Millennial-scale Climate Change Research Articles

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 time scale remain unclear. We present multiproxy 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 (EAM) proxies shows a gradual weakening trend from glacial inceptions into glacial maxima, inversely proportional to that of the 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 a reduction in North Atlantic SST and wind anomalies, subsequently propagating dampened millennial-scale variability into the midlatitude 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.

Planktonic foraminifera response to orbital and millennial-scale climate variability at the southern Iberian Margin (IODP Site U1385) during Marine Isotope Stages 20 and 19

The orbital configuration of Marine Isotope Stage (MIS) 19 provides a good analogue to our present interglacial, and it is marked by millennial-scale climate variability. To evaluate how orbital and millennial-scale climate changes interact during this interglacial we have conducted a high-resolution study of planktonic foraminifera assemblages at International Ocean Discovery Program (IODP) Site U1385, SW Iberian Margin, encompassing late MIS 20 and MIS 19. Estimates of sea surface temperature (SST), using transfer-functions, are compared with geochemical, XRF elemental data, biomarker and pollen records from the same site. These results are then compared with SST and ice-rafted debris records from North Atlantic IODP Site U1314 to reconstruct basin-wide palaeoceanographic conditions. During MIS 20, the large size of the ice sheets imparted a strong cooling in the subpolar gyre whereas the Iberian Margin remained under the influence of the subtropical gyre with the development of a high meridional thermal gradient in the North Atlantic. During MIS 20 terminal stadial (794–789 ka) and MIS 19b-a stadial events, the meltwater discharges related to the instability of ice sheets affected both the North Atlantic and the Iberian Margin leading to a weaker thermal gradient. Our data indicate that Termination IX (TIX, ∼795–788 ka) was punctuated by short-term warming/cooling phases in the ocean coupled with warming/cooling events on land. A short-term cooling episode, recognized in the ocean and on land, occurred on Termination IX and preceded the beginning of MIS 19c. During MIS 19c, the planktonic foraminifera SST indicates warm and almost stable conditions in the sea decoupling the cool and dry millennial-scale events on land inferred by pollen assemblages. Starting from 780 ka towards MIS 18, the planktonic foraminifera assemblages and SSTs indicate a cooling trend along the Iberian Margin related to a progressive southward migration of the polar front.

Anthropogenic activity and millennial climate variability affect Holocene mercury deposition of an alpine wetland near the largest mercury mine in China

Mercury (Hg) is a potentially toxic element that can be transported globally through the atmosphere, once deposited in the environment, has strong bioaccumulation and extreme toxicity in food webs, especially in wetland ecosystems. Anthropogenic Hg emissions have enhanced Hg deposition by 3–5 times since the industrial revolution, and the mining and smelting of Hg ore are important emission sources. However, the dynamics in Hg deposition around the largest Hg mine in China before the industrial revolution and their driving forces remain poorly explored. Here we reconstruct the atmospheric Hg depositional fluxes (named here Hg influx (Hginflux)) during the Holocene using a 450-cm alpine wetland sediment core taken from the Jiulongchi wetland, which is only 65 km to the Wanshan Mercury Mine. Our record shows an abrupt rapid increase in Hg concentration since 2500 cal yr BP, suggesting that Hg mining in southwest China may have started before the establishment of the Qin dynasty. Two major Hginflux peaks were found during the periods 10,000–6000 and 6000 - 3800 cal yr BP, with an increase in Hg deposition by a factor of 4–8. These two peaks are also found in other terrestrial archives from several sites across the Northern Hemisphere. We speculate that critical millennial-scale climate changes, i.e., the Holocene Climatic Optimum (HCO) and the Mid-Holocene Transition (MHT), were the potential triggers of these two Hginflux peaks. This study highlights the importance of climatic variability and local Hg mining in controlling atmospheric Hg deposition during the Holocene.

