Early Ocean Research Articles

Bacteria Battled for Iron in Earth’s Early Oceans

Billions of years ago, iron-oxidizing microbes may have competed for dissolved iron in the ocean, with some strains producing toxic gases that smothered their rivals.

Detectability of biosignatures in warm, water-rich atmospheres

Warm rocky exoplanets within the habitable zone of Sun-like stars are favoured targets for current and future missions. Theory indicates these planets could be wet at formation and remain habitable long enough for life to develop. However, it is unclear to what extent an early ocean on such worlds could influence the response of potential biosignatures. In this work we test the climate-chemistry response, maintenance, and detectability of biosignatures in warm, water-rich atmospheres with Earth biomass fluxes within the framework of the planned LIFE mission. We used the coupled climate-chemistry column model 1D-TERRA to simulate the composition of planetary atmospheres at different distances from the Sun, assuming Earth's planetary parameters and evolution. We increased the incoming instellation by up to 50 percent in steps of 10 percent, corresponding to orbits of 1.00 to 0.82 AU. Simulations were performed with and without modern Earth’s biomass fluxes at the surface. Theoretical emission spectra of all simulations were produced using the GARLIC radiative transfer model. LIFEsim was then used to add noise to and simulate observations of these spectra to assess how biotic and abiotic atmospheres of Earth-like planets can be distinguished. Increasing instellation leads to surface water vapour pressures rising from 0.01 bar (1.31<!PCT!>, S = 1.0) to 0.61 bar (34.72<!PCT!>, S = 1.5). In the biotic scenarios, the ozone layer survives because hydrogen oxide reactions with nitrogen oxides prevent the net ozone chemical sink from increasing. Methane is strongly reduced for instellations that are 20<!PCT!> higher than that of the Earth due to the increased hydrogen oxide abundances and UV fluxes. Synthetic observations with LIFEsim, assuming a 2.0 m aperture and resolving power of a R = 50, show that ozone signatures at 9.6 mu m reliably point to Earth-like biosphere surface fluxes of O$_2$ only for systems within 10 parsecs. The differences in atmospheric temperature structures due to differing H$_2$O profiles also enable observations at 15.0 mu m to reliably identify planets with a CH$_4$ surface flux equal to that of Earth's biosphere. Increasing the aperture to 3.5 m and increasing instrument throughput to 15<!PCT!> increases this range to 22.5 pc.

Evolution of gas envelopes and outgassed atmospheres of rocky planets that formed via pebble accretion

In this work, we present results of numerical simulations of the formation and early evolution of rocky planets through pebble accretion, with an emphasis on hydrogen envelope longevity and the composition of the outgassed atmosphere. We modelled planets with a range in mass from 0.1 to 5 Earth masses that orbit between 0.7 and 1.7 AU. The composition of the outgassed atmosphere was calculated with the partial pressure of free oxygen fit to geophysical models of magma ocean self-oxidation. The combined X-ray and UV (XUV) radiation-powered photoevaporation is considered as the main driver of atmospheric escape. We modelled planets that remain below the pebble isolation mass and hence accrete tenuous envelopes only. We considered slow, medium, or fast initial stellar rotation for the temporal evolution of the XUV flux. The loss of the envelope is a key event that allows the magma ocean to crystallise and outgas its bulk volatiles. The atmospheric composition of the majority of our simulated planets is dominated by CO2. Our planets accrete a total of 11.6 Earth oceans of water, the majority of which enters the core. The hydrospheres of planets lighter than the Earth reach several times the mass of the Earth’s modern oceans, while the hydrospheres of planets ranging from 1 to 3.5 Earth masses are comparable to those of our planet. However, planets of 4–5 Earth masses have smaller hydrospheres due to the trapping of volatiles in their massive mantles. Overall, our simulations demonstrate that hydrogen envelopes are easily lost from rocky planets and that this envelope loss triggers the most primordial partitioning of volatiles between the solid mantle and the atmosphere.

