Deep Water Research Articles

Origin of fluids in the Araró-Simirao geothermal system, Central Mexico

The Araró-Simirao geothermal system is located in the eastern part of Cuitzeo Lake in Michoacán, Mexico. It is a liquid-dominated convective system featuring a high salinity, rapid discharge, and heat loss derived into a self-sealing process. The reservoir temperature is higher than 200 °C, associated with a fracture zone linked to the Araró-Simirao fault. Samples of thermal fluids (water and gases) were collected from springs, wells, a mud pool, and runoff water in the study area. The waters had temperatures ranging from 31 °C and 76 °C and near-neutral pH values. Three hydrogeochemical facies types were identified, Na+- Cl−, Ca2+-Na+ - HCO3−, and Na+ -HCO3−, associated with deep thermal water, groundwater, and recently infiltrated water, respectively.According to the stable isotopes systematics, a binary mixture of thermal water and groundwater was calculated at a proportion from 61 % to 80 % of the thermal component. In the mud pool sample, the chemical composition of bubbling gas is CO2-dominated, with a mostly magmatic origin according to the Rc/Ra (5.19), CO2/3He (4.12 × 109) ratios, and the isotopic composition of δ13C(CO2) (−8 ‰). The gases dissolved in waters are characterized by higher N2 and CO2 concentrations compared to the other gases, representing possible mixing processes between an end-member enriched in CO2 and the chemical composition of air-saturated water. Regarding helium isotopes, the gases are the result of mixing origins between crustal, atmospheric, and mantellic helium, and 3 groups were identified: 1) high contribution of mantle helium ranging from 21 to 66 % up to (Mud pool, LS07 and LS07A) 2) high contribution of crustal helium (LSA-02, LSA-08A, Araró) ranging from 55 to 80 % and 3) high contribution of atmospheric helium of 84 % (LSA-08). The δ13C(CO2) results show a primary interaction with magmatic environments and a slightly sedimentary origin. The origin of CO2, MORB-type, as well as other gases, may be similar to that in Los Azufres. However, these gases reach the surface through different vertical paths, resulting in varying fluid compositions. In the study area, the Araró-Simirao and Huigo faults would act as zones for these gas ascents from the degassing source (magma) at depth.According to the estimates of the magma aging model, the age of the mud pool sample is estimated to be 2.7 × 106 ± 1.2 × 106 years, which is younger than the andesitic basement rocks. Additionally, there is evidence of a more recent 3He input in the sample. However, the Los Azufres geothermal system has a 3He input from rocks that are even younger (1.5 × 105 years). This suggests that Los Azufres may have a more recent 3He input than Araro-Simirao.

The molybdenum cycle in the oxygenated Neoproterozoic ocean was coupled to manganese carbonate mineralization

The Neoproterozoic oxygenation event is a milestone in Earth’s history, yet the redox structure and elemental cycling of the Neoproterozoic ocean remain debated. Here, we investigated iron speciation, molybdenum, and nitrogen isotopes in black shales and manganese carbonates from the upper Ediacaran Doushantuo Formation, South China, to examine the links between redox state, manganese mineralization, and molybdenum cycling. In both lithologies, high pyritic iron ratios (> 0.8) indicate a localized euxinic zone, while estimated seawater molybdenum (1.9‰) and sediment nitrogen isotopic compositions (4.19 ± 1.96‰) resemble modern values, suggesting oxygenated surface waters over euxinic depths. Negative molybdenum isotope in manganese(II) carbonates points to manganese(IV) oxide reduction, acting as a molybdenum shuttle from oxygenated surface to euxinic deep waters. Periodic euxinic contractions drove manganese(II) oxidation and mineralization, shaping molybdenum cycling. This study highlights essential manganese(II) oxidation for manganese carbonate mineralization and offers new insights into molybdenum geochemistry and ancient ocean oxygenation events.

