Northward Transport Research Articles

Recent Freshening of the Subpolar North Atlantic Increased the Transport of Lighter Waters of the Irminger Current From 2014 to 2022

AbstractStarting in 2012, the eastern subpolar North Atlantic experienced the strongest surface freshening in the past 120 years. It is yet unknown whether this salinity anomaly propagated downward into the water column and affected the properties of the boundary currents of the subpolar gyre, which could slow down the overturning. Here, we investigate the imprint of this salinity anomaly on the warm and saline Irminger Current (IC) in the decade thereafter. Using daily mooring data from the IC covering the period 2014–2022 combined with hydrographic sections across the adjacent basins from 1990, the evolving signal of the salinity anomaly over the water column and its imprint on the transport variability is studied. We find that due to the salinity anomaly, the northward freshwater transport of the IC increased by 10 mSv in summer 2016 compared to summer 2015. In 2018, the salinity anomaly covered the water column down to 1,500 m depth. Hydrographic sections across the basin showed that this recent freshening signal spread across the Irminger Sea. Overall, the freshwater transport of the IC increased by a factor of three between 2014–2015 and 2021–2022. The associated density decrease over the upper 1,500 m of the water column resulted in an increase in the northward transport of waters lighter than σ0 = 27.55 kg m−3 from 1.7 to 4.2 Sv. This change in northward IC transport by density class may impact the characteristics of the overturning in the Northeastern Atlantic, its strength and the density at which it peaks.

Delayed ENSO impact on phytoplankton variability over the Western-North Pacific Ocean

Abstract The El Niño-Southern Oscillation (ENSO) is a prominent climatological phenomenon in the Pacific Ocean that exerts a significant influence on both physical states and biological activities across the globe through oceanic and atmospheric teleconnections. In this study, we investigate the impact of ENSO on phytoplankton variability in the Western North Pacific (WNP) region, revealing a delayed relationship with a time lag of more than one year. During the boreal early spring after the peak phase of El Niño, we find a significant increase in chlorophyll-a concentrations in the WNP. This delayed ENSO impact is due to the propagation of reflected ocean Rossby waves from the eastern to the western Pacific. As the Rossby waves reach the western Pacific, they initiate continuous northward transports of the nutrients. The increased nutrient supply promotes phytoplankton growth in the WNP region, where phosphate (PO4) - limited conditions prevail. Our finding suggests the role of ENSO in shaping the biological dynamics in the WNP over an extended time scale through the specific mechanisms involved. Long-term climate model simulation supports these observed findings.

The Bering Strait Throughflow Component of the Global Mass, Heat and Freshwater Transport

AbstractAs the only oceanic connection between the Pacific and Arctic‐Atlantic Oceans, Bering Strait throughflow carries a climatological northward transport of about 1 Sv, contributing to the Atlantic Meridional Overturning Circulation (AMOC). Here, Lagrangian analysis quantifies the global distributions of volume transport, transit‐times, thermohaline properties, diapycnal transformation, heat and freshwater transports associated with Bering Strait throughflow. Virtual Lagrangian parcels, released at Bering Strait, are advected by the velocity of Estimating the Circulation and Climate of the Ocean, backward and forward in time. Backward trajectories reveal that Bering Strait throughflow enters the Pacific basin on the southeast side, as part of fresh Antarctic Intermediate Water, then follows the wind‐driven circulation to Bering Strait. Median transit time from S in Indo‐Pacific to Bering Strait is 175 years. Sixty‐four percent of Bering Strait throughflow enters the North Atlantic through the Labrador Sea. The remaining 36% flows through the Greenland Sea, warmed and salinified by the northward flowing Atlantic waters. Deep water formation of water flowing through Bering Strait occurs predominantly in the Labrador Sea. Subsequently, this water joins the lower branch of AMOC, flowing southward in the deep western boundary current as North Atlantic Deep Water. Median transit time from Bering Strait to S in South Atlantic is 160 years. The net heat transport of Bering Strait throughflow is northward everywhere, and net freshwater transport by Bering Strait throughflow is mostly northward. The freshwater transport is largest in the subpolar region of basin sectors: northward in the Pacific and Arctic and southward in the Atlantic.

