Ice Volume Research Articles

Reduced magnitude of Early Pleistocene intensification of Northern Hemisphere Glaciation

Increased magnitude and expanding geographic distribution of ice-berg rafted debris in deep ocean sediment cores and increasing amplitude of variability in the benthic oxygen isotope (δ18O) proxy-global ice volume from ∼2.7 Ma marks the intensification of the Northern Hemisphere glaciation (iNHG). However, the location, extent and volume of Northern Hemisphere Ice Sheets (NHISs) is poorly constrained by proximal geologic evidence, and global sea-level records cannot determine individual polar ice sheet contributions alone.Quantitative relationships between sediment transport, water depth and grain size on a wave-graded continental shelf were previously applied to Pliocene shallow-marine sedimentary deposits in Whanganui Basin, New Zealand to provide an independent relative sea level record (PlioSeaNZ; 3.3–2.5 Ma). Here, we extend the duration of the sea-level record from 3.3 to 1.7 Ma (X-PlioSeaNZ) using a well-documented, shallow-marine sedimentary succession, that outcrops in the Rangitikei River Valley of the Whanganui Basin.The resulting glacial-interglacial, relative sea-level fluctuations are up to 45 ± 12.5 m paced by 41 kyr-obliquity frequency during the Early Pleistocene, but also contain modulation of 100 kyr-eccentricity cycle. These maximum sea-level amplitudes are more comparable to the mean of those previously reconstructed from calibrated benthic δ18O (e.g. Miller et al., 2020), and are significantly lower than estimates provided by albeit limited geological evidence proximal to the NHIS (Batchelor et al., 2019). Here we suggest that while NHISs acquired continental extent by 2.6 Ma, their collective volume may be overestimated in benthic δ18O calibrations and area-volume reconstructions, by as much as 50%.We propose that a reduced aspect ratio of ice sheets during iNHG was driven by 41-kyr changes in integrated summer insolation and enhanced by a subglacial regolith feedback reducing resistance to basal sliding. Regardless, the lower ice volume through the iNHG implies a lower ice sheet sensitivity (ice equivalent sea-level per degree Celsius change in temperature) under higher atmospheric CO2 of 4–6 m/°C compared to ∼20 m/°C for the period since the Last Glacial Maximum. This ice sheet sensitivity still has significant implications for society and sea-level will continue to rise under current emissions.

Induced polarization in the transient electromagnetic method for detection of subsurface ice on Earth, Mars, and the Moon

The transient electromagnetic method (TEM) can capture an induced polarization (IP) signature of subsurface ice. Using numerical modeling of a horizontally layered earth, we investigate how IP in TEM can be exploited for subsurface ice detection on Earth, Mars, and the Moon. In the model we implement electrical parameters from laboratory measurements of ice, planetary regolith simulants, and terrestrial soil from the literature. In contrast to currently applied forward models, we include two Cole–Cole relaxation terms to model the dielectric relaxation of adsorbed water or salt hydrate in addition to the relaxation of ice. On Earth, IP signals of shallow layers of silt mixed with 44–100 vol% ice embedded in resistive host layers of 3 kΩm can be detected. Both at mid (45∘ N) and lower (35∘ N) latitudes on Mars, meter thick layers of massive ice can be detected at 10 m depth if the ice contains salts. Corresponding layers of 60 vol% ice mixed with Martian regolith simulant show similar detectability. For IP signals of lunar ice to be detected in ice volume fractions of 7.4%–46%, a development in TEM technology is required, including mitigation of early time interference, or enhancing the signal to noise level.

A pronounced deep water cooling in the Indian Ocean at ∼ 3.3–2.3 Ma linked to a major increase in the Antarctic ice volume

