Past Interglacials Research Articles

Millennial‐Scale Climate Variability Potentially Shaped the Early Interglacial Optimum in Southern Europe

AbstractThe seasonal and latitudinal distribution of insolation is considered the main factor controlling the magnitude and timing of interglacial periods. However, despite small differences in insolation forcing, vegetation and hydrology in southern Europe during past interglacials are variable and the gradual change in insolation cannot explain the observed short‐lived forest optimum. Here we focus on vegetation and hydroclimatic changes at orbital‐ and suborbital‐scales in southwestern Europe during two past warm interglacial periods with reduced ice‐sheets, namely Marine Isotope Stages (MIS) 9e and 5e. We provide new pollen and sea surface temperatures records for MIS 9e from IODP Site U1385. This pollen record shows a forest expansion in southern Iberia over a 14 ky interval, bracketed by the millennial‐scale cooling events of Termination IV and MIS 9d. Between 334.5 and 332.5 ka, forest expansion reached a maximum, suggesting increased winter moisture during early MIS 9e. Model‐data comparison for MIS 9e and 5e shows that insolation is the main driver of the orbital‐scale vegetation and precipitation changes in Iberia, atmospheric CO2 forcing playing a secondary role. The high‐frequency component of the MIS 9e and 5e forest timeseries highlights the early interglacial forest and precipitation maxima as prominent suborbital events lasting ∼2 ky. We propose that the primarily insolation‐driven forest and precipitation optima were fostered by the non‐equilibrium conditions generated by the millennial‐scale deglacial variability during the early interglacials. Additionally, the early end of these optima may have been favored by a cooling and drying event that is part of the persistent intra‐interglacial variability.

Paleoclimatic significance of the organic carbon isotopes of the Tajikistan loess in arid Central Asia, on orbital timescales since the last interglacial

During the past few decades, the stable carbon isotope composition of bulk organic matter (δ13Corg) in loess sediments has been increasingly used for reconstructing changes in the terrestrial vegetation and climate in several regions, including Europe, Xinjiang (the eastern part of arid central Asia, ACA), and the Chinese Loess Plateau (CLP). However, previous research indicates significant differences in the climatic significance of δ13Corg between the loess-paleosol sequences of Europe and the western and eastern ACA, compared to the loess of the central and southern CLP in monsoonal Asia. The δ13Corg values of loess-paleosol sequences in western and eastern ACA on different timescales exhibit consistent patterns of variation, suggesting that loess δ13Corg in these areas may be influenced by similar climatic factors and have similar mechanisms. However, the lack of detailed δ13Corg studies in central ACA limits our understanding of their applicability to long loess sequences within this region. This limitation not only constrains our understanding of the paleoclimatic significance of loess δ13Corg in central ACA, but it also affects the practical application of loess δ13Corg as a reliable paleoclimate proxy in this region. Consequently, it impedes a comprehensive understanding and in-depth analysis of loess δ13Corg across the mid-latitude Eurasian continent. To address this deficiency, we conducted a δ13Corg study of the Darai Kalon (DK) loess section, in southern Tajikistan, central ACA, since the last interglacial, with the aim of exploring the environmental significance of loess δ13Corg and the origin of the climatic record of this section, on orbital timescales. The results show that the ecosystem in southern Tajikistan, and throughout ACA, was dominated by C3 vegetation since the last interglacial. Loess δ13Corg records can be used as a precipitation proxy in ACA, at least since the last interglacial. However, regional comparisons revealed negative correlations between loess δ13Corg values and pedogenic intensity in Europe, ACA, and the western CLP, which is the opposite to the positive correlations observed in the central and southern CLP. Comparison of the paleoclimate record of the DK section with those of loess-paleosol sequences from monsoonal Asia indicated that warm, humid conditions occurred during past interglacials (MIS5, MIS1) and interstadials (MIS3), and cold, arid conditions occurred during the glacial/stadial periods (MIS4, MIS2) in both ACA and monsoonal Asia. We propose that changes in Northern Hemisphere insolation were responsible for this in-phase pattern of climate change between these two regions on orbital timescales since the last interglacial.

