The measurement campaign, known as EXPORT — short for EXperiments with the Portable Observatory for aeRosol Transport — was led by Andebo Waza, Konrad Kandler, Franz Kanngießer, Stephanie Fiedler, and colleagues from institutions including the GEOMAR Helmholtz Center for Ocean Research Kiel and Technische Universität Darmstadt. Expedition M207 departed Belém, Brazil, on January 3, 2025, and concluded in Mindelo, Cabo Verde, on February 11, 2025, tracing a northbound course directly through the dust corridor. Expedition M208 then began and ended in Mindelo, running from February 15 to March 17, 2025, keeping the ship and its instruments close to the African continent where dust outbreaks are most intense. Together, the two cruises captured continuous aerosol and meteorological observations across three distinct, multi-day Saharan dust events: the first over the tropical mid-Atlantic, and the latter two nearer the African coast.

What makes the EXPORT dataset unusual is its combination of ground-based in-situ sampling and remote sensing of lofted dust layers, all from a moving platform in a region where such measurements are rare. At the heart of the in-situ package was an optical particle counter, or OPC, which measured particulate matter concentrations and particle size distributions for diameters up to roughly 35 micrometers — a size range that includes the coarse dust grains responsible for much of the atmospheric dust mass burden. Complementing the optical counts, the team deployed a flat plate sampler to collect deposited particles, which were then analyzed using scanning electron microscopy coupled with energy-dispersive X-ray analysis, or SEM-EDX. This technique allowed the researchers to determine particle size, morphology, and elemental composition, from which they derived deposition rates — a key quantity for estimating how much dust, and the nutrients it carries, actually reaches the ocean surface.

Above the ship, a battery of remote sensing instruments probed the vertical structure of the atmosphere. CALITOO and MICROTOPS sun photometers measured aerosol optical depth at several wavelengths, providing a column-integrated measure of how much sunlight the dust attenuated. A Vaisala CL61 ceilometer recorded fine-scale layering of aerosol plumes, including depolarization measurements that help distinguish irregularly shaped mineral dust particles from spherical marine aerosols such as sea spray. A wind lidar profiled wind speeds aloft, an optical disdrometer characterized precipitation, and a broadband radiation sensor tracked the radiative effects of the dust. Nearly 90 radiosonde launches — balloon-borne instrument packages that profile temperature, humidity, and winds — stitched these observations into a three-dimensional picture of the dust-laden atmosphere.

The scientific stakes are considerable. Saharan dust influences climate in multiple, competing ways: it scatters and absorbs solar radiation, alters cloud formation by serving as ice-nucleating particles, and fertilizes ocean ecosystems with iron and other micronutrients. Yet climate and weather models still struggle to represent dust transport accurately, in part because ground-truth observations over the remote tropical Atlantic are so sparse. Most long-term dust records come from land-based stations in Africa or from satellite retrievals, which infer column properties but cannot resolve the vertical distribution, particle microphysics, or surface deposition directly. Ship-based campaigns like EXPORT fill precisely this gap, offering calibration points for satellites and validation data for reanalysis products and forecast models.

Indeed, the EXPORT team documented their measurements with a first comparison against reanalysis datasets and the METEOR’s own meteorological sensors, an early sanity check that will help future users judge how well existing models capture the observed dust events. The three dust outbreaks sampled during the cruises serve as illustrative case studies: one plume encountered far from any landmass in the tropical mid-Atlantic, and two others observed closer to West Africa, where fresh outbreaks loft dense dust into the Saharan Air Layer — the hot, dry, elevated air current that carries dust across the basin. Comparing in-situ size distributions and concentrations against model output during these events can reveal where models overestimate or underestimate coarse-particle transport, a persistent problem because large dust grains settle out faster than many models assume.

The winter timing of the campaign is itself scientifically meaningful. Between December and March, the Saharan dust belt shifts southward, and dust transport toward the Amazon becomes most pronounced. This seasonal dust delivery is thought to supply phosphorus and other nutrients that sustain the rainforest’s productivity, compensating for losses from leaching and runoff. Capturing this season with direct measurements — rather than extrapolating from other times of year — matters for quantifying the ocean and land fertilization budgets, for understanding how dust radiative forcing modulates the tropical Atlantic energy balance, and for constraining how dust may respond to changing land use and climate in North Africa.