Investigation of micropolar dusty fluid flow in a rotational frame with magnetic field: A meshless radial basis function pseudospectral approach

AbstractRotational flow has numerous applications across a wide range of fields, including industrial processes for mixing, pumping, and processing materials, geophysical fluid dynamics for studying the Earth's atmosphere and oceans, aerospace engineering for designing and testing aircraft and spacecraft, medical imaging for creating detailed images of the human body, and environmental engineering for studying the transport of pollutants in water and air. In rotational flow, pumping power is an important parameter that measures the amount of energy required to maintain the flow of the fluid in a rotating frame. It is significant because the presence of the Coriolis force and other rotational effects can substantially alter the fluid dynamics, making it difficult to maintain a steady flow. The present study deals with the flow of micropolar dusty fluid in a rotating frame under the influence of the magnetic field, applied transversely to the flow in a horizontal channel. The fluid is induced to flow between two parallel plates by the movement of the upper plate and a constant pressure gradient. A meshless radial basis function pseudospectral approach is employed to derive a set of partial differential equations that determine the primary and secondary velocity profiles of the fluid, as well as the particle and microrotation velocities and temperature distribution. The pumping power required to sustain the flow in the absence of a pressure gradient is also calculated based on these velocity profiles. The findings provide valuable insights into the behavior of micropolar dusty fluids in a rotational channel and can potentially inform the design of industrial processes involving such fluids.

Water Evolution and Inventories of Super-Earths Orbiting Late M Dwarfs

Super-Earths orbiting M dwarf stars may be the most common habitable planets in the Universe. However, their habitability is threatened by intense irradiation from their host stars, which drives the escape of water to space and can lead to surface desiccation. We present simulation results of a box model incorporating deep-water cycling between interior and atmosphere and water loss to space for terrestrial planets of mass 1–8 M ⊕ orbiting in the habitable zone of a late M dwarf. Energy-limited loss decreases with planetary mass, while diffusion-limited loss increases with mass. Depending on where it orbits in the habitable zone, a 1 M ⊕ planet that starts with 3–8 Earth Oceans can end up with an Earthlike surface of oceans and exposed continents; for an 8 M ⊕ super-Earth, that range is 3–12 Earth Oceans. Planets initialized with more water end up as waterworlds with no exposed continents, while planets that start with less water have desiccated surfaces by 5 Gyr. Since the mantles of terrestrial planets can hold much more water than is currently present in Earth’s atmosphere, none of our simulations result in Dune planets—such planets may be less common than previously thought. Further, more water becomes sequestered within the mantle for larger planets. A super-Earth at the inner edge of the habitable zone tends to end up as either a waterworld or with a desiccated surface; only a narrow range of initial water inventory yields an Earthlike surface.

Trace element partitioning in a deep magma ocean and the origin of the Hf-Nd mantle array.

Crystallization in Earth's deep magma ocean could have caused trace element fractionation in the lower mantle that might be inherited to the isotopic compositions of the present-day mantle. However, the trace element partitioning has been experimentally investigated only up to the uppermost lower-mantle pressures. Here, we determined the bridgmanite/melt partition coefficients D of La, Nd, Sm, Lu, and Hf from 24 to 115 gigapascals, covering the wide pressure range of the lower mantle. Results demonstrate substantial reductions in DLu and DHf from >1 to ≪1 with increasing pressure to 91 gigapascals. We also found DLu/DHf > 1 and DSm/DNd < 1 under deep lower-mantle conditions, evolving melts toward low Lu/Hf and high Sm/Nd ratios by crystallizing bridgmanite. If residual melts form a dense hidden reservoir in the lowermost mantle, the complementary accessible mantle has the Hf and Nd isotopic compositions matching the observed terrestrial mantle array that deviates from the bulk silicate Earth reference.

Standardized Methods to Assess the Impacts of Thermal Stress on Coral Reef Marine Life.

The Earth's oceans have absorbed more than 90% of the excess, climate change-induced atmospheric heat. The resulting rise in oceanic temperatures affects all species and can lead to the collapse of marine ecosystems, including coral reefs. Here, we review the range of methods used to measure thermal stress impacts on reef-building corals, highlighting current standardization practices and necessary refinements to fast-track discoveries and improve interstudy comparisons. We also present technological developments that will undoubtedly enhance our ability to record and analyze standardized data. Although we use corals as an example, the methods described are widely employed in marine sciences, and our recommendations therefore apply to all species and ecosystems. Enhancing collaborative data collection efforts, implementing field-wide standardized protocols, and ensuring data availability through dedicated, openly accessible databases will enable large-scale analysis and monitoring of ecosystem changes, improving our predictive capacities and informing active intervention to mitigate climate change effects on marine life.

