A global review of long-range transported lead concentration and isotopic ratio records in snow and ice.

Lead (Pb) has been used for centuries in currency, transportation, building materials, cookware, makeup, and medicine. Mining of Pb in the Roman era matched the ever-increasing demand for metallurgy, transportation, and industry, resulting in a marked deposition of human activity in the geologic record. Researchers use global snowpacks and ice cores to study the historic anthropogenic use of Pb and subsequent deposition into the environment. As the cryosphere resources erode with climate warming, there is an increased urgency to map the content and source of Pb distribution in the environment. In this systematic literature review, we examine studies of long-traveled background atmospheric lead signals in natural, undisturbed snowpacks and ice cores globally. After a systematic review of the literature, we have synthesized 165 published papers to contextualize current data availability and examine spatial and temporal coverage of existing long-range transported Pb records. Cumulatively, these papers contain 560 records for individual and transect sample sites. Of these site records, 147 are ice core analyses, 389 are from snowpits, and 24 span the snow to ice transition. The records are globally distributed, with a high concentration of records at the poles and fewer records at low latitude alpine sites. Long timescale records are available from the Greenland and Antarctic ice sheets (>100 000 years). Shorter timescale records are available for alpine glaciers (>15 000 years) and persistent snowpacks (generally <5 years). To illustrate the research potential of these records, we selected key global records to analyze and contextualize the Pb pollution record from the North Pacific, noting its unique record of China's industrial revolution and the subsequent explosion of industrial output from China over the last 45 years. Finally, we provide recommendations for future studies aimed at reducing current temporal and spatial gaps in the records. We suggest analyzing archived ice cores never before analyzed for Pb, focused proposals on regions with critical data gaps, continuous resampling of sites to include modern Pb emission sources, and use of analysis techniques which have low sample preparation requirements, high sensitivity, and capability for ultra-trace concentration Pb analysis.