C4 vegetation characteristics in the monsoon rainforest of the Pearl River delta during the MIS 2 period

The impact of abrupt climate change during glacial periods on terrestrial ecosystems are widely acknowledged by paleoecology and paleoclimate communities as key issues in the ongoing debate on geographical distribution and patterns of genetic diversity of species. However, the C4 plant expansion in subtropical South China at the mouth of the Pearl River during the glaciated Marine Isotope Stage 2 (MIS 2) in response to millennial-scale climate changes is largely unknown. In this study we present results of the isotopic composition of sediment organic carbon (δ13CTOC) obtained from a high-resolution fluvial sequence from the Pearl River delta plain in southern China to show millennial-scale C3/C4 ecosystem changes during the MIS 2 interval. Three major C4 grassland expansions and declines of the monsoon rainforest landscape are identified during the MIS 2 period. Our results reveal that during MIS 2 δ13CTOC values shifted profoundly from about −29 ‰ to enriched values of up to −17 ‰ three times and we interpret these as due to episodic expansions of the C4 plants to form a mixed C3/C4 plant ecosystem with the collapse of a pure C3 monsoon rainforest community in this region. These drastic expansions of C4 ecological systems occurred at 24.8–24 ka, 23.8–21 ka, and 18–15.6 ka cal BP intervals, equivalent to well-known Heinrich Stadial (HS) 2, Last Glacial Maximum (LGM), and HS1 super-cold Northern Hemisphere intervals. We found that these drastic changes of plant ecosystems closely tracked the monsoon records during the significant weakening of Asian Summer Monsoon Intervals (WSMIs) of the MIS 2 period.

Millennial-scale hydroclimate changes in Indian monsoon realm during the last deglaciation

In the Indian monsoon realm, spatial homogeneity of hydroclimate response to glacial abrupt climate events in the North Atlantic Ocean and its underlying mechanism are contentious. Here we reconstruct sea surface temperature (SST) and seawater oxygen isotope (δ18Osw) in the central Andaman Sea, which span over the past 26,000 years, to investigate the potential driving mechanism of millennial-scale climate changes in tropical Indian Ocean. Our results demonstrate that millennial-scale SST and δ18Osw changes during the last deglaciation are associated with changes in Asian monsoon system which follows North Atlantic climate changes. In particular, during the transition from BØlling/AllerØd (B/A) to Younger Dryas (YD), the strengthening of East Asian winter monsoon (EAWM) promotes southward invasion of northern cold air masses to Indo-China Peninsula, cooling the Andaman Sea. Meanwhile, the enriching δ18Osw is a consequence of reducing local rainfall amount and Irrawaddy River inflow due to a weakening Indian summer monsoon (ISM). With aid of an isotope-enabled climate model, our results further demonstrate that the changes in EAWM and ISM during B/A-YD transition are closely coupled with variations of Atlantic meridional overturning circulation (AMOC), corroborating its pivotal role in millennial-scale changes in tropical Indian Ocean hydroclimate during the last deglaciation.

Flood activity revealed millennial-scale climatic changes during the late Holocene in the Qaidam Basin, northeastern Tibetan Plateau

Flood activity in arid region is not only crucial process for evolution of rivers and terminal salt lakes, but also sensitive indicator of paleoclimatic changes. Here, slackwater paleoflood sediments of the Nalinggele River, the largest river in the Qaidam Basin, were studied with optically stimulated luminescence dating and grain size analysis to reconstruct flood events, mechanisms and their climatic implications. Seven slackwater deposit layers which show a weak hydrodynamic sedimentary environment, were dated to three main flood stages at ca. 3.6–3.4 ka, 2.2 ka and 1.0 ka. These stages correspond to similar millennial-scale flood activities in the basin bordering Kunlun Mountains, millennial-scale humid intervals in the eastern Qaidam Basin, glacial melting events on the Tibetan Plateau, and as well warm intervals between cold ice-rafted debris events in the North Atlantic, which may triggered by and the intensified solar activities. These flood stages were attributed to increased precipitation from the enhanced Asian Summer Monsoon and increased glacial meltwater delivery during the late Holocene. The findings suggest that a climate on the northeastern Tibtean Plateau that was fluctuant and with humid periods during the late Holocene, and not undergoing a constant drying trend as previously understood.