This study investigates changes in the bottom water circulation of the Indian Ocean since 6.5 Ma, based on benthic foraminiferal relative abundances and their stable isotope ratios from Ocean Drilling Program (ODP) Sites 709 and 758. A significant shift, from dominant North Indian Deep Water (NIDW) to Antarctic Bottom Water (AABW) circulation, is documented at ∼3.3 Ma. Principal Component Analysis (PCA) reveals two major benthic foraminiferal assemblages (PCA1 and PCA2). PCA2 is dominated by Nuttallides umbonifera, Globocassidulina subglobosa, and Epistominella exigua, representing cold and well‑oxygenated bottom water conditions between 3.3 and 2.3 Ma. The increased δ18O values of Cibicides wuellerstorfi and high relative abundance of N. umbonifera between ∼3.3 and 2.3 Ma at both sites, indicate an increased influence of AABW in the Indian Ocean due to a major increase in Antarctic ice volume. PCA1 is dominated by Uvigerina proboscidea, Fissurina spp., and miliolids, indicating oxygen-poor bottom waters and high surface productivity between 1.7 and 0.5 Ma associated with an influence of NIDW. The high relative abundance of U. proboscidea and low relative abundance of E. exigua signify low seasonality and sustained flux of organic matter with a signature of strong South Equatorial Counter Current formed by the seasonal reversal of winds during 1.7–0.5 Ma at Site 709.

Predicting trends in atmospheric CO2 across the Mid-Pleistocene Transition using existing climate archives

Abstract. During the Mid-Pleistocene Transition (MPT), ca. 1200–800 000 years ago (ka), the Earth's glacial cycles changed from 41 to 100 kyr periodicity. The emergence of this longer ice age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume in interglacial periods. Since there is no known change in external orbital forcing across the MPT, it is generally agreed that the cause of this transition is internal to the Earth system. Resolving the climate, carbon cycle, and cryosphere processes responsible for the MPT remains a major challenge in Earth and palaeoclimate science. To address this challenge, the international ice core community has prioritised recovery of an ice core record spanning the MPT interval. Here we present results from a simple generalised least-squares (GLS) model that predicts atmospheric CO2 out to 1.8 Myr. Our prediction utilises existing records of atmospheric carbon dioxide (CO2) from Antarctic ice cores spanning the past 800 kyr along with the existing LR04 benthic δ18Ocalcite stack (Lisiecki and Raymo, 2005; hereafter “benthic δ18O stack”) from marine sediment cores. Our predictions assume that the relationship between CO2 and benthic δ18O over the past 800 000 years can be extended over the last 1.5 million years. The implicit null hypothesis is that there has been no fundamental change in feedbacks between atmospheric CO2 and the climate parameters represented by benthic δ18O, global ice volume, and ocean temperature. We test the GLS-model-predicted CO2 concentrations against observed blue ice CO2 concentrations, δ11B-based CO2 reconstructions from marine sediment cores, and δ13C of leaf-wax-based CO2 reconstructions (Higgins et al., 2015; Yan et al., 2019; Yamamoto et al., 2022). We show that there is no clear evidence from the existing blue ice or proxy CO2 data to reject our predictions or our associated null hypothesis. A definitive test and/or rejection of the null hypothesis may be provided following recovery and analysis of continuous oldest ice core records from Antarctica, which are still several years away. The record presented here should provide a useful comparison for the oldest ice core records and an opportunity for further constraints on the processes involved in the MPT.

Thermal Performance Enhancement of Ice Storage Capsule by Dandelion-Shaped Fins

Limited thermal conductivity of water hinders the performance of ice storage systems. This study proposes a novel approach to enhance ice storage performance using nature-inspired, dandelion-shaped fins with multi-level branches within spherical capsules. We aim to optimize the fin configuration to maximize the cooling energy storage capacity. Based on the enthalpy-porosity method, the solidification of water inside spherical ice storage capsules is investigated numerically. Compared to finless capsules, dandelion-shaped fins significantly improve heat transfer. Fins with two levels of branches outperform other fin types that averagely 34.64% increment in dimensionless cooling energy storage capacity per unit time is achieved with less than 6% loss in dimensionless cooling energy storage capacity per unit weight. Notably, a higher fractal dimension of length further enhances the performance of fins. Aluminum is identified as the optimal fin material due to its efficiency and cost-effectiveness. Finally, a normalized equation is proposed to predict the ice volume fraction under different cooling temperatures.