The Impact of Extreme Precipitation on Soil Moisture Transport in Apple Orchards of Varying Ages on the Loess Plateau

The long-term cultivation of apple trees with deep root systems can significantly deplete moisture from the deep soil layers, while extreme rainfall events can rapidly replenish this moisture. Therefore, it is of great academic significance to investigate the influence of extreme precipitation on soil water dynamics in apple orchards of varying ages. This study was conducted on agricultural land and apple orchards of 12 years, 15 years, 19 years and 22 years (12 y, 15 y, 19 y and 22 y) to examine the impact of extreme precipitation on soil moisture transport. Soil moisture content and hydrogen and oxygen isotope (2H, 18O and 3H) data were collected before (October 2020 and May 2021) and after the extreme precipitation event (May 2022). This comprehensive analysis focuses on two aspects: soil moisture distribution and soil water recharge. The following main conclusions were drawn: (1) Extreme precipitation significantly enhanced deep soil water recharge in apple orchards: the depths of soil water supply for apple orchards of 12 y, 15 y, 19 y and 22 y were recorded as 282 mm, 180 mm, 448 mm and 269 mm, respectively. Correspondingly, the recharge depths were measured at approximately 12, 10, 10 and 7 m, respectively. It was observed that the recharge depth decreased with increasing age of the orchard. (2) Extreme precipitation did not have a significant impact on the values of δ2H and δ18O of deep soil moisture due to a limited infiltration depth through the piston flow mechanism (the maximum infiltration depth being around 3 m). (3) In agricultural land as well as apple orchards of 12 y, 15 y and 22 y in 2020, the tritium peak occurred at soil depths of 7.2, 6.9, 6.7 and 5.7 mm, respectively; in 2022, the corresponding values increased to 7.9, 8.7, 6.7 and 5.9 mm, respectively. This indicates that planting apple trees hindered the transport of soil moisture. The peak concentration of tritium in both agricultural land and different-aged apple orchards decreased after experiencing extreme precipitation. The findings will provide a scientific basis for water resource management and efforts toward ecological restoration on the Loess Plateau.

Data mining-based machine learning methods for improving hydrological data: a case study of salinity field in the Western Arctic Ocean

The Beaufort Gyre is the largest freshwater reservoir in the Arctic Ocean. Long-term changes in freshwater reservoirs are critical for understanding the Arctic Ocean, and data from various sources, particularly observation or reanalysis data, must be used to the greatest extent possible. Over the past two decades, a large number of intensive field observations and ship surveys have been conducted in the western Arctic Ocean to obtain a large amount of CTD (Conductivity, Temperature, and Depth) data. Multi-machine learning methods were assessed and merged to reconstruct the annual salinity product in the Western Arctic Ocean over the period 2003-2022. Data mining-based machine learning methods reconstructed salinity product based on input variables determined by physical processes, such as sea level pressure, bathymetry, sea ice concentration, and sea ice drift. The root-mean-square error of sea surface salinity, in comparison to deep water, was effectively managed during machine learning, which exhibits higher sensitivity to variations in the atmosphere, sea ice, and ocean. The mean absolute errors in freshwater content and halocline depth within the Beaufort Gyre region for the salinity product from 2003 to 2022 are 0.98 m and 1.31 m, respectively, when compared to observational data. The salinity product provides reliable characterizations of freshwater content in the Beaufort Gyre and its variations at halocline depth. In polar regions where lacking observed data, we can build data mining-based machine learning methods to generate reliable data products to compensate for the inconvenience. Furthermore, the application potential of this multi-machine learning results approach for evaluating and integrating extends beyond the salinity field, encompassing hydrometeorology, sea ice thickness, polar biogeochemistry, and other related fields.