All of the EXPORT datasets are now publicly available through the PANGAEA data repository, spanning optical particle counter measurements, flat plate sampler collections, sun photometer retrievals, Maritime Aerosol Network observations, radiation and ceilometer profiles, radiosonde soundings, wind lidar data, and disdrometer records for both cruises. The ship’s own meteorological data are archived separately through the dship.o2a-data.de portal operated by Universität Hamburg. This open release means that atmospheric modelers, satellite validation teams, and aerosol researchers worldwide can immediately begin mining the data — comparing it against dust reanalyses, testing transport schemes, or refining retrieval algorithms for spaceborne lidars and imagers.

For a field that has long relied on sparse island stations and satellite proxies, a two-month, instrument-dense transect through the heart of the winter dust corridor is a rare and valuable resource. As the preprint moves through peer review at Earth System Science Data, the EXPORT measurements stand ready to sharpen estimates of how much African dust crosses the Atlantic, at what heights, in what particle sizes, and with what consequences for climate, clouds, and ecosystems on both sides of the ocean.

Subject of Research: Trans-Atlantic transport of Saharan mineral dust measured from a research vessel during two 2025 expeditions

Article Title: Trans-Atlantic aerosol transport from January to March 2025 – measurements from two expeditions on a research vessel

Article References: Trans-Atlantic aerosol transport from January to March 2025 – measurements from two expeditions on a research vessel. (n.d.). https://doi.org/10.5194/essd-2026-733

Image Credits: AI Generated

DOI: 10.5194/essd-2026-733

Keywords: Saharan dust, mineral dust, aerosol transport, tropical Atlantic, R/V METEOR, research expedition, aerosol optical depth, ceilometer, radiosondes, SEM-EDX, dust deposition, Earth System Science Data

The team’s central finding is quantitative and unambiguous. Before the early 1980s, only 51.8 percent of mature eastern-pole cooling events went on to develop into a full, two-poled dipole pattern. After the early 1980s, that success rate jumped to 82.1 percent during the period from 1981 to 2023. In other words, over the past four decades, the eastern and western halves of the Indian Ocean have become far more tightly coupled, so that a cooling anomaly near Sumatra is now much more likely to be mirrored by warming near Africa. This is not a trivial bookkeeping detail. The spatial shape of the IOD determines where its climatic fingerprints land, from East African long rains to East Asian summer monsoon rainfall, so knowing whether a dipole will fully form is essential for seasonal prediction.

To understand the mechanism behind this shift, the researchers turned to a mixed-layer heat budget analysis, a diagnostic technique that tracks every major term contributing to temperature change in the upper ocean. Their analysis singled out one player as decisive: the strength of zonal wind anomalies along the equatorial Indian Ocean. When easterly wind anomalies blow from east to west along the equator, they do two things at once. They drive the local Bjerknes feedback that amplifies the dipole by reinforcing the east-west temperature contrast, and, crucially, they trigger downwelling oceanic Rossby waves that propagate westward toward the thermocline ridge region of the western Indian Ocean. These waves deepen the local thermocline, trap warm water in the subsurface, and set the stage for the warm western pole that completes the dipole.

The logic of the mechanism is elegant. Eastern-pole cooling, often initiated by coastal upwelling off Sumatra driven by southeasterly winds, is only the first act of the drama. The second act depends on whether the equatorial easterlies are strong enough to launch the Rossby waves that warm the west. In the decades before the early 1980s, those winds were frequently too weak, so the eastern cooling fizzled into a monopole rather than a dipole. Since the early 1980s, stronger and more persistent easterly anomalies have made the full two-poled pattern the norm rather than the exception. The dipole, in this view, is not a self-contained Indian Ocean phenomenon but the end product of a chain of interactions that spans the entire tropical belt.

