World Ocean Research Articles

Amphidinium spp. as a Source of Antimicrobial, Antifungal, and Anticancer Compounds.

Dinoflagellates make up the second largest marine group of marine unicellular eukaryotes in the world ocean and comprise both heterotrophic and autotrophic species, encompassing a wide genetic and chemical diversity. They produce a plethora of secondary metabolites that can be toxic to other species and are mainly used against predators and competing species. Dinoflagellates are indeed often responsible for harmful algal bloom, where their toxic secondary metabolites can accumulate along the food chain, leading to significant damages to the ecosystem and human health. Secondary metabolites from dinoflagellates have been widely investigated for potential biomedical applications and have revealed multiple antimicrobial, antifungal, and anticancer properties. Species from the genus Amphidinium seem to be particularly interesting for the production of medically relevant compounds. The present review aims at summarising current knowledge on the diversity and the pharmaceutical properties of secondary metabolites from the genus Amphidinium. Specifically, Amphidinium spp. produce a range of polyketides possessing cytotoxic activities such as amphidinolides, caribenolides, amphidinins, and amphidinols. Potent antimicrobial properties against antibiotic-resistant bacterial strains have been observed for several amphidinins. Amphidinols revealed instead strong activities against infectious fungi such as Candida albicans and Aspergillus fumigatus. Finally, compounds such as amphidinolides, isocaribenolide-I, and chlorohydrin 2 revealed potent cytotoxic activities against different cancer cell lines. Overall, the wide variety of antimicrobial, antifungal, and anticancer properties of secondary metabolites from Amphidinium spp. make this genus a highly suitable candidate for future medical applications, spanning from cancer drugs to antimicrobial products that are alternatives to currently available antibiotic and antimycotic products.

Floating marine debris influx in the intertidal zone of offshore islands in Bangladesh: A case study of Manpura Island

Marine Debris is all-pervading in the world's oceans. In this research, for the first time, Floating Marine Debris (FMD) accumulation in the intertidal zone of Manprua island, an offshore island of Bangladesh, is reported. The assessment has been done by integrating both physical investigations and questionnaire survey. The Study shows high debris density on the windward and river-facing sides of the island. The density of debris items in this area varies from 550,000 to 60,000 items per km2 (8.5 to 0.08 g/m2) for transect samples during low tide and 350,000 to 60,000 items per km2 (5.76 to 1.20 g/m2) for net samples during high tide. However, the most damaging debris items are uprooted trees and water hyacinths because they hinder fishing activities. This study provides baseline information on FMD in the Meghna Estuary, which can be used as a reference for sustainable monitoring and management of marine pollution.

Genomic Divergence and the Evolution of Ecotypes in Bottlenose Dolphins (Genus Tursiops).

Climatic changes have caused major environmental restructuring throughout the world's oceans. Marine organisms have responded to novel conditions through various biological systems, including genomic adaptation. Growing accessibility of next-generation DNA sequencing methods to study nonmodel species has recently allowed genomic changes underlying environmental adaptations to be investigated. This study used double-digest restriction-site associated DNA (ddRAD) sequence data to investigate the genomic basis of ecotype formation across currently recognized species and subspecies of bottlenose dolphins (genus Tursiops) in the Southern Hemisphere. Subspecies-level genomic divergence was confirmed between the offshore common bottlenose dolphin (T. truncatus truncatus) and the inshore Lahille's bottlenose dolphin (T. t. gephyreus) from the southwestern Atlantic Ocean (SWAO). Similarly, subspecies-level divergence is suggested between inshore (eastern Australia) Indo-Pacific bottlenose dolphin (T. aduncus) and the proposed Burrunan dolphin (T. australis) from southern Australia. Inshore bottlenose dolphin lineages generally had lower genomic diversity than offshore lineages, a pattern particularly evident for T. t. gephyreus, which showed exceptionally low diversity. Genomic regions associated with cardiovascular, musculoskeletal, and energy production systems appear to have undergone repeated adaptive evolution in inshore lineages across the Southern Hemisphere. We hypothesize that comparable selective pressures in the inshore environment drove similar adaptive responses in each lineage, supporting parallel evolution of inshore bottlenose dolphins. With climate change altering marine ecosystems worldwide, it is crucial to gain an understanding of the adaptive capacity of local species and populations. Our study provides insights into key adaptive pathways that may be important for the long-term survival of cetaceans and other organisms in a changing marine environment.