What Is the Future of the Atlantic Surfclam (Spisula solidissima) Fishery Under Climate‐Induced Warming on the Mid‐Atlantic Bight Continental Shelf: A Multidecadal Assessment

ABSTRACTThe Atlantic surfclam, Spisula solidissima supports a lucrative commercial fishery in the Mid‐Atlantic Bight (MAB) worth roughly $30 million in revenue per year. Rapid climate change is expected to modify the geographic range of the Atlantic surfclam, with consequences for the surfclam fishery. This study evaluated fishery‐based indicators projected from 2020 through 2095 based on anticipated changes in the geographic range and biomass of the Atlantic surfclam, using a Spatially Explicit, agent‐based Fisheries and Economics Simulator (SEFES). Simulations generally showed a positive trend in Atlantic surfclam biomass throughout the next three‐quarters of the 21st century as the clam's range continues to shift offshore and northward along the continental shelf. A general decrease in fishing mortality rate is projected given the present fleet capacity, with a simultaneous increase in catch and landings per unit effort (LPUE), signaling future potential growth in the surfclam fishery. Regionally, forecasts show biomass expanding into deeper waters particularly off New Jersey, Long Island, and southern New England starting in the early 2050s, whereas populations on Georges Bank and off Delmarva gradually decline. Trends in time spent fishing, catch, and LPUE parallel those of biomass in each region. These results can inform managers and business interests that rely on this fishery, as well as other users of the continental shelf, to provide a basis for the development of anticipatory management for the socio‐ecological and economic impacts that may result from future changes in the Atlantic surfclam range and carrying capacity consequent of climate change.

Increased use of mud bottom by juvenile American Lobsters (Homarus americanus) in Maces Bay and Seal Cove, Bay of Fundy, after 3 decades of population increases and predator declines

In the Bay of Fundy, American lobster (Homarus americanus) abundance has soared since the early 1990s, and predators have declined, either of which could have caused juvenile lobster populations in preferred hard-bottom habitat to expand onto less-protective mud bottom. To investigate whether juvenile lobsters have increased use of mud bottom, we used SCUBA surveys (1989-2021) in Maces Bay and Seal Cove, in the Bay of Fundy. Whereas the 1990s surveys found no juveniles on mud at either site (though they were present on hard bottom), in subsequent decades, juveniles inhabited mud burrows at densities of 0.00039 m-2 to 0.0081 m-2. In Maces Bay, mud occupancy occurred after juvenile density increases on hard bottom, but evidence was mixed as to whether increased competition within hard-bottom habitat drove this change. Concurrent cod, haddock, hake, and wolffish declines suggest reduced predation also increased occupancy and survival on mud. Although it supports low juvenile densities, mud habitat may contribute to recruitment given its prevalence, particularly as warming seas allow lobster recruitment into cooler, deeper water over mud bottom.

A pronounced deep water cooling in the Indian Ocean at ∼ 3.3–2.3 Ma linked to a major increase in the Antarctic ice volume

This study investigates changes in the bottom water circulation of the Indian Ocean since 6.5 Ma, based on benthic foraminiferal relative abundances and their stable isotope ratios from Ocean Drilling Program (ODP) Sites 709 and 758. A significant shift, from dominant North Indian Deep Water (NIDW) to Antarctic Bottom Water (AABW) circulation, is documented at ∼3.3 Ma. Principal Component Analysis (PCA) reveals two major benthic foraminiferal assemblages (PCA1 and PCA2). PCA2 is dominated by Nuttallides umbonifera, Globocassidulina subglobosa, and Epistominella exigua, representing cold and well‑oxygenated bottom water conditions between 3.3 and 2.3 Ma. The increased δ18O values of Cibicides wuellerstorfi and high relative abundance of N. umbonifera between ∼3.3 and 2.3 Ma at both sites, indicate an increased influence of AABW in the Indian Ocean due to a major increase in Antarctic ice volume. PCA1 is dominated by Uvigerina proboscidea, Fissurina spp., and miliolids, indicating oxygen-poor bottom waters and high surface productivity between 1.7 and 0.5 Ma associated with an influence of NIDW. The high relative abundance of U. proboscidea and low relative abundance of E. exigua signify low seasonality and sustained flux of organic matter with a signature of strong South Equatorial Counter Current formed by the seasonal reversal of winds during 1.7–0.5 Ma at Site 709.