Transformation in the forest: the role for restoration in the transition away from native forestry in Australia

The native forestry industry is being reconsidered, or actively phased out, across most parts of Australia. This kind of transition has happened elsewhere in the world but, in Australia, there is no clarity from governments about what those forestry areas will become, from an ecological or legal perspective. In this research, we investigate the ecological, climatic, and governance contexts for this transition away from native forestry, placing our results in the context of the Global Biodiversity Framework's push to restore 30% of the Earth's land, coasts and oceans. We demonstrate important gaps in government planning for the future of former native forestry coupes, arguing that “after forestry” many of these places will need active intervention to recover these ecosystems and address historic land degradation. This case study combines legal analysis with a review of the restoration literature to illustrate the importance of the governance framework within which restoration science is evolving. We demonstrate the complexity of governing restoration at large scales as the climate changes, as well as potential opportunities to reconcile fragmented governance arrangements, to ensure that this transition results in resilient forest ecosystems in currently degraded areas.

Snapshot of a Paleoarchean seafloor: Evidence from 3.43-3.35 Ga Strelley Pool chert-pebble conglomerate for deposition, silicification, and erosion of hydrothermal greenalite-apatite precipitates

Some of the oldest, well-preserved exhalative sedimentary rocks (ferruginous cherts and jaspilites) occur in volcanic-dominated Paleoarchean sequences in the northern Pilbara Craton, Australia. Jaspilites contain fine-grained hematite particles that have been interpreted to have formed following seawater oxidation of vent-derived Fe2+(aq) by photoautotrophs. However, recent studies suggest that most of the iron in the jaspilites was originally deposited as Fe(II)-rich silicates such as greenalite, sparking renewed debate about how iron was precipitated in the early oceans. Here we show that rounded clasts of dusty ferruginous chert in basal conglomerates of the 3.43–3.35 Ga Strelley Pool Formation, North Pole Dome, Pilbara Craton, Australia, contain abundant nanoparticles of greenalite and apatite that are texturally, mineralogically and chemically near-identical to occurrences in Neoarchean banded iron formations in the Hamersley Group, Australia. Hematite where present occurs in trace amounts and its distribution along the edges of clasts implies that at least some of the hematite formed during weathering. The greenalite-rich clasts display a pronounced positive shale-normalized Eu anomaly, small positive Y anomaly and lack a positive La anomaly, features typical of Paleoarchean exhalites. The co-occurrence of greenalite- and apatite-rich chert-pebbles with clasts of hydrothermal black chert and silicified felsic volcaniclastic sedimentary rocks points to a volcanically active provenance with vigorous hydrothermal activity, consistent with derivation from the underlying 3.43 Ga Panorama Formation. We argue that the greenalite and apatite nanoparticles precipitated during mixing between hydrothermal vent fluids and anoxic seawater and were silicified on the seafloor. The round to oval shape of the chert clasts indicates that the silica cement had recrystallized prior to erosion, consistent with the presence of polygonal shrinkage structures in the dusty chert clasts. Our findings imply that greenalite, contrary to recent suggestions, not only formed in Paleoarchean seawater, but was also stable during deposition, diagenesis, and resedimentation. The precipitation and non-dissolution of apatite nanoparticles in Paleoarchean seawater points to elevated phosphate concentrations, whereas the absence of primary hematite is consistent with models advocating a role for abiotic iron deposition during the Archean.

Homogenization for convection-enhanced thermal transport in sea ice

Sea ice regulates heat exchange between the ocean and atmosphere in Earth’s polar regions. The thermal conductivity of sea ice governs this exchange, and is a key parameter in climate modelling. However, it is challenging to measure and predict due to its sensitive dependence on temperature, salinity and brine microstructure. Moreover, as temperature increases, sea ice becomes permeable, and fluid can flow through the porous microstructure. While models for thermal diffusion through sea ice have been obtained, advective contributions to transport have not been considered theoretically. Here, we homogenize a multiscale advection–diffusion equation that models thermal transport through porous sea ice when fluid flow is present. We consider two-dimensional models of convective flow and use an integral representation to derive bounds on the thermal conductivity as a function of the Péclet number. These bounds guarantee enhancement in the thermal conductivity due to the added flow. Further, we relate the Péclet number to temperature, making these bounds useful for global climate models. Our analytic approach offers a mathematical theory which can not only improve predictions of atmosphere–ice–ocean heat exchanges in climate models, but can provide a theoretical framework for a range of problems involving advection–diffusion processes in various fields of application.

