Southern Middle Latitudes Research Articles

10Be chronology of the Last Glacial Maximum and Termination in the Andes of central Chile: The record of the Universidad Glacier (34° S)

Reconstructing mid-latitude glacier variations is a prerequisite for unveiling the interhemispheric climate linkages and atmospheric-ocean forcings that triggered those changes during the last glacial cycle. Nonetheless, the timing, magnitude, and structure of glacier fluctuations in the southern mid-latitudes remain incomplete. Here, we present a new 10Be chronology of the Universidad Glacier in the Andes of central Chile (34° S, 70° W; ∼2500 m a.s.l.) based on 21 cosmogenic-exposure ages of boulders on discrete moraine ridges defining former ice margins. Our findings include the mapping and dating of three moraines, UNI I, UNI II, and UNI III, located ∼20 km, 15 km, and 10 km down-valley from the present-day glacier front, respectively. The 10Be exposure ages of the UNI I moraine range from 135.9 ± 7.1 to 51.4 ± 2.7 ka (n = 3). The UNI II moraine gave a mean age of 18.0 ± 0.9 (n = 15) and the UNI III moraine yielded a mean age of 13.9 ± 0.8 ka (n = 3). The UNI I moraine implies the largest ice extent during a pre-Last Glacial Maximum (pre-LGM) period, including the penultimate glaciation. The UNI II is a moraine complex that represents cold and humid conditions in central Chile at the end of the LGM, which we attribute to the northward-shift of the Southern Westerly Winds (SWW). The UNI III moraine represents a return to glacial conditions interrupting the Termination, evidencing both a double-step deglacial trend observed through the southern middle and high latitudes at the end of the last ice age. The Andes at this subtropical latitude record a global signal of glacial and climate change.

Mars: Abundant Recurring Slope Lineae (RSL) Following the Planet‐Encircling Dust Event (PEDE) of 2018

AbstractRecurring slope lineae (RSL) are dark linear markings on Mars that regrow annually and likely originate from the flow of either liquid water or granular material. Following the great dust storm (or planet‐encircling dust event, PEDE) of Mars year (MY) 34, Mars Reconnaissance Orbiter/High Resolution Imaging Science Experiment has seen many more candidate RSL than in typical Mars years. They have been imaged at more than 285 unique locations from August 2018 (when the atmosphere was clearing as the PEDE decayed) to August 2019, about half (157) of which are locations where RSL have not been documented previously. In MY34, 150 active RSL sites were identified in the southern middle latitudes (SML, ‐60° to ‐30°), whereas an average of 36 active sites were observed in each previous year (MY28–33). Post‐PEDE RSL are also present during southern summer over a wider range of latitude, slope aspect, andLs(areocentric longitude of the sun) than in prior years. These RSL sites usually show evidence for recent dust deposition: obscuration of relatively dark areas, an overall brighter and redder surface than in prior years, and dust devil tracks, which indicate dust lifting by several mechanisms. We speculate that dust‐lifting processes may initiate and sustain RSL activity. The RSL may form from flows of dust (perhaps clumped) and/or sand that is destabilized by dust movement or directly mobilized by dust devils. If this is the case, then the otherwise puzzling recurrence and year‐to‐year variability of RSL activity can be at least partly explained. The dust replenishment varies from year to year, which could explain interannual variations in RSL activity.

Relations Between Durability of Spring Frosts and North Advection on Omega Blocking Over Iran

Blocking of atmospheric systems may lead to slowing down and even stopping the movement of western wind waves. This condition prolongs the warm days in catchment areas in front of the wave and induces continuation of cold and frost days in catchment areas behind the wave. The effect of cold and frost on the crops, especially in spring, is undeniable. Therefore, analyzing the blocking systems, named as omega, is important in Iran’s spring frost duration in southern middle latitudes. The daily minimum temperature data of 69 meteorological stations were collected from the Iranian Meteorological Organization from March 20, 1968, to June 21, 2014, in order to determine the effects of omega blocking systems on duration of the spring frost waves in Iran (equivalent to spring season in the Iranian calendar). By adjusting the tables of daily temperature distribution and plotting the frequency variation diagrams, 114 synoptic waves lasting 3–25 days were identified. Four durable waves (> 12 days) and ten low-durability waves (< 12 days) were identified by dividing the 114 waves into two groups (47 durable waves and 67 low-durability waves) and designing the atmospheric circulation pattern for the middle eastern region based on the air maps of 500 hPa. The results showed that blocking patterns usually occur in the areas of central Europe to the Black Sea basin and cause advective cold air from Scandinavian and central Russia basins to Iran, thereby resulting in durable frosts during spring.