Prediction of dominant roof water inrush windows and analysis of control target area based on set pair variable weight - Forward correlation cloud model

Coal mining disturbs the roof overlying rock, forming a channel for roof water inrush. This process destroys the primary seepage state of the deep aquifer, resulting in waste and pollution of deep water resources and posing a significant threat to coal mining. Therefore, through field measurement and numerical simulation, this paper comprehensively analyzes the development law of coal seam mining overlying rock fracture, and determines the influence range of coal seam roof water inrush. Then, a set pair variable weight - forward associated cloud prediction model is constructed to predict the dominant water inrush window and seepage channel of coal seam roof, and the key protection area of coal mining roof water inrush is delineated. The results show that with the continuous advance of the coal face, the stress shifts to both sides of the face, forming a stress concentration area, and the vertical fissure develops intensively, which becomes the main channel of water inrush. After the development is stable, it is comprehensively determined that the fissure production ratio of the coal seam is 11.7, and the fracture zone extends to the aquifer area are the water inrush source. Then, through the prediction model, the edge of the danger area near the high-risk area is defined as the advantage window of coal seam roof water inrush, and the result is consistent with the actual water inrush event. Therefore, the target of water inrush in roof is determined, and the effective measures of water reduction mining are put forward. This study is of great significance for protecting deep water resources, ensuring mine safety, and creating efficiency and increasing income.

Advancements in Hydroponic Systems: A Comprehensive Review

Hydroponics, the practice of growing plants without soil using mineral nutrient solutions in water, represents a significant shift in agricultural methodologies. Modern hydroponic systems have evolved substantially since the early 20th century, with advancements in system design, automation, nutrient management, and environmental control enhancing efficiency, scalability, and applicability. This review examines recent innovations that have addressed traditional challenges and created new opportunities for hydroponic cultivation. Hydroponics offers advantages over traditional soil-based agriculture, including precise nutrient control, reduced water usage, and the elimination of soil-borne diseases and pests. These benefits are critical in addressing modern agricultural challenges such as soil degradation, water scarcity, and the need for increased food production for a growing global population. Hydroponic systems can be implemented in diverse environments, making them adaptable solutions for enhancing food security and sustainability. Key developments in various hydroponic systems are highlighted, including the Nutrient Film Technique (NFT), Deep Water Culture (DWC), Ebb and Flow, Aeroponics, Wick Systems, and Drip Systems. Innovations in these systems focus on optimizing nutrient delivery, oxygenation, and integrating sensors for precise control, improving overall performance and yield. Technological advancements, such as automation and control systems, sensors, and monitoring technologies, have revolutionized hydroponic farming by enabling real-time data collection and environmental management. The integration of the Internet of Things (IoT) and smart farming practices, combined with data analytics and machine learning, has further optimized system performance and decision-making. LED lighting and vertical farming techniques have maximized space utilization and improved crop yields, particularly in urban environments. Advances in nutrient solutions, disease management, and water quality have optimized plant health and resource efficiency. Economic and environmental considerations, including cost-benefit analyses and comparisons with traditional agriculture, highlight the potential for hydroponics to offer better returns on investment and reduce environmental impact. Despite the significant progress, challenges such as high initial setup costs and technical complexities remain. Future research opportunities and interdisciplinary collaborations are essential to address these challenges and drive further innovation in hydroponic farming.

Exploring the deep water mass turnovers in the Eastern Indian Ocean since the late Oligocene: Significance of ocean gateways and paleoclimate

