CCH) material (n = 1), a cryoconite hole layer from an ice core (n = 1), and a floating algal biofilm (n = 1) were collected. Ice and snow samples were collected from the top 3-5 cm of surface into sterile plastic bags, melted at ambient temperatures (5-10 degrees Celsius). Aliquots of filtered melted samples were processed as described below for fluid chemistry analyses. While on the ice, melted samples were filtered through glass fiber filters (GFF, pore size: 0.7 micrometer), from which the accumulated LAP were removed using a stainless steel spatula. The collected solid LAP were air-dried and stored in glass vials.

Three rock samples representing lithologies in the catchment area draining the west Greenland Ice Sheet were collected from outcrops near the terminus of Russell Glacier.

The phosphorus content of the Hbio ice, DCC ice, Hbio snow, and CCH samples was determined using a modified version of the SEDEX sequential extraction protocol20. Steps I, III, IV, and V were completed as a means of quantifying loosely bound/exchangeable P (Pexch), mineral P (Pmin), and organic P (Porg). The extracted P was measured in the fluid phase as described below for the melted ice samples.

Melted surface samples and supraglacial stream water samples were filtered using 0.22 micrometer single use syringe filters into acid-washed Nalgene bottles. Inductively-coupled plasma mass spectroscopy (ICP-MS; Thermo Fisher iCAPQc) was used to measure fluid phase cations in the filtered water samples that were acidified using Aristar HNO3. ICP-MS was conducted by Stephen Reid at the University of Leeds, UK. Phosphorus was either measured using segmented flow-injection analysis (AutoAnalyser3, Seal Analytical), or for samples containing lower concentration of phosphorus using a 100cm WPI Liquid Waveguide Capillary Cell in conjunction with an Ocean Optics USB2000+ spectrophotometer with a precision of 1.6 percentage and a LOD of 2nmolL^-1. Aliquots of the non-acidified 0.22 micrometer filtered samples were also analyzed in replicates by ion chromatography by Andrea Viet-Hillebrand at the German Research Centre for Geosciences, Potsdam, Germany. Analyses were carried out with a conductivity detector on a Dionex ICS 3000 system, equipped with an AS 11 HC Dionex analytical column run at 35 degrees Celsius for chromatographic separation of the anions. 

Aliquots from the 0.7 micrometer GFF filtered, dried and hand-milled samples were analyzed for their bulk total and organic carbon (TC and TOC) and total nitrogen (TN) content. This was done for the Hbio ice, DCC ice, Hbio snow, and cryoconite hole material using an elemental analyzer (NC2500 Carlo Erba, standard deviation less than 0.2 percent, precision 0.1 percent) and with the TOC concentrations subsequently measured following an in situ decalcification step. Note, the organic carbon fraction includes a contribution from black carbon. TC/TN analyses were conducted by Birgit Plessen and Sylvia Pinkerneil at the German Research Centre for Geosciences, Potsdam, Germany. 

The mineralogy of the dust was determined using a Bruker D8 Advance Eco X-ray diffractometer (Bruker, Billerica, USA) with a Cu source, operated at 40 kV and 40 mA at the University of Leeds, UK. Samples were hand-milled in an agate mortar and pestle prior to loading in 5 or 10 mm low-background silicon mounts. The small quantity of material per sample necessitated the use of shallow sample mounts, thereby making the sample not infinitely thick with respect to X-rays, and thus rendering this analysis semi-quantitative. Furthermore, because it was necessary to rely on hand grinding, XRD patterns exhibit the effects of non-ideal particle size statistics and preferred orientation on some phases, which can result in higher Rwp values. The 2016 COD and 1996 ICDD databases were used to complete phase identification for each sample, in conjunction with DIFFRACplus Eva v.2 software56. Topas V 4.256 and the fundamental parameters approach57 were used to complete Rietveld refinements25,58,59. No preferred orientation corrections were used because refinements are typically more accurate for samples containing many phases that are known to exhibit severe preferred orientation (e.g. phyllosilicates) when such corrections are excluded60. In some cases, the use of multiple K-feldspar, plagioclase feldspar, and orthopyroxene structures were used in a single refinement because this approach provided substantially improved fit statistics and visual fits to observed XRD patterns. This may reflect the incorporation of dust from multiple source rocks of differing mineralogical composition. Mineral phases identified using XRD were grouped into the following classes: quartz, plagioclase feldspars (albite/andesine/anorthite), amphiboles (refined using the structure of actinolite), potassium feldspars (orthoclase/microcline), pyroxene (enstatite/augite/diopside), and micas (refined using the structure of muscovite).

The health and productivity of glacier algae assemblages were monitored using rapid light response curves17 performed with pulse amplitude modulation (PAM) fluorometery at 24, 72, 120h. Code for processing the rapid light curves (RLC) was produced by C Williamson and is available here: https://github.com/chrisjw18/rlcs. Curve fitting was completed using R (v.3.6.0). 

A total of 26 samples comprising 15 high algal biomass ice (Hbio ice), two high algal biomass snow (Hbio snow), one biofilm, four dispersed cryoconite (DCC) (macroscopically visible particles), and four clean ice (CI) samples (without macroscopically visible particles) were collected into sterile 50 mL centrifuge tubes (Hbio ice, Hbio snow, DCC, Biofilm) or sterile sampling bags (CI). After gentle thawing at field-lab temperatures (5-10  degrees Celsius), and concentrating by gravimetric settling of particles (for Hbio ice, Hbio snow, DCC, Biofilm) or filtering (CI) through sterile Nalgene single-use filtration units (pore size 0.22 micrometer), up to 5 replicate from the concentrates or 1 filter per sampling event were transferred to 5ml cryo-tubes and immediately frozen in liquid nitrogen. Samples were returned to the German Research Centre for Geosciences in Potsdam, Germany in a cryo-shipper at liquid nitrogen temperatures and stored at -80 degrees Celsius until processing.

