Response of a marine-terminating Greenland outlet glacier to abrupt cooling 8200 and 9300 years ago

Long-term records of Greenland outlet-glacier change extending beyond the satellite era can inform future predictions of Greenland Ice Sheet behavior. Of particular relevance is elucidating the Greenland Ice Sheet's response to decadal- and centennial-scale climate change. Here, we reconstruct the early Holocene history of Jakobshavn Isbræ, Greenland's largest outlet glacier, using 10Be surface exposure ages and 14C-dated lake sediments. Our chronology of ice-margin change demonstrates that Jakobshavn Isbræ advanced to deposit moraines in response to abrupt cooling recorded in central Greenland ice cores ca. 8,200 and 9,300 years ago. While the rapid, dynamically aided retreat of many Greenland outlet glaciers in response to warming is well documented, these results indicate that marine-terminating outlet glaciers are also able to respond quickly to cooling. We suggest that short lag times of high ice flux margins enable a greater magnitude response of marine-terminating outlets to abrupt climate change compared to their land-terminating counterparts

A beryllium-10 chronology of late-glacial moraines in the upper Rakaia valley, Southern Alps, New Zealand supports Southern- Hemisphere warming during the Younger Dryas

Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination

Spatiotemporal patterns of fault slip rates across the Central Sierra Nevada frontal fault zone

Patterns in fault slip rates through time and space are examined across the transition from the Sierra Nevada to the Eastern California Shear Zone–Walker Lane belt. At each of four sites along the eastern Sierra Nevada frontal fault zone between 38 and 39° N latitude, geomorphic markers, such as glacial moraines and outwash terraces, are displaced by a suite of range-front normal faults. Using geomorphic mapping, surveying, and 10Be surface exposure dating, mean fault slip rates are defined, and by utilizing markers of different ages (generally, ~ 20 ka and ~ 150 ka), rates through time and interactions among multiple faults are examined over 104–105 year timescales. At each site for which data are available for the last ~ 150 ky, mean slip rates across the Sierra Nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval (~ 20 ky and ~ 150 ky timescales): 0.3 ± 0.1 mm year− 1 (mode and 95% CI) at both Buckeye Creek in the Bridgeport basin and Sonora Junction; and 0.4 + 0.3/−0.1 mm year− 1 along the West Fork of the Carson River at Woodfords. Data permit rates that are relatively constant over the time scales examined. In contrast, slip rates are highly variable in space over the last ~ 20 ky. Slip rates decrease by a factor of 3–5 northward over a distance of ~ 20 km between the northern Mono Basin (1.3 + 0.6/−0.3 mm year− 1 at Lundy Canyon site) to the Bridgeport Basin (0.3 ± 0.1 mm year− 1). The 3-fold decrease in the slip rate on the Sierra Nevada frontal fault zone northward from Mono Basin is indicative of a change in the character of faulting north of the Mina Deflection as extension is transferred eastward onto normal faults between the Sierra Nevada and Walker Lane belt. A compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the Eastern California Shear Zone-Walker Lane belt. South of the Mina Deflection, extension is accommodated within a diffuse zone of normal and oblique faults, with extension rates increasing northward on the Fish Lake Valley fault. Where faults of the Eastern California Shear Zone terminate northward into the Mina Deflection, extension rates increase northward along the Sierra Nevada frontal fault zone to ~ 0.7 mm year− 1 in northern Mono Basin. This spatial pattern suggests that extension is transferred from more easterly fault systems, e.g., Fish Lake Valley fault, and localized on the Sierra Nevada frontal fault zone as the Eastern California Shear Zone–Walker Lane belt faulting is transferred through the Mina Deflection

Chronology of glaciations in the Sierra Nevada, California from 10Be surface exposure dating

We use 10Be surface exposure dating to construct a high-resolution chronology of glacial fluctuations in the Sierra Nevada, California. Most previous studies focused on individual glaciated valleys, whereas our study compares chronologies developed throughout the range to identify regional patterns in the timing of glacier response to major climate changes. Sites throughout the range indicate Last Glacial Maximum retreat at 18.8 ± 1.9 ka (2σ) that suggests rather consistent changes in atmospheric variables, e.g., temperature and precipitation, throughout the range. The penultimate glacial retreat occurred at ca 145 ka. Our data suggest that the Sierra Nevada landscape is dominated by glacial features deposited during marine isotope stage (MIS) 2 and MIS 6. Deposits of previously recognized glaciations between circa 25 and 140 ka, e.g., MIS 4, Tenaya, early Tahoe, cannot be unequivocally identified. The timing of Sierra Nevada glacial retreat correlates well with other regional paleoclimate proxies in the Sierra Nevada, but differs significantly from paleoclimate proxies in other regions. Our dating results indicate that the onset of LGM retreat occurred several thousand years earlier in the Sierra Nevada than some glacial records in the western US

