Hemispheric Temperature Changes Research Articles

The Relative Importance of Antarctic Sea Ice Loss within the Response to Greenhouse Warming

Abstract The response to Antarctic sea ice loss within a coupled modeling framework is examined in comparison to the response to Arctic sea ice loss and within the context of general greenhouse warming. Sea ice loss responses are found to be linear (particularly in response to Antarctic or global sea ice loss) with respect to the degree of imposed perturbation and additive when perturbations are applied in hemispheres separately and concurrently. Globally, and in the tropical Pacific in particular, Antarctic sea ice loss plays a relatively larger role than Arctic sea ice loss in both the atmosphere and the ocean, within the parameters of our experiments. The pattern of response to Antarctic sea ice loss is also found to more closely resemble that of greenhouse warming, again particularly in the tropics. An extension to multiparameter pattern scaling is developed to include a scaling factor for Antarctic change in addition to those for tropical warming and Arctic sea ice loss. The decomposition is applied to the modeled response to Antarctic sea ice loss to break it down into component partial responses that scale with Antarctic, tropical, and Arctic changes. This reveals the aspects of the response that are directly related to Antarctic change, such as an equatorward intensification of tropical precipitation in the Northern Hemisphere, and those that are modified via the induced changes in the tropics and Arctic, such as Northern Hemisphere temperature change. With this, we hope to gain a deeper understanding of the role of each of these changes for the development of physical mechanisms of the response.

An extended exponential SEMIFAR model with application in R

The article at hand provides a detailed description of the esemifar R-package, which is an extension of the already published smoots R-package, enabling the data-driven local-polynomial smoothing of trend-stationary time series with long memory. In this regard, a simple data-driven algorithm is proposed based on the well-known iterative plug-in algorithm for SEMIFAR (semiparametric fractional autoregressive) models. Two new functions for data-driven estimation of the trend and its derivatives in the presence of long memory are introduced. esemifar is applied to various environmental and financial time series with long memory, for example, mean monthly Northern Hemisphere temperature changes, daily observations of the air quality index of London (Britain), quarterly G7-GDP and daily trading volume of the S & P500. It is worth mentioning that this package can be applied to any suitable time series.

Southern hemisphere forced millennial scale Indian summer monsoon variability during the late Pleistocene

Peninsular India hosts the initial rain-down of the Indian Summer Monsoon (ISM) after which winds travel further east inwards into Asia. Stalagmite oxygen isotope composition from this region, such as those from Belum Cave, preserve the vital signals of the past ISM variability. These archives experience a single wet season with a single dominant moisture source annually. Here we present high-resolution δ18O, δ13C and trace element (Mg/Ca, Sr/Ca, Ba/Ca, Mn/Ca) time series from a Belum Cave stalagmite spanning glacial MIS-6 (from ~ 183 to ~ 175 kyr) and interglacial substages MIS-5c-5a (~ 104 kyr to ~ 82 kyr). With most paleomonsoon reconstructions reporting coherent evolution of northern hemisphere summer insolation and ISM variability on orbital timescale, we focus on understanding the mechanisms behind millennial scale variability. Finding that the two are decoupled over millennial timescales, we address the role of the Southern Hemisphere processes in modulating monsoon strength as a part of the Hadley circulation. We identify several strong and weak episodes of ISM intensity during 104–82 kyr. Some of the weak episodes correspond to warming in the southern hemisphere associated with weak cross-equatorial winds. We show that during the MIS-5 substages, ISM strength gradually declined with millennial scale variability linked to Southern Hemisphere temperature changes which in turn modulate the strength of the Mascarene High.

