Austral Winter Research Articles

Impact of Early Winter Antarctic Sea Ice Reduction on Antarctic Stratospheric Polar Vortex

AbstractThe impact of Antarctic sea ice reduction during early austral winter on the austral winter Antarctic stratospheric polar vortex is investigated using reanalysis data set and model simulations. Both reanalysis data set and model simulations show that the reduction of Antarctic sea ice during early austral winter leads to a northward displacement of the tropospheric mid‐latitude jet, resembling the negative phase of the Southern Annular Mode. Meanwhile, the reduction of sea ice induces a weaker Antarctic stratospheric polar vortex during winter, which is accompanied by a weaker polar night jet. Further analysis indicates that the Antarctic sea ice reduction could lead to a greater excitation of Rossby waves and significant positive geopotential height anomalies over the Antarctic continent. The zonal wave 1 and 2 components of geopotential height anomalies are in phase with the climatology, corresponding to enhanced upward propagation of wave activity flux in early austral winter. Meanwhile, the reduction of sea ice in early austral winter could result in a more favorable atmospheric environment for the propagation of planetary waves into the stratosphere. These processes ultimately weaken the Antarctic stratospheric polar vortex and the polar night jet in winter. The reduction of sea ice in the Amundsen Sea sector enhances the upward propagation of planetary wave, while the reduction of sea ice in the Indian Ocean sector has the opposite effect.

Processes and microorganisms driving nitrous oxide production in the Benguela Upwelling System

AbstractUpwelling systems and their associated oxygen deficient zones (ODZs) are hotspots of nitrous oxide (N2O) production in the ocean. The Benguela Upwelling System (BUS) is a highly productive region and an important, yet variable source of N2O to the atmosphere. This study examined underlying processes and microbial key players governing N2O production in the BUS during the austral winter. 15N‐tracer incubation experiments were conducted to track N2O production from NH4+ oxidation and denitrification. N2O production and consumption mechanisms over a longer temporal scale were determined through natural‐abundance isotope analyses. Metagenomics and 16S rRNA gene amplicon sequencing were used to identify potential key prokaryotes driving N2O production. Our results showed that, compared with permanent ODZs, the BUS is characterized by a higher oxidative and a lower reductive N2O production, both of which exhibit substantial spatial variability. N2O production peaked in low‐oxygen (O2) waters, with nearly equal contributions of oxidative and reductive processes, suggesting their co‐occurrence across an O2 concentration range broader than previously thought. However, the observed N2O isotope signatures implied a legacy of recent and extensive N2O reduction to N2. Metagenomic and 16S rRNA gene data identified denitrifiers belonging to Thioglobaceae and the archaeal ammonia‐oxidizers Nitrosopumilaceae among the potential key drivers of N2O production. Our study provides a comprehensive picture of N2O production in the BUS, revealing significant variability in the N‐cycling regime and underlying N2O production mechanisms, and demonstrating the value of combining direct rate measurements with more integrative approaches, such as molecular omics and natural‐abundance stable isotope tracers.

The Responses of Antarctic Sea Ice and Overturning Cells to Meridional Wind Forcing

Abstract Meridional winds over the seasonal ice zone of the Antarctic have undergone changes and likely contributed to sea ice extent variability in recent decades. In this study, using observations and an eddy-resolving channel model of the Antarctic seasonal ice zone, we investigate the influence of meridional wind changes on the sea ice distribution and document how the underlying ocean might change. We find that southerly wind anomalies in austral winter lead to an increase in sea ice extent by encouraging equatorward sea ice drift. This results in more leads and polynyas, ice production, and buoyancy loss near the coastal region and freshening out in the open ocean near the Antarctic Circumpolar Current. In contrast, summertime southerly wind anomalies reduce sea ice extent due to warming anomalies near the sea ice edge. This is a consequence of enhanced meridional overturning circulation (MOC) triggered by enhanced buoyancy loss through surface heat flux and brine rejection, which brings relatively warm water toward the summertime sea ice edge. A water-mass transformation analysis reveals the increased bottom water formation caused by brine rejection and heat loss in leads and polynyas. Changes in sea ice extent and MOC behave in the opposite way when the sign of the wind anomaly is switched from southerly to northerly. Our study shows that meridional wind anomalies can modify not only the sea ice distribution, extent of polynyas, and air–sea buoyancy fluxes but also the ocean’s MOC and bottom water properties.

