High-precision 10Be chronology of moraines in the Southern Alps indicates synchronous cooling in Antarctica and New Zealand 42,000 years ago

Millennial-scale temperature variations in Antarctica during the period 80,000 to 18,000 years ago are known to anti-correlate broadly with winter-centric cold–warm episodes revealed in Greenland ice cores. However, the extent to which climate fluctuations in the Southern Hemisphere beat in time with Antarctica, rather than with the Northern Hemisphere, has proved a controversial question. In this study we determine the ages of a prominent sequence of glacial moraines in New Zealand and use the results to assess the phasing of millennial climate change. Forty-four 10Be cosmogenic surface-exposure ages of boulders deposited by the Pukaki glacier in the Southern Alps document four moraine-building events from Marine Isotope Stage 3 (MIS 3) through to the end of the Last Glacial Maximum (∼18,000 years ago; LGM). The earliest moraine-building event is defined by the ages of nine boulders on a belt of moraine that documents the culmination of a glacier advance 42,000 years ago. At the Pukaki locality this advance was of comparable scale to subsequent advances that, from the remaining exposure ages, occurred between 28,000 and 25,000, at 21,000, and at 18,000 years ago. Collectively, all four moraine-building events represent the LGM. The glacier advance 42,000 years ago in the Southern Alps coincides in Antarctica with a cold episode, shown by the isotopic record from the EPICA Dome C ice core, between the prominent A1 and A2 warming events. Therefore, the implication of the Pukaki glacier record is that as early as 42,000 years ago an episode of glacial cold similar to that of the LGM extended in the atmosphere from high on the East Antarctic plateau to at least as far north as the Southern Alps (∼44°S). Such a cold episode is thought to reflect the translation through the atmosphere and/or the ocean of the anti-phased effects of Northern Hemisphere interstadial conditions to the southern half of the Southern Hemisphere. Regardless of the mechanism, any explanation for the cold episode at 42,000 years ago must account for its widespread atmospheric footprint not only in Antarctica but also within the westerly wind belt in southern mid-latitudes

Paleoclimate Insights from ¹⁰Be Surface-Exposure Dating of Moraine Sequences in the Southern Alps of New Zealand

This thesis presents 10Be surface-exposure chronologies of moraines deposited by mountain glaciers in the Southern Alps of New Zealand during the past 35,000 years. These chronologies are based on a new determination of a local in situ 10Be production rate for the Southern Alps. Seventy-three 10Be dates of terminal moraines place expansions of the Lake Ohau glacier tongue to Last Glacial Maximum (LGM) positions at 32,520 ± 520 yrs ago, 22,510 ± 660 yrs ago, 18,220 ± 500 yrs ago, and 17,690 ± 350 yrs ago, corresponding to snowlines 850 - 750 m below present values. Beryllium-10 dates record a 40% reduction in length of the Lake Ohau glacier tongue by 17,380 ± 510 yrs ago. Twenty-six 10Be dates from late-glacial moraines document resurgence of the Tasman Glacier that culminated at 12,970 ± 300 yrs ago in response to a snowline ~500 m lower than present. Finally, forty-five10Be dates on moraines in the forefield of Cameron Glacier of the Arrowsmith Range, Southern Alps, track fluctuating recession of the glacier terminus since early Holocene time. Palaeo-snowlines were 240 m below present values during the early Holocene, and rose to 110 m below present by late Holocene time. The last resurgence of Cameron Glacier culminated by 523 yrs ago, followed by slow oscillating retreat of the terminus to the present day. Key conclusions are as follows. (1) The timing and magnitude of the LGM at Lake Ohau corresponds closely with glacier signatures in both polar hemispheres and in the tropics, suggesting that LGM cooling was globally synchronous. One possibility is that lower atmospheric CO2 produced global cooling during the LGM. (2) Major recession of the Ohau glacier beginning about 18,000 yrs ago was coeval with the northern Heinrich Stadial-1, implicating a bipolar seesaw mechanism for initiating the southern termination. (3) Tasman Glacier registered the Antarctic Cold Reversal in antiphase with northern stadials, suggesting that a bipolar seesaw mechanism operated in the south over a large geographical footprint. (4) Asynchronous Holocene glacier behavior in the Southern and European Alps reflects either direct summer radiation forcing and/or southward migration of Earth\u27s thermal equator