Pliocene–Pleistocene warm-water incursions and water mass changes on the Ross Sea continental shelf (Antarctica) based on foraminifera from IODP Expedition 374

Abstract. International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to reconstruct paleoenvironments, track the history of key water masses, and assess model simulations that show warm-water incursions from the Southern Ocean led to the loss of marine-based Antarctic ice sheets during past interglacials. IODP Site U1523 (water depth 828 m) is located at the continental shelf break, northeast of Pennell Bank on the southeastern flank of Iselin Bank, where it lies beneath the Antarctic Slope Current (ASC). This site is sensitive to warm-water incursions from the Ross Sea Gyre and modified Circumpolar Deep Water (mCDW) today and during times of past warming climate. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred at Site U1523 after 3.8 Ma and prior to ∼ 1.82 Ma. Many of these warm-water taxa incursions likely represent interglacials of the latest Early Pliocene and Early Pleistocene, including Marine Isotope Stage (MIS) Gi7 to Gi3 (∼ 3.72–3.65 Ma), and Early Pleistocene MIS 91 or 90 (∼ 2.34–2.32 Ma) and MIS 77–67 (∼ 2.03–1.83 Ma) and suggest warmer-than-present conditions and less ice cover in the Ross Sea. However, a moderately resolved age model based on four key events prohibits us from precisely correlating with Marine Isotope Stages established by the LR04 Stack; therefore, these correlations are best estimates. Diatom-rich intervals during the latest Pliocene at Site U1523 include evidence of anomalously warm conditions based on the presence of subtropical and temperate planktic foraminiferal species in what likely correlates with interglacial MIS G17 (∼ 2.95 Ma), and a second interval that likely correlates with MIS KM3 (∼ 3.16 Ma) of the mid-Piacenzian Warm Period. Collectively, these multiple incursions of warmer-water planktic foraminifera provide evidence for polar amplification during super-interglacials of the Pliocene and Early Pleistocene. Higher abundances of planktic and benthic foraminifera during the Mid- to Late Pleistocene associated with interglacials of the MIS 37–31 interval (∼ 1.23–1.07 Ma), MIS 25 (∼ 0.95 Ma), MIS 15 (∼ 0.60 Ma), and MIS 6–5e transition (∼ 0.133–0.126 Ma) also indicate a reduced ice shelf and relatively warm conditions, including multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A decrease in sedimentation rate after ∼ 1.78 Ma is followed by a major change in benthic foraminiferal biofacies marked by a decrease in Globocassidulina subglobosa and a decrease in mud (< 63 µm) after ∼ 1.5 Ma. Subsequent dominance of Trifarina earlandi biofacies beginning during MIS 15 (∼ 600 ka) indicate progressive strengthening of the Antarctic Slope Current along the shelf edge of the Ross Sea during the mid to Late Pleistocene. A sharp increase in foraminiferal fragmentation after the MPT (∼ 900 ka) and variable abundances of T. earlandi indicate higher productivity, a stronger but variable ASC during interglacials, and/or corrosive waters, suggesting changes in water masses entering (mCDW) and exiting (High Salinity Shelf Water or Dense Shelf Water) the Ross Sea since the MPT.

Intermediate water warming caused methane hydrate instability in South China Sea during past interglacials

Methane hydrates are widely distributed along continental margins, representing a potential source of methane to the ocean and atmosphere, possibly influencing Earth’s climate. Yet, little is known about the response of methane hydrates to global climate change, especially at the timescale of glacial-interglacial cycles. Here we present a chronology of methane seepage from seep carbonates derived from a series of tens to hundreds of meters long hydrate-bearing sediment records from the South China Sea, drilled at water depths of 664−871 m. We find that six out of seven episodes of intense methane seepage during the last 440,000 years were related to hydrate dissociation, all coinciding with major interglacials, the so-called Marine Isotope Stages 1, 5e, 7c, 9c, and 11c. Using numerical modeling, we show that these events of methane hydrate instability were possibly triggered by the rapid warming of intermediate waters by ∼2.5−3.5 °C in the South China Sea. This finding provides direct evidence for the sensitivity of the deep marine methane hydrate reservoir to glacial-interglacial climatic and oceanographic cyclicity.

