Ocean Structure Research Articles

Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities.

Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities.

Lebranche mullet Mugil liza population structure and connectivity patterns in the southwest Altantic ocean using a multidisciplinary approach

Previous meristic analysis of the oblique scale counts (OSC) of Mugil liza showed a bimodal pattern within the southern stock, between São Paulo, Brazil (−24°S), and Samborombón Bay, Argentina (−35°S), allowing the identification of two morphotypes (BR1 and BR2). The Brazilian group with lower number of OSC was represented by morphotype 1 (BR1), while the group with higher number of OSC was referred as morphotype 2 (BR2), which could represent distinct subpopulation-units. This study aims at evaluating 1) the population structure of M. liza in Brazilian waters through meristics and body morphometrics from individuals captured by the industrial purse seine fishery, and 2) to assess the possible connectivity between individuals collected off southeast-south Brazil with specimens sampled in Argentinean waters (AR) through otolith shape and microchemistry analyses. Combined meristic and morphometric analyses of fish bodies captured in Brazilian waters allowed to discriminate morphotypes (BR1 and BR2) characterized by different body proportions, head profiles and relative positions of the eye. BR1 presented on average 34 OSC, contrasting with 36 of BR2. For mullets born in two-time distinct intervals, (i) 2008–2011 and (ii) 2011–2014, otolith shape analyses associated AR to BR2, and evidenced a distinct otolith outline from BR1, while multi-elemental otolith core analyses showed no significant differences between AR and BR2. It suggests that the mechanisms responsible for the elemental deposition during the early life history for these two sub-populations (AR + BR2) were significantly different compared to BR1. Univariate analyses of the otolith fingerprints (core and edge) showed higher significant levels in Cd/Ca, Cu/Ca, Fe/Ca, Li/Ca, Mn/Ca, Ni/Ca and Zn/Ca for BR1 compared to AR and BR2. The hereby morpho-meristic data and univariate elemental fingerprints suggest distinct environments inhabited by fish along the western coast of South America. Furthermore, the multi-elemental otolith core results suggested the existence of more than one nursery area for the species. In conclusion, the two morphotypes identified (BR1 and BR2+AR) should be considered as two sub-populations within the mullets southern stock for fisheries management purposes.

Acoustic travel-time variability observed on a 150-km radius tomographic array in the Canada Basin during 2016-2017.

The Arctic Ocean is undergoing dramatic changes in response to increasing atmospheric concentrations of greenhouse gases. The 2016-2017 Canada Basin Acoustic Propagation Experiment was conducted to assess the effects of the changes in the sea ice and ocean structure in the Beaufort Gyre on low-frequency underwater acoustic propagation and ambient sound. An ocean acoustic tomography array with a radius of 150 km that consisted of six acoustic transceivers and a long vertical receiving array measured the impulse responses of the ocean at a variety of ranges every four hours using broadband signals centered at about 250 Hz. The peak-to-peak low-frequency travel-time variability of the early, resolved ray arrivals that turn deep in the ocean was only a few tens of milliseconds, roughly an order of magnitude smaller than observed in previous tomographic experiments at similar ranges, reflecting the small spatial scale and relative sparseness of mesoscale eddies in the Canada Basin. The high-frequency travel-time fluctuations were approximately 2 ms root-mean-square, roughly comparable to the expected measurement uncertainty, reflecting the low internal-wave energy level. The travel-time spectra show increasing energy at lower frequencies and enhanced semidiurnal variability, presumably due to some combination of the semidiurnal tides and inertial variability.

Design of central symmetric lattice structure for ocean engineering based on fluid-solid-interaction

Some structures that constitute underwater vehicles and other ocean engineering structures, such as the shell of underwater vehicles, shafting of power systems, compressor impellers and propeller hubs, all have central symmetric or rotationally symmetric cross sections. In this paper, a kind of central symmetric lattice is designed. The lightweight design of the above structure with this lattice can significantly reduce the weight of the structure on the premise of reducing the static response of the structure. Combined with the ANSYS Parameter Design Language (APDL), the homogenization method is used to analyze the static response of the rotationally symmetric lattice structure and the parallel pattern lattice structure under pressure. The fluid load (pressure) of impeller is calculated by CFX. The results show that the structural stress of the central symmetric lattice structures with the same volume fraction is smaller than that of parallel pattern lattice under the same load when the rotationally symmetric structures have the same form. The application of the homogenization method proves that the above conclusions also improve the efficiency of the static response calculation of the central symmetric lattice structure. The design and research methods in this paper provide technical support for the realization of lightweight design of small and medium-sized underwater rotationally symmetric structures.

