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At least 127 records · Page 7Linked to original sources
USGS2016

A multi-decade record of high-quality fCO2 data in version 3 of the Surface Ocean CO2 Atlas (SOCAT)

The Surface Ocean CO 2 Atlas (SOCAT) is a synthesis of quality-controlled f CO 2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million f CO 2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million f CO 2 values relative to version 2 and extends the record from 2011 to 2014. Version 3 also significantly increases the data availability for 2005 to 2013. SOCAT has an average of approximately 1.2 million surface water f CO 2 values per year for the years 2006 to 2012. Quality and documentation of the data has improved. A new feature is the data set quality control (QC) flag of E for data from alternative sensors and platforms. The accuracy of surface water f CO 2 has been defined for all data set QC flags. Automated range checking has been carried out for all data sets during their upload into SOCAT. The upgrade of the interactive Data Set Viewer (previously known as the Cruise Data Viewer) allows better interrogation of the SOCAT data collection and rapid creation of high-quality figures for scientific presentations. Automated data upload has been launched for version 4 and will enable more frequent SOCAT releases in the future. High-profile scientific applications of SOCAT include quantification of the ocean sink for atmospheric carbon dioxide and its long-term variation, detection of ocean acidification, as well as evaluation of coupled-climate and ocean-only biogeochemical models. Users of SOCAT data products are urged to acknowledge the contribution of data providers, as stated in the SOCAT Fair Data Use Statement. This ESSD (Earth System Science Data) “living data” publication documents the methods and data sets used for the assembly of this new version of the SOCAT data collection and compares these with those used for earlier versions of the data collection (Pfeil et al., 2013; Sabine et al., 2013; Bakker et al., 2014).

Earth System Science Data↗
USGS1987

Distribution of ferromanganese nodules in the Pacific Ocean.

The occurrence and distribution of deep-ocean ferromanganese nodules are related to the lithology of pelagic surface-sediment, sediment accumulation rates, sea-floor bathymetry, and benthic circulation. Nodules often occur in association with both biosiliceous and pelagic clay, and less often with calcareous sediment. Factors which influence the rather complex patterns of sediment lithology and accumulation rates include the supply of material to the sea-floor and secondary processes in the deep ocean which alter or redistribute that supply. The supply is largely controlled by: 1) proximity to a source of alumino-silicate material and 2) primary biological productivity in the photic zone of the ocean. Primary productivity controls the 'rain' to the sea-floor of biogenic detritus, which consists mostly of siliceous and calcareous tests of planktonic organisms but also contains smaller proportions of phosphatic material and organic matter. The high accumulation rate (5 mm/1000 yr) of sediment along the equator is a direct result of high productivity in this region of the Pacific. Secondary processes include the dissolution of particulate organic matter at depth in the ocean, notably CaCO3, and the redistribution of sedimentary particles by deep-ocean currents. -J.M.H.

Chemie der Erde↗
USGS2009

Pliocene three-dimensional global ocean temperature reconstruction

A snapshot of the thermal structure of the mid-Piacenzian ocean is obtained by combining the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM3) multiproxy sea-surface temperature (SST) reconstruction with bottom water tempera-5 ture estimates produced using Mg/Ca paleothermometry. This reconstruction assumes a Pliocene water mass framework similar to that which exists today, with several important modifications. The area of formation of present day North Atlantic Deep Water (NADW) was expanded and extended further north toward the Arctic Ocean during the mid-Piacenzian relative to today. This, combined with a deeper Greenland-Scotland Ridge, allowed a greater volume of warmer NADW to enter the Atlantic Ocean. In the Southern Ocean, the Polar Front Zone was expanded relative to present day, but shifted closer to the Antarctic continent. This, combined with at least seasonal reduction in sea ice extent, resulted in decreased Antarctic BottomWater (AABW) production (relative to present day) as well as possible changes in the depth of intermediate wa15 ters. The reconstructed mid-Piacenzian three-dimensional ocean was warmer overall than today, and the hypothesized aerial extent of water masses appears to fit the limited stable isotopic data available for this time period. ?? Author(s) 2009.