Strong Asymmetry of Interhemispheric Ice Volume During MIS 11, MIS 9, and MIS 7 Drives Heterogeneity of Interglacial Precipitation Intensity Over Asia

AbstractGaining insight into the characteristics of past interglacials enhances our understanding of the current warm period and improves predictions of future climate. In this study, we analyze precipitation records of the past 900 ka and find that precipitation intensity during interglacials varied across Asia, especially between interglacials that occurred before and after the mid‐Brunhes transition. To clarify the mechanism of precipitation intensity variation during interglacials, we present a high‐resolution eolian record documenting the past 900 ka, which is from the thickest loess core (202.49 m) drilled in Ili Basin, Central Asia and conduct modeling with Community Earth System Model 1.2.2. We propose that sorting coefficient of Ili loess is a sensitive proxy for wind intensity, and it indirectly reflects Northern Hemisphere ice volume. Supported by numerical modeling experiments, we suggest that strong asymmetry of interhemispheric ice volume during marine isotope stages 11, 9, and 7 drives heterogeneity of interglacial precipitation intensity over Asia.

Palaeoenvironmental dynamics of the MIS 11 interglacial in north-western Europe based on the malacological succession from La Celle (Seine Valley, France): Relationship with glacial refugia and palaeobiodiversity

In north-western Europe, continental records of Pleistocene interglacials are well preserved in fluvial sequences and particularly within calcareous tufas that formed at the top of the series. They are the sole deposits recording the full optima. Tufas contain rich malacological communities that allow the detailed palaeoenvironmental history of past interglacials to be reconstructed. Several tufas have been investigated in the study area, which have led to the recognition of the « Lyrodiscus fauna » as a characteristic biostratigraphical signature of tufa sequences of MIS 11 age in north-western Europe. Among these, the site at La Celle in the Seine valley (France) is the only one where tufa has accumulated a substantial thickness (almost 9 m) in which the complete development of the Lyrodiscus fauna is represented, yielding a detailed record of the forest expansion during the MIS 11 interglacial. The La Celle succession therefore provides a regional framework into which other sequences can be set, shedding lights on various aspects of palaeoenvironmental dynamics, biostratigraphy, palaeogeography and palaeobiodiversity. Combined malacological and isotopic records from La Celle demonstrate a close correlation between increasing temperatures and the development of forest land snail communities. The palaeoecological framework of forest extension inferred from the malacological succession of La Celle allows the shorter successions from northern France and south-eastern England to be located within the maximum development of the humid forest biotope during MIS 11c. The order of occurrence of forest snails indicates that Atlantic and Central European refugia are the original sources of recolonizations for north-western European sites. Strict Mediterranean species reach the area only at the MIS 11c climatic optimum. Many species present during MIS 11c no longer live in this part of Europe, indicating a northward shift in the location of the modern alpine biodiversity hotspot.

Enhanced western mediterranean rainfall during past interglacials driven by North Atlantic pressure changes

There is increasing concern with anthropogenic greenhouse gas emissions that ocean warming, in concert with summer and winter precipitation changes, will induce anoxia in multiple ocean basins, such as in the Mediterranean Sea. Although the hydrological changes in the eastern Mediterranean are quite well constrained, quantitative evidence of changes in sea surface temperature (SST) and winter rainfall in the western Mediterranean across the past interglacials is relatively scarce. In this study, we use a combination of trace element (Ba/Ca and Mg/Ca) and stable oxygen isotope composition of planktonic foraminifera from a sediment core located off the Golo River, Corsica (northern Tyrrhenian Sea) to reconstruct variations in SSTs and sea surface salinities (SSS) during the Holocene (MIS 1) and warm periods of the past two interglacials (MIS 5, 7). We also analyse PMIP3 model simulations for the mid-Holocene to investigate the mechanism for moisture transport in the western Mediterranean. Our Mg/Ca-SSTs, Ba/Ca-salinity and derived δ18O-seawater records suggest that the warm periods of the past interglacials were characterized by high river discharge and lower SSS in the northern Tyrrhenian Sea. Since this region is ideally located on the trajectory of wintertime storm tracks across the North Atlantic into the Mediterranean Sea and is also outside the influence of the ITCZ-controlled summer monsoon rains, we suggest enhanced winter rainfall during the past interglacials. Our analysis of PMIP3 model simulations for mid-Holocene also support increased south-westerly moisture transport into the western Mediterranean originating from the North Atlantic. We also find evidence that long-term amplitude of the salinity decrease tightly follows eccentricity. We suggest that these hydrologic changes in the western Mediterranean, and the northern Mediterranean borderlands as a whole, were a contributing factor, together with local cyclogenesis and African summer monsoon rainfall, to basin-wide anoxia in the past. Our findings offer new constraints to the amplitude and cause of winter rainfall changes in the Mediterranean during past warm periods.

