Warm Stages Research Articles

Paleontological records indicate the occurrence of open woodlands in a dry inland climate at the present-day Arctic coast in western Beringia during the Last Interglacial

Permafrost records, accessible at outcrops along the coast of Oyogos Yar at the Dmitry Laptev Strait, NE-Siberia, provide unique insights into the environmental history of Western Beringia during the Last Interglacial. The remains of terrestrial and freshwater organisms, including plants, coleopterans, chironomids, cladocerans, ostracods and molluscs, have been preserved in the frozen deposits of a shallow paleo-lake and indicate a boreal climate at the present-day arctic mainland coast during the Last Interglacial. Terrestrial beetle and plant remains suggest the former existence of open forest-tundra with larch ( Larix dahurica), tree alder ( Alnus incana), birch and alder shrubs ( Duschekia fruticosa, Betula fruticosa, Betula divaricata, Betula nana), interspersed with patches of steppe and meadows. Consequently, the tree line was shifted to at least 270 km north of its current position. Aquatic organisms, such as chironomids, cladocerans, ostracods, molluscs and hydrophytes, indicate the formation of a shallow lake as the result of thermokarst processes. Steppe plants and beetles suggest low net precipitation. Littoral pioneer plants and chironomids indicate intense lake level fluctuations due to high evaporation. Many of the organisms are thermophilous, indicating a mean air temperature of the warmest month that was greater than 13 °C, which is above the minimum requirements for tree growth. These temperatures are in contrast to the modern values of less than 4 °C in the study area. The terrestrial and freshwater organism remains were found at a coastal exposure that was only 3.5 m above sea level and in a position where they should have been under sea during the Last Interglacial when the global sea level was 6–10 m higher than the current levels. The results suggest that during the last warm stage, the site was inland, and its modern coastal situation is the result of tectonic subsidence.

Climate Change in Eurasia: Perspectives over Space and Time

A prominent physical geographer offers a brief primer on climate change in general and then brings spatial and temporal perspectives to bear in an assessment of the past, present, and future changes of climate over Eurasia. More specifically, he addresses climate change and feedbacks for Eurasia over longer (tectonic forcing, >105 years), intermediate (Earth's orbital relations, 104-105 years), and shorter timeframes (<104 years), emphasizing that climates change more or less continuously in response to many forcing factors (solar output, Earth's eccentric orbit, rotational tilt, precession, and interactive atmosphere-ocean-land systems, including human impacts). Although these factors operate at different rates and timescales, they may coincide at times to promote rapid change. The nesting of the current, three-decade pattern of warming within longer centennial- and millennial-scale cycles of warming and cooling since the Holocene Optimum (itself a warm interglacial stage within warm and cold cycles in the late Cenozoic over the last 50 million years) shows that the recent rapid warming since 1980 is not unique in Earth history, although it does warrant concern and raises questions of global significance.

Geochemical characteristics of sediments from Lake El’gygytgyn, Chukotka Peninsula, as indicators of climatic variations for the past 350 ka

This paper presents data on the inorganic geochemical characteristics of the sediments from Hole LZ1024 (Lake El’gygytgyn, Chukotka, 67°30′ N 172°08′ E). It is demonstrated how these data are associated with climatic variations during isotope stages 1–9. The sediments of the warm stages are characterized by elevated contents of SiO2, CaO, Na2O, K2O, and Sr and low concentrations of TiO2, Al2O3, MgO, and Fe2O3. It has been established that the geochemical parameters correlate with global climatic variations.

Neotectonics of the Deryugin Basin area (Sea of Okhotsk)

