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Marine Isotope Stage (MIS) 5e (130–116 ka) represents a "laboratory" for evaluating climate model performance under warmer‐than‐present conditions. Climate model simulations for MIS 5e have previously failed to produce Southern Ocean (SO) sea‐surface temperatures (SSTs) and sea‐ice extent reconstructed from marine sediment core proxy records. Here we compare state of the art HadGEM3 and HadCM3 simulations of Peak MIS 5e SO summer SSTs and September sea‐ice concentrations with the latest marine sediment core proxy data. The model outputs and proxy records show the least consistency in the regions located near the present‐day SO gyre boundaries, implying the possibility that model simulations are currently unable to fully realize changes in gyre extent and position during MIS 5e. Including Heinrich 11 meltwater forcing in Peak MIS 5e climate simulations improves the likeness to proxy data but it is clear that longer (3–4 ka) run times are required to fully test the consistency between models and data. Plain Language Summary: Investigating past warm periods can provide us with an analog for how climate will respond to future warming. In this study we compare the latest model simulations of Southern Ocean (SO) sea‐surface temperatures and Antarctic winter sea‐ice extent from 130,000 years ago with data from marine sediment cores. The simulations and sediment core data show the least match in the areas near the boundaries of the present day SO gyres (large, circulating ocean currents), implying that possibly changes in the position and size of the gyres are not fully recreated in the computer simulations. The inclusion of ice sheet meltwater into the North Atlantic improves the comparison between the simulations and sediment core data but it is clear that longer run times are required to fully test their consistency. Key Points: Different areas of the Southern Ocean (SO) show different consistency between model simulations and proxy dataRegions along the edges of the modern day SO gyres show the least consistency between models and proxy dataInclusion of Heinrich 11 meltwater forcing improves the match between model simulations and proxy data [ABSTRACT FROM AUTHOR]

The latitudinal temperature gradient is a fundamental state parameter of the climate system tied to the dynamics of heat transport and radiative transfer. Thus, it is a primary target for temperature proxy reconstructions and global climate models. However, reconstructing the latitudinal temperature gradient in past climates remains challenging due to the scarcity of appropriate proxy records and large proxy-model disagreements. Here, we develop methods leveraging an extensive compilation of planktonic foraminifera d18O to reconstruct a continuous record of the latitudinal sea-surface temperature (SST) gradient over the last 95 million years (My). We find that latitudinal SST gradients ranged from 26.5 to 15.3 °C over a mean global SST range of 15.3 to 32.5 °C, with the highest gradients during the coldest intervals of time. From this relationship, we calculate a polar amplification factor (PAF; the ratio of change in >60° S SST to change in global mean SST) of 1.44 6 0.15. Our results are closer to model predictions than previous proxy-based estimates, primarily because d18O-based high-latitude SST estimates more closely track benthic temperatures, yielding higher gradients. The consistent covariance of d18O values in low- and high-latitude planktonic foraminifera and in benthic foraminifera, across numerous climate states, suggests a fundamental constraint on multiple aspects of the climate system, linking deep-sea temperatures, the latitudinal SST gradient, and global mean SSTs across large changes in atmospheric CO2, continental configuration, oceanic gateways, and the extent of continental ice sheets. This implies an important underlying, internally driven predictability of the climate system in vastly different background states. [ABSTRACT FROM AUTHOR]

