The stable isotope composition of radiogenic and natural elements provides a powerful tool for unraveling element sources and biogeochemical processes in the marine environment. Depending on the element, trace element isotope ratios can (1) narrow possible sources of the element in a sample and/or (given a temporal history boundary condition) constrain the time the when the element departed the ocean surface (e.g., Pb, Nd), (2) provide information on redox processes that the element is directly or indirectly involved in (e.g., Fe, Mo, Tl), (3) indicate the extent of biological uptake and/or ocean mixing of the element (e.g., Cd, Zn).However, these trace metals occur at picomolar to nanomolar concentrations, and precise stable isotope measurements require 100-1000 times more sample than required for concentration determination. AbstractWe report data on the isotopic composition of cadmium, copper, iron, lead, zinc, and molybdenum at the GEOTRACES IC1 BATS Atlantic intercalibration station. In general, the between lab and within-lab precisions are adequate to resolve global gradients and vertical gradients at this station for Cd, Fe, Pb, and Zn. Cd and Zn isotopes show clear variations in the upper water column and more subtle variations in the deep water; these variations are attributable, in part, to progressive mass fractionation of isotopes by Rayleigh distillation from biogenic uptake and/or adsorption. Fe isotope variability is attributed to heavier crustal dust and hydrothermal sources and light Fe from reducing sediments. Pb isotope variability results from temporal changes in anthropogenic source isotopic compositions and the relative contributions of U.S. and European Pb sources. Cu and Mo isotope variability is more subtle and close to analytical precision. Although the present situation is adequate for proceeding with GEOTRACES, it should be possible to improve the within-lab and between-lab precisions for some of these properties.

A record of the hydrogen isotopic composition of terrestrial leaf waxes (δDwax) in sediment cores from Lake Titicaca provides new insight into the precipitation history of the Central Andes and controls of South American Summer Monsoon (SASM) variability since the last glacial period. Comparison of the δDwax record with a 19-kyr δD record from the nearby Illimani ice core supports the 2 0 1 4 ) 2 interpretation that precipitation δD is the primary control on δDwax with a lesser but significant role for local evapotranspiration and other secondary influences on δDwax. The Titicaca δDwax record confirms overall wetter conditions in the Central Andes during the last glacial period relative to a drier Holocene. During the last deglaciation, abrupt δDwax shifts correspond to millennial-scale events observed in the high-latitude North Atlantic, with dry conditions corresponding to the Bølling-Allerød and early Holocene periods and wetter conditions during late glacial and Younger Dryas intervals. We observe a trend of increasing monsoonal precipitation from the early to the late Holocene, consistent with summer insolation forcing of the SASM, but similar hydrologic variability on precessional timescales is not apparent during the last glacial period. Overall, this study demonstrates the relative importance of high-latitude versus tropical forcing as a dominant control on glacial SASM precipitation variability. , E A R T H A N D P L A N E T A R Y S C I E N C E L E T T E R S 4 0 8 (

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Wildfires have increased in California in recent decades, linked to rising temperatures coinciding with high offshore winds and later onsets of the rainy season (Goss et al., 2020). Extreme fire-inducing conditions in late 2017 led the 2017-2018 Thomas Fire to become the largest wildfire in California's history at the time (Cal Fire, 2018). The Thomas Fire began on December 4, 2017 when two separate fires ignited south of Thomas Aquinas College in Ventura County. Several factors including dry vegetation, unusually strong Santa Ana winds, and low humidity in the winter of 2017 contributed to the spread of the fire. In

Stable isotope analysis of leaf waxes in a sediment core from Laguna La Gaiba, a shallow