Changes in the Snow Cover Extent in Eurasia from Satellite Data in Relation to Hemispheric and Regional Temperature Changes

Changes in the Snow Cover Extent in Eurasia from Satellite Data in Relation to Hemispheric and Regional Temperature Changes

The Late Quaternary Hydrological Changes in the Eastern Tarim Basin Inferred From 10Be Exposure Ages of River Terraces

AbstractReliable information on the dynamics of hydrological changes is crucial for the social and economic stabilities and sustaining developments in arid Central Asia. However, the few long‐term hydrological records limit understanding of the relationship between meltwater runoff and climate changes, because the short‐term observations show a paradoxical runoff trend with climate warming across Central Asia. Here, we made a systematic analysis on the 10Be exposure ages of the river terraces developed in the eastern Tarim Basin and reconstructed the hydrological regime changes during the past 170 ka. These data, together with the ages of the river terraces in the water source areas, suggest that the exposure ages of river terraces in the eastern Tarim Basin reflect the depositional time of alluvial sediments. The meltwater runoff displays an inverse relation with the North Hemisphere Summer Insolation and temperature changes on both orbital and millennial time scale, indicating that low temperatures favor high runoff fluxes. The observed correlation between the hydrological regimes and temperature changes suggests that the runoff will decrease and thus climate will become drying with global warming in arid Central Asia.

Midlatitude Southern Hemisphere Temperature Change at the End of the Eocene Greenhouse Shortly Before Dawn of the Oligocene Icehouse

AbstractThe Eocene‐Oligocene transition (EOT) marked the initiation of large‐scale Antarctic glaciation. This fundamental change in Cenozoic climate state is recorded in deep‐sea sediments by a rapid benthic foraminiferal δ18O increase and appearance of ice‐rafted debris in the Southern Ocean. However, we know little about the magnitude of cooling associated with the EOT in shallow water environments, particularly at middle to high latitudes. Here we present new stratigraphic records of the C13r/C13n magnetochron boundary and the EOT in the clay‐rich Blanche Point Formation, South Australia. The Blanche Point Formation was deposited in a shallow shelf setting (water depths of <100 m) at a paleolatitude of ~51°S. We present high‐resolution δ18O, δ13C, and Mg/Ca records of environmental change from well‐preserved benthic foraminifera of latest Eocene age at this site. A marked, negative δ13C excursion occurs immediately before EOT Step 1 and may be a globally representative signal. An ~2 °C cooling of shallow shelf seawater is evident from benthic foraminiferal Mg/Ca across Step 1. This cooling signal is both sufficient to account fully for the δ18O increase in our data and is of similar amplitude to that documented in published records for shallow shelf and upper water column open ocean settings, which suggests no obvious polar amplification of this cooling signal. Our results strengthen the evidence base for attributing EOT Step 1 to global cooling with little contribution from ice volume growth and contradict the mechanism suggested to explain the inferred northward migration of the intertropical convergence zone in the contemporaneous equatorial Pacific Ocean.

Competing Temperature and Atmospheric Circulation Effects on Southwest Madagascan Rainfall During the Last Deglaciation

AbstractThe global paleomonsoon concept predicts an antiphase response of monsoon rainfall in the Northern and Southern Hemispheres at timescales where there is asymmetric solar forcing and/or asymmetric hemispheric temperature changes. However, as different monsoon systems have different sensitivities to local, regional, and global forcing, rainfall response may vary regionally, particularly during large global climatic changes such as the last deglaciation where warming occurred in both hemispheres. Despite its role as a key Southern Hemisphere counterpart to the Arabian and Indian summer monsoons, the behavior of the summer monsoon in the Southern Hemisphere of the Indian Ocean during the last deglaciation is unknown. Therefore, we present a new high‐resolution, precisely dated, and replicated speleothem stable isotope record from Tsimanampesotse National Park in southwest Madagascar that covers the last deglaciation. We show that speleothem growth phases respond largely to movements of the Southern Hemisphere summer Hadley circulation (summer extent of the tropical rainbelt/mean Intertropical Convergence Zone location), with some contribution from sea surface temperature changes at key times, such as during the Bølling‐Allerød. In contrast, speleothem δ18Ο responds primarily to sea surface temperature, in particular the location of the deep atmospheric convection isotherm, while summer Hadley circulation changes take a secondary role. Separating the varying influences of temperature and atmospheric circulation in controlling southwest Madagascan rainfall is critical to understanding rainfall variability in both the past and the future.