Refinements of the algorithms needed to retrieve atmospheric vertical thermodynamic profiles from GNSS radio occultations

Abstract In this work we consider some refinements to the Boundary Profile eValuation (BPV) method, developed by Vespe et al. (2004), Vespe and Persia (2006), Vespe (2016), Andrisani and Vespe (2020) in order to retrieve atmospheric thermodynamic profiles from Radio Occultation (RO) observations. Former BPV models solved typical rank deficiencies in treating RO data by applying parametric dry refractivity models for the atmosphere, such as the CIRA86aQ or Hopfield (1969). The involved parameters were selected by fitting those dry models with the refractivity observed in the stratosphere, where water vapor concentrations are negligible, with the usual Least Square Error (LSE) method. Dry refractivity is then extrapolated down to the Earth surface. Nevertheless, unphysical occurrence of negative values of humidity concentrations, typical for the so called “simple models” (Kursinski and Kursinski, 2013) can occur in the lower troposphere. This problem is solved with a non-negative residuals constrained fitting for the total refractivity, obtained with different mathematical methodologies. Other refinements include the departure from the ideal state equation for a more realistic state equation concerning compressibility factors for the dry and wet components of the atmosphere. An application to 848 RO observations from COSMIC_1 space mission, covering tropical and middle latitudes during the months of January, March and May 2009, together with a statistical comparison with other atmospheric models and experimental data, was made in order to estimate the accuracy of the BPV method. The results show a description about the thermodynamic state of the atmosphere in line with other recognized atmospheric models, in particular for what concerns the tropics and the southern middle latitudes.

A Belt-like Distribution of Gaseous Hydrogen Cyanide on Neptune’s Equatorial Stratosphere Detected by ALMA

Abstract We present a spatially resolved map of integrated-intensity and abundance of Neptune’s stratospheric hydrogen cyanide (HCN). The analyzed data were obtained from the archived 2016 observation of the Atacama Large Millimeter/submillimeter Array. A 0.″42 × 0.″39 synthesized beam, which is equivalent to a latitudinal resolution of ∼20° at the disk center, was fine enough to resolve Neptune’s 2.″24 diameter disk. After correcting the effect of different optical path lengths, a spatial distribution of HCN emissions is derived over Neptune’s disk, and it clearly shows a band-like HCN enhancement at the equator. Radiative transfer analysis indicates that the HCN volume mixing ratio measured at the equator was 1.92 ppb above the 10−3 bar pressure level, which is 40% higher than that measured at the southern middle and high latitudes. The spatial distribution of HCN can be interpreted as either the effect of the transportation of N2 from the troposphere by meridional atmospheric circulation, or an external supply such as cometary collisions (or both of these reasons). From the meridional circulation point of view, the observed HCN enhancement on both the equator and the pole can be explained by the production and accumulation of HCN at the downward branches of the previously suggested two-cell meridional circulation models. However, the HCN-depleted latitude of 60° S does not match with the location of the upward branch of the two-cell circulation models.

Global-scale albedo and spectro-photometric properties of Ryugu from NIRS3/Hayabusa2, implications for the composition of Ryugu and the representativity of the returned samples

