Glacial-interglacial Timescales Research Articles

One-third of Southern Ocean productivity is supported by dust deposition.

Natural iron fertilization of the Southern Ocean by windblown dust has been suggested to enhance biological productivity and modulate the climate1-3. Yet, this process has never been quantified across the Southern Ocean and at annual timescales4,5. Here we combined 11 years of nitrate observations from autonomous biogeochemical ocean profiling floats with a Southern Hemisphere dust simulation to empirically derive the relationship between dust-iron deposition and annual net community production (ANCP) in the iron-limited Southern Ocean. Using this relationship, we determined the biological response to dust-iron in the pelagic perennially ice-free Southern Ocean at present and during the last glacial maximum (LGM). We estimate that dust-iron now supports 33% ± 15% of Southern Ocean ANCP. During the LGM, when dust deposition was 5-40-fold higher than today, the contribution of dust to Southern Ocean ANCP was much greater, estimated at 64% ± 13%. We provide quantitative evidence of basin-wide dust-iron fertilization of the Southern Ocean and the potential magnitude of its impact on glacial-interglacial timescales, supporting the idea of the important role of dust in the global carbon cycle and climate6-8.

No detectable influence of the carbonate ion effect on changes in stable carbon isotope ratios (δ13C) of shallow dwelling planktic foraminifera over the past 160 kyr

Abstract. Laboratory experiments showed that the isotopic fractionation of δ13C and of δ18O during calcite formation of planktic foraminifera are species-specific functions of ambient CO32- concentration. This effect became known as the carbonate ion effect (CIE), whose role for the interpretation of marine sediment data will be investigated here in an in-depth analysis of the 13C cycle. For this investigation, we constructed new 160 kyr long mono-specific stacks of changes in both δ13C and δ18O from either the planktic foraminifera Globigerinoides ruber (rub) or Trilobatus sacculifer (sac) from 112 and 40 marine records, respectively, from the wider tropics (latitudes below 38°). Both mono-specific time series Δ(δ13Crub) and Δ(δ13Csac) are very similar to each other, and a linear regression through a scatter plot of both data sets has a slope of ∼ 0.99 – although the laboratory-based CIE for both species differs by a factor of nearly 2, implying that they should record distinctly different changes in δ13C, if we accept that the carbonate ion concentration changes on glacial–interglacial timescales. For a deeper understanding of the 13C cycle, we use the Solid Earth version of the Box model of the Isotopic Carbon cYCLE (BICYLE-SE) to calculate how surface-ocean CO32- should have varied over time in order to be able to calculate the potential offsets which would by caused by the CIE quantified in culture experiments. Our simulations are forced with atmospheric reconstructions of CO2 and δ13CO2 derived from ice cores to obtain a carbon cycle which should at least at the surface ocean be as close as possible to expected conditions and which in the deep ocean largely agrees with the carbon isotope ratio of dissolved inorganic carbon (DIC), δ13CDIC, as reconstructed from benthic foraminifera. We find that both Δ(δ13Crub) and Δ(δ13Csac) agree better with changes in simulated δ13CDIC when ignoring the CIE than those time series which were corrected for the CIE. The combination of data- and model-based evidence for the lack of a role for the CIE in Δ(δ13Crub) and Δ(δ13Csac) suggests that the CIE as measured in laboratory experiments is not directly transferable to the interpretation of marine sediment records. The much smaller CIE-to-glacial–interglacial-signal ratio in foraminifera δ18O, when compared to δ13C, prevents us from drawing robust conclusions on the role of the CIE in δ18O as recorded in the hard shells of both species. However, theories propose that the CIE in both δ13C and δ18O depends on the pH in the surrounding water, suggesting that the CIE should be detectable in neither or both of the isotopes. Whether this lack of role of the CIE in the interpretation of planktic paleo-data is a general feature or is restricted to the two species investigated here needs to be checked with further data from other planktic foraminiferal species.

