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ArticleModeled flooding by tsunamis and a storm versus observed extent of coral erratics on Anegada, British Virgin Islands-further evidence for a great Caribbean earthquake six centuries ago(American Geophysical Union, 2024-03-14)Models of near-field tsunamis and an extreme hurricane provide further evidence for a great precolonial earthquake along the Puerto Rico Trench. The models are benchmarked to brain-coral boulders and cobbles on Anegada, 125 km south of the trench. The models are screened by their success in flooding the mapped sites of these erratics, which were emplaced some six centuries ago. Among 25 tsunami scenarios, 19 have megathrust sources and the rest posit normal faulting on the outer rise. The modeled storm, the most extreme of 15 hurricanes of category 5, produces tsunami-like bores from surf beat. In the tsunami scenarios, simulated flow depth is 1 m or more at all the clast sites, and 2 m or more at nearly all, given either a megathrust rupture 255 km long with 7.5 m of dip slip and M8.45, or an outer-rise rupture 130 km long with 11.4 m of dip slip and M8.17. By contrast, many coral clasts lie beyond the reach of simulated flooding from the extreme hurricane. The tsunami screening may underestimate earthquake size by neglecting trees and shrubs that likely impeded both the simulated flows and the observed clasts; and it may overestimate earthquake size by leaving coastal sand barriers intact. The screening results broadly agree with those from previously published tsunami simulations. In either successful scenario, the average recurrence interval spans thousands of years, and flooding on the nearest Caribbean shores begins within a half-hour.
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ArticleHolocene Foraminifera, Climate, and Decelerating Rise in Sea Level on the Mud Patch, Southern New England Continental Shelf(Cushman Foundation for Foraminiferal Researc, 2024-04-15)We examined Holocene benthic foraminiferal biofacies, % planktonic foraminifera, and lithofacies changes from New England mud patch cores and present a relative sea-level (RSL) record to evaluate evolution of these rapidly deposited (30–79 cm/kyr) muds. Sandy lower Holocene sections are dominated by Bulimina marginata. The mud patch developed from 11–9 ka as RSL rise slowed from 10 to 7 mm/yr; mud deposition began when the cores (69 to 91 m modern) were inundated below storm wave base. An Elphidium-B. marginata fauna developed at ca. 7–6 ka as RSL rise slowed from approximately 7 to 2 mm/yr. A Globobulimina fauna developed at 3 ka as RSL rise slowed to 1 mm/yr, reflecting lower O2 conditions. Single specimen δ18O analyses of Globobulimina show ∼1‰ variations over the past 3 kyr, reflecting a shelf bottom water seasonal cycle of 4–5°C, and a temperature minimum during the Little Ice Age with warming since.
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ArticleFeature-based maximum entropy for geophysical properties of the seabeda)(Acoustical Society of America, 2024-06-03)The coherent recombination of a direct and seabed reflected path is sensitive to the geophysical properties of the seabed. The concept of feature-based inversion is used in the analysis of acoustic data collected on a vertical line array (VLA) on the New England continental shelf break in about 200 m of water. The analysis approach for the measurements is based on a ray approach in which a direct and bottom reflected path is recombined, resulting in constructive and destructive interference of the acoustic amplitudes with frequency. The acoustic features have the form of prominent nulls of the measured received levels as a function of frequency as a broadband (500–4500 Hz) source passes the closest point of approach to the VLA. The viscous grain shearing (VGS) model is employed to parameterize a two-layer seabed model. The most likely seabed is a sand sediment with a porosity of about 0.42. There is a possibility of a thin (less than 0.5 m) surface layer having a slightly higher porosity between 0.45 and 0.50. Using the estimates for the VGS parameters inferred from the short-range frequency features, a normal mode model is used to predict the received acoustic levels over larger range scales.