The type C asteroid Ryugu has been visited by the JAXA Hayabusa2 mission, a first for a primitive asteroid in the Solar System exploration. Samples have been collected at its surface by the spacecraft and are now on their way back to Earth. The surface of Ryugu has also been observed both in the visible and infrared wavelengths with the objective of characterizing its properties at a global scale. Here, we report on the albedo and spectro-photometric properties of Ryugu as derived from the NIRS3 IR spectrometer. Thanks to an innovative technique based on a Bayesian approach, we retrieved the Hapke photometric parameters from multi-geometric NIRS3 observations over the NIR spectral range and different areas of Ryugu, including the first collection site. Results reveal an overall spatial homogeneity of the photometric parameters, though some small variations can be highlighted. A new photometric correction was derived and applied to NIRS3 data. Reflectance spatial heterogeneity was quantitatively investigated, in particular by deriving and mapping the single scattering albedo (SSA) at various spatial scales. This parameter could be derived with confidence on about one fourth of Ryugu’s surface, especially around the equatorial region and the southern middle latitudes. Although Ryugu is to first order homogeneous with a typical SSA of 0.045–0.050, we demonstrate with a local-scale photometric correction (1) the presence of a large “bright” area between ∼190∘E and ∼290∘E longitude around the equator and the southern middle latitudes, and (2) the presence of darker areas with a clear connection to geomorphological features. We show here that these darker regions tend to have a slightly deeper 2.72μm feature, at least compared to the surrounding areas, which can be explained by an enrichment of the top-surface in dark fines coupled to hydrated phases. Some spatial variability observed in the coupling between the SSA at 1.89μm and the 2.72μm absorption feature also suggests that Ryugu exhibits some (slight) heterogeneity in its building blocks.

Simulations for CMIP6 With the AWI Climate Model AWI‐CM‐1‐1

AbstractThe Alfred Wegener Institute Climate Model (AWI‐CM) participates for the first time in the Coupled Model Intercomparison Project (CMIP), CMIP6. The sea ice‐ocean component, FESOM, runs on an unstructured mesh with horizontal resolutions ranging from 8 to 80 km. FESOM is coupled to the Max Planck Institute atmospheric model ECHAM 6.3 at a horizontal resolution of about 100 km. Using objective performance indices, it is shown that AWI‐CM performs better than the average of CMIP5 models. AWI‐CM shows an equilibrium climate sensitivity of 3.2°C, which is similar to the CMIP5 average, and a transient climate response of 2.1°C which is slightly higher than the CMIP5 average. The negative trend of Arctic sea‐ice extent in September over the past 30 years is 20–30% weaker in our simulations compared to observations. With the strongest emission scenario, the AMOC decreases by 25% until the end of the century which is less than the CMIP5 average of 40%. Patterns and even magnitude of simulated temperature and precipitation changes at the end of this century compared to present‐day climate under the strong emission scenario SSP585 are similar to the multi‐model CMIP5 mean. The simulations show a 11°C warming north of the Barents Sea and around 2°C to 3°C over most parts of the ocean as well as a wetting of the Arctic, subpolar, tropical, and Southern Ocean. Furthermore, in the northern middle latitudes in boreal summer and autumn as well as in the southern middle latitudes, a more zonal atmospheric flow is projected throughout the year.

Revisiting global satellite observations of stratospheric cirrus clouds

Abstract. As knowledge about the cirrus clouds in the lower stratosphere is limited, reliable long-term measurements are needed to assess their characteristics, radiative impact and important role in upper troposphere and lower stratosphere (UTLS) chemistry. We used 6 years (2006–2012) of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements to investigate the global and seasonal distribution of stratospheric cirrus clouds and compared the MIPAS results with results derived from the latest version (V4.x) of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data. For the identification of stratospheric cirrus clouds, precise information on both the cloud top height (CTH) and the tropopause height is crucial. Here, we used lapse rate tropopause heights estimated from the ERA-Interim global reanalysis. Considering the uncertainties of the tropopause heights and the vertical sampling grid, we define CTHs more than 0.5 km above the tropopause as stratospheric for CALIPSO data. For MIPAS data, we took into account the coarser vertical sampling grid and the broad field of view so that we considered cirrus CTHs detected more than 0.75 km above the tropopause as stratospheric. Further sensitivity tests were conducted to rule out sampling artefacts in MIPAS data. The global distribution of stratospheric cirrus clouds was derived from night-time measurements because of the higher detection sensitivity of CALIPSO. In both data sets, MIPAS and CALIPSO, the stratospheric cirrus cloud occurrence frequencies are significantly higher in the tropics than in the extra-tropics. Tropical hotspots of stratospheric cirrus clouds associated with deep convection are located over equatorial Africa, South and Southeast Asia, the western Pacific, and South America. Stratospheric cirrus clouds were more often detected in December–February (15 %) than June–August (8 %) in the tropics (±20∘). At northern and southern middle latitudes (40–60∘), MIPAS observed about twice as many stratospheric cirrus clouds (occurrence frequencies of 4 %–5 % for MIPAS rather than about 2 % for CALIPSO). We attribute more frequent observations of stratospheric cirrus clouds with MIPAS to the higher detection sensitivity of the instrument to optically thin clouds. In contrast to the difference between daytime and night-time occurrence frequencies of stratospheric cirrus clouds by a factor of about 2 in zonal means in the tropics (4 % and 10 %, respectively) and at middle latitudes for CALIPSO data, there is little diurnal cycle in MIPAS data, in which the difference of occurrence frequencies in the tropics is about 1 percentage point in zonal mean and about 0.5 percentage point at middle latitudes. The difference between CALIPSO day and night measurements can also be attributed to their differences in detection sensitivity. Future work should focus on better understanding the origin of the stratospheric cirrus clouds and their impact on radiative forcing and climate.