The data of the bottom “summit” surface were used for compiling the schematic structural-neotectonic map and map of the main neotectonic structural elements. Their comparison with the schematic paleogeographic maps of the lithophysical complexes for four periods (K2-\( _{1 - 2} \), \( \rlap{--} P_3 \)-N11, N11–2, and N13-N2) reveals that the largest part of the considered area was characterized by either a continental or relatively shallow-sea environment, except for the western areas occupied at that time by the relatively deep trough with its axis located substantially westward of the neotectonic Deryugin Basin and the Staritskii Trough. In the Late Pliocene, the deep paleotrough (\( \rlap{--} P_3 \)-N22) and Deryugin Basin were likely occupied by shelf settings with continuing sedimentation. The paleogeographic environments of the area for the period from the terminal Pliocene to the late Riss (Taz) Glaciation (Q26; MIS6) are unknown so far. The most complete Quaternary section recovered by Core LV 28-34-2 consists of six units; the odd (1, 3, and 5) and even (2, 4, and 6) among them correspond to the warm and cold marine isotopic stages, respectively. Judging from the benthic foraminiferal assemblages, the water depths during cold periods were shallower as compared with the warm stages, which is explained by the respective ascending and descending bottom movements and, partially, by the eustatic sea level fluctuations. In the Late Pleistocene-Holocene (∼17 ka), the bottom of the Deryugin Basin and the summit part of the Institut Okeanologii Rise subsided with average rates of 8 and 3 cm/year, respectively.

Response of the paleomagnetic record to environmental changes in the late Pleistocene

During revisiting the Upper Pleistocene Pekla loess-soil section located on the Sea of Azov coast of the Taman Peninsula, its lower 6 m were continuously sampled, which led to an increase in the age range from ∼50 to 400 ka. The detailed rock magnetic study of the structure, grain-size, and concentrations of magnetic mineral (natural remanent magnetization (NRM) carrier) in the collected rock samples revealed regular changes in rock magnetic characteristics along the section and their correlation with climatic fluctuations. Magnetite and hematite both deposited during the transport of sedimentary material and formed during pedogenesis, which involved the entire section to a varying extent, represent the main magnetic minerals in the examined rocks. Automorphic paleosoils that were formed during warm and humid periods corresponding to odd stages of the MIS scale are characterized by elevated concentrations of magnetic mineral (NRM, magnetic susceptibility (K lf), saturation isothermal remanent magnetization (SIRM), and anhysteresis (ideal) remanent magnetization (ARM)) parameters and share of superparamagnetic particles (up to 80%, according to elevated values of the frequency-dependent magnetic susceptibility K td) as well as by lowered rigidity parameter (B cr) and grain size (ARM/K parameter). Such changes in the paleosoils may be explained by the occurrence of newly formed fine-grained magnetite particles close in size to its superparamagnetic and single-domain varieties due to the activation of bio/geochemical processes during warm stages. The growth of the above-mentioned rock magnetic parameters in automorphic soils may be considered as serving a quantitative criterion for defining the boundary between warm and cold periods even in poorly developed soils.

Uranium-series dating of fen peat horizons from pit Nachtigall in northern Germany

Peat and other terrestrial sediments are important archives of climate forcing. This study discusses the numerical age determination of stratigraphically important Quaternary sequences from clay pit Nachtigall near Holzminden in northern Germany, which have been the subject of debate concerning their chronological classification since they were first described by Grupe in 1929. Uranium-series dating ( 230Th/U) of different organic horizons as well as sedimentology, including loss-on-ignition (LOI) and palynology was carried out to set up a more reliable chronological framework for the Weser river area. 230Th/U ages were calculated using an isochron approach with the leachate/leachate method for chemical preparation. Open system requirements and specification of sample selection criteria for organic samples are investigated by determination of uranium and thorium composition of the rim layers. Different organic sediments are investigated. The organic deposits from Nachtigall show Middle Pleistocene 230Th/U ages ranging from 227 +9 −8 ka to 201 +15 −13 ka and appear to represent a warm temperate phase preceding the Eemian Interglacial (MIS 5e) and the Drenthe Stadial (MIS 6), indicating a correlation with marine isotope substage MIS 7c. These results are in good agreement with the investigation of the pollen spectra indicating a correlation with a warm stage within the Lower Saalian Complex.