Millennial-scale oscillations in the Kuroshio\u2013Oyashio boundary during MIS 19 based on the radiolarian record from the Chiba composite section, central Japan

Marine isotope stage (MIS) 19 is considered to be the best orbital analog for the present interglacial. Consequently, clarifying the climatic features of this period can provide us with insights regarding a natural baseline for assessing future climate changes. A high-resolution radiolarian record from 800 to 750 ka (MIS 20 to MIS 18) was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the Global Boundary Stratotype Section and Point for the lower–middle Pleistocene boundary on the Boso Peninsula on the Pacific side of central Japan. Millennial-scale oscillations in the Kuroshio warm and Oyashio cold currents were revealed by the Tr index, which is estimated using a simple equation based on radiolarian assemblages. The estimated Tr values ranged between 0.1 and 0.8 for MIS 18 through MIS 19, with minimum and maximum values corresponding to values observed off present day Aomori (41°N) and the Boso Peninsula (35°N), respectively. The observed patterns tended to be synchronous with the total radiolarian abundance associated with their production. Multiple maxima in radiolarian abundance occurred during periods of the Oyashio expanded mode before 785 ka and during periods of Kuroshio extension after 785 ka in MIS 19. Such increases in radiolarian abundance with the Kuroshio extension during MIS 19 are likely related to improvements in nutrient and photic environments with the development of a two-layer structure along the Kuroshio–Oyashio boundary zone. A similar pattern of millennial-scale climatic changes was also recognized in a precipitation record from the Sulmona Basin in central Italy, suggesting a close relationship with the CbCS record as a result of a large-scale climate system similar to the Arctic Oscillation in the northern hemisphere.

Late Quaternary Climate Reconstruction and Lead-Lag Relationships of Biotic and Sediment-Geochemical Indicators at Lake Bolshoe Toko, Siberia

Millennial-scale climate change history in eastern Siberia and relationships between diatom diversity, paleoclimate, and sediment-geochemical lake system trajectories are still poorly understood. This study investigates multi-proxy time series reaching back to the Late Pleistocene derived from radiocarbon dated Lake Bolshoe Toko sediment cores, southeastern Yakutia, Russia. We analyzed diatoms, elements (XRF), minerals (XRD), grain-size, organic carbon, and included chironomid analyses and published pollen-data for quantitative paleoclimate reconstruction. Changes in diatom species abundances reveal repeated episodes of thermal stratification indicated by shifts from euplanktonicAulacoseiratoCyclotellaspecies. Chironomid and pollen-inferred temperature reconstruction reveal that the main shift between these diatom species is related to the onset of Holocene Thermal Maximum (HTM) at 7.1 cal ka BP. Comparison to other paleoclimate records along a north-south transect through Yakutia shows that the HTM was delayed as far south as the Stanovoy mountains. Relationships between sediment-geochemistry, paleoclimate variability and diatom species richness (alpha diversity) was tested in a moving temporal offset approach to detect lead-lag relationships. Sediment-geochemical data, mainly uniform during the Holocene, revealed strongest positive or negative correlations ahead of species richness changes. Mean July air temperature (TJuly) reconstructions correlate with both Hill numbers and relative assemblage changes indicated by sample scores of multidimensional scaling analysis (MDS) over the entire time series. We found that sediment organic carbon revealed distinct positive correlations, i.e., centennial-scale delay to increases in diatom effective richness (Hill numbers N0 and N2). We conclude that a lag of deposited organic carbon concentrations behind changes in diatom alpha diversity reveals that species richness can augment the production and thus sequestration of organic matter in comparable lake systems.

