Interglacial Peaks Research Articles

Weathering pulses during glacial-interglacial transitions: Insights from well-dated paleosols in the Azores volcanic province (Central North Atlantic)

Volcanic islands evolve through complex interactions between volcano growth and surface processes. Climate changes impact the physical and chemical processes that drive weathering and denudation. While global paleoclimate has been extensively studied for the late Quaternary, elucidating the local climatic response to global forcing on such islands remains challenging. São Miguel is a volcanic island in the Eastern Azores, located in the Central North Atlantic, a region susceptible to changes in large-scale atmospheric and oceanic dynamics. It comprises numerous paleosols (PSs), whose geochemistry results from volcanic rocks' weathering and can serve as a proxy to reconstruct paleoclimatic conditions. New K–Ar and 40Ar/39Ar ages of volcanic units “bracketing” (under and overlying) PSs reveal four periods of enhanced soil formation (∼820–765 ka, ∼425–430 ka, ∼170–75 ka, <10 ka), coinciding with rapid glacial-interglacial transitions (Terminations I, II, V, IX). Our reconstructed mean annual precipitation (MAP; 500–1200 mm yr−1) and air temperature (MAAT; 12–18 °C) are higher during interglacial peaks. This, in addition to the coherence of MAAT with previous Sea Surface Temperature reconstructions, shows consistency between local and global climate dynamics. The texture of parental rocks played a significant role in weathering, with PSs predominantly restricted to the brecciated upper part of lava flows and to pyroclastic deposits, which exhibited distinctive precipitation thresholds for their formation (∼800 mm yr−1 and ∼500 mm yr−1, respectively). PSs developed on basaltic lava flows exhibit greater elemental loss, due to a high glass proportion and low permeability, which prevents fluids percolation out of the soils. As present-day precipitation and temperature exceed those of the past, enhanced weathering is expected in São Miguel and other volcanic islands, with local to global impacts (e.g., carbon cycling), especially in the context of ongoing global warming.

Covariation of Deep Antarctic Pacific Oxygenation and Atmospheric CO2 during the Last 770 kyr

Abstract We present new geochemical evidence of changes in oxygenation of the deep Antarctic Pacific over the last 770 kyr. Our data are derived from redox-sensitive metals and export production proxies extracted from gravity core ANT34/A2-10 at 4217 m water depth. Our results show that oxygen levels in the deep Antarctic Zone (AZ) varied in line with the release of deeply sequestered remineralized carbon to the atmosphere during glacial–interglacial (G–IG) cycles, with lower oxygen concentrations and more carbon storage during glacial periods. Subsequent reductions in the amount of carbon stored at depth were closely associated with improved ventilation during glacial terminations. The systematic and repeated glacial-to-interglacial increases in export production in the AZ region indicate a robust pattern of enhanced Southern Ocean (SO) ventilation during interglacial periods. In addition to the decline in atmospheric CO2 caused by iron fertilization in the Subantarctic AZ (SAZ) during the latter half of the glacial progression, decreases in productivity in the central AZ suggest that the weakening of SO ventilation induced deep AZ carbon sequestration and that this might have made a continuous additional contribution to the CO2 decline from each interglacial peak to glacial maximum. Observed variations in the degree of deep oxygenation and “organic carbon pump” efficiency in the central AZ might be driven primarily by physical “ventilation” processes (i.e., overturning circulation, mixing, and/or air–sea gas exchange). Our records of abyssal oxygenation in the central AZ, which vary in concert with atmospheric CO2 levels over the last several G–IG cycles, provide strong evidence that SO ventilation plays a significant role in controlling variations in both the amount of respired carbon sequestered in the deep ocean and atmospheric CO2 concentrations on G–IG timescales. Specifically, we suggest that the “organic carbon pump” (OCP) in the SAZ and the physical ventilation processes in the AZ (the “carbon venting valve”) acted together synergistically, but dominated at different intervals over G–IG cycles, to repeatedly switch the SO between carbon sink and carbon source, thereby modulating the atmospheric CO2 over the last 770 kyr. These findings provide new insights into the role of the AZ in controlling deep SO carbon sequestration and atmospheric CO2 levels in G–IG cycles.