Investigation of the consistency of changes in the wavelet phase characteristics of heliocosmic and climatic variables and changes in the components of the word water balance. Part 3

The relevance of research is due to the need to establish the true causes and patterns of changes in the hydrometric characteristics of the global water balance as a whole and its components, natural environments on Earth.
 Purpose of research: to establish patterns and causes of changes in the components of the global water balance on Earth: trends in the increase in water mass reserves, dynamics of the water balance of the South Seas of Europe, the Black Sea, dynamics of levels of the Indian Ocean, Western and Central Pacific Ocean, Eastern Pacific and Atlantic Oceans, level fluctuations of the World Ocean, changes in sea ice cover, river resources, reservoirs, variability of sea levels in the Arctic Ocean according to observations at coastal stations, changes in the balance of ice masses in glacial areas, changes in interseasonal thawing in the permafrost zones of the continent.
 Objects of research: time series of heliocosmic, climatic variables, hydrometric characteristics of the components of the global water balance.
 Methods of research: developed by the author, a method for interaction of observations of a variable or variables with groups of specified heliocosmic and climatic factors in the frequency and time domains, obtained using wavelet transformations of observations with the calculation of phase-frequency and phase-time characteristics in equal time intervals; comparative analysis of changes in the obtained phase characteristics of groups of variables with the calculation of their consistency matrices and the construction of graphs in the frequency and time domains.
 Main results of research: in the observed time intervals, in the trend of periodic changes in the reserves of water masses (glaciers, groundwater, lakes, reservoirs) in the frequency domain, significant negative unidirectional influences of changes in heliocosmic and multidirectional influences of climatic variables are observed; changes in the reserves of the World Ocean are more influenced by multidirectional changes in climatic factors compared to the unidirectional influences of heliocosmic factors; the frequency bands of changes in water mass reserves are less than the frequency bands of heliocosmic factors, due to the influence of climatic factors; The variability of water mass reserves on Earth is significantly and unidirectionally consistent with changes in evaporation, evaporation and precipitation on land, and in different directions with changes in cloudiness on the continents. Similar patterns are observed in changes in the water balance of the South Seas in Europe, the Black Sea, sea ice cover, river resources, reservoirs on land, ice mass balances in glacial areas, and interseasonal thawing in the permafrost zones of the continent. In the dynamics of the levels of the Indian, Western and Central Pacific, Eastern Pacific and Atlantic, fluctuations in the level of the World Ocean, significant multidirectional changes in levels in the frequency domain are observed on the effects of heliocosmic variables with the greatest influences of solar activity and long-term solar insolation, the Ap-index of geomagnetic activity, the parameter the ratio of plasma pressure to magnetic solar wind, changes in the ozone layer in the ionosphere, changes in the speed of rotation of the Earth, the influence of climate variables in the frequency domain with the greatest influences of solar radiation, precipitation, atmospheric processes, PTV is significant. The variability of sea levels in the Arctic Ocean, as observed at coastal stations, is characterized by significant multidirectional changes in the frequency domain due to the influence of heliocosmic and climatic factors, multidirectional mutual consistency of the component levels of the ocean seas, caused by anomalous changes in the Earths magnetic field in areas of the Northern Hemisphere. In changes in the phase-time characteristics of groups of factors, lattice structures of differently and unidirectional changes in variables are observed, characterizing the cyclical nature of climate change on Earth.