Greening of India and revival of the South Asian summer monsoon in a warmer world

While it is accepted that the tropical hydrological cycle has intensified during past interglacial periods due to changes in insolation, greenhouse gases and ice volume, their respective influences are uncertain. Here we present a pollen record from Bengal Bay to reconstruct vegetation changes in India’s core monsoon zone during two warm periods, the current and last interglacial, comparing the data with numerical model simulations to assess the influence of different forcing mechanisms. Results show tropical forest expansion between 11.7-5 ka and 127-120 ka, defining two Indian humid periods, with the last interglacial showing the strongest monsoon activity, consistent with salinity reconstructions. Model-data comparison highlights boreal summer insolation as the primary driver of vegetation dynamics and monsoon intensity during interglacial periods, with CO2 and ice-sheets having a limited effect. Vegetation remains unaffected by pre-industrial CO2 variations above 250 ppmv, a threshold value that characterizes most interglacials of the last million years.

North Pacific warmth synchronous with the Miocene Climatic Optimum

Peak Neogene warmth and minimal polar ice volumes occurred during the Miocene Climatic Optimum (MCO, ca. 16.95−13.95 Ma) followed by cooling and ice sheet expansion during the Middle Miocene Climate Transition (MMCT, ca. 13.95−12.8 Ma). Previous records of northern high-latitude sea surface temperatures (SSTs) during these global climatic transitions are limited to Atlantic sites, and none resolve orbital-scale variability. Here, we present an orbital-resolution alkenone SST proxy record from the subpolar North Pacific that establishes a local maximum of SSTs during the MCO as much as 16 °C warmer than modern with rapid warming initiating the MCO, cooling synchronous with Antarctic ice sheet expansion during the MMCT, and high variability on orbital time scales. Persistently cooler North Pacific SST anomalies than in the Atlantic at equivalent latitudes throughout the Miocene suggest enhanced Atlantic northward heat transport under a globally warm climate. We conclude that a global forcing mechanism, likely elevated greenhouse gas concentrations, is the most parsimonious explanation for synchronous global high-latitude warmth during the Miocene.

Multidecadal decline in sea ice meltwater volume and Pacific Winter Water salinity in the Bering Sea revealed by ocean observations

Large amounts of freshwater and nutrients pass through the Bering Strait to the Arctic Ocean, making the Bering Sea a crucial marginal sea of the North Pacific Ocean. The hydrography and biological production of the Bering Sea are strongly influenced by the amount of sea ice produced and melted. The sea ice extent and production exhibited large interannual variability but no visible trend until 2016 when a strong decrease began. However, records of sea ice before 1979 and the beginning of satellite-based estimates do not exist. In this paper, we devised a methodology using historical temperature and salinity data, supplemented by historical oxygen isotope (δ18O) data, to estimate sea ice melt and its temporal variability in the Bering Sea from 1950 onward. Our results, consistent with estimates of sea ice thickness, indicate that the sea ice melt volume has declined significantly —following lower sea ice extent and production— with a decrease between 35 and 50 km3 (from 442 km3) between pre-1980 and post-1980 climatologies. In particular, our meltwater time series reveals a decline of 160 km3 between 2012 and 2018, which also reflects the strong decrease in sea ice volume between 2016 and 2018 that numerous previous studies have highlighted. We also evaluated the change in the salinity of the Pacific Winter Water (PWW), whose formation is also related to sea ice production. The time series of PWW salinity exhibits a strong decreasing trend, with a freshening of about 0.3 between the mid-1950 s and the mid-2010 s, that we attribute to a combination of a reduced sea ice production and the freshening of the Alaskan Coastal Current water. The decline in meltwater volume and PWW salinity that we observed strongly influences the stratification over the Bering shelf, with a significant weakening of the stratification in coastal polynya regions, and a stronger and increasingly temperature-controlled stratification in the rest of the shelf. These changes could have adverse consequences on the biological productivity of the northern Bering Sea.

Estimation of glacier-stored freshwater volume present in major tributaries of the Brahmaputra basin.