Tectonically driven adjustments within ocean gateways and their impacts on deep water production, thermohaline circulation, and nutrient distribution are well constrained. With no deep water formation in the modern northern Indian Ocean, this study aims to reconstruct the possible source and pathways of deep circulation since the late Oligocene, altering the water mass properties at study sites in the eastern Indian Ocean. Our benthic foraminifera results suggest that tectonic gateways influenced the deep water masses in the eastern Indian Ocean. Significant changes in deep water masses at the studied sites commenced with a gradual reduction in corrosive deep water in the eastern equatorial Indian Ocean (EIO) due to the inflow of relatively warmer and less corrosive Tethyan Overflow Water (TOW) through the Tethyan Gateway in the late Oligocene (∼24 Ma). The EIO gradually became less corrosive from the late Oligocene to the middle Miocene (∼24 to 14 Ma). This turnover reflects the intrusion of southward-flowing TOW and a reduction in the Antarctic Bottom Water (AABW) between ∼24 and ∼ 14.5 Ma in the Indian Ocean. Hereafter, a significant switch in deep water mass was established, contemporaneous with the expansion of Antarctic ice sheets that led to the enhanced production of cold and corrosive AABW that replaced the warm and less corrosive TOW at ∼14 Ma. Furthermore, between ∼12 and 8 Ma the closure of the Tethys Seaway caused a significant hydrological reorganization, replacing the TOW with the Pacific Deep Water (PDW) and North Component Water (NCW). At ∼8 Ma, the contribution of the PDW diminished and AABW flow increased again after a reduction between 12 and 8 Ma, leading to a gradual increase in corrosive deep water. Since 8 Ma, a circulation pattern resembling the modern framework was established with the intrusion of the North Atlantic Deep Water into the CDW, and this pattern was developed by ∼5.7 Ma. Furthermore, the final closure of the Central American Seaway increased the formation of the NADW and its intrusion into the CDW after ∼3.2 Ma.

Automatic Identification and Suppression of Random Noise and Methods for Profile Splicing in the Sub-Bottom Profile of Deep Water

The complex topography of deep sea presents numerous challenges for the accurate exploration of sub-bottom profiles. These include real-time tracking of seafloor reflectors, acquisition and storage of deep-sea long-term reflection data, and splicing of successive profiles. Based on the actual survey data of deep sea, we have developed automatic positioning and noise suppression algorithms, namely the double-difference threshold of proximity points. Furthermore, we have created automatic algorithms, namely content expansion and group data moving, based on extremum in seafloor’s depth. These have been designed to automatically suppress the random noise and effectively splice the sub-bottom profile data in deep water. The aforementioned processing techniques facilitate the enhancement of the quality of deep-water sub-bottom profile data, thereby enabling the provision of a comprehensive and successively long profile for interpretation in the context of deep-water sub-bottom profile data.

Social capital and women's earnings in traditional fisheries: Evidence from the Campos Basin (State of Rio de Janeiro, Brazil)

The PESCARTE Environmental Education Project (PEA) is an initiative to mitigate the socio-environmental impacts generated by the oil and gas exploration industry in deep waters off the marine coast of the Campos basin (state of Rio de Janeiro - Brazil). This project, through a census research, has made possible to identify the levels of participation of fishers in professional and community organizations that defend their interests. Using census data, we explored the asymmetries in the social capital of men and women in the project's area of intervention. Log-lin regression models, controlled by endogeneity tests, made it possible to identify the negative impact on labor income of low female participation in professional organizations (Colonias de Pesca). In this way, we can perceive the profound invisibility of women's work in traditional fishing activities. Forbidden from participating in the capture of marine resources, they have been relegated to secondary activities in the fish processing chain (filleting and peeling). This article is the result of research funded by PEA PESCARTE project, which is a mitigation measure required by Federal Environmental Licensing, conducted by Brazilian Institute of Environment and Renewable Resources (IBAMA).

Preparation and Characterization of Temperature-Sensitive Gel Plugging Agent.

In order to use intelligent gel systems to realize deep source water control in medium and high water cut reservoirs, and also to solve the shortcomings of conventional gels, such as the high chemical dose required, large profile control radius, poor temperature resistance, shear resistance, and plugging performance, a temperature-sensitive gel based on natural cellulose was developed, and the temperature resistance, rheological performance, and plugging performance of the temperature-sensitive gel were tested and evaluated. The results show that the system can maintain a viscosity retention rate of up to 95% after high-temperature aging at 90-120 °C for 50 days. When using medium- to low-salinity calcium chloride formation water for preparation, the gelation effect is good. The rheometer oscillation frequency scanning test shows that the system gel is a strong elastic body dominated by elasticity. The core displacement experiment shows that the highest sealing rate of the system is 97%, and the breakthrough pressure can reach 2.5 MPa at this time. The microstructure of the gel system was tested by infrared, and it was found that the gel system had strong hydrogen bonding and the gel had good stability. The research results contribute to improving the recovery rate of high water cut oil reservoirs.