Towards Stage Subdivision of the Vendian

Abstract —The way towards the stage subdivision of the Vendian starts with the assemblage of a complete composite geological section of this interval of the Earth’s history, a succession of geological bodies each reflecting a certain ecosystem state. A Vendian composite section of the Siberian Platform, which is a succession of regional to sub-global scale geological bodies reflecting particular states or unidirectional transformations determined by episodic expansion of relatively oxygen-rich environments onto the shelf and alternating with large-scale oceanic anoxia and euxinia events is proposed as a reference for constructing the stage subdivision of the Vendian. The redox instability had to be accompanied by changes in nutrient availability and could not but affect the course of macroevolution and macroecology. The geological record of the Vendian of the Siberian Platform is also marked by episodic increase in alkalinity of the World Ocean. At least five such alkalinity events could be provisionally identified in the composite section of the Vendian of the Siberian Platform. A hypothesis is proposed suggesting that the alkalinity events could control the appearance and disappearance in the geological record of a distinctive suite of sedimentary structures in carbonates, the discrete nature of early diagenetic cementation of aluminosilicoclastic sediments, and fossilization of soft-bodied organisms in the Vendian.

Developing a New Oxygen Atlas of the World’s Oceans Using Data Interpolating Variational Analysis

Abstract We present a new global oxygen atlas. This atlas uses all of the available full water column profiles of oxygen, salinity, and temperature available as part of the World Ocean Database released in 2018. Instead of optimal interpolation, we use the Data Interpolating Variational Analysis (DIVA) approach to map the available profiles onto 108 depth levels between the surface and 6800 m, covering more than 99% of ocean volume. This 1/2° × 1/2° atlas covers the period 1955–2018 in 1-yr intervals. The DIVA method has significant benefits over traditional optimal interpolation. It allows the explicit inclusion of advection and boundary constraints, thus offering improvements in the representations of oxygen, salinity, and temperature in regions of strong flow and near coastal boundaries. We demonstrate these benefits of this mapping approach with some examples from this atlas. We can explore the regional and temporal variations of oxygen in the global oceans. Preliminary analyses confirm earlier analyses that the oxygen minimum zone in the eastern Pacific Ocean has expanded and intensified. Oxygen inventory changes between 1970 and 2010 are assessed and compared against prior studies. We find that the full ocean oxygen inventory decreased by 0.84% ± 0.42%. For this period, temperature-driven solubility changes explain about 21% of the oxygen decline over the full water column; in the upper 100 m, solubility changes can explain all of the oxygen decrease; for the 100–600 m depth range, it can explain only 29%, 19% between 600 and 1000 m, and just 11% in the deep ocean. Significance Statement The purpose of this study is to create a new oxygen atlas of the world’s oceans using a technique that better represents the effects of ocean currents and topographic boundaries, and to investigate how oxygen in the ocean has changed over recent decades. We find the total quantity of oxygen in the world’s oceans has decreased by 0.84% since 1970, similar to previous studies. We also examine how much of this change can be explained by changes in water temperature; we find that this can explain all the changes in the upper 100 m but only 21% of the oxygen decline over the whole water column.

The protist Aurantiochytrium has universal subtelomeric rDNAs and is a host for mirusviruses

Viruses are the most abundant biological entities in the world's oceans, where they play important ecological and biogeochemical roles. Metagenomics is revealing new groups of eukaryotic viruses, although disconnected from known hosts. Among these are the recently described mirusviruses, which share some similarities with herpesviruses.1 50 years ago, "herpes-type" viral particles2 were found in a thraustochytrid member of the labyrinthulomycetes, a diverse group of abundant and ecologically important marine eukaryotes,3,4 but could not be further characterized by methods then available. Long-read sequencing has allowed us to connect the biology of mirusviruses and thraustochytrids. We sequenced the genome of the genetically tractable model thraustochytrid Aurantiochytrium limacinum ATCC MYA-1381 and found that its 26 linear chromosomes have an extraordinary configuration. Subtelomeric ribosomal DNAs (rDNAs) found at all chromosome ends are interspersed with long repeated sequence elements denoted as long repeated-telomere and rDNA spacers (LORE-TEARS). We identified two genomic elements that are related to mirusvirus genomes. The first is a ∼300-kbp episome (circular element 1 [CE1]) present at a high copy number. Strikingly, the second, distinct, mirusvirus-like element is integrated between two sets of rDNAs and LORE-TEARS at the left end of chromosome 15 (LE-Chr15). Similar to metagenomically derived mirusviruses, these putative A.limacinum mirusviruses have a virion module related to that of herpesviruses along with an informational module related to nucleocytoplasmic large DNA viruses (NCLDVs). CE1 and LE-Chr15 bear striking similarities to episomal and endogenous latent forms of herpesviruses, respectively, and open new avenues of research into marine virus-host interactions.