Climate of the Past Discussions↗
USGS2019

The benthic foraminifera cassidulina from the Arctic Ocean: Application to paleoceanography and biostratigraphy

We investigated the morphology, biostratigraphy, shell stable isotope composition and paleogeography of the common Arctic benthic foraminifera, Cassidulina teretis (Tappan 1951) (sometimes assigned to Islandiella (Nørvang 1958), for application to Quaternary paleoceanography. Cassidulina teretis, which has been studied by several generations of Arctic foraminiferal specialists, is used in Arctic Ocean paleoceanographic reconstructions based on foraminiferal assemblages and, increasingly, isotope shell chemistry. Here we review its modern and fossil distribution including discussions of its taxonomy, ecology, biostratigraphy and shell chemistry. Cassidulina teretis Tappan 1951, originally described from the Gubik Formation, northern Alaska coastal plain, has variability in test size, apertural morphology and development of an umbilical boss representing intra- and inter-population differences across the Arctic and subarctic in modern, Quaternary and Pliocene assemblages. Nonetheless, our studies and those previously published lead us to conclude that populations from the Arctic Ocean represent a single species proposed by Tappan as Cassidulina teretis. Its modern distribution is mainly 200 to 1000 m water depth, often living within the core of the relatively warm Atlantic Layer. However, shallower occurrences suggest other factors, such as food supply, are also critical to its ecology. The Holocene distribution of Cassidulina teretis in the Beaufort Sea boundary indicate millennial-scale changes in relative abundance related to changing Atlantic Layer influence, sea-ice cover, surface productivity and food availability. There are extremely large changes in its abundance during the last deglacial interval on the Yermak Plateau, Barents Sea slope and the Laptev Sea reflecting rapid ocean changes during the Bølling-Allerød, Younger Dryas, and Preboreal. Similarly, C. teretis abundance changes during the last 300,000 years allow us to use it, at least regionally, as a useful biostratigraphic marker. The stable isotopic composition of Cassidulina teretis tests holds promise for establishing an isotope stratigraphy across the Arctic Ocean and perhaps also in the Nordic Seas, off Iceland and in the northern North Atlantic Ocean, once disequilibrium values and offsets from other Arctic benthic species are more firmly established.

Micropaleontology↗
USGS2012

Implementation of the vortex force formalism in the coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system for inner shelf and surf zone applications

The coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST) enables simulations that integrate oceanic, atmospheric, wave and morphological processes in the coastal ocean. Within the modeling system, the three-dimensional ocean circulation module (ROMS) is coupled with the wave generation and propagation model (SWAN) to allow full integration of the effect of waves on circulation and vice versa. The existing wave-current coupling component utilizes a depth dependent radiation stress approach. In here we present a new approach that uses the vortex force formalism. The formulation adopted and the various parameterizations used in the model as well as their numerical implementation are presented in detail. The performance of the new system is examined through the presentation of four test cases. These include obliquely incident waves on a synthetic planar beach and a natural barred beach (DUCK' 94); normal incident waves on a nearshore barred morphology with rip channels; and wave-induced mean flows outside the surf zone at the Martha's Vineyard Coastal Observatory (MVCO). Model results from the planar beach case show good agreement with depth-averaged analytical solutions and with theoretical flow structures. Simulation results for the DUCK' 94 experiment agree closely with measured profiles of cross-shore and longshore velocity data from and . Diagnostic simulations showed that the nonlinear processes of wave roller generation and wave-induced mixing are important for the accurate simulation of surf zone flows. It is further recommended that a more realistic approach for determining the contribution of wave rollers and breaking induced turbulent mixing can be formulated using non-dimensional parameters which are functions of local wave parameters and the beach slope. Dominant terms in the cross-shore momentum balance are found to be the quasi-static pressure gradient and breaking acceleration. In the alongshore direction, bottom stress, breaking acceleration, horizontal advection and horizontal vortex forces dominate the momentum balance. The simulation results for the bar/rip channel morphology case clearly show the ability of the modeling system to reproduce horizontal and vertical circulation patterns similar to those found in laboratory studies and to numerical simulations using the radiation stress representation. The vortex force term is found to be more important at locations where strong flow vorticity interacts with the wave-induced Stokes flow field. Outside the surf zone, the three-dimensional model simulations of wave-induced flows for non-breaking waves closely agree with flow observations from MVCO, with the vertical structure of the simulated flow varying as a function of the vertical viscosity as demonstrated by Lentz et al. (2008).