Fossil maerl beds as coastal indicators of late Holocene palaeo-environmental evolution in the Bay of Brest (Western France)

The Bay of Brest (BB) is a mixed, tide-dominated estuarine system. The shore terraces of this bay are occupied by modern free-living (calcareous) coralline algae locally termed “maerl”, organized in bed-like morphologies (rhodolith deposits). Cores retrieved from around the bay reveal fossilized primitive maerl beds of Holocene age, interbedded in sandy-silt sedimentation. The alternation between biogenic constructions and estuarine sedimentation may provide evidence of varying environmental conditions of the late-Holocene period. This paper mainly focuses on the results of chronostratigraphic and bio-sedimentological interpretations of coring data collected in less than 15 m of water depth in an attempt to decipher the main stages of maerl colonization in the bay. In particular, this study raises several significant points allowing to draw links between centennial to millennial-scale climatic changes in marine estuary sedimentation and episodes within the development of maerl biocenoses. The paleo-bathymetry of the coastal terraces has not changed significantly over the last 5000 years. Yet, the first maerl occurrence only appeared around 2000 cal yr B.P., likely showing that the environmental conditions were not favorable for their emergence prior to that time. Pioneer maerl beds developed on coarse shell deposits inherited from the paleostorms affecting the Atlantic coasts during the colder climatic period of the Iron Age (3100–1950 cal yr B.P.). The accumulations then aggraded at various and discontinuous rates, sometimes reaching up to 2.1 m/kyr. Maerl beds temporarily disappeared in the southern part of the Bay of Brest when sedimentation rates increased throughout the bay during the Dark-Age cold period (1375–1250 cal yr B.P.), suggesting that maerl formations could not keep up with sedimentation rate exceeded a certain threshold. Muddy sedimentation conditions also dramatically changed on two occasions, with the establishment of coarse storm levels, set at the intervals 825–600 cal yr B.P. (MWP) and 113–0 cal yr B.P. But maerl deposits reseed the environment as a result of each new cold period, demonstrating the persistence of such coralline algae against drastic palaeoenvironmental changes in coastal areas.

Last Lateglacial glacier advance in the Gran Paradiso Group reveals relatively drier climatic conditions established in the Western Alps since at least the Younger Dryas

The Late Pleistocene to Holocene transition in the Northern Hemisphere was characterized by abrupt millennial-scale climatic changes testified in the Alpine Chain by proxy records derived from glacial landforms and deposits. A detailed reconstruction of the paleo-glaciers during the deposition of the pre-Little Ice Age (LIA) moraines and newly obtained 10Be exposure ages provide information on the timing of a glacier advance in the Gran Paradiso Group (Western Alps, Italy) related to the regional Egesen stadial as a response to the climatic deterioration at around 12.9–11.7 ka (corresponding to the Younger Dryas in northern Europe and to the Greenland stadial 1 in the INTIMATE event stratigraphy). The study area represents a key site to define the behaviour of the Egesen paleo-glaciers, since they are located in a significant climatic area between the moister Maritime Alps and the Northern Alps. The ELA reconstructions and the comparison with other Alpine sectors provide evidence that current relatively drier conditions in the area postdate the LGM and were already present during the Egesen stadial. Our results support a strong positive YD Arctic Oscillation index, which led to drier conditions in southern Europe and caused negative winter precipitation anomalies.

Synergy of the westerly winds and monsoons in the lake evolution of global closed basins since the Last Glacial Maximum and implications for hydrological change in central Asia

Abstract. The monsoon system and westerly circulation, to which climate change responds differently, are two important components of global atmospheric circulation interacting with each other in the middle to low latitudes. Relevant research on global millennial-scale climate change in monsoon and westerly regions is mostly devoted to multi-proxy analyses of lakes, stalagmites, ice cores, and marine and eolian sediments. Different responses from these proxies to long-term environmental change make understanding climate change patterns in monsoon and westerly regions difficult. Accordingly, we disaggregated global closed basins into areas governed by monsoon and westerly winds, unified paleoclimate indicators, and added lake models and paleoclimate simulations to emphatically track millennial-scale evolution characteristics and mechanisms of East Asian summer monsoon and westerly winds since the Last Glacial Maximum (LGM). Our results reveal that millennial-scale water balance change exhibits an obvious boundary between global monsoon and westerly regions in closed basins, particularly in the Northern Hemisphere. The effective moisture in most closed basins of the midlatitude Northern Hemisphere mainly exhibits a decreasing trend since the LGM, while that of the low latitudes shows an increasing trend. In the monsoon-dominated closed basins of Asia, a humid climate prevails in the early to mid-Holocene, and a relatively dry climate appears in the LGM and late Holocene. In the westerly-wind-dominated closed basins of Asia, the climate is characterized by a humid LGM and mid-Holocene (MH) compared with the dry early and late Holocene, which is likely to be connected to precipitation brought by the westerly circulation. This study provides insight into the long-term evolution and synergy of westerly winds and monsoon systems as well as a basis for the projection of future hydrological balance.