This study examines the slow modulation of El Niño–Southern Oscillation (ENSO) intensity and its underlying mechanism. A 10–15-yr ENSO intensity modulation cycle is identified from historical and paleoclimate data by calculating the envelope function of boreal winter Niño-3.4 and Niño-3 sea surface temperature (SST) indices. Composite analyses reveal interesting spatial asymmetries between El Niño and La Niña events within the modulation cycle. In the enhanced intensity periods of the cycle, El Niño is located in the eastern tropical Pacific and La Niña in the central tropical Pacific. The asymmetry is reversed in the weakened intensity periods: El Niño centers in the central Pacific and La Niña in the eastern Pacific. El Niño and La Niña centered in the eastern Pacific are accompanied with basin-scale surface wind and thermocline anomalies, whereas those centered in the central Pacific are accompanied with local wind and thermocline anomalies. The El Niño–La Niña asymmetries provide a possible mechanism for ENSO to exert a nonzero residual effect that could lead to slow changes in the Pacific mean state. The mean state changes are characterized by an SST dipole pattern between the eastern and central tropical Pacific, which appears as one leading EOF mode of tropical Pacific decadal variability. The Pacific Walker circulation migrates zonally in association with this decadal mode and also changes the mean surface wind and thermocline patterns along the equator. Although the causality has not been established, it is speculated that the mean state changes in turn favor the alternative spatial patterns of El Niño and La Niña that manifest as the reversed ENSO asymmetries. Using these findings, an ENSO–Pacific climate interaction mechanism is hypothesized to explain the decadal ENSO intensity modulation cycle.

It is well established that greenhouse conditions prevailed during the Cretaceous Period (~ 145–66 Ma). Determining the exact nature of the greenhouse-gas forcing, climatic warming and climate sensitivity remains, however, an active topic of research. Quantitative and qualitative geochemical and palaeontological proxies provide valuable observational constraints on Cretaceous climate. In particular, reconstructions of Cretaceous sea-surface temperatures (SSTs) have been revolutionised firstly by the recognition that clay-rich sequences can host exceptionally preserved planktonic foraminifera allowing for reliable oxygen-isotope analyses and, secondly by the development of the organic palaeothermometer TEX 86, based on the distribution of marine archaeal membrane lipids. Here we provide a new compilation and synthesis of available planktonic foraminiferal δ 18 O (δ 18 O pl ) and TEX 86 -SST proxy data for almost the entire Cretaceous Period. The compilation uses SSTs recalculated from published raw data, allowing examination of the sensitivity of each proxy to the calculation method (e.g., choice of calibration) and places all data on a common timescale. Overall, the compilation shows many similarities with trends present in individual records of Cretaceous climate change. For example, both SST proxies and benthic foraminiferal δ 18 O records indicate maximum warmth in the Cenomanian–Turonian interval. Our reconstruction of the evolution of latitudinal temperature gradients (low, <±30°, minus higher, >±48°, palaeolatitudes) reveals temporal changes. In the Valanginian–Aptian, the low-to-higher mid-latitudinal temperature gradient was weak (decreasing from ~ 10–17 °C in the Valanginian, to ~ 3–5 °C in the Aptian, based on TEX 86 -SSTs). In the Cenomanian–Santonian, reconstructed latitudinal temperature contrasts are also small relative to modern (< 14 °C, based on low-latitude TEX 86 and δ 18 O pl SSTs minus higher latitude δ 18 O pl SSTs, compared with ~ 20 °C for the modern). In the mid-Campanian to end-Maastrichtian, latitudinal temperature gradients strengthened (~ 19–21 °C, based on low-latitude TEX 86 and δ 18 O pl SSTs minus higher latitude δ 18 O pl SSTs), with cooling occurring at low-, middle- and higher palaeolatitude sites, implying global surface-ocean cooling and/or changes in ocean heat transport in the Late Cretaceous. These reconstructed long-term trends are resilient, regardless of the choice of proxy (TEX 86 or δ 18 O pl ) or calibration. This new Cretaceous SST synthesis provides an up-to-date target for modelling studies investigating the mechanics of extreme climates. [ABSTRACT FROM AUTHOR]