Sea surface temperature and subtropical front movement in the South Tasman Sea during the last 800 ka

Hemisphere mid-latitude westerlies contribute to the ventilation of the deep Southern Ocean (SO), and drive changes in atmospheric carbon dioxide (CO2) and the global climate. As the westerlies control directly oceanic fronts, the movement of the subtropical front (STF) reflects the westerlies migration. Thus it is important to understand the relationships between STF movement and the weaterlies, ventilation of the deep SO, ice volume and atmospheric CO2. To this end, we use two new high-resolution records from early Marine Isotope Stage (MIS) 20 (∼800 ka) of sea surface temperature (SST) based on U37k’ paleo-thermometer and benthic oxygen isotope (δ18OB) at Ocean Drilling Program (ODP) Site 1170B in the southern Tasman Sea (STS), to construct linkages between the marine records and atmospheric proxies from Antarctic ice-cores. During the last 800 ka, the average SST (10.2°C) at Site 1170B is 1.8°C lower than today (annual average 12°C). The highest average SST of 11.6°C occurred during MIS 1, and the lowest average SST of 7.8°C occurred during MIS 2. The warmest and coldest records of 14.7°C and 6.2°C occurred in the MIS 5 and MIS 2, respectively. In the glacial-interglacial cycles of the last 800 ka, variability of reconstructed SST shows that the STF moved northward or southward more than 3° of latitude compared with its present location. In the warmest stage MIS 5, the STF shifted to its southernmost location of ∼49°S. In contrast, in the coldest stage MIS 2, the STF moved to its northernmost location of ∼43°S. In response to orbital cycles, the westerlies movement led ice volume and atmospheric CO2 changes, but it was in phase with change in Antarctic atmospheric temperature. Ice volume only preceded atmospheric CO2 only a little at the 23-ka precession band, lagged the atmospheric CO2 at the 100-ka eccentricity band, and was in phase with atmospheric CO2 at the 40-ka obliquity band.

Middle and late Pleistocene glaciations in the Campo Felice Basin (central Apennines, Italy)

The present paper refers to research conducted in the tectonic-karst depression of Campo Felice in the central Apennines (Italy), in which glacial, alluvial and lacustrine sediments have been preserved. Stratigraphic interpretations of sediments underlying the Campo Felice Plain are based on evidence obtained from nine continuous-core boreholes. The boreholes reach a depth of 120 m and provide evidence of five sedimentation cycles separated by erosion surfaces. Each cycle is interpreted as an initial response to a mainly warm stage, characterized by low-energy alluvial and colluvial deposition, pedogenesis, and limited episodes of marsh formation. In turn, a mainly cold stage follows during which a lake formed, and glaciers developed and expanded, leading to deposition of glacial and fluvioglacial deposits. The chronological framework is established by eleven accelerator mass spectrometer 14C ages and three 39Ar– 40Ar ages on leucites from interbedded tephra layers. These age determinations indicate five glacial advances that respectively occurred during marine oxygen isotope stages 2, 3–4, 6, 10 and 14.

Variations of the Antarctic Circumpolar Current intensity during the past 500 ka

We examine the past variations of the Antarctic Circumpolar Current (ACC) by using variations in size and abundance of the magnetic grains deposited by this current at a site east the Kerguelen‐Crozet plateau. Core MD00‐2375G was taken at a midlatitude site during the ANTAUS cruise conducted in 2000 by the French R/V Marion Dufresne. Marine isotope stages (MIS) down to MIS 13 are identified, and an age model is derived from a correlation to the ice core isotopic record obtained from EPICA in Antarctica. Continuous records of abundance and size of the magnetic grains were obtained using environmental magnetism methods. Results show a strong modulation of the ACC flow intensity in response to glacial and interglacial cycles. The low abundance and the small size of magnetic grains indicate that the ACC was weak during warm stages and strong during glacial epochs. A large modulation is also observed at the sub‐stage scale during the interglacials. A minimum in concentration and grain size occurs at the onset of MIS 11. At the MIS 6–5, 10–9, and possibly 12–11 transitions, observed variations suggest a mechanism involving both rapid and progressive variations of the ACC flow at deglaciations.