A robust approach for balancing the color and light integrity of underwater images

Abstract As light travels under the deep water, it scatters and is absorbed, resulting in a loss of intensity and altered color perception—a phenomenon known as underwater light attenuation. Images captured under these low light conditions suffered from color distortions, as you go deeper, colors fade in this order: red, orange, and yellow, while green and blue become more prominent. The red channel experiences significant attenuation due to the scattering properties of light under the deep water. As a consequence, deep water images often display noticeable color casts. Researchers encounter various challenges when enhancing low-light underwater images, such as reduced contrast, detail loss, artifacts, noise, and color distortion. In this paper, we present a novel Adaptive Color and Light Correction (ACLC) method for color correction and an Intuitionistic Fuzzy Generator (IFG) for enhancing low-light underwater images. The proposed Adaptive Color and Light Correction (ACLC) method tackles color casts on individual pixels by considering the scene depth. The proposed Intuitionistic Fuzzy Generator (IFG) method balances the image contrast by computing an intuitionistic fuzzy image representation using the proposed IFG approach. Experimental results reveal that the proposed approach significantly improves the color quality and contrast of the output image. The proposed ACLC and IFG methods exceed existing underwater color correction and low-light image enhancement techniques in visual and quantitative evaluations, as evidenced by extensive experimentation on well-established underwater image datasets, such as UIEB, Ocean dark, and LSUI.

Hydrochemical processes and fluoride enrichment patterns in high-fluoride geothermal water in the Weihe Basin, China

The enrichment of fluoride in the deep geothermal water of the Lantian – Bahe Formation in parts of the Weihe Basin in China is a potential health hazard for the millions of inhabitants of this region. We conducted hydrochemical and hydrogeological analyses of water samples from 31 geothermal wells in the Weihe Basin, with the aims of determining the distribution characteristics, enrichment patterns, hydrochemical processes, and the factors influencing the geochemistry of deep geothermal fluids. We also evaluated the potential health hazards of fluoride ions in these fluids. Our results show that geothermal fluids with high fluoride content are widely distributed in the deep aquifers of the Weihe Basin. The principal hydrochemical types are: HCO3–Na and SO4⋅HCO3⋅Cl–Na. We used hydrodynamic simulation and regression analysis to show that the high proportion of HCO3– in the geothermal water facilitates the precipitation of Ca2+ and the dissolution of fluorine-bearing minerals. The high temperature, alkaline environment, cation exchange reactions, and dissolution and precipitation processes lead to Ca2+ depletion, which facilitates the release of fluoride ions from the surrounding rocks into the geothermal fluids. A human health risk assessment shows that the hazard quotient (HQ) values of geothermal water for adult males, adult females, children, and infants are: 3.96 – 14.41 (median 6.55), 3.32 – 12.08 (median 4.50), 4.63 – 16.84 (median 5.50), and 7.48 – 27.22 (median 9.00), respectively. Infants are the most susceptible to the effects of high fluoride in groundwater due to their physiological characteristics. while the potential health risks of F− for children and adult women/men are relatively low. Therefore, in the process of developing deep geothermal water, it is necessary to prevent it from mixing into shallow drinking water as much as possible. If the fluoride ion content in the shallow water exceeds the standard, it may have an impact on the local environment and residents' health. These findings provide a scientific foundation for the effective management of high fluoride groundwater in the Weihe Basin and analogous regions elsewhere.

Superhydrophobicity With Self-Adaptive Water Pressure Resistance and Adhesion of Pistia Stratiotes Leaf.