Spatio-temporal expressions of precessional-scale stalagmite δ18O variations from the Asian monsoon area

Changes in orbital-scale stalagmite δ 18 O (δ 18 O s ) recorded from two caves in southern China reveal a clear precessional cycle during Marine Isotope Stage (MIS) 5 and from MIS 9.3 to MIS 8.3. At these sites, δ 18 O s values in MIS 5.5 and MIS 9 were relatively lower than MIS 5.3, 5.1 and MIS 8, and gradually increased towards MIS 5.1 and MIS 8.3, respectively. A similar pattern of variability of δ 18 O s can be observed in other cave records south of 30° N. This southern mode of variability of δ 18 O s closely mimics changes in northern summer insolation, the areal extent of continental ice sheets and atmospheric CO 2 concentrations, suggesting that the direct forcing of summer insolation on landward transport of monsoonal moisture can be further modulated by the Earth's boundary conditions. In contrast, δ 18 O s records around 30° N or northward register a relatively stable precessional cycle, among which δ 18 O s values during the precession minimum (P min ) are similar. This regional disparity implies that during the P min , the strength of northward propagation of monsoonal moisture probably remained constant at northern sites. Moreover, a dampening effect may have limited 18 O-depleted moisture transfer to mid- and high-latitude cave sites, especially during peak interglacials (i.e., MIS 5.5, MIS 9), which may be associated with shifts in the southern edge of the Westerly jet and the average position of the Intertropical Convergence Zone. Another possibility could be that more locally-recycled or near-sourced (isotopically-enriched) moisture contributed to precipitation changes at the northern sites. • A gradual enrichment of δ 18 O s values in Pmin in southern China • A stable precessional cycle in δ 18 O s records around 30°N and northward • Control of NHSI and Earth's boundary conditions on southern δ 18 O s variability • Interplay of Westerly wind and ITCZ on stalagmite δ 18 O records at northern sites

North Atlantic Deep Water during Pleistocene interglacials and glacials

The global ocean overturning circulation is a major means of distributing heat around the Earth, and an important trigger or amplifier of climate change. This study presents a 1.5-Myr-long neodymium (Nd) isotope record of Deep Sea Drilling Project Site 607, in the core of present-day North Atlantic Deep Water (NADW), the water mass that drives the overturning circulation and its Atlantic end-member (Broecker, 1991; Gordon, 1991), in order to document its composition through time. This time interval is marked by major changes in fundamental aspects of the Earth's climate, including the Mid-Pleistocene Transition (MPT) from ∼41-kyr to ∼100-kyr interglacial-glacial cycles and more intense glacials. The new record, mainly focusing on interglacial and glacial peaks, shows a pattern that mimics the record of benthic foraminiferal δ18O (Lisiecki and Raymo, 2005) in that the magnitude of interglacial-glacial Nd isotope shifts were smaller in the 41-kyr world than in the 100-kyr world. During the “900 ka event” (Clark et al., 2006), between ∼960 and 860 ka, marking the first 100-kyr interglacial-glacial cycle, the Nd isotope ratios shift abruptly to higher values, consistent with increased incursion of Southern Ocean water masses into the deep North Atlantic. This pattern was previously observed in the South Atlantic over the same time interval and interpreted as a weakened presence of NADW signal that reflected a period of disrupted deep ocean overturning circulation, termed the “MPT-AMOC crisis” (Pena and Goldstein, 2014). The Site 607 data support this interpretation and show the effects to be basin-wide. Following the disruption, an enhanced southern-sourced Nd isotope signature remained for ∼200 kyr during the period of “lukewarm interglacials” (Howe and Piotrowski, 2017; Jaccard et al., 2013), consistent with weaker overturning circulation. With the exception of this “MPT-AMOC crisis and recovery” interval, the Nd isotope ratios during interglacial peaks have been similar to present-day NADW, indicating similar interglacial North Atlantic ocean circulation dynamics both before and after the MPT. This contrasts with the pattern during glacial periods of the 100-kyr world, during which Nd isotopes have continued to follow the pattern of the 900-kyr event indicating a strong southern water mass signal, interpreted as intensified incursions of Southern Ocean water into the deep North Atlantic and consistent with a generally weaker overturning circulation during glacials.

Variation of summer precipitation δ18O on the Chinese Loess Plateau since the last interglacial

ABSTRACTOrbital‐scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice‐volume forcings. Here we integrate a new microcodium δ18O record from a high‐resolution last interglacial loess profile with previously published data and provide a composite microcodium δ18O record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium δ18O record displays distinct precessional cycles, consistent with speleothem δ18O records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem δ18O records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem δ18O records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium δ18O from the Chinese loess–paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity.