Rare Earth Element (REE) analysis was conducted on Hbio ice, DCC ice, and cryoconite hole particulate solid materials filtered onto 0.7 micrometer GFF and hand-milled in an agate mortar and pestle. To remove organic matter, samples were ashed in a slightly open ceramic crucible in a muffle furnace at 450 degrees Celsius for 4 h. Rock samples collected from site 6 by Gilda Varliero and Gary Barker (University of Bristol, UK) (representing lithologies of the catchment area) were cut into centimeter-sized cubes prior to milling in a tungsten ring mill. Acid dissolution of the mineral fraction was achieved in Savillex beakers using pro-analysis acids previously purified by distillation and sub-boiling. Dissolution was first performed with 2 mL 14 M HNO3 and 1mL 23M HF on a hot plate at 120 degrees Celsius for 48h and later, after evaporation to dryness, with 2mL 6M HCl on a hot plate at 120 degrees Celsius for 24h. REE concentrations were determined using HR-ICP-MS (ThermoFisher Element 2) at the Vrije Universiteit Brussel, Belgium. Trace element concentrations were calibrated using elemental standard solutions and USGS reference material (AGV-2). Precision for all elements is better than 2 percent RSD. 

16S, 18S and ITS2 libraries were individually imported into Qiime2 (v.2019.1). Itsxpress was used to extract the precise ITS2 region, and thus removing the conserved regions, from the ITS2 libraries before further processing (--p-region ITS2, --p-taxa ALL). The imported libraries were quality-filtered using the dada2 pipeline (16S: --p-trunc-len-f=280, --p-trunc-len-r=200, --p-trim-feft-f=10, --p-trim-left-r=10; 18S: --p-trunc-len-f=250, --p-trunc-len-r=200, --p-trim-feft-f=10, --p-trim-left-r=10; ITS2: --p-trunc-len-f=0, --p-trunc-len-r=0, --p-trim-feft-f=0, --p-trim-left-r=0). The amplicon sequence variants (ASV) in the filtered libraries were classified using classify-sklearn and the respective databases Greengenes (16S, ''gg-13-8-99-nb-classifier''), Silva (18S, ''silva-132-99-nb-classifier''), and Unite (ITS2, ''unite_ver8_99_02.02.2019''). ASVs skewing the results were removed from each data set (16S: --p-exclude Chloroplast, mitochondria; 18S: --p-exclude Archaea, Bacteria). Feature tables containing solely algal (18S: --p-include Chloroplastida, Ochrophyta) or fungal (ITS2: --p-include Fungi) sequences were created. The filtered feature tables were imported into R (v.3.6.0). Non-metric multidimensional scaling (NMDS) analyses were performed using the ''metaMDS'' function (Bray-Curtis distances) of the R package ''vegan''. Analysis of similarities (ANOSIM) was carried out using the ''anosim'' function of the ''vegan'' package and ''sites'' and ''habitats'' as treatment groups.

The ggplot2 package 
(v3.2.1 https://cran.r-project.org/web/packages/ggplot2/readme/README.html) was used in R (v3.6.0) to process and plot the particle size distribution data.
description: Scanning electron microscopy data was collected by J. McCutcheon using a Hitatchi 8230 SEM at the Leeds Electron Microscopy and Spectroscopy Centre (LEMAS), University of Leeds, UK. X-ray diffraction was conducted by J. McCutcheon using a Bruker D8 Advance Eco X-ray diffractometer (Bruker, Billerica, USA) with a Cu source at the University of Leeds, UK. ICP-MS was conducted by S. Reid using a Thermo Fisher iCAPQc ICP-MS at the University of Leeds, UK. Phosphorus was measured either using segmented flow-injection analysis (AutoAnalyser3, Seal Analytical), or for samples containing lower concentrations of phosphorus by A. Stockdale, using a 100 cm WPI Liquid Waveguide Capillary Cell in conjunction with an Ocean Optics USB2000+ spectrophotometer. Both analyses were conducted at the University of Leeds, UK. Ion chromatography was conducted by A. Viet-Hillebrand at the German Research Centre for Geosciences, Potsdam, Germany using a conductivity detector on a Dionex ICS 3000 system, equipped with an AS 11 HC Dionex analytical column. Carbon and nitrogen analysis was conducted by B. Plessen and S. Pinkerneil at German Research Centre for Geosciences, Potsdam, Germany using an NC2500 Carlo Erba elemental analyser. Amplicon libraries were sequenced on the Illumina MiSeq using paired 300-bp reads at the University of Bristol Genomics Facility, Bristol, UK. Rare Earth element concentrations were measured by A. Vanderstraeten using HR-ICP-MS (ThermoFisher Element 2) at the Vrije Universiteit Brussel, Belgium. Particle size distribution was measured by K. Jurkschat using a DC24000 CPS disc centrifuge at Oxford Materials Characterisation Services, Oxford, UK.
description: No data were excluded from the study. Reproducibility in the data was verified by collecting and analysing as many samples as was possible given the time and space constraints of remote fieldwork. This study characterized heterogeneous naturally occurring samples and therefore randomisation was not required.