Poisson and non-Poisson uncertainty estimations of 10Be/9Be measurements at LLNL–CAMS

We quantify the routine performance and uncertainties of 10Be measurements made on the CAMS FN accelerator mass spectrometer in combination with the CAMS high-intensity cesium sputter source. Our analysis compiles data from 554 primary and secondary standard targets measured on 47 different wheels in nine different run campaigns over a 1-year interval (September 2009–September 2010). The series includes 87, 86, and 85 measurements of each of three different secondary standards and 296 measurements of our primary standard, KNSTD3110 (01-5-4). The average initial 9Be3+ beam current is 22 ± 3 μA (1 standard deviation). Secondary standard targets, which are measured as unknowns in each of the wheels, have average statistical uncertainties based on counting statistics of 1.8%, 1.3%, and 0.8% (1σ) (September 2009–March 2010) and 1.3%, 1.0%, and 0.6% (April 2010–September 2010) for standard materials with 10Be/9Be = 5.35 × 10−13, 9.72 × 10−13, and 8.56 × 10−12, respectively. The mean measured ratio for each of the secondary standards (normalized to the primary standard) falls within the 1.1% uncertainties of the reported values for each standard material. The weighted standard deviation around the mean of this large number of runs is 2.5%, 2.0%, and 1.2% (September 2009–March 2010) and 1.5%, 1.1%, and 1.2% (April 2010–September 2010) for each secondary standard. These data indicate an additional source of uncertainty, 0.9–1.8% (April 2010–September 2010) and 0.2–1.0% (April 2010–September 2010), above that calculated from counting statistics alone. These 10Be AMS results demonstrate the precision and accuracy of the LLNL–CAMS system

Glacier extent during the Younger Dryas and 8.2-ka event on Baffin Island, Arctic Canada

Greenland ice cores reveal that mean annual temperatures during the Younger Dryas (YD) cold interval—about 12.9 to 11.7 thousand years ago (ka)—and the ~150-year-long cold reversal that occurred 8.2 thousand years ago were ~15° and 3° to 4°C colder than today, respectively. Reconstructing ice-sheet response to these climate perturbations can help evaluate ice-sheet sensitivity to climate change. Here, we report the widespread advance of Laurentide Ice Sheet outlet glaciers and independent mountain glaciers on Baffin Island, Arctic Canada, in response to the 8.2-ka event and show that mountain glaciers during the 8.2-ka event were larger than their YD predecessors. In contrast to the wintertime bias of YD cooling, we suggest that cooling during the 8.2-ka event was more evenly distributed across the seasons

Age of the Fjord Stade moraines in the Disko Bugt region, western Greenland, and the 9.3 and 8.2 ka cooling events

Retreat of the western Greenland Ice Sheet during the early Holocene was interrupted by deposition of the Fjord Stade moraine system. The Fjord Stade moraine system spans several hundred kilometers of western Greenland’s ice-free fringe and represents an important period in the western Greenland Ice Sheet’s deglaciation history, but the origin and timing of moraine deposition remain uncertain. Here, we combine new and previously published 10Be and 14C ages from Disko Bugt, western Greenland to constrain the timing of Fjord Stade moraine deposition at two locations w60 km apart. At Jakobshavn Isfjord, the northern of two study sites, we show that Jakobshavn Isbræ advanced to deposit moraines ca 9.2 and 8.2e8.0 ka. In southeastern Disko Bugt, the ice sheet deposited moraines ca 9.4e9.0 and 8.5e8.1 ka. Our ice-margin chronology indicates that the Greenland Ice Sheet in two distant regions responded in unison to early Holocene abrupt cooling 9.3 and 8.2 ka, as recorded in central Greenland ice cores. Although the timing of Fjord Stade moraine deposition was synchronous in Jakobshavn Isfjord and southeastern Disko Bugt, within uncertainties, we suggest that Jakobshavn Isbræ advanced while the southeastern Disko Bugt ice margin experienced stillstands during the 9.3 and 8.2 ka events based on regional geomorphology and the distribution of 10Be ages at each location. The contrasting style of ice-margin response was likely regulated by site-specific ice-flow characteristics. Jakobshavn Isbræ’s high ice flux results in an amplified ice-margin response to a climate perturbation, both warming and cooling, whereas the comparatively low-flux sector of the ice sheet in southeastern Disko Bugt experiences a more subdued response to climate perturbations. Our chronology indicates that the western Greenland Ice Sheet advanced and retreated in concert with early Holocene temperature variations, and the 9.3 and 8.2 ka events, although brief, were of sufficient duration to elicit a significant response of the western Greenland Ice Sheet