New U-series dates from Stump Cross Caverns, Yorkshire, UK, and constraints on the age of the Banwell Bone Cave Mammal Assemblage Zone

Stump Cross Caverns house one of the important Pleistocene fossil bone beds of the UK. Yet, the dates of the Banwell Bone Cave Mammal Assemblage Zone (MAZ), to which these belong, have not yet been well constrained. Here we present new U-Th dates showing that Late-MIS 5 bison-reindeer-wolverine fauna was present in northern England at least as early as 91.9 ± 0.5 ka (the oldest date yet published); and that the Banwell Bone Cave fauna probably occupied the Yorkshire Dales from soon after ∼100 ka to 80 ka (late MIS 5c-early MIS 5a). This adds to the very small number of dates for this fauna, is somewhat older than the timing proposed in the literature, and suggests that the fauna arrived in NW Britain more than 5 kyr in advance of SW Britain. We also found an older bone bed dating from 175 to 172 ka, MIS 6d. This is only the second reported occurrence in the Yorkshire Dales of a fauna that pre-dates the Last Interglacial. Our results confirm that calcite deposition in this cave is precluded during interglacial peaks by local flooding, but at other times is similar to other caves of NW Europe. The oldest dates, on calcites from the uppermost levels, show dewatering by at least ∼430 ka (early MIS 11), adding to our understanding of the antiquity of the caves and the geomorphology of the region.

CO2‐Induced Decoupling of Tropical Surface and Thermocline Water Temperature at the Onset of Interglacials

AbstractTropical air‐sea interaction is important in global climate change; its behavior over geological history is poorly understood but can be explored by examining reconstructed sea surface temperature (SST) and thermocline water temperature (TWT). Here, deglacial‐interglacial air‐sea interactions over the past 500 ka were studied by comparing UK'37‐derived SST0‐30m and TEXH86‐derived TWT75m in a sediment core from the southern South China Sea. During deglacials, SST0‐30m and TWT75m varied synchronously toward interglacial peaks, while during the peak interglacials, TWT75m decreased earlier than SST0‐30m. These changes have been found ubiquitously in tropical oceans during the last two glacial‐interglacial cycles. We propose that the prolonged warm interglacial SST was probably sustained by the natural CO2 “overshoot” greenhouse effect at the end of most terminations. The early interglacial TWT decrease following local insolation is driven by the decreasing downward heat transport efficiency induced by weakening wind stirring.

Atmospheric dust flux in northeastern Gondwana during the peak of the late Paleozoic ice age

The silicate mineral fraction of shallow marine carbonates archives dust contributions to the Central Persian Terranes along the northeastern margin of Gondwana (∼30ºS paleolatitude), enabling reconstruction of atmospheric dust loading and circulation for intervals of the late Paleozoic ice age. The Central Persian Terranes hosted cyclic deposition of warm water carbonates from middle Pennsylvanian to earliest Permian time, and our data set includes two ∼28 m sections from the Moscovian and Asselian sampled at 20 cm intervals. Bounding surfaces between successive cycles (high-frequency sequences) are recognized by either abrupt basinward shifts in facies or subtle exposure features; these high-frequency sequences range from 1 m to 5 m thick and are interpreted to record glacioeustatic variations. Time series analysis of the dust fraction through the studied interval supports the hypothesis of orbital forcing for the dust signal. The stratigraphic pattern of the dust flux indicates minimal flux during interglacial highstands (0.19−0.27 g/cm2/kyr) and peak flux during glacial lowstands (3.77−4.57 g/cm2/kyr) after accounting for hiatal time at sequence boundaries. Grain size analysis of the dust for all samples (n = 230) reveals modal sizes (volume-based) of 1−15 µm through the Moscovian interval and 10−75 µm through the Asselian interval. Dust deposition increased during glacial times relative to interglacial times by a factor of 16 to 19. Additionally, the Asselian interval exhibits higher dust flux overall relative to the Moscovian interval, which is interpreted to reflect the more extreme icehouse conditions of the Asselian. Variation in the dust content through the studied sections provides an indicator of temporal changes in atmospheric loading that varied at both glacial−interglacial and higher-frequency (&amp;lt;104 yr) scales. Geochemical data reveal that the Arabian−Nubian Shield and southwestern Pangaea (South America) are the most likely sources of dust deposition in the Central Persian Terranes, with sources shifting during different phases. Increased dust flux during glacials likely reflects multiple factors, including enhanced aridity in the source region, exposure of shelf regions, and potential changes in winds. However, the discrepancy in model reconstructions of the amplitude of glacial−interglacial dust variations indicates that increased production of dust sourced by dynamic glaciation played a large role in enhancing dust flux during glacial phases.