Decadal variability of oxygen uptake, export, and storage in the Labrador Sea from observations and CMIP6 models

The uptake of dissolved oxygen from the atmosphere via air-sea gas exchange and its physical transport away from the region of uptake are crucial for supplying oxygen to the deep ocean. This process takes place in a few key regions that feature intense oxygen uptake, deep water formation, and physical oxygen export. In this study we analyze one such region, the Labrador Sea, utilizing the World Ocean Database (WOD) to construct a 65–year oxygen content time series in the Labrador Sea Water (LSW) layer (0–2200 m). The data reveal decadal variability associated with the strength of deep convection, with a maximum anomaly of 27 mol m–2 in 1992. There is no long-term trend in the time series, suggesting that the mean oxygen uptake is balanced by oxygen export out of the region. We compared the time series with output from nine models of the Ocean Model Intercomparison Project phase 1 in the Climate Model Intercomparison Project phase 6, (CMIP6-OMIP1), and constructed a “model score” to evaluate how well they match oxygen observations. Most CMIP6-OMIP1 models score around 50/100 points and the highest score is 57/100 for the ensemble mean, suggesting that improvements are needed. All of the models underestimate the maximum oxygen content anomaly in the 1990s. One possible cause for this is the representation of air-sea gas exchange for oxygen, with all models underestimating the mean uptake by a factor of two or more. Unrealistically deep convection and biased mean oxygen profiles may also contribute to the mismatch. Refining the representation of these processes in climate models could be vital for enhanced predictions of deoxygenation. In the CMIP6-OMIP1 multi-model mean, oxygen uptake has its maximum in 1980–1992, followed by a decrease in 1994–2006. There is a concurrent decrease in export, but oxygen storage also changes between the two periods, with oxygen accumulated in the first period and drained out in the second. Consequently, the change in oxygen export (5%) is much less than that in uptake (28%), suggesting that newly ventilated LSW which remains in the formation region acts to buffer the linkage between air-sea gas exchange and oxygen export.

Variability in zinc:phosphorous and zinc:silicon ratios and zinc isotope fractionation in Southern Ocean diatoms: Observations from laboratory and field experiments

We studied the impact of iron limitation on zinc uptake and the zinc isotope (δ66Zn) composition for Southern Ocean phytoplankton. We undertook laboratory culture and field incubation experiments, and linked these to in situ depth profiles of dissolved (dZn) and particulate (pZn) zinc collected from three sites in the Southern Ocean. For the laboratory experiments, diatom growth rates, cellular zinc accumulation, and δ66Zn all responded to changes in iron and zinc bioavailability. A significant increase in the cellular quota for zinc (expressed as zinc:phosphorous (Zn:P)) occurred upon iron limitation and zinc enrichment. At the same time, δ66Zn for organic tissues became isotopically light under high zinc and low iron concentrations. The opposite occurred for frustule δ66Zn values. Here δ66Znfrustule-organic for cultured phytoplankton became isotopically heavier under high zinc and low iron concentrations. For senescing and dead cells, Zn:P declined and δ66Zn increased, indicating a loss of isotopically light zinc from organic matter. For field incubation experiments, δ66Znfrustule was isotopically heavier than seawater, except for added zinc treatments. The percentage of zinc associated with frustule material for laboratory and field incubations encompassed a wide range with values between 1 and 57%. Depth profiles of δ66Zn for dZn and pZn varied, with dZn being isotopically lighter than pZn in low dZn concentration subantarctic waters, whereas the opposite occurred in polar waters where dZn was isotopically heavier than pZn at higher dZn concentrations. Our results show that iron and zinc availability regulates the zinc content of phytoplankton and the δ66Zn composition of the Southern Ocean, which is propagated to other parts of the world ocean.

