Warm Intervals Research Articles

Abrupt fluctuations in North Pacific Intermediate Water modulated changes in deglacial atmospheric CO2

As a major reservoir of heat and CO2, the Pacific Ocean is an important component of the global climate system, but the nature of its circulation under different climatic conditions remains poorly understood. We present sedimentary records of surface water hydrography and nutrient dynamics from the subarctic Pacific Ocean, with the aim of investigating changes in sea-ice coverage, biological productivity, and sea surface temperature in the subarctic Northwest Pacific since 32 kyr. Our records indicate an enhanced North Pacific surface water stratification from the last glacial to Heinrich Stadial 1, which generally limited the siliceous productivity supply to the surface water. A productivity peak during the Bølling/Allerød warm interval was associated with an increase in the atmospheric pCO2, and it was driven by the increased supply of nutrient- and CO2-rich waters. This process can be attributed to the collapse of the North Pacific Intermediate Water formation at the onset of the Bølling/Allerød interstadial. Moreover, a northward shift of the westerly winds and the gyre boundary could have modulated the expansion of the subpolar gyre, driving changes in poleward heat transport, biogeochemistry, and the hydroclimate of the North Pacific. Our results are consistent with modern evidence for a northward shift of the westerlies in response to global warming, which will likely result in CO2 outgassing from the subarctic Pacific Ocean in the future.

Mid-latitude precipitation in East Asia influenced by a fluctuating greenhouse climate during the latest Cretaceous through the earliest Paleogene

Deep-time records from greenhouse climate periods (e.g., the Late Cretaceous) provide a reference point for understanding how high atmospheric CO 2 concentrations influence precipitation in the mid-latitude Northern Hemisphere (e.g., East Asia). In this study, we quantitatively reconstruct mean annual precipitation (MAP) in East Asia during the latest Cretaceous through the earliest Paleogene (~76–65.5 Ma), based on a well-studied paleosol sequence from the Sifangtai and Mingshui Formations from the SK-1n scientific borehole in the Songliao Basin, northeastern China. We use several proxies, including sedimentary-based observational proxies (e.g., depth to the calcic horizon, DTC) and elemental geochemistry proxies in the paleosol B horizon (e.g., the chemical index of alteration minus potassium, CIA-K; the calcium‑magnesium weathering index, CALMAG), which show the consistency with weathering proxies and previously published isotopic records. Changes in the MAP are associated with warming and cooling events. In the warciaming period (e.g., at ~69.5–68.5 Ma), an increase in the land-sea thermal contrast led to an expanded, enhanced, poleward-shifted thermal low-pressure system over the East Asian continent, which triggered an enhanced hydrological cycle and increasing MAP in the Songliao Basin. During the cooling period (e.g., at ~72.5–69.5 Ma and ~68.5–66.5 Ma), weakened East Asian monsoon and strengthened equatorward-shifted westerlies allowed for colder and arid air masses to encroach upon the Songliao Basin, which led to decreased MAP. Changes in MAP across the K-Pg boundary coincide with climate fluctuations and catastrophic geological events. Furthermore, our work compares three warming intervals in deep-time (middle Maastrichtian, late Maastrichtian and earliest Paleogene) with Shared Socio-economic Pathway scenarios used by the IPCC for the end of the 21st century, and indicates MAP increases in East Asia with ongoing anthropogenic CO 2 emissions. • The first high-resolution quantitative precipitation record in mid-latitude East Asia during ~76−65.5 Ma.. • Changes in the mean annual precipitation (MAP) associated with climate fluctuations and catastrophic geological events. • Geological records suggest MAP in East Asia will likely increase under ongoing anthropogenic CO 2 emissions.

Latitudinal Variance in the Drivers and Pacing of Warmth During Mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean

AbstractEarly Pleistocene Marine Isotope Stage (MIS)‐31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000‐year resolution, spanning 1.110–1.030 Ma, diatom‐based reconstruction of primary productivity, relative sea surface temperature changes, sea‐ice proximity/open ocean conditions and diatom species absolute abundances during MIS‐31, from the Scotia Sea (59°S) using deep‐sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time‐stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS‐31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere‐phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea‐ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub‐ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS‐31, a warmer than Holocene interglacial.