Characterization of organic aerosol across the global remote troposphere: a comparison of ATom measurements and global chemistry models

Abstract. The spatial distribution and properties of submicron organic aerosol (OA) are among the key sources of uncertainty in our understanding of aerosol effects on climate. Uncertainties are particularly large over remote regions of the free troposphere and Southern Ocean, where very few data have been available and where OA predictions from AeroCom Phase II global models span 2 to 3 orders of magnitude, greatly exceeding the model spread over source regions. The (nearly) pole-to-pole vertical distribution of non-refractory aerosols was measured with an aerosol mass spectrometer onboard the NASA DC-8 aircraft as part of the Atmospheric Tomography (ATom) mission during the Northern Hemisphere summer (August 2016) and winter (February 2017). This study presents the first extensive characterization of OA mass concentrations and their level of oxidation in the remote atmosphere. OA and sulfate are the major contributors by mass to submicron aerosols in the remote troposphere, together with sea salt in the marine boundary layer. Sulfate was dominant in the lower stratosphere. OA concentrations have a strong seasonal and zonal variability, with the highest levels measured in the lower troposphere in the summer and over the regions influenced by biomass burning from Africa (up to 10 µg sm−3). Lower concentrations (∼0.1–0.3 µg sm−3) are observed in the northern middle and high latitudes and very low concentrations (&lt;0.1 µg sm−3) in the southern middle and high latitudes. The ATom dataset is used to evaluate predictions of eight current global chemistry models that implement a variety of commonly used representations of OA sources and chemistry, as well as of the AeroCom-II ensemble. The current model ensemble captures the average vertical and spatial distribution of measured OA concentrations, and the spread of the individual models remains within a factor of 5. These results are significantly improved over the AeroCom-II model ensemble, which shows large overestimations over these regions. However, some of the improved agreement with observations occurs for the wrong reasons, as models have the tendency to greatly overestimate the primary OA fraction and underestimate the secondary fraction. Measured OA in the remote free troposphere is highly oxygenated, with organic aerosol to organic carbon (OA ∕ OC) ratios of ∼2.2–2.8, and is 30 %–60 % more oxygenated than in current models, which can lead to significant errors in OA concentrations. The model–measurement comparisons presented here support the concept of a more dynamic OA system as proposed by Hodzic et al. (2016), with enhanced removal of primary OA and a stronger production of secondary OA in global models needed to provide better agreement with observations.