The radiative and geometric properties of melting first-year landfast sea ice in the Arctic

Abstract. In polar regions, sea ice is a crucial mediator of the interaction between Earth's atmosphere and oceans. Its formation and breakup is intimately connected with large-scale climatic processes, local weather patterns, and the use of sea ice in coastal Arctic regions by Indigenous people. In order to investigate the physical phenomena at the heart of this process, a set of targeted, intensive observations were made over spring sea ice melt and breakup in Kotzebue Sound, Alaska. These observations were planned and executed through a collaborative effort in which an Indigenous Elder advisory council from Kotzebue and scientists participated in co-production of hypotheses and observational research, including a stronger understanding of the physical properties of sea ice during spring melt. Here we present the results of observations performed using high-endurance, fixed-wing uncrewed aerial vehicles (UAVs) containing custom-built scientific payloads. Repeated flights over the measurement period captured the early stages of the transition from a white, snow-covered state to a broken-up, bare blue-green state. We found that the reflectance of sea ice features depends strongly on their size. Snow patches get darker as they get smaller, an effect owed to the geometric relationship between the bright interior and the darker, melting feature edges. Conversely, bare patches get darker as they get larger. For the largest ice features observed, bare blue-green ice patches were found to be ≈ 20 % less reflective than average across all observational cases, while large snowy white ice patches were found to be ≈ 20 % more reflective than that same average.

The missing piece – New insights to comprehend enigmatic Miocene palaeoceanography of the Mediterranean Sea using the Nd isotopic record

The evolution of the Mediterranean-Paratethys marine system during the Miocene represents one of the crucial milestones in the Earth's oceans history. It fundamentally affected the climate evolution not just in Europe and the adjacent continents, but also on a global scale. The progressive transition of the Mediterranean-Paratethys system from a latitudinal marine domain connecting two main Earth's oceans to a modern-day enclosed setting happened mainly from the Burdigalian (∼16–18 Ma) to Serravallian period (∼13.8–12.6 Ma). It triggered a complex interplay of palaeoceanographic events such as overturns in water circulation regimes that affected the large-scale palaeoclimatic settings. Here, we present 3D palaeoceanographic models from the late Burdigalian to the Serravallian that are based on a comprehensive 143Nd/144Nd dataset containing 59 individual measurements. Our results imply that the first indications of separation between the western and eastern parts of the Mediterranean occurred during the late Langhian (∼16–13.8 Ma) and were linked to the pronounced circulation overturn. The modern-day setting with the characteristic εNd signatures for the Western and Eastern Mediterranean developed during the Serravallian. Altogether, our set of models demonstrates the dynamics of the two-step closure of the Indian-Atlantic gateway and the palaeoceanographic evolution of this area during the middle Miocene.

Sea Surface Wind Speed Estimation From the Combination of Satellite Scatterometer and Radiometer Parameters

AbstractSatellite research on global sea surface winds is crucial for understanding and monitoring the dynamics of earth's oceans, providing valuable insights into weather patterns, climate changes, and oceanographic processes. This study investigates the fusion of active (microwave scatterometer) and passive (microwave radiometer) satellite data using Machine learning (ML) for sea surface wind speed estimation. Employing Random Forest Regression (RF), Convolutional Neural Network Regression (CNN), and Multiple Linear Regression (MLR). Evaluation against reference data sets (Advanced Scatterometer, ERA5, Cross‐Calibrated Multi‐Platform (CCMP), buoy wind speeds) highlights the robustness of the proposed models. The research findings indicate that both RF and CNN exhibit superior accuracy in the active, passive, and joint active‐passive models compared to the simplistic MLR model. The joint models of the three regression methods outperform the individual active or passive models. The root mean square deviation (RMSD) accuracy of RF and CNN joint models, when compared with ASCAT, is in the order of 0.7 m/s, and when compared with buoys, the RMSD accuracy is around 1.1 m/s. The ML models, especially RF and CNN, demonstrate superior performance, providing accurate and reliable estimations crucial for meteorological and oceanographic applications. These findings underscore the potential operational use of ML techniques in enhancing remote sensing applications.

