ALBERT

Description: Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south ((Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador Sea region during the last 5700 years. Fresh and cold conditions, probably accompanied by seasonal sea ice, prevailed both north and south of Newfoundland from c. 5.7 to 4.0 cal. kyr BP. This may be linked to intensified Labrador Current export of cold meltwater and/or sea ice from the Arctic, presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong (north)westerly winds. After c. 4.0 cal. kyr BP, sea-surface conditions warmed up and sea ice decreased northeast of Newfoundland, but conditions were still cold south of Newfoundland. This suggests a decrease in Arctic meltwater export and westerly wind strength. After 2.9 - 2.5 cal. kyr BP, only minor changes in sea-surface conditions affected the study sites. Sea-surface temperatures increased and sea ice decreased at both sites, which may be related to a more meridional atmospheric circulation pattern associated with the general Northern Hemisphere neoglacial cooling. In Placentia Bay the warmest part of the record corresponds to the Roman Warm Period, while the warmest part of the records in Bonavista Bay notably corresponds to the Dark Ages.

Description: The concentration of radiocarbon (14C) differs between ocean and atmosphere. Radiocarbon determinations from samples which obtained their 14C in the marine environment therefore need a marine-specific calibration curve and cannot be calibrated directly against the atmospheric-based IntCal20 curve. This paper presents Marine20, an update to the internationally-agreed marine radiocarbon age calibration curve that provides a non-polar global-average marine record of radiocarbon from 0 – 55 cal kBP and serves as a baseline for regional oceanic variation. Marine20 is based upon 500 simulations with an ocean/atmosphere/biosphere box-model of the global carbon cycle that has been forced by posterior realisations of our Northern Hemispheric atmospheric IntCal20 14C curve and reconstructed changes in CO2 obtained from ice core data. These forcings enable us to incorporate carbon cycle dynamics and temporal changes in the atmospheric 14C level. The box-model simulations of the global-average marine radiocarbon reservoir age are similar to those of a more complex three-dimensional ocean general circulation model. However, simplicity and speed of the box model allow us to use a Monte Carlo approach to rigorously propagate the uncertainty in both the historic concentration of atmospheric 14C and other key parameters of the carbon cycle through to our final Marine20 calibration curve. This robust propagation of uncertainty is fundamental to providing reliable precision for the radiocarbon age calibration of marine based samples. We make a first step towards deconvolving the contributions of different processes to the total uncertainty; discuss the main differences of Marine20 from the previous age calibration curve Marine13; and identify the limitations of our approach together with key areas for further work. The updated values for 𝛥𝑅, the regional marine radiocarbon reservoir age corrections required to calibrate against Marine20, can be found at the data base http://calib.org/marine/. This data set includes: - the data plotted in the related manuscript, including Marine20, and IntCal20, the most recent version of the radiocarbon age calibration curves - the 500 northern hemispheric atmospheric Δ14C realisations of IntCal20 used as input for the calculation of Marine20 - a netCDF file from the LSG OCGCM with spatially resolved marine reservoir ages.

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.