Estimating thermohaline structures in the tropical Indian Ocean from surface parameters using an improved CNN model

Accurately estimating the ocean’s subsurface thermohaline structure is essential for advancing our understanding of regional and global ocean dynamics. In this study, we propose a novel neural network model based on Convolutional Block Attention Module-Convolutional Neural Network (CBAM-CNN) to simultaneously estimate the ocean subsurface thermal structure (OSTS) and ocean subsurface salinity structure (OSSS) in the tropical Indian Ocean using satellite observations. The input variables include sea surface temperature (SST), sea surface salinity (SSS), sea surface height anomaly (SSHA), eastward component of sea surface wind (ESSW), northward component of sea surface wind (NSSW), longitude (LON), and latitude (LAT). We train and validate the model using Argo data, and compare its accuracy with that of the original Convolutional Neural Network (CNN) model using root mean square error (RMSE), normalized root mean square error (NRMSE), and determination coefficient (R²). Our results show that the CBAM-CNN model outperforms the CNN model, exhibiting superior performance in estimating thermohaline structures in the tropical Indian Ocean. Furthermore, we evaluate the model’s accuracy by comparing its estimated OSTS and OSSS at different depths with Argo-derived data, demonstrating that the model effectively captures most observed features using sea surface data. Additionally, the CBAM-CNN model demonstrates good seasonal applicability for OSTS and OSSS estimation. Our study highlights the benefits of using CBAM-CNN for estimating thermohaline structure and offers an efficient and effective method for estimating thermohaline structure in the tropical Indian Ocean.

The impact of economics and urbanization on marine fisheries sustainability in Atlantic coastal Africa

The sustainability and management of marine environment and resources, especially fish stocks and fisheries, are issues drawing considerable attention internationally because fishing is the most direct anthropogenic factor affecting the ocean's structure, function and biodiversity. As the impacts of fisheries on ecosystems cannot be fully assessed by examining catches of only a single species, this paper incorporates mean trophic level (TLm), relative primary production required (%PPR), and loss in secondary production index (L index) to quantify fisheries expansion and limitation and to measure the ecological footprint of fisheries. It also constructs a pathway model based on the Environmental Kuznets Curve (EKC) hypothesis to assess ecosystem-level impacts by analyzing how economic growth and urbanization affect the structural diversity of marine ecosystems to examine the more complete processes associated with marine resource depletion. Our results indicate that increased urbanization and biodiversity conservation are compatible goals, but economic growth would degrade marine ecosystems. These results raise important questions about the abiotic factors that influence overexploitation and biodiversity decline and highlight the importance of considering social and economic factors in developing sustainable fisheries management policy.

Vertical‐Slice Ocean Tomography With Seismic Waves

AbstractSeismically generated sound waves that propagate through the ocean are used to infer temperature anomalies and their vertical structure in the deep East Indian Ocean. These T waves are generated by earthquakes off Sumatra and received by hydrophone stations off Diego Garcia and Cape Leeuwin. Between repeating earthquakes, a T wave's travel time changes in response to temperature anomalies along the wave's path. What part of the water column the travel time is sensitive to depends on the frequency of the wave, so measuring travel time changes at a few low frequencies constrains the vertical structure of the inferred temperature anomalies. These measurements reveal anomalies due to equatorial waves, mesoscale eddies, and decadal warming trends. By providing direct constraints on basin‐scale averages with dense sampling in time, these data complement previous point measurements that alias local and transient temperature anomalies.

Island formation adjacent to a large-scale slope failure in Central Peru: The Nazca Ridge subducted relief hypothesis