The Combined and Isolated Impacts of El Niño and Positive Indian Ocean Dipole Events on South American Precipitation During Austral Winter and Spring Depending on the Atlantic Multidecadal Oscillation Phases

ABSTRACTThe isolated/combined impacts of the positive Indian Ocean Dipole (pIOD) and El Niño (EN) events on precipitation in South America (SA) were investigated during austral winter and spring for the 1901–2012 period, considering both Atlantic Multidecadal Oscillation (AMO) phases. Under the warm phase (WAMO), EN events are well characterised in winter and, in spring, are accompanied by anomalous warming of the Tropical North Atlantic (TNA); thus, variations in the Walker circulation and the northward shifted Intertropical Convergence Zone (ITCZ) reduce precipitation over northern SA. In the cold AMO phase (CAMO), EN events are weak in winter. At the same time, an intense cooling in the equatorial North Atlantic, favoured by the CAMO, enhances moisture transport from the Amazon to central and southeastern Brazil, increasing precipitation in the South Atlantic Convergence Zone region. As EN develops in spring, the anticyclone off the east coast of SA associated with the Pacific‐South American (PSA) pattern decreases (increases) precipitation in central (southeastern) SA. The pIOD events predominantly occur during WAMO phase, when warming in the TNA is favoured by AMO. In winter, the moisture transport to northern SA is weakened, and the ITCZ remains northward shifted, inhibiting the precipitation over northeastern Brazil and southeastern Amazon. In spring, pIOD intensified ascending motions in equatorial Atlantic, increasing precipitation over northeastern Brazil. A wave train from the Indian Ocean strengthens the South Atlantic subtropical high, suppressing precipitation in central and eastern SA. EN‐pIOD events are well established in both AMO phases, though the sea surface temperature anomalies in the TNA depend on the AMO. During WAMO, reduced precipitation in western Amazon and northeastern SA is influenced by the Walker circulation, while in CAMO, TNA cooling enhances moisture transport from the Amazon into southeastern SA, where the PSA pattern and wave train from the Indian Ocean increase precipitation.

Interannual Variability and Trends in Extreme Precipitation in Dronning Maud Land, East Antarctica

This study examines the trends and interannual variability of extreme precipitation in Antarctica, using six decades (1963–2023) of daily precipitation data from Russia’s Novolazarevskaya Station in East Antarctica. The results reveal declining trends in both the annual number of extreme precipitation days and the total amount of extreme precipitation, as well as a decreasing ratio of extreme to total annual precipitation. These trends are linked to changes in northward water vapor flux and enhanced downward atmospheric motion. The synoptic pattern driving extreme precipitation events is characterized by a dipole of negative and positive height anomalies to the west and east of the station, respectively, which directs southward water vapor flux into the region. Interannual variability in extreme precipitation days shows a significant correlation with the Niño 3.4 index during the austral winter semester (May–October). This relationship, weak before 1992, strengthened significantly afterward due to shifting wave patterns induced by tropical Pacific sea surface temperature anomalies. These findings shed light on how large-scale atmospheric circulation and tropical-extratropical teleconnections shape Antarctic precipitation patterns, with potential implications for ice sheet stability and regional climate variability.