Steering iceberg armadas.

The Asian-Pacific tropics likely instigated millennial-scale climate changes

Evidence for Solar Modulation on the Millennial-Scale Climate Change of Earth

In this study, we use available reconstructed data to investigate periodicities of solar activity (i.e., sunspot number) and the Earth’s climate change (temperatures of Lake Qinghai in China and Vostok in Antarctica, the GISP δ18O climate record of Greenland, and the stalagmite δ18O monsoon records of Dongge Cave in China) as well as their cross-wavelet coherences on millennial scale. We find that the variations of the Earth’s climate indices exhibited the 1000-year cyclicity, which was recently discovered in solar activity (called Eddy cycle). The cross-wavelet correlations between the millennium-cycle components of sunspot number and the Earth’s climate change remains both strong and stable during the past 8640 years (BC 6755–AD 1885). The millennial variation of sunspot number keeps in-phase with variations of Lake Qinghai temperature, Greenland temperature, and East Asian Monsoon, but anti-phase with the variation of Antarctica temperature. The strong and stable resonant relationships between sunspot numbers and these climate indices indicate that solar variability may have played a role in modulation on this millennial seesaw pattern of the Earth’s climate change before the modern industrial era.

The Holocene Cedrus pollen record from Sierra Nevada (S Spain), a proxy for climate change in N Africa

Comprehending the effects of climate variability and disturbance on forested ecosystems is paramount to successfully managing forest environments under future climate scenarios (e.g., global warming, aridification increase). Changes in fossil pollen abundance in sedimentary archives record past vegetation dynamics at regional scales, mainly related to climate changes and, in the last few millennia, to human impact. Pollen records can thus provide long databases with information on how the environment reacted to climate change before the historical record. In this study, we synthesized fossil pollen data from seven sites from the Sierra Nevada in southern Spain to investigate the response of forests in the western Mediterranean area to millennial-scale climate changes and to human impact during the Holocene. In particular, here we focused on Cedrus pollen abundances, which most-likely originated from Northern Africa and were carried to Sierra Nevada by wind. Cedrus pollen has received little attention in the Iberian Peninsula palynological records, for it occurs in low concentrations and has an African source, and thus this article explores the potential to reconstruct its past history and climate. Although Cedrus abundances are generally lower than 1% in the studied pollen samples, a comparison with North African (Moroccan) Cedrus pollen records shows similar trends at long- and short-term time-scales. Therefore, this record could be used as a proxy for changes in this forest species in North Africa. As observed in the Sierra Nevada synthetic record, the increasing trend of Cedrus pollen during the Middle and Late Holocene closely correlates with decreasing summer insolation. This would have produced overall cooler annual temperatures in Northern Africa (Middle Atlas and Rif Mountains) as well as lower summer evaporation, benefiting the growth of this cool-adapted montane tree species while increasing available moisture during the summer, which is critical for this water-demanding species. Millennial-scale variability also characterizes the Sierra Nevada Cedrus synthetic pollen record. Cedrus abundance oscillations co-vary with well-known millennial-scale climatic variability that controlled cedar abundance and altitudinal distribution in montane areas of N Africa.