Estimation of the glacier-stored freshwater is important to understand the water security in the Himalayan region. While previous work has studied the western and central Himalayan glaciers, the eastern counterpart received less and more scattered attention. In this study, an attempt is made to quantify the total glacier-stored freshwater in the Brahmaputra basin and later compared with previous global models. Using open-source tools such as COSI-Corr and the Himalayan Glacier Thickness Mapper (HIGTHIM), the surface velocity and thickness of 1075 glaciers (> 1 km2) in the Brahmaputra basin were estimated, resulting in a current ice-volume estimate of 283 × 109 m3. Based on the laminar flow model, the mean ice volume ranges from 8284 to 230,186 m3, with an average of 36,570 m3. Sub-basin-wise evaluations of the total glacier-stored freshwater availability in the basin were also conducted, revealing that the Siang (89.998 × 109 m3, 31.45%) and Lohit (84.371 × 109 m3, 29.49%) sub-basins have significantly larger ice volumes than others. The average mean ice volume for each sub-basin are as follows: Teesta (45,233 m3), Sankosh (45,552 m3), Manas (39,581.7 m3), Subansiri (40,922.4 m3), Kameng (41,241.2 m3), Siang (36,120.5 m3), Dibang (31,792.2 m3), and Lohit (30,340.6 m3). Teesta, Sankosh, and Manas exhibit relatively higher average mean ice volumes than others. In comparison with the global studies, the present study's findings are acceptable with ensemble ice-volume estimates considering an uncertainty of ± 17.35%. Therefore, these results serve as a primary input for assessing the future changes in water resources and hazards related to water in the Brahmaputra basin.

Seroprevalence of Erysipelothrix rhusiopathiae in Beaufort Sea Polar Bears (Ursus maritimus) is Linked to Ringed Seal (Pusa hispida) Demographics.

Polar bear (Ursus maritimus) life history is intimately associated with the distribution of sea ice and their prey in Arctic ecosystems. These ecosystems are changing in response to climate warming, resulting in the increased prevalence of pathogens in polar bears. Erysipelothrix rhusiopathiae has a long history of infection in domestic species and more recently in wildlife in the Canadian Arctic. As a result of increasing reports of E. rhusiopathiae causing morbidity and mortality in Arctic terrestrial mammals, we tested the seroprevalence of E. rhusiopathiae in Beaufort Sea polar bears sampled in 1985-87, 1992, 1994, and 2003-11. Our sample of 180 polar bears (117 females, 61 males, two unknown) with a median age of 9 yr (range 1-26 yr) had a seropositivity of 27.2% (49/180 individuals). We used binomial logistic regressions to investigate biotic and abiotic factors that may be linked to seropositivity. The resulting top model found that increased predation on adult ringed seals (Pusa [Phoca] hispida) and negative winter Arctic Oscillation Index (AOI) years were associated with a higher probability of seropositivity. Ringed seals may be a reservoir for E. rhusiopathiae via their consumption of infected prey, as the pathogen can persist in marine fish, molluscs, and crustaceans. Negative winter AOIs in our data set reflected high ice volume years, which reduced ringed seal natality, resulting in fewer seal pups available as prey. Our results suggest that exposure to E. rhusiopathiae in Beaufort Sea polar bears is modulated by a predator-prey mechanism.

Arctic and Antarctic Sea Ice Thickness and Volume Changes From Observations Between 1994 and 2023

AbstractBoth Arctic and Antarctic sea ice are affected by climate change. While Arctic sea ice has been declining for several decades, Antarctic sea ice extent slowly increased until 2015, followed by a sharp drop in 2016. Quantifying sea ice changes is essential to assess their impacts on the ocean, atmosphere, ecosystems and Arctic communities. In this study, we combine sea ice thickness estimates from four satellite radar altimeters to derive the longest time series of homogeneous sea ice thickness for both hemispheres over 30 years (1994–2023). The record supports the rapid loss of sea ice in the Arctic for each month of the year and the heterogeneous changes in sea ice thickness in the Antarctic. The study confirms that most of the volume variability is due to the thickness variability, which holds true for both hemispheres. The sea ice thickness time series presented here offer new insights for models, in particular the possibility to evaluate sea ice reanalyses and to initialize forecasts, especially in the Antarctic, where the data set presented here has no equivalent in terms of spatial and temporal coverage.