Seasonal Mixed Layer Temperature in the Congolese Upwelling System

AbstractThe Congolese upwelling system (CoUS), located along the West African coast north of the Congo River, is one of the most productive and least studied systems in the Gulf of Guinea. The minimum sea surface temperature in the CoUS occurs in austral winter, when the winds are weak and not particularly favorable to coastal upwelling. Here, for the first time, we use a high‐resolution regional ocean model to identify the key atmospheric and oceanic processes that control the seasonal evolution of the mixed layer temperature in a 1°‐wide coastal band from 6°S to 4°S. The model is in good agreement with observations on seasonal timescales, and in particular, it realistically reproduces the signature of the surface upwelling during the austral winter, the shallow mixed layer due to salinity stratification, and the signature of coastal wave propagation. The analysis of the mixed layer heat budget for the year 2016 reveals a competition between warming by air‐sea fluxes, dominated by the incoming shortwave radiation throughout the year, and cooling by vertical mixing at the base of the mixed layer, as other tendency terms remain weak. The seasonal cooling is induced by vertical mixing, where local wind‐driven dynamics play a secondary role compared to subsurface processes. A subsurface analysis shows that remotely forced coastal‐trapped waves raise the thermocline from April to August, which strengthens the vertical temperature gradient at the base of the mixed layer and leads to the mixing‐induced seasonal cooling in the Congolese upwelling system.

The decomposition process in two restricted access environments in a temperate climate: Hard-covered suitcases and wheeled bins.

The succession, development, and behavior of necrophagous insects on decomposing remains are used by forensic entomologists to estimate the minimum post-mortem interval (minPMI). Carcasses are often recovered from concealed environments, such as burials, wrapping, suitcases and waste bins, where they are protected from abiotic and biotic factors, including carrion fauna. The present study represents the first comprehensive research on concealed environments in Australia. Stillborn piglets (Sus scrofa domesticus L.) placed in hard-covered suitcases (N = 40, restricted access) and wheeled bins (N = 20, partially restricted access) were compared with controls (N = 5, exposed) placed on the soil surface, over a period of 164 days (Austral winter to spring). The analysis compared the decomposition process patterns and considered the insect assemblages colonizing the carcasses in each concealment type and the controls. Results show that 1) insects were attracted to the control carcasses within hours of placement in the field (Day 1, D1), followed by wheeled bin carcasses (D3) and suitcase carcasses (D4); 2) carcasses reached skeletonization on D65 (exposed), D108 (wheeled bin) and D136 (suitcase); 3) the assemblages of necrophagous insect species were different between the exposed and the concealed carcasses; 4) blowflies (Diptera: Calliphoridae) were the most prevalent insects colonizing the controls and wheeled bins, while coffin flies (Diptera: Phoridae) were the most prevalent in the suitcases, with some colonized by black soldier flies (Diptera: Stratyiomiidae). The results of this research contribute to the understanding of decomposition processes and insect activity in restricted access environments and help provide a more accurate estimation of the minPMI in forensic cases.

Preliminary Evaluation of a Numerical System of Prediction for Surface Solar Irradiance and Cloudiness in a Site with a Subtropical Humid Climate

This study explores a prediction system for global horizontal irradiance and cloudiness in a humid subtropical terrestrial region. This system consists of regional simulations performed with the Weather Research and Forecasting model using the initial and boundary conditions from the Global Forecast System. The predictions show significant biases for the variable of interest, with notable variations within the daily and annual cycles. This study also finds significant biases in cloud incidence and clarity index predictions, with relevant diurnal and seasonal variations. During austral summer, multiplying the relative humidity of initial and boundary conditions by a fixed factor improves the forecasts of global horizontal irradiance and cloud incidence for the central hours of the day and the afternoon. During austral winter, an empirical correction of the clarity index obtained from the simulation’s outputs also shows the potential to improve the forecasts’ biases. This work proposes a hypothesis about the causes of the forecast biases.

