Description: Significance: Cold and dry glacial-state climate conditions persisted in the Southern Hemisphere until approximately 17.7 ka, when paleoclimate records show a largely unexplained sharp, nearly synchronous acceleration in deglaciation. Detailed measurements in Antarctic ice cores document exactly at that time a unique, ∼192-y series of massive halogen-rich volcanic eruptions geochemically attributed to Mount Takahe in West Antarctica. Rather than a coincidence, we postulate that halogen-catalyzed stratospheric ozone depletion over Antarctica triggered large-scale atmospheric circulation and hydroclimate changes similar to the modern Antarctic ozone hole, explaining the synchronicity and abruptness of accelerated Southern Hemisphere deglaciation. Abstract: Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found 〉2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.

Description: Assessments of climate sensitivity to projected greenhouse gas concentrations underpin environmental policy decisions, with such assessments often based on model simulations of climate during recent centuries and millennia1, 2, 3. These simulations depend critically on accurate records of past aerosol forcing from global-scale volcanic eruptions, reconstructed from measurements of sulphate deposition in ice cores4, 5, 6. Non-uniform transport and deposition of volcanic fallout mean that multiple records from a wide array of ice cores must be combined to create accurate reconstructions. Here we re-evaluated the record of volcanic sulphate deposition using a much more extensive array of Antarctic ice cores. In our new reconstruction, many additional records have been added and dating of previously published records corrected through precise synchronization to the annually dated West Antarctic Ice Sheet Divide ice core7, improving and extending the record throughout the Common Era. Whereas agreement with existing reconstructions is excellent after 1500, we found a substantially different history of volcanic aerosol deposition before 1500; for example, global aerosol forcing values from some of the largest eruptions (for example, 1257 and 1458) previously were overestimated by 20–30% and others underestimated by 20–50%.

Description: The firn core OH-12 was retrieved from Plateau Laclavere, a small ice cap on the northernmost end of the Antarctic Peninsula at about 1090 m above sea level in January 2016. The core was drilled down to 19.93 m depth. Subsamples for stable water isotope analysis were obtained from the core at 5 cm resolution. Stable water isotope measurements were performed in autumn 2016 using cavity ring-down spectrometers L2130-i and L2140-i (Picarro Inc.) coupled to an auto-sampler (L2130-i: PAL HTC-xt, CTC Analytics AG; L2140-i: Picarro Autosampler, Picarro Inc.). Glacio-chemical parameters (hydrogen peroxide, sulphur, sodium, black carbon) were determined in summer 2017 using a Continuous Flow Analysis (CFA) system as described by Röthlisberger et al. (2000) and McConnell et al. (2002, 2007). Sulphur and sodium concentrations were measured using two Thermo Finnigan Element2 High Resolution-Inductively Coupled Plasma-Mass Spectrometry (HR-ICP-MS) instruments. Black carbon (BC) was analyzed with a Single Particle Soot Photometer inter-cavity laser system (SP2, Droplet Measurement Technologies). Values of sea-salt sodium (ssNa) and non-sea-salt sulphur (nssS) were calculated from sodium and sulphur concentrations applying the approach of Röthlisberger et al. (2002) and Sigl et al. (2013) and using relative abundances from Bowen (Bowen, 1979). The core was dated using annual layer counting of hydrogen peroxide measurements. We additionally accounted for precipitation intermittency at the drill site by using precipitation data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 Reanalysis extracted from the grid point closest to the firn-core drill site. The core covers the period from July 2011 to January 2016. The data has been used for investigating recent climate and environmental changes in the northern Antarctic Peninsula region providing the basis for the retrieval and analysis of a deeper ice core from the same site.

Description: Rhodes et al. 2015 (doi:10.1126/science.1262005) The causal mechanisms responsible for the abrupt climate changes of the Last Glacial Period remain unclear. One major difficulty is dating ice rafted debris (IRD) deposits associated with Heinrich events: Extensive icebergs influxes into the North Atlantic Ocean, linked to global impacts on climate and biogeochemistry. In a new ice core record of atmospheric methane with ultra-high temporal resolution, we find abrupt methane increases within Heinrich stadials 1, 2, 4 and 5 that, uniquely, have no counterparts in Greenland temperature proxies. Using a heuristic model of tropical rainfall distribution, we propose that Hudson Strait Heinrich events caused rainfall intensification over Southern Hemisphere land areas, thereby producing excess methane in tropical wetlands. Our findings suggest that the climatic impacts of Heinrich events persisted for 740 to 1520 years. --- Rhodes et al. 2017 (doi:10.1002/2016GB005570) In order to understand atmospheric methane (CH_4) biogeochemistry now and in the future, we must apprehend its natural variability, without anthropogenic influence. Samples of ancient air trapped within ice cores provide the means to do this. Here we analyze the ultrahigh-resolution CH_4 record of the West Antarctic Ice Sheet Divide ice core 67.2-9.8 ka and find novel, atmospheric CH_4 variability at centennial time scales throughout the record. This signal is characterized by recurrence intervals within a broad 80-50 year range, but we find that age-scale uncertainties complicate the possible isolation of any periodic frequency. Lower signal amplitudes in the Last Glacial relative to the Holocene may be related to incongruent effects of firn-based signal smoothing processes. Within interstadial and stadial periods, the peak-to-peak signal amplitudes vary in proportion to the underlying millennial-scale oscillations in CH_4 concentration-the relative amplitude change is constant. We propose that the centennial CH_4 signal is related to tropical climate variability that influences predominantly low-latitude wetland CH_4 emissions.

Description: The firn core OH-12 was retrieved from Plateau Laclavere, a small ice cap on the northernmost end of the Antarctic Peninsula at about 1090 m above sea level in January 2016. The core was drilled down to 19.93 m depth. Glacio-chemical parameters (hydrogen peroxide, sulphur, sodium, black carbon) were determined in summer 2017 using a Continuous Flow Analysis (CFA) system as described by Röthlisberger et al. (2000) and McConnell et al. (2002, 2007). Sulphur and sodium concentrations were measured using two Thermo Finnigan Element2 High Resolution-Inductively Coupled Plasma-Mass Spectrometry (HR-ICP-MS) instruments. Values of sea-salt sodium (ssNa) and non-sea-salt sulphur (nssS) were calculated from sodium and sulphur concentrations applying the approach of Röthlisberger et al. (2002) and Sigl et al. (2013) and using relative abundances from Bowen (Bowen, 1979). The core was dated using annual layer counting of hydrogen peroxide measurements. We additionally accounted for precipitation intermittency at the drill site by using precipitation data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 Reanalysis extracted from the grid point closest to the firn-core drill site. The core covers the period from July 2011 to January 2016. The data has been used for investigating recent climate and environmental changes in the northern Antarctic Peninsula region providing the basis for the retrieval and analysis of a deeper ice core from the same site.