A terrestrial record of climate variation during MIS 11 through multiproxy palaeotemperature reconstructions from Hoxne, UK

AbstractA terrestrial (lacustrine and fluvial) palaeoclimate record from Hoxne (Suffolk, UK) shows two temperate phases separated by a cold episode, correlated with MIS 11 subdivisions corresponding to isotopic events 11.3 (Hoxnian interglacial period), 11.24 (Stratum C cold interval), and 11.23 (warm interval with evidence of human presence). A robust, reproducible multiproxy consensus approach validates and combines quantitative palaeotemperature reconstructions from three invertebrate groups (beetles, chironomids, and ostracods) and plant indicator taxa with qualitative implications of molluscs and small vertebrates. Compared with the present, interglacial mean monthly air temperatures were similar or up to 4.0°C higher in summer, but similar or as much as 3.0°C lower in winter; the Stratum C cold interval, following prolonged nondeposition or erosion of the lake bed, experienced summers 2.5°C cooler and winters between 5°C and 10°C cooler than at present. Possible reworking of fossils into Stratum C from underlying interglacial assemblages is taken into account. Oxygen and carbon isotopes from ostracod shells indicate evaporatively enriched lake water during Stratum C deposition. Comparative evaluation shows that proxy-based palaeoclimate reconstruction methods are best tested against each other and, if validated, can be used to generate more refined and robust results through multiproxy consensus.

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.

Eruptive tempo of Emeishan large igneous province, southwestern China and northern Vietnam: Relations to biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary

Abstract The Emeishan large igneous province (LIP), southwestern China and northern Vietnam, is thought to have been a potential driver for the biotic crises and paleoclimate changes around the Guadalupian-Lopingian boundary (GLB; Permian), but the lack of high-precision radiometric dates to constrain the duration and eruption rates of the volcanism has limited the assessment of their relationship. We present new chemical abrasion–isotope dilution–isotope ratio mass spectrometry U-Pb zircon geochronology of three samples from the lowermost and uppermost parts of the volcanic succession in the central portion of the Emeishan LIP. The results demonstrate that Emeishan volcanism began by 260.55 ± 0.07 Ma and persisted until at least 257.22 ± 0.37 Ma. Combined with a previously published age of 259.1 ± 0.5 Ma for silicic ignimbrites, we estimate that ~85% of Emeishan LIP volume erupted within 1.45 ± 0.50 m.y. Our new results confirm that the Emeishan volcanism began slightly prior to the initiation of the associated mass extinction event and was contemporaneous with the associated warming interval. The new data support the hypothesis that the Emeishan LIP likely triggered the biotic crises and paleoclimate changes around the GLB.

Evaluating the paleoenvironmental significance of sediment grain size in Bering Sea sediments during Marine Isotope Stage 11

Grain size is an important textural property of sediments and is widely used in paleoenvironmental studies as a means to infer changes in the sedimentary environment. However, grain size parameters are not always easy to interpret without a full understanding of the factors that influence grain size. Here, we measure grain size in sediment cores from the Bering slope and the Umnak Plateau, and review the effectiveness of different grain size parameters as proxies for sediment transport, current strength, and primary productivity, during a past warm interval (Marine Isotope Stage 11, 424-374 ka). In general, sediments in the Bering Sea are hemipelagic, making them ideal deposits for paleoenvironmental reconstructions, but there is strong evidence in the grain size distribution for contourite deposits between ~408-400 ka at the slope sites, suggesting a change in bottom current transport at this time.We show that the grain size of coarse (>150 micrometers) terrigenous sediment can be used effectively as a proxy for ice rafting, although it is not possible to distinguish between iceberg and sea ice rafting processes, based on grain size alone. We find that the mean grain size of bulk sediments can be used to infer changes in productivity on glacial-interglacial timescales, but the size and preservation of diatom valves also exert a control on mean grain size. Lastly, we show that the mean size of sortable silt (10-63 micrometers) is not a valid proxy for bottom current strength in the Bering Sea, because the input of ice-rafted silt confounds the sortable silt signal.