Analysis of the Ocean–Atmosphere Interface in the Brazil Current Region

ABSTRACTThe Brazil current (BC) is a westerly current that flows south along the Brazilian coast, being part of the Southern Brazilian Continental Shelf (SBCS). Recent studies have indicated a trend towards intensification and a shift to the south of the region where this current predominates. We analysed the seasonality of the relationship between atmospheric variables and sea surface temperature (SST) with potential trends and changes in the spatio‐temporal pattern of these variables from 1980 to 2020 over the BCs area in the South Atlantic Ocean. For this purpose, monthly data on SST, air temperature at 2 m above the surface (T2M), mean sea level pressure (MSLP), zonal wind (U10) and meridional wind (V10), obtained from ERA5 reanalysis, were used. Descriptive statistical analyses, trends using the Mann‐Kendall test, correlation matrices and Pettitt's test revealed a significant spatial correlation between the variables, with temporal trends of variation, especially over the BCs area. The meridional (zonal) wind predominantly exhibited a north–south (west–east) direction, supporting the hypothesis that the study region was displaced. Additionally, statistically significant positive trends were observed for SST (0.02°C ∙ dec−1 in austral autumn, winter and spring and 0.01°C ∙ dec−1 in austral summer), T2M (0.02°C ∙ dec−1 in austral winter and spring), MSLP (0.05°C ∙ dec−1 in austral autumn) and negative for U10 (−0.01°C ∙ dec−1 in austral spring). Pettitt's test results confirm significant changes in the behaviour of most analysed variables from the late 1990s to the early 2000s. The post‐breakpoint periods of the variables consistently showed above‐average values compared to the pre‐breakpoint periods, supporting positive upward trends consistent with literature findings. In particular, they highlight the notable upward slope in SST in the BC region.

Spatial variability of cold waves over Southern Africa and their potential physical mechanisms

Abstract Despite significant evidence of global warming, cold waves still happen occasionally and are of great concern in regions such as Southern Africa. They are associated with negative impacts such as loss of lives, destruction of infrastructure, loss of crops, livestock and high peak demand of electricity consumption. In this study, we examine the cold wave characteristics over the southern African region for the extended austral winter (May to September) over the 1979-2021 period, using reanalysis products. Principal Component Analysis (PCA) was performed on the cold waves to extract their dominant modes. Linear regression, Spearman rank correlation as well as lagged correlations were employed to find the links between the cold wave characteristics and different climate drives. Results from the study reveal that the lowest nighttime temperatures are found in interior South Africa and Lesotho. There is a decreasing trend in terms of the number of cold wave events over southern Africa, especially north of latitude 15˚S. Local and remote seasonal sea surface temperatures have the potential to change the likelihood of cold wave characteristics over Southern Africa. Also, seasonal mean circulation results contain seasonal mean ridge/trough structures, which suggests the role of these synoptic features and cold fronts in modulating cold waves over Southern Africa. A future study is needed to analyze the impact of these climate drivers at daily and intraseasonal timescales. There is moderate to high lead correlation between El Ninõ Southern Oscillation (ENSO) and some of the cold wave characteristics, hence ENSO, sea surface temperatures surrounding Southern Africa are good indicators for predicting cold waves over the region. Findings from this study can be useful in improving weather and climate forecasting over the region. Also, these results can support local authorities and communities at risk in developing early actions for tackling cold waves.

The Winter Foehn Footprint Across McMurdo Dry Valleys of Antarctica Using a Satellite‐Derived Data Set‐AntAir v1.0

AbstractContinental‐scale mosaics of satellite‐based surface brightness temperature from thermal infrared band measurements and derived near‐surface air temperatures from geostatistical modeling provide new opportunities for understanding wintertime Foehn wind warming and its potential impacts on the valley floor warming. We have detected and assessed Foehn signatures using a combined data analysis approach from previously developed and validated Antarctic‐wide near‐surface Air temperature data set (AntAir), automatic weather stations from the McMurdo Dry Valleys, and regional climate model simulations at 10 km spatial grid resolution. Self‐organizing maps and data compositing methods on regional climate model outputs provided meteorological context for the AntAir‐derived surface climate information. We conclude that AntAir is suitable for surface climatological analyses and improvements are underway to enhance the spatial resolution to sub‐kilometer grid scales. Finally, by applying a Foehn detection algorithm over 13 years, we present the spatial climatological footprints of Foehn‐induced warming across the Dry Valleys of Antarctica for the first time over the austral winters.