North Atlantic influence on the glacial amplitude of East Asian millennial-scale monsoon variability

Abstract Millennial-scale climate change is thought to be synchronous throughout the northern hemisphere and has been demonstrated to be strongly modulated by longer-term glacial-interglacial and orbital scale processes. However, processes that modulate the magnitude of millennial-scale variability (MMV) at the glacial-interglacial timescale remain unclear. We present multi-proxy evidence showing out-of-phase relationships between the MMV of East Asian and North Atlantic climate proxies at the eccentricity band. During most late Pleistocene glacial intervals, the MMV in North Atlantic SST and East Asian Monsoon proxies show a gradual weakening trend from glacial inceptions into glacial maxima, inversely proportional to that of North Atlantic ice rafted detritus record. The inverse glacial-age trends apply to both summer- and winter-monsoon proxies across the loess, speleothem, and marine archives, indicating fundamental linkages between MMV records of the North Atlantic and East Asia. We infer that intensified glacial-age iceberg discharge is accompanied by weakened Atlantic meridional overturning circulation via changes in freshwater input and water-column stability, leading to reduction in North Atlantic SST and wind anomalies, subsequently propagating dampened millennial-scale variability into the mid-latitude East Asian Monsoon region via the westerlies. Our results indicate that the impact of North Atlantic iceberg discharge and the associated variability in water-column stability at the millennial-scale is a primary influence on hydroclimate instability in East Asia.

Extracting paleo-weathering signals from authigenic phases in lake sediments: A case-study of Lake Baikal

Authigenic phases in lake sediments hold the potential to record changes in the isotope compositions of past lake water, potentially yielding valuable information on secular changes in continental weathering patterns and rates, including over past glacial cycles.Here, different leaching approaches are investigated with the aim of extracting Sr, Nd, Pb, and Be hosted in authigenic Fe-Mn (oxy)hydroxide sediment phases for precise isotope measurements. Elemental Al/Mn, Ca/Mn, and P/Mn ratios obtained via a mild reductive leach agree well with the composition of marine authigenic Fe-Mn phases. For core top sediments, leached Sr isotope compositions obtained with this leach agree well with the composition of lake water. The Be and Nd isotope compositions of core top leachates are consistent with the spatial variability observed in the water column. Due to high concentrations in Fe-Mn phases, leachate compositions are dominated by authigenic Be, Sr, Nd, and Pb, even in cases when as much as 40% of leached phases (by mass) are non-authigenic. These lines of evidence suggest that the mild reductive leach successfully extracts the modern lake isotope composition from modern sediments in terms of the isotope systems investigated. We further show that the leaching method is also reliable for older sediments (<340 ka): leached paleo-Sr isotope compositions are consistent between the current and previous interglacial periods, as well as for glacial periods. This suggests that reconstructed water isotope compositions are not affected by early diagenetic processes, instead reflecting environmental factors around the lake that determine the composition of weathering fluxes. Although more difficult to assess for Be, Nd, and Pb due to the heterogeneity of modern lake water, the data we present indicate the overall robustness of the leaching approach.These promising results open up lakes as archives for paleo-weathering reconstructions. Given that marine reconstructions face some important limitations (e.g., integration of basin-wide changes in weathering processes, long residence times for Sr, etc.Fe), lake records provide an avenue to improve our understanding of changes in regional weathering processes over glacial-interglacial timescales. The mild reductive leach used here may also be useful for meteoric Be studies in marine shelf settings, to prevent leaching of terrestrial sedimentary Fe-Mn oxy(hydroxide) phases.

Paleo±Dust: quantifying uncertainty in paleo-dust deposition across archive types