Differentiated influences of anomalous subtropical high on extreme persistent precipitation and heatwave events in the Yangtze River Valley

AbstractIn the summers of 2020 and 2022, the Western Pacific Subtropical High (WPSH) intensified extremely and extended westward. However, in summer 2020, the Yangtze River Valley (YRV) witnessed record‐breaking floods, while in 2022, an unprecedented and prolonged heatwave occurred. Distinctly, these two extreme events were caused by different effects of the WPSH: one is enhancement of the transportation of water vapor and the other is adiabatic heating caused by the descending airflow. In June–July 2020, the stable extension of the WPSH ridge line to South China directed a southwesterly airflow along its northwest flank, leading to sustained precipitation in the YRV. Additionally, the midlatitude circulation pattern featured two troughs and two ridges. Such a circulation configuration, combined with the strong and westward WPSH, enabled the continuous southward intrusion of cold air and northward transport of warm moist air, converging over the YRV, and thus influenced extreme persistent precipitation. In contrast, the WPSH covered the YRV almost entirely during summer 2022. Under this influence, the clear‐sky condition and descending airflow through adiabatic warming directly resulted in the heatwave. In addition, local land–atmosphere feedback was crucial in its development and persistence. The soil moisture deficit induced by high temperatures increased the sensible heat flux between the soil and atmosphere upward, further enhanced the surface air temperature and strengthened the heat dry condition.

Interannual Variability and Trend of the Bering Strait Throughflow Gleaned from Satellite Altimeters

Abstract Beginning with the TOPEX/Poseidon altimetry mission in 1992, along-track satellite sea surface height (SSH) estimates have been taken every 6-7 km at 10-day intervals at a cluster of satellite tracks across the Bering Strait near 66°N where the satellite tracks turn. Year-to-year geostrophic SSH estimates of the Bering Strait flow show that the flow in the warmer months is almost entirely confined to a 50m depth channel rather than the whole cross-sectional area, and that the peak-to-peak transport change is comparable to the approximate 0.8 Sverdrup mean. Energy flux calculations using the high-resolution SSH across Bering Strait, as well as an analysis of historical coastal Russian sea levels and wind stress along the Russian Arctic shelf and Bering Sea shelves, suggest that the interannual Bering Strait transport in the warmer water months can be described using wind-forced Arrested Topographic Waves (ATWs) driven by along-shelf wind stress on both the Russian Arctic and Bering Sea shelves. Most of the Bering Strait transport is barotropic in the 50m-depth channel, but analysis of SSH and in situ Alaskan coastal sea level shows that interannual transport variations in the narrow baroclinic Alaskan Coastal Current are not negligible. In disagreement with previous transport estimates, the satellite SSH analysis and almost all of the in situ current measurements do not indicate a significant long-term trend in barotropic Bering Strait northward transport in the warmer water late-summer/fall months.

Wind Forcing Controls on Antarctic Bottom Water Export From the Weddell Sea via Bottom Boundary Layer Processes

AbstractThe Antarctic Bottom Water (AABW) exported from the Weddell Sea has experienced warming and contraction in the past 30 yrs. Superposed on this decadal trend is substantial annual and interannual variability in the volume and properties of Weddell‐sourced AABW. Several mechanisms have been suggested to explain these variations, many of which highlight a role of wind stress, but the comparative importance and possible simultaneity of the different mechanisms remains unclear. Using data from two mooring sites within the Weddell Sea, we find a rapid intensification of the abyssal boundary current carrying AABW through Orkney Passage (OP), the most direct export pathway of AABW from the Weddell Sea, in response to periods of strong zonal wind stress and anomalous wind stress curl along the South Scotia Ridge upstream of OP. This acceleration is concomitant with a 40% reduction in northward AABW transport in late 2015. The changes in transport follow anomalous wind forcing by approximately 3 months, with the short timescale indicative of a barotropic response in the flow through OP. The bottom boundary layer over the OP's sloping topography is found to have a key role in regulating export on monthly to interannual timescales. Increased boundary current velocity leading up to the passage forms a thickened bottom boundary layer, resulting in reduced AABW thickness and density, and thus restricting northward transport of AABW through the passage. Whilst other processes are likely to dominate on longer (decadal) periods, the dynamics identified here can explain significant variability on timescales up to interannual.

