ABSTRACT. The Southern Hemisphere SHCal04 radiocarbon calibration curve has been updated with the addition of new data sets extending measurements to 2145 cal BP and including the ANSTO Younger Dryas Huon pine data set. Outside the range of measured data, the curve is based upon the ern Hemisphere data sets as presented in IntCal13, with an interhemispheric offset averaging 43 ± 23 yr modeled by an autoregressive process to represent the short-term correlations in the offset.

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From 2012 to 2016, California experienced one of the worst droughts since the start of observational records. As in previous dry periods, precipitation-inducing winter storms were steered away from California by a persistent atmospheric ridging system in the North Pacific. Here we identify a new link between Arctic sea-ice loss and the North Pacific geopotential ridge development. In a two-step teleconnection, sea-ice changes lead to reorganization of tropical convection that in turn triggers an anticyclonic response over the North Pacific, resulting in significant drying over California. These findings suggest that the ability of climate models to accurately estimate future precipitation changes over California is also linked to the fidelity with which future sea-ice changes are simulated. We conclude that sea-ice loss of the magnitude expected in the next decades could substantially impact California’s precipitation, thus highlighting another mechanism by which human-caused climate change could exacerbate future California droughts.

3a). Covering a landscape with ice stops cosmogenic nuclide production in the underlying rock. 65Subsequent glacial erosion first removes the most highly dosed, near-surface material before 66 excavating rock from depths containing progressively lower isotope concentrations ( Figure 3b). 67Thermal conditions at the ice sheet bed control its ability to erode, incorporate, and 68 transport rock and sediment. Warm-based ice (at the pressure melting point) can effectively 69 erode rock and transport sediment to and off the coast 14 ; thus, the isotopic record we present here 70 is strongly biased toward areas of the ice sheet that were warm based 15 . Cold-based ice, below 71 the pressure melting point, is frozen to the bed and generally non-erosive 16 ; it buries and 72 preserves ancient landscapes rather than eroding them. 73The ratio of the cosmogenic nuclides 26 Al and 10 Be provides additional information about 74 burial after initial exposure 12 . Because 26 Al (t 1/2 , 0.71 Myr) radiodecays more rapidly than 10 Be 75 (t 1/2 , 1.39 Myr), burial of previously exposed material will, over time, lower both the 26 Al/ 10 Be 76 ratio and the concentration of both isotopes ( Figure 3b). 26 Al and 10 Be are produced at a ratio of Miocene-age (7.5 Myr) sediment than to any of Quaternary age (Table SI1). This 10 Be-rich Table 131 SI1), which suggests that IRD there was derived from glacial erosion of material that was deep 132 below the land surface before East Greenland was ice-covered (Figure 3a). Such efficient erosion The best hope for detecting short periods of deglaciation is the 26 Al/ 10 Be ratio. 166Contemporary Greenlandic river sand, both glacially and non-glacially sourced, has a 26 Al/ 10 Be 167 ratio of 7.6±2.1 (1σ, n=5), which is likely the result of landscape re-exposure during substantial 168 mid-Holocene retreat 25 (SI Table 2). Sand deposited in the Keglen delta at Kangerlussuaq during 169 the end of the last glaciation ~7 kyr ago 26 has a lower than production 26 Al/ 10 Be ratio (Table SI2) 170 of 4.54±0.58, fully consistent with ratios we measured in marine cores over the last million 171 years. Thus, high precision 26 Al/ 10 Be ratio measurements of quartz extracted from a well-dated, 172high deposition rate core may reveal glacial/interglacial cycles and could be used to better assess 173 the lag time between exposure and marine deposition 27 . 174Cosmogenic isotopes preserved in marine sediment record progressive erosion of the pre-175 glacial landscape in East Greenland from ~7.5 to 2.7 My, the first growth of a full ice sheet at

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Lakes are highly sensitive recorders of climate processes, but are extremely difficult to correlate precisely to ice-core and marine records, especially in the absence of reliable radiocarbon dates. Relative paleointensity (RPI) of Earth's magnetic field is an independent method of correlating high-resolution climate records, and can be applied to both marine and terrestrial sediments, as well as (inversely) correlated to the cosmogenic nuclide records preserved in ice cores. Here we present the correlation of an RPI record from Mono Lake, California to GLOPIS, the Global PaleoIntensity Stack, which increases the age estimation of the basal Mono Lake sediments by N 20 000 yr (20 kyr), from ∼40 ka (kyr before present) to 67 ka. The Mono Lake sediments thus preserve paleoclimatic records of most of the last glacial period, from 67 to 14 ka. In addition, the paleointensity-based age of 40 ka for the geomagnetic excursion preserved at Mono Lake indicates that this is a record of the global Laschamp excursion.

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