The last glacial termination in the Coyhaique sector of central Patagonia

Southern South America is the only continental landmass that intersects the core of the Southern Westerly Winds (SWW), and thus is important for studying their role as a driver/conduit for the initiation/propagation of climate signals since the last glaciation. Their interaction with the Southern Ocean (SO) affects global climate through its influence on high-latitude upwelling and biological productivity, deep-water convection sites and, consequently, ventilation of CO2 from the deep ocean. Variations in the SWW-SO coupled system have been postulated as fundamental drivers of climate change during glacial terminations and the current interglacial. Hence, deciphering the evolution of the SWW from sensitive locations in the southern middle latitudes is essential for understanding important climatic transitions during and since the Last Glacial Termination (T1). Terrestrial records from the central Patagonian Andes (CPA) (44°-49°S), however, show heterogeneities in the timing, rates, and direction of climate change during T1, impeding detailed assessment of its drivers at regional, hemispheric, and global scales. Here we present new data on glacier, vegetation, and fire-regime changes in the Coyhaique sector (45°34′S) of CPA to improve our understanding on the timing and structure of the T1, including the behavior of the SWW. Our results indicate glacial recession from the youngest Last Glacial Maximum moraines just before ∼17.9 ka and development of an ice-dammed proglacial lake during the early stages of T1. Drainage of the ice-dammed lake, triggered by renewed glacial recession, was near-synchronous with the onset of a gradual multi-millennial trend toward arboreal dominance that started at ∼16 ka east and west of the Andes at that latitude. We detect increased influence of the SWW at ∼45°S starting at ∼16.6 ka, relative to the first millennium of T1, that led to positive anomalies in precipitation between ∼16–14.4 and ∼12.8–11.5 ka, followed by negative anomalies between ∼11.5–9 ka. The synchronous spread of arboreal vegetation east and west of the CPA divide during T1, despite the trans-Andean precipitation contrasts, suggests an upward shift in the temperature-controlled Andean tree line, underscoring the role of deglacial warming as the critical driver for afforestation at regional scale.

Sixty Years of Widespread Warming in the Southern Middle and High Latitudes (1957–2016)

AbstractTemperature trends across Antarctica over the last few decades reveal strong and statistically significant warming in West Antarctica and the Antarctic Peninsula (AP) contrasting with no significant change overall in East Antarctica. However, recent studies have documented cooling in the AP since the late 1990s. This study aims to place temperature changes in the AP and West Antarctica into a larger spatial and temporal perspective by analyzing monthly station-based surface temperature observations since 1957 across the extratropical Southern Hemisphere, along with sea surface temperature (SST) data and mean sea level pressure reanalysis data. The results confirm statistically significant cooling in station observations and SST trends throughout the AP region since 1999. However, the full 60-yr period shows statistically significant, widespread warming across most of the Southern Hemisphere middle and high latitudes. Positive SST trends broadly reflect these warming trends, especially in the midlatitudes. After confirming the importance of the southern annular mode (SAM) on southern high-latitude climate variability, the influence is removed from the station temperature records, revealing statistically significant background warming across all of the extratropical Southern Hemisphere. Antarctic temperature trends in a suite of climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are then investigated. Consistent with previous work the CMIP5 models warm Antarctica at the background temperature rate that is 2 times faster than that observed. However, removing the SAM influence from both CMIP5 and observed temperatures results in Antarctic trends that differ only modestly, perhaps due to natural multidecadal variability remaining in the observations.

Morphology of the equatorial ionization anomaly in Africa and Middle East due to a sudden stratospheric warming event

Using total electron content (TEC) data deduced from 18 Global Positioning System (GPS) receivers in Africa and Middle East, we investigated the morphology of the equatorial ionization anomaly (EIA) and its underlying variations before, during and after the 2009 sudden stratospheric warming (SSW) event. A southern EIA crest stronger than the northern EIA crest was observed for most of the days before the SSW event, while the EIA troughs were significantly obliterated after these SSW induced phases. In addition to the observed marked depletion of the hemispheric EIA crests during the SSW peak phase, we observed a terdiurnal variation straddling the northern EIA crests. This background terdiurnal signature is suggested to be partly responsible for the transport of more plasma to the northern hemisphere at the expense of southern hemisphere during the SSW peak phase. The consequences are higher pre-noon and post noon crests in the northern hemisphere compared to a single crest in the southern hemisphere. Contrary to previous modeling and experimental reports that the reductions in ionospheric TEC are due to semidiurnal variations resulting from the SSW peak phase, our results show that a terdiurnal variation was responsible for reducing the EEJ strength and TEC at the E-region and F2-region's topside, respectively. At the southern middle latitudes, an underlying diurnal variation was seen to initiate an increment in TEC during the SSW descending phase.