Some Factors Influencing the Germination of the Common Hornbeam (Carpinus betulus L.) Seeds

Common hornbeam ( Carpinus betulus L.) seeds, in order to be successfully used for forestry and horticulture, need to go through class ical warm-cold stratification in a wet peat-sand substrate to break their dormancy. Hundred seeds s amples of the species were put into stratification using 5 different methods: 1/ check - classical met hod with warm: 4 weeks at 20-22 o C and cold: 16 weeks at 3-5 o C, treatment in a substrate of peat and sand, 2/ a treatment without the substrate but soaking the seeds in water (20-22 o C) for 1 hour every week (warm stage) or every 2 weeks (cold stage), 3/ a treatment without the substrate but mo istening the seeds for 10 seconds into water (20- 22 o C) every week (warm stage) or every 2 weeks (cold stage), 4/ a treatment without the substrate but preliminary soaking the seeds in the 0.1% GA 3 solution for 24 hours at 20-22 o C and then following the moistening procedure described before, 5/ a treatme nt without the substrate done the same way as before but using 0.5% GA 3 solution. In all the treatments, every week in the warm and cold stage of the stratification, the seeds were put on a routine germination test to evaluate their germination capacity. The conducted experiments proved that the common hornbeam seeds could successfully germinate when in the classical warm-cold stratific ation method the peat-sand substrate was replaced by cyclic water soaking or moistening of the seeds. The freshly harvested seeds had germination inhibitors, but their washing away with water neith er shorten their stratification time nor improved t he seeds germination. The used soaking in the 0.5% GA 3 solution did shorten the stratification time of th e seeds. The final germination capacity depended also on the health status of the seeds.

Molecular evidence for glacial expansion and interglacial retreat during Quaternary climatic changes in a montane temperate pine (Pinus kwangtungensis Chun ex Tsiang) in southern China

It has been suggested that the eastern Asian temperate flora have responded to Quaternary climatic changes in a different way compared with temperate plants in Europe and Northern America. However, knowledge about their phylogeographic structure and evolutionary history is still limited. In this study we investigated mitochondrial DNA variation in 17 populations of Pinus kwangtungensis, a five-needled pine inhabiting in isolated mountains of southern China and northern Vietnam. A total of ten mitochondrial haplotypes (mitotypes) were characterized by the polymorphisms of two fragments (cox-1-2 and nad7 intron1), and total genetic diversity was high (h T = 0.847). The construction of phylogenetic relationships of the ten mitotypes detected three major, well-distinct clades, largely corresponding to four population groups identified by SAMOVA analysis. SAMOVA also indicated that most genetic variance should be attributed to among-group differentiation (F CT = 0.868), consistent with the substantial genetic structure found within P. kwangtungensis (G ST = 0.751). The genetic distances of P. kwangtungensis weakly but significantly correlated with geographical distances (R = 0.228, P = 0.03), revealing a pattern of isolation-by-distance. Demographic analysis did not detect any bottleneck events in the recent history of P. kwangtungensis. These results clearly suggested that there were three major refugia for this montane temperate conifer during warm stages (along with other minor refugia), and that the species would have tracked Quaternary climatic changes by expanding to nearby lowlands in the glacial periods, and by retreating to mountaintops (the refugia) during interglacial warmer stages, experiencing fragmentation and isolation among refugia.

A continuous high‐resolution dust record for the reconstruction of wind systems in central Europe (Eifel, Western Germany) over the past 133 ka

The last glacial cycle in Central Europe is dominated by processes of aeolian dust transport and accumulation. These dust deposits are preserved in soils and lake sediments and provide detailed information about the climate variability during cold and dry periods. Especially the transitions from warm into cold periods are characterized by turbulent climate conditions. The main problems of terrestrial paleoclimate reconstructions are the completeness of the core material and a sampling resolution. To detect single dust storms we use a particle detection method, which allows high resolution, sub‐annual analyses of sediment structures in undisturbed samples. The ELSA (Eifel Laminated Sediment Archive) stack is a compilation of four different lake sediment cores of the Eifel region (Western Germany) and comprise the period of the last 133 ka. The results of our analyses show high frequencies of dust storm events during the first cold events C24 and C23 after the last warm stage. In opposition, the coldest periods of the last glacial cycle OIS‐4 (70–60 ka BP) and OIS‐2 (35–14 ka BP) are characterized by stable climate conditions that provide the accumulation of homogenous dust sediments.