So what strengthened the winds? The study points to two remote drivers operating through the tropical atmosphere. The first is the El Niño-Southern Oscillation, the dominant mode of Pacific climate variability. During El Niño events, shifts in deep convection over the Pacific excite atmospheric circulation anomalies that extend across the Maritime Continent into the Indian Ocean basin, a pathway long described in the literature as the atmospheric bridge. After the early 1980s, the linkage between ENSO and the IOD strengthened, meaning that El Niño events more effectively excite the easterly wind anomalies over the equatorial Indian Ocean that are needed to warm the western subsurface. A stronger ENSO handshake, in effect, has been pulling the Indian Ocean’s two poles into tighter synchronization.

The second driver comes from an ocean basin that most people would not suspect: the tropical Atlantic. The researchers found that sea surface temperature anomalies in the tropical North Atlantic influence the winds over the equatorial Indian Ocean through Gill-Matsuno-type atmospheric responses, in which heating or cooling over the Atlantic generates Rossby and Kelvin wave patterns in the atmosphere that reach across Africa and the Indian Ocean. Before the early 1980s, cold sea surface temperature anomalies in the tropical North Atlantic worked in the opposite direction to El Niño, suppressing the easterly wind anomalies over the equatorial Indian Ocean. This suppression inhibited the subsurface warming in the western Indian Ocean and impeded dipole development. After the early 1980s, with stronger ENSO forcing no longer being undercut by Atlantic cooling, the easterlies could do their work unimpeded, and full dipoles became far more common.

The evidence base for these conclusions is unusually broad. The team analyzed multiple independent sea surface temperature datasets, including the NOAA Extended Reconstructed Sea Surface Temperature version 5 and the Met Office Hadley Centre’s HadISST, together with atmospheric reanalyses from the European Centre for Medium-Range Weather Forecasts, including ERA-20C and ERA5, and ocean reanalysis products such as SODA and GODAS. Triangulating across datasets matters enormously in this field, because the Indian Ocean’s observational record before the satellite era is sparse, and spurious trends in any single product can masquerade as interdecadal change. The authors also conducted model simulations using the GFDL-CM4 coupled climate model to test the causal chain, complementing the observational diagnostics with controlled numerical experiments.

The findings add an important nuance to a lively scientific debate. Previous studies have documented changes in the ENSO-IOD relationship over recent decades, with some analyses suggesting a weakening of the coupling and others pointing to enhanced ENSO influence on the dipole under greenhouse warming. This study reframes the question: what matters for the dipole’s spatial completeness is not simply whether ENSO and the IOD co-occur, but whether the cross-basin forcing is strong enough to activate the oceanic pathway, the Rossby waves and thermocline deepening, that builds the western pole. It also echoes and extends earlier work showing that the influence of north tropical Atlantic sea surface temperatures on the IOD strengthened after the mid-1980s, placing that result within a unified cross-basin framework that includes the Pacific as well.

There are practical consequences for climate prediction. Seasonal forecast systems and the coupled models used for climate projection often struggle to reproduce the IOD’s amplitude and spatial pattern, and a recent companion study by overlapping authors traced some of those biases to the models’ representation of dipole dynamics. If the probability that an eastern-pole event becomes a full dipole depends on interdecadal states of the Pacific and Atlantic, then forecast systems need to capture those cross-basin links to predict the dipole’s shape, not just its existence. For the roughly two billion people living around the Indian Ocean rim, whose agriculture, fisheries and flood defenses respond to IOD-driven rainfall anomalies, the difference between a monopole and a full dipole can be the difference between a manageable season and a disaster.

The study also carries a cautionary message for the future. As greenhouse warming continues to alter the mean states of all three tropical oceans, the cross-basin interactions identified here will not remain static. Research has already suggested that the frequency of extreme positive IOD events may increase under warming, while other work indicates that long-term projections of dipole variability remain deeply uncertain. What this new analysis makes clear is that the Indian Ocean Dipole cannot be understood, modeled, or predicted in isolation. It is a node in a planetary network of tropical ocean-atmosphere interactions, and its behavior over the past four decades has been quietly rewritten by forces originating thousands of kilometers away in the Pacific and Atlantic. Recognizing that connectivity, the authors argue, is a key step toward improving the predictability of the IOD’s spatial pattern and, by extension, the climate of the regions that depend on it.