Exploring Sources of Gravity Waves in the Southern Winter Stratosphere Using 3‐D Satellite Observations and Backward Ray‐Tracing

AbstractDuring austral winter, the southern high latitudes has some of the most intense stratospheric gravity wave (GW) activity globally. However, producing accurate representations of GW dynamics in this region in numerical models has proved exceptionally challenging. One reason for this is that questions remain regarding the relative contributions of orographic and non‐orographic sources of GWs here. We use three‐dimensional (3‐D) satellite GW observations from the Atmospheric Infrared Sounder in austral winter 2012 in combination with the Gravity‐wave Regional Or Global Ray Tracer to backward trace GW rays to their sources. We trace over 14.2 million rays, through ERA5 reanalysis background atmosphere, to their lower atmospheric sources. We find that GWs observed thousands of km downstream can be traced back to key orographic regions, and that on average, all waves (orographic and non‐orographic) converge meridionally over the Southern Ocean. We estimate that across this winter, orographic sources contribute around 5%–35% to the total momentum flux (MF) observed near 60S. The remaining proportion consists of waves from non‐orographic sources, which although typically carry lower MF, the large spatial extent of non‐orographic sources leads to a higher overall contribution. We also quantify the proportion of MF traced back to different regions across the whole southern high latitudes area in order to measure the relative importance of these different regions. These results provide the important insights needed to advance our knowledge of the atmospheric momentum budget in the southern high latitudes.

Early‐Stage Extratropical Cyclones' Mechanisms Over South America: RCM Added Value and Future Changes in a Warmer Planet

ABSTRACTRegional climate models (RCMs) from the CORDEX enable further investigations of the regional aspects of climate change impacts in South America. Here, we assess the CORDEX‐RCMs' present and future projections of extratropical cyclones, focusing on their frequency, early‐stage synoptic features, and added value relative to the global climate models (GCMs). Cyclones were tracked using a common algorithm in the present (1985–2005) and future RCP8.5 scenarios (2080–2099). ERA5 reanalysis was used as reference data in the present climate. Both GCMs and RCMs can identify the three major cyclone hot spots in South America: Argentina (ARG), La Plata Basin (LPB), and the south‐southeast Brazilian coast (SBR). RCMs improve GCMs' representation of the cyclogenesis frequency, adding value by decreasing the biases (~10%). Early‐stage cyclone synoptic structure also indicates RCMs' improvement of the low‐level fields by presenting mesoscale structures of warm/cold advection and moisture flux convergence/divergence in greater agreement with ERA5 (except for moisture flux divergence for LPB). RCMs and GCMs project a general decrease in cyclogenesis for the end of the century. For the cyclogenesis cores, GCMs' and RCMs' projections agree on the trend signals in SBR, LPB, and ARG in austral winter and disagree in ARG in austral summer. For LPB and SBR cyclogenesis, the RCMs and GCMs suggest a future increase in moisture flux convergence and warm advection at low levels, while a decrease in upper level divergence is projected. This indicates a reinforcement of cyclogenesis (negative sea‐level pressure trend) in the future due to the low‐level features and associated diabatic processes. For ARG, the future trends in the mean structure of cyclogenesis are relatively weak. Following other studies, cyclogenesis frequency may decrease; however, changes could occur in some important physical processes, such as low‐level moisture flux convergence and warm advection, suggesting more intense events in the future.