In situ10Be production-rate calibration from a 14C-dated late-glacial moraine belt in Rannoch Moor, central Scottish Highlands

An objective of terrestrial in situ cosmogenic nuclide research is to obtain precise and accurate production-rate estimates on the basis of geological calibration sites from a diverse range of latitudes and altitudes. However, a challenge has been to establish production rates on the basis of landforms for which independent ages have been determined directly using absolute isotopic dating techniques. Here we present a 10Be production-rate calibration from a recessional moraine belt located in Rannoch Moor, central Scottish Highlands (56.63°N, 4.77°W; ∼310 330 m a.s.l.). This moraine belt was deposited at the margin of the disintegrating late-glacial West Highland ice field (WHIF) during the final stages of deglaciation. Minimum-limiting 14C dates on macrofossils of the earliest terrestrial vegetation to arrive on the landscape place the timing of moraine abandonment, and hence exposure of morainal boulder surfaces to the cosmic-ray flux, to no later than 12,480 ± 100 calendar years before C.E. 1950 (cal yrs BP). Maximum-limiting 14C dates on marine shells incorporated into basal tills deposited during expansion of the WHIF to its full late-glacial extent place the onset of deglaciation, and thus deglaciation of Rannoch Moor, to no earlier than 12,700 ± 100 cal yrs BP. After removal of a single high-concentration outlier, surface 10Be concentrations of 11 boulders rooted in two sub-parallel moraine ridges exhibit a high degree of internal consistency and affords an arithmetic mean of 6.93 ± 0.24 [x104] atoms g−1 (1σ). This data set yields a site-specific 10Be production rate of 5.50 ± 0.18 at g−1 yr−1, based on the midpoint age 12,590 ± 140 cal yrs BP of the bracketing 14C chronology. Transforming this result to sea-level/high-latitude (SLHL) neutron-spallation 10Be production-rate values using Version 3 of the University of Washington (UW) Online Production-Rate Calculator yields upper and lower bounds, and a mid-point rate. Maximum-limiting SLHL 10Be production rates, based on minimum-limiting 14C age control, are 3.95 ± 0.11 (2.7%) at g−1 yr−1 for the commonly used Lm and St scaling protocols. The corresponding (non-dimensional) correction factor for a reference production rate determined by the LSDn scaling model is 0.79 ± 0.02 (2.7%). Minimum-limiting SLHL reference 10Be production rates, based on maximum-limiting 14C age control, are 3.88 ± 0.11 (2.7%) at g−1 yr−1 (St) and 3.89 ± 0.11 (2.7%) at g−1 yr−1 (Lm). The corresponding correction factor for LSDn scaling is 0.77 ± 0.02 (2.7%). SLHL reference production-rate values based on a midpoint age of 12,590 ± 140 yrs are 3.91 ± 0.11 (2.8%) at g−1 yr−1 (St) and 3.92 ± 0.11 (2.8%) at g−1 yr−1 (Lm). The corresponding correction factor for LSDn scaling is 0.78 ± 0.02. The production-rate calibration data set presented here for Scotland yields SLHL values that agree with those determined from calibration data sets based on directly dated landforms from northeastern North America, the Arctic, the Swiss Alps, the Southern Hemisphere middle latitudes, and from the high tropical Andes. We suggest that this production-rate calibration data set from the central Scottish Highlands, used together with the UW online calculators, will produce accurate 10Be surface-exposure ages in the British Isles.We acknowledge support from the Dan and Betty Churchill Exploration Fund and the Lamont-Doherty Earth Observatory (LDEO) Climate Center. A.E.P and G.R.M.B. each acknowledge support from the LDEO Postdoctoral Fellowship. A.E.P. acknowledges the Lenfest Foundation, the Comer Family Foundation, and the Quesada Family Fund. J.M.S. acknowledges support from the Lamont Climate Center. We thank R. Schwartz and J. Frisch for assistance in the laboratory, as well as D. Duerden, E. Watson, and H. Senn for their help during field work at Rannoch Moor. This is LDEO contribution number 8267.2020-11-2