The Peruvian coastal upwelling is one of the most productive systems in the global ocean, with important impacts on the carbon cycle. Primary productivity there displays strong variations at the interannual to decadal timescales. However, down-core investigations rarely reach sufficient temporal resolution to assess the response of productivity to climatic variations at these timescales beyond the instrumental and historical periods. We here analyzed diatom assemblages, sea-surface temperatures (SSTs), and nitrogen and organic carbon contents on a laminated sediment core from the Peruvian continental shelf to trace variations in regional productivity over the last 3000 years. Our record provides evidence for different climatic and oceanic conditions with more humid and less productive conditions older than 2500 cal. yr BP and drier and more productive conditions younger than 2500 cal. yr BP. The last 2500 years also present much stronger centennial-scale variability with the occurrence of six intervals with higher total diatom abundances and stronger percentages in upwelling-related diatom species, representative of intensified productivity, congruent to lower percentages in benthic diatoms, indicative of reduced rainfall. These six periods were synchronous to intervals of enhanced Walker circulation, suggesting a strong imprint of the Pacific zonal circulation on productivity variations off Peru. Our record also demonstrates that SSTs did not vary in phase with productivity, arguing against the idea of regional SSTs controlled by the upwelling intensity, but were rather in agreement to SST records off southern Chile, suggesting that Peruvian SST variations were largely controlled by oceanic currents at southern high latitudes. [ABSTRACT FROM AUTHOR]

Silver Lake is the modern terminal playa of the Mojave River in southern California (USA). As a result, it is well located to record both influences from the winter precipitation dominated San Bernardino Mountains – the source of the Mojave River – and from the late summer to early fall North American monsoon at Silver Lake. Here, we present various physical, chemical and biological data from a new radiocarbon-dated, 8.2 m sediment core taken from Silver Lake that spans modern through 14.8 cal ka BP. Texturally, the core varies between sandy clay, clayey sand, and sand-silt-clay, often with abrupt sedimentological transitions. These grain-size changes are used to divide the core into six lake status intervals over the past 14.8 cal ka BP. Notable intervals include a dry Younger Dryas chronozone, a wet early Holocene terminating 7.8 – 7.4 cal ka BP, a distinct mid-Holocene arid interval, and a late Holocene return to ephemeral lake conditions. A comparison to potential climatic forcings implicates a combination of changing summer – winter insolation and tropical and N Pacific sea-surface temperature dynamics as the primary drivers of Holocene climate in the central Mojave Desert. [ABSTRACT FROM AUTHOR]

The proposed flexible threshold selection and fuzzy inference system-based fault detection system (FTSFFDS) is a simple and efficient method of fault localization which forms the basis for the structural health monitoring of offshore wind farms. Based on the actual parameter readings obtained by the sensors attached to the towers, one can remotely observe and monitor the health condition of wind farm. The simulation considers day time and night time collected data for wave-height and sea-surface temperatures. The correlation between the data sets indicates the choice of adaptive (dynamic) thresholds. The method involves quantization for extracting meaningful information from the collected samples. A fuzzy inferencing system is proposed which uses combination-summation and flow-direction of received data to accurately predict faults in the wind farm. The method is compared with primitive mean method. The proposed method provides a simple approach for detecting real-time fault occurrences and in-effect helps in reducing the message size considerably to increase the network lifetime of the wireless sensor network by nearly ten times. The results confirm that the proposed method FTSFFDS has better fault-prediction accuracy over the existing method. [ABSTRACT FROM PUBLISHER]

The authors define a spatio-statistical response of hurricane frequency to the solar cycle. Previous research indicates reduced (increased) hurricane intensities and frequency in the western (eastern) tropical Atlantic. However, no formal quantitative relationship has been spatially established between hurricane frequency and solar activity. The authors use a Bayesian hierarchical space-time model, an increasingly popular approach due to its advantage in facilitating regression modeling of space-time phenomena in the context of large data sets. Regional hurricane frequency over the period 1866-2010 is examined in response to September sunspot number (SSN) while controlling for other relevant climate factors. The response features a 13 % reduction in probability of annual hurricane occurrence for southeastern Cuba, the southern Bahama islands, Haiti, and Jamaica when the SSN is 80 sunspots. In contrast, hurricane risk in regions of the southeastern Atlantic is predicted to increase by 73 % when the SSN is 160 sunspots. The model can be ported to explore other relationships over contiguous space. [ABSTRACT FROM AUTHOR]