Pleistocene climate change, natural environments and Palaeolithic occupation of East Kazakhstan

The territory of East Kazakhstan (the Southern Altai Mountains, the Bukhtarma and Zaisan/Black Irtysh Basins), still insufficiently investigated because of its proximity to the Kazakh–Russian–Chinese border zone, shows a complex Quaternary history and the associated environmental transformations reflected by intensive geomorphic processes related to the past global climate evolution in conjunction with the regional neotectonic activity. The marked climatic changes are indicated by the preserved palaeolandscape forms in both the mountain and steppe regions, as well as by the glacial and sedimentary geology, palaeoecology and geoarchaeology proxy records indicating long-term variations in temperature as well as humidity. Following the generally warmer Early Pleistocene climates, witnessed by the distribution of deeply weathered red palaeosols, the increased continentality and relief gradient during the Middle and particularly the Late Pleistocene led to establishment of the present-type forest-steppe/semi-desert during warm stages, and the periglacial arid steppe during cold stages correlated with the glaciations in the southern Altai Mountains, and loess deposition in the foothills. The mapped glacigenic and high-resolution loess-palaeosol sections, and contextual environmental archaeology data from the Pleistocene occupation sites provide new evidence of a rather pronounced natural dynamics. Spectacular glaciofluvial terraces in the principal mountain valleys indicate the presence of deep ice-dammed last glacial lakes documented from other parts of the Altai that were subjected to cataclysmic drainages during deglaciations. The recently discovered localities in the Bukhtarma River valley in diverse settings bear witness of a much earlier (Middle–Upper Palaeolithic) inhabitation of this geographically marginal area and adaptation to local mountain and steppe environments predating the Holocene prehistoric cultures. This paper summarizes some results of the initial multidisciplinary Quaternary field studies in the southern Altai region of East Kazakhstan and the adjacent part of Gorno Altai (2003-2007).

Chronostratigraphy of loess deposits in northeast Iran

Little information is available on the paleoclimate evolution of northeast Iran relating to global cold and warm stages. The loess/paleosol sequences from southern Mashhad and Kalat-e Naderi areas were studied to determine the landscape evolution and to set up the first chronological framework for the Pleistocene deposits in northeast Iran. The loess deposits in these areas are less thick (up to 12 m) and have a more patchy distribution than in the Caspian Lowland of northern Iran. Infrared stimulated luminescence (IRSL) dating of loess or loess derivatives from the Robat-e Khakestari, Tappeh Salam and Deh Gheybi sections (a) and (b) from southern Mashhad, as well as Kalat-e Naderi sections (a) and (b) in Kalat-e Naderi area provides a more reliable chronological framework for climate and environmental changes taken place over for the time period including the penultimate and last interglacial/glacial cycles. The Robat-e Khakestari section, the Kalat-e Naderi sections (a) and (b), and to some extent the Tappeh Salam section include loess/paleosol sequences, which are chronologically in excellent agreement with the loess record of the Caspian Lowland in northern Iran. The Deh Gheybi sections (a) and (b) include loess-like sediments and fluvial deposits that make their interpretation difficult. Loess accumulated during MIS 2 at the Robat-e Khakestari section and at the Kalat-e Naderi sections (a) and (b) suggesting a more windy and arid Last Glacial Maximum (LGM) in northeast Iran. Paleosols, correlating most likely with MIS 5, were covered by fluvial sediments at the Kalat-e Naderi section (a). The absence of loess deposits correlating to MIS 3 and MIS 4 at the Robat-e Khakestari section is very likely to have been caused by fluvial processes and water erosion.

Palaeoenvironmental changes from pollen record in deep sea core PC-1 from northern Okinawa Trough, East China Sea during the past 24 ka