Abstract. Mineral dust aerosol concentrations in the atmosphere varied greatly on glacial–interglacial timescales. The greatest changes in global dust activity occurred in response to changes in orbital parameters (which affect dust emission intensity through glacial activity) and the lifetime of dust in the atmosphere (caused by changes in the global hydrological cycle). Long-term changes in the surface dust deposition rate are registered in geological archives such as loess, peats, lakes, marine sediments, and ice. Data provided by these archives are crucial for guiding simulations of dust and for better understanding the natural global dust cycle. However, the methods employed to derive paleo-dust deposition rates differ markedly between archives and are subject to different sources of uncertainty. Here, we present Paleo±Dust, an updated compilation of bulk and &lt;10 µm paleo-dust deposition rates with quantitative 1σ uncertainties that are inter-comparable among archive types. Paleo±Dust incorporates a total of 285 pre-industrial Holocene (pi-HOL) and 209 Last Glacial Maximum (LGM) dust flux constraints from studies published until December 2022, including, for the first time, peat records. We also recalculate previously published dust fluxes to exclude data from the last deglaciation and thus obtain more representative constraints for the last pre-industrial interglacial and glacial end-member climate states. Based on Paleo±Dust, the global LGM:pi-HOL ratio of &lt;10 µm dust deposition rates is 3.1 ± 0.7 (1σ). We expect Paleo±Dust to be of use for future paleoclimate dust studies and simulations using Earth system models of high to intermediate complexity. Paleo±Dust is publicly accessible at https://doi.org/10.1594/PANGAEA.962969 (Cosentino et al., 2024).

Organic carbon burial and their implication on sea surface primary productivity in the middle Okinawa Trough over the past 200 ka

The long-term burial of organic carbon in marginal seas plays a critical role in Earth’s carbon cycle and climate change. However, the mechanism of organic carbon (OC) burial in the Okinawa Trough (OT) during glacial-interglacial timescales remains unclear. In this study, we analyzed the foraminiferal carbon isotopes, total organic carbon (TOC), and δ13C-TOC over the past 200 ka in core Z1 collected in the central OT. We aimed to reveal the history of OC burial in the middle Okinawa Trough during the past 200 ka, and we combined our findings with relevant paleoenvironmental indices to reveal underlying mechanisms. We found reduced surface primary productivity during MIS 6, which may indicate changes in the pathways of the Kuroshio Current (KC). Furthermore, we observed decoupling between high TOC flux and low OC burial during glacial periods. We proposed that the dilution effect caused by the high sedimentation rate and poor OC preservation during the glacial period resulted in the low TOC content. Ventilation of the North Pacific Intermediate Water (NPIW) regulated the redox conditions of the intermediate water in the Okinawa Trough. Additionally, the intensified Kuroshio Current during interglacial phases led to water column stratification, creating reducing conditions in the bottom water and facilitating improved OC preservation. Subsequently, the enhanced water column oxygenation resulting from the oxygen carried by the intensified glacial NPIW weakened the burial of OC. This study sheds new light on our understanding of the carbon cycle in marginal seas on a glacial-interglacial timescale.

Chronology and paleoclimatic context of hominin occupations in the Fenhe River Basin of northern China during the middle to Late Pleistocene

The relationship between climate change and hominin evolution over the Pleistocene in East Asia is still poorly understood, in particular due to the limited number of archaeological finds and fossils with reliable chronologies. Paleolithic sites preserved in loess-paleosol sequences in eastern Chinese Loess Plateau provide prospective evidence for understanding hominin evolution and dispersion across the Middle to Late Pleistocene in northern China. The Fenhe River Basin has been known as a key area for paleolithic sites and fossil hominins. Here, quartz Optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating was employed on 61 samples from 13 paleolithic sites in the Fenhe River Basin. The reliability of the ages are checked by analysis of luminescence characteristics and comparison between quartz OSL and K-feldspar pIRIR ages. Paleoclimatic records were established using alternating loess-paleosol sequences, and multi-proxy indices of grain size, magnetic susceptibility, CaCO3 and color from the dated sites. These results provide the reliable chronology for hominin presence in the Fenhe River Basin spanning the past three glacial-interglacial cycles. Our results show that this region experienced predominantly dusty, dry and cold conditions during glacials and comparatively moist and warm interglacial conditions, that are sensitive to variations in East Asian Summer and Winter Monsoon (EASM and EAWM respectively) intensities over glacial-interglacial timescales. The Fenhe River Basin is a key geographic refuge for hominins during glacial-interglacial climatic changes in northern China. It was occupied over glacial and interglacial periods spanning at least the last 370 ky, and the evidence for hominin presence is especially clear from ∼250 to 60 ka and since ∼35 ka. The frequency of hominin activity, as indicated by the number of archaeological sites and density of stone artifacts, increased during warm and humid periods of MIS 7 and MIS 5, in contrast to the cold, windy, and dry period of MIS 6. Site numbers increased in MIS 3 and the Last Glacial Maximum, in association with microblade technology. The dating results indicate that hominins with ‘modern’ features may have occurred in the Fenhe River Basin ∼140 ka ago, however, the exact timing of modern human occupation in the region needs a more combined approach consisting of morphological, ancient DNA and geochronological studies.