Vertical tectonics and mass wasting activity along convergent margins are geodynamic processes commonly associated with the subduction of oceanic plate structures. At the Central Peruvian margin, the connection of the small Hormigas de Afuera Islands (HAI) (12°S) with a large-scale slope failure suggests the surficial expression of the subducted relief of the Nazca Ridge. This hypothesis is supported by the idea that the Tuamotu Ridge relief on the Pacific Plate is the analog of the subducted roughness of the Nazca Ridge based on their mirror-image location relative to the East Pacific Rise. Here, we use bathymetry, multichannel seismic data, subbottom profiling data and published findings to analyze the massive slope collapse near the HAI. At the shelf break, the HAI reflect uplift of the metamorphic basement and mark a N-S transition between post-Pliocene onlapping sediments and seafloor erosion of an uplifted, tectonically deformed sequence. W of the shelf break, the HAI scar is a trench-parallel, two-horseshoe-shaped escarpment in the upper slope (1300 m high and 1690 km2 area) that has lost mass with a total volume of 810 km3. Within this large escarpment, two cliffs show differences in size, seafloor morphology, and basement uplift. An embayment at the base of the HAI scar aligns with a downslope mass of 285 km3 volume in the middle slope. A bathymetric bulge of 800 m height characterizes the toe of this mass deposit. When the HAI are projected onto the Tuamotu Ridge northeastern flank, a seamount-shaped platform-like feature of 12,000 km3 is found. Our study area coincides with the well-known and highly coupled segment of the Central Peru subduction, which suggests an association with the history of large megathrust earthquakes in this area such as the great 1746 MW 8.8 Callao-Lima earthquake. Based on these findings, we postulate that the formation and spatial association of the small HAI with the HAI mass wasting result from the tectonic control imposed by the subducted roughness of the Nazca Ridge.

Prediction of bearing capacities and fracture processes in open-hole plates using a hybrid model of peridynamics and FEM

Holes or cutouts are unavoidable during the construction and service of ocean engineering structures. However, open holes in a plate can cause large stress concentrations that can have a great impact on the structural strength and make the structure more prone to brittle failure. Therefore, a new hybrid model that combines peridynamics (PD) and the finite element method (FEM) was proposed to predict the bearing capacity and fracture process in plates with open holes. The surface effect of PD was removed by directly coupling PD grids with FEM meshes without an overlapping zone, and the improved bond-based PD model was utilized for the regions where failure was expected. Additionally, a new fracture criterion was given to evaluate the damage, and the accuracy of the proposed hybrid model was verified through three examples. Ultimately, by calculating and comparing the bearing capacity and fracture process of brittle plates with different open hole arrangements, it was concluded that the number and contribution of open holes had a substantial effect on the bearing capacity and crack propagation path and that reasonable circular hole arrangements could increase the load capacity by more than 50%. Several reliable open hole arrangements were suggested, and they may provide a reference for the future design of structures with good reliability.

Subsurface Thermohaline Biases in the Southern Tropical Pacific and the Roles of Wind Stress and Precipitation

Abstract Thermohaline structure and time evolution in the subsurface ocean play a critical role in climate variability and predictability. They are still poorly represented in ocean and climate models. Here, the characteristics of subsurface thermohaline biases in the southern tropical Pacific and their causes are investigated through CMIP-based analyses and model-based experiments. There exists a pronounced subsurface cold bias at 200-m depth over the southern tropical Pacific in CMIP6 simulations with an ensemble mean of about −4°C and an extreme close to −10°C. This cold bias is accompanied by a fresh subsurface bias of about −0.9 psu in the ensemble mean (−1.9 psu minimum). Similar subsurface thermohaline biases also exist in CMIP5 outputs, indicating that reduction of these biases remains a long-standing challenge for model developments. To understand the causes of these biases, attribution analyses and POP2-based sensitivity experiments are performed. It is found that the subsurface thermohaline biases are attributed to the model deficiencies in simulating wind stress curl and precipitation in the southern tropical Pacific. By conducting CESM2-based coupled experiments, a warm SST bias in the southeastern tropical Pacific is found to be responsible for the poor simulations in wind stress curl and precipitation. The consequences of these biases are also analyzed. The subsurface thermohaline biases cause the density field to increase substantially along 10°S, flattening the zonal isopycnal surface and reducing equatorward interior transport. In addition, the anomalously cold and fresh subsurface signals in the southern tropical Pacific are seen to propagate to the equator, leading to an overall spurious cooling in the equatorial subsurface. Significance Statement Subsurface biases severely degrade the credibility of climate models in their predictions and projections; hence, it is important to understand the causes of these subsurface biases. Our study analyzes the characteristics of subsurface thermohaline biases in the southern tropical Pacific and investigates their causes. A pronounced subsurface cold bias is found over the southern tropical Pacific, accompanied by an obvious subsurface fresh bias. By performing attribution analyses and numerical experiments, it is found that the subsurface thermohaline biases are attributed to the model deficiencies in simulating wind stress and precipitation, which are further attributed to the warm SST bias in the southeastern tropical Pacific. These results provide a guide for improving climate model performances.