Abstract: The TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) sea-surface temperature (SST) proxy is based on the distribution of isoprenoid glycerol dialkyl glycerol tetraether (GDGT) membrane lipids of pelagic Thaumarchaeota that are preserved in marine sediments. It is a valuable tool for reconstructing past SSTs from sedimentary archives; however there are still major uncertainties as to the effects of variables other than temperature on the proxy. Here we present the first study of GDGT variability across early Cretaceous interbedded pelagic and shelf-sourced turbiditic sediments from two Deep Sea Drilling Project (DSDP) sites in the western North Atlantic. The results indicate that a small, but consistent, offset in TEX86 ratios, equivalent to ~1–2°C of temperature difference, occurs between interbedded lithologies of a similar age. The offset can be attributed to spatial differences in sea-surface temperatures or thaumarchaeotal populations between the shelf and the open ocean, or to secondary diagenetic effects related to oxic degradation of the GDGTs. Of these, a difference in either thaumarchaeotal taxa or ecology between those living in the shelf and ocean areas seems most plausible. Regardless of the root cause of the offset, these findings highlight the necessity of careful sample selection prior to TEX86 analysis, to ensure robust interpretation of palaeotemperature trends. [Copyright &y& Elsevier]

We investigate how differently-constructed indices for North Atlantic sea-surface temperatures (NASSTs) describe the 'Atlantic Multidecadal Variability' (AMV) in a suite of unperturbed as well as externally-forced millennial (pre-industrial period) climate simulations. The simulations stem from an ensemble of Earth system models differing in both resolution and complexity. Different criteria exist to construct AMV indices capturing different aspects of the phenomenon. Although all representations of the AMV maintain strong multidecadal variability, they depict different characteristics of simulated low-frequency NASST variability, evolve differently in time and relate to different hemispheric teleconnections. Due to such multifaceted signatures in the ocean-surface as well as in the atmosphere, reconstructions of past AMV may not univocally reproduce multidecadal NASST variability. AMV features under simulated externally-forced pre-industrial climate conditions are not unambiguously distinguishable, within a linear framework, from AMV features in corresponding unperturbed simulations. This prevents a robust diagnosis of the simulated pre-industrial AMV as a predominantly internal rather than externally-forced phenomenon. We conclude that a multi-perspective assessment of multidecadal NASSTs variability is necessary for understanding the origin of the AMV, its physics and its climatic implications. [ABSTRACT FROM AUTHOR]

Abstract: Planktic foraminiferal assemblages in a composite section from two cores (MD06-2989/2986) off the west coast of New Zealand''s South Island (42–43.5°S) provide a 1myr (MIS 31–1) sea-surface temperature (SST) record (~3–4kyr resolution) in the Tasman Sea. A significant overall faunal change occurred near the end of the mid-Pleistocene Climate Transition (MPT) at ~600ka (MIS 15). Mean annual SSTs were estimated using the Artificial Neural Network (ANN) method. Glacial–interglacial (G–I) cycles in the MPT had ~9°C SST range, whereas in the post-MPT SST range was ~6–7°C. The SST and faunal changes imply that the Subtropical Front (STF) migrated ~6° in latitude to lie just north of the sites in MPT glacials (MIS 28–16), but only migrated 3–5° north in post-MPT glacials. These G–I latitudinal migrations of the STF west of New Zealand contrast with the situation east of New Zealand, where migrations of both the STF and Subantarctic Front were prevented by the Chatham Rise and Campbell Plateau. Subtropical Water is inferred to have only flowed around the south of New Zealand (as it does today) during MIS 11 and the Late Pleistocene–Holocene (MIS 5–1). [Copyright &y& Elsevier]