Mesospheric radar wind comparisons at high and middle southern latitudes

We compare hourly averaged neutral winds derived from two meteor radars operating at 33.2 and 55 MHz to estimate the errors in these measurements. We then compare the meteor radar winds with those from a medium-frequency partial reflection radar operating at 1.94 MHz. These three radars are located at Davis Station, Antarctica. We then consider a middle-latitude 55 MHz meteor radar wind comparison with a 1.98 MHz medium-frequency partial reflection radar to determine how representative the Davis results are. At both sites, the medium-frequency radar winds are clearly underestimated, and the underestimation increases from 80 km to the maximum height of 98 km. Correction factors are suggested for these results.

Retrieval of ozone profiles from OMPS limb scattering observations

Abstract. This study describes a retrieval algorithm developed at the University of Bremen to obtain vertical profiles of ozone from limb observations performed by the Ozone Mapper and Profiler Suite (OMPS). This algorithm is based on the technique originally developed for use with data from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument. As both instruments make limb measurements of the scattered solar radiation in the ultraviolet (UV) and visible (Vis) spectral ranges, an underlying objective of the study is to obtain consolidated and consistent ozone profiles from the two satellites and to produce a combined data set. The retrieval algorithm uses radiances in the UV and Vis wavelength ranges normalized to the radiance at an upper tangent height to obtain ozone concentrations in the altitude range of 12–60 km. Measurements at altitudes contaminated by clouds in the instrument field of view are identified and filtered out. An independent aerosol retrieval is performed beforehand and its results are used to account for the stratospheric aerosol load in the ozone inversion. The typical vertical resolution of the retrieved profiles varies from ∼ 2.5 km at lower altitudes ( &lt; 30 km) to ∼ 1.5 km (about 45 km) and becomes coarser at upper altitudes. The retrieval errors resulting from the measurement noise are estimated to be 1–4 % above 25 km, increasing to 10–30 % in the upper troposphere. OMPS data are processed for the whole of 2016. The results are compared with the NASA product and validated against profiles derived from passive satellite observations or measured in situ by balloon-borne sondes. Between 20 and 60 km, OMPS ozone profiles typically agree with data from the Microwave Limb Sounder (MLS) v4.2 within 5–10 %, whereas in the lower altitude range the bias becomes larger, especially in the tropics. The comparison of OMPS profiles with ozonesonde measurements shows differences within ±5 % between 13 and 30 km at northern middle and high latitudes. At southern middle and high latitudes, an agreement within 5–7 % is also achieved in the same altitude range. An unexpected bias of approximately 10–20 % is detected in the lower tropical stratosphere. The processing of the 2013 data set using the same retrieval settings and its validation against ozonesondes reveals a much smaller bias; a possible reason for this behaviour is discussed.

Change in the Relationship between the Southern Subtropical Dipole Modes and the Southern Annular Mode in the Mid-1980s

Abstract The southern subtropical dipole modes (SSDMs) and southern annular mode (SAM) are important climate modes, which are dominant in the southern middle and high latitudes, respectively, with considerable regional climatic impacts. However, the relationship between the two modes remains unclear. A close inspection reveals that the SAM was significantly correlated with the SSDMs during the austral summer before the mid-1980s. However, the correlations have degraded since then. This decadal shift in the relationship between these two southern dominant modes is due to a weakened connection between the SAM and the subtropical highs that control the SSDMs. This decadal change could be traced back to a poleward shift in the southern westerly belt. El Niño–Southern Oscillation (ENSO) typically plays a moderate role in influencing the precipitation in Australia and a minor role in influencing the precipitation in Africa and South America. Nevertheless, the two southern modes could still affect the austral summer rainfall in the midlatitudes, even though the ENSO signal is absent. All these links between the two southern modes and southern land precipitation may be attributable to the associated transport of moisture in the lower-level circulation.