Vegetation and climate record from Abric Romaní (Capellades, northeast Iberia) during the Upper Pleistocene (MIS 5d−3)

This study addresses the pollen record of Abric Romaní archaeological site and the climate evolution of the last interglacial and glacial stadials in the Iberian Peninsula. The new pollen record spans the interval from 110,000 to 55,000 years ago. In general, the glacial/stadial vegetation is characterized by a steppe and herbaceous communities indicating dry and cold climatic conditions, whereas the vegetation optimum of past interglacials can be described as pine-oaks with mediterranean forest indicating milder and moister climatic conditions. During the first half of the MIS 5a and the MIS 5c, the region was warmer, which is characterized by temperate forests. However, the existence of Artemisia steppes during the second part of the MIS 5a indicates that the degree of continentality can be related to the low winter temperatures and precipitation. During MIS 4, a colder and dryer climate enabled the development of open vegetation (dominated by Artemisia with Poaceae and other Asteraceae) around the study site.

Challenges and research priorities to understand interactions between climate, ice sheets and global mean sea level during past interglacials

Quaternary interglacials provide key observations of the Earth system's responses to orbital and greenhouse gas forcing. They also inform on the capabilities of Earth system models, used for projecting the polar ice-sheet and sea-level responses to a regional warmth comparable to that expected by 2100 C.E. However, a number of uncertainties remain regarding the processes and feedbacks linking climate, ice-sheet and sea-level changes during past warm intervals. Here, we delineate the major research questions that need to be resolved and future research directions that should be taken by the paleoclimate, sea-level and ice-sheet research communities in order to increase confidence in the use of past interglacial climate, ice-sheet and sea-level reconstructions to constrain future predictions. These questions were formulated during a joint workshop held by the PAGES-INQUA PALSEA (PALeo constraints on SEA level rise) and the PAGES-PMIP QUIGS (QUaternary InterGlacialS) Working Groups in September 2018.

Stratification-induced variations in nutrient utilization in the Polar North Atlantic during past interglacials

Vertical water mass structure in the Polar North Atlantic Ocean plays a critical role in planetary climate by influencing the formation rate of North Atlantic deepwater, which in turn affects surface heat transfer in the northern hemisphere, ventilation of the deep sea, and ocean circulation on a global scale. However, the response of upper stratification in the Nordic seas to near-future hydrologic forcing, as surface water warms and freshens due to global temperature rise and Greenland ice demise, remains poorly known. While past major interglacials are viewed as potential analogues of the present, recent findings suggest that very different surface ocean conditions prevailed in the Polar North Atlantic during Marine Isotope Stage (MIS) 5e and 11 compared to the Holocene. It is thus crucial to identify the causes of those differences in order to understand their role in climatic and oceanographic variability. To resolve this, we pair here bulk sediment δ15N isotopic signatures with planktonic foraminiferal assemblages and their isotopic composition across major past interglacials. The comparison defines for the first time stratification-induced variations in nitrate utilization up to 25% between and within all of these warm periods that highlight changes in the thickness of the mixed-layer throughout the previous interglacials. That thickness directly controls the depth-level of Atlantic water inflow. The major changes of nitrate utilization recorded here thus suggest that a thicker mixed-layer prevailed during past interglacials, probably related to longer freshwater input associated with the preceding glacial termination. This would have caused the Atlantic water to flow at greater depth during MIS 5e and 11. These results call for caution when using older interglacials as modern or near-future climate analogues and contribute to the improvement of our general comprehension of the impact of freshwater input near a globally important deep-water formation site like the Nordic Seas. This is crucial when assessing the negative impacts on the Greenland Ice Sheet of climate change and global warming.