Ocean Modelling↗
USGS2024

Modeled coastal-ocean pathways of land-sourced contaminants in the aftermath of Hurricane Florence

Extreme precipitation during Hurricane Florence, which made landfall in North Carolina in September 2018, led to breaches of hog waste lagoons, coal ash pits, and wastewater facilities. In the weeks following the storm, freshwater discharge carried pollutants, sediment, organic matter, and debris to the coastal ocean, contributing to beach closures, algae blooms, hypoxia, and other ecosystem impacts. Here, the ocean pathways of land-sourced contaminants following Hurricane Florence are investigated using the Regional Ocean Modeling System (ROMS) with a river point source with fixed water properties from a hydrologic model (WRF-Hydro) of the Cape Fear River Basin, North Carolina's largest watershed. Patterns of contaminant transport in the coastal ocean are quantified with a finite duration tracer release based on observed flooding of agricultural and industrial facilities. A suite of synthetic events also was simulated to investigate the sensitivity of the river plume transport pathways to river discharge and wind direction. The simulated Hurricane Florence discharge event led to westward (downcoast) transport of contaminants in a coastal current, along with intermittent storage and release of material in an offshore (bulge) or eastward (upcoast) region near the river mouth, modulated by alternating upwelling and downwelling winds. The river plume patterns led to a delayed onset and long duration of contaminants affecting beaches 100 km to the west, days to weeks after the storm. Maps of the onset and duration of hypothetical water quality hazards for a range of weather conditions may provide guidance to managers on the timing of swimming/shellfishing advisories and water quality sampling.

Journal of Geophysical Research: Oceans↗
USGS1996

Southern Ocean monthly wave fields for austral winters 1985-1988 by Geosat radar altimeter

Four years of monthly averaged wave height fields for the austral winters 1985–1988 derived from the Geosat altimeter data show a spatial variability of the scale of 500–1000 km that varies monthly and annually. This variability is superimposed on the zonal patterns surrounding the Antarctic continent and characteristic of the climatology derived from the U.S. Navy [1992] Marine Climatic Atlas of the World. The location and the intensity of these large-scale features, which are not found in the climatological fields, exhibit strong monthly and yearly variations. A global underestimation of the climatological mean wave heights by more than 1 m is also found over large regions of the Southern Ocean. The largest monthly averaged significant wave heights are above 5 m and are found during August of every year in the Indian Ocean, south of 40°S. The monthly wave fields show more variability in the Atlantic and Pacific Oceans than in the Indian Ocean. The Seasat data from 1978 and the Geosat data from 1985 and 1988 show an eastward rotation of the largest wave heights. However, this rotation is absent in 1986 and 1987; the former was a year of unusually low sea states, and the latter was a year of unusually high sea states, which suggests a link to the El Niño-Southern Oscillation event of 1986.

Journal of Geophysical Research C: Oceans↗
USGS2017

Arctic deep-water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean

Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits. The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.