Geological and hydrological histories of the Argyre province, Mars

The geologic history of the multi-ringed Argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative-age dating of rock materials and structures. The impact formed a primary basin, rim materials, and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin, as well as structurally-controlled local basins. Since its formation, the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice, debris flows, and groundwater through and over its basement structures. The basin is interpreted to have been occupied by lakes, including a possible Mediterranean-sized sea that formed in the aftermath of the Argyre impact event. The hypothesized lakes froze and diminished through time, though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time. At its deepest, the main Argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the Sun, but with impact-induced hydrothermal heat, geothermal heat flow due to long-lived radioactivities in early martian history, and concentration of solutes in sub-ice brine, liquid water may have persisted beneath thick ice for many millions of years. Existence of an ice-covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions. The Argyre rock materials, diverse in origin and emplacement mechanisms, have been modified by impact, magmatic, eolian, fluvial, lacustrine, glacial, periglacial, alluvial, colluvial, and tectonic processes.Post-impact adjustment of part of the impact-generated basement structural fabric such as concentric faults is apparent. Distinct basin-stratigraphic units are interpreted to be linked to large-scale geologic activity far from the basin, including growth of the Tharsis magmatic–tectonic complex and the growth into southern middle latitudes of south polar ice sheets. Along with the migration of surface and sub-surface volatiles towards the central part of the primary basin, the substantial difference in elevation with respect to the surrounding highlands and Tharsis and the Thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation, even today. In addition, the impact event caused long-term (millions of years) hydrothermal activity, as well as deep-seated basement structures that have tapped the internal heat of Mars, as conduits, for far greater time, possibly even today. This possibility is raised by the observation of putative open-system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures. Long-term water and heat energy enrichment, complemented by the interaction of the nutrient-enriched primordial crustal and mantle materials favorable to life excavated to the surface and near-surface environs through the Argyre impact event, has not only resulted in distinct geomorphology, but also makes the Argyre basin a potential site of exceptional astrobiological significance.

Warming and glacier recession in the Rakaia valley, Southern Alps of New Zealand, during Heinrich Stadial 1

The termination of the last ice age featured a major reconfiguration of Earthʼs climate and cryosphere, yet the underlying causes of these massive changes continue to be debated. Documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers. Here, we present a 10Be surface-exposure chronology and glaciological reconstruction of ice recession following the Last Glacial Maximum (LGM) in the Rakaia valley, Southern Alps of New Zealand. Innermost LGM moraines at Big Ben have an age of 17,840 ± 240 yrs, whereas ice-marginal moraines or ice-molded bedrock surfaces at distances up-valley from Big Ben of 12.5 km (Lake Coleridge), ∼25 km (Castle Hill), ∼28 km (Double Hill), ∼43 km (Prospect Hill), and ∼58 km (Reischek knob) have ages of 17,020 ± 70 yrs, 17,100 ± 110 yrs, 16,960 ± 370 yrs, 16,250 ± 340 yrs, and 15,660 ± 160 yrs, respectively. These results indicate extensive recession of the Rakaia glacier, which we attribute primarily to the effects of climatic warming. In conjunction with geomorphological maps and a glaciological reconstruction for the Rakaia valley, we use our chronology to infer timing and magnitude of past atmospheric temperature changes. Compared to an overall temperature rise of ∼4.65 °C between the end of the LGM and the start of the Holocene, the glacier recession between ∼17,840 and ∼15,660 yrs ago is attributable to a net temperature increase of ∼4.0 °C (from −6.25 to −2.25 °C), accounting for ∼86% of the overall warming. Approximately 3.75 °C (∼70%) of the warming occurred between ∼17,840 and ∼16,250 yrs ago, with a further 0.75 °C (∼16%) increase between ∼16,250 and ∼15,660 yrs ago. A sustained southward shift of the Subtropical Front (STF) south of Australia between ∼17,800 and ∼16,000 yrs ago coincides with the warming over the Rakaia valley, and suggests a close link between Southern Ocean frontal boundary positions and southern mid-latitude climate. Most of the deglacial warming in the Southern Alps occurred during the early part of Heinrich Stadial 1 (HS1) of the North Atlantic region. Because the STF is associated with the position of the westerly wind belt, our findings support the concept that a southward shift of Earthʼs wind belts accompanied the early part of HS1 cooling in the North Atlantic, leading to warming and deglaciation in southern middle latitudes.