A pollen record of core PC-1 from the northern Okinawa Trough, East China Sea (ECS), provides information on vegetation and climate changes since 24 cal. kaBP. A total of 103 samples were palynologically analyzed at 8 cm intervals with a time resolution of 230 a. Four pollen zones are recognized: zone I (812-715 cm, 24.2-21.1 cal. kaBP), zone II (715-451 cm, 21.1-15.2 cal. kaBP), zone III (451-251 cm, 15.2-10.8 cal. kaBP), zone IV (251-0 cm, 10.8-0.3 cal. kaBP), corresponding to Late MIS 3, Last Glacial Maximum (LGM), deglaciation and Holocene, respectively. The LGM is characterized by the dominance of herbs, mainly Artemisia, and high pollen influx, implying an open vegetation on the exposed continental shelf and a cool and dry climate. The deglaciation is a climate warming stage with Pinus percentage increased and Artemisia percentage decreased and a rapid sea-level rise. The Holocene is characterized by predominance of tree pollen with rapid increase in Castanea-Castanopsis indicating the development of mixed evergreen and deciduous broad-leaved forest and a warm, humid climate. Low pollen influx during the Holocene probably implies submergence of the continental shelf and retreat of the pollen source area. The vegetation indicated by pollen assemblage found in this upper zone is consistent with the present vegetation found in Kyushu, Japan. Originating from the humid mountain area of North Luzon of the Philippines, Tasmania and New Zealand, Phyllocladus with sporadic occurrence throughout PC-1 core probably suggests the influence of Palaeo-Kuroshio Current or intense summer monsoon. The observed changes in Pinus and Herbs percentage indicate fluctuations of the sea level, and high Pinus percentage corresponds to high sea level. Spectrum analysis of the pollen percentage record reveals many millennial-scale periodicities, such as periodicities of 6.8, 3.85 2.2, 1.6 ka.

Sea surface temperature record from the north of the East China Sea since late Holocene

Using the alkenone paleotemperature index U37k, a high-resolution sea surface temperature (SST) record since 3600 a BP was reconstructed from the mud area in the north of the East China Sea. Combining with the grain size distribution curve of sensitive grain size group, which may reflect the East Asia Winter Monsoon activity, the palaeoenvironmental evolution cycle throughout the late Holocene in the area was obtained. The marine environment evolution during the last 3600 years displays a five-stage trend. (1) Temperature descending period from 0.85 cal. ka BP to present. The maximum temperature decrease amplitude is 2°C. The winter monsoon intensified and ‘Little Ice Age’ were recorded in this period. (2) Warming period from 1.90 to 0.85 cal. ka BP. The mean temperature increase amplitude is 0.8°C. The Sui-Tang warming period was recorded at about 0.85–1.35 cal. ka BP and a prominent cooling event was recorded at 1.4 cal. ka BP in this period. (3) Temperature descending period from 2.55 to 1.90 cal. ka BP. Temperature cooling amplitude is 0.9°C. This period is coincident with an integrated temperature circle recorded in the Antarctic ice core, with the temperature changes from a slow cooling stage to a rapid warming stage. (4) Temperature comparatively stable with a little ascending period from 3.2 to 2.55 cal. ka BP. Temperature warming amplitude is 0.3°C. This period is coincident with the temperature fluctuant ascending period recorded in Antarctic ice core. (5) Temperature comparatively stable with little descending period from 3.6 to 3.2 cal. ka BP. This period corresponds with the temperature fluctuant cooling period recorded in Antarctic ice core. Basically, those five periods were coincident with the Antarctic ice core record. During the global cooling stage, the SST change in the continental shelf sea can be adjusted simultaneously.

Understanding the ocean temperature change in global warming: the tropical Pacific

The response mechanisms of the tropical Pacific Ocean temperature to increased atmospheric CO 2 are investigated in a coupled climate model. Ensemble simulations are performed under both the transient and stable CO 2 forcing. It is found that the dominant mechanism for temperature change differs in different stages of global warming. During the transient stage, the surface heat flux is a major driving factor for the tropical surface warming. During the equilibrium stage, the dominant mechanism to maintain the surface warming is the meridional advection. The heat flux forcing becomes a damping factor instead, particularly for the western tropical Pacific. Different from the surface warming, the subsurface warming results from the oceanic mixings during the entire period of global warming, whereas the advection terms generally play a cooling role, consistent with the slowdown of the shallow meridional overturning circulation. This paper emphasizes the deterministic role of the dynamic adjustment of the ocean circulation in the long-term change of ocean climate.