Seasonal variation of intermediate meridional overturning circulation in the South China Sea

The seasonal variation of intermediate meridional overturning circulation (IMOC) in the South China Sea (SCS) is investigated using the Simple Ocean Data Assimilation version 2.2.4 (SODA2.2.4) product for the period of 1950–2010. The SCS IMOC displays distinct seasonal features, with a counterclockwise cell dominating the interior SCS (12∼18°N, 200∼700 m) in winter and a broader clockwise cell occupying the region for (7∼20°N, 50∼900 m) in summer. By removing the 12-month average, the main characteristics of the seasonal IMOC is captured deeply. There is a counterclockwise anomaly in winter and a clockwise anomaly in summer occurring in the region for (8∼20°N, 100∼1000 m). And the strongest anomalies of the overturning stream functions are mainly located in (12∼17°N, 200∼400 m) that is taken as the representative region to study the seasonal IMOC. A dynamical decomposition of the IMOC seasonal anomaly allows a further look into the seasonal variation of the SCS IMOC. The IMOC seasonal anomaly is decomposed into three components: the Ekman component, the vertical shear component, and the external component. The Ekman component exhibits a full cell clockwise in winter and counterclockwise in summer with a negative contribution to the IMOC anomaly. The vertical shear component has a strong cell counterclockwise in winter and clockwise in summer occupying most of the areas above 1000 m with a positive contribution to the IMOC anomaly. The external component has a relatively complex structure, and its positive and negative contributions to the IMOC anomaly alternate with increasing latitude at 200∼1000 m. According to the seasonal fractional covariance of these three components on the IMOC anomaly in the representative region, the vertical shear component and the Ekman component have the main contributions to the IMOC seasonal anomaly, and the external component has a limited impact. The vertical shear and its meridional difference can lead to a downward motion at around 12°N and an upward motion at around 17°N in winter, and reverse motions in summer. The seasonal vertical motions will cause an overturning counterclockwise in winter and clockwise in summer. The Ekman component is mainly driven by the monsoon over the SCS that generates the Ekman transport northward in winter and southward in summer. The seasonal Ekman transport and its return flow together form an overturning clockwise in winter and counterclockwise in summer. And the external component counterclockwise in winter and clockwise in summer between 14°N and 17°N is associated with the horizontal flow northeastward in winter and southwestward in summer zonally going over shallower or greater depths, which can induce seasonal reverse upwelling and downwelling at different latitudes.

Large-scale dynamic processes during the minor and major sudden stratospheric warming events in January–February 2023

Using data from reanalyses of meteorological information, this study examines peculiarities of the thermodynamic regime of the Arctic stratosphere in the winter season of 2022–2023. For this purpose, components of the global meridional circulation, wave activity fluxes, volume of polar stratospheric clouds type I (PSC NAT) are analyzed, as well as changes in these indicators during sudden stratospheric warming (SSW) events formed in January–February. The main features of the 2022–2023 winter season were the following: (1) a persistent cold stratospheric polar vortex was observed until mid-January, which caused the PSC NAT volume growth to its maximum values since 1980; (2) enhanced wave activity from mid-January led to the formation of a minor SSW at the end of January, an increase in the temperature of the lower stratosphere and a sharp reduction in PSC NAT; (3) a week of intensification of the polar vortex was then observed, followed by a weakening due to the next burst of wave activity propagation during the second SSW event in mid-February. This second SSW event was major, accompanied by a reversal of the mean zonal wind, which lasted until early March; (4) meridional heat flux in January–February 2023 was the highest since 1948, resulting in unprecedented warming of the lower Arctic stratosphere and preventing ozone depletion in March; (5) the minor SSW at the end of January was accompanied by a more intense change in the meridional circulation than the major SSW in mid-February. Formation of ozone mini-hole over Northern and Central Europe in February 2023 was associated with the strengthening of the anticyclone, leading to a stratopause elevation and northward transport of ozone-poor air masses from the subtropics along the western periphery of the anticyclone additionally to related to the major SSW temperature changes affected the ozone concentration in the lower stratosphere.