A stable isotope record of Holocene precipitation dynamics in the Baltic region from Lake Nuudsaku, Estonia

A long-term perspective of past hydroclimate variability for the Baltic region provides important context for evaluating the potential impacts of Northern Hemisphere temperature changes and shifting ocean-atmospheric interactions on northern European climate. Lake Nuudsaku is an open-basin lake in south-central Estonia with seasonal overflow fed by active springs and groundwater. Stable isotope analyses of surface water samples from regional lakes, rivers, wetlands, and precipitation indicate that Lake Nuudsaku water δ18O values are consistent with the isotopic composition of inflowing meteoric water. The isotopic composition of fine-grained (<63 μm) endogenic CaCO3 (δ18Ocalcite) samples from Lake Nuudsaku vary between ∼14 to -9‰ (VPBD) over the last ∼9400 years. Based on sensitivity tests, we interpret the δ18Ocalcite variations from Lake Nuudsaku as a record of meteoric inputs; principally reflecting variations in the seasonality of precipitation, with temperature changes as a secondary influence. The δ18Ocalcite record indicates the early Holocene at ∼9400 calendar years before present (cal yr BP) was characterized by a high proportion of cold season (November through April) precipitation and lower temperatures, followed by waning cold season precipitation and higher temperatures until ∼8200 cal yr BP. The middle Holocene (8200–4200 cal yr BP) was likely a period of overall reduced cold season precipitation and higher temperatures, and/or increased warm season (May through October) precipitation. The late Holocene transition at ∼4200 cal yr BP generally marks a shift to lower δ18Ocalcite values that we interpret largely the result of increased cold season precipitation amounts. This was followed by the onset of more variable precipitation amounts and temperatures after ∼3600 cal yr BP, which gave way to less variable conditions during the last ∼2600 years. The Medieval Climate Anomaly (MCA) is marked by δ18Ocalcite values that are near the Holocene and present-day averages. The period spanning the Little Ice Age (LIA) is marked by low δ18Ocalcite values, suggesting temperatures were lower and cold season conditions were wetter than present-day. Proxy evidence from Lake Nuudsaku further indicates that centennial to millennial-scale hydroclimate shifts in the Baltic region were likely associated with changes in North Atlantic ocean-atmospheric circulation dynamics.

The ‘Little Ice Age’ in the Himalaya: A review of glacier advance driven by Northern Hemisphere temperature change

Northern Hemisphere cooling between 1400 and 1900 in the Common Era (CE) resulted in the expansion of glaciers during a period known as the ‘Little Ice Age’ (LIA). Early investigation of recent advances of Himalayan glaciers assumed that these events were synchronous with LIA advances identified in Europe, based on the appearance and position of moraines and without numerical age control. However, applications of Quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred. This paper reviews geochronological evidence for the last advance of glaciers in the Himalaya. The 66 ages younger than 2000 years (0–2000 CE) calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300 and 1600 CE, slightly earlier than the coldest period of Northern Hemisphere air temperatures. The timing of LIA advances varied spatially, likely influenced by variations in topography and meteorology across and along the mountain range. Palaeoclimate proxies indicate cooling air temperatures from 1300 CE leading to a southward shift in the Asian monsoon, increased Westerly winter precipitation and generally wetter conditions across the range around 1400 and 1800 CE. The last advance of glaciers in the Himalaya during a period of variable climate resulted from cold Northern Hemisphere air temperatures and was sustained by increased snowfall as atmospheric circulation reorganised in response to cooling during the LIA.

Endovascular external carotid artery occlusion for brain selective targeting: a cerebrovascular swine model.