Long-term carbon sequestration in the Eocene of the Levant Basin through transport of organic carbon from nearshore to deep marine environments

This study addresses a specific component associated with mass transport complexes in marine systems: the role of hyperpycnal flows, dense shelf water cascading, submarine canyons, distributary channels, and other transport mechanisms in transferring organic matter from continental and shallow marine settings into deep-marine environments. We speculate that during the Eocene, allowing for only 0.1‰ of shelf carbon to be preserved through transport mechanisms would account for up to 13.7% of all organic carbon burial. As such, the potential to mobilize through this mechanism large quantities of organic carbon is significant.Our case study focuses on a 150 m Eocene sequence composed of organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones, with low-diversity assemblages of large benthic foraminifera associated with planktonic foraminifera, suggesting deposition under low-energy conditions within the oligophotic zone on the outer ramp. Transport overprints include soft-sediment deformation, partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and syn-sedimentary shear. These features indicate detachment, movement and emplacement following initial sedimentation, in some cases more than once. Emplacement occurs into a chalk facies that can vary in appearance from darker (higher TOC) and lighter (lower TOC) lithofacies.Combination between the sedimentological, petrophysical, and elemental analyses indicates shifts between autochthonous and allochthonous sedimentation, whereas the organic geochemical analysis reveals a correlation between modes of sedimentation and preservation/composition of organic matter. Organic richness seems to increase within intervals of allochthonous sedimentation, with lower TOC values within intervals of autochthonous sedimentation. Organic matter preservation is enhanced due to poor oxygenation of the sea floor, further depleted by rapid burial beneath mass-transport deposits, increasing sedimentation rates and thus organic matter preservation. Horizons rich in organic matter may be derived from three different sources: organic matter with a fingerprint of terrestrial sources (e.g., enhanced contribution of plant leaf waxes) transported from nearshore environments; an allochthonous marine fingerprint with sulfurized hopanoids, which seem to be reworked from pre-existing Cretaceous organic-rich carbonates entrained within fined-grained micro-turbidites in the para-autochthonous facies; and productivity-derived organic matter deposited on the seafloor of the deep marine environment.This study demonstrates how transport mechanisms allow for the long-term burial of organic carbon in marine systems. When taking into consideration similar processes reported to occur in the world oceans today, it is clear that sediment transport and long-term burial of organic carbon is a fundamental part of the global carbon cycle.

Simulated inventory and distribution of 137Cs released from multiple sources in the global ocean

Radioactive cesium (137Cs) is distributed in the world's oceans as a result of global fallout from atmospheric nuclear weapons tests, releases from fuel reprocessing plants, and inputs from nuclear power plant accident. In order to detect future radionuclide contamination, it is necessary to establish a baseline global distribution of radionuclides such as 137Cs and to understand the ocean transport processes that lead to that distribution. In order to aid in the interpretation of the observed database, we have conducted a suite of simulations of the distribution of 137Cs using a global ocean general circulation model (OGCM). Simulated 137Cs radioactivity concentrations agree well with observations, and the results were used to estimate the changes in inventories for each ocean basin. 137Cs activity concentration from atmospheric nuclear weapons tests are expected to be detectable in the world ocean until at least 2030.