Sediment resuspension and transport in the offshore subaqueous Yangtze Delta during winter storms

Storm-induced episodic sediment redistribution in coastal systems can reshape geomorphic bodies, disrupt ecosystems, and cause economic damage. However, cold-wave-storm-induced hydrodynamic changes and residual sediment transport in large, exposed subaqueous deltas, such as the Yangtze Delta, are poorly understood because it is typically expensive and difficult to obtain systematic field data in open coast settings during storm events. We conducted a successful field survey of waves, currents, changes in water depth, and turbidity at a station (time-averaged water depth of 20 m) in the offshore subaqueous Yangtze Delta over 10 days during winter, covering two storms and two fair-weather periods. During the storm events, strong northerly winds drove southward longshore currents (~0.2 m/s) and resulted in increased wave height and sediment resuspension, thereby leading to massive southward sediment transport. In contrast, both southward and northward transports were limited during the fair-weather periods. A better understanding of the storm-induced sediment transport can be obtained by using an approximately half-day lag in sediment transport behind wind force, given the time needed to form waves and longshore drift, the inertia of water motion, and the slow settling velocity of fine-grained sediment. Our results directly support previous findings of southward sediment transport from the Yangtze Delta during winter, which is deposited in the Zhejiang–Fujian mud belt in the inner shelf of the East China Sea. In addition, the southward sediment transport from the Yangtze Delta occurs mainly during episodic storm events, rather than during the winter monsoon, and winter storms dominate over typhoons in driving southward sediment transport from the delta. This study highlights the importance of storms, especially during winter storms, in coastal sediment redistribution, which is of particular significance when considering the projected increase in storm intensity with global warming.

Lagged effect of Southern Annular Mode on chlorophyll-a in the mid-latitude South Pacific and Indian Oceans

This study investigates the influence of the Southern Annular Mode (SAM) on chlorophyll-a (Chl-a) concentrations and the underlying mechanisms governing their associated environmental variations in the mid-latitude (35–50° S) ocean from 1998 to 2021. The intensification of westerly winds during positive SAM phases influences meridional water transport and mixed layer depth (MLD), which are both critical factors that affect surface nutrient availability. A marked contrast in the relationship between the meridional current anomaly and the SAM was observed, with reduced northward transport of nutrient-rich water in regions north of 50° S during positive SAM phases. This reduction could be attributed to the poleward migration of the westerly winds, which impeded the meridional current from reaching the mid-latitudes. The relationship between SAM and MLD south of 50° S was positive whereas that in the mid-latitude eastern (60–110° E) South Indian Ocean and eastern (90–140° W) South Pacific Ocean was negative or weak. The immediate effect of a more positive SAM on Chl-a in the mid-latitude ocean was reduced productivity caused by enhanced nutrient depletion. However, in the mid-latitude eastern South Pacific Ocean, the northward migration of the zonal mean meridional current anomaly closely aligned with the lagged correlation pattern between SAM variability and Chl-a over time, suggesting that the delayed northward transport of nutrient-rich waters may partially counterbalance the immediate effects of the SAM on ocean productivity. This mechanism was not present in the mid-latitude eastern South Indian Ocean, implying that future climate change may variably affect these regions. Our findings emphasize the importance of considering regional differences and temporal lags when evaluating the influence of SAM variability on ocean productivity and nutrient dynamics in the context of climate change.

