The Sediment Green-Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin

Sediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard-generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate-related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high-resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox-sensitive sedimentary U/Th generally co-varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B-derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet-alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high-resolution paleoceanographic records that circumvent the traditionally laborious methodology.publishedVersio

Deep submarine infiltration of altered geothermal groundwater on the south Chilean Margin

Submarine groundwater discharge is increasingly recognized as an important component of the oceanic geochemical budget, but knowledge of the distribution of this phenomenon is limited. To date, reports of meteoric inputs to marine sediments are typically limited to shallow shelf and coastal environments, whereas contributions of freshwater along deeper sections of tectonically active margins have generally been attributed to silicate diagenesis, mineral dehydration, or methane hydrate dissociation. Here, using geochemical fingerprinting of pore water data from Site J1003 recovered from the Chilean Margin during D/V JOIDES Resolution Expedition 379 T, we show that substantial offshore freshening reflects deep and focused contributions of meteorically modified geothermal groundwater, which is likely sourced from a reservoir ~2.8 km deep in the Aysén region of Patagonia and infiltrated marine sediments during or shortly after the last glacial period. Emplacement of fossil groundwaters reflects an apparently ubiquitous phenomenon in margin sediments globally, but our results now identify an unappreciated locus of deep submarine groundwater discharge along active margins with potential implications for coastal biogeochemical processes and tectonic instability.publishedVersio

Glacial-interglacial changes in central tropical Pacific surface seawater property gradients

Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific).This is the publisher’s final pdf. The article is copyrighted by American Geophysical Union and published by John Wiley & Sons Ltd. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/journal/10.1002/%28ISSN%291944-9186/Keywords: tropical Pacific, oxygen isotopes, foraminifer

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Organic carbon percentage for site J1007, Chilean Margin

Sediment core J1007 was collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) in 2019. Measured organic carbon contents were compared to the G/B to test the utility of G/B as a proxy for diatom productivity. Laboratory measurements in this study were conducted in 2020 at Rutgers University

Reconstructed biogenic opal percentage and accumulation for site J1007, Chilean Margin

Sediment cores at sites J1007 were collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) in 2019. Sedimentary Green/Blue (G/B) ratio data were collected during the expedition. We calculated the opal mass accumulation rate (MAR) at Site J1007 over the last ~150,000 years. Laboratory measurements in this study were conducted in 2020 at Rutgers University

Uranium and thorium concentrations for sites J1002, Chilean Margin

Sediment cores at sites J1002 awere collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) in 2019. Sedimentary U/Th derived from natural gamma radiation data were collected during the expedition. U/Th was further used as a non-quantitative indicator of redox conditions of the sediments

Reconstructed biogenic opal percentage for site J1002, Chilean Margin

Sediment cores at sites J1002 were collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) in 2019. Sedimentary Green/Blue (G/B) ratio data were collected during the expedition. We calculated the opal pecentages at Site J1002 over the last ~150,000 years. Laboratory measurements in this study were conducted in 2020 at Rutgers University

Age model, biogenic opal contents and sedimentary U/Th for sites J1002 and J1007, Chilean Margin

Sediment cores at sites J1002 and J1007 were collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) in 2019. Sedimentary Green/Blue (G/B) ratio and sedimentary U/Th derived from natural gamma radiation data were collected during the expedition. We generated age models for sites J1002 and J1007 with radiocarbon dates and visual correlation of δ18O records of benthic foraminifera to the LR04 benthic stack. Measured biogenic opal contents and organic carbon contents were compared to the G/B to test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007. Sedimentary U/Th was further used as a non-quantitative indicator of redox conditions of the sediments. Lastly, we calculated the opal mass accumulation rate (MAR) at Site J1007 over the last ~150,000 years. Laboratory measurements in this study were conducted in 2020 at Rutgers University