Climate-driven connectivity changes of the Black Sea since 430 ka: Testing a dual palynological and geochemical approach

The Black Sea experienced multiple episodes of connection with both the Mediterranean and Caspian seas during the Quaternary. Global sea-level variation has been proposed as the main driver of changes in Mediterranean-Black Sea connectivity, while positive water budgets drove Caspian overspill. We present a new, two proxy, low-resolution record from the Black Sea that allows reconstruction of connectivity history from 430 to 50 ka: dinoflagellate cysts (dinocysts) provide direct evidence for properties of surface waters and strontium isotopes constrain the source(s) of water entering the basin. Dinocysts and 87Sr/86Sr suggest that the Black Sea was isolated from the Mediterranean during global sea-level lowstands associated with glacials MIS 4, 8 and 10. Both proxies also strongly suggest that marine (Mediterranean) water flowed into the Black Sea during the eustatic highstands associated with peak interglacials during MIS 5 and 9. However, while the contribution of marine waters during MIS 5e was similar to the present day, lower 87Sr/86Sr during MIS 9 suggests lower than present input. Connectivity during MIS 11, MIS 7 and MIS 6 is more enigmatic. Lower 87Sr/86Sr than those of the isolated Black Sea and dinocyst assemblages dominated by species of Paratethyan lineage are compatible with input from the Caspian Sea. Dinocyst taxa recovered in MIS 11 can be found in both the Caspian Sea and the Black Sea today. All four interglacials studied contain different dinocyst assemblages, suggesting that different conditions may have prevailed during each warm period. However, high-resolution studies are needed to confirm this observation. Further work on the same sequence could be valuable in elucidating the connectivity history of the Black Sea over the glacial-interglacial cycles of the late Quaternary.

A decrease in temperature during the late Middle Pleistocene interglacial stage (MIS 7.3) altered montane zone floral diversity: Plant macrofossil evidence from central Japan

Plant fossils from the Early and Middle Pleistocene have mainly been obtained from lowland sediments, and consequently, there is currently limited information on changes in montane zone vegetation prior to the last glacial stage. However, fossil plant assemblages occurring at high altitudes can be used to assess the influence of climate change on the vertical distribution of plants and vegetation. In this study, we analysed plant macrofossil assemblages from fluvial deposits in the upper Middle Pleistocene strata outcropping in a riverbed at 1160–1180 m a.s.l. in the southeastern foothills of Mt. Yatsugatake, central Japan. Ages of the assemblages were constrained by two widespread tephras that were detected above the interglacial peak of marine isotope stage (MIS) 7.3 (~212 ka). The annual mean temperature in the lower and middle sections of the profile was estimated to be warmer than that at present, based on the coldest temperatures limiting the distribution of Phytolacca japonica and Selaginella remotifolia, and the temperature decreased in the upper section. Since MIS 7.4, the fluctuation in plant altitudinal distribution has been exemplified by changes in the limits of S. remotifolia and Larix kaempferi distribution, and their coexistence at the same altitude varied depending on climate settings. Species diversity, estimated by rarefaction analysis of plant macrofossil assemblage composition, declined as temperatures decreased after the peak of MIS 7.3. Decreasing floral diversity during the subsequent cooling phase possibly coincided with a downward migration of the vegetation zone and extirpation of plants from the inland basin in central Japan.