The Cyclic and Episodic Transition of Strong El Niño and Implications for South American Precipitation During Their Peak and Decay Stages

ABSTRACTThe mechanisms associated with the transitions of strong El Niño (EN) events and their implications for the South American precipitation were investigated for the 1950–2023 period. Strong EN events exhibit cyclic or episodic characteristics in their transitions. Cyclic EN events are both preceded and followed by La Niña (LN) conditions, whereas episodic EN events are preceded by neutral conditions, with a more uncertain transition following. For cyclic EN, tropical Pacific mechanisms initiates and peak warming in the eastern tropical Pacific from austral winter to early summer. In contrast, for episodic EN, coupled subtropical and tropical Pacific mechanisms, respectively, initiate and peak warming in the central tropical Pacific from autumn to late summer. The Pacific Decadal Oscillation (PDO) mean state modulates EN's decay stage. During the +PDO mean state, cyclones in the eastern subtropical Pacific of both hemispheres sustain the warming of episodic EN, whereas during the −PDO mean state, anticyclones in the eastern subtropical Pacific accelerate the decay of cyclic EN, favouring its transition to an LN. These mechanisms explain why episodic EN initiates earlier, peaks later, is more intense and decays more slowly than cyclic EN. During an episodic EN summer, the strengthened atmospheric circulation maintains the Atlantic Intertropical Convergence Zone (ITCZ) north of the equator, causing persistent negative precipitation anomalies in north–northeastern South America (SA) until the following winter, while positive precipitation anomalies in southeastern SA are driven by south–southeastward moisture transport from equatorial Atlantic. Conversely, during a cyclic EN summer, negative (positive) precipitation anomalies impact north–northwestern (southeastern) SA; however, the anomalous atmospheric circulation and precipitation in SA quickly return to normal conditions in the autumn, and positive precipitation anomalies appear in northern SA in the following winter. Understanding these mechanisms is crucial for predicting EN's future changes and, consequently, their potential socio‐economic impacts globally.

A Multimarker Approach to Identify Microbial Bioindicators for Coral Reef Health Monitoring—Case Study in La Réunion Island

The marine microbiome arouses an increasing interest, aimed at better understanding coral reef biodiversity, coral resilience, and identifying bioindicators of ecosystem health. The present study is a microbiome mining of three environmentally contrasted sites along the Hermitage fringing reef of La Réunion Island (Western Indian Ocean). This mining aims to identify bioindicators of reef health to assist managers in preserving the fringing reefs of La Réunion. The watersheds of the fringing reefs are small, steeply sloped, and are impacted by human activities with significant land use changes and hydrological modifications along the coast and up to mid-altitudes. Sediment, seawater, and coral rubble were sampled in austral summer and winter at each site. For each compartment, bacterial, fungal, microalgal, and protist communities were characterized by high throughput DNA sequencing methodology. Results show that the reef microbiome composition varied greatly with seasons and reef compartments, but variations were different among targeted markers. No significant variation among sites was observed. Relevant bioindicators were highlighted per taxonomic groups such as the Firmicutes:Bacteroidota ratio (8.4%:7.0%), the genera Vibrio (25.2%) and Photobacterium (12.5%) dominating bacteria; the Ascomycota:Basidiomycota ratio (63.1%:36.1%), the genera Aspergillus (40.9%) and Cladosporium (16.2%) dominating fungi; the genus Ostreobium (81.5%) in Chlorophyta taxon for microalgae; and the groups of Dinoflagellata (63.3%) and Diatomea (22.6%) within the protista comprising two dominant genera: Symbiodinium (41.7%) and Pelagodinium (27.8%). This study highlights that the identified bioindicators, mainly in seawater and sediment reef compartments, could be targeted by reef conservation stakeholders to better monitor La Réunion Island’s reef state of health and to improve management plans.

