Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

/pdf/antarctic-surface-temperature-and-elevation-during-the-last-4t4lojjgbp.pdf

Antarctic surface temperature and elevation during the Last Glacial Maximum

Abstract. The injection of sulfur into the stratosphere by volcanic eruptions is the dominant driver of natural climate variability on interannual to multidecadal timescales. Based on a set of continuous sulfate and sulfur records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to 1900 CE), constituting an extension of the previous record by 7000 years. The database incorporates new-generation ice-core aerosol records with a sub-annual temporal resolution and a demonstrated sub-decadal dating accuracy and precision. By tightly aligning and stacking the ice-core records on the WD2014 chronology from Antarctica, we resolve long-standing inconsistencies in the dating of ancient volcanic eruptions that arise from biased (i.e., dated too old) ice-core chronologies over the Holocene for Greenland. We reconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolar sulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locations is in agreement with prior reconstructions for the past 2500 years. In total, these eruptions injected 7410 Tg S into the stratosphere: 70 % from tropical eruptions and 25 % from NH extratropical eruptions. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the HolVol VSSI estimates, representing the first Holocene-scale reconstruction constrained by Greenland and Antarctica ice cores. These new long-term reconstructions of past VSSI and SAOD variability confirm evidence from regional volcanic eruption chronologies (e.g., from Iceland) in showing that the Early Holocene (9500–7000 BCE) experienced a higher number of volcanic eruptions (+16 %) and cumulative VSSI (+86 %) compared with the past 2500 years. This increase coincides with the rapid retreat of ice sheets during deglaciation, providing context for potential future increases in volcanic activity in regions under projected glacier melting in the 21st century. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/PANGAEA.928646 (Sigl et al., 2021). 

https://essd.copernicus.org/articles/14/3167/2022/essd-14-3167-2022.pdf

Volcanic stratospheric sulfur injections and aerosol optical depth during the Holocene (past 11 500 years) from a bipolar ice-core array

The $\delta$D and $\delta^{18}$O values of water are key measurements in polar ice-core research, owing to their strong and well-understood relationship with local temperature. Deuterium excess, $d$, the deviation from the average linear relationship between $\delta$D and $\delta^{18}$O, is also commonly used to provide information about the oceanic moisture sources where polar precipitation originates. Measurements of $\delta^{17}$O and ``$^{17}$O excess" ($\Delta^{17}$O) are also of interest because of their potential to provide information complementary to \textit{d}. Such measurements are challenging because of the greater precision required, particularly for $\Delta^{17}$O. Here, high-precision measurements are reported for $\delta^{17}$O, $\delta^{18}$O, and $\delta$D on a new ice core from the South Pole, using a continuous-flow measurement system coupled to two cavity ring-down laser spectroscopy (CRDS) instruments. Replicate measurements show that at 0.5 cm resolution, external precision is $\sim0.2 \permil$ for $\delta^{17}$O and $\delta^{18}$O, and $\sim1 \permil$ for $\delta$D. For $\Delta^{17}$O, achieving external precision of $\sim 0.01 \permil$ requires depth averages of $\sim$50 cm. The resulting $\sim$54,000 year record of the complete oxygen and hydrogen isotope ratios from the South Pole ice core is discussed. The time series of $\Delta^{17}$O variations from the South Pole shows significant millennial-scale variability, and is correlated with the logarithmic formulation of deuterium excess ($d_{ln}$), but not the traditional linear formulation ($d$).

/pdf/continuous-flow-analysis-of-d17o-d18o-and-dd-of-h2o-on-an-2w4ytzziid.pdf

Continuous-Flow Analysis of δ17O, δ18O, and δD of H2O on an Ice Core from the South Pole

The rate and magnitude of the Antarctic Ice Sheet (AIS) contribution to global sea-level rise beyond 2100 ce remains highly uncertain. Past changes of the AIS, however, offer opportunities to understand contemporary and future ice sheet behaviour. In this Review, we outline how the AIS evolved through the pre-industrial Holocene, 11,700 years ago to 1850 ce. Three main phases of ice sheet behaviour are identified: a period of rapid ice volume loss across all sectors in the Early and Mid Holocene; a retreat inland of the present-day ice sheet margin in some sectors, followed by readvance; and continued ice volume loss in several sectors during the past few millennia, and in some areas up to and into the industrial era. Global sea levels rose by 2.4–12 m owing to the period of rapid Antarctic ice loss and possibly fell by 0.35–1.2 m owing to subsequent readvance. Changes in the AIS during the Holocene were likely driven by similar processes to those acting today and predicted for the future, which are associated with oceanic and atmospheric conditions as well as bed topography. Further work is required to better understand these processes and to quantify Antarctica’s contribution to past sea-level change. The Antarctic Ice Sheet (AIS) underwent dramatic changes over the Holocene, impacting global sea levels. In this Review, Jones et al. discuss changes in this ice sheet during the pre-industrial Holocene. The drivers behind these past changes are explored, as well as their relevance for current and future changes in the AIS. 

