Explore the vast range of titles available.

Drake Passage is a key region for transport between the surface and interior ocean, but a mechanistic understanding of this exchange remains immature. Here, we present wintertime, submesoscale‐resolving hydrographic transects spanning the southern boundary of the Antarctic Circumpolar Current and the Polar Front (PF). Despite the strong surface wind and buoyancy forcing, a freshwater lens suppresses surface‐interior exchange south of the PF; ventilation is instead localized to the PF. Multiple lines of the analysis suggest submesoscale processes contribute to ventilation at the PF, including small‐scale, O(10 km), frontal structure in water mass properties below the mixed layer and modulation of a surface eddy diffusivity at sub‐50 km scales. These results show that ventilation is sensitive to both submesoscale properties near fronts and non‐local processes, for example, sea‐ice melt, that set stratification and mixed layer properties. This highlights the need for adaptive observing strategies to constrain Southern Ocean heat and carbon budgets. Plain Language Summary Drake Passage is a region of the Southern Ocean between the southern tip of South America and the Antarctic Peninsula. Due to its relative accessibility as compared to the rest of the polar ocean, it is the most frequently occupied region of the Southern Ocean. Most occupations by ships in Drake Passage acquire measurements at 20–100 km spacing or “mesoscale” resolution. Here, we present data collected by piloted robotic underwater vehicles that sampled across the southern section of Drake Passage with submesoscale, or 1–10 km, resolution in wintertime. These novel observations indicate that while the southernmost region of Drake Passage is strongly stratified in density, the Polar Front (PF), one of the major dynamical features of the Southern Ocean, is more weakly stratified. The reduced stratification at the PF presents a pathway for the localized exchange of water between the surface and interior ocean. In addition, this study finds that the PF is eddy‐suppressing, meaning that the mean flow of the PF can transport oceanic properties away before they can be stirred. These findings have implications for the estimation of carbon fluxes between the atmosphere and the Southern Ocean, a vital part of the climate system. Key Points High‐resolution hydrographic sections across the Drake Passage provide insight into spatial variability in surface‐interior exchange Wintertime observations suggest ventilation is spatially localized to the Polar Front and influenced by submesoscale processes A mixing length estimate shows modulation at submesoscales and mixing suppression in the upper layers of the Polar Front

This study reveals a marked enhancement in the relationship between the variations in location of the winter East Asian Polar Front Jet (EAPJ) and the surface air temperature (SAT) in Eurasia since the mid-1990s. Before the mid-1990s, an evident wave train related to the meridional location of the EAPJ exhibited an anticyclonic anomaly over northern Europe and a cyclonic anomaly in northwestern Asia. With an equatorward shift of the EAPJ after the mid-1990s, the wave train experiences a notable adjustment that is conducive to East Asian cooling, displaying an anticyclonic anomaly around the Kara-Laptev Seas and a cyclonic anomaly near northeastern Asia. Arctic warming anomalies and sea ice loss contributed significantly to these decadal changes. Simulation experiments forced by observed Arctic sea-ice variability further confirm this result. Since the mid-1990s, Arctic sea ice loss (or Arctic warming anomaly) has contributed to a reduction in westerly winds in high latitudes by modulating the meridional temperature gradient. The deaccelerated winds intensify the Arctic cold air propagating to the south, enhancing the atmospheric baroclinicity and the westerly flow in the upper level at the south side of the EAPJ, favoring the southward shift of the EAPJ. With the equatorward shift of the EAPJ, the corresponding SAT anomalies in East Asia are more salient.

The upper-level jet stream is a critical element of atmospheric circulation, driving synoptic systems and extreme weather events. This study analyzes the impact of upper-level jets on South American (SA) summer temperature and precipitation under different El Niño-Southern Oscillation (ENSO) phases. Using the ERA5 reanalysis dataset from 1979 to 2022, we perform a daily multiparametric characterization of the jet stream, considering its spatial and temporal discontinuities. Besides latitude and intensity, we find that the departure and number of branches of the subtropical jet (STJ) and the longitudinal extent of the Pacific branch of the polar front jet (PFJ) are needed for their description. An additional parameter is required to characterize the STJ due to its absence on around 40% of summer days over SA. Moreover, we observe distinct long-term changes in PFJ parameters across different ocean basins. Three synoptic weather types (WTs) of the upper-level zonal wind are identified: normal conditions, a prominent STJ pattern, and a PFJ-only pattern. The latter pattern is associated with anticyclonic anomalies at 500 hPa in the South Atlantic Ocean and an active SA Convergence Zone, which favors clear skies and warm (wet and cold) conditions in southern SA (Brazil). Consistently, the probability of experiencing warm spells in central Argentina is increased more than twofold. Finally, we detect that the temperature anomalies associated with the WTs are independent of the ENSO phase. However, ENSO modulates the frequency of the WTs: during La Niña (El Niño), the PFJ-only (prominent STJ) pattern is more common.