Diagenesis in Pleistocene (80 to 500 ka) corals from the Ironshore Formation: Implications for paleoclimate reconstruction

Fossil corals provide a unique opportunity for paleoclimate research because they can be dated and they incorporate climate controlled seawater proxies into their aragonitic skeletons during growth. Coral skeletons, however, can only produce reliable environmental information if they have not been diagenetically altered, an issue that becomes increasingly probable as the age of the corals increase. Although commonly used analytical techniques, such as thin section, Scanning Electron Microscopy, and X-Ray diffraction, can highlight obvious mineralogical changes, subtle changes in the trace element and isotopic composition of the skeletons may not be evident. This premise is assessed by examining Orbicella annularis and Montastrea cavernosa corals from the Pleistocene Ironshore Formation (Units A-F) on Grand Cayman (80–500 ka) to determine the diagenetic effects on both physical and chemical properties of corals. In the Ironshore Formation, the corals in Units A and C were altered in a semi-open diagenetic system by seawater diluted by meteoric water, which resulted in chemical diagenesis that changed the elemental and isotopic composition of the corals even though their aragonitic skeletons show no obvious signs of change. In contrast, the limestones in Unit B have been pervasively recrystallized in an open diagenetic system by meteoric waters that caused both chemical and physical changes. The corals in Units D to F, however, underwent minimal diagenesis and show no evidence of alteration. For altered corals from the Ironshore Formation, elevated Mg/Ca and low Sr/Ca ratios provide evidence of subtle chemical diagenetic changes even in corals that have retained their primary aragonitic skeleton. Thus, corals that are formed of >95 wt% aragonite, show no evidence of cementation, and have Mg/Ca ratios <12.0 mmol mol−1, Sr/Ca ratios >8.0 mmol mol−1, δ18O values >−5.7‰, and δ13C values >−3.0‰, are ideal candidates for paleoclimate reconstruction. Adoption of these criteria shows that the corals from Units D to F can be used to calculate sea surface temperatures (SST), whereas those from Units A to C cannot be used for this purpose. The calculated SST and the corresponding temperature profiles derived from the corals in Units D to F are consistent with global SST reconstructions during the Pleistocene. Unit D corals record an overall increase in SST, which is consistent with elevated temperatures associated with Marine Isotope Stage (MIS) 5e, whereas Units E and F record overall cooling, which is consistent with the end of the peak interglacials of MIS 5c and 5a, respectively.

Wetland expansion on the continental shelf of the northern South China Sea during deglacial sea level rise

To identify environmental causes for past changes in vegetation in subtropical East Asia, we present carbon isotope compositions of plant-wax n-alkanes and provide estimates of the C4-plant contribution across the past four glacial terminations and interglacials, based on cores recovered from the northern South China Sea. Our results show a comparable C4-plant contribution between the Last Glacial Maximum (LGM) and the Holocene. An increase of the C4-plant contribution by 15–20% is found for Terminations IV, II and I relative to subsequent interglacial peaks, coeval with an expansion of Cyperaceae and Poaceae. In contrast, Termination V reveals a lower C4-plant contribution than Marine Isotope Stage (MIS) 11c. The data exhibit a long-term trend, with a stepwise increase of the C4-plant contribution across interglacials MIS 11c, 9e, 7e and 1. We suggest that no substantial changes in humidity levels over glacial-interglacial cycles occurred facilitating a similar C3/C4-plant ratio for the LGM and the Holocene. Instead, deglacial sea-level rises caused an extensive development of floodplains and wetlands on the exposed continental shelf, providing habitats for the spread of C4 sedges and grasses. The progressive subsidence of Chinese coastal areas and the broadening of the continental shelf over the late Quaternary explains the nearly absence of C4 plant occurrence during Termination V and a gradual increase of the C4-plant contribution across interglacial peaks. Taken together, changes in coastal environments should be considered when interpreting marine-based vegetation reconstructions from subtropical Asia.

Palaeoenvironmental changes recorded by speleothems of the southern Alps (Piani Eterni, Belluno, Italy) during four interglacial to glacial climate transitions

Three stalagmites, which grew in the high altitude (∼1800 m a.s.l.) Piani Eterni karst system (northern Italy), represent the longest speleothem palaeoclimate-environmental record from the southern Alps. U-Th dating shows their discontinuous formation during Marine Isotope Stage (MIS) 10, 8, 7d, 6 and 5d–b, with carbonate deposition prevented during both full interglacial and full glacial stages. Speleothem formation was inhibited during interglacial peaks because local base level rise, connected to global climate changes, caused the alluviation of the main epiphreatic levels of the cave system. Drainage of the hydrological pathways, caused by the progressive decrease of rainfall and the accumulation of a perennial snow pack, stopped carbonate deposition during glacials. Thus, Piani Eterni speleothems function as indicators of transitional interglacial to glacial (IG–G) climate periods over the last ∼400 thousand years (kyrs). Analysis of δ18O and δ13C suggest that: i) seasonal snow melt occurred in these high altitude terrains during IG–G times, allowing meteoric water to efficiently penetrate the karst network; ii) soils were restored during MIS 5c–b, but absent during MIS 10, 8, 7d and 6 due to denudation of the karst surfaces; and iii) rainfall perturbations modulated the IG–G shifts in the southern Alps. Rainfall variation is connected to solar radiation changes at orbital timescales during MIS 5c–b, and mimics Dansgaard-Oeschger (DO) cycle variability during DO 23 and 22. DO cycle-like variability is also suspected during MIS 10, 8 and 6. The most important result is that, from a geochemical perspective, this study demonstrates that drivers of δ18O in southern alpine speleothems are similar to Mediterranean, Middle Eastern and Asian speleothems in that they are prevalently controlled by the rainfall amount effect. This contrasts with speleothem records from the more continental northern alpine sector where the air temperature effect on δ18O of precipitation dominates.