Paleo-surfaces of glacio-eustatically forced aggradational successions in the coastal area of Rome: Assessing interplay between tectonics and sea-level during the last ten interglacials

Abstract Recently acquired geochronological and stratigraphic data provide new information on the sedimentary successions deposited by the Paleo-Tiber River in the coastal and near-coastal area of Rome in consequence of the glacio-eustatic changes, allowing to better define their inner geometry and palaeogeographic spatial distribution. In the present work we use this revised sedimentary dataset to provide a geochronologically constrained and tectonically adjusted record of paleo sea-level indicators. Aimed at this scope, we review literature data acquired in the last 35 years and using the new geochronological constraints we pinpoint the coastal-to-fluvial terraces of MIS 5 and MIS 7, mapping their relic surfaces in an area of 30 km along the coast north and south of the Tiber River mouth, and 20 km inland of the fluvial valleys of Tiber and Aniene rivers. The geometry of these paleo-surfaces provides constraints on the relative elevation of the sea-level during the last interglacials and on the uplift rates in this region during the last 200 ka. In particular, we recognize the previously undetected terraces of MIS 5.3 and MIS 5.1 interstadials, and we assess their spatial relationship with respect to MIS 5.5, providing important information on sea-level oscillations during this time span. Comparison with sea-level indicators provided by previous aggradational successions deposited during past interglacials spanning MIS 9 through MIS 21 in the coastal area of Rome, also allows us to reconstruct the tectonic history and investigate its relationships with the Middle-Pleistocene volcanic activity of the Roman Comagmatic Region along the Tyrrhenian Sea margin of Italy in the last 900 ka.

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

Abstract. The fast growing calcareous skeletons of zooxanthellate reef corals (z corals) represent unique environmental proxy archives through their oxygen and carbon stable isotope composition (δ18O, δ13C). In addition, the accretion of the skeleton itself is ultimately linked to the environment and responds with variable growth rates (extension rate) and density to environmental changes. Here we present classical proxy data (δ18O, δ13C) in combination with calcification records from 15 massive z corals. The z corals were sampled from four interglacial units of the Florida carbonate platform (USA) dated approximately 3.2, 2.9, 1.8 and 1.2 Ma (middle Pliocene to early Pleistocene). The z corals (Solenastrea, Orbicella, Porites) derive from unlithified shallow marine carbonates and were carefully screened for primary preservation suited for proxy analysis. We show that skeletal accretion responded with decreasing overall calcification rates (decreasing extension rate but increasing density) to warmer water temperatures. Under high annual water temperatures, inferred from sub-annually resolved δ18O data, skeletal bulk density was high, but extension rates and overall calcification rates were at a minimum (endmember scenario 1). Maximum skeletal density was reached during the summer season giving rise to a growth band of high density within the annually banded skeletons (“high density band”, HDB). With low mean annual water temperatures (endmember scenario 2), bulk skeletal density was low but extension rates and calcification rates reached a maximum, and under these conditions the HDB formed during winter. Although surface water temperatures in the Western Atlantic warm pool during the interglacials of the late Neogene were ∼ 2 °C higher than they are in the present day, intermittent upwelling of cool, nutrient-rich water mitigated water temperatures off south-western Florida and created temporary refuges for z coral growth. Based on the sub-annually resolved δ18O and δ13C records, the duration of the upwelling episodes causing the endmember 2 conditions was variable and lasted from a few years to a number of decades. The episodes of upwelling were interrupted by phases without upwelling (endmember 1) which lasted for at least a few years and led to high surface water temperatures. This variable environment is likely one of the reasons why the coral fauna is dominated by the eurytopic genus Solenastrea, also a genus resistant to high turbidity. Over a period of ∼ 50 years, the oldest sub annually resolved proxy record available (3.2 Ma) documents a persistent occurrence of the HDB during winter. In contrast, the HDB forms in summer in modern z corals from the Florida reef tract. We suggest this difference should be tested as being the expression of a tendency towards decreasing interglacial upwelling since the middle Pliocene. The number of z coral sclerochronological records for the Plio-Pleistocene is still rather low, however, and requires more data and an improved resolution, through records from additional time slices. Nonetheless, our calcification data from the warm periods of past interglacials may contribute to predicting the effects of future ocean warming on z coral health along the Florida reef tract. The inconsistent timing of the HDB within single coral records or among specimens and time slices is unexpected and contrasts the common practice of establishing chronologies on the basis of the density banding.