Glacier expansion in southern Patagonia throughout the Antarctic cold reversal

Resolving debated climate changes in the southern middle latitudes and potential teleconnections between southern temperate and polar latitudes during the last glacial-interglacial transition is required to help understand the cause of the termination of ice ages. Outlet glaciers of the Patagonian Ice Fields are primarily sensitive to atmospheric temperature and also precipitation, thus former ice margins record the extent and timing of past climate changes. 38 10 Be exposure ages from moraines show that outlet glaciers in Torres del Paine (51°S, south Patagonia, Chile) advanced during the time of the Antarctic cold reversal (ACR; ca. 14.6– 12.8 ka), reaching a maximum extent by ~14,200 ± 560 yr ago. The evidence here indicates that the South Patagonian Ice Field was responding to late glacial climate change distinctly earlier than the onset of the European Younger Dryas stadial (ca. 12.9 ka). Major glacier recession and deglaciation in the Torres del Paine region occurred by 12.5 ka and thus early in the Younger Dryas. We provide direct evidence for extensive ice in Patagonia at the very start of the ACR that agrees with atmospheric and marine records from the Southern Ocean and Antarctica. Atmospheric conditions responsible for the early late glacial expansion at Torres del Paine resulted from a climate reorganization that prompted a northern migration of the south westerly wind belt to the latitude of Torres del Paine at the onset of the ACR chronozone.

Polar methane accumulation and rainstorms on Titan from simulations of the methane cycle

Titan has a methane cycle akin to Earth's water cycle. It has lakes in polar regions, preferentially in the north; dry low latitudes with fluvial features and occasional rainstorms; and tropospheric clouds mainly (so far) in southern middle latitudes and polar regions. Previous models have explained the low-latitude dryness as a result of atmospheric methane transport into middle and high latitudes. Hitherto, no model has explained why lakes are found only in polar regions and preferentially in the north; how low-latitude rainstorms arise; or why clouds cluster in southern middle and high latitudes. Here we report simulations with a three-dimensional atmospheric model coupled to a dynamic surface reservoir of methane. We find that methane is cold-trapped and accumulates in polar regions, preferentially in the north because the northern summer, at aphelion, is longer and has greater net precipitation than the southern summer. The net precipitation in polar regions is balanced in the annual mean by slow along-surface methane transport towards mid-latitudes, and subsequent evaporation. In low latitudes, rare but intense storms occur around the equinoxes, producing enough precipitation to carve surface features. Tropospheric clouds form primarily in middle and high latitudes of the summer hemisphere, which until recently has been the southern hemisphere. We predict that in the northern polar region, prominent clouds will form within about two (Earth) years and lake levels will rise over the next fifteen years.

Features of the middle- and low-latitude ionosphere during solar minimum as revealed from COSMIC radio occultation measurements

In this study, the ionospheric electron density profiles retrieved from radio occultation measurements of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) mission are analyzed to determine the F-2 layer maximum electron density (NmF2), peak height (h(m)F(2)), and Chapman scale height (H-m). During the deep solar minimum of 2008-2009, NmF2, h(m)F(2), and H-m show complicated seasonal variations, which are generally consistent with those in previous solar minima. Besides the equinoctial asymmetry, nonseasonal and semiannual anomalies are present in daytime NmF2; the Weddell Sea anomaly appears in nighttime NmF2 in all seasons except the June solstice. Unusually higher values of h(m)F(2) and H-m appear at southern middle latitudes in the region centered at 70 degrees E in the daytime and h(m)F(2) at 70 degrees W in the nighttime. Wave-like longitudinal patterns are evidently present at low latitudes in all three parameters, showing diurnal and seasonal nature. The values of the parameters under study are smaller in 2008-2009 than the rest of the COSMIC period examined in this study. The seasonal and latitudinal pattern of daytime NmF2 on the solar sensitivity not only confirms our earlier investigation but also explains the observed small NmF2 in 2008-2009 in response to the reduced solar extreme ultraviolet radiance.