Response of oceanic subsurface chlorophyll maxima to environmental drivers in the Northern Indian Ocean

Subsurface Chlorophyll Maxima (SCM) contributes a significant proportion to depth-integrated ocean primary production, making it important to understand its spatiotemporal variability in changing environmental conditions. Based on field observations and in situ data, we studied SCM characteristics in four distinct environmental settings across Northern Indian Ocean: SEAS-south eastern Arabian Sea (coastal upwelling zone), SAS-Southern Arabian Sea (Arabian Sea mini warm pool-ASMWP), SBOB-Southern Bay of Bengal (presence of mesoscale eddies) and ANS-Andaman Sea (region of active volcanoes). SCM displayed significant spatial variability: ZSCM (SCM depth) ranged between 25 and 88 m (mean = 59.5 m), Chlmax (SCM magnitude) ranged between 0.07 and 0.2 mg m−3 (mean = 0.12 mg m−3) while TSCM (SCM thickness) ranged between 33 and 100 m (mean = 69 m). Major factors affecting the ZSCM were light and nutrients, since ZSCM was closely related to Zeu (euphotic depth) and ZN (nitracline depth). Positive relation between Chlmax and micro phytoplankton suggests micro phytoplankton to be a major contributor in increasing Chlmax. TSCM was associated to ZT (thermocline depth) and nutrient concentration. Increase in stratification and oligotrophy, resulted in deeper, thicker peaks of lower magnitude, and such nature of peaks could increase in continued warming scenarios. Dinoflagellates increased in warmer oligotrophic environments. Nanophytoplankton were higher at deeper ZSCM, possibly due to their adaptability to low light. Upwelling caused shoaling of SCM with higher Chlmax in SEAS. SCM deepened in SAS and SBOB, dominated by picophytoplankton due to the influence of ASMWP (in SAS) and anticyclonic eddy (in SBOB). Ammonia and nutrient inputs from submarine vents in ANS, caused shoaling of ZN and ZSCM. Globally, multiple physical processes operate at short spatiotemporal scale, causing SCM variability, and the same should not be overlooked while estimating primary production or carbon export to deep ocean, through generalisations established at larger scale in the world ocean.

Force impact of a flow of an infinitely deep liquid on a source under ice cover

A characteristic natural factor of the polar regions of the World Ocean and freezing sea areas is the presence of ice cover. The floating ice cover, which determines the dynamic interaction between the ocean and the atmosphere, affects the dynamics of not only the sea surface, but also subsurface waters, while both the ice cover and the entire mass of liquid beneath it participate in the general vertical movement. It is assumed that the ice cover is continuous, that is, its horizontal scales exceed the lengths of the excited waves and, under fairly natural conditions, is modeled by a thin elastic plate, the deformations of which are small and the plate is physically linear. The problem of calculating the force impact of a flow of an infinitely deep homogeneous liquid on a localized source under the ice cover is solved. The problem is solved for the two-dimensional case. Integral representation of the solution for wave drag and lift is obtained, which arise due to the presence of an ice cover and act on the source. The results of calculations of the force action acting on a localized source, simulating a blunt semi-infinite body of finite width, and a dipole, simulating a cylinder, are presented for various values of the oncoming flow velocity and their immersion depth. Numerical calculations show that as the depth of the source immersion increases, the force effect of the fluid flow, which occurs due to the presence of an ice cover, decreases. The dependences of the wave resistance and lift force on the velocity of the incoming fluid flow demonstrate a qualitatively different behavior. The obtained results with different values of the physical parameters included in them make it possible to evaluate the characteristics of ice cover disturbances and its impact on various sources of natural and anthropogenic disturbances observed in real marine conditions.

The impact of rough topography on behaviors of mesoscale eddies as revealed by submesoscale resolving simulations

Mesoscale eddies are ubiquitous in the world ocean and are a key factor in maintaining the global oceanic energy balance. Geophysical turbulence theory predicts that the eddy length scale should increase to Rhines scale as it inherits the inverse energy cascade from smaller scales that help to stabilize the ocean circulation system. However, satellite-observed mesoscale eddies are much smaller than predicted, which indicates that unclear forward energy cascades prevail in their life cycles. In this study, we explore the role of finite rough topography in modulating eddy kinetic energy and horizontal length scales by using a series of submesoscale resolving numerical simulations with parameters typical of the Drake Passage. Our results show that, when compared with those generated over a flat bottom, the presence of rough topography can substantially reduce the horizontal length scales of eddies by approximately 60%–70%, even in upper layers 2–3 km above the bottom. Rough topography also consumes significant amounts of eddy kinetic energy, as the volume-mean eddy kinetic energy over a rough bottom decreases by about 70%–80% when compared with that over a flat bottom. By using a dynamics-based decomposition method, we subtracted the submesoscale motions from total flow and found that, in addition to energetic internal lee waves, deep-ocean submesoscale processes (integrated over the bottommost 1 km) contributed roughly 22% of the total viscosity dissipation across the whole research domain over a rough bottom. Therefore, this study indicates that the role of deep-ocean submesoscale motions in the energy cascade and abyssal mixing should be considered in ocean model parameterizations in the future.