Calculation of mass discharge of the Greenland ice sheet in the Earth System Model

Mass discharge calculation is a challenging task for the ice sheet modeling aimed at evaluation of their contribution to the global sea level rise during past interglacials, as well as one of the consequences of future climate change. In Greenland, ablation is the major source of fresh water runoff. It is approximately equal to the dynamical discharge (iceberg calving). Its share might have still larger during the past interglacials when the margins of the GrIS retreated inland. Refreezing of the melted water and its retention are two poorly known processes playing as a counterpart of melting and, thus, exerting influence on the run off. Interaction of ice sheets and climate is driven by energy and mass exchange processes and is complicated by numerous feed-backs. To study the complex of these processes, coupling of an ice sheet model and a climate model (i.e. models of the atmosphere and the ocean) in one model is required, which is often called the Earth System Model (ESM). Formalization of processes of interaction between the ice sheets and climate within the ESM requires elaboration of special techniques to deal with dramatic differences in spatial and temporal variability scales within each of three ESM’s blocks. In this paper, we focus on the method of coupling of a Greenland ice sheet model (GrISM) with the climate model INMCM having been developed in the Institute of Numerical Mathematics of Russian Academy of Sciences. Our coupling approach consists in applying of a special buffer model, which serves as an interface between GrISM and INMCM. A simple energy and water exchange model (EWBM-G) allows realistic description of surface air temperature and precipitation fields adjusted to a relief of elevation of the GrIS surface. In a series of diagnostic numerical experiments with the present-day GrIS geometry and the modeled climate we studied sensitivity of the modeled surface mass balance and run off to the key EWBM-G parameters and compared our results with similar model studies. In addition to the atmospheric, oceanic, and ice sheet blocks the ESM normally contains blocks accounting for dynamics of the biosphere, sea ice, hydrological cycle, etc. In practice, application of ESMs for research studies has become possible not long ago owing to the fast progress in computing facilities. Nevertheless, still now ESMs are rather computer time demanding. To provide long runs of a fully coupled ESM at a lower computational cost, we utilized an asynchronous coupling when a 100-yr run of the GrISM corresponds to 1-yr run of the INMCM. The weak point of the numerical experiments is comparison of the results with observations. The lack of observations in Greenland and significant inter-annual variability of air temperature, precipitation, surface melting, and run off do not allow formulation of a reliable reference «climate» and corresponding equilibrium state of GrIS. In practice it means that more or less accurate estimates of the past or future changes of the runoff and total GrIS mass discharge is reasonable to obtain in the form of deviations from a reference undisturbed model state.

Dinoflagellate cyst population evolution throughout past interglacials: Key features along the Iberian margin and insights from the new IODP Site U1385 (Exp 339)

IODP 339 Site U1385 (“Shackleton site”, e.g. Hodell et al., 2013a), from the SW Iberian margin, offers the opportunity to study marine microfossil population dynamics by comparing several past interglacials and to test natural shifts of species that occurred across these warm periods, in a subtropical context. Here, more specifically, we present results obtained for the dinoflagellate cyst (dinocyst) population integrated at a regional scale thanks to the addition of data from proximal sites from southern Iberian margin. When possible, observations made using the dinocyst bio-indicator are compared to additional proxies from the same records in order to test the synchronicity of the marine biota response. Pollen data available for some of the compiled marine sequences also offer the opportunity to directly compare marine biota with terrestrial ecosystem responses. This spatio-temporal compilation reveals that, over the last 800ka, surface waters around Iberia were tightly coupled to (rapid) climate changes and were characterised by coherent dinocyst assemblage patterns, highlighting a permanent connection between Atlantic and Mediterranean waters as evidenced through a continuous exchange of dinocyst populations. Some index species well illustrate the evolution of the regional hydrographic context along time, as for instance Spiniferites and Impagidinium species, together with Lingulodinium machaerophorum, Bitectatodinium tepikiense and heterotrophic brown cysts. They constitute key bio-indicators in context of natural environmental shifts at long and short timescales.

A GCM comparison of Pleistocene super-interglacial periods in relation to Lake El'gygytgyn, NE Arctic Russia

Abstract. Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate–vegetation–land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS l1c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial.