BackgroundThe choice of an animal model for cerebrovascular research is often determined by the disease subtype to be studied (e.g. ischemic stroke, hemorrhage, trauma), as well as the nature of the intervention to be tested (i.e. medical device or pharmaceutical). Many initial studies are performed in smaller animals, as they are cost-effective and their encephalic vasculature closely models that of humans. Non-human primates are also utilized when confirmation or validation is required on higher levels and to test larger devices. However, working with primates is complex and expensive. Intermediate sized animal models, such as swine and sheep, may represent a valuable compromise. Their cerebrovascular anatomy, however, comes with challenges because of the natural higher external carotid artery perfusion and the existence of a rete mirabile. We describe a modification to the traditional swine cerebrovascular model that significantly enhances selective brain hemispheric perfusion, limiting external carotid perfusion and dilution.ResultsWe investigated whether unilateral endovascular coil-embolization of external carotid artery branches in swine would lead to increased brain perfusion, altering cerebral circulation so that it more closely models human cerebral circulation. Equal amounts of approximately 4 °C cold saline were injected in 6 Yorkshire pigs into the ipsilateral common carotid artery before and after embolization. Hemispheric temperature changes from pre- and post-embolization were obtained as a measure of brain perfusion and averaged and compared using non-parametric statistical tests (Wilcoxon signed rank test, Mann–Whitney U Test). Graphs were plotted with absolute changes in hemispheric temperature over time to determine peak temperature drop (PTD) and corresponding time to peak (TTP) following the cold bolus injection. There was a 288 ± 90 % increase in ipsilateral brain cooling after embolization indicating improved selective blood flow to the brain due to this vascular modification.ConclusionWe have developed an effective, selective vascular brain model in swine that may be useful as a practical and cost-reducing intermediate step for evaluating target dose–responses for central nervous system drugs and brain selective interventions, such as local hypothermia.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1714-7) contains supplementary material, which is available to authorized users.

Austral Spring Southern Hemisphere Circulation and Temperature Changes and Links to the SPCZ

Abstract Significant austral spring trends have previously been observed in West Antarctica and Antarctic Peninsula temperatures and in atmospheric circulation across the southern Pacific and Atlantic. Here, physical mechanisms for the observed trends are investigated through analysis of monthly circulation and temperatures from the ERA-Interim dataset and outgoing longwave radiation (OLR) data. The negative pressure trend over the South Pacific during spring is strongest in September, while the positive pressure trend over the South Atlantic is strongest in October. Pressure trends in November are generally nonsignificant. The authors demonstrate that a significant September trend toward increased convection (reduced OLR) in the poleward portion of the South Pacific convergence zone (SPCZ) is statistically related to Rossby wave–like circulation changes across the southern oceans. The wave response is strongest over the South Pacific in September and propagates eastward to the South Atlantic in October. OLR-related changes are linearly congruent with around half of the observed total changes in circulation during September and October and are consistent with observed trends in South Pacific sea ice concentration and surface temperature over western West Antarctica and the western Antarctic Peninsula. These results suggest SPCZ variability in early spring, especially on the poleward side of the SPCZ, is an important contributor to circulation and surface temperature trends across the South Pacific/Atlantic and West Antarctica.

Orbital-scale climate variability in Arabia as a potential motor for human dispersals

The Arabian Peninsula is situated at an important crossroads for the movement of Pleistocene human populations out of, and into, Africa. Although the timings, routes and frequencies of such dispersals have not yet been confirmed by genetic, fossil or archaeological evidence, expansion into Arabia would have been facilitated by humid periods driven by incursions of monsoon rainfall, potentially from both Indian Ocean and African monsoon systems. Here we synthesise terrestrial and marine core palaeoclimatic data in order to establish the spatial and temporal variability of humid periods in Arabia between late Marine Isotope Stage (MIS) 7 and 3. Incursions of monsoon rainfall occurred during periods of insolation maxima at ca. 200–190, 170, 155, 130–120, 105–95, 85–75 and 60–55ka, providing multiple ‘windows’ of favourable climatic conditions that could have facilitated demographic expansion through Arabia. Strong summer monsoons are generally associated with mid-high latitude interglacials, however, enhanced monsoon convection also brought rainfall into Arabia during global glacial phases, possibly due to a strengthened winter monsoon and a greater influence of southern hemispheric temperature changes. Key periods for dispersal into northern regions of Arabia correspond with the synchronous intensification of both eastern Mediterranean and monsoon rainfall systems at insolation maxima during MIS 7 and MIS 5, which may have facilitated demographic connectivity between the Levant and the Arabian interior. Environmental conditions throughout southern and southeast regions were also favourable to expansion during these times, although strong monsoons in these regions during MIS 6 and MIS 3 suggest further opportunities for demographic expansion and exchange. Terrestrial and marine evidence show that during early MIS 3 (ca. 60–50ka), a strengthened monsoon led to the activation of interior drainage systems and increased productivity in coastal zones, indicating that favourable environmental conditions existed along both coastal and interior routes at that time.