To extend the linear stochastically forced paradigm of tropical sea surface temperature (SST) variability to the subsurface ocean, a linear inverse model (LIM) is constructed from the simultaneous and 3-month lag covariances of observed 3-month running mean anomalies of SST, thermocline depth, and zonal wind stress. This LIM is then used to identify the empirically-determined linear dynamics with physical processes to gauge their relative importance to ENSO evolution. Optimal growth of SST anomalies over several months is triggered by both an initial SST anomaly and a central equatorial Pacific thermocline anomaly that propagates slowly eastward while leading the amplifying SST anomaly. The initial SST and thermocline anomalies each produce roughly half the SST amplification. If interactions between the sea surface and the thermocline are removed in the linear dynamical operator, the SST anomaly undergoes less optimal growth but is also more persistent, and its location shifts from the eastern to central Pacific. Optimal growth is also found to be essentially the result of two stable eigenmodes with similar structure but differing 2- and 4-year periods evolving from initial destructive to constructive interference. Variations among ENSO events could then be a consequence not of changing stability characteristics but of random excitation of these two eigenmodes, which represent different balances between surface and subsurface coupled dynamics. As found in previous studies, the impact of the additional variables on LIM SST forecasts is relatively small for short time scales. Over time intervals greater than about 9 months, however, the additional variables both significantly enhance forecast skill and predict lag covariances and associated power spectra whose closer agreement with observations enhances the validation of the linear model. Moreover, a secondary type of optimal growth exists that is not present in a LIM constructed from SST alone, in which initial SST anomalies in the southwest tropical Pacific and Indian ocean play a larger role than on shorter time scales, apparently driving sustained off-equatorial wind stress anomalies in the eastern Pacific that result in a more persistent equatorial thermocline anomaly and a more protracted (and predictable) ENSO event. [ABSTRACT FROM AUTHOR]

Abstract: In 2007, a daily temperature series, which has been collected from 1885 to 1967 at the Marseilles tide recorder, was published here. Upon the available information provided by the data managing office, they were considered as sea-surface temperatures. Unfortunately they were not but air temperature inside the building. In the present paper, the authors correct this error by studying the true seawater temperature series which had been dug out after the publication of the precedent paper. The study of this slightly shorter series (1895–1956) leads to close conclusions. Along these 61 years, the warming trend of the surface seawater rises to +1.6°C, to +1.3°C if only January to May and December are selected and +2.2°C during the June to November period. In the first half part of the series (1895–1925), the average value of each month distributions (except January) and annual minimal (except 1956) are significantly lower than along the second (1925–1956). [Copyright &y& Elsevier]

Abstract: Uniquely in the Southern Hemisphere the New Zealand micro-continent spans the interface between a subtropical gyre and the Subantarctic Circumpolar Current. Its 20° latitudinal extent includes a complex of submerged plateaux, ridges, saddles and basins which, in the present interglacial, are partial barriers to circulation and steer the Subtropical (STF) and Subantarctic (SAF) fronts. This configuration offers a singular opportunity to assess the influence of bottom topography on oceanic circulation through Pleistocene glacial – interglacial (G/I) cycles, its effect on the location and strength of the fronts, and its ability to generate significant differences in mixed layer thermal history over short distances. For this study we use new planktic foraminiferal based sea-surface temperature (SST) estimates spanning the past 1 million years from a latitudinal transect of four deep ocean drilling sites. We conclude that: 1. the effect of the New Zealand landmass was to deflect the water masses south around the bathymetric impediments; 2. the effect of a shallow submerged ridge on the down-current side (Chatham Rise), was to dynamically trap the STF along its crest, in stark contrast to the usual glacial–interglacial (G–I) meridional migration that occurs in the open ocean; 3. the effect of more deeply submerged, downstream plateaux (Campbell, Bounty) was to dynamically trap the SAF along its steep southeastern margin; 4. the effects of saddles across the submarine plateaux was to facilitate the development of jets of subtropical and subantarctic surface water through the fronts, forming localized downstream gyres or eddies during different phases in the G–I climate cycles; 5. the deep Pukaki Saddle across the Campbell-Bounty Plateaux guided a branch of the SAF to flow northwards during each glacial, to form a strong gyre of circumpolar surface water in the Bounty Trough, especially during the mid-Pleistocene Climate Transition (MIS 22-16) when exceptionally high SST gradients existed across the STF; 6. the shallower Mernoo Saddle, at the western end of the Chatham Rise, provided a conduit for subtropical water to jet southwards across the STF in the warmest interglacial peaks (MIS 11, 5.5) and for subantarctic water to flow northwards during glacials; 7. although subtropical or subantarctic drivers can prevail at a particular phase of a G–I cycles, it appears that the Antarctic Circumpolar Current is the main influence on the regional hydrography. Thus complex submarine topography can affect distinct differences in the climate records over short distances with implications for using such records in interpreting global or regional trends. Conversely, the local topography can amplify the paleoclimate record in different ways in different places, thus enhancing its value for the study of more minor paleoceanographic influences that elsewhere are more difficult to detect. Such sites include DSDP 594, which like some other Southern Ocean sites, has the typical late Pleistocene asymmetrical saw-tooth G–I climate pattern transformed to a gap-tooth pattern of quasi-symmetrical interglacial spikes that interrupt extended periods of minimum glacial temperatures. [Copyright &y& Elsevier]