Dynamic Component of the Asthenosphere: Lateral Viscosity Variations Due To Dislocation Creep at the Base of Oceanic Plates

AbstractThe asthenosphere is commonly defined as an upper mantle zone with low velocities and high attenuation of seismic waves, and high electrical conductivity. These observations are usually explained by the presence of partial melt, or by a sharp contrast in the water content of the upper mantle. Low viscosity asthenosphere is an essential ingredient of functioning plate tectonics. We argue that a substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic plates. Numerical simulations of subduction show that dynamic weakening scales with the surface velocity both below the subducting and the overriding plate, and that the viscosity decrease reaches up to two orders of magnitude. The resulting scaling law is employed in an apriori estimate of the lateral viscosity variations (LVV) below Earth's oceans. The obtained LVV help in explaining some of the long‐standing as well as recent problems in mantle viscosity inversions.

End of the Cretaceous

Abstract The Cretaceous ended when the Chicxulub asteroid struck the Yucatán platform, and all deposits and landforms generated are earliest Paleocene in age. Drill core from the Cretaceous–Paleogene (K–Pg) boundary sequence deposited on top of the Chicxulub impact structure's peak ring paired with geophysical data within the crater and other well-preserved marine and terrestrial K–Pg boundary sites provide insight into impact processes and effects on Earth's ecosystems, in terms of extinction and recovery. Key findings as reviewed here are: (1) the confirmation of acoustic fluidization as a physical principle to explain impact structure formation; (2) the importance of the target rock properties and marine setting for impactite depositional processes and drivers of climate change; (3) the state of understanding of extinction mechanisms and ecological recovery; and (4) implications for impact-generated hydrothermal habitat creation. Areas highlighted for the next stages of discovery include: (1) physics and chemistry of impact vapour plumes and ejecta processes; (2) sampling of the K–Pg boundary deposit and impact melt sheet within the central basin of the impact structure; (3) examination of ecosystem recovery in an ‘Early Ocean’ scenario at a range of K–Pg boundary sites; and (4) experiments and observations of impact hydrothermal systems as habitats on Earth and other worlds.

Importance-performance dynamics and willingness to pay in coastal areas for climate-adaptive Marine Debris Management

This study focused on evaluating the adaptive capacity of coastal communities to manage marine debris, a critical issue intensified by the effects of human-induced climate change on the Earth's oceans. The detrimental impacts of climate change, including rising sea levels, ocean acidification, and changes in ocean currents and temperatures, pose significant threats to marine ecosystems and human societies. The study specifically investigated the factors influencing the willingness to pay (WTP) for adaptive Marine Debris Management (MDM) services. It involved diverse community groups, including passive observers, compliant followers, and eco-champions, each exhibiting unique approaches and capacities for managing marine debris. The research revealed that while passive observers and compliant followers favor asset-based programs, eco-champions are more inclined towards enhancing environmental awareness and enforcing policies. A critical methodological aspect of the study was the quantification of WTP, set at IDR 10,000 /month/household, to assess the communities' financial commitment to MDM. The study found that WTP is influenced by factors such as awareness of environmental issues, behavioral responses to regulations, beach clean-up participation, environmental education, and recycling training. Of these, income emerged as the most impactful factor on WTP, followed by education level, age, place of residence, and eco-champion classification. Furthermore, the provision of adaptive MDM services positively influenced community WTP. These findings highlight the need for MDM policymakers to develop customized strategies that address different community groups' distinct needs and priorities. The study recommends that such strategies focus on improving understanding and responsiveness to environmental regulations and providing specialized educational programs. By adopting this approach, not only can the immediate challenge of marine debris be tackled, but it can also lead to the establishment of a more sustainable and community-focused model of environmental stewardship.