Southern Hemisphere imprint for Indo-Asian summer monsoons during the last glacial period as revealed by Arabian Sea productivity records

Abstract. The monsoon is one of the most important climatic phenomena: it promotes inter-hemispheric exchange of energy and affects the economical prosperity of several countries exposed to its seasonal seesaw. Previous studies in both the Indian and Asian monsoon systems have generally suggested a dominant northern hemispheric (NH) control on summer monsoon dynamics at the scale of suborbital–millennial climatic changes, while the forcing/response of Indian and Asian monsoons at the orbital scale remains a matter of debate. Here, six marine sediment cores distributed across the whole Arabian Sea are used to build a regional surface marine productivity signal. The productivity signal is driven by the intensity of Indian summer monsoon winds. Our results demonstrate the existence of an imprint of suborbital southern hemispheric (SH) temperature changes (i.e. Antarctica) on the Indian summer monsoon during the last glacial period that is generally not recognized. During the last deglaciation, the NH played a more significant role. This suggests that fluctuations in the Indian monsoon are better explained in a bipolar context. The δ18O signal recorded in the Asian monsoon speleothem records could be exported by winds from the Indian summer monsoon region, as recently proposed in modelling exercise, explaining the SH signature observed in Asian cave speleothems. Contrary to the view of a passive response of Indian and Asian monsoons to NH anomalies, the present results appear to suggest that the Indo-Asian summer monsoon plays an active role in amplifying millennial inter-hemispheric asymmetric patterns. Additionally, this study confirms previously observed differences between Indian and Asian speleothem monsoonal records at the orbital-precession scale.

Causes of Greenland temperature variability over the past 4000 yr: implications for northern hemispheric temperature changes

Abstract. Precise understanding of Greenland temperature variability is important in two ways. First, Greenland ice sheet melting associated with rising temperature is a major global sea level forcing, potentially affecting large populations in coming centuries. Second, Greenland temperatures are highly affected by North Atlantic Oscillation/Arctic Oscillation (NAO/AO) and Atlantic multidecadal oscillation (AMO). In our earlier study, we found that Greenland temperature deviated negatively (positively) from northern hemispheric (NH) temperature trend during stronger (weaker) solar activity owing to changes in atmospheric/oceanic changes (e.g. NAO/AO) over the past 800 yr (Kobashi et al., 2013). Therefore, a precise Greenland temperature record can provide important constraints on the past atmospheric/oceanic circulation in the region and beyond. Here, we investigated Greenland temperature variability over the past 4000 yr reconstructed from argon and nitrogen isotopes from trapped air in a GISP2 ice core, using a one-dimensional energy balance model with orbital, solar, volcanic, greenhouse gas, and aerosol forcings. The modelled northern Northern Hemisphere (NH) temperature exhibits a cooling trend over the past 4000 yr as observed for the reconstructed Greenland temperature through decreasing annual average insolation. With consideration of the negative influence of solar variability, the modelled and observed Greenland temperatures agree with correlation coefficients of r = 0.34–0.36 (p = 0.1–0.04) in 21 yr running means (RMs) and r = 0.38–0.45 (p = 0.1–0.05) on a centennial timescale (101 yr RMs). Thus, the model can explain 14 to 20% of variance of the observed Greenland temperature in multidecadal to centennial timescales with a 90–96% confidence interval, suggesting that a weak but persistent negative solar influence on Greenland temperature continued over the past 4000 yr. Then, we estimated the distribution of multidecadal NH and northern high-latitude temperatures over the past 4000 yr constrained by the climate model and Greenland temperatures. Estimated northern NH temperature and NH average temperature from the model and the Greenland temperature agree with published multi-proxy temperature records with r = 0.35–0.60 in a 92–99% confidence interval over the past 2000 yr. We found that greenhouse gases played two important roles over the past 4000 yr for the rapid warming during the 20th century and slightly cooler temperature during the early period of the past 4000 yr. Lastly, our analysis indicated that the current average temperature (1990–2010) or higher temperatures occurred at a frequency of 1.3 times per 1000 yr for northern high latitudes and 0.36 times per 4000 yr for NH temperatures, respectively, indicating that the current multidecadal NH temperature (1990–2010) is more likely unprecedented than not (p = 0.36) for the past 4000 yr.