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ArticleShort-term sediment dispersal on a large retreating coastal river delta via 234Th and 7Be sediment geochronology: the Mississippi River Delta Front(MDPI, 2024-01-31)Many Mississippi River Delta studies have shown recent declines in fluvial sediment load from the river and associated land loss. In contrast, recent sedimentary processes on the subaqueous delta are less documented. To help address this knowledge gap, multicores were collected offshore from the three main river outlets at water depths of 25–280 m in June 2017 just after the peak river discharge period, with locations selected based on 2017 U.S. Geological Survey seabed mapping. The coring locations included the undisturbed upper foreset, mudflow lobes, gullies, and the undisturbed prodelta. Nine multicores were analyzed for Beryllium-7 activity, and four cores were analyzed for excess Thorium-234 activity via gamma spectrometry, granulometry and X-radiography. Our results indicate a general trend of declining 7Be and 234Th activities and inventories with increasing distance from sources and in deeper water. The core X-radiographs are graded from the predominantly physically stratified nearshore to the more bioturbated offshore, consistent with the sedimentation patterns. Sediment focusing assessed via the 7Be and 234Th sediment inventories shows preferential sedimentation in gully and lobe environments, whereas the upper foreset and prodelta focusing factors are relatively depleted. Overall, short-term sediment deposition from the main fluvial source remains active offshore from all three major river outlets, despite the overall declining river load.
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ArticleExpanding our view of the cold-water coral niche and accounting of the ecosystem services of the reef habitat(Nature Research, 2023-11-09)Coral reefs are iconic ecosystems that support diverse, productive communities in both shallow and deep waters. However, our incomplete knowledge of cold-water coral (CWC) niche space limits our understanding of their distribution and precludes a complete accounting of the ecosystem services they provide. Here, we present the results of recent surveys of the CWC mound province on the Blake Plateau off the U.S. east coast, an area of intense human activity including fisheries and naval operations, and potentially energy and mineral extraction. At one site, CWC mounds are arranged in lines that total over 150 km in length, making this one of the largest reef complexes discovered in the deep ocean. This site experiences rapid and extreme shifts in temperature between 4.3 and 10.7 °C, and currents approaching 1 m s−1. Carbon is transported to depth by mesopelagic micronekton and nutrient cycling on the reef results in some of the highest nitrate concentrations recorded in the region. Predictive models reveal expanded areas of highly suitable habitat that currently remain unexplored. Multidisciplinary exploration of this new site has expanded understanding of the cold-water coral niche, improved our accounting of the ecosystem services of the reef habitat, and emphasizes the importance of properly managing these systems.
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ArticleCrustal structure across the central Dead Sea Transform and surrounding areas: insights into tectonic processes in continental transforms(Wiley, 2023-07-19)New geophysical profiles across the central Dead Sea Transform (DST) near the Sea of Galilee, Israel, and surrounding highlands, augmented by static stress modeling, allow us to study continental transform plate deformation. The DST separates a ∼10 km thick sedimentary column above a thinned (16–23 km) crust to the west from a ∼7 km column above a ∼30-km thick crust to the east. Crustal thinning starts under the DST, as observed also farther south, indicating that the DST is indeed located along the boundary between the Arabian plate and its continental margin. Moho step here is gradual. The DST's eastern shoulder dips westward toward the DST unlike the upward flexed shoulder observed farther south, perhaps delineating the northern limit of a thinner and hotter lithosphere. The shape of the Sea of Galilee is modeled as an asymmetric pull-apart basin formed by a left-lateral stepover of 2.6 km between slightly divergent and underlapping strike-slip fault strands dipping 70° to the west. Reflection data indicate that these strands are not connected. Several fault traces within the Sea of Galilee have previously been suggested to carry part of the relative plate motion. However, given slip along the main DST faults, Coulomb stress will increase only on fault portions in the northern part of the lake, in accord with the geographical distribution of seismicity, suggesting that these faults are likely secondary. Mismatch between the DST strand locations in the geophysical profiles and the subsidence model, may reflect temporal changes in fault geometry.
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ArticleAcoustic ducting by shelf water streamers at the New England shelfbreak(Acoustical Society of America, 2023-08-01)Greater sound speed variability has been observed at the New England shelfbreak due to a greater influence from the Gulf Stream with increased meander amplitudes and frequency of Warm Core Ring (WCR) generation. Consequently, underwater sound propagation in the area also becomes more variable. This paper presents field observations of an acoustic near-surface ducting condition induced by shelf water streamers that are related to WCRs. The field observations also reveal the subsequent disappearance of the streamer duct due to the passage of a WCR filament. These two water column conditions are investigated with sound propagation measurements and numerical simulations.