New Insights Into the Rift‐To‐Drift Process of the Northern South China Sea Margin Constrained by a Three‐Dimensional Wide‐Angle Seismic Velocity Model

AbstractA three‐dimensional (3D) P‐wave seismic velocity (Vp) model of the crust in the northern South China Sea margin drilled by IODP Expeditions 367/368/368X has been obtained with first‐arrival travel‐time tomography using wide‐angle seismic data from a network of 49 OBSs and 11 air‐gun shot lines. The 3D Vp distribution constrains the extent, structure and nature of the continental, continent to ocean transition (COT), and oceanic domains. Continental crust laterally ranges in thickness from ∼8 to 20 km, a ∼20 km‐width COT contains no evidence of exhumed mantle, and crust with clear oceanic seismic structure ranges in thickness from ∼4.5 to 9 km. A high‐velocity (7.0–7.5 km/s) lower crust (HVLC) ranges in thickness from ∼1 to 9 km across the continental and COT domains, which is interpreted as a proxy of syn‐rift and syn‐breakup magma associated to underplating and/or intrusions. Continental crust thinning style is abrupter in the NE segment and gradual in the SW segment. Abrupter continental thinning exhibits thicker HVLC at stretching factor (β) < ∼3, whereas gentler thinning associates to thinner HVLC at β > ∼4. Opening of the NE segment thus occurred by comparatively increased magmatism, whereas tectonic extension was more important in the SW segment. The Vp distribution shows the changes in deformation and magmatism are abrupt along the strike of the margin, with the segments possibly bounded by a transfer fault system. No conventional model explains the structure and segmentation of tectonic and magmatic processes. Local inherited lithospheric heterogeneities during rifting may have modulated the contrasting opening styles.

Response of Surface Ocean pCO2 to Tropical Cyclones in Two Contrasting Basins of the Northern Indian Ocean

AbstractThis study examines the impact of two very severe tropical cyclonic events, Phailin (over the Bay of Bengal) and Ockhi (over the Arabian Sea), on surface ocean pCO2 and the associated changes in the upper ocean structure using a coupled biogeochemical ROMS model. The primary productivity averaged over the mixed layer is increased from 6.9 to 12.0 (7.2–45.6) mgCm−3d−1 in response to Phailin (Ockhi). A decomposition analysis reveals that the mean contribution of temperature‐driven changes in inducing pCO2 variability in response to pre‐ and post‐cyclonic conditions, in case of Phailin (Ockhi), are 5.4 (−8.8) and −7.6 (−58.8) μatm whereas dissolved inorganic carbon (DIC) driven changes are 23.6 (19.5) and 27.8 (78.0) μatm. Although salinity and total alkalinity have a relatively lesser control in inducing pCO2 variability, salinity's response to the post‐Phailin conditions is significant owing to strong salinity stratification in the Bay of Bengal. The enhancement of DIC is more in the near‐surface waters than its removal by net biological processes resulting in the dominance of cyclone‐induced upwelling and associated vertical mixing driven changes over the enhanced biology‐driven changes in controlling pCO2 variability during both cyclones. Despite comparable magnitudes of environmental forcing during both cyclones, the oceanic response to Phailin is comparatively short‐lived and subdued due to stronger stratification in the Bay of Bengal. A relatively large ratio of DIC to total alkalinity in the upper layers of Arabian Sea facilitates a higher pCO2 response to Ockhi. This makes Ockhi a greater source of CO2 to the atmosphere.

Redox-stratified seawater during the GOE: Evidences from rare earth elemental and C-O isotopic compositions of Paleoproterozoic BIF and carbonate rocks from the Taihua Group, North China Craton