Seismic Stratigraphy of Contourite Drift Deposits Associated With the Loop Current on the Eastern Campeche Bank, Gulf of Mexico

AbstractThe Loop Current is a key component of global circulation via the northward transport of warm, salty water, and an important influence on Gulf of Mexico hydrography. Understanding how the Loop Current will respond to ongoing anthropogenic warming is critically important, but the history of the Loop Current is poorly known. Here, we present the results of a high resolution (3–8 m) multichannel seismic survey of pelagic carbonate sediment drifts on the eastern Campeche Bank associated with the Loop Current. We identify three seismic megasequences: Megasequence A is a Lower Cretaceous carbonate platform, Megasequence B comprises Cretaceous to lower Cenozoic pelagic carbonates with weak/no contour current flow, and Megasequence C comprises a series of large (100s of m thick) contourite drifts representing the inception and history of the Loop Current. The base of the contourites is marked by a regionally mappable unconformity eroding underling strata, sometimes incising hundreds of meters. The drifts contain a succession of sequence sets separated from each other by regional unconformities and comprising plastered drifts and massive mounded drifts, which characterize modern deposition with active moats on the seafloor. A lack of sediment cores in the study area precludes age determination of these drifts, except for the youngest (Late Pleistocene). Comparison to legacy seismic lines across Deep Sea Drilling Project Site 95, outside our study area, implies that the base of Megasequence C is Oligocene in age, and that the Loop Current developed during the global reorganization of ocean circulation around the Eocene‐Oligocene Transition.

Subsurface eddies east of the Philippines: Geographic characteristics, vertical structures, volume and thermohaline transport

Energetic subsurface eddies (SSEs) play a significant role in regulating the subthermocline circulation east of the Philippines. However, due to the paucity of targeted observations, they remain largely unexplored. By analyzing the outputs from an eddy-resolving ocean general circulation model (OGCM), this study investigated the statistics of SSEs east of the Philippines, including their geographic characteristics, vertical structures, and eddy-induced transport. During the period of 2009–2019, approximately 1927 and 1176 SSEs were detected to be anticyclonic and cyclonic, respectively, indicating the predominance of subsurface anticyclonic eddies (SSAE). The hotspot area of SSEs is in the latitude band of 6° N–15° N off the Philippine coast, especially around 10° N and 14° N–15° N prevailing abundant SSEs. Most SSEs originate at ∼138° E furthest with a mean lifespan of 55 days and a westward translation speed of 6 cm/s. The composite SSAE exhibits a typical subsurface-intensified feature with a velocity core at ∼520 m, while the subsurface cyclonic eddy (SSCE) has a relatively shallow core at ∼420 m and exhibits considerable strength near the surface with a rotating speed is around 5 cm/s. Temperature anomalies induced by SSEs show a dual-core structure associated with lens-like isopycnal undulations, and salinity anomalies are characterized by an alternating positive and negative signal owing to the complexity of the water masses. SSEs-induced meridional volume transport mainly occurs off the Philippine coast, where the northward transport is approximately 0.3 Sv and the southward transport is approximately 0.5 Sv. The zonal volume transport of SSEs is 1–2 Sv per latitude and mainly occurs in the North Equatorial Current (NEC) region. SSEs-induced stirring heat/salt transport is 1–2 orders larger than the trapping component and is mainly concentrated near the Mindanao coast. The meridional stirring heat transport is equatorward, which is up to 2.7 × 107 W/m, and the salt transport is northward with a magnitude of ∼100 kg·m−1·s−1 between 200 m and 2000 m. At the 8°N section, the mean salt transport associated with SSEs is about 24% of that induced by the Mindanao Undercurrent (MUC).