Causes and consequences of Arctic freshwater routing into the Nordic Seas during late Marine Isotope Stage 5

ABSTRACTSediment core PS1904 reveals continuous records of planktic and benthic foraminiferal stable isotopes (δ18O/δ13C) from the north‐eastern Greenland continental margin. The data show good comparability with other records from the Nordic Seas, allowing the stratigraphic range of PS1904 to be dated to Marine Isotope Stage (MIS) 6. Focusing on MIS 5 reveals light δ18O values during MIS 5a compared to the last interglacial peak (MIS 5e) which indicates that surface and bottom water layers were strongly affected by freshwater during the former event. We present two possible scenarios explaining the origin and routing of the freshwater: (i) drainage of a Eurasian proglacial lake coupled with the collapse of the Kara Sea Ice Sheet at the MIS 5b/a boundary, and (ii) destabilization and melting of the nearby Greenland Ice Sheet. Although both scenarios could have acted simultaneously, sediment records from the Eurasian sector of the Arctic Ocean hint at the proglacial lake system in north‐western Siberia as the largest freshwater source. Regardless of the actual source, the freshwater lowered the surface ocean salinity causing water column stratification and sea ice expansion. Increased sea‐ice abundance led to a higher albedo and probably contributed to the cooling and global ice sheet growth that occurred subsequently during MIS 4.

Precession and glacial-cycle controls of monsoon precipitation isotope changes over East Asia during the Pleistocene

Precipitation isotope reconstructions derived from speleothems and plant waxes are important archives for understanding hydroclimate dynamics. Their climatic significance in East Asia, however, remains controversial. Here we present terrestrial plant-wax stable hydrogen isotope (δDwax) records over periods covering the last four interglacials and glacial terminations from sediment cores recovered from the northern South China Sea (SCS) as an archive of regionally-integrated precipitation isotope changes in Southeast China. Combined with previous precipitation isotope reconstructions from China, we find that the SCS δDwax and Southwest-Central China stalagmite δ18O records show relatively enriched and depleted isotopic values, respectively, during interglacial peaks; but relatively similar isotopic variations during most sub-interglacials and glacial periods over the past 430 thousand years. During interglacial peaks, strong summer insolation should have intensified the convection intensity, the isotopic fractionation along moisture trajectories and the seasonality, which are all in favor of causing isotopically-depleted rainfall over the East Asian monsoon regime. These effects in combination with a relatively high proportion of Indian Ocean- versus Pacific-sourced moisture influx should have resulted in strongly depleted precipitation isotopes (stalagmite δ18O) over most parts of China. However, Southeast China should have been affected by a relatively low ratio of Indian Ocean- versus Pacific-sourced moisture influx, which dominated over effects yielding depleted precipitation isotopes and led to enriched precipitation isotopes (δDwax). It is thus concluded that glacial boundary conditions and insolation forcing are the two most important factors for causing regional differences in precipitation isotope compositions over subtropical East Asia on orbital timescales.