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ArticleLate Pleistocene-Holocene age and stratigraphy of the Currituck Slide Complex, U.S. mid-Atlantic continental slope: Implications for landslide triggering(Elsevier, 2023-06-16)Considerable effort has been made to link submarine slope failures to changes in local and global-scale environmental conditions, in order to assess landslide hazard probability. Here we provide the first radiocarbon dates of hemipelagic sediment overlying mass transport deposits and inferred failure surfaces of the Currituck Slide Complex (CSC), a prominent landslide scar on the U.S. mid-Atlantic continental slope. The dates, taken from both the upper and lower scars of the complex, constrain the age of the last major failure event to 13,835 and 16,020 years BP. Time correlation of the hemipelagic sediments across the landslide scar and proximal deposit suggests a single failure of both the upper and lower parts of this 160 km3 volume. A higher rate of sediment supply from the periglacial Appalachian Mountains and from glacial melt-water pulses, with an exposed continental shelf at that time, may have enlarged a shelf-edge delta at the site of the CSC, which may have facilitated or triggered failure. A smaller landslide at the southern edge of the complex with a less well-defined geomorphologic footprint is dated at 5500 BP and possibly represents the reshaping of the seafloor around the CSC triggered by low-frequency earthquakes on the nearby continental margin.
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ArticleEpisodic intraplate magmatism fed by a long-lived melt channel of distal plume origin(American Association for the Advancement of Science, 2023-06-09)In the past decade, marine geophysical observations have led to the discovery of thin channels at the base of oceanic plates with anomalous physical properties that indicate the presence of low-degree partial melts. However, mantle melts are buoyant and should migrate toward the surface. We show abundant observations of widespread intraplate magmatism on the Cocos Plate where a thin partial melt channel was imaged at the lithosphere-asthenosphere boundary. We combine existing geophysical, geochemical, and seafloor drilling results with seismic reflection data and radiometric dating of drill cores to constrain the origin, distribution, and timing of this magmatism. Our synthesis indicates that the sublithospheric channel is a regionally extensive (>100,000 km2) and long-lived feature that originated from the Galápagos Plume more than 20 Ma ago, supplying melt for multiple magmatic events and persisting today. Plume-fed melt channels may be widespread and long-lived sources for intraplate magmatism and mantle metasomatism.
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ArticleCategorizing active marine acoustic sources based on their potential to affect marine animals(MDPI, 2022-09-09)Marine acoustic sources are widely used for geophysical imaging, oceanographic sensing, and communicating with and tracking objects or robotic vehicles in the water column. Under the U.S. Marine Mammal Protection Act and similar regulations in several other countries, the impact of controlled acoustic sources is assessed based on whether the sound levels received by marine mammals meet the criteria for harassment that causes certain behavioral responses. This study describes quantitative factors beyond received sound levels that could be used to assess how marine species are affected by many commonly deployed marine acoustic sources, including airguns, high-resolution geophysical sources (e.g., multibeam echosounders, sidescan sonars, subbottom profilers, boomers, and sparkers), oceanographic instrumentation (e.g., acoustic doppler current profilers, split-beam fisheries sonars), and communication/tracking sources (e.g., acoustic releases and locators, navigational transponders). Using physical criteria about the sources, such as source level, transmission frequency, directionality, beamwidth, and pulse repetition rate, we divide marine acoustic sources into four tiers that could inform regulatory evaluation. Tier 1 refers to high-energy airgun surveys with a total volume larger than 1500 in3 (24.5 L) or arrays with more than 12 airguns, while Tier 2 covers the remaining low/intermediate energy airgun surveys. Tier 4 includes most high-resolution geophysical, oceanographic, and communication/tracking sources, which are considered unlikely to result in incidental take of marine mammals and therefore termed de minimis. Tier 3 covers most non-airgun seismic sources, which either have characteristics that do not meet the de minimis category (e.g., some sparkers) or could not be fully evaluated here (e.g., bubble guns, some boomers). We also consider the simultaneous use of multiple acoustic sources, discuss marine mammal field observations that are consistent with the de minimis designation for some acoustic sources, and suggest how to evaluate acoustic sources that are not explicitly considered here.