Understanding the ocean temperature change in global warming: the tropical Pacific

The response mechanisms of the tropical Pacific Ocean temperature to increased atmospheric CO2 are investigated in a coupled climate model. Ensemble simulations are performed under both the transient and stable CO2 forcing. It is found that the dominant mechanism for temperature change differs in different stages of global warming. During the transient stage, the surface heat flux is a major driving factor for the tropical surface warming. During the equilibrium stage, the dominant mechanism to maintain the surface warming is the meridional advection. The heat flux forcing becomes a damping factor instead, particularly for the western tropical Pacific. Different from the surface warming, the subsurface warming results from the oceanic mixings during the entire period of global warming, whereas the advection terms generally play a cooling role, consistent with the slowdown of the shallow meridional overturning circulation. This paper emphasizes the deterministic role of the dynamic adjustment of the ocean circulation in the long-term change of ocean climate.

Anatomizing the Ocean’s Role in ENSO Changes under Global Warming*

Abstract A revisit on observations shows that the tropical El Niño–Southern Oscillation (ENSO) variability, after removing both the long-term trend and decadal variation of the background climate, has been enhanced by as much as 50% during the past 50 yr. This is inconsistent with the changes in the equatorial atmosphere, which shows a slowdown of the zonal Walker circulation and tends to stabilize the tropical coupling system. The ocean role is highlighted in this paper. The enhanced ENSO variability is attributed to the strengthened equatorial thermocline that acts as a destabilizing factor of the tropical coupling system. To quantify the dynamic effect of the ocean on the ENSO variability under the global warming, ensemble experiments are performed using a coupled climate model [Fast Ocean Atmosphere Model (FOAM)], following the “1pctto2x” scenario defined in the Intergovernmental Panel on Climate Change (IPCC) reports. Term balance analyses on the temperature variability equation show that the anomalous upwelling of the mean vertical temperature gradient (referred as the “local term”) in the eastern equatorial Pacific is the most important destabilizing factor to the temperature variabilities. The magnitude of local term and its change are controlled by its two components: the mean vertical temperature gradient Tz and the “virtual vertical heat flux” −w′T ′. The former can be viewed as the background of the latter and these two components are positively correlated. A stronger Tz is usually associated with a bigger upward heat flux −w′T ′, which implies a bigger impact of thermocline depth variations on SST. The Tz is first enhanced during the transient stage of the global warming with a 1% yr−1 increase of CO2, and then reduced during the equilibrium stage with a fixed doubled CO2. This turnaround in Tz determines the turnaround of ENSO variability in the entire global warming period.

Factors affecting the efficiency of producing porcine embryos expressing enhanced green fluorescence protein by ICSI-mediated gene transfer method

This study aims to investigate factors that affect the efficiency of blastocyst development and enhanced green fluorescence protein (EGFP) expression in porcine embryos following intracytoplasmic sperm injection (ICSI)-mediated DNA transfer. Frozen-thawed dead spermatozoa were exposed to different concentrations (0.01 μg/mL, 0.05 μg/mL or 0.1 μg/mL) of EGFP DNA solution, and then microinjected into in vitro matured oocytes. The optimal concentration for EGFP expression of resultant embryos was 0.05 μg/mL. When oocytes were microinjected on a warm stage at 30 °C, the percentage of EGFP-expressing embryos was higher than that at 38.5 °C (40.1% vs. 20.9%, P < 0.01). The efficiency of EGFP expression in embryos following ICSI using linear EGFP DNA-exposed spermatozoa was higher than using circular DNA (40.8% vs. 28.2%, P < 0.05). ICSI oocytes treated with 6-DMAP after electro-activation had a higher percentage of embryos expressing EGFP than those not treated (52.5% vs. 26.3%, P < 0.01). However, neither incubation temperatures of spermatozoa and DNA (4 °C, 24 °C or 39 °C) nor BSA addition to the incubation medium affected the efficiency of producing EGFP-expressing embryos. Furthermore, treatment with DNase I after preincubation of sperm and DNA prevented the embryos from expressing EGFP. The EGFP expression of ICSI oocytes was affected neither by intracytoplasmic injection using sperm heads or whole spermatozoa, nor by washing of the sperm after preincubation. The above-mentioned factors did not affect embryonic developmental competence, apart from 6-DMAP treatment after electro-activation. In conclusion, most exogenous DNA molecules were tightly bound on the membranes of sperm head after incubation of DNA and sperm, and the temperature during ICSI, 6-DMAP treatment, exogenous DNA concentrations and constructs could significantly affect EGFP expression in porcine embryos following ICSI-mediated DNA transfer.