The Implications of Thermal Hydrodynamic Atmospheric Escape on the TRAPPIST-1 Planets

JWST observations of the seven-planet TRAPPIST-1 system will provide an excellent opportunity to test outcomes of stellar-driven evolution of terrestrial planetary atmospheres, including atmospheric escape, ocean loss, and abiotic oxygen production. While most previous studies use a single luminosity evolution for the host star, we incorporate observational uncertainties in stellar mass, luminosity evolution, system age, and planetary parameters to statistically explore the plausible range of planetary atmospheric escape outcomes. We present probabilistic distributions of total water loss and oxygen production as a function of initial water content, for planets with initially pure water atmospheres and no interior–atmosphere exchange. We find that the interior planets are desiccated for initial water contents below 50 Earth oceans. For TRAPPIST-1e, f, g, and h, we report maximum water-loss ranges of 8.0−0.9+1.3 , 4.8−0.4+0.6 , 3.4−0.3+0.3 , and 0.8−0.1+0.2 Earth oceans, respectively, with corresponding maximum oxygen retention of 1290−75+75 , 800−40+40 , 560−25+30 , and 90−10+10 bars. We explore statistical constraints on initial water content imposed by current water content, which could inform evolutionary history and planet formation. If TRAPPIST-1b is airless while TRAPPIST-1c possesses a tenuous oxygen atmosphere, as initial JWST observations suggest, then our models predict an initial surface water content of 8.2 −1.0+1.5 Earth oceans for these worlds, leading to the outer planets retaining >1.5 Earth oceans after entering the habitable zone. Even if TRAPPIST-1c is airless, surface water on the outer planets would not be precluded.

Quantifying the Potential for Nitrate-Dependent Iron Oxidation on Early Mars: Implications for the Interpretation of Gale Crater Organics.

Geological evidence and atmospheric and climate models suggest habitable conditions occurred on early Mars, including in a lake in Gale crater. Instruments aboard the Curiosity rover measured organic compounds of unknown provenance in sedimentary mudstones at Gale crater. Additionally, Curiosity measured nitrates in Gale crater sediments, which suggests that nitrate-dependent Fe2+ oxidation (NDFO) may have been a viable metabolism for putative martian life. Here, we perform the first quantitative assessment of an NDFO community that could have existed in an ancient Gale crater lake and quantify the long-term preservation of biological necromass in lakebed mudstones. We find that an NDFO community would have the capacity to produce cell concentrations of up to 106 cells mL-1, which is comparable to microbes in Earth's oceans. However, only a concentration of <104 cells mL-1, due to organisms that inefficiently consume less than 10% of precipitating nitrate, would be consistent with the abundance of organics found at Gale. We also find that meteoritic sources of organics would likely be insufficient as a sole source for the Gale crater organics, which would require a separate source, such as abiotic hydrothermal or atmospheric production or possibly biological production from a slowly turning over chemotrophic community.

New Estimates of Nitrogen Fixation on Early Earth.

Fixed nitrogen species generated by the early Earth's atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth's N2/CO2-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NOx species (i.e., no HCN formation) via the thermochemical dissociation of N2 and CO2 in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth's early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN2, inspired by the experimental results which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN2 reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe.

Dark-soliton asymptotics for a repulsive nonlinear system in a baroclinic flow

In geophysical hydrodynamics, baroclinic instability denotes the process in which the perturbations draw the energy from the mean flow potential power. Researchers focus their attention on the baroclinic instability in the Earth's atmosphere and oceans for the meteorological diagnosis and prediction. Under investigation in this paper is a repulsive nonlinear system modeling the marginally unstable baroclinic wave packets in a baroclinic flow. With respect to the amplitude of the baroclinic wave packet and correction to the mean flow resulting from the self-rectification of the baroclinic wave, we present a Lax pair with the changeable parameters and then derive the N-dark-dark soliton solutions, where N is a positive integer. Asymptotic analysis on the N-dark-dark solitons is processed to obtain the algebraic expressions of the N-dark-dark soliton components. We find that the obtained phase shift of each dark-dark soliton component is relevant with the N − 1 spectral parameters. Furthermore, we take N = 3 as an example and graphically illustrate the 3-dark-dark solitons, which are consistent with our asymptotic-analysis results. Our analysis may provide the explanations of the complex and variable natural mechanisms of the baroclinic instability.