Large shift in the upper water column characteristics of the west-central Bay of Bengal during the last glacial-interglacial transition

The upper water column structure in the Bay of Bengal is strongly influenced by the monsoon and associated processes. However, the records of variation in water column stratification during different monsoon phases, are scarce from this region. Here, we have reconstructed the variation in monsoon induced upwelling, mixed layer and thermocline during the last glacial-interglacial transition, by using the relative abundance of mixed layer and thermocline dwelling planktic foraminifera, relative abundance of Globigerina bulloides and the stable oxygen isotopic ratio (δ18O) of surface dwelling Globigerinoides ruber. We report a weaker upwelling during the last glacial interval and late Greenlandian-Northgrippian Age, and strong upwelling during the deglaciation and Meghalayan Age. The intense upwelling shoaled the thermocline during the early glacial interval, last glacial maximum, late deglaciation and the Meghalayan Age. The mixed layer depth increased during the early deglaciation and Late Greenlandian-Northgrippian due to the reduced upwelling and stronger winter monsoon. The shift in the position of the core site with respect to the low salinity coastal currents, due to the rising sea level, also influenced the upper water column structure in the west-central Bay of Bengal. Therefore, the reorganization of the upper water column structure in the west-central Bay of Bengal, on the glacial-interglacial time scale, was mainly influenced by a combination of the upwelling, fresh water influx, sea level and winter monsoon.

The Coupled Ice Sheet–Earth System Model Bern3D v3.0

Abstract Understanding climate variability from millennial to glacial–interglacial time scales remains challenging due to the complex and nonlinear feedbacks between ice, ocean, sediments, biosphere, and atmosphere. Complex climate models generally struggle to dynamically and comprehensively simulate such long time periods as a result of the large computational costs. Here, we therefore coupled a dynamical ice sheet model to the Bern3D Earth system model of intermediate complexity, which allows for simulating multiple glacial–interglacial cycles. The performance of the model is first validated against modern observations and its response to abrupt perturbations, such as atmospheric CO2 changes and North Atlantic freshwater hosing, is investigated. To further test the fully coupled model, the climate evolution over the entire last glacial cycle is explored in a transient simulation forced by variations in the orbital configuration and greenhouse gases and aerosols. The model simulates global mean surface temperature in fair agreement with reconstructions, exhibiting a gradual cooling trend since the last interglacial that is interrupted by two more rapid cooling events during the early Marine Isotope Stage (MIS) 4 and Last Glacial Maximum (LGM). Simulated Northern Hemispheric ice sheets show pronounced variability on orbital time scales, and ice volume more than doubles from MIS3 to the LGM in good agreement with recent sea level reconstructions. At the LGM, the Atlantic overturning has a strength of about 14 Sv (1 Sv ≡ 106 m3 s−1), which is a reduction by about one-quarter compared to the preindustrial. We thus demonstrate that the new coupled model is able to simulate large-scale aspects of glacial–interglacial cycles.