The Paleoproterozoic Great Oxidation Event (GOE) is known for the dramatic change in atmospheric composition that led to oxygen becoming a persistent component of global surface processes. Drastic environmental changes greatly affected ocean and atmosphere chemistry. However, the distribution of dissolved oxygen in the ocean during the GOE is still unclear as rare contemporary sediment-records have been found. In order to identify the redox state of both shallow and deep water, and reveal the ocean redox structure during this time, we present new major and trace elemental and C-O isotopic data of bulk samples of the banded iron formation (BIF), dolomitic marble, and graphite-bearing marble of the early Paleoproterozoic upper Taihua Group in the Lushan area, southern margin of the North China Craton (NCC). The BIF samples exhibit typical major and trace element characteristics akin to very pure marine chemical sediments, such as the shale-normalized positive La, Ga, and Y anomalies, indicative of a marine depositional setting. In these BIF samples, both negative Ce anomalies and the lack of Ce anomalies reflect the presence of both oxic and suboxic/anoxic water in the ocean. Samples of the dolomitic marble are characterized by extremely low amounts of crustal material (such as Al, Ti, Zr, Hf) and high Y/Ho ratios (46–66), also implying a pure marine chemical origin. Excluding some contaminated samples, the rest of the graphite-bearing marble samples display similar features of the dolomitic marble. Significant positive Ce anomalies and high light to heavy REE (Pr/Yb(SN)) ratios in both dolomitic marble and graphite-bearing marble are essentially consistent with the 2.2–2.1 Ga carbonates from the Guanmenshan Formation of the Liaohe Group in the NE Sino-Korean Craton. Combined with the Ce anomalies in the BIF samples, we consider that the seawater when the upper Taihua Group deposited was redox-stratified from oxic shallow water to deeper anoxic water. Besides, the graphite-bearing marble record coeval surface water in the column that was enriched in nutritive materials and beneficial to microbiology and high productivity. Moreover, the early Paleoproterozoic IFs in the Songshan Group and the Lüliang Group in the NCC also exhibit significant both positive and negative Ce anomalies and enrichment of redox sensitive elements. These evidences, therefore, suggest that redox-stratified seawater occurred extensively during the GOE.

Upper ocean structure determines the contrasting typhoon-induced chlorophyll-a responses in the northwest Pacific

Upper ocean structure determines the contrasting typhoon-induced chlorophyll-a responses in the northwest Pacific

Vibrational characteristic simulations regarding connecting two different semi-spheroidal shells and a full-spheroidal shell with a conical shell categorized in underwater structures

Recently, the related structures of marine, underwater, and ocean structures, covering, ice-breaking devices, riser pipes, ballast water gears, gliders, and underwear noise migrations, can be counted by Connected Shells (CSs). Accordingly, for the first time, the investigation related to vibration outputs associated with connecting two different semi-spheroidal shells and a full-spheroidal shell with a conical shell, namely Connected Spheroidal-Conical Shell Assembly (CSCSA) organized in three assembly groups is examined here. In detail, General Shell Hypothesis (GSH) and the First Shear Deformation Theory (FSDT) are connected to find the main formulations of the CSCSAs' shell elements. Addedly, the Motion Governing Differential Equations (MGDEs) associated with each shell element related to the CSCSAs are identified as implementing Hamilton's principle. Addedly, the MGDEs associated with the CSCSA components are discretized, realizing the Generalized Differential Quadrature Method (GDQM). Thereafter, the Natural Frequency Factors (NFFs) of the CSCSAs are determined by implementing the eigenvalue determination. Also, the NFFs measured by the suggested context are linked to the NFFs determined using classical FEM-constructed commercial software to validate the provided approach since previous research has not been conducted on these structures in the literature (except one type related to the CSCSAs). More importantly, the largest observed inaccuracy is less than 1%. Consistent with this, the responses of this investigation may be operated as the benchmark. Finally, the impacts of the geometrical parameters connected to the CSCSAs on the NFFs of the structure are identified via the design and solution of original cases.

Study on vertical line source Green's function for hydrodynamic calculations of ocean structures in water with ice cover

The numerical calculation of panel integrals associated with the Green's function satisfying water surface condition with ice cover is the basis for the boundary element method (BEM) to solve hydrodynamic problems of ocean structures in ice regions. In order to simplify the calculation process and reduce the time consuming, the vertical line source representing the analytical integral of ice-covered Green's function over vertical line segment is firstly derived in this paper. Then a semi-analytical quadrature, which accumulates a series of vertical line sources distributing along the horizontal direction, can be derived for the panel integral. In the numerical implementation, the asymptotic analysis method is employed to eliminate the singularity at zero point of the denominator, variable substitution is performed to treat the integral at infinite and approximate polynomials are introduced to evaluate the Bessel functions. Through the calculations of vertical line and panel integrals of Green's function and its derivatives, the analytical expression of vertical line source is proved to be accurate and more efficient than the normal numerical quadrature. Based on this, a BEM program is developed and applied in the hydrodynamic calculations of submerged structures with ice cover. The computed results are found to be in excellent agreement those of the validated BEM based on point source, which further verifies the reliability and practicability of utilization of vertical line source.