Environmental changes clarified by pollen and diatom proxy records in the sedimentary archive of the northwestern Japan Sea during last 21.0 kyr

High-temporal resolution pollen and diatom records from the northwestern Japan Sea document environmental changes over the last 21.0 kyr. Vegetation and climate changes were evaluated using the forest-steppe (SFI) and the pollen temperature (Tp) indices. The highest SFI occurred between ca. 21.0 ka and 16.6 ka and indicates the presence of a relatively dry climate and large areas of forest-steppe in the region. Boreal forests covered the mountain slopes. The broad-leaved trees survived in refugia located in lower mountain belts. Beginning ca. 16.6 ka, SFI decreases, while Tp increases, especially between ca. 11.0 ka and 5.7 ka. However, variations in these indices indicate fluctuating climates during the deglaciation. Significant vegetation changes occurred in the Holocene. Mixed deciduous forests with a predominance of Quercus became widely present beginning ca. 9.8 ka. The area of forest-steppe was reduced occurring only in local habitats. Pinus became one of the most common taxa in the forest ca. 5.3 ka. The geographic features of the coring area have determined in the past the persistence throughout the record of cold-water diatom flora. Cold-water diatoms have dominated in both cool and warm intervals; however, a small increase in the percentage and species diversity of warm-water diatoms was noted for warming. Low sea level during the Last Glacial Maximum (LGM) and early Holocene changed the general patterns in the sea circulation and in the vectors of the longshore currents, which transported the waters formed in the shallow areas of the northeastern and northern parts of the Japan Sea. A slight increase in sublittoral benthic diatoms indicates a lowered sea level during the LGM. The increase in sublittoral planktonic diatoms reflects a gradual rise in sea level during the Bølling–Allerød (BA) and Younger Dryas (YD). A greater component of oceanic diatom species at Holocene indicates the inflow of Pacific waters across both the Tsushima and Tsugaru straits. This study of pollen and diatom records demonstrates a clear response to climatic fluctuations and sea level changes in the Japan Sea during the Late Pleistocene and Holocene.

Glacier Recession in the Altai Mountains after the LIA Maximum

The study aims to reconstruct the Altai glaciers at the maximum of the LIA, to estimate the reduction of the Altai glaciers from the LIA maximum to the present, and to analyze glacier reduction rates on the example of the Tavan Bogd mountain range. Research was based on remote sensing and field data. The recent glaciation in the southern part of the Altai is estimated (1256 glaciers with the total area of 559.15 ± 31.13 km2), the area of the glaciers of the whole Altai mountains is estimated at 1096.55 km2. In the southern part of Altai, 2276 glaciers with a total area of 1348.43 ± 56.16 km2 were reconstructed, and the first estimate of the LIA glacial area for the entire Altai mountain system was given (2288.04 km2). Since the LIA, the glaciers decrease by 59% in the southern part of Altai and by 47.9% for the whole Altai. The average increase in ELA in the southern part of Altai was 106 m. The larger increase of ELA in the relatively humid areas was probably caused by a decrease in precipitation. Glaciers in the Tavan Bogd glacial center degraded with higher rates after 1968 relative to the interval between 1850–1968. One of the intervals of fast glacier shrinkage in 2000–2010 was caused by a dry and warm interval between 1989 and 2004. However, the fast decrease in glaciers in 2000–2010 was mainly caused by the shrinkage or disappearance of the smaller glaciers, and large valley glaciers started a fast retreat after 2010. The study results present the first evaluation of the glacier recession of the entire Altai after the LIA maximum.

Anthropogenic warming reduces the carbon accumulation of Tibetan Plateau peatlands

Peatland carbon accumulation generally increased during past intervals of natural warming. With recent anthropogenically-dominated warming being unprecedented over the past ∼2000 years, however, it is unclear how peatland carbon dynamics may operate compared to those under historical natural warmings. Here we examine the impacts of the recent warming from 1850 CE to present (Recent Warm Period; RWP) and the historical warming during 1000–1300 CE (Medieval Warm Period; MWP) on peatland carbon accumulation of the Tibetan Plateau using two continuous peat core records. We observed major seasonal difference between the two warming periods, with growing season (summer) warming dominating the MWP, while greater non-growing season warming characterizing the RWP. Consequently, we found a high net carbon balance during the MWP, suggesting that warming increased plant production more than decomposition of organic matter. In contrast, a low net carbon balance was observed during the RWP because non-growing season warming greatly enhanced soil carbon decomposition that could have completely offset plant carbon uptake. Therefore, recent anthropogenic warming might have induced a different ecosystem response with lower net carbon balance over the past millennium than that during historical natural warmings. As other regions of the globe have similar growing season versus non-growing season warming patterns, the risk of carbon loss from global peatlands may have been underestimated, implying that there is an even greater challenge for managing ecosystem carbon sinks under future climate change.