Oxygen isotope constraints on the ventilation of the modern and glacial Pacific

Changes in Pacific tracer reservoirs and transports are thought to be central to the regulation of atmospheric CO2 on glacial–interglacial timescales. However, there are currently two contrasting views of the circulation of the modern Pacific; the classical view sees southern sourced abyssal waters upwelling to about 1.5 km depth before flowing southward, whereas the bathymetrically constrained view sees the mid-depths (1–2.5 km) largely isolated from the global overturning circulation and predominantly ventilated by diffusion. Furthermore, changes in the circulation of the Pacific under differing climate states remain poorly understood. Through both a modern and a Last Glacial Maximum (LGM) analysis focusing on oxygen isotopes in seawater and benthic foraminifera as conservative tracers, we show that isopycnal diffusion strongly influences the mid-depths of the Pacific. Diapycnal diffusion is most prominent in the subarctic Pacific, where an important return path of abyssal tracers to the surface is identified in the modern state. At the LGM we infer an expansion of North Pacific Intermediate Water, as well as increased layering of the deeper North Pacific which would weaken the return path of abyssal tracers. These proposed changes imply a likely increase in ocean carbon storage within the deep Pacific during the LGM relative to the Holocene.

Co-evolution of orbital-to-millennial East Asian monsoon and westerlies variability over the past 150 ka

Understanding the evolution and interaction of the mid-latitude westerlies and East Asian monsoon (EAM) is crucial for comprehending Asian climate dynamics. While abundant evidence from loess, lake and speleothem records in arid Central Asia (ACA) and East Asia has revealed the interplay between the mid-latitude westerlies and the EAM on orbital and millennial scales, most of these records only cover the period since the last glacial maximum. Thus, the trade-off relationship between the mid-latitude westerlies and the EAM on glacial-interglacial to millennial timescale since the last interglacial period remains unclear. In this study, we present 150 ka-long grain-size and organic carbon records from two loess sections in the western Chinese Loess Plateau (CLP) and Yili Basin to assess the wind intensity and moisture variability between East Asia and ACA at glacial-interglacial to millennial timescales. Our results indicate that the East Asian winter monsoon (EAWM) and westerly wind exhibit synchronous glacial-interglacial and precession-scale fluctuations. However, the moisture exhibits consistent variations between East Asia and ACA on glacial-interglacial timescale, whereas inconsistent pattern at precessional timescale. The moisture variations in ACA lagged those in the East Asia by 2 kyr during marine isotope stages (MIS)5. Millennial-scale wind and moisture variability in East Asia and ACA are broadly correlated with cooling events in the North Atlantic. Based on the modeling results of the TraCE-21 ka, we suggest that the wind and moisture variations in East Asia and ACA are controlled by the combined effects of ice sheets, insolation, and meltwater flux from orbital to millennial timescales. Therefore, our study provides new insights into the complex interplay between the EAM and mid-latitude westerlies, which can contribute to a better understanding of Asian climate dynamics.

Batagay megaslump: A review of the permafrost deposits, Quaternary environmental history, and recent development

AbstractThe Batagay megaslump, in the Yana Uplands of northern Yakutia, Russia, is the largest known retrogressive thaw slump in the world. The slump exposes a remarkable sequence of Ice Age permafrost deposits that record the interaction of colluvial, eolian and periglacial processes on a hillslope episodically forested during the last 650 ka or more in response to climate variability on glacial–interglacial timescales. Numerous bones, teeth, and occasional carcasses of Pleistocene and Holocene mammals have been recovered from the permafrost. The megaslump developed over the course of several decades in three stages: (1) gullying, (2) thaw slumping, and (3) megaslumping. After disturbance to the taiga vegetation cover in the 1940s–1960s, a hillslope gully formed by the early 1960s. The gully initiated thaw slumping along its central part during the 1980s, with the slump enlarging to megaslump (&gt;20 ha) proportions during the 1990s. By 2019, the area of the slump had reached about 80 ha and its headwall above the slump floor was up to about 55 m high. The main geomorphic processes of slump growth are headwall ablation and thermal erosion, producing a distinctive terrain of icy badlands on the slump floor. Though much of the megaslump is rapidly growing at present, it will probably stabilize eventually as an irregular terrain characterized by sandy ridges and sand‐filled elongate depressions formed by degradation of the badlands. Comparison of the Batagay megaslump with megaslumps from northwest Canada reveals several similarities and differences in terms of their geomorphology, permafrost deposits, and Quaternary history.