Transport dynamics in a complex coastal archipelago

Abstract. The Archipelago Sea (in the Baltic Sea) is characterised by thousands of islands of various sizes and steep gradients of the bottom topography. Together with the much deeper Åland Sea, the Archipelago Sea acts as a pathway to the water exchange between the neighbouring basins, Baltic proper and Bothnian Sea. We studied circulation and water transports in the Archipelago Sea using a new configuration of the NEMO 3D hydrodynamic model that covers the Åland Sea–Archipelago Sea region with a horizontal resolution of around 500 m. The results show that currents are steered by the geometry of the islands and straits and the bottom topography. Currents are highest and strongly aligned in the narrow channels in the northern part of the area, with the directions alternating between south and north. In more open areas, the currents are weaker with wider directional distribution. During our study period of 2013–2017, southward currents were more frequent in the surface layer. In the bottom layer, in areas deeper than 25 m, northward currents dominated in the southern part of the Archipelago Sea, while in the northern part southward and northward currents were more evenly represented. Due to the variation in current directions, both northward and southward transports occur. During our study period, the net transport in the upper 20 m layer was southward. Below 20 m depth, the net transport was southward at the northern edge and northward at the southern edge of the Archipelago Sea. There were seasonal and inter-annual variations in the transport volumes and directions in the upper layer. Southward transport was usually largest in spring and summer months, and northward transport was largest in autumn and winter months. The transport dynamics in the Archipelago Sea show different variabilities in the north and south. A single transect cannot describe water transport through the whole area in all cases. Further studies on the water exchange processes between the Baltic proper and the Bothnian Sea through the Archipelago Sea would benefit from using a two-way nested model set-up for the region.

Morphology of Hobagella saltata n. gen. and n. sp. (Syndiniophyceae, Miozoa) infecting the marine dinoflagellate Cucumeridinium coeruleum (Dinophyceae, Miozoa) and its potential onshore advection

Over the past decade, molecular phylogenies have placed endoparasites of the genus Euduboscquella in a distinct subclade within clade 4 of the Marine Alveolate (MALV) Group I. Recently, however, rRNA gene sequences have become available for four novel Euduboscquella-like species that infect dinoflagellates, with phylogenies including these sequences indicating that the genus Euduboscquella is paraphyletic. Here, we provide a morphological characterization of the intracellular and extracellular life-cycle stages of a novel species that infects Cucumeridinium coeruleum, a warm water pelagic species sometimes found in coastal environments. We formally describe the novel parasite, Hobagella saltata n. gen, n. sp., and identify a constellation of morphological and developmental characters that distinguish it, as well as Euduboscquella melo and E. nucleocola, both parasites of dinoflagellates, from Euduboscquella species that infect ciliates. We recommend the reassignment of E. melo and E. nucleocola as Hobagella melo n. comb. and H. nucleocola n. comb., respectively. We also propose the family Hobagellidae for these three congeners. We anticipate that the character set developed for distinguishing species of Euduboscquella and Hobagella will be valuable for sorting other Euduboscquella-Hobagella-like taxa scattered across the Group I phylogeny and will provide insight into morphological evolutionary patterns within Group I. Lastly, we consider the potential influence of summer-fall typhoons on the occurrence of H. saltata and its host C. coeruleum in near-shore waters along the southeastern coast of Korea and propose a hypothesis regarding the northward transport and onshore advection of host and parasite populations. If future research supports the hypothesized mechanisms, it could help us better understand parasite distribution and potential changes in biogeography associated with ongoing global changes in surface seawater temperature.

Water masses stratification and circulation in the southern part of Banggai Upwelling Region in Maluku Sea

Banggai Waters is in the western Maluku Sea, where the secondary pathway of Indonesian Throughflow passes and seasonal coastal upwelling takes place in this region, providing a high marine productivity and potential fishing ground. This study aims to describe water mass stratification and circulation using CTD casts and SADCP section datasets from the BUDEE cruise in September 2022 onboard RV Baruna Jaya VIII. The results show that mixed layer depth varies between 43-112 m with a mean temperature of 25.82(± 0.88) ºC. North Pacific water origin (NPSW and NPIW) is present in this southern section. The depth of chlorophyll maximum is much shallower in the upwelling center. Furthermore, for the first time, we identified a strong northward flow from the Bote Strait, disrupting Banggai upwelling water with cooler and fresher Banda water. Estimates of northward transport volume through this strait is about 0.531 Sv.

