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The englacial stratigraphic architecture of internal reflection horizons (IRHs) as imaged by ice‐penetrating radar (IPR) across ice sheets reflects the cumulative effects of surface mass balance, basal melt, and ice flow. IRHs, considered isochrones, have typically been traced in interior, slow‐flowing regions. Here, we identify three distinctive IRHs spanning the Institute and Möller catchments that cover 50% of West Antarctica's Weddell Sea Sector and are characterized by a complex system of ice stream tributaries. We place age constraints on IRHs through their intersections with previous geophysical surveys tied to Byrd Ice Core and by age‐depth modeling. We further show where the oldest ice likely exists within the region and that Holocene ice‐dynamic changes were limited to the catchment's lower reaches. The traced IRHs from this study have clear potential to nucleate a wider continental‐scale IRH database for validating ice sheet models. Plain Language Summary: Ice‐penetrating radar is widely used to measure the thickness of ice sheets, critical to assessments of global sea level rise potential. This technique also captures reflections from chemical contrasts within the ice sheet, caused by the atmospheric deposition of conductive impurities, known as "internal reflection horizons" (IRHs) that can be traced over large distances. As these deposits are laid down in distinct events, most IRHs are isochronous age tracers and contain valuable information on past ice sheet processes. In this paper we trace and place age constraints on stratigraphic horizons across a large portion of the West Antarctic Ice Sheet, including regions where fast ice flow has disrupted the ice sheet stratigraphy. The resulting data set allows us to identify where the oldest ice is buried in the study region and provides evidence that flow of the ice sheet interior has been stable during the Holocene. Our results can be used to test the performance of ice sheet models, which seek to simulate the response of ice sheets to long‐term environmental change. Key Points: We measure and date individual isochronal radar internal reflection horizons across the Weddell Sea sector of the West Antarctic Ice SheetHorizons dated to 1.9–3.2, 3.5–6.0, and 4.6–8.1 ka are widespread and linked to previous radar surveys of the Ross and Amundsen Sea sectorsThese form the basis for a wider database of ice sheet architecture for validating and calibrating ice sheet models of West Antarctica [ABSTRACT FROM AUTHOR]

We report on an accumulation of mummified southern elephant seals (Mirounga leonina) from Inexpressible Island on the Victoria Land Coast (VLC), western Ross Sea, Antarctica. This accumulation is unusual, as elephant seals typically breed and molt on sub‐Antarctic islands further north and do not currently occupy the VLC. Prior ancient DNA analyses revealed that these seals were part of a large, Antarctic breeding population that crashed ~1,000 yr ago. Radiocarbon dates for Inexpressible Island mummies range from 380 to 3,270 yr before present, too old to have been created by Scott's Northern Party in 1912 and varying too widely in age to represent a catastrophic death assemblage. Skeletal measurements reveal that most Inexpressible Island mummies are adult or subadult males. The presence of male elephant seals on Inexpressible Island until several hundred years ago suggests that, at a minimum, it served as a haul‐out site for the large Antarctic population and may have hosted a breeding colony. The conditions that allowed this Antarctic population to use the Ross Sea, the factors spurring its decline, and the implications for the adaptability and sensitivity of the species to environmental change all merit further study. [ABSTRACT FROM AUTHOR]

The Indo‐Pacific Warm Pool (IPWP) contains the warmest surface ocean waters on our planet making it a major source of heat and moisture to the atmosphere. Changes in the extent and position of the IPWP likely impacted the tropical and global climate in the past and may also do in the future. With the aim to put recent ocean changes into a longer temporal context, we present new paleoceanographic sea surface temperature reconstructions from the heart of the Western Pacific Warm Pool, which is the warmest region within the IPWP, across the last 17,000 years. To provide an improved spatial and temporal regional context we use new and published sea surface temperature records from the IPWP and update previous compilation efforts (Linsley et al., 2010, https://doi.org/10.1038/ngeo1920). We similarly conclude that the IPWP was warmer in the early Holocene compared to the late Holocene. However, with the new data we are able to argue against a western displacement/expansion of the IPWP and suggest a warmer southern IPWP in the early Holocene. We explore the potential drivers of the Holocene IPWP cooling and propose a combination of processes including changes in the monsoonal winds associated with the position of the rain belt, the tropical Pacific mean climate, and upper water column mixing. The proposed climatic processes differentially impacted the IPWP subregions resulting in spatially diverse trends. Additionally, the late deglacial section of the records mostly show a gradual IPWP warming similar in structure to the atmospheric CO2 and/or Antarctica rising temperatures. Key Points: The Western Pacific Warm Pool was warmer in the early Holocene and cooled toward the present because of changes in insolation‐driven tropical Pacific mean stateThe Holocene cooling was mostly felt in the southern Indo‐Pacific Warm Pool regions likely responding to a complex combination of climatic processesThe deglacial Indo‐Pacific Warm Pool temperatures raised gradually similar to the atmospheric CO2 and/or Antarctica temperature changes [ABSTRACT FROM AUTHOR]