This study investigates seasonal variations and influencing factors on the Deep Chlorophyll Maximum (DCM) in the Subtropical Front (STF) and Polar Front (PF) regions of the Indian Sector within the Southern Ocean, utilizing Bio-Argo floats data. Our analysis reveals distinct seasonal and regional patterns in salinity, temperature, and DCM dynamics. The STF region, characterized by warmer, saltier waters and a shallower Mixed Layer Depth (MLD), facilitates stronger stratification and nutrient retention, resulting in an enhanced DCM of 1.55 mg/m 3 . In contrast, the PF’s colder, fresher waters exhibit deeper MLDs and reduced stratification, leading to lower mean DCM concentrations of 0.88 mg/m 3 . The depth of the DCM increased along this gradient, deepening from a median of 42 m at the STF to 78 m at the PF. We identify a robust correlation between DCM, Photosynthetically Active Radiation (PAR), and MLD, highlighting how environmental conditions profoundly influence DCM and its depth in these critical oceanic zones. This study shows that the DCM is present year-round in the STF, while it exhibits seasonal variability in the PF.

Subseasonal variability of atmospheric circulation in mid-high latitudes is highly correlated to the upper-level jet streams, acting as a major contributor to the global or regional persistent climate anomalies. In this study, the features of subseasonal concurrent variations (SCVs) between East Asian Polar Front Jet (EAPJ) and Subtropical Jet (EASJ), and corresponding atmospheric circulation and temperature anomalies in China are investigated by using the observational data and NCEP/NCAR reanalysis datasets. Results show that the main variability modes of the winter upper-level wind fields on subseasonal time scales are characterized by the meridional shift in opposite directions and out-of-phase variations in the intensity of the EASJ and EAPJ. These concurrent variations between the two jets have a significant oscillation cycle with a period of 10–25 days. Accompanied by the location (intensity) SCV of the two jets, the mid-latitude circulation systems show significant zonal shifts (local intensity changes), resulting in alternations of the atmospheric circulation between zonal and meridional types. The typical meridional circulation is characterized by a strong East Asian trough and its upstream strong high-pressure ridges. Meanwhile, gradient force between Siberian high and the Aleutian low is anomalously strong. As a result, the SCVs between two jets can cause widespread and persistent low temperature anomalies over China, usually lasting more than three days. In the case of the location SCV of the two jets, the low temperature anomalies concentrate in northern China, particularly in north of 40°N. In the case of the intensity SCV of the two jets, the low temperature anomalies occur in most parts of China, notably in south of 40°N. These results are helpful to improve the prediction of atmospheric circulation and temperature anomalies in East Asia during winter.

No other group of animals typifies the uniqueness of Antarctic life more than Pycnogonida (sea spiders), with 20% of all known species found in the Southern Ocean, and 64% of these endemic to the Antarctic. Despite nearly 200 years of research into pycnogonids and other benthic phyla in Antarctica, the parameters which drive the distribution and diversity of benthic fauna are still poorly understood. This study aimed to investigate the diversity and connectivity of pycnogonid communities on either side of the Antarctic Polar Front, with an emphasis on the role of water depth, using an occurrence dataset containing 254 pycnogonid species from 2187 sampling locations. At depths shallower than 1000 m, communities to the north and south of the Antarctic Polar Front were distinct, while below this depth this geographic structure disintegrated. The Polar Front, or the expanse of deep ocean it bisects, seemingly acts as a semipermeable barrier to species exchange between well-sampled shallow communities. The less sampled and less understood deep sea appears to be better connected, with high levels of shared species following the northward flow of Antarctic Bottom Water. The exceptionally high diversity and endemism of Antarctic pycnogonids may reflect an apparent competitive advantage in cold waters which leaves them vulnerable to ongoing ocean warming, with increased competition and predation pressures.

Since the 1980s, rapid Arctic sea ice loss has been observed, and its potential influences on the midlatitude weather and climate have been extensively examined, but strongly debated. This study instead investigates influences of Arctic sea ice loss on the Eastern Hemisphere westerly wind on the poleward side of the polar front jet (PFJ), which has significantly weakened in winter but strengthened in summer since 1980s. Observational analyses indicate that the Eastern Hemisphere PFJ anomalies in winter and summer are strongly correlated with Northern Hemisphere (NH) atmospheric circulation, surface air temperature and precipitation changes, and that the winter PFJ variability is significantly correlated to Barents-Kara sea ice anomalies from autumn and winter at interannual time scales. About 58% of the observed winter PFJ weakened trend during 1979–2014 is congruent with the autumn sea ice index over the Barents-Kara Seas. Atmospheric model ensemble simulations from four models show that Arctic sea ice loss contributes to Arctic warming in winter and reduces the northern Eurasia-pole temperature contrast, leading to an significant weakening winter PFJ. Ensemble mean effects of four models and each model due to Arctic sea ice loss explain about 10–20% of the observed winter PFJ weakening trend, because the model simulations underestimate observed impacts of sea ice reduction on Arctic troposphere warming. In summer, the strengthening PFJ is mostly controlled by increasing greenhouse gases and sea surface temperature changes outside the Arctic, but is little affected by Arctic sea ice loss. Our observational and numerical results consistently suggest that a dynamical pathway linking observed Arctic sea ice loss to northern Eurasian winter is through its weakening effect on the westerly wind on the poleward side of the PFJ.