Abstract: In the past two decades, the understanding of the important large-scale phenomena (El Niño, upwelling, California current, etc) that drive physical, chemical, and biological processes along the US West Coast has greatly improved. However, the ability to predict the influence of annual and inter-annual events on a regional scale still remains limited. High-resolution hourly data from 6 National Oceanographic and Atmospheric Administration (NOAA) buoys deployed since the early 1980''s off Central California were analyzed to improve our understanding of spatial and temporal variability of oceanographic and meteorologic forcing along the coastline. Seasonal to inter-annual trends in wave height, wave period, sea level barometric pressure, sea-surface temperature, and wind direction were identified, as were significant departures in these trends during El Niño and La Niña periods. The results suggest there are increasing wave heights and wave periods, decreasing sea level barometric pressures and variability in sea-surface temperatures, and increasingly variable winds off Central California between 1980 and 2002. The impact of these climatic trends on coastal physical, geological and biologic processes will also be addressed. [Copyright &y& Elsevier]

Accelerator mass spectrometry (AMS) radiocarbon dating of basal high-marsh sediments from Romney Marsh, Revere, Massachusetts, provides a revised reconstruction of the late Holocene relative sea-level history of the region. After correction for changes in tidal amplitude, the sea-level change envelope reconstructed from five AMS radiocarbon dates of basal marsh sediments at Romney Marsh in Revere, Massachusetts, indicates a rise in mean sea level (MSL) of close to 2.6 m in the past 3300 years. The data indicate a possible decrease in the average rate of rise from 0.80 ± 0.25 mm/y between 3300 to 1000 YBP to a rate of 0.52 ± 0.62 mm/y between 1000 YBP and the past 150 to 500 years. An increase in the rate of sea-level rise is evident over the past few hundred years. A slowing of the rate of sea-level rise between 1000 YBP and historic times and the increase in the rate of rise to modern values is also evident in other sea-level records from Maine and Connecticut. The coherence between these sea-level records and concomitant climate changes in and around the North Atlantic indicates that regional-scale sea-level fluctuations in the region may be driven by climate forcing. However, earlier sea-level fluctuations correlated to sea-surface temperature variability are not well-resolved by this record or other records in the region and may indicate that changes in sea level are not tightly coupled with sea-surface temperature changes. [ABSTRACT FROM AUTHOR]

Abstract: A geochemical and paleontological reconstruction of paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling. [Copyright &y& Elsevier]

Intrashell oxygen and carbon stable isotope profiles (δ18O, δ13C) were established for Mesodesma donacium shells from the preceramic archaeological site, Quebrada de los Burros in coastal southern Peru, to reconstruct the sea-surface temperature (SST) variations and to estimate changes of the El Niño-Southern Oscillation (ENSO) interannual variability from the early Holocene to the present. Very strong oxygen isotopic excursions attributed to El Niño events are evident in three shells dated between 9 and 7.9 ka. This indicates that short and strong warm events were breaking the mean cooler surface conditions (2—3°C cooler compared with today SSTs) in relation with an intense upwelling system. At 4.8 ka, slightly lower mean SST (cooler than today by 0.7°C) and a reduced seasonality confirms the previous hypothesis of a weak ENSO variability at this period. [ABSTRACT FROM AUTHOR]