Weakened Yellow Sea Warm Current over the last 2–3 centuries

Variations of oceanic currents beyond the instrumental period are often difficult to characterize, although sea surface temperature (SST) changes along current pathways could provide some indirect information. Here we reconstruct four U37K′-based annual SST records over the past 2–3 centuries from muddy areas in the Yellow Sea (YS) and the northern East China Sea (ECS) to characterize the regional SST variation patterns and to assess whether such patterns could be used to infer current changes. Three offshore sites are located along the pathway of the Yellow Sea Warm Current (YSWC) and an additional coastal site near the Yangtze River mouth with the minimal YSWC influence. The records show SSTs dropped 3–6 °C over the last 2–3 centuries at the three offshore sites, and a warming trend toward the present at the coastal site. The cooling SST trend observed at the three offshore sites is at odds with the average Northern Hemisphere temperature and solar irradiance changes, strongly suggesting that regional processes or drivers in the YS and northern ECS regions overturned the global temperature signal. Accordingly, we propose that the YSWC weakened over the last 2–3 centuries, which might be linked to the East Asian winter monsoon variability.

Discrepancies between the modeled and proxy‐reconstructed response to volcanic forcing over the past millennium: Implications and possible mechanisms

We show that a systematic discrepancy between model simulations and proxy reconstructions of hemispheric temperature changes over the past millennium appears to arise from a small number of radiatively large volcanic eruptions. Past work has shown that accounting for this mismatch alone appears to reconcile inconsistencies between the overall amplitude of simulated and proxy‐reconstructed temperature changes. We provide empirical support for the previously posited hypothesis that this discrepancy may arise from threshold growth effects in tree line‐proximal trees that limit their response to large volcanic cooling events. Such threshold responses could lead to an absence of growth rings (as many as six accumulated years over the past eight centuries) for some fraction of tree line‐proximal trees, leading to a potential misalignment of volcanic cooling events in trees from climatically distinct regions, and a further attenuation and smearing of the volcanic cooling signal. Since the high‐frequency component of nearly all proxy reconstructions of past hemispheric temperature change is derived from tree ring data, this bias would likely impact nearly all such reconstructions. We show here that the discrepancy may have led to an underestimation bias in past studies attempting to infer equilibrium climate sensitivity from proxy temperature reconstructions of the past millennium.

Northern Hemisphere temperature patterns in the last 12 centuries

Abstract. We analyse the spatio-temporal patterns of temperature variability over Northern Hemisphere land areas, on centennial time-scales, for the last 12 centuries using an unprecedentedly large network of temperature-sensitive proxy records. Geographically widespread positive temperature anomalies are observed from the 9th to 11th centuries, similar in extent and magnitude to the 20th century mean. A dominance of widespread negative anomalies is observed from the 16th to 18th centuries. Though we find the amplitude and spatial extent of the 20th century warming is within the range of natural variability over the last 12 centuries, we also find that the rate of warming from the 19th to the 20th century is unprecedented in the context of the last 1200 yr. The positive Northern Hemisphere temperature change from the 19th to the 20th century is clearly the largest between any two consecutive centuries in the past 12 centuries. These results remain robust even after removing a significant number of proxies in various tests of robustness showing that the choice of proxies has no particular influence on the overall conclusions of this study.