Superhydrophobic surfaces are promising for optimizing amphibious aircraft by minimizing water drag and adhesion. Achieving this involves ensuring these surfaces can resist high liquid pressure caused by deep water and fluid flow. Maximizing the solid-liquid contact area is a common strategy to improve liquid pressure resistance. However, this approach inevitably increases solid-liquid adhesion, making it challenging to guarantee a trade-off between the two wetting characteristics. Here, it is found that the Pistia stratiotes leaf exhibits superhydrophobicity with high water pressure resistance and low adhesion, attributed to its self-adaptive deformable microstructure with unique re-entrant features. Under pressure, these microstructures deform to increase the solid-liquid contact area, thereby enhancing water pressure resistance. The re-entrant features elevate the deformation threshold, enabling higher modulus microstructures to achieve adaptive response. This facilitates the recovery of deformed microstructures, restoring the air layer and maintaining low adhesion. Following these concepts, Pistia stratiotes leaf-inspired surfaces are fabricated, achieving an 183% improvement in water impact resistance and an ≈80% reduction in adhesion after overpressure compared to conventional superhydrophobic surfaces. The design principles inspired by Pistia stratiotes promise significant advancements in amphibious aircraft and other trans-media vehicles.

Killer whales in the Gulf of Mexico and North Atlantic off the Southeastern United States

Killer whales occur in the Gulf of Mexico (GoMex) and the North Atlantic, including off the southeastern United States (SEUS). Data from cetacean surveys during 1990 – 2021 and other sources were combined to assess killer whale biology, including spatial and temporal distribution, social structure, genetics, morphology, acoustics, and predatory behavior. GoMex records occurred predominantly in oceanic waters (>200 m) during spring and summer. SEUS records occurred primarily in winter and spring off the North Carolina region along the shelf-edge and deeper waters, and off the east coast of Florida. Photo-identification analysis of GoMex killer whales resulted in 49 individuals sighted up to seven times with sighting histories up to 26 years, and social analysis provided evidence of long-term relationships up to 16 years. The GoMex genetic samples revealed two mtDNA haplotypes, one of which does not match any outside the GoMex. Most GoMex whales had wide non-faint saddle patches and many had cookiecutter shark scars while no scars were noted on SEUS whales. Three groups recorded in the GoMex made few calls, but a group harassing sperm whales produced many. Cetaceans and tuna are known prey in the GoMex and SEUS, respectively. Directed studies of killer whales in the GoMex areas would be difficult to implement as this species is very rare. It is therefore important to pursue ongoing efforts to collect behavioral, acoustic and any biological samples that will contribute to improve our understanding of the biology and ecology of killer whales in tropical and subtropical regions.

Generalized stability landscape of the Atlantic meridional overturning circulation

Abstract. The Atlantic meridional overturning circulation (AMOC) plays a crucial role in shaping climate conditions over the North Atlantic region and beyond, and its future stability is a matter of concern. While the AMOC stability when faced with surface freshwater forcing (FWF) has been thoroughly investigated, its equilibrium response to changing CO2 remains largely unexplored, precluding a comprehensive understanding of its stability under global warming. Here we use an Earth system model to explore the stability of the AMOC when faced with combined changes in FWF in the North Atlantic and atmospheric CO2 concentrations between 180 and 560 ppm. We find four different AMOC states associated with qualitatively different convection patterns. Apart from an “Off” AMOC state with no North Atlantic deep-water formation and a “Modern”-like AMOC with deep water forming in the Labrador and Nordic seas as observed at present, we find a “Weak” AMOC state with convection occurring south of 55° N and a “Strong” AMOC state characterized by deep-water formation extending into the Arctic. The Off and Weak states are stable for the entire range of CO2 but only for positive FWF. The Modern state is stable under higher than pre-industrial CO2 for a range of positive FWF and for lower CO2 only for negative FWF. Finally, the Strong state is stable only for CO2 above 280 ppm and FWF < 0.1 Sv. Generally, the strength of the AMOC increases with increasing CO2 and decreases with increasing FWF. Our AMOC stability landscape helps to explain AMOC instability in colder climates, and although it is not directly applicable to the fundamentally transient AMOC response to global warming on a centennial timescale, it can provide useful information about the possible long-term fate of the AMOC. For instance, while under pre-industrial conditions the AMOC is monostable in the model, the Off state also becomes stable for CO2 concentrations above ∼ 400 ppm, suggesting that an AMOC shutdown in a warmer climate might be irreversible.