The variability of the North Atlantic polar front jet stream is crucial in determining summer weather around the North Atlantic basin. Recent extreme summers in western Europe and North America have highlighted the need for greater understanding of this variability, in order to aid seasonal forecasting and mitigate societal, environmental and economic impacts. Here we find that simple linear regression and composite models based on a few predictable factors are able to explain up to 35 % of summertime jet stream speed and latitude variability from 1955 onwards. Sea surface temperature forcings impact predominantly on jet speed, whereas solar and cryospheric forcings appear to influence jet latitude. The cryospheric associations come from the previous autumn, suggesting the survival of an ice-induced signal through the winter season, whereas solar influences lead jet variability by a few years. Regression models covering the earlier part of the twentieth century are much less effective, presumably due to decreased availability of data, and increased uncertainty in observational reanalyses. Wavelet coherence analysis identifies that associations fluctuate over the study period but it is not clear whether this is just internal variability or genuine non-stationarity. Finally we identify areas for future research.

Across the Drake Passage, planktonic ostracods are a significant component of mesozooplankton communities. Thus, the aim of this study was to investigate their composition structure and distribution within the upper 300-m layer in summer 2010. Our study revealed a complex pattern in their assemblages along the south–north transect, which strongly coincides with three distinct hydrographic regimes the transect crossed: the Antarctic Zone (AZ), the Polar Frontal Zone (PFZ), and the Subantarctic Zone (SAZ). Superimposed on this hydrographic zonation was a northward gradient in increasing ostracod abundance. The overall species number was low—just 12 species—but the composition of ostracod assemblages reflected the origin of the water masses well, since the numerically dominant species in the three hydrographic zones were: Alacia hettacra, in the AZ; Discoconchoecia elegans, in the PFZ; and Pseudoconchoecia serrulata, in the SAZ. Although the Passage acts as a physical bottleneck, diverting typically Antarctic waters further north than in other sectors of the Southern Ocean (SO), the distributional ranges of Conchoecia magna, Obtusoecia antarctica, and P. serrulata were observed further south than had previously been reported. A possible explanation for this shift is that the Polar Front position is located further south than in the other Atlantic part of the SO. It is also likely that, in such a narrow passage containing pelagic fauna of various hydrographical zones, even subtle shifts in distribution, including changes in climate, will be observed at first; therefore, our data might constitute important reference material for tracking further zooplankton biogeography in Antarctic waters.

This study investigates the concurrent variations in the location and intensity of the East Asian subtropical jet (EASJ) and polar front jet (EAPJ) with a focus on the relationship between the variations and the atmospheric circulation in the mid-latitude region. The possible mechanisms for the concurrent variations of the EASJ and EAPJ are explored. The wintertime upper-level zonal wind variation over the landmass (50°–100°E) is characterized by two principal modes, i.e., the out-of-phase variations in the intensity and the meridional displacements of the EASJ/EAPJ. The EASJ and EAPJ are intensified (weakened) when they are located close to (far away from) each other, corresponding to a weakened (intensified) East Asian trough over the northern Pacific region and a decreased (increased) geopotential height in the mid-latitude over central Asia. The spatial pattern of 500 hPa geopotential height anomaly is similar to the Eurasian teleconnection pattern, while the pattern of sea level pressure anomaly shows a feature similar to the Arctic oscillation. Analyses of related thermal-dynamical processes indicate that the increased (decreased) diabatic heating and horizontal heat transport lead to a larger (smaller) meridional temperature gradient over the EASJ/EAPJ regions, which subsequently intensifies (weakens) the East Asian jets. Severe (weak) convective activities accompanied with warmer (colder) SST in the tropics also contribute to the intensification (weakening) of the EASJ and EAPJ. Dynamically, the strong (weak) divergence of the eddy vorticity flux along the northern Tibetan Plateau and that of the Eliassen–Palm flux of the synoptic-scale stationary waves are favorable for the intensification (weakening) of zonal winds through the wave-mean flow interactions. As a result, the EASJ and EAPJ are intensified (weakened).