/pdf/stability-of-the-antarctic-ice-sheet-during-the-pre-2yd34yc6.pdf

Stability of the Antarctic Ice Sheet during the pre-industrial Holocene

. A new ice core drilled at the South Pole provides a 54 000-year paleoenvironmental record including the composition of the past atmosphere. This paper describes the SP19 chronology for the South Pole atmospheric gas record and complements a previous paper (Winski et al., 2019) describing the SP19 ice chronology. The gas chronology is based on a discrete methane (CH4) record with 20- to 190-year resolution. To construct the gas time scale abrupt changes in atmospheric CH4 during the glacial period and centennial CH4 variability during the Holocene were used to synchronize the South Pole gas record with analogous data from the West Antarctic Ice Sheet Divide ice core. Stratigraphic matching based on visual optimization was verified using an automated matching algorithm. The South Pole ice core recovers all expected changes in CH4 based on previous records. Smoothing of the atmospheric record due to gas transport in the firn is evident but relatively minor, despite the deep lock-in depth in the modern South Pole firn column. The new gas chronology, in combination with the existing ice age scale from Winski et al. (2019), allows a model-independent reconstruction of the gas age-ice age difference through the whole record, which will be useful for testing firn densification models.

/pdf/the-sp19-chronology-for-the-south-pole-ice-core-part-2-gas-24ufuhrxnt.pdf

The SP19 chronology for the South Pole Ice Core – Part 2: gas chronology, Δage, and smoothing of atmospheric records

. The South Pole Ice Core (SPICEcore) was drilled in 2014–2016 to provide a
detailed multi-proxy archive of paleoclimate conditions in East Antarctica
during the Holocene and late Pleistocene. Interpretation of these records
requires an accurate depth–age relationship. Here, we present the SPICEcore (SP19) timescale for the age of the ice of SPICEcore. SP19 is synchronized to the
WD2014 chronology from the West Antarctic Ice Sheet Divide (WAIS Divide) ice
core using stratigraphic matching of 251 volcanic events. These events
indicate an age of 54  302±519  BP (years before 1950) at the
bottom of SPICEcore. Annual layers identified in sodium and magnesium ions
to 11 341 BP were used to interpolate between stratigraphic volcanic tie
points, yielding an annually resolved chronology through the Holocene.
Estimated timescale uncertainty during the Holocene is less than 18 years
relative to WD2014, with the exception of the interval between 1800 to 3100
BP when uncertainty estimates reach ±25  years due to widely spaced
volcanic tie points. Prior to the Holocene, uncertainties remain within 124 years relative to WD2014. Results show an average Holocene accumulation rate
of 7.4 cm yr −1 (water equivalent). The time variability of accumulation rate
is consistent with expectations for steady-state ice flow through the modern
spatial pattern of accumulation rate. Time variations in nitrate
concentration, nitrate seasonal amplitude and δ15 N of N2 in turn are as expected for the accumulation rate variations. The highly
variable yet well-constrained Holocene accumulation history at the site can
help improve scientific understanding of deposition-sensitive climate
proxies such as δ15 N of N2 and photolyzed chemical
compounds.

/pdf/the-sp19-chronology-for-the-south-pole-ice-core-part-1-1jmtxgevtq.pdf

The SP19 chronology for the South Pole Ice Core – Part 1: volcanic matching and annual layer counting

The Santa Barbara post-wildfire debris flows and the Brumadinho tailing-dam failure were two of the most catastrophic flood events of the late 2010s. Both these events carried so much solid-phase material, that classic, clear-water, flood risk approaches cannot replicate them, or forecast other events like them. This case study applied the new non-Newtonian features in HEC-RAS 6.1 to these two events, testing the most widely used flood risk model on the two most common mud and debris flow hazards (post-wildfire floods and mine tailing dam failures). HEC-RAS reproduced the inundation boundaries and the event timing (where available) for both events. The ratio between the largest debris flow clasts and the channel size, parametric trade-offs, the “convex” alluvial plain topography, and the stochasticity introduced by urban infrastructure made the Santa Barbara modeling more difficult and less precise than Brumadinho. Despite these challenges, the results provide prototype scale validation and verification of these new tools in this widely applied flood risk model.

/pdf/prototype-scale-evaluation-of-non-newtonian-algorithms-in-ism0y0sr.pdf

Prototype Scale Evaluation of Non-Newtonian Algorithms in HEC-RAS: Mud and Debris Flow Case Studies of Santa Barbara and Brumadinho

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The SP19 chronology for the South Pole Ice Core – Part 1: volcanic matching and annual layer counting

Prototype Scale Evaluation of Non-Newtonian Algorithms in HEC-RAS: Mud and Debris Flow Case Studies of Santa Barbara and Brumadinho