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ArticleOxygenation of a karst subterranean estuary during a tropical cyclone: mechanisms and implications for the carbon cycle(Association for the Sciences of Limnology and Oceanography, 2022-09-23)Seasonal precipitation affects carbon turnover and methane accumulation in karst subterranean estuaries, the region of coastal carbonate aquifers where hydrologic and biogeochemical processes regulate material exchange between the land and ocean. However, the impact that tropical cyclones exert on subsurface carbon cycling within karst landscapes is poorly understood. Here, we present 5‐month‐long hydrologic and chemical records from 1 and 2 km inland from the coastline within the Ox Bel Ha Cave System in the northeastern Yucatan Peninsula. The record encompasses wet and dry seasons and includes the impact of rainfall during the development of Tropical Storm Hanna in October 2014. Methane accumulated in highest concentrations at the inland site, especially during the wet season preceding the storm. Intense rainfall led to episodic increases in water level and salinity shifts at both sites, indicating a spatially widespread hydrologic response. The most profound storm effect was a ~ 0.8 mg L−1 pulse of dissolved oxygen that declined to zero within 2 weeks and corresponded with a reduction of methane. A positive shift in methane's stable carbon isotope content from −62.6‰ ± 0.6‰ before the storm to −44.0‰ ± 2.4‰ after the storm indicates microbial methane oxidation was a mechanism for the loss of groundwater methane. Post‐storm methane concentrations did not recover to pre‐storm levels during the observation period, suggesting tropical cyclones have long‐lasting (months) effects on the carbon cycle. Compared to seasonal effects, mixing and oxygen inputs during storm‐induced hydrologic forcing have an outsized biogeochemical influence within stratified coastal aquifers.
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ArticleLong-wavelength propagation in fractured rock masses (3D Stress Field)(American Geophysical Union, 2022-09-05)Fractured rocks affect a wide range of natural processes and engineering systems. In most cases, the seismic characterization of fractured rock masses in the field involves wavelengths much longer than the fracture spacing; reproducing this condition in the laboratory is experimentally challenging. This experimental investigation explores the effect of fracture rock fabric and the 3D stress field on P wave propagation in the long‐wavelength regime using a large‐scale true triaxial device. P wave velocities increase with stress in the propagation direction and follow a power law of the form Vp = α(σ’/kPa)β; analyses and experimental results show that stress‐sensitive fracture stiffness and fracture density define the α‐factor and β‐exponent; conversely, long‐wavelength velocity versus stress data can be analyzed to identify the stress‐dependent fracture stiffness. P wave velocities exhibit hysteretic behavior caused by inelastic fracture deformation and fabric changes. During deviatoric loading, the P wave velocity decreases in the two constant‐stress directions due to the development of internal force chains and the ensuing three‐dimensional deformation. Following a load increment, time‐dependent contact deformations result in P wave velocity changes during the first several hours for the tested carbonate rocks; the asymptotic change in velocity is more pronounced for higher stress changes and stress levels. The fracture network geometry that defines the rock fabric acts as a low‐pass filter to wave propagation, so that wavelengths must be longer than two times the fracture spacing to propagate (Brillouin dispersion); the long‐wavelength velocity and the fracture spacing determine the cutoff frequency. Fabric anisotropy contributes to anisotropic low‐pass filtering effects in the rock mass.Plain Language SummarySeismic waves provide a convenient method to characterize fractured rock masses for various applications, from infrastructure engineering to reservoir characterization and production monitoring. But what do wave propagation parameters tell us about the rock mass? Results from this study show that the propagation velocity is a function of the confining stress and that both fracture geometry and stress anisotropy cause velocity anisotropy. We also found that only waves with a wavelength much longer than the spacing between fractures can traverse the medium (short wavelengths get trapped bouncing between fractures); therefore, a high‐frequency cutoff can be used to infer the fracture density in the direction of propagation.Key PointsLong‐wavelength P wave propagation velocity in fractured rocks increases with effective stress due to the stress‐dependent fracture stiffnessRelated phenomena include velocity‐stress hysteresis, fabric‐dependent low‐pass filtering, and creep‐induced stiffness changes in short time scalesLong‐wavelength P wave propagation parameters reflect both fabric and stress anisotropy
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ArticleMature diffuse tectonic block boundary revealed by the 2020 southwestern Puerto Rico seismic sequence(American Geophysical Union, 2022-02-08)Distributed faulting typically tends to coalesce into one or a few faults with repeated deformation. The progression of clustered medium-sized (≥Mw4.5) earthquakes during the 2020 seismic sequence in southwestern Puerto Rico (SWPR), modeling shoreline subsidence from InSAR, and sub-seafloor mapping by high-resolution seismic reflection profiles, suggest that the 2020 SWPR seismic sequence was distributed across several short intersecting strike-slip and normal faults beneath the insular shelf and upper slope of Guayanilla submarine canyon. Multibeam bathymetry map of the seafloor shows significant erosion and retreat of the shelf edge in the area of seismic activity as well as slope-parallel lineaments and submarine canyon meanders that typically develop over geological time. The T-axis of the moderate earthquakes further matches the extension direction previously measured on post early Pliocene (∼>3 Ma) faults. We conclude that although similar deformation has likely taken place in this area during recent geologic time, it does not appear to have coalesced during this time. The deformation may represent the southernmost part of a diffuse boundary, the Western Puerto Rico Deformation Boundary, which accommodates differential movement between the Puerto Rico and Hispaniola arc blocks. This differential movement is possibly driven by the differential seismic coupling along the Puerto Rico—Hispaniola subduction zone. We propose that the compositional heterogeneity across the island arc retards the process of focusing the deformation into a single fault. Given the evidence presented here, we should not expect a single large event in this area but similar diffuse sequences in the future.