Synoptic conditions of fine-particle transport to the last interglacial Red Sea-Dead Sea from Nd-Sr compositions of sediment cores

The sediments deposited at the depocenter of the Dead Sea comprise high-resolution archive of hydrological changes in the lake's watershed and record the desert dust transport to the region. This paper reconstructs the dust transport to the region during the termination of glacial Marine Isotope Stage 6 (MIS 6; ∼135–129 ka) and the last interglacial peak period (MIS5e, ∼129–116 ka). We use chemical and Nd and Sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the Dead Sea. The data is integrated with data achieved from cores drilled at the floor of the Red Sea, thus, forming a Red Sea-Dead Sea transect extending from the desert belt to the Mediterranean climate zone. The Dead Sea accumulated flood sediments derived from three regional surface cover types: settled desert dust, mountain loess-soils and loess-soils filling valleys in the Dead Sea watershed termed here “Valley Loess”. The Valley Loess shows a distinct 87Sr/86Sr ratio of 0.7081 ± 1, inherited from dissolved detrital calcites that originate from dried waterbodies in the Sahara and are transported with the dust to the entire transect.Our hydro-climate and synoptic conditions reconstruction illustrates the following history: During glacial period MIS6, Mediterranean cyclones governed the transport of Saharan dust and rains to the Dead Sea watershed, driving the development of both mountain soils and Valley Loess. Then, at Heinrich event 11, dry western winds blew Saharan dust over the entire Red Sea - Dead Sea transect marking latitudinal expansion of the desert belt. Later, when global sea-level rose, the Dead Sea watershed went through extreme aridity, the lake retreated, depositing salt and accumulating fine detritus of the Valley Loess. During peak interglacial MIS 5e, enhanced flooding activity flushed the mountain soils and fine detritus from all around the Dead Sea and Red Sea, marking a significant “contraction” of the desert belt. At the end of MIS 5e the effect of the regional precipitation diminished and the Dead Sea and Red Sea areas re-entered sever arid conditions with extensive salt deposition at the Dead Sea.

Productivity-climate coupling recorded in Pleistocene sediments off Prydz Bay (East Antarctica)

Export-production in the Southern Ocean is thought to be tightly correlated with atmospheric CO2 fluctuations over geological times. Relevant studies are, however, mainly confined to the Atlantic and Pacific sectors of the Southern Ocean and often only cover the last glacial-interglacial cycle. Here, we present a sediment record retrieved off Prydz Bay (East Antarctica) spanning the last ~520kyrs. We show that the distribution pattern of local export production is closely coupled with global climate change on orbital time scales. We propose that the dominant factors controlling local export production include the amount of nutrients supply from the ocean interior and the extent of sea ice cover, thus representing the combined history of deep water exposure/ventilation and the sea ice coverage in the studied area. Sharp increases in the local export production coincide with abrupt increase in atmospheric CO2 concentrations during deglacial periods, indicating drastic outgassing of the upwelled deep water in the Southern Ocean. Gradually decrease in the export production following interglacial peaks concurs with decrease in deep water exposure/ventilation and increase in sea ice cover, explaining the early decline in atmospheric CO2 over a glacial-interglacial cycle.

Insights into North Atlantic deep water formation during the peak interglacial interval of Marine Isotope Stage 9 (MIS 9)

Foraminifera abundance and stable isotope records from ODP Site 984 (61.25°N, 24.04°W, 1648 m) in the North Atlantic are used to reconstruct surface circulation variations and the relative strength of the North Atlantic Deep Water (NADW) formation over the period spanning the peak warmth of Marine Interglacial Stage (MIS) 9e (~324–336 ka). This interval includes the preceding deglaciation, Termination 4 (T4), and the subsequent glacial inception of MIS 9d. The records indicate a greatly reduced contribution of NADW during T4, as observed in more recent deglaciations. In contrast with the most recent deglaciation, the lack of a significant NADW signal extended from T4 well into the peak interglacial MIS 9e and persisted nearly until the transition to the subsequent glacial stage MIS 9d. Although NADW formation resumed during MIS 9e, only depths greater than 2000 m appear to have been ventilated. The poorly ventilated intermediate depth of Site 984 (<2000 m) may have resulted on one hand from a general reduction of deep water ventilation by NADW during the study interval or, on the other hand, from different pathways of the spread of newly formed NADW that bypassed the study location. The intermediate depths may have also been invaded by southern-sourced waters as the formation of intermediate depth NADW weakened. The absence of any significant NADW signal at the water depth of Site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks (MIS 5e and the Holocene). Despite the perturbed intermediate depth circulation, oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of MIS 9e.