Establishment of numerical model for precooling broccoli with ice water integrated with salicylic acid and its effect on broccoli apparent quality

Postharvest precooling is crucial for delaying yellowing of broccoli efficiently removing field heat. In this experiment, a numerical model for ice water precooling broccoli was established, and based on this, the main precooling parameters were optimized. Furthermore, the appropriate concentration of salicylic acid (SA) in the process of ice water integrated with SA precooling was determined. Through numerical simulation and experimental validation, the ice water precooling treatment with a 30 % ice volume fraction and a 1:1 mass ratio of ice water to broccoli was identified as optimal for achieving the best precooling uniformity and meeting the specified temperature requirements. Application of 2 mmol L-1 SA integrated with ice water precooling treatment effectively delayed yellowing, and maintained the apparent quality of broccoli, manifested as a higher h° value (chromaticity value) and chlorophyll content, a lower yellowing index. The shelf life of the treated broccoli was extended by 3 d

Evaluating water quality of rock glacier outflows in the Western Alps, Italy: a regional perspective.

Intact rock glaciers (RG) are considered valuable water storage because containing permafrost ice volumes. The hydrological relevance of RG is forecasted to increase with respect to glaciers under climate change scenarios, as well as RG's role as water resources in alpine basins for multiple uses. Besides the assessment of water amount stored in intact rock glaciers, the evaluation of water quality is of primary importance. Here, we present the results of a chemical survey performed on five outflows from intact RG in 2020-2023 in the Piedmont region, Western Alps, Italy, along a latitudinal gradient and in different geological settings. The survey aimed to assess the water quality of RG outflows based on chemical indicators (major ions, nutrients, trace metals). Sampling and analyses were performed according to standard methods for freshwater samples, paying specific attention to the analytical quality and consistency of the data. We considered seasonal and interannual variability of the main chemical variables and the possible effects of RG outflows on the chemistry of lakes and ponds located in proximity to the RG. All the investigated sites were characterized by low to moderate ion content, low nutrients, and trace metals close to or below the detection limit, indicating a good water quality status. Results suggested lithology as the main factor affecting the chemical composition of RG outflows. The results of this study indicate it is advisable to develop shared protocols and joint monitoring programs for data collecting at RG outflow sites all over the Alps, possibly integrating chemical and biological indicators, with the final aim of monitoring the water quality of these valuable resources and its temporal evolution under climate change.

Aeolian dust dynamics in southern Central Asia revealed by the multi-timescale loess records in southern Tajikistan

Dust activity in Central Asia (CA) holds significant scientific interest due to their broad social and environmental impacts. Loess deposits in CA serve as crucial natural archives, recording regional atmospheric characteristics and dust dynamics. The oldest loess in CA has been discovered in southern Tajikistan. However, debates persist regarding the wind dynamics of the Tajikistan loess deposition, which motivates our current study. By analyzing grain sizes of the last glacial loess and previous loess records since 800 ka, we determined that the Tajikistan loess consisted of post-storm floating dust and fine-grained dust transported by the westerlies. The reduced grain sizes may indicate less frequent dust storms. Our results provided explanation for the influence of global ice volume changes on the dust dynamics in southern Tajikistan, primarily by modulating sea-level pressure differences between the Caspian Sea and Hindu Kush/Pamirs. These ice volume changes also intensified rapid atmospheric fluctuations in CA, suggesting a sensitive response of the latter to glacial boundary conditions. Moreover, although precipitation variations may influence dust activities, their impact appears to be minimal. Collectively, our findings offer vital insights into the formation of loess strata and the development of extensive modern loess landforms in southern CA.

Evaluation of the ArcIOPS sea ice forecasts during 2021–2023

The operational sea ice forecasts from the Arctic Ice Ocean Prediction System (ArcIOPS) during 2021–2023 are validated against satellite-retrieved sea ice concentration and drift data, in situ and reanalyzed sea ice thickness data. The results indicate that the ArcIOPS has a reliable capacity on the Arctic sea ice forecasts for the future 7 days. Over the validation period, the root mean square error (RMSE) of the ArcIOPS sea ice concentration forecasts at a lead time of up to 168 h ranges between 8% and 20%, and the integrated ice edge error (IIEE) is lower than 1.6 × 106 km2 with respect to the Hai Yang 2B (HY-2B) sea ice concentration data. Compared to the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), sea ice volume evolution from the ArcIOPS forecasts is closer to that derived from the CS2SMOS sea ice thickness observations, which have been assimilated into the ArcIOPS. Sea ice thickness comparisons at three locations in the Beaufort Sea between the ArcIOPS forecasts and in situ mooring observations also prove that the sea ice thickness forecasts are credible, which sets a solid basis for supporting ice-breaker navigation in the Arctic thick ice zone. The sea ice drift deviations between the ArcIOPS forecasts and the National Snow and Ice Data Center (NSIDC) data are lower than 4 cm/s in most of the months. Future work will emphasize on developing multi-variable data assimilation scheme and fully coupled air‒ice‒ocean forecasting system for the Arctic sea ice forecasts.