Subject of Research: Interdecadal strengthening of the coupling between the eastern and western poles of the Indian Ocean Dipole through tropical cross-basin interactions with ENSO and the tropical Atlantic

Article Title: Strengthened coupling between the eastern and western poles of the Indian Ocean Dipole since the early 1980s: roles of tropical cross-basin interactions

Article References: Ju, X., Chen, S., Chen, L., Cao, X., Wang, Z., Wu, R., & Chen, W. (2026). Strengthened coupling between the eastern and western poles of the Indian Ocean Dipole since the early 1980s: roles of tropical cross-basin interactions. Climate Dynamics, 64(11), Article 452. https://doi.org/10.1007/s00382-026-08412-9

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08412-9

Keywords: Indian Ocean Dipole, ENSO, tropical Atlantic, cross-basin interactions, sea surface temperature, interdecadal variability, oceanic Rossby waves, zonal wind anomalies, climate prediction, Climate Dynamics, thermocline, atmospheric bridge

The research, led by Ingo Richter of the Japan Agency for Marine-Earth Science and Technology together with colleagues from institutions in Japan, the United States, Norway, and Brazil, rests on an unusually broad foundation of evidence. The team compared simulations of a pre-industrial climate with projections of a high-emissions future, known as scenario ssp585, drawn from 23 state-of-the-art climate models participating in the Coupled Model Intercomparison Project Phase 6, the same modeling framework that underpins the assessments of the Intergovernmental Panel on Climate Change. By contrasting these two worlds, one without human interference and one heated by sustained emissions, the researchers could isolate how the machinery of Atlantic variability itself changes when the planet warms.

The headline finding confirms a trend that earlier studies had already hinted at: the variability of sea-surface temperatures along the equatorial Atlantic, the signature of the Atlantic Zonal Mode, weakens under global warming. In plain terms, the Atlantic Niño becomes less intense, swinging less dramatically between warm and cold phases. Off the equator, by contrast, the picture is different, with sea-surface temperature variability tending to increase slightly in the flanking regions of the tropical Atlantic. That split result matters, because the equatorial mode is the one most tightly linked to the seasonal rains that farmers and water managers from Senegal to Angola depend upon, and its weakening has been flagged in previous work as a potential source of forecast uncertainty.

What makes the new analysis distinctive is its dissection of why the weakening occurs. The Atlantic Niño, like its Pacific counterpart, is sustained by the Bjerknes feedback, a self-reinforcing loop in which a warm anomaly in the eastern equatorial ocean weakens the prevailing easterly trade winds, which in turn suppresses the upwelling of cold subsurface water, further warming the surface. The study finds that this feedback is losing its grip. Contrary to some earlier projections, the team found that the mean-state equatorial Atlantic thermocline, the sharp vertical boundary between warm surface water and cold deep water, actually shoals slightly under radiative forcing, a change that should, on its own, strengthen the mode by making the surface more sensitive to subsurface dynamics. The decline of the Atlantic Niño therefore cannot be blamed on a deepening thermocline. Instead, the culprits are a weakening of the mean upwelling that supplies cold water to the surface and a reduced sensitivity of surface winds to sea-surface temperature anomalies, both of which blunt the Bjerknes feedback at its most critical links.

The second major discovery concerns the changing character of the mode’s forcing. In the pre-industrial simulations, the Atlantic Zonal Mode is driven primarily by dynamic forcing, meaning anomalies in surface wind stress that stir the ocean and rearrange its heat content. In the high-emissions future, the composites of Atlantic Niño events show that this dynamic pathway diminishes, while thermodynamic forcing takes on a more prominent role. Thermodynamic forcing operates through the exchange of heat at the ocean surface, particularly through latent heat flux, the energy carried away by evaporation, and through shortwave radiation, the sunlight that warms the upper ocean. In a warmer world, the Atlantic Niño becomes less a story of winds pushing water around and more a story of clouds, evaporation, and radiant heat reshaping the sea surface.