Geochemistry, Geophysics, Geosystems↗
USGS1994

Tectonics and geology of spreading ridge subduction at the Chile Triple Junction: a synthesis of results from Leg 141 of the Ocean Drilling Program

An active oceanic spreading ridge is being subducted beneath the South American continent at the Chile Triple Junction. This process has played a major part in the evolution of most of the continental margins that border the Pacific Ocean basin. A combination of high resolution swath bathymetric maps, seismic reflection profiles and drillhole and core data from five sites drilled during Ocean Drilling Program (ODP) Leg 141 provide important data that define the tectonic, structural and stratigraphic effects of this modern example of spreading ridge subduction. A change from subduction accretion to subduction erosion occurs along-strike of the South American forearc. This change is prominently expressed by normal faulting, forearc subsidence, oversteepening of topographic slopes and intensive sedimentary mass wasting, overprinted on older signatures of sediment accretion, overthrusting and uplift processes in the forearc. Data from drill sites north of the triple junction (Sites 859-861) show that after an important phase of forearc building in the early to late Pliocene, subduction accretion had ceased in the late Pliocene. Since that time sediment on the downgoing oceanic Nazca plate has been subducted. Site 863 was drilled into the forearc in the immediate vicinity of the triple junction above the subducted spreading ridge axis. Here, thick and intensely folded and faulted trench slope sediments of Pleistocene age are currently involved in the frontal deformation of the forearc. Early faults with thrust and reverse kinematics are overprinted by later normal faults. The Chile Triple Junction is also the site of apparent ophiolite emplacement into the South American forearc. Drilling at Site 862 on the Taitao Ridge revealed an offshore volcanic sequence of Plio-Pleistocene age associated with the Taitao Fracture Zone, adjacent to exposures of the Pliocene-aged Taitao ophiolite onshore. Despite the large-scale loss of material from the forearc at the triple junction, ophiolite emplacement produces a large topographic promontory in the forearc immediately after ridge subduction, and represents the first stage of forearc rebuilding. ?? 1994 Springer-Verlag.

Geologische Rundschau↗
USGS1970

Water content of basalt erupted on the ocean floor

Deep sea pillow basalts dredged from the ocean floor show that vesicularity changes with composition as well as with depth. Alkalic basalts are more vesicular than tholeiitic basalts erupted at the same depth. The vesicularity data, when related to experimentally determined solubility of water in basalt, indicate that K-poor oceanic tholeiites originally contained about 0.25 percent water, Hawaiian tholeiites of intermediate K-content, about 0.5 percent water, and alkali-rich basalts, about 0.9 percent water. Analyses of fresh basalt pillows show a systematic increase of H 2 O + as the rocks become more alkalic. K-poor oceanic tholeiites contain 0.06–0.42 percent H 2 O + , Hawaiian tholeiites, 0.31–0.60 percent H 2 O + , and alkali rich basalts 0.49–0.98 percent H 2 O + . The contents of K 2 O, P 2 O 5 , F, and Cl increase directly with an increase in H 2 O + content such that at 1.0 weight percent H 2 O + , K 2 O is 1.58 percent, P 2 O 5 is 0.55 percent, F is 0.07 percent, and Cl is 0.1 percent. The measured weight percent of deuterium on the rim of one Hawaiian pillow is −6.0 (relative to SMOW); this value, which is similar to other indications of magmatic water, suggests that no appreciable sea water was absorbed by the pillow during or subsequent to eruption on the ocean floor. Concentrations of volatile constituents in the alkali basalt melts relative to tholeiitic melts can be explained by varying degrees of partial melting of mantle material or by fractional crystallization of a magma batch.

Contributions to Mineralogy and Petrology↗
USGS2011

Book review: Rogue waves in the ocean

Rogue Waves in the Ocean (2009) is a follow-on text to Extreme Ocean Waves (2008) edited by Pelinovsky and Kharif, both published by Springer. Unlike the earlier text, which is a compilation of papers on a variety of extreme waves that was the subject of a scientific conference in 2007, Rogues Waves in the Ocean is written, rather than edited, by Kharif, Pelinovsky, and Slunyaev and is focused on rogue waves in particular. The book consists of six chapters covering 216 pages. As the subject matter of each chapter is distinct, references appear at the end of each chapter rather than at the end of the book. The preface shows how each of the chapters relates to the larger study of rogue waves. The result is a book with a nice mix of eyewitness observations, physical theory, and statistics. Review info: Rogue Waves in the Ocean. Advances in Geophysical and Environmental Mechanics and Mathematics. B y Christian Kharif, Efim Pelinovsky and Alexey Slunyaev, 2009. ISBN: 978-3540884187, xiii, 216 pp.