The Younger Dryas stadial (Greenland Stadial 1) has long been recognized in proxy records throughout the North Atlantic region as a stable, cool period that started and ended abruptly. However, modeling experiments in which the Younger Dryas cooling was forced by meltwater predict much more unstable climatic conditions compared to the proxy records. Here we present evidence of a climatically unstable Younger Dryas based on a decadal-resolution marine proxy record from the Norwegian continental shelf. This record shows that the North Atlantic was characterized in the early Younger Dryas by Arctic Water and an increasing accumulation of fresh surface water that peaked at 12,500 calendar yr B.P. For ∼300 yr during the late Younger Dryas, the sea-surface temperatures fluctuated between glacial values (∼2 °C) and interglacial values (∼10 °C) on a subdecadal to multidecadal time scale. This period of extreme instability preceded the more stable and warm Holocene, starting ca. 11,500 calendar yr B.P. These results are consistent with modeling experiments that link the Younger Dryas climate changes to fluctuations of the North Atlantic thermohaline circulation. [ABSTRACT FROM AUTHOR]

This study characterizes late-Holocene (past 3300 years) variations in organic matter deposition in the outer part of Igaliku Fjord, South Greenland, and uses this information to assess palaeohydrographic conditions. Except for two, all residues were characterized by abundant organic matter, with amorphous material dominating. The late-Holocene sediments in the deeper parts of the outer Igaliku Fjord have generally been deposited under anoxic to suboxic conditions with relatively low terrestrial/freshwater influx. The organicwalled dinoflagellate cyst assemblages suggest the continuous presence of water masses derived from the East Greenland Current, while changes in sea-surface temperature during the last 3300 years have also been interpreted. Terrestrial influx was reflected by the continuous occurrence of leaf tissue, which increased in abundance in sediments younger than AD 960. Pseudo-amorphous phytoclasts occurred in sediments older than AD 770, and sporomorphs were rare throughout. Acritarchs and organic-walled dinoflagellate cysts dominated the assemblages in the sediments. Relatively high amounts of benthic foraminiferal linings in the interval AD 960-1285 suggests increased nutrient availability, which may be ascribed to strong, wind-induced mixing of the watercolumn or higher fluxes of organic material. Sparse organic matter was recorded in sediments of age c. AD 1125 pointing to significant oxidation due to highly oxic bottom-water conditions. [ABSTRACT FROM AUTHOR]

Records of skeletal δ18O in monthly and Sr/Ca ratios in half-yearly resolution were obtained from a Bermuda coral (Diploria labyrinthiformis) for the time period 1520–1603 (±15 yr) AD within the Little Ice Age. Annual and decadal averages of both sea-surface temperature proxies indicate temperature variabilities of 0.5°C (standard deviation) and 0.3°C, respectively. Both numbers are close to recent instrumental observations. Approximately 30% of the interannual time series variance of δ18O is concentrated in broad bands centered at periods of ∼30, 16, and 7.8 yr, the last two reflecting the influence of the North Atlantic Oscillation. Although this large-scale climate signal is present in the record, there is no correlation with other contemporaneous northern hemisphere proxy data, resulting from spatial differences in climate variability. [Copyright &y& Elsevier]

Summary 1.The brown locust Locustana pardalina is a major agricultural pest in southern Africa, with populations periodically reaching plague proportions. Management and control would benefit from a predictive capacity at seasonal time scales, as yet unavailable. 2.The results of a study into the dynamics and potential predictability of locust populations in southern Africa are presented here. The number of districts reporting locust control measures was used as a proxy for swarming brown locust populations. 3.Spectral analysis of the annual number of brown locust infestations over southern Africa revealed dominant periodicity at 17·3 years. The data were low-pass filtered and the low-frequency and high-frequency components were retained. The low-frequency component led the observed 18-year cycle in southern African rainfall by about 3 years, and was therefore likely to reflect endogenous controls on populations. 4.Variability in the interannual high-frequency component of brown locust infestations was strongly related to rainfall over the Karoo and Eastern Cape regions of South Africa. The highest correlations were with rainfall over the 12 months prior to the locust season (r = 0·64) and in particular with rainfall during December (r = 0·55). 5.Evidence is presented that the high-frequency component is related to the Pacific El Niño/Southern Oscillation (ENSO) and that high-frequency locust activity is abnormally high (low) during La Niña (El Niño) events. 6.The high-frequency component of locust activity correlates positively and negatively, respectively, with sea-surface temperatures over the tropical western and eastern Pacific Ocean many months in advance of the locust season. Activity also correlates positively (negatively) with sea-surface temperatures over the south-west Indian Ocean and the Southern Ocean (west and north-west Indian Ocean). These relationships occur later than those in the Pacific, developing in the... [ABSTRACT FROM AUTHOR]