Human occupation, slash-burning and vegetation response from the final Pleistocene to the middle Holocene, Daling River basin, NE China

We present new radiocarbon dating, pollen and microcharcoal date from a section at a well-known early Neolithic site, Chahai, in Northeast China, to reconstruct vegetation and human occupation history and to evaluate human influence on the regional vegetation. The results suggested that the site was occupied in at least four main stages, 12,700–12,570, 10,200–9300, 7200–6300 and 2070–1920 cal yr BP, and that the periodic occupation and abandonment of the Chahai site was probably related to global millennial scale climate change. The regional vegetation change in Chahai region showed an increasing trend in humidity from the final Pleistocene to the middle Holocene; the vegetation was successively dominated by an arid steppe (12,700–12,570 cal yr BP) and moist meadow (10,200–9300 and 7200–6300 cal yr BP). Nevertheless, the reduction of the regional forest cover, indicated by a decrease in the proportion of tree pollen, was synchronous with population expansion locally around 7200–6300 cal yr BP. Our results demonstrate that the vegetation succession in the Chahai region was mainly controlled by climate change in the final Pleistocene and the early Holocene (12,700–12,570 and 10,200–9300 cal yr BP), while increased human activities and agricultural behavior played major roles in the degradation of the regional forest during the middle Holocene (7200–6300 cal yr BP).

Latest Pleistocene to Holocene loess in the central Great Plains: Optically stimulated luminescence dating and multi-proxy analysis of the enders loess section (Nebraska, USA)

Loess deposits of the central Great Plains, USA, and their intercalated soils provide a detailed record of climatically driven changes within the aeolian system during the Pleistocene-Holocene transition and the Holocene. Here we present a detailed optically stimulated luminescence (OSL) chronology as well as multi-proxy analysis obtained for the first time on the Enders section, located in southwestern Nebraska, central Great Plains. The section records multiple episodes of rapid loess deposition alternating with soil formation. Rapid accumulation of Late Pleistocene Peoria Loess was replaced around 13–14 ka by formation of the Brady Soil until 9.5 ± 0.6 ka. The Holocene Bignell Loess then buried the Brady Soil and accumulated episodically throughout the Holocene. The loess-paleosol stratigraphy since the Late Pleistocene at the Enders site is very similar to that at other sites in western Nebraska, and the newly developed OSL chronology (based on three grain size classes) adds new confidence to earlier dating. The high-resolution grain size profile from Enders shares many features with similar data from the previously studied Wauneta site, including three peaks of fine-grained material just above and within the Brady Soil, likely representing response to millennial-scale climatic changes during the Pleistocene-Holocene transition. This study demonstrates the potential for developing high-resolution, well-dated paleoclimatic records from the loess of the central Great Plains. Contrasts between Great Plains and Eurasian loess records reflect differences in the Late Pleistocene to Holocene climatic evolution and other factors influencing the loess system.

Millennial-scale climate changes manifest Milankovitch combination tones and Hallstatt solar cycles in the Devonian greenhouse world

Sub-Milankovitch rhythmic features in sedimentary records have been reported from throughout geological time. However, their origin remains enigmatic, in particular during so-called greenhouse periods in Earth’s history. To better understand such short-term climatic changes, we sampled two 3-m-thick intervals of early Devonian hemipelagic carbonate at 1 cm resolution in the Pod Barrandovem section (Czech Republic). Greenhouse conditions prevailed during early Devonian times, and the chosen resolution enables the detection of millennial-scale climate change as recorded by elemental abundances. We used a previously published astrochronology for the section to transform the studied series from the stratigraphic into the time domain. Spectral analysis of the time-calibrated log-transformed Ti records reveal obliquity and precession cycles, confirming the applied astrochronology. Additional spectral peaks with periods of 2.3–2.7, 6–8, and 10–12 k.y. appear in both records. Furthermore, a 1.5 k.y. periodicity, close to the Pleistocene Dansgaard-Oeschger oscillation, is also identified, but only in the record with higher accumulation rate (∼3.5 cm/k.y.). Bi-coherence spectra reveal that the 6–8 and 10–12 k.y. periodic components are combination tones of Milankovitch cycles. We infer the shorter ∼2.5 k.y. periodicity to be the result of solar forcing, related to the Hallstatt cycle. These new observations strengthen the case for an external origin of millennial-scale features.