Sea level response to late Pliocene-Quaternary erosion and deposition in Scandinavia

Erosion and deposition can perturb regional sea level significantly by altering the Earth's surface and by redistributing mass. However, no studies have investigated the importance of these geomorphic processes for glacial settings on glacial-interglacial time scales, despite large erosion rates and the inherent importance of sea-level changes for ice-sheet dynamics and stability. Here we quantify how glacial erosion and depositional processes have affected relative sea level in western Scandinavia where glacial activity has reoccured periodically throughout the late Pliocene-Quaternary. By comparing offshore sediment volumes with onshore topographic relief, we quantify erosion and deposition for the last two glacial cycles as well as the entire late Pliocene-Quaternary. Specifically, we develop a history of erosion and deposition for the last two glacial cycles by scaling the erosion rate with the normalised global ice volume through time. We use the ice model ICE6G_C as a global ice history and calculate sea-level changes through time as a result of ice, water, and sediment loading using a global gravitationally self-consistent sea-level model. Our results show that geomorphic mass redistribution, excluding direct changes in ocean depth owing to erosion and deposition, has caused a sea-level fall of ≈50–100 m along the southern coast of Norway during the last two glacial cycles reaching ≈120 m in the offshore Skagerak region. During the late Pliocene-Quaternary, the total sea-level fall reach as much as ≈ 310 m in Skagerak. These results showcase the importance of erosion and deposition for the relative sea-level history of Scandinavia with implications for studies of ice-sheet history and regional glacial rebound in this region and elsewhere.

Response of Magnetic Minerals to the Mid-Brunhes Climate Event Recorded in Deep-Sea Sediments of the West Philippine Sea

The Mid-Brunhes Event (MBE) was one of the most important global climate events since 800 ka. The deep-sea palaeoceanographic changes in the Western Pacific might have been more sensitive to the MBE and they have not been well documented yet. In this study, we investigated a deep-sea core collected from the Western Philippine Sea and then obtained the magnetism record since around 900 ka. The MBE signal in the deposition process was derived from the concentration-dependent (χ, χARM and SIRM) and the grain-size-dependent magnetic parameters (χARM/χ and χARM/SIRM). Across the MBE, the content of magnetic minerals and the fluctuation of the grain size decreased. Both the content and grain-size indices calculated from magnetic parameters are well correlated with the glacial–interglacial alternations and display a major shift at the MBE. The decreased grain size of magnetic minerals may be associated with the flourishing biota in the tropical Pacific during interglacial intervals. The accumulation of magnetic minerals in the Western Philippine Sea was mainly regulated by the sediment accumulation rate, which may be related to the shoaling of the carbonate compensation depth. Overall, this study expanded the environmental magnetism record for the MBE, suggested a new possible influence of this critical climatic event on the deep-sea deposition process in Western Philippine Sea and inferred the interactions between various environmental systems on glacial–interglacial timescales.

Kalimantan hydroclimate variability since the last glacial period

Changes in convective activity and hydroclimate over Northeastern Kalimantan are key features to understand glacial to interglacial climate evolution in the center of the West Pacific Warm Pool during the Late Pleistocene to Holocene. We use high-resolution X-ray fluorescence (XRF) scanner-derived elemental ratios in sediment Core SO217-18522 (1º 24.106’ N, 119º 4.701’E, 975 m water depth) recovered from the northern Makassar Strait to reconstruct changes in precipitation-related weathering and erosion over Northeastern Kalimantan over the last 50 kyr. Enhanced seasonality of rainfall and an extended dry season during Heinrich Stadials (HS4 to HS1) and the Younger Dryas (YD) suggest weakening of the tropical convection associated with a southward shift of the tropical rain belt and the annual mean position of the Intertropical Tropical Convection Zone. Increasing sediment discharge and intensification of convective activity occurred during the early to mid-Holocene during an interval of high Northern Hemisphere insolation, elevated atmospheric pCO2 levels and global warming. Our reconstructions in comparison with regional terrestrial and marine records highlight the high spatial variability of Kalimantan hydroclimate on millennial to glacial-interglacial timescales.