Refining upon the climatic background of the Early Pleistocene hominid settlement in western Europe: Barranco León and Fuente Nueva-3 (Guadix-Baza Basin, SE Spain)

The Early Pleistocene sites of Barranco León and Fuente Nueva-3 (Guadix-Baza Basin, SE Spain) have yielded thousands of Mode 1 or Oldowan lithic artifacts (both sites) and one tooth (in layer D, formerly 5 of Barranco León), today considered to be some of the earliest evidence of humans in western Europe at ca. 1.2–1.5 Ma. Previous quantitative paleoclimatic reconstructions based on herpetile assemblages indicated that, during the formation of these two sites, the mean annual temperature and mean annual precipitation were higher than they are now in the southeastern Iberian Peninsula, with lower continentality. Here, we propose new climatic reconstructions where the mean monthly temperature and precipitation and the difference between the four driest months and the four rainiest months are estimated. Climatograms are built in order to specify the distribution and variation of temperature and precipitation during the year, and the Aridity Indices of Gaussen, Lautensach-Mayer, Dantin-Revenga and De Martonne are used to characterize ombroclimatic differences. According to these new climatic parameters, rainfall distribution through the year shows considerably higher precipitation in every season except summer and early autumn, which remain drier and thus consistent with a Mediterranean climate pattern. No change is observed in the duration of the aridity period, which remains four months long. However, the value of the Aridity Index of De Martonne is higher than 20 (subhumid climate) in Barranco León and Fuente Nueva-3, whereas today it is lower than 20 (semi-arid climate), suggesting major changes in the ombroclimatic type. These results yield a more precise scenario for the paleoclimatic conditions that prevailed during the late Early Pleistocene in the Guadix-Baza Basin and permit us to contrast the ages obtained from numerical dating and biochronology. The very warm and humid climate reconstructed for both Barranco León and Fuente Nueva-3 suggests that, in accordance with the numerical dating, these two sites are contemporaneous with the particularly warm interglacial peaks of Marine Isotope Stages 43–49 (i.e. between 1.35 and 1.47 Ma). The similarity between reconstructed climates, the high overlap between their estimated precipitation and between the difference of the driest from the rainiest season suggest that these sites may correspond to the same part of a climatic glacial/interglacial cycle, but because the evolutionary degree of the rodent Mimomys savini shows a slightly more derived state for Fuente Nueva-3 than for Barranco León (i.e a short chronological difference between the two sites), they may correspond to two consecutive warm interglacial peaks.

Cenozoic mean greenhouse gases and temperature changes with reference to the Anthropocene.

Cenozoic greenhouse gases (GHG) variations and warming periods underscore the extreme rates of current climate change, with major implications for the adaptability and survivability of terrestrial and marine habitats. Current rise rate of greenhouse gases, reaching 3.3ppm CO2 per year during March 2015-2016, is the fastest recorded since the Paleocene-Eocene Thermal Event (PETM) when carbon release to the atmosphere was about an order of magnitude less than at present. The ice core evidence of concentration of (GHG) and temperatures in the atmosphere/ocean/cryosphere system over the last 740 kyr suggests that the rate of rise in GHG over the last ~260 years, CO2 rates rising from 0.94 ppm yr-1 in 1959 (315.97 ppm) to 1.62 ppm yr-1 in 2000 (369.52 ppm) to 3.05 ppm yr-1 in 2015 (400.83 ppm), constitutes a unique spike in the history of the atmosphere. The reliance of pre-740 kyr paleoclimate estimates on multiple proxies, including benthic and plankton fossils, fossil plants, residual organic matter, major and trace elements in fossils, sediments and soils, place limits on the resolution of pre-upper Pleistocene paleoclimate estimates, rendering it likely recorded mean Cenozoic paleoclimate trends may conceal abrupt short-term climate fluctuations. However, as exemplified by the Paleocene-Eocene thermal maximum (PETM) and earlier GHG and temperature spikes associated with major volcanic and asteroid impact events, the long-term residence time of CO2 in the atmosphere extends the signatures of abrupt warming events to within detection limits of multiple paleoproxies. The mean post-1750 temperature rise rate (approximately ~0.0034°C per yr, or ~0.008°C per yr where temperature is not masked by sulfur aerosols) exceeds those of the PETM (approximately ~0.0008-0.0015°C per yr) by an order of magnitude and mean glacial termination warming rates (last glacial termination [LGT] ~ 0.00039; Eemian ~0.0004°C per yr) by near to an order of magnitude. Consistent with previous interglacial peaks an increasing likelihood of collapse of the Atlantic Meridional Ocean Circulation is threatening a severe stadial event.