ALBERT

Description: The oxygen isotopic composition of benthic foraminifera (d18Ob) is widely used to date and correlate marine sediment sequences. However, d18Ob has found comparatively little use in the Arctic Ocean due both to uncertainty in Arctic marine sediment chronology and the lack of resemblance between Arctic and open ocean d18Ob records. We address this issue by combining Arctic d18Ob records (Cronin et al., 2019) with benthic ostracode Mg/Ca-BWT reconstructions (Cronin et al., 2017) to create a composite record of the history of seawater d18O in the intermediate-to-deep Arctic Ocean over the last 600 kyr. Seawater d18O and its uncertainty was calculated using PSU Solver (Thirumalai et al., 2016).

Description: Composite sediment core OD1507-03TC-41GC-03PC was collected at an average water depth of 976 m in outer Petermann Fjord during The Petermann 2015 Expedition to Petermann Fjord and adjacent Hall Basin in Nares Strait, northern Greenland. Previous results showed that the splice covers large parts of the Holocene, from the present to 6,900 cal yrs BP (Reilly et al. 2019). The core was sampled approximately every 5 cm for sea-ice related biomarker and total organic carbon (TOC) analyses and approximately every 10 cm for foraminiferal abundance counts. Where enough material was available, the depth of foraminiferal samples match the depth of biomarker samples. Sea-ice related biomarkers (IP25, HBI II, Brassicasterol, Cholesterol, Dinosterol, Campesterol, and β-sitosterol) where extracted using saponification (5% potassium hydroxide (KOH) in methanol (MeOH):H2O (9:1, v/v); 70°C, 1 h) followed by extraction of the non-saponifiable lipids into hexane (3 x 2 mL). After sample purification the different biomarkers were analysed on an Agilent 7890B GC fitted with an HP-5ms Ultra Inert column (30 m x 250 μm x 0.25 μm) coupled to a 5977A series mass selective detector and equipped with a Gerstel multipurpose sampler (MPS) at Aarhus University. TOC measurements and analysis of the carbon isotopic composition of the TOC were performed on 10 mg of the same sample material as for biomarker analyses. The samples were treated with 35% HCl prior to analyses, to remove inorganic carbon. The stable isotope δ13Corg and % wt TOC were measured using a continuous-flow IsoPrime IRMS coupled to an Elementar PyroCube elemental analyser at the Aarhus AMS Centre (AARAMS), Aarhus University, Denmark. Samples for foraminiferal abundance counts were wet sieved at 63 µm and counted wet, submerged in a 'storage' solution of 70 % distilled water and 30 % ethanol with baking soda to preserve fragile calcareous and agglutinated tests. A wet splitter was used when necessary to achieve a count of at least 200-300 benthic foraminifers.

Description: This project explores grain-scale signatures of subglacial sediment transport and subglacial hydrologic processes using grain shape and microtexture. We compare grain-shape distributions for grains from meltwater plume deposits to those of subglacial till and ice-proximal diamicton from the same glacial setting. The study incorporates samples from marine sediment cores collected offshore of Ryder Glacier in northwest Greenland, in the central Barents Sea, and Antarctic samples from Marguerite Bay, offshore Thwaites and Pine Island glaciers, and in the western Ross Sea. This dataset contains a MATLAB script used to process grain images and calculate individual grain-shape metrics (including circularity, solidity, and eccentricity), and an Excel spreadsheet containing the grain-shape measurements. Grain images were collected in 2022-23 using a Bettersizer S3 Plus particle size and shape analyzer at the University of Virginia.