FALL OF RELATIVE SEA LEVELS DURING THE LGM AND THE ROLE OF THE LOWER MANTLE LAYERS IN MANIFESTATION OF THE EFFECT OF HYDROISOSTASY

The structure and functioning of coastal geosystems depend on the interaction of exogenous and endogenous factors. The results of such interaction can dramatically affect both the ecological situation and economic activity. Hydroisostasis, as one of the consequences of the change of sea level during glacial-to-interglacial changes and the resulting change in the solid earth’s surface loading, affects the stress-strain state of the interior part of the earth. Until recently, the study of the role of hydroisostasis for the Russian coastal regions was not sufficiently involved in research activity. In this work, special attention is paid to two aspects that cause and accompany hydroisostasis: a decrease in the level of the World Ocean by about 120 meters during the last glacial maximum about 20 thousand years ago and involvement of layers of the lower mantle in its accompanying deformations and displacements.

Global Winds Shape Planetary‐Scale Lamb Waves

AbstractIn 2022, the Hunga volcano eruption in Tonga generated atmospheric pressure waves that propagated globally and produced tsunamis in all the world's oceans. The largest pressure wave, with an amplitude of several hundred pascals, is the Lamb wave. Standard Lamb wave models, incorporating the sound‐speed as a function of temperature, satisfactorily explain observations in the near‐field but not in the far‐field. We show that an augmented Lamb wave model that includes the effects of wind and topography accurately reproduces the wavefronts observed by satellites and barometers, including those close to the antipode. Winds, first suggested to explain the travel times of Lamb waves from Krakatau in 1883, are now shown to also play a major role in shaping their waveforms; temperature and topography play smaller, but still detectable, roles. Our augmented model provides a significant advance for the development of early warning and hazard assessments for the meteotsunamis these waves produce.

Irreversible loss in marine ecosystem habitability after a temperature overshoot

Anthropogenic warming of the oceans and associated deoxygenation are altering marine ecosystems. Current knowledge suggests these changes may be reversible on a centennial timescale at the ocean surface but irreversible at deeper depths even if global warming were to ameliorate. In contrast, the marine ecosystem’s response to these persistent changes remains poorly elucidated. Here we explore to what extent global warming may drive alterations in marine habitats by exploring the evolution of a metabolic index that captures marine organisms’ ecophysiological response to both temperature and oxygen changes, throughout an idealised ramp-up/ramp-down atmospheric carbon dioxide concentration and an overshoot scenarios. Using a multi-model approach; we find that changes in ocean temperature and oxygen drive a centuries-long irreversible loss in the habitable volume of the upper 1000 m of the world ocean. These results suggest that the combined effect of warming and deoxygenation will have profound and long-lasting impacts on the viability of marine ecosystems, well after global temperatures have peaked.

The Possible Failed Pre-Linnaean Introduction in the Mediterranean Sea: An Archival Case Study of the Brown Mussel Perna perna

Most species arriving from a donor to a recipient area do not succeed in establishing long-lasting self-sustaining populations. However, successful introductions are far better documented than those that failed, especially those occurring before or near the advent of the Linnaean binomial nomenclature. We report here an introduction from the mid-18th century (possibly in 1750 or 1751) of an exotic mussel transported as fouling on ship hulls from the western coast of Morocco (Atlantic Ocean) to the port of Marseilles (Mediterranean Sea). The exotic mussel, which survived several years, has been identified as probably being the brown mussel, Perna perna, a species with warm-water affinities, which much later became invasive in several areas of the world ocean. The documents of the 18th and early 19th century, which mentioned the event, held ‘the curious’ and ‘amateurs’, who harvested the mussels, responsible for its extirpation. More realistically, it is hypothesised that the mussel population did not survive the return of severe cold weather conditions, after a few relatively mild decades, in the context of the Little Ice Age (LIA). These conclusions were deduced from historical data and are therefore open to discussion.