Thermal response to sequential tropical cyclone passages: Statistic analysis and idealized experiments

The cold wake caused by a tropical cyclone (TC) extends for hundreds of kilometers and persists for several weeks, thus influencing the surface response for any subsequent TCs that might pass over it. It is commonly accepted that sea-surface temperature (SST) cooling, as produced by a single TC, occurs primarily through vertical mixing. However, when there are sequential TCs, the earlier TC can dramatically change the thermal structure of the upper ocean, which may influence the subsequent development of a latter-occurring TC (LTC). Therefore, the contribution of horizontal advection and vertical mixing to SST-cooling during the passage of LTCs is of great interest. Using a 19-year-long observational dataset and the heat budget analysis of an idealized numerical simulation, the SST change during the passage of sequential TCs is investigated. The results demonstrate that, on average, the SST cooling caused by the LTC shows an overall decreasing trend with enhanced lingering wakes. Budget analysis of the model simulations suggests that an earlier TC can suppress the vertical mixing induced by an LTC mainly through an alteration of dynamics within the deepened mixed layer and that the contribution of vertical mixing to the SST cooling is weaker due to the intensification of the earlier TC. The weakened vertical mixing dominates the decreased SST cooling induced by an LTC. In contrast, the cold wake generated by an earlier TC can produce more cold water on the right side of the TC’s track, which contributes to stronger horizontal advection upon the arrival of the LTC. In general, the effects of the earlier TC can suppress the sea-surface thermal response to an LTC. If the contribution of the horizontal advection to SST cooling is neglected, the SST cooling induced by an LTC could be reduced by about 40%. As for the response of the sub-surface water to the passage of an LTC, the weakened warm anomaly induced by vertical mixing and the enhanced cooling anomaly caused by the vertical advection explain the reduced tendency for the mixed layer to deepen. As a result, the tendency for the mixed layer depth (MLD) to increase is suppressed during the passage of an LTC. These results highlight the importance of optimally depicting cold wakes in numerical simulations to improve the prediction of the upper ocean’s response to sequential TCs.

Chromosome-level genome of the three-spot damselfish, Dascyllus trimaculatus.

Damselfishes (Family: Pomacentridae) are a group of ecologically important, primarily coral reef fishes that include over 400 species. Damselfishes have been used as model organisms to study recruitment (anemonefishes), the effects of ocean acidification (spiny damselfish), population structure, and speciation (Dascyllus). The genus Dascyllus includes a group of small-bodied species, and a complex of relatively larger bodied species, the Dascyllus trimaculatus species complex that is comprised of several species including D. trimaculatus itself. The three-spot damselfish, D. trimaculatus, is a widespread and common coral reef fish species found across the tropical Indo-Pacific. Here, we present the first-genome assembly of this species. This assembly contains 910 Mb, 90% of the bases are in 24 chromosome-scale scaffolds, and the Benchmarking Universal Single-Copy Orthologs score of the assembly is 97.9%. Our findings confirm previous reports of a karyotype of 2n = 47 in D. trimaculatus in which one parent contributes 24 chromosomes and the other 23. We find evidence that this karyotype is the result of a heterozygous Robertsonian fusion. We also find that the D. trimaculatus chromosomes are each homologous with single chromosomes of the closely related clownfish species, Amphiprion percula. This assembly will be a valuable resource in the population genomics and conservation of Damselfishes, and continued studies of the karyotypic diversity in this clade.

Crevasse refreezing and signatures of retreat observed at Kamb Ice Stream grounding zone

Ice streams flowing into Ross Ice Shelf are presently responsible for around 10% of the mass flux from West Antarctica, with the noteworthy exception of Kamb Ice Stream, which stagnated in the late 1800s. The subsequent reduction in ice supply led to grounding-line retreat at the coastal margin where Kamb transitions into the floating Ross Ice Shelf. Grounding-line migration is linked to broader changes in ice-sheet mass balance and sea level, but our understanding of related ice, ocean and seafloor interactions is limited by the difficulty in accessing these remote regions. Here we report in situ observations from an underwater vehicle deployed at Kamb that show how fine-scale variability in ice and ocean structure combine to influence a diversity of ice–ocean interactions. We found a stratified water column within a tenth of a degree of freezing at the ice base and mapped basal crevasses with supercooled water and active marine ice formation. At the seafloor, we interpret parallel ridges as crevasse impressions left as the ice lifted off during grounding-line retreat. These observations from a recently ungrounded sub-shelf environment illuminate both the geomorphological signatures of past grounding-line retreat and the fine-scale sensitivity of ongoing ice–ocean interactions to ice topography.

Profiles of Two JOMAE Associate Editors (The Fifth in a Continuing Series)

Profiles of Two JOMAE Associate Editors (The Fifth in a Continuing Series)