Uncertainties in the Arctic Ocean response to CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}: a process-based analysis

Using an ensemble of atmosphere–ocean general circulation models (AOGCMs) in an idealized climate change experiment, this study evaluates the contribution of different ocean processes to Arctic Ocean warming. On the AOGCM-mean, the Arctic Ocean warming is greater than the global ocean warming, both in the volume-weighted mean, and at most depths within the upper 2000 m. However, the uncertainty of Arctic Ocean warming is much larger than the uncertainty of global ocean warming. The Arctic warming is greatest a few 100 m below the surface and is dominated by the import of extra heat, which is added to the ocean at lower latitudes and is conveyed to the Arctic mostly by the large-scale barotropic ocean circulation. The change in strength of this circulation in the North Atlantic is relatively small and not correlated with the Arctic Ocean warming. The Arctic Ocean warming is opposed and substantially mitigated by the weakening of the Atlantic meridional overturning circulation (AMOC), though the magnitude of this effect has a large model spread. By reducing the northward transport of heat, the AMOC weakening causes a redistribution of heat from high latitudes to low latitudes. Within the Arctic Ocean, the propagation of heat anomalies is influenced by broadening of cyclonic circulation in the east and weakening of anticyclonic circulation in the west. On the model-mean, the Arctic Ocean warming is most pronounced in the Eurasian Basin, with large spread across the AOGCMs, and accompanied by subsurface cooling by diapycnal mixing and heat redistribution by mesoscale eddies.

Saharan, Aral-Caspian and Middle East dust travels to Finland (1980–2022)

Studies on atmospheric dust and long-range transport of mineral dust have been a focus of atmospheric science in recent years. With its wide range of direct and indirect effects, mineral dust is one of the most uncertain elements in the mechanisms of climate change, and a deeper understanding of its role is essential for understanding future processes.The aim of our research was to provide the first systematic data on the so far episodically documented northward transport mineral dust from arid-semiarid areas. So, in this paper, we present dust storm events from lower latitudes reaching the Finnish atmosphere, based on the MERRA-2 model Dust Column Mass Density data and after a multistep verification procedure using independent data source. In total, 86 long-range dust storm events were identified between 1980 and 2022, when air masses loaded with dust reached Finland. Based on backward-trajectories different sources were identified: 59 were Saharan, 22 were Aral-Caspian, and five were associated with Middle Eastern source areas. Considerable variation in inter-annual frequencies was observed among the source areas, which may be due to changes in circulation conditions and the effects of human activity (agriculture and land use changes in Aral Sea region).There is a clear maximum of dust events in spring (60%), followed by summer and autumn (where 10 of the 11 autumn episodes were from the Sahara). However, the number and proportion of scarce winter events have more than doubled since 2010 compared to the preceding 30 years, but no autumn events were registered during this period. This clear temporal variation coincides with changes in dust transport observed in other regions of Europe, driven by greater atmospheric meridionality associated with climate change and driven by reduced temperature difference between low and high latitudes due to enhanced temperature increases at Arctic regions.

The role of waves in the resuspension and transport of fine sediment and mine tailings from the Fundão Dam failure, Doce River, Brazil

In one of the world's worst mining disasters, after flowing 670 km down the Doce River, about 20 million m3 of tailings reached the coast of Brazil in November 2015. The occurrence of persistent northerly winds favored the detachment of the river plume from the coastline and its displacement southward. However, observations of the sediment plume along the coast during the year following the breach, using aerial photographs, indicated that the plume is more extensive and persistent in a northerly direction. Previous studies have shown that although the most persistent winds are from the northern sector (70%), there is a greater incidence of waves from the southern sector (62%), especially with greater heights and periods. In this research, the effect of gravity waves on the transport of sediments is investigated, and, therefore, tailings from the Doce River and deposited on the adjacent inner continental shelf, mixed with the fluvial mud deposit also are investigated. Two mechanisms were investigated: 1) the effect of waves on sediment resuspension and their combination with tidal and wind forcings, using a two-dimensions in the horizontal directions (2DH) numerical model within the DELFT3D software, and 2) the capture of the fluvial plume by littoral drift, calculated by means of analytical models using data from wave propagation modeling. Both mechanisms were studied for 2019, also considering two major meteorological events in the region. Both effects were relevant for the northward dispersion of fine sediment, highlighting the effect of waves on the potential for northward transport of tailings towards the Abrolhos Bank.