Pure and Applied Geophysics↗
USGS2014

Unexpected hydrogen isotope variation in oceanic pelagic seabirds

Hydrogen isotopes have significantly enhanced our understanding of the biogeography of migratory animals. The basis for this methodology lies in predictable, continental patterns of precipitation δD values that are often reflected in an organism’s tissues. δD variation is not expected for oceanic pelagic organisms whose dietary hydrogen (water and organic hydrogen in prey) is transferred up the food web from an isotopically homogeneous water source. We report a 142 ‰ range in the δD values of flight feathers from the Hawaiian petrel ( Pterodroma sandwichensis ), an oceanic pelagic North Pacific species, and inquire about the source of that variation. We show δD variation between and within four other oceanic pelagic species: Newell’s shearwater ( Puffinus auricularis newellii) , Black-footed albatross ( Phoebastria nigripes ), Laysan albatross ( Phoebastria immutabilis ) and Buller’s shearwater ( Puffinus bulleri ). The similarity between muscle δD values of hatch-year Hawaiian petrels and their prey suggests that trophic fractionation does not influence δD values of muscle. We hypothesize that isotopic discrimination is associated with water loss during salt excretion through salt glands. Salt load differs between seabirds that consume isosmotic squid and crustaceans and those that feed on hyposmotic teleost fish. In support of the salt gland hypothesis, we show an inverse relationship between δD and percent teleost fish in diet for three seabird species. Our results demonstrate the utility of δD in the study of oceanic consumers, while also contributing to a better understanding of δD systematics, the basis for one of the most commonly utilized isotope tools in avian ecology.

Oecologia↗
USGS1996

Global distribution of beryllium isotopes in deep ocean water as derived from Fe-Mn crusts

The direct measurement of the ratio of cosmogenic 10 Be ( T 1 2 = 1.5 Ma "> T12= 1.5 Ma ) to stable terrigenously sourced 9 Be in deep seawater or marine deposits can be used to trace water mass movements and to quantify the incorporation of trace metals into the deep sea. In this study a SIMS-based technique has been used to determine the 10 Be 9 Be "> 10Be9Be ratios of the outermost millimetre of hydrogenetic ferromanganese crusts from the worlds oceans. 10 Be 9 Be "> 10Be9Be ratios, time-corrected for radioactive decay of cosmogenic 10 Be using 234 U 238 U "> 234U238U , are in good agreement with AMS measurements of modern deep seawater. Ratios are relatively low in the North and equatorial Atlantic samples (0.4–0.5 × 10 −7 ). In the Southwest Atlantic ratios increase up to 1 × 10 −7 , they vary between 0.7 and 1.0 × 10 −7 in Indian Ocean samples, and have a near constant value of 1.1 ± 0.2 × 10 −7 for all Pacific samples. If the residence time of 10 Be ( τ 10 Be ) in deep water is constant globally, then the observed variations in 10 Be 9 Be "> 10Be9Be ratios could be caused by accumulation of 10 Be in deep water as it flows and ages along the conveyor, following a transient depletion upon its formation in the Northern Atlantic. In this view both 10 Be and 9 Be reach local steady-state concentration in Pacific deep water and the global τ10 Be ≌ 600 a ">≌ τ10Be≌ 600a . An alternative possibility is that the Be isotope abundances are controlled by local scavenging. For this scenario τ 10 Be would vary according to local particle concentration and would ≌ 600 a in the central Pacific, but τ10 Be ≌ 230 a ">≌ τ10Be≌ 230a in the Atlantic. Mass balance considerations indicate that hydrothermal additions of 9 Be to the oceans are negligible and that the dissolved riverine source is also small. Furthermore, aeolian dust input of 9 Be appears insufficient to provide the dissolved 9 Be inventory. The dissolution of only a small proportion (2%) of river-derived particulates could in principle supply the observed seawater 9 Be content. If true, ocean margins would be the sites for 9 Be addition. Due to the particle-reactive nature of Be, these would also be the primary sites of Be removal. A possible net result of horizontal water masses passing through these marginal areas might be a decrease in seawater 10 Be 9 Be "> 10Be9Be , and establishment of a relatively constant 9 Be concentration. As τ 10 Be (∼ 600 a) is less than the apparent age of deep water in the Pacific (∼ 1500 a), the Pacific record of 10 Be 9 Be "> 10Be9Be is not expected to show secular variations due to changes in deep-water flow, despite the large variations in 10 Be 9 Be "> 10Be9Be between different water masses. Because of this insensitivity to deep-water flow, however, it is suggested that the 10 Be 9 Be "> 10Be9Be ratio, determined in the authigenic phase of marine sediments or hydrogenetic precipitates, should be a suitable tool for monitoring changes in continental input or cosmic ray intensity on longer time scales.