A 4.2 million years record of interglacial paleoclimate from sclerochronological data of Florida carbonate platform (Early Pliocene to recent)

The climate of the Pliocene and early Pleistocene was in a transient mode from generally warmer climates of the early Neogene to the maximum glaciations of the late Quaternary. Increasingly severe coolings occurred episodically in the high latitudes, whereas the low latitudes remained warm. For the last 5 million years (Ma), rather constant sea surface temperatures have been recorded in the Western Atlantic warm pool; however, direct climate data on temperature and humidity from shallow near-shore settings are lacking so far. In this study we present a synthesis of 26 new and 46 (incl. 24 recent) published sclerochronogical stable isotope records (18O/16O, 13C/12C) with a sub-annual resolution from reef corals (z-corals) and mollusks. The fossils were sampled from shallow-water carbonate deposits of the Florida carbonate platform and belong to 12 interglacial time-slices spanning collectively the period from the Early Pliocene to the recent (4.2 to 0Ma). Although platform carbonates are believed to undergo rapid diagenetic stabilization due to the dissolution of metastable aragonite shells, we show that there is still a wealth of material to be recovered for large-scale systematic geochemical studies. We rule out significant diagenetic modifications of the stable isotope data because measured 18O/16O ratios from z-corals and mollusks converted into temperature give consistent results. Accordingly, annual mean temperatures have risen during the last 4.2Ma from ~23°C to 26°C in open waters, given the modern seawater value of 18O/16O is valid for Neogene. However, the global water value has changed due to long-term increases in ice volume even during interglacials, equivalent with a 2.3°C temperature rise. A net 5.3°C temperature increase over the last 4.2Ma is inconsistent with the deep-sea record, however, and suggestive of an overall increase of humidity effects in measured 18O/16O instead. Particularly cool temperatures have been registered at 1.9 and 2.5Ma, but combined 18O/16O and 13C/12C data identify these as artifacts from intensified evaporation which fits the overall restricted marine aspect of the fossil fauna in these time-slices. Seasonal temperature contrasts seem to have been high within restricted settings (~11°C) and small in mixed open marine units (7–8°C). Although this finding fits the modern situation with coastal environments undergoing 14°C seasonal change and the reef tract 7–9°C only, circumstantial evidence suggests reconstructions to be biased by sub-annual changes in the local seawater value for 18O/16O. Since 18O/16O seasonality has increased over the last 4.2Ma, we suggest the humidity of modern Florida to have evolved from dryer precursor climates of past interglacials, whereas temperatures in essence remained the same. This trend possibly represents the expression of the growing relevance of the Bermudas High pressure cell. Glacial climates of Florida cannot be reconstructed using our methodology as the Florida platform was emergent during sea level lowstands.

Mollusc succession of a prehistoric settlement area during the Holocene: A case study of the České středohoří Mountains (Czech Republic)

Some Central European areas were attractive for the first agricultural settlements due to their suitable natural conditions. The Holocene development of such areas was thus under long-term human pressure, whose impact on the whole landscape is still poorly understood. One of such areas is the České středohoří Mountains. While pollen analyses can provide the general pattern of the landscape development, the analyses of mollusc succession provide landscape details, which are important primarily in landscapes with high habitat diversity. Based on the study of 11 mollusc successions situated at the České středohoří Mountains, we describe the postglacial development of the area and show the moderate fluctuation of woodland, wetland and open country habitats without any distinct succession peaks of particular habitat types during the whole Holocene. However, a detailed look of species exchange has provided additional information of succession pattern. The impoverishment of woodland communities is probably caused by human pressure, not natural processes, because fully developed woodland assemblages had occurred there during the past interglacials. It seems for now that humans had affected the whole landscape of the prehistoric settlement area, including hard-to-access sites, not only the nearby surroundings of their settlement.

The 4th PAGES past interglacials workshop

The 4th PAGES past interglacials workshop

Sea surface Temperature similarities during the Present and Past Interglacials

Sea surface Temperature similarities during the Present and Past Interglacials

Variations in the Polar-Directed Oceanic Heat During Past Interglacials: Causes and Consequences

Variations in the Polar-Directed Oceanic Heat During Past Interglacials: Causes and Consequences