A Great Basin lake-level response to 38–34 ka Dansgaard–Oeschger oscillations

Paleontological, geochemical, and geophysical data from pluvial Lake Chewaucan, Oregon, northwestern Great Basin provide a high-resolution paleoclimate record spanning the interval (38–34 ka) that includes the Mono Lake paleomagnetic excursion, Dansgaard–Oeschger Interstadials #8–#6, and the end of Heinrich Event 4. New climate proxies presented here from the BB3-I core, whose chronology was established in a recent publication focusing on its paleomagnetic record, consist of sediment grain-size, Corg/N, ostracode faunal counts, lipid molecular stratigraphy, and palynology. They build on previously publised proxies from this basin based on environmental magnetism and supporting lithological features found in outcrop and core. Results from granulometry, geochemical analysis and the presence of the ostracode Cytherissa lacustris consistently demonstrate the correspondence of low lake conditions and colder water temperatures during Dansgaard–Oeschger stadials during a time interval including the low magnetic intensity feature of the Mono Lake Excursion, a paleomagnetic event found both in the lake core of this study and the composite Greenland ice core record between Interstadials #7 and #6. Pollen data also support this finding, suggesting colder and drier continental montane woodland conditions during stadials versus warmer and wetter semi-arid woodland conditions during interstadials. This is further supported with lipid molecular stratigraphy, indicating a consistent tendency toward terrestrial-sourced vegetation, reflecting increased stream discharge into deeper lakes during interstadials versus dominance of aquatic vegetation during low-discharge, low lake stadials. These results suggesting wet interstadials confirm those of earlier studies at Summer Lake and for other lake records in the Great Basin for millennial-scale climate change during MIS 3 age.

The rock shelter Abrigo del Molino (Segovia, Spain) and the timing of the late Middle Paleolithic in Central Iberia

AbstractThe timing of the late Middle Paleolithic and late disappearance of Neanderthals in the Iberian Peninsula are hotly debated subjects in Paleolithic archeology. Several studies suggested a late survival in South and Central Iberia until about 32 ka, but were probably subject to significant age underestimation due to contamination of dating samples, undiagnostic lithic assemblages, and/or lack of stratigraphic integrity. We conducted a radiocarbon and luminescence-dating study backed by detailed sedimentological and micromorphological investigations at the newly discovered rock shelter sequence of Abrigo del Molino (Central Spain). Accumulation of the sediment sequence was rapid. It started with deposition of paleoflood slack-water deposits at around 48 ka and continued until about 41 ka with deposition of colluvial and detrital sediments. These contain two Mousterian levels, which place the latest Neanderthal occupation at around 45 to 41 ka, i.e., between Heinrich Stadials 5 and 4, and probably during a time of climate amelioration. Abrigo del Molino thus provides a detailed and chronologically well-constrained record of Late Neanderthal presence and morphodynamic change in Central Iberia during times of millennial-scale climate changes. The site gives further evidence for an early disappearance of Neanderthals in Central Iberia.

The dynamic relationship between temperate and tropical circulation systems across South Africa since the last glacial maximum

A fundamental and long-standing question of southern African palaeoclimatology is the way tropical and temperate climate system dynamics have influenced rainfall regimes across the subcontinent since the Last glacial maximum. In this paper, we analyse a selection of recently published palaeoclimate reconstructions along a southwest-northeast transect across South Africa. These records span the last 22,000 years, and encompass the transition between the region's winter and summer rainfall zones. In synthesis, these records confirm broad elements of the dominant paradigm, which proposes an inverse coeval relationship between temperate and tropical systems, with increased precipitation in the winter (summer) rainfall zone during glacial (interglacial) periods. Revealed, however, is a substantially more complex dynamic, with millennial-scale climate change events being strongly – even predominantly – influenced by the interaction and combination of temperate and tropical systems. This synoptic forcing can create same sign anomalies across the South African rainfall zones, contrary to expectations based on the classic model of phase opposition. These findings suggest a new paradigm for the interpretation of southern African palaeoenvironmental records that moves beyond simple binary or additive influences of these systems.