Regional precipitation variations during Heinrich events and Dansgaard-Oeschger cycles in the northern margin of the East Asian summer monsoon region

Due to the scarcity of long, high-resolution paleoclimate records, the effects of abrupt climatic events on regional climate variations in middle to high latitudes of East Asia are unclear. We present a detailed pollen record for the past 35,000 years, with an AMS 14C chronology, from Hulun Lake in northern China. The results reveal four episodes of regional vegetation change during the Last Glaciation, characterized by increases in cold-resistant and drought-tolerant plants and decreased regional vegetation cover. These episodes coincided with Heinrich events (H3, H2 and H1) and the Younger Dryas event (YD) that originated in the North Atlantic region. Additionally, during the warm intervals of the Dansgaard-Oeschger (D-O) cycles and the Bølling-Allerød (B/A) interstadial recorded in Greenland ice cores, patches of broadleaved deciduous forest expanded in the surrounding mountains while typical steppe vegetation expanded in the vicinity of Hulun Lake. Overall, the structure and amplitude of regional vegetation change in the Hulun Lake region during abrupt climatic events differ from the registration of these events in the oxygen isotope records from Greenland ice cores; however, they are similar to coeval stalagmite oxygen isotope records from East Asia. Thus, we suggest that the regional climate variations were characterized by increased or decreased precipitation during H events and D-O cycles in the Hulun Lake region, which was mainly controlled by changes in the intensity of the East Asian summer monsoon (EASM). Our results suggest that the variability of the EASM was physically linked to the North Atlantic climate system on centennial- to millennial-scale. In addition, the amplitude of regional precipitation variations during H events and D-O cycles was low during the interstadial of the Last Glaciation and the Last Glacial Maximum; however, the amplitude of regional precipitation variations during H1 event and B/A warming event was substantially greater during the Last Deglaciation. We suggest that differences in NHSI and land surface conditions (ice sheets and sea level) were responsible for the contrasting responses of EASM precipitation to these abrupt climatic events during different intervals.

Decadal Temperature Variations Over the Northwestern Tibetan Plateau Deduced From a 489‐Year Ice Core Stable Isotopic Record

AbstractInformation on decadal temperature variations over the northwestern Tibetan Plateau (TP) is still very limited due to a lack of long‐term instrumental data. In this paper, we present a 489‐year (1524–2012 A.D.) reconstruction of annual mean temperature for the northwestern TP using the δ18O record of a 58.82 meter‐long shallow ice core retrieved on the Chongce ice cap in the western Kunlun Mountains. The reconstructed temperature exhibits significant decadal variations, which were mainly driven by the Atlantic Multidecadal Variability. Decadal temperature variation during the Little Ice Age (LIA) is significantly larger than that during the post‐industrial warming period, possibly due to such external forcing as large fluctuations of solar activity and frequent major volcanic eruptions during the LIA. In addition, our reconstruction shows that the recent warming since the 1980s is moderate, comparable to an earlier warm interval in the mid‐20th century, which may partly explain the relatively stable status of glaciers in this region since 1970s.

Assessment of Phytogeographic Reference Regions for Cenozoic vegetation: a case study on the Miocene flora of Wiesa (Germany)

During the Miocene Climatic Optimum, a global long-term warm interval, European mid-latitude regions experienced a subtropical palaeoclimate. In particular, areas in eastern Germany were part of a vegetational zone with evergreen broadleaved forests, characterized by subtropical taxa. Regional palaeofloristic concepts denominated this palaeovegetation Younger Mastixioideae Flora sensu Mai (1964). Type assemblage is the late Early Miocene flora of Wiesa. Here, we reevaluate its floristic composition with respect to nearest living relatives of fossil-taxa, and introduce the new approach Phytogeographic Reference Region Assessment (PRRA) to ascertain the area of most similar extant vegetation for the Wiesa assemblage. The southern belt of SE Asian subtropical evergreen broadleaved forest and its transition to tropical mountain evergreen broadleaved forest in SW China represent the most similar extant vegetation. The Wiesa assemblage is compared to two diverse plant macroassemblages from the late Oligocene and the Late Miocene, respectively, coming from the same region and palaeoenvironmental setting. It is demonstrated that diversity and abundances of subtropical taxa markedly increased towards the Early Miocene, and specific climate-sensitive taxa occurred. The regional palaeoclimate was subtropical-humid (Köppen-Trewartha type Cf), with a growing season eleven months long. The late Oligocene and Late Miocene climates were mainly distinct in nine-month growing season lengths and cooler winters (1–3 °C).