Miocene ice sheet dynamics and sediment deposition in the central Ross Sea, Antarctica

Drill cores from the Antarctic continental shelf are essential for directly constraining changes in past Antarctic Ice Sheet extent. Here, we provide a sedimentary facies analysis of drill cores from International Ocean Discovery Program (IODP) Site U1521 in the Ross Sea, which reveals a unique, detailed snapshot of Antarctic Ice Sheet evolution between ca. 18 Ma and 13 Ma. We identify distinct depositional packages, each of which contains facies successions that are reflective of past baseline shifts in the presence or absence of marine-terminating ice sheets on the outermost Ross Sea continental shelf. The oldest depositional package (>18 Ma) contains massive diamictites stacked through aggradation and deposited in a deep, actively subsiding basin that restricted marine ice sheet expansion on the outer continental shelf. A slowdown in tectonic subsidence after 17.8 Ma led to the deposition of progradational massive diamictites with thin mudstone beds/laminae, as several large marine-based ice sheet advances expanded onto the mid- to outer continental shelf between 17.8 Ma and 17.4 Ma. Between 17.2 Ma and 15.95 Ma, packages of interbedded diamictite and diatom-rich mudstone were deposited during a phase of highly variable Antarctic Ice Sheet extent and volume. This included periods of Antarctic Ice Sheet advance near the outer shelf during the early Miocene Climate Optimum (MCO)—despite this being a well-known period of peak global warmth between ca. 17.0 Ma and 14.6 Ma. Conversely, there were periods of peak warmth within the MCO during which diatom-rich mudstones with little to no ice-rafted debris were deposited, which indicates that the Antarctic Ice Sheet was greatly reduced in extent and had retreated to a smaller terrestrial-terminating ice sheet, most notably between 16.3 Ma and 15.95 Ma. Post-14.2 Ma, diamictites and diatomites contain unambiguous evidence of subglacial shearing in the core and provide the first direct, well-dated evidence of highly erosive marine ice sheets on the outermost continental shelf during the onset of the Middle Miocene Climate Transition (MMCT; 14.2−13.6 Ma). Although global climate forcings and feedbacks influenced Antarctic Ice Sheet advances and retreats during the MCO and MMCT, we propose that this response was nonlinear and heavily influenced by regional feedbacks related to the shoaling of the continental shelf due to reduced subsidence, sediment infilling, and local sea-level changes that directly influenced oceanic influences on melting at the Antarctic Ice Sheet margin. Although intervals of diatom-rich muds and diatomite indicating open-marine interglacial conditions still occurred during (and following) the MMCT, repeated advances of marine-based ice sheets since that time have resulted in widespread erosion and overdeepening in the inner Ross Sea, which has greatly enhanced sensitivity to marine ice sheet instability since 14.2 Ma.

Glacial interglacial variations in the natural iron fertilization during the low sea ice periods along the eastern continental margin of Antarctica

The Southern Ocean sequesters atmospheric CO2 through biological pumps, though its driving factors are debated. Modern productivity is regulated by natural iron fertilization from micronutrient influx through dust, regeneration, and Antarctic glaciers and sea ice melting (ice melt). The productivity along the eastern Antarctic continental margin was low during the last glacial period and gradually increased through the deglacial to Late Holocene, marked by distinct productivity peaks. The micronutrients also varied similarly, with reduced glacial influx and an increase in the Holocene, which may cause productivity peaks. Therefore, the coherence of enhanced productivity and micronutrient influx is considered as enhanced iron fertilization period. The productivity peaks declined within ∼1.5 kyr, mostly due to the Ekman transport and sea ice formation. Along with ice melt, the independent weathering pattern that responds with glacial- interglacial ice volume changes suggest the source of micronutrients is not terrigenous. Shelf interaction of oceanic currents can influence the water column nutrient stock significantly, while its utilization occurs during reduced ice periods (low sea ice and high glacier melting) for productivity. Therefore, enhanced natural iron fertilization periods are considered as ice low periods that occurred in a periodicity of 2 kyrs, at ∼7.5 kyr BP, ∼5.5 kyr BP, ∼4 kyr BP, ∼ 2.5 kyr BP, and ∼0.5 kyr BP, likely due to the combined effects of atmospheric and oceanographic factors driven by the high amplitude regional temperature variability during the mid to late Holocene.