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ArticleEarthquake magnitude distributions on northern Caribbean faults from combinatorial optimization models(American Geophysical Union, 2021-10-11)On-fault earthquake magnitude distributions are calculated for northern Caribbean faults using estimates of fault slip and regional seismicity parameters. Integer programming, a combinatorial optimization method, is used to determine the optimal spatial arrangement of earthquakes sampled from a truncated Gutenberg-Richter distribution that minimizes the global misfit in slip rates on a complex fault system. Slip rates and their uncertainty on major faults are derived from a previously published GPS block model for the region, with fault traces determined from offshore geophysical mapping and previously published onshore studies. The optimal spatial arrangement of the sampled earthquakes is compared with the 500-year history of earthquake observations. Rupture segmentation of the subduction interface along the Hispaniola-Puerto Rico Trench (PRT) fault and seismic coupling on the PRT fault appear to exert the primary control over this spatial arrangement. Introducing a rupture barrier for the Hispaniola-PRT fault northwest of Mona Passage, based on geophysical and seismicity observations, and assigning a low slip rate of 2 mm/yr on the PRT fault are most consistent with historical earthquakes in the region. The addition of low slip-rate secondary faults as well as segmentation of the Hispaniola and Septentrional strike-slip fault improves the consistency with historical seismicity. An important observation from the modeling is that varying the slip rate on the PRT fault and different segmentation scenarios result in significant changes to the optimal magnitude distribution on faults farther away. In general, optimal on-fault magnitude distributions are more complex and inter-dependent than is typically assumed in probabilistic seismic hazard analysis and probabilistic tsunami hazard analysis.
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ArticleHydrate formation on marine seep bubbles and the implications for water column methane dissolution(American Geophysical Union, 2021-09-01)Methane released from seafloor seeps contributes to a number of benthic, water column, and atmospheric processes. At seafloor seeps within the methane hydrate stability zone, crystalline gas hydrate shells can form on methane bubbles while the bubbles are still in contact with the seafloor or as the bubbles begin ascending through the water column. These shells reduce methane dissolution rates, allowing hydrate-coated bubbles to deliver methane to shallower depths in the water column than hydrate-free bubbles. Here, we analyze seafloor videos from six deepwater seep sites associated with a diverse range of bubble-release processes involving hydrate formation. Bubbles that grow rapidly are often hydrate-free when released from the seafloor. As bubble growth slows and seafloor residence time increases, a hydrate coating can form on the bubble's gas-water interface, fully coating most bubbles within ∼10 s of the onset of hydrate formation at the seafloor. This finding agrees with water-column observations that most bubbles become hydrate-coated after their initial ∼150 cm of rise, which takes about 10 s. Whether a bubble is coated or not at the seafloor affects how much methane a bubble contains and how quickly that methane dissolves during the bubble's rise through the water column. A simplified model shows that, after rising 150 cm above the seafloor, a bubble that grew a hydrate shell before releasing from the seafloor will have ∼5% more methane than a bubble of initial equal volume that did not grow a hydrate shell after it traveled to the same height.