Rapid Northwestward Extension of the East Asian Summer Monsoon Since the Last Deglaciation: Evidence From the Mollusk Record

The magnitude and rate of the expansion of the East Asian summer monsoon (EASM) rain belt under future climatic warming are unclear. Appropriate ecological proxy data may provide an improved understanding of the spatial extension of the EASM during past warming intervals. We reconstructed the spatiotemporal pattern of the extension of the EASM since the Last Glacial Maximum (LGM), using six well-dated mollusk fossil sequences from Chinese loess sections located on the modern northern edge of the EASM. The abundance of typical dominant mollusk species indicative of EASM intensity shows a delayed response, from ∼17 ka in the southeastern sections to ∼9 ka in the northwestern sections, during the last deglacial warming. Isoline plots based on a mollusk data synthesis show that the mollusk EASM indicators have a northeast–southwest zonal distribution for both the present-day, the cold LGM, and the warm mid-Holocene, which is consistent with the spatial pattern of modern precipitation. The resulting estimated expansion rate of EASM intensity accelerated during ∼12–9 ka (∼50 km/ka), which corresponds to the early Holocene interval of rapid climatic warming, a northwestward shift of ∼150 km compared to today. This implies that the northern fringe of the EASM in northern China will become wetter in the coming century, under moderate warming scenarios.

Palaeoenvironmental changes and their chronology during the latter half of MIS 5 on the south-eastern coast of the Gulf of Finland

This paper presents an overview of the results obtained by collaborative use of integrative multidisciplinary investigation of a highly unique geological section discovered in the south-eastern part of the Gulf of Finland. The main aim of this study is to identify the Late Pleistocene palaeoenvironmental and palaeoclimatic changes in the study area during one of the most controversial periods in the Late Pleistocene history, which is the MIS 5. Our approach to achieving the goal is based on the investigation of feldspar-based infrared optically stimulated luminescence (IR-OSL) dated records of pollen-induced palaeoclimate and palaeoenvironmental proxies. Palynological analysis and IR-OSL dates of 29 samples for the first time produced a detailed, characterised and dated sequence of palynological zones M6 to M8 ranging from ca. 94 ka to ca. 70 ka and made it possible to determine the chronological sequence of climate changes in this interval. Representative pollen spectra from 69 samples provided convincing evidence of a warm interval of interglacial rank at least during the latter half of MIS 5. The data obtained in the present study from well-preserved deposits of the second half of MIS 5 provided a novel insight into the palaenvironmental conditions during this period. These results seem to contradict the widely held view according to which the last interglacial stage with the climate conditions similar or warmer than today corresponds to only a small part of marine isotope stage (MIS) 5 of the deep-sea stratigraphy, i.e. MISs 5e lasting ca. 11 ka, and the period from 100 ka to 80 ka is attributed to an Early Weichselian glaciation, which in Northern Eurasia reached its maximum at about 90 ka. However, the findings obtained during the present study are also convincingly confirmed by those of our previous long-term investigations of warm climate-related shell-bearing deposits of various origins from Northern Eurasia including climatically highly sensitive Eurasian Arctic palaeo-shelf area. These results indicated that the overwhelming majority of the warm climate-related dates (ca. 82%) is also concentrated in the latter half of MIS 5 in the time range between 110 ka and 70 ka.

An Early Jurassic (Sinemurian–Toarcian) stratigraphic framework for the occurrence of Organic Matter Preservation Intervals (OMPIs)