Contrasting the Penultimate Glacial Maximum and the Last Glacial Maximum (140 and 21 ka) using coupled climate–ice sheet modelling

Abstract. The configuration of the Northern Hemisphere ice sheets during the Penultimate Glacial Maximum differed to the Last Glacial Maximum. However, the reasons for this are not yet fully understood. These differences likely contributed to the varied deglaciation pathways experienced following the glacial maxima and may have had consequences for the interglacial sea level rise. To understand the differences between the North American Ice Sheet at the Last and Penultimate glacial maxima (21 and 140 ka), we perform two perturbed-physics ensembles of 62 simulations using a coupled atmosphere–ice sheet model, FAMOUS-ice, with prescribed surface ocean conditions, in which the North American and Greenland ice sheets are dynamically simulated with the Glimmer ice sheet model. We apply an implausibility metric to find ensemble members that match reconstructed ice extent and volumes at the Last and Penultimate glacial maxima. We use a resulting set of “plausible” parameters to perform sensitivity experiments to decompose the role of climate forcings (orbit, greenhouse gases) and initial conditions on the final ice sheet configurations. This confirms that the initial ice sheet conditions used in the model are extremely important in determining the difference in final ice volumes between both periods due to the large effect of the ice–albedo feedback. In contrast to evidence of a smaller Penultimate North American Ice Sheet, our results show that the climate boundary conditions at these glacial maxima, if considered in isolation, imply a larger Penultimate Glacial Maximum North American Ice Sheet than at the Last Glacial Maximum by around 6 m sea level equivalent. This supports the notion that the growth of the ice sheet prior to the glacial maxima is key in explaining the differences in North American ice volume.

Patterns of Plio‐Pleistocene Ice Volume Variability Recorded by the Large‐Magnitude Explosive Eruptions From the Kamchatka‐Kurile Volcanic Arc

AbstractMarine fallout ash beds can provide continuous, time‐precise records of highly explosive arc volcanism that can be linked with the climate record. An evaluation of revised Plio‐Pleistocene (0–4 Myr) tephrostratigraphies from Ocean Drilling Program Sites 881, 882, and 884 confirms cyclicity of the Kamchatka‐Kurile arc volcanism and a marked increase just after the intensification of the Northern Hemisphere glaciation at 2.73 Ma. The compositional constancy of the Kamchatka‐Kurile volcano‐magma systems through time points to external modulation of volcanic cyclicity and frequency. The stacked tephra record reveals periodic peaks in arc volcanicity at ∼0.3, ∼1.0, ∼1.6, ∼2.5, and ∼3.8 Myr that coincide with maxima of the global ice volume variability that have been linked with the amplitude modulation of the precession (0.3, 1.0 Myr) and obliquity (1.6, 2.5 and 3.8 Myr) bands. A simple model of a decreasing obliquity variance across the mid‐Pleistocene Transition at constant precession variance produces an excellent correlation of ash bed cycles with the variability of global benthic δ18O (r2 = 0.75), which implies that climate, and not direct orbital forcing, modulates Kamchatka‐Kurile arc volcanism. The rising influence of precession variance in the Kamchatka‐Kurile ash bed record after the mid‐Pleistocene Transition contrasts with the dominant 100 kyr signal in the benthic δ18O global ice volume variability, which may either reflect limitations of the ash bed record or an regional rather than global influence of ice volume variability. Our results indicate that climate influences the Kamchatka‐Kurile arc volcanism, which may influence climate only by feedback.

ICE volume 45 issue 10 Cover and Back matter

ICE volume 45 issue 10 Cover and Back matter