Cross-Seasonal Effect on Tropical Pacific Precipitation: Implication of South Pacific Quadrupole Simulation in CMIP6

Abstract The tropical Pacific convergence zone plays a crucial role in the global climate system. Previous research studies emphasized the cross-seasonal influence of the South Pacific quadrupole (SPQ) mode on the tropical Pacific climate. This study assesses the relationship between austral summer SPQ and austral winter tropical precipitation in phase 6 of the Coupled Model Intercomparison Project (CMIP6) models. The analysis emphasizes the historical experiments conducted within this time frame, spanning from 1979 to 2014. Our findings reveal that the SPQ is accurately represented in all CMIP6 models, but the connection between SPQ and precipitation is inadequately simulated in most models. To investigate the reasons behind these intermodel differences in reproducing SPQ-related processes, we categorize models into two groups. The comparisons demonstrate that the fidelity of model simulations in replicating the SPQ–tropical precipitation relationship hinges significantly on their capacity to reproduce the positive wind–evaporation–sea surface temperature (WES; SST) feedback over both the southwestern Pacific (25°–10°S; 150°E–160°W) and the southeastern Pacific (30°–10°S; 140°–80°W). This positive WES feedback propagates the SPQ signal into the tropics, intensifying the meridional gradient of SST anomaly in the tropical western-central Pacific, which consequently amplifies convection and rainfall in that area. In the group of models that failed to simulate this relationship accurately, the weakened WES feedback can be traced back to biases in wind speed and its variation. Furthermore, this WES feedback establishes a connection between SPQ and El Niño–Southern Oscillation (ENSO). A better rendition of the SPQ–tropical rainfall connection tends to result in a better simulation of the onset of SPQ-related ENSO events. As a result, this study advances our comprehension of extratropical impacts on the tropics, with the potential to enhance the accuracy of tropical climate simulation and prediction. Significance Statement Tropical rainfall plays an important role in the global climate system. Beyond the well-known influence of El Niño–Southern Oscillation (ENSO) on the tropical rainfall, the sea surface temperature (SST) anomaly in the South Pacific has a cross-seasonal impact on the precipitation over the tropical Pacific via air–sea coupled processes. Such SST anomaly pattern shows a quadrupole structure in the extratropical South Pacific, known as the South Pacific quadrupole (SPQ) mode. However, the relationship between SPQ and tropical precipitation remains poorly simulated in most state-of-the-art climate models. One primary reason for this gap between observed and simulated relationships is the underestimation of wind speed and its variation over the south tropical Pacific in these models. This limitation undermines their ability to accurately represent the air–sea interactions that drive tropical precipitation patterns, leading to inaccuracies in simulations. Our study aims to bridge this knowledge gap by enhancing our understanding of the extratropical effects on the tropical Pacific. By exploring the mechanisms underlying the SPQ–precipitation connection, we expect to improve the simulation and prediction capabilities of tropical climate models, thereby enhancing our ability to forecast and adapt to future climatic changes.

An integrated multi-omics analysis identifies novel regulators of circadian rhythm and sleep disruptions under unique light environment in Antarctica.

Light is the dominant zeitgeber for biological clocks, and its regulatory mechanism for sleep-wake activity has been extensively studied. However, the molecular pathways through which the unique Antarctic light environment, with polar days in summer and polar nights in winter, affects human sleep and circadian rhythm remain largely unidentified, although previous studies have observed delayed circadian rhythm and sleep disruptions among expeditioners during polar nights. In this study, we conducted comprehensive dynamic research on the expeditioners residing in Antarctica for over one year. By integrating the phenotypic changes with multi-omics data, we tried to identify the novel candidate regulators and their correlation networks involved in circadian and sleep disorders under abnormal light exposure. We found that during the austral winter, expeditioners exhibited delayed bedtime and getting up time, reduced sleep efficiency, and increased sleep fragmentation. Meanwhile, serum dopamine metabolite levels significantly increased, while serotonin metabolites and antioxidants decreased. These changes were accompanied by altered expression of genes and proteins associated with neural functions, cellular activities, transcriptional regulation, and so on. Through the correlation and causal mediation analysis, we identified several potential pathways modulating human sleep-wake activity, involving genes and proteins related to neural function, glucose metabolism, extracellular matrix homeostasis, and some uncharacterized lncRNAs. Based on the identified causal mediators, LASSO regression analysis further revealed a novel candidate gene, Shisa Family Member 8 (SHISA8), as a potential key regulatory hub in this process. These findings shed light on the probable molecular mechanisms of sleep disorders in Antarctica and suggest SHISA8 as a novel candidate target for medical intervention in sleep disorders under unique light environments.