Earth and Planetary Science Letters↗
USGS1983

Hafnium isotope results from mid-ocean ridges and Kerguelen

176Hf/177Hf ratios are presented for oceanic volcanics representing both extremes of the range of mantle HfNdSr isotopic variation. Hf from critical mid-ocean ridgebasalts shows that 176Hf/177Hf does indeed have a greater variability than 143Nd/144Nd and 87Sr/86Sr in the depleted mantle. This extra variation is essentially of a random nature, and can perhaps be understood in terms of known Rb/SrSm/NdLu/Hf fractionation relationships. At the other extreme of mantle isotopic composition, 176Hf/177Hf ratios for igneous rocks from the Indian Ocean island of Kerguelen show a closely similar variation to published 143Nd/144Nd ratios for the same samples. Comparison of HfNdSr c relationships for Tristan da Cunha, Kerguelen and Samoa reveals divergences in the mantle array for ocean island magma sources, and perhaps suggests that these irregularities are largely the result of an extra component of 87Sr/86Sr variation. ?? 1983.

LITHOS↗
USGS1995

Biostratigraphic and paleoclimatic significance of a new Pliocene foraminiferal fauna from the central Arctic Ocean

A Pliocene benthic foraminiferal fauna containing a previously unknown species association was found in the basal section of a piston core collected from the crest of Northwind Ridge (NWR) in the central Arctic Ocean. The fauna is dominated by Epistominella exigua, Cassidulina reniforme, Eponides tumidulus, Cibicides scaldisiensis, Lagena spp., Cassidulina teretis, Eponides weddellensis, Bolivina arctica , and Patellina corrugata . The presence of Cibicides scaldisiensis in the assemblage and the occurrence of Cibicides grossus higher in the core are indicative of an early Pliocene age. The morphologically distinctive species Cibicidoides sp. 795 of McNeil (in press) which occurs in the NWR core sample was previously known only from Oligocene through Miocene deposits in the Beaufort-Mackenzie Basin of Arctic Canada. Ehrenbergina sp. A and Cibicidoides aff. C . sp. 795, also present in the core, are new and endemic to the Arctic late Miocene and early Pliocene. These species, and possibly others, are survivors of the late Miocene (Messinian) sea-level crisis, which caused a significant faunal turnover in the Arctic Ocean. The predominantly calcareous assemblage indicates deposition above the calcium carbonate compensation depth in an upper bathyal environment. Paleogeographic affinities for the bulk of the assemblage indicate probable connections between the Arctic and the North Atlantic Oceans, but the endemic species identify environmental differences or partial isolation of the western Arctic Ocean. The species association suggests a cold but milder paleoclimate than that which existed during Pleistocene glacial intervals.