Placing the 2012-2015 California-Nevada drought into a paleoclimatic context: Insights from Walker Lake, California-Nevada, USA

Assessing regional hydrologic responses to past climate changes can offer a guide for how water resources might respond to ongoing and future climate change. Here we employed a coupled water balance and lake evaporation model to examine Walker Lake behaviors during the Medieval Climate Anomaly (MCA), a time of documented hydroclimatic extremes. Together, a C-14-based shoreline elevation chronology, submerged subfossil tree stumps in the West Walker River, and regional paleoproxy evidence indicate a similar to 50 year pluvial episode that bridged two 140+ year droughts. We developed estimates of MCA climates to examine the transient lake behavior and evaluate watershed responses to climate change. Our findings suggest the importance of decadal climate persistence to elicit large lake-level fluctuations. We also simulated the current 2012-2015 California-Nevada drought and found that the current drought exceeds MCA droughts in mean severity but not duration

Correlation of Glacier ELA/Snowlines & Temperature Station data with ERA5 Temperature and Wind Speed, 1979 to 2017

This dataset contains the gridded correlation results from a study that sought to better understand the climatic footprint monitored by antipodal mid-latitude glacier populations. Understanding the links between glaciers and climate is critical for accurately interpreting contemporary cryosphere changes, and interrogating the causes of past glacier behavior. However, work is still needed to refine the extent to which they capture regional to hemisphere-scale atmospheric processes. A Pearson's correlation was performed between yearly summer seasonal data from the ERA5 gridded reconstructions of global temperature and wind changes on each available ERA5 pressure level and yearly glacier snowline/ELA elevations in the Southern Alps of New Zealand and in the European Alps. December-Febuary austral summer data was correlated with the Southern Alps records and June-August Northern Hemisphere summer data was correlated with the European Alps. The ERA5 input dataset was regridded onto a new monthly axis representing the true month lengths. Then the weighted seasonal average (December-February and June-August) was calculated. Individuals glaciers with Equilibrium Line Altitude (ELA; European Alps) and End of Summer Snowlines (EOSS; Southern Alps) were selected with respective records covering at least 80% of the 1979-2017/15 analysis period. The records from each glacier were then standardized and an EOF analysis was performed to obtain each location's First Principle Component for input into the Pearson's Correlation. A nearly identical set of analyses was performed using weather stations temperature data instead of glacier ELA/snowlines. The New Zealand station equivalent is from the National Institute of Water and Atmospheric Research (NIWA) New Zealand seven-station (NZ7S) series. The European Alps equivalent is from the HistAlp regional weather station syntheses. This companion analysis allows the glacier's ability to record the climate to be compared to that of meteorological instruments

Using photogrammetry to create virtual permanent plots in rare and threatened plant communities

Abstract Premise Many plant communities across the world are undergoing changes due to climate change, human disturbance, and other threats. These community‐level changes are often tracked with the use of permanent vegetative plots, but this approach is not always feasible. As an alternative, we propose using photogrammetry, specifically photograph‐based digital surface models (DSMs) developed using structure‐from‐motion, to establish virtual permanent plots in plant communities where the use of permanent structures may not be possible. Methods In 2021 and 2022, we took iPhone photographs to record species presence in 1‐m2 plots distributed across alpine communities in the northeastern United States. We then compared field estimates of percent coverage with coverage estimated using DSMs. Results Digital surface models can provide effective, minimally invasive, and permanent records of plant species presence and percent coverage, while also allowing managers to mark survey locations virtually for long‐term monitoring. We found that percent coverage estimated from DSMs did not differ from field estimates for most species and substrates. Discussion In order to continue surveying efforts in areas where permanent structures or other surveying methods are not feasible, photogrammetry and structure‐from‐motion methods can provide a low‐cost approach that allows agencies to accurately survey and record sensitive plant communities through time