Understanding the drivers and predictability of record low Antarctic sea ice in austral winter 2023

Since the start of the satellite record in 1978, the three lowest summertime minima in Antarctic sea ice area all occurred within the last seven years and culminated in record low sea ice in austral winter 2023. During this period sea ice area was over 2 million km2 below climatology, a 5 sigma anomaly and 0.9 million km2 below the previous largest seasonal anomaly. Here we show that a fully-coupled Earth System Model nudged to observed winds reproduces the record low, and that the 2023 transition from La Niña to El Niño had minimal impact. Using an ensemble, we demonstrate that ~ 70% of the anomaly was predictable six months in advance and driven by warm Southern Ocean conditions that developed prior to 2023, with the remaining ~ 30% attributable to 2023 atmospheric circulation. An ensemble forecast correctly predicted that near record low sea ice would persist in austral winter 2024, due to persistent warm Southern Ocean conditions.

Strength and timing of austral winter Angolan coastal upwelling

The tropical Angolan upwelling system (tAUS) is a highly productive ecosystem of great socio-economic importance. Productivity peaks in austral winter and is linked to the passage of remotely forced upwelling coastal trapped waves (CTWs), where the strength of the productivity peak is associated with the amplitude of the upwelling CTW. Here, we analyze the year-to-year variability in the timing and amplitude of the austral winter upwelling CTW by examining sea surface temperature, sea level anomaly, and wind fields. Our results show that the timing of the CTW is influenced by variability in the equatorial region and along the southern African coast. Weaker equatorial easterlies from April to July delay the generation of the upwelling Kelvin wave, leading to a later arrival of the upwelling CTW. In contrast, the amplitude of the CTW is primarily influenced by variability in the eastern equatorial Atlantic and the central South Atlantic, where the South Atlantic Anticyclone is located. A cooling in the eastern equatorial Atlantic three to four months before the arrival of the CTW causes stronger zonal winds, ultimately leading to a stronger austral winter upwelling CTW. Our results suggest that the timing and amplitude of the upwelling CTW in the tAUS during austral winter are predictable on seasonal time scales.

Tropical teleconnections through the Amundsen Sea Low impact Antarctic toothfish recruitment within the Ross Gyre

Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region are believed to spawn predominantly in the northern parts of the Ross Gyre during the austral winter with fluctuations in their recruitment observed. This Lagrangian modelling study attempts to explain these fluctuations and shows how sea-ice drift impacts the buoyant eggs and the overall recruitment of juveniles reaching the Amundsen shelf break. Interannual variations in the Amundsen Sea Low, linked to tropical sea surface temperatures, cause modulations in the sea-ice drift and subsequent recruitment. When the Amundsen Sea Low is weaker, consistent with El Niño conditions, the northward sea-ice drift reduces, and more eggs remain within the Ross Gyre leading to a larger recruitment success. Conversely, recruitment success reduces during La Niña conditions. The sea-ice drift may explain about 80% of the interannual Antarctic toothfish recruitment variability over the period 1975–2016 and is of particular importance during the first year after spawning. These results enable future interannual changes in Antarctic toothfish recruitment success based on remote observations to be anticipated. Our findings suggest that ongoing climate change strengthening of the Amundsen Sea Low, will likely contribute to a long-term toothfish recruitment decline in the Ross Gyre region.