Sedimentary organic matter and carbonate variations in the Chukchi Borderland in association with ice sheet and ocean-atmosphere dynamics over the last 155 kyr

Abstract. Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), CaCO3, benthic foraminiferal δ18O and the coarse grain size fraction from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on oxygen stratigraphy, radiocarbon dating and lithological constraints suggests that the piston core records paleoenvironmental changes of the last 155 kyr. TOC shows orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacial-interglacial cycles. At millennial scales, increases in TOC might correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 45 ka before present (BP) indicating a possible response to abrupt northern hemispheric temperature changes. Between 70 and 45 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC variability. CaCO3 content tends to anti-correlate with TOC on both orbital and millennial time scales, which we interpret in terms of enhanced sediment advection from the carbonate-rich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased organic carbon advection from the Siberian Arctic during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital- and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.

Vertical structure of Jupiter’s Oval BA before and after it reddened: What changed?

To constrain the properties of Oval BA before and after it reddened, we use Hubble methane band images from 1994 to 2009 to find that the distribution of upper tropospheric haze atop the oval and its progenitors remained unchanged, with reflectivity variations of less than 10% over this time span. We quantify measurement uncertainties and short-term fluctuations in velocity fields extracted from Cassini and Hubble data, and show that there were no significant changes in the horizontal velocity field of Oval BA in 2000, 2006, and 2009. Based on models of the oval’s dynamics, the static stability of the oval’s surroundings was also unchanged. The vertical extent of the oval did not change, based on the unchanged haze reflectivity and unchanged stratification. Published vortex models require Brunt–Väisälä frequencies of about 0.08 s −1 at the base of the vortex, and we combine this value with a review of prior constraints on the vertically variable static stability in Jupiter’s troposphere to show that the vortex must extend down to the condensation level of water in supersolar abundance. The only observable change was an increase in short-wavelength optical absorption that appeared not at the core of the oval, but in a red annulus. The secondary circulation in the vortex keeps this red annulus warmer than the vortex core. Although the underlying cause of the color change cannot be proven, we explore the idea that the new chromophores in the red annulus may be related to a global or hemispheric temperature change.

Last glacial–interglacial vegetation and environmental dynamics in southern Siberia: Chronology, forcing and feedbacks

Radiocarbon-dated pollen and diatom records from Lake Kotokel in southern Siberia help to reconstruct the environmental history of the area since ~ 47 kyr BP. Pollen spectra composition and reconstructed biome scores suggest predominance of a tundra–steppe vegetation and variable woody cover (5–20%) between ~ 47 and 30 kyr BP, indicating generally a harsh and unstable climate during this interval, conventionally regarded as the interstadial within the last glacial. The short-term climate amelioration episodes in the glacial part of the records are marked by the peaks in taiga and corresponding minima in steppe biome scores and appear synchronously with the hemispheric temperature and precipitation changes recorded in the Greenland ice cores and Chinese stalagmites. Transition to full glacial environments occurred between 32 and 30 kyr BP. The interval at ~ 30–24 kyr BP was probably the driest and coldest of the whole record, as indicated by highest scores for steppe biome, woody coverage < 5%, absence of diatoms and reduced size of the lake. A slight amelioration of the regional climate at ~ 24–22 kyr BP was followed by a shorter than the previous and less pronounced deterioration phase. The late-glacial (~ 17–11.65 kyr BP) is marked by a gradual increase in tree/shrub pollen percentages and re-appearance of diatoms. After 14.7 kyr BP the climate became warmer and wetter than ever during ~ 47–14.7 kyr BP, resulting in the deepening of the lake and increase in the woody coverage to 20–30% ~ 14.5–14 kyr and ~ 13.3–12.8 kyr BP. These two intervals correspond to the Meiendorf and Allerød interstadials, which until now were interpreted as part of the undifferentiated Bølling/Allerød interstadial complex in the Lake Baikal region. The increase in tundra biome scores and pronounced change in the diatom composition allow (for the first time) the unambiguous identification of the Younger Dryas (YD) in the Lake Baikal region at ~ 12.7–11.65 kyr BP, in agreement with the formal definition and dating of the YD based on the Greenland NGRIP ice core records. The maximal spread of the taiga communities in the region is associated with a warmer and wetter climate than the present prior to ~ 7 kyr BP. This was followed by a wide spread of Scots pine, indicating the onset of modern environments.