Marine Micropaleontology↗
USGS2021

Ocean floor manganese deposits

Much of the dissolved Mn delivered to the oceans is slowly oxidized and precipitated alongside varying amounts of Fe into Mn and ferromanganese (FeMn) mineral deposits that occur extensively in the deep ocean wherever sediment accumulation is low and substrate is available. FeMn crusts grow as pavements on rock outcrops throughout the global ocean whereas nodules form as individual FeMn-encrusted particles on the sediment-covered abyssal plains. Both crusts and nodules are composed predominantly of Fe and Mn oxide minerals that precipitate from seawater and for some nodules also from porewaters of deep-sea sediment. In contrast, hydrothermal oxide deposits consist predominantly of Mn or Fe oxide. FeMn crusts and nodules exhibit very high specific surface areas that allow them to scavenge abundant metals and other elements, recording the history of the source waters. Crusts especially serve as an important record of paleoceanographic conditions over the past 70 + million years. Critical metals essential to many computer, military, and green technologies are enriched in crust and nodule deposits to concentrations high enough to compare with, or exceed, typical terrestrial deposits, and they can be considered as potential resources for mining in the near future. Twenty-three contracts pertaining to exploration for nodules and crusts have been signed with the International Seabed Authority, and resource/reserve, baseline, and environmental impact assessments are underway. Many challenges remain to be addressed before full-scale mining of marine FeMn deposits will occur. However, their unique genesis and the growing worldwide need for rare and critical metals keep these deep-ocean deposits relevant to industry, scientists, and governments.

Book chapter↗
USGS2005

Antipodal hotspots and bipolar catastrophes: Were oceanic large-body impacts the cause?

One aspect of the hotspot distribution that has received little attention is its antipodal character. Of 45 ‘primary’ hotspots found in most hotspot compilations 22 (49%) form antipodal pairs within observed hotspot drift limits (≤ 20 mm/yr). In addition, the available ages, or possible age ranges, for both hotspots of an antipodal pair tend to be similar (≤ 10 Myr difference) or overlap. Monte Carlo simulations indicate that the antipodal primary hotspots' locations and ages are not due to chance at the > 99% confidence level ( p < 0.01). All hotspot pairs include at least one oceanic hotspot, and these are consistently opposite those hotspots related to large igneous provinces (LIPs) and continental volcanism. A mechanism of formation is considered in which minor hotspot volcanism is induced at, and flood basalt volcanism is triggered by seismic energy focused antipodal to, oceanic large-body impact sites. Because continental impacts are expected to have lower seismic efficiencies, continents possibly acted as shields to the formation of antipodal hotspot pairs. Published numerical models indicate that large oceanic impacts (10-km-diameter bolide) generate megatsunami capable of altering coastal depositional environments on a global scale. Past impact-generated megatsunami, consequently, could have left widespread stratigraphic records, possibly misinterpreted as indicating large rapid changes in eustatic sea level, and widely disrupted continental and marine sediment reservoirs responsible for abrupt changes in the isotopic composition of seawater. Phanerozoic mass extinction events, therefore, might have resulted primarily from catastrophic megatsunami in a dominantly oceanic hemisphere and the near contemporaneous effusion of vast quantities of noxious gases from flood basalt eruptions in a dominantly continental one.

Earth and Planetary Science Letters↗
USGS2011

Rapid cooling rates at an active mid-ocean ridge from zircon thermochronology

Oceanic spreading ridges are Earth's most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3 − 4.6 + 4.8 ka; 1σ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7 ± 1.6 ka) within uncertainty. Based on similar 238 U− 230 Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~ 10–20 ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900 °C and pressures > 70–150 MPa are calculated from H 2 O solubility models. These time-temperature constraints translate into a magma cooling rate of ~ 2 × 10 − 2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series ( 238 U– 230 Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability.

Juan de Fuca ridge and the Blanco transform fault ↗