Description: Geological archives record multiple reversals of Earth’s magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.

Description: We performed geochemical and sedimentological analyses on a 12.2 m long, radiocarbon-dated sediment core collected from Wide Channel (50°S; Chile) to reconstruct fluctuations of the marine-terminating HPS19, Penguin and Europa glaciers, located along the western side of the Southern Patagonian Icefield. The JPC42 sediment core was collected with a Jumbo Piston corer onboard the RV/IB Nathaniel B. Palmer in July 2005. An additional 1.5 m long Kasten core (KC41) was retrieved to sample the sediment-water interface. Both cores were scanned on an ITRAX XRF core scanner at WHOI in August 2008 and then sampled in 2 cm thick slices (ca.10 cm³) every 10 cm at the Marine and Geology Repository of Oregon State University in February 2021. Samples were freeze-dried at Ghent University, and all discrete analyses were performed at a 10 cm interval, except for CaCO3 in the lower 5.9 m of the core, which was analyzed at a 20 cm interval.

Description: Organic geochemical and sedimentological data analyzed at a 10 to 20 cm interval on the JPC42 and KC41 cores including total organic carbon content, stable carbon isotopes, marine organic carbon content, calcium carbonate, grain-size mode, and ice-rafted debris (particles 〉150 µm).

Description: Inorganic geochemical data of the JPC42 and KC41 cores obtained by ITRAX XRF core scanning (Cox Analytical Instruments) at the Woods Hole Oceanographic Institution, PC1 scores, and detrended PC1 scores, at a resolution of 2 mm. The XRF scanner was operated with 20 s scan times using a Mo X- Ray tube set to 30 kV and 45 mA. Elemental variations are expressed in terms of centered log-ratios (clr) to avoid dilution effects and to overcome the closed-sum effect and non-negative nature of compositional data (Weltje et al., 2015, doi:10.1007/978-94-017-9849-5_21). The table contains both the raw (cps; counts per second) and processed clr (dimensionless) data. Principal Component Analysis (PCA) was conducted with XLSTAT v2016 and used to examine the covariance within the XRF core scanner data. Increasing PC1 scores are interpreted to represent a relative increase in terrestrial sediment supply, and vice versa.

Description: Mean grain size predicted at a 2 mm resolution using the XRF intensities of Fe, K, Ti, Rb, Zr and Mn following Liu et al. (2019, doi:10.1029/2018GC008154). A set of 112 samples was used to calibrate the prediction model.

Description: Age-depth model of the JPC42 sediment core. The core chronology is based on the radiocarbon ages published in Caniupán et al. (2014, doi:10.1016/j.yqres.2014.07.009). All radiocarbon ages were re-calibrated using the SHCal20 calibration curve (Hogg et al., 2020, doi:10.1017/RDC.2020.59) and a marine reservoir age of 780 yr (Caniupán et al., 2014). The age-depth model and sedimentation rates were calculated using the BACON 2.5.5 software (Blaauw and Christen, 2011, doi:10.1214/11-BA618) in R (R Core Team, 2020, https://www.R-project.org/), taking into account the instantaneous deposition of the four turbidites at 1089 - 1049, 551 - 516, 383 - 364, and 171 - 158 cm. The table contains the mean age of the sediment every 1 mm.

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.