Provenance variations of the loess deposits in the East Asian monsoon boundary zone, Northeast China: Response to the variations of climate and wind regimes

Provenance studies are critical for the paleoclimatic reconstruction of loess. However, very little information is available about the provenance variations of the loess in the monsoon boundary zone, limiting our understanding of aeolian dust dynamics, the evolution of atmospheric circulation and driving mechanisms on the glacial-interglacial timescale. To this end, the integration of grain size end-member modeling, machine learning, sediment fingerprinting and wavelet transform analysis is performed for the Harbin loess in Northeast China to understand the long-term provenance variations, atmospheric circulation evolutions and forcing mechanisms. The results show the Harbin loess comprises three grain size end-members, EM1 (7.81 μm), EM2 (27.2 μm) and EM3 (54.41 μm), and they correspond to the background of atmospheric dust, the intensity of the southwesterly and of the East Asian Winter Monsoon (EAWM), respectively, indicating the three transport dynamics of dust delivered to this region. The quantitative source reconstruction indicates that the loess experienced the dramatic source variations, characterized by an abrupt termination of the dust contribution from the Hulun Buir Sandy Land at ∼ 250 ka, and by variations in the relative contribution of the dust sources (i.e., Songnen Sandy Land, Horqin Sandy Land, Onqin Daga Sandy Land, and to a lesser extent, Hulun Buir Sandy Land) during the glacial-interglacial cycles. The comparisons between the indicators, e.g., EM2, the deep-sea oxygen isotopes and the rate of dust accumulation in the North Pacific, combined with wavelet transform analysis indicating a dramatic shift of orbital cycles from the significant 100-kyr and 41-kyr cycles to a weakened 100-kyr cycle, suggest that the weakened EAWM induced by both reduced the Northern Hemisphere ice volume and summer solar radiation, accounted for a termination of the Hulun Buir Sandy Land as the loess source. However, the change in wind regimes due to the glacial-interglacial cycles, and climate change (e.g., enhanced aridification) are the dominant forcing for the variations in the relative contribution of the dust sources to the Harbin loess.

Climatic and hydrological variations on the southwestern Tibetan Plateau during the last 30,000 years inferred from a sediment core of Lake Zabuye

Climate change on the Tibetan Plateau (TP) is governed by the mid-latitude westerlies and Indian summer monsoon (ISM). However, the past hydrological changes on the TP induced by interactions between the westerlies and the ISM remain unclear. A sediment core from Lake Zabuye on the southwestern TP was analyzed to reconstruct climatic and hydrological variability over the last 30 kyr. Stable isotopic compositions (δ13C and δ18O) of authigenic carbonate act as an indicator of hydrological status for closed-basin lakes on the TP. Four major climatic and hydrological stages were identified: (1) last glacial maximum (29.8–18.9 cal kyr BP), the influence of the westerlies dominated, and a cold-wet climate prevailed; (2) last deglaciation (18.9–11.8 cal kyr BP), the influence of the westerlies receded, and a general trend of decreased wetness was interrupted by two pronounced glacial meltwater events recorded at 17.2 and 15.2 cal kyr BP, respectively; (3) early and middle Holocene (11.8–3.8 cal kyr BP), the Holocene climate optimum was attained and sustained under the dominance of ISM circulation; (4) late Holocene (from 3.8 cal kyr BP to the present), the ISM collapsed during the middle to late Holocene, and a hypersaline lacustrine environment was ultimately formed, as inferred from mirabilite deposition and isotopic signals. Our lake record demonstrates an anti-phase relationships between the westerlies and the ISM on the glacial-interglacial timescale over the southwestern TP. We suggest that both North Atlantic climate and tropical ocean temperature are major drivers of climatic variations on the TP.