Spatial Distribution and Decadal Variability of 129I and 236U in the Western Mediterranean Sea

This study investigates the spatial and temporal distribution of the artificial radionuclides 129I and 236U in the Western Mediterranean Sea, focusing on their connection to radionuclide sources and circulation dynamics. Taking advantage of unprecedented precision of accelerator mass spectrometry, both tracers were firstly investigated in 2013. Here, we examine tracer observations obtained along four stations (re-)visited during the TAlPro2022 expedition in May 2022. Distributions of both 129I and 236U were related to water masses and clearly linked to local circulation patterns: a tracer-poor surface Atlantic inflow, a thining of the tracer minimum at intermediate depths, and a higher tracer signal in Western Mediterranean Deep Waters due to dense water formation in the Algero-Provençal basin. The comparison to 2013 tracer data indicated recent deep ventilation of the Tyrrhenian Sea, the mixing of deep waters and enhanced stratification in intermediate waters in the Algero-Provençal basin due to a temperature and salinity increase between 2013 and 2022. We estimate an overall 129I increase of 20% at all depths between 0 and 500m with respect to 2013, which is not accompanied by 236U. This suggests either the lateral transport of 129I from the Eastern Mediterranean Sea, or an additional source of this tracer. The inventories of 129I calculated for each water mass at the four stations point to the deposition of airborne releases from the nuclear reprocessing plants (La Hague and Sellafield) on the surface Mediterranean waters as the more likely explanation for the 129I increase. This work demonstrates the great potential of including measurements of anthropogenic radionuclides as tracers of ocean circulation. However, a refinement of the anthropogenic inputs is necessary to improve their use in understanding ventilation changes in the Mediterranean Sea.

Orbital timescale CaCO3 burial and dissolution changes off the Chilean margin in the subantarctic Pacific over the past 140 kyr

Calcium carbonate (CaCO3) dissolution at the Southern Ocean seafloor has hypothetically contributed to lowering the atmospheric carbon dioxide concentration by increasing ocean alkalinity during glacial periods. We present new CaCO3 burial and dissolution records from two sediment cores obtained off the Chilean margin in the subantarctic SE Pacific and covering the past 140 kyr since Marine Isotope Stage (MIS) 6. These records include CaCO3 contents and mass accumulation rates, and microfossil-based analysis results, including fragmentation ratios, sieve-based weights (SBWs), and ultrastructural observations of planktic foraminiferal tests. Our bulk CaCO3-based analyses and Globorotalia inflata SBWs revealed three major CaCO3 dissolution events during colder stages of MIS 5d and 5b and at the MIS 5/4 boundary that are traceable events in the eastern South Pacific along the Chilean margin and in the Drake Passage. Furthermore, CaCO3 burial exhibited pronounced glacial/interglacial fluctuations, with almost no burial during glacials (MIS 6, 4, 3, and 2) and recovery during interglacials (MIS 5e and 1) and early glacials (MIS 5d–a). This pattern agrees with previous observations over a wide area of the Southern Ocean, except in the deep Cape Basin > 4600 m in the South Atlantic Ocean. Considering that our sites were located upstream of the Drake Passage, the Circumpolar Deep Water, which was influenced by carbon-rich Pacific Deep Water, likely propagated from the subantarctic eastern Pacific to the South Atlantic at least at depths of ~ 3000 to ~ 4000 m and decreased CaCO3 burial during glacials. These findings supported the importance of carbonate compensation in the Southern Ocean for the carbon cycle on the glacial/interglacial timescale.