Tonga volcanic eruption triggered anomalous Arctic warming in early 2022

On 15 January 2022, the submarine volcano on Hunga Tonga-Hunga Ha'apai Island erupted and injected a small amount of SO2 but an unprecedent amount of water vapor into the stratosphere. The impact of Tonga eruption on climate was dynamically simulated using a fully coupled climate prediction system FIO-CPS v2.0 by considering both SO2 and water vapor injections into the stratosphere, which is the first attempt to incorporate the volcanic water vapor injection in a climate prediction system to evaluate its effect on surface climate response. Model results indicated that the surface air temperature (SAT) over the Arctic region was significantly warmer in early 2022 as a response to the co-injection of SO2 and water vapor from Tonga eruption, although its effect on global mean SAT was found to be insignificant. In February 2022, the average warming anomaly in the Arctic area reached up to 1.1 °C, with zonal mean warming of 2.0 °C near the North Pole. The Tonga eruptions induced anomalous heat transport which primarily contributed to the Arctic warming in February. However, it had a cooling effect on the Arctic area in January and March. In addition to heat transport, the eruption also triggered anomalous northward transport of water vapor. This led to an increase in the water vapor content, which further enhanced the downward longwave radiation and cloud-radiative feedback over the Arctic region, ultimately contributing to the Arctic SAT warming in early 2022. In the simulation only SO2 injection was considered without water vapor injection, the pattern of SAT response showed warming over the Eurasian continent and cooling in the north over Arctic Ocean, which is opposite to that in the simulation with co-injection of SO2 and water vapor. This indicated that volcanic water vapor injection of Tonga eruption played a dominant role in the Arctic warming. Consequently, submarine volcano should receive more attention due to its potential climate effects, especially when it involves significant water vapor releases.

Interdecadal variation and possible causes of summer extreme precipitation over northern Xinjiang province, northwestern China

Using daily precipitation data from 25 stations, NCEP/NCAR reanalysis data, and 12 climate indices for boreal summers from 1963 to 2017, we investigate the interdecadal variation and causes of extreme precipitation in northern Xinjiang Province (NXJ), northwestern China. The summer frequency of daily precipitation extremes (DPEs), summer precipitation from DPEs, and contribution of precipitation from DPEs to total summer precipitation have increased significantly since the early 1990s, and this increase in extreme precipitation is more intense at stations in the eastern part of NXJ. Comparing the periods 1963–1988 and 1992–2017, the anomalous circulation over the Mongolian Plateau changed from cyclonic to anti-cyclonic, and the center of the anomalous cyclonic circulation over Central Asia shifted northward from the Iranian Plateau to the Aral Sea. These changes in anomalous circulation pattern induced changes in the paths of water vapor transport and the distribution of moisture convergence, which explain well the interdecadal increase in extreme precipitation and its spatial variability. Further analysis confirms evident impacts of the Indian Ocean basin mode (IOBM) and Scandinavia teleconnection pattern on the development of anomalous circulation related to the interdecadal increase in extreme precipitation. A positive IOBM favors the northward transport of moisture from the northern Indian Ocean to Xinjiang Province and the development of anomalous cyclonic circulation over Central Asia in the middle and upper troposphere. The negative phase of the Scandinavia pattern, which has prevailed since the late 1970s, and the enhanced out of phase connection between the anomalous circulation over Scandinavia Peninsula and the West Siberia during 1992–2017 favors the development of anomalous anti-cyclonic circulation over the Mongolian Plateau.