SignificanceThe temperature difference between low and high latitudes is one measure of the efficiency of the global climate system in redistributing heat and is used to test the ability of models to represent the climate system through time. Here, we show that the latitudinal temperature gradient has exhibited a consistent inverse relationship with global mean sea-surface temperature for at least the past 95 million years. Our results help reduce conflicts between climate models and empirical estimates of temperature and argue for a fundamental consistency in the dynamics of heat transport and radiative transfer across vastly different background states.

Since the end of the Cretaceous, Africa's latitudinal drift has been relatively small and has not significantly modified the general pattern of stepwise cooling and aridification that has characterized the Cainozoic era. Tectonic uplift has, in contrast, strongly influenced regional climates in east and southern Africa, especially during the late Neogene, and has accentuated the east-west moisture gradient which has prevailed, with minor interruptions, since the Oligocene. In common with most other midlatitude regions, southern African environments responded dramatically to the global episode of cooling and drying between 2.8 and 2.6 myr which ushered in the cyclical fluctuations of the Pleistocene. The establishment of a winter rainfall regime in the southwestern part of the subcontinent probably dates from around 2.6 myr. In the north east, new proxy data spanning the last 200 000 years indicate that summer rainfall varied in relation to receipts of solar insolation at precessional frequencies. Superimposed upon these cyclical changes were a number of less regular variations which, on the basis of the larger body of evidence available for the Holocene, elicited specific localized responses. These diachronistic changes argue for the involvement of factors other than solar insolation alone in the more recent evolution of southern African climates. [ABSTRACT FROM PUBLISHER]

Tornadoes were reported in south-central Chile on 30 and 31 May 2019. To better understand the mechanisms that supported the organization and severity of the storms that generated them, a series of high-resolution sensitivity simulations were conducted using the Weather Research and Forecast (WRF) model. In addition to a control simulation, three simulations were run that successively reduced the topography to 50%, 25%, and 0% of original height; three more simulations were run that increased SST by 2 K everywhere, decreased it by 2 K everywhere, and set all SSTs greater than 16 °C to exactly 16 °C; finally, two more simulations were run to explore the combined effects of SST changes and lower topography. Results indicate that as topography was lowered, a strong northerly low-level jet along the upslope of the Andes weakened and broadened in both vertical and horizontal extent. Values of 0–6-km bulk shear and 0–3-km storm-relative helicity (SRH) over the regions where the tornadoes occurred diminished with successive reduction of the topography. As a result, simulated brightness temperatures were warmer, and swaths of updraft helicity were fewer and shorter. These results indicate that on 30–31 May 2019, flow blocking by the Andes topography generated mesoscale wind shear conditions that favored tornadoes. When SSTs were increased, instability (quantified by convective available potential energy, CAPE) also increased, although primarily offshore, and updraft helicity swath length increased, indicating a positive impact on simulated storm intensity. When SSTs were decreased, CAPE also decreased along with a decline in magnitude of updraft helicity. These results suggest that SSTs also impact storm severity via an influence on atmospheric instability. When the two factors were combined, warmer SSTs were not able to overcome a reduction in wind shear associated with a decrease in the topography. This suggests that in south-central Chile, wind shear is more important than CAPE for tornadic thunderstorms, as has been found for other regions around the world). • The low-level wind regime is modified by the Andes, generating favorable conditions for tornado formation. • SSTs impact storm severity by increasing atmospheric instability. • Wind shear seems to be more important for tornadic thunderstorms in south-central Chile than CAPE. [ABSTRACT FROM AUTHOR]