Lower Jurassic sedimentary successions in the Atlantic margin basins include several organic-rich intervals, some with source rock potential; time-equivalent units are also identified in on- and offshore areas worldwide. Despite decades of research, it is still unclear which mechanisms lead to the deposition of organic-rich sediments during the Early Jurassic. The objectives of this study are to construct a detailed temporal and geographical framework of Sinemurian–Toarcian organic matter preservation intervals (OMPIs; subdivided into local, regional, and superregional) and roughly constrain the relationship of OMPIs with the Lower Jurassic δ 13 C record. This survey combines an in-depth analysis of literature on the distribution of organic-rich facies in the Sinemurian–Toarcian with new geochemical studies [total organic carbon (TOC) and organic matter pyrolysis] from selected outcrop sections from Portugal, Spain, and Morocco. Strong local control on OMPIs during most of the Sinemurian is suggested. Regionally widespread organic-rich facies are associated with the most negative δ 13 C values of the broad Sinemurian–Pliensbachian negative carbon isotopic trend recorded in organic matter (including the Sinemurian–Pliensbachian Boundary Event). Pliensbachian OMPIs are expressive in the areas bordering the proto-Atlantic Ocean and are often linked with positive δ 13 C excursions and short-lived warm intervals, but OMPIs are also defined for the Late Pliensbachian cool interval. Early Toarcian superregional OMPIs are associated with some of the most pronounced δ 13 C excursions of the Mesozoic. Toarcian maximum TOC content occurs with the positive δ 13 C (recovery) trend following the δ 13 C negative shift typically linked with the Early Toarcian Oceanic Anoxic Event (T-OAE), supporting the notion that peak carbon sequestration/ocean anoxia post-dated the main phase of carbon input into the atmosphere, as also suggested by recent modelling efforts. However, additional superregional OMPIs predate and postdate the T-OAE, indicating that conditions favouring preservation of organic matter (increased productivity and/or enhanced preservation) during the Early Toarcian were not restricted to the T-OAE interval. The compilation of Sinemurian–Toarcian OMPIs presented in this paper demonstrates that organic-rich intervals of regional and superregional expression in the Lower Jurassic sedimentary record are ubiquitous and may even be more numerous than in the Cretaceous. Considering the association of some of the Sinemurian, Pliensbachian, and Toarcian (not taking into account the T-OAE related OMPIs) regional and superregional OMPIs with well-defined carbon isotopic excursions, it is here suggested that these hold the same relevance as the secondary OAEs of the Cretaceous, such as the Valanginian OAE (Weissert Event), Hauterivian OAE (Faraoni Event), and Late Aptian–Early Albian OAE (OAE 1b cluster).

Warming‐Induced Northwestward Migration of the Asian Summer Monsoon in the Geological Past: Evidence From Climate Simulations and Geological Reconstructions

AbstractThe cold and warm intervals during the Plio‐Pleistocene provide an opportunity to assess the response of the Asian summer monsoon (ASM) to different levels of global warming. In this study, the northern edge of the ASM, a sensitive indicator of the advance and retreat of the ASM rain belt, was analyzed using climate outputs from PMIP3 and PlioMIP1, for the Last Glacial Maximum (LGM, ∼21,000 yr BP), the preindustrial, the mid‐Holocene (∼6,000 yr BP), and the mid‐Pliocene (∼3.3–3.0 Ma), among which the global temperature increased sequentially. The results show that the northern edge of the ASM migrated northwestward by ∼200 km, ∼50 km, and ∼50 km with global warming from the LGM to preindustrial, from the preindustrial to mid‐Holocene, and from the mid‐Holocene to mid‐Pliocene, respectively. These results are generally consistent with geological records. The simulations show that the western Pacific subtropical high (WPSH) intensified and expanded geographically, and the intertropical convergence zone (ITCZ) migrated northward over the Indian Ocean and was shifted southward over the western Pacific. This led to a northwestward shift of the Asian monsoonal rain belt, and consequently to wetter conditions in India and northern China. During the mid‐Pliocene, pronounced warming substantially intensified the WPSH, leading to the suppression of moisture transport from the Indian Ocean to southern China and the Indo‐China Peninsula. Our results suggest that if the planet returns to a Pliocene warm world, precipitation will increase in northern China, while southern China and the Indo‐China Peninsula will experience more frequent droughts.

Palaeoenvironmental changes in the Iberian central system during the Late-glacial and Holocene as inferred from geochemical data: A case study of the Navamuño depression in western Spain