Catchment vegetation and erosion controlled soil carbon cycling in south-eastern Australia during the last two glacial-interglacial cycles

Vegetation structure in vast semi-arid to temperate continental land masses, such as Australia, plays a considerable role in global terrestrial carbon sequestration. However, whether soil carbon from these regions is a net atmospheric carbon source or sink remains contentious, introducing large uncertainties on long-term storage of vegetation-sequestered carbon dioxide. We investigate the interplay between catchment erosion quantified using uranium isotopes, vegetation (pollen), catchment carbon cycling, wetland response (diatoms), and lake carbon accumulation on glacial-interglacial timescales in south-eastern Australia. The analyses are applied to sediments from Lake Couridjah, in the Sydney Basin during the last (133.5 ka to 107.6 ka) and current (17.8 cal ka BP to present day) glacial-interglacial transitions. Robust phase-relationships between catchment erosion, vegetation composition and carbon cycling during both glacial-interglacial periods were revealed by statistical analyses. Vegetation structure had a direct control on catchment erosion, and, thus, on soil organic carbon (SOC) erosion in the catchment. Overall wetter and warmer peak interglacial conditions promoted the expansion of a canopy and mid-storey vegetation cover reducing catchment erosion, while simultaneously increasing SOC storage, catchment and lake primary productivity, and lake carbon storage. The results suggest increased terrestrial carbon sequestration in temperate Australian landscapes in warmer and wetter climates. • Novel trace metal isotope method quantifies “palaeo-sediment residence times” as proxy for catchment erosion • First continuous catchment erosion record for the last and current glacial-interglacial cycle in SE Australia • Link between catchment vegetation cover and erosion highlights the role of Australia as global carbon sink

Molecular biomarkers in Batagay megaslump permafrost deposits reveal clear differences in organic matter preservation between glacial and interglacial periods

Abstract. The Batagay megaslump, a permafrost thaw feature in north-eastern Siberia, provides access to ancient permafrost up to ∼650 kyr old. We aimed to assess the permafrost-locked organic matter (OM) quality and to deduce palaeo-environmental information on glacial–interglacial timescales. We sampled five stratigraphic units exposed on the 55 m high slump headwall and analysed lipid biomarkers (alkanes, fatty acids and alcohols). Our findings revealed similar biogeochemical signatures for the glacial periods: the lower ice complex (Marine Isotope Stage (MIS) 16 or earlier), the lower sand unit (sometime between MIS 16–6) and the upper ice complex (MIS 4–2). The OM in these units has a terrestrial character, and microbial activity was likely limited. Contrarily, the n-alkane and fatty acid distributions differed for the units from interglacial periods: the woody layer (MIS 5), separating the lower sand unit and the upper ice complex, and the Holocene cover (MIS 1), on top of the upper ice complex. The woody layer, marking a permafrost degradation disconformity, contained markers of terrestrial origin (sterols) and high microbial decomposition (iso- and anteiso-fatty acids). In the Holocene cover, biomarkers pointed to wet depositional conditions and we identified branched and cyclic alkanes, which are likely of microbial origin. Higher OM decomposition characterised the interglacial periods. As climate warming will continue permafrost degradation in the Batagay megaslump and in other areas, large amounts of deeply buried ancient OM with variable composition and degradability are mobilised, likely significantly enhancing greenhouse gas emissions from permafrost regions.

Bottom water oxygenation changes in the southwestern Indian Ocean as an indicator for enhanced respired carbon storage since the last glacial inception

Abstract. We present downcore records of redox-sensitive authigenic uranium (U) and manganese (Mn) concentrations based on five marine sediment cores spanning a meridional transect encompassing the Subantarctic and Antarctic zones in the southwestern Indian Ocean covering the last glacial cycle. These records signal lower bottom water oxygenation during glacial climate intervals and generally higher oxygenation during warm periods, consistent with climate-related changes in deep-ocean remineralized carbon storage. Regional changes in the export of siliceous phytoplankton to the deep sea may have entailed a secondary influence on oxygen levels at the water–sediment interface, especially in the Subantarctic Zone. The rapid reoxygenation during the deglaciation is in line with increased ventilation and enhanced upwelling after the Last Glacial Maximum (LGM), which in combination conspired to transfer previously sequestered remineralized carbon to the surface ocean and the atmosphere, contributing to propel the Earth's climate out of the last ice age. These records highlight the still insufficiently documented role that the Southern Indian Ocean played in the air–sea partitioning of CO2 on glacial–interglacial timescales.