Gordon R.M. Bromley

Paleoindian settlement of the high-altitude Peruvian Andes

Mountain dwellers of the Pleistocene Humans colonized the inhospitable high Andes at least 11.5 thousand years ago. Rademaker et al. unearthed evidence of hunter-gatherer occupation at heights of almost 4500 m in Peru in two open-air sites. The sites contained more than 750 tools, including likely spearheads and scrapers. A nearby rockshelter with sooted ceilings and floor detritus may have been a campsite. The sites were probably used seasonally for hunting vicuña and other high-altitude prey. Science, this issue p. 466 Artifacts and rock shelters indicate hunter-gatherer presence at ~4500 meters above sea level, 12.8 to 11.5 thousand years ago. Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival. The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions, hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the initial entry of humans to South America.

Younger Dryas deglaciation of Scotland driven by warming summers

Significance Resolving the full manifestation of past abrupt climate change is key to understanding the processes driving and propagating these events. As a principal component of global heat transport, the North Atlantic Ocean also is susceptible to rapid disruptions of meridional overturning circulation and thus widely invoked as a cause of abrupt climate variability in the Northern Hemisphere. We assess the impact of one such North Atlantic cold event—the Younger Dryas Stadial—on an adjacent ice mass and show that, rather than instigating a return to glacial conditions, this abrupt climate event was characterized by deglaciation. We suggest this pattern indicates summertime warming during the Younger Dryas, potentially as a function of enhanced seasonality in the North Atlantic. The Younger Dryas Stadial (YDS; ∼12,900–11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial–interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159–1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS.

Rapid Early-Holocene Deglaciation in the Ross Sea, Antarctica†

Deglaciation of the Ross Sea following the last ice age provides an important opportunity to examine the stability of marine ice sheets, and their susceptibility to changing environmental conditions. Insufficient chronology for Ross Sea deglaciation has helped sustain (i) the theory that this region contributed significantly to Meltwater Pulse 1A (MWP-1A), and (ii) the idea that Ross Sea grounding-line retreat occurred in a ‘swinging gate’ pattern hinged north of Roosevelt Island. We present deglaciation records from southern Transantarctic Mountain glaciers, which delivered ice to the central Ross Sea. Abrupt thinning of these glaciers 9-8 kyr BP coincided with deglaciation of the Scott Coast, ∼800 km to the north, and ended with the Ross Sea grounding line near Shackleton Glacier. This deglaciation removed grounded ice from most of the central and western Ross Sea in less than 2 kyr. The Ross Sea Sector neither contributed nor responded significantly to MWP-1A.

Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields

his work was supported by NSF grant EAR‐9118375 and National Geographic/WAITT Foundation grant 450‐16. A.E. Putnam acknowledges support from the Comer Family Foundation, the Lenfest Foundation, a Lamont‐Doherty Earth Observatory postdoctoral fellowship, and NSF grant EAR‐1554990. The data reported and discussed in this paper are listed in the references, tables, and supporting information.

Holocene ice recession at Polygon Spur, Reedy Glacier, Antarctica

The Holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the East Antarctic Ice Sheet. Here, we present both new radiocarbon and recalculations of previously published cosmogenic exposure-age data that constrain Holocene ice dynamics along upper Reedy Glacier in the southernmost Transantarctic Mountains. Ice remained at or close to its last glacial maximum position until the early Holocene, at which time it underwent thinning. A period of apparent relative stability in the mid-Holocene led to the formation of ice-dammed proglacial ponds, as well as of moraines located roughly two-thirds of the distance from the maximum position to the present-day ice margin. Renewed thinning began after 3600 yr BP, with ice reaching present-day levels by 2400 yr BP. Ice variations along upper Reedy Glacier likely reflect the balance between upstream propagation of mechanical thinning events at the glacier mouth and regional accumulation changes.