Comparative Population Transcriptomics Provide New Insight into the Evolutionary History and Adaptive Potential of World Ocean Krill.

Genetic variation is instrumental for adaptation to changing environments but it is unclear how it is structured and contributes to adaptation in pelagic species lacking clear barriers to gene flow. Here, we applied comparative genomics to extensive transcriptome datasets from 20 krill species collected across the Atlantic, Indian, Pacific, and Southern Oceans. We compared genetic variation both within and between species to elucidate their evolutionary history and genomic bases of adaptation. We resolved phylogenetic interrelationships and uncovered genomic evidence to elevate the cryptic Euphausia similis var. armata into species. Levels of genetic variation and rates of adaptive protein evolution vary widely. Species endemic to the cold Southern Ocean, such as the Antarctic krill Euphausia superba, showed less genetic variation and lower evolutionary rates than other species. This could suggest a low adaptive potential to rapid climate change. We uncovered hundreds of candidate genes with signatures of adaptive evolution among Antarctic Euphausia but did not observe strong evidence of adaptive convergence with the predominantly Arctic Thysanoessa. We instead identified candidates for cold-adaptation that have also been detected in Antarctic fish, including genes that govern thermal reception such as TrpA1. Our results suggest parallel genetic responses to similar selection pressures across Antarctic taxa and provide new insights into the adaptive potential of important zooplankton already affected by climate change.

GOBAI-O2: temporally and spatially resolved fields of ocean interior dissolved oxygen over nearly 2 decades

Abstract. For about 2 decades, oceanographers have been installing oxygen sensors on Argo profiling floats to be deployed throughout the world ocean, with the stated objective of better constraining trends and variability in the ocean's inventory of oxygen. Until now, measurements from these Argo-float-mounted oxygen sensors have been mainly used for localized process studies on air–sea oxygen exchange, upper-ocean primary production, biological pump efficiency, and oxygen minimum zone dynamics. Here, we present a new four-dimensional gridded product of ocean interior oxygen, derived via machine learning algorithms trained on dissolved oxygen observations from Argo-float-mounted sensors and discrete measurements from ship-based surveys and applied to temperature and salinity fields constructed from the global Argo array. The data product is called GOBAI-O2, which stands for Gridded Ocean Biogeochemistry from Artificial Intelligence – Oxygen (Sharp et al., 2022; https://doi.org/10.25921/z72m-yz67); it covers 86 % of the global ocean area on a 1∘ × 1∘ (latitude × longitude) grid, spans the years 2004–2022 with a monthly resolution, and extends from the ocean surface to a depth of 2 km on 58 levels. Two types of machine learning algorithms – random forest regressions and feed-forward neural networks – are used in the development of GOBAI-O2, and the performance of those algorithms is assessed using real observations and simulated observations from Earth system model output. Machine learning represents a relatively new method for gap filling ocean interior biogeochemical observations and should be explored along with statistical and interpolation-based techniques. GOBAI-O2 is evaluated through comparisons to the oxygen climatology from the World Ocean Atlas, the mapped oxygen product from the Global Ocean Data Analysis Project and to direct observations from large-scale hydrographic research cruises. Finally, potential uses for GOBAI-O2 are demonstrated by presenting average oxygen fields on isobaric and isopycnal surfaces, average oxygen fields across vertical–meridional sections, climatological seasonal cycles of oxygen averaged over different pressure layers, and globally integrated time series of oxygen. GOBAI-O2 indicates a declining trend in the oxygen inventory in the upper 2 km of the global ocean of 0.79 ± 0.04 % per decade between 2004 and 2022.