That shift in mechanism is tied to a striking change in the Atlantic’s relationship with the Pacific. The analysis reveals that the influence of the El Niño-Southern Oscillation on the Atlantic Zonal Mode strengthens under global warming, to the point that a positive correlation emerges between the two phenomena, with Pacific events preceding their Atlantic counterparts by roughly half a year. In today’s climate, the connection between El Niño and the Atlantic Niño has long been described as inconsistent and fragile, appearing in some decades and vanishing in others, a puzzle that has occupied tropical climate scientists for years. The new projections suggest that the greenhouse-warmed atmosphere will knit the two basins together more tightly, transmitting Pacific signals across Central America and the tropical atmosphere with greater reliability.

Two processes appear to explain this tightening bond. First, El Niño itself grows stronger in the high-emissions simulations, and a more powerful Pacific oscillator naturally broadcasts a louder signal into neighboring basins. Second, and perhaps more intriguingly, the weakening of the coupled air-sea feedbacks within the equatorial Atlantic leaves that ocean more susceptible to external forcing. A system whose internal feedbacks have gone quiet is one that listens more attentively to remote voices. When the Atlantic’s own Bjerknes feedback can no longer dominate its variability, the Pacific’s influence, arriving through atmospheric bridges such as shifts in the Walker circulation and changes in tropical tropospheric temperature, finds less resistance and leaves a clearer imprint on Atlantic sea-surface temperatures.

Paradoxically, this foreign domination may carry a silver lining for forecasters. A simple linear analysis performed by the team indicates that, in some of the models, the association of the Atlantic Zonal Mode with El Niño makes the Atlantic mode more predictable, even as its amplitude fades. The logic is straightforward: if a large fraction of Atlantic variability can be traced back to a Pacific precursor that emerges about six months in advance, then forecast systems that skillfully predict El Niño gain, for free, a measure of skill in predicting the Atlantic Niño. Seasonal prediction centers in Africa, Europe, and the Americas could eventually exploit this teleconnection to extend the useful lead time of rainfall outlooks for the Sahel, the Guinea Coast, and northeastern Brazil, regions where the Atlantic mode’s influence on the West African monsoon and coastal precipitation is well documented.

The study also underscores how much remains uncertain. The 23 models do not speak with one voice; the emergence of the ENSO-Atlantic correlation is clear in the ensemble but varies in strength from model to model, and tropical Atlantic simulations remain haunted by persistent mean-state biases that have plagued coupled models for decades. The researchers cross-checked their projections against observational and reanalysis products, including the ERA5 atmospheric reanalysis, the ORAS5 ocean reanalysis, and the HadISST sea-surface temperature dataset, all of which are publicly available, but the fundamental limits of simulating a basin as small and as seasonally locked as the equatorial Atlantic still apply. Whether the real ocean will follow the models’ script is a question that only the coming decades of observation can answer.

Still, the implications are hard to ignore. A tropical Atlantic that dances increasingly to the Pacific’s tune would alter the risk landscape for coastal fisheries, which are disrupted when the cold tongue fails to deliver its usual nutrient-rich upwelling, and for agricultural planners who rely on the statistical rhythms of Atlantic variability. It would also complicate attribution studies, since an Atlantic event that once looked like a local fluke may in the future be the distant echo of an El Niño half a world away. The research, published in Climate Dynamics as volume 64, article 450, offers both a warning and a tool: the Atlantic Niño of the future may be weaker and less self-reliant, but by borrowing predictability from the Pacific, it may also become a signal that humanity can see coming with more confidence than ever before.

Subject of Research: Projected changes in tropical Atlantic sea-surface temperature variability and its coupling to ENSO under global warming

Article Title: Strengthened tropical Pacific influence on tropical Atlantic variability in global warming projections

Article References: Richter, I., Chang, P., Kataoka, T., Kido, S., Keenlyside, N., Kosaka, Y., Okumura, Y., Tokinaga, H., Tozuka, T., & Vilela, I. (2026). Strengthened tropical Pacific influence on tropical Atlantic variability in global warming projections. Climate Dynamics, 64(11), Article 450. https://doi.org/10.1007/s00382-026-08390-y

Image Credits: AI Generated

DOI: 10.1007/s00382-026-08390-y

Keywords: Atlantic Niño, Atlantic Zonal Mode, ENSO, CMIP6, Bjerknes feedback, tropical Atlantic, sea-surface temperature, climate change, thermocline, seasonal prediction, Walker circulation, Climate Dynamics