The Iberian Central System (ICS) is a clue region to reveal Mediterranean/Atlantic inferences over Iberia. We present a multidisciplinary study from western Spain conducted in the Navamuño depression (ND), covering the last 16.8 ka (cal BP). A reconstruction of the palaeotemperature from the resulting geochemical data highlights four cold and dry intervals, namely, the Oldest Dryas, Older Dryas, Intra-Allerød Cold Period (IACP), and the Younger Dryas, along with warmer intervals: the Bølling (14.7–14 ka) and the Allerød (12.9–12.6 ka); however, the Greenland Interstadial GI-1c (13.4–13.1 ka) is barely distinguishable in the ND. Despite the shortage of biomass to sustain fire, the earliest charcoals are from ~14.4–13.8 ka. Evidence of ash/dust events overprinting the geochemical background starts at ~13.8–12.8 ka. Significant fire activity in the Early Holocene at ~11.7–10.6 ka affected the ND, matching the westernmost ICS data. This period includes short oceanic spells inferred from Cl peaks at ~10.9–10.2 ka and three cold intervals at 11.4, 9.3, and 8.2 ka disrupted the progressive temperature increase. The Mid-Holocene showed a continuously increasing trend towards an arid climate, peaking at 4.2 ka under a pervasive dust influx from North Africa, which has prevailed since almost ~7.9 ka. A prominent volcanic event at ~6.8–5.8 ka is in Navamuño and Roñanzas (Asturias, N Spain; Gallego et al., 2013) identified from heavy metal-rich layer, synchronous with the last known eruption of the Calatrava volcanic field (South-Central Spain; Poblete-Piedrabuena et al., 2019). This volcanic eruption could affect many other regions half north of Iberia. The pervasive presence of oceanic aerosols in the last three millennia (2.8 ka ~ ) allowed the formation of a Cl-rich peat layer during the Ibero-Roman humid period ~2.1 ka, before a changing around ~0.4 ka toward colder and drier conditions at the Little Ice Age (LIA) period.

Calcareous dinoflagellate cyst distribution across the K/Pg boundary at DSDP site 577, Shatsky Rise, western North Pacific Ocean

An analysis of calcareous dinoflagellate cysts has been carried out on sixteen samples from across the K/Pg boundary interval from Deep Sea Drilling Project Site 577 situated on Shatsky Rise in the western North Pacific. This is the first time that a detailed study of this microfossil group has been undertaken from deep sea sediments of Late Cretaceous–early Paleocene age in the North Pacific realm. Eight species of calcareous dinoflagellate cysts were found to comprise low diversity assemblages of which half are representative of extant taxa. The most pronounced bioevent is that of Cervisiella operculata reaching its highest proportions at the K/Pg boundary transition underscoring the utility and cosmopolitan distribution of the species with its acme as a marker for the earliest Danian. We also identify an indirect sea surface paleotemperature signal as represented by variance in wall thickness in two distinct morphotypes of Thoracosphaera heimii (morphotypes A and B). The cyst concentrations and relative abundances of these taxa are interpreted to reflect the late Maastrichtian warming event and subsequent late Maastrichtian cooling phase prior to the interval of gradual warming in the early Danian marked by the opportunistic capitalization of Cervisiella operculata during a time of ocean recovery following the terminal Cretaceous.

Searching for Function: Reconstructing Adaptive Niche Changes Using Geochemical and Morphological Data in Planktonic Foraminifera

Dead species remain dead. The diversity record of life is littered with examples of declines and radiations, yet no species has ever re-evolved following its true extinction. In contrast, functional traits can transcend diversity declines, often develop iteratively and are taxon-free allowing application across taxa, environments and time. Planktonic foraminifera have an unrivaled, near continuous fossil record for the past 200 million years making them a perfect test organism to understand trait changes through time, but the functional role of morphology in determining habitat occupation has been questioned. Here, we use single specimen stable isotopes to reconstruct the water depth habitat of individual planktonic foraminifera in the genus Subbotina alongside morphological measurements of the tests to understand trait changes through the Middle Eocene Climatic Optimum [MECO: ∼40 Myr ago (mega annum, Ma)]. The MECO is a geologically transient global warming interval that marks the beginning of widespread biotic reorganizations in marine organisms spanning a size spectrum from diatoms to whales. In contrast to other planktonic foraminiferal genera, the subbotinids flourished through this interval despite multiple climatic perturbations superimposed on a changing background climate. Through coupled trait and geochemical analysis, we show that Subbotina survival through this climatically dynamic interval was aided by trait plasticity and a wider ecological niche than previously thought for a subthermocline dwelling genus supporting a generalist life strategy. We also show how individually resolved oxygen isotopes can track shifts in depth occupancy through climatic upheaval. During and following the MECO, temperature changes were substantial in the thermocline and subthermocline in comparison to the muted responses of the surface ocean. In our post-MECO samples, we observe restoration of planktonic foraminifera depth stratification. Despite these changing temperatures and occupied depths, we do not detect a contemporaneous morphological response implying that readily available traits such as test size and shape do not have a clear functional role in this generalist genus. Modern imaging measurement technologies offer a promising route to gather more informative morphological traits for functional analysis, rather than the traditional candidates that are most easily measured.