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ArticleLimited mantle hydration by bending faults at the Middle America Trench(American Geophysical Union, 2020-12-15)Seismic anisotropy measurements show that upper mantle hydration at the Middle America Trench (MAT) is limited to serpentinization and/or water in fault zones, rather than distributed uniformly. Subduction of hydrated oceanic lithosphere recycles water back into the deep mantle, drives arc volcanism, and affects seismicity at subduction zones. Constraining the extent of upper mantle hydration is an important part of understanding many fundamental processes on Earth. Substantially reduced seismic velocities in tomography suggest that outer rise plate‐bending faults provide a pathway for seawater to rehydrate the slab mantle just prior to subduction. Estimates of outer‐rise hydration based on tomograms vary significantly, with some large enough to imply that, globally, subduction has consumed more than two oceans worth of water during the Phanerozoic. We found that, while the mean upper mantle wavespeed is reduced at the MAT outer rise, the amplitude and orientation of inherited anisotropy are preserved at depths >1 km below the Moho. At shallower depths, relict anisotropy is replaced by slowing in the fault‐normal direction. These observations are incompatible with pervasive hydration but consistent with models of wave propagation through serpentinized fault zones that thin to <100‐m in width at depths >1 km below Moho. Confining hydration to fault zones reduces water storage estimates for the MAT upper mantle from ∼3.5 wt% to <0.9 wt% H20. Since the intermediate thermal structure in the ∼24 Myr‐old MAT slab favors serpentinization, limited hydration suggests that fault mechanics are the limiting factor, not temperatures. Subducting mantle may be similarly dry globally.
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ArticleEstimating the impact of seep methane oxidation on ocean pH and dissolved inorganic radiocarbon along the US Mid-Atlantic Bight(American Geophysical Union, 2020-12-23)Ongoing ocean warming can release methane (CH4) currently stored in ocean sediments as free gas and gas hydrates. Once dissolved in ocean waters, this CH4 can be oxidized to carbon dioxide (CO2). While it has been hypothesized that the CO2 produced from aerobic CH4 oxidation could enhance ocean acidification, a previous study conducted in Hudson Canyon shows that CH4 oxidation has a small short‐term influence on ocean pH and dissolved inorganic radiocarbon. Here we expand upon that investigation to assess the impact of widespread CH4 seepage on CO2 chemistry and possible accumulation of this carbon injection along 234 km of the U.S. Mid‐Atlantic Bight. Consistent with the estimates from Hudson Canyon, we demonstrate that a small fraction of ancient CH4‐derived carbon is being assimilated into the dissolved inorganic radiocarbon (mean fraction of 0.5 ± 0.4%). The areas with the highest fractions of ancient carbon coincide with elevated CH4 concentration and active gas seepage. This suggests that aerobic CH4 oxidation has a greater influence on the dissolved inorganic pool in areas where CH4 concentrations are locally elevated, instead of displaying a cumulative effect downcurrent from widespread groupings of CH4 seeps. A first‐order approximation of the input rate of ancient‐derived dissolved inorganic carbon (DIC) into the waters overlying the northern U.S. Mid‐Atlantic Bight further suggests that oxidation of ancient CH4‐derived carbon is not negligible on the global scale and could contribute to deepwater acidification over longer time scales.
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ArticleIdeas and perspectives: a strategic assessment of methane and nitrous oxide measurements in the marine environment(European Geosciences Union, 2020-11-26)In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment.
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ArticleAlong-margin variations in breakup volcanism at the Eastern North American Margin(American Geophysical Union, 2020-11-16)We model the magnetic signature of rift‐related volcanism to understand the distribution and volume of magmatic activity that occurred during the breakup of Pangaea and early Atlantic opening at the Eastern North American Margin (ENAM). Along‐strike variations in the amplitude and character of the prominent East Coast Magnetic Anomaly (ECMA) suggest that the emplacement of the volcanic layers producing this anomaly similarly varied along the margin. We use three‐dimensional magnetic forward modeling constrained by seismic interpretations to identify along‐margin variations in volcanic thickness and width that can explain the observed amplitude and character of the ECMA. Our model results suggest that the ECMA is produced by a combination of both first‐order (~600–1,000 km) and second‐order (~50–100 km) magmatic segmentation. The first‐order magmatic segmentation could have resulted from preexisting variations in crustal thickness and rheology developed during the tectonic amalgamation of Pangaea. The second‐order magmatic segmentation developed during continental breakup and likely influenced the segmentation and transform fault spacing of the initial, and modern, Mid‐Atlantic Ridge. These variations in magmatism show how extension and thermal weakening was distributed at the ENAM during continental breakup and how this breakup magmatism was related to both previous and subsequent Wilson cycle stages.