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At least 1,153 records · Page 64Linked to original sources
USGS2014

Widespread gas hydrate instability on the upper U.S. Beaufort margin

The most climate-sensitive methane hydrate deposits occur on upper continental slopes at depths close to the minimum pressure and maximum temperature for gas hydrate stability. At these water depths, small perturbations in intermediate ocean water temperatures can lead to gas hydrate dissociation. The Arctic Ocean has experienced more dramatic warming than lower latitudes, but observational data have not been used to study the interplay between upper slope gas hydrates and warming ocean waters. Here we use (a) legacy seismic data that constrain upper slope gas hydrate distributions on the U.S. Beaufort Sea margin, (b) Alaskan North Slope borehole data and offshore thermal gradients determined from gas hydrate stability zone thickness to infer regional heat flow, and (c) 1088 direct measurements to characterize multidecadal intermediate ocean warming in the U.S. Beaufort Sea. Combining these data with a three-dimensional thermal model shows that the observed gas hydrate stability zone is too deep by 100 to 250 m. The disparity can be partially attributed to several processes, but the most important is the reequilibration (thinning) of gas hydrates in response to significant (~0.5°C at 2σ certainty) warming of intermediate ocean temperatures over 39 years in a depth range that brackets the upper slope extent of the gas hydrate stability zone. Even in the absence of additional ocean warming, 0.44 to 2.2 Gt of methane could be released from reequilibrating gas hydrates into the sediments underlying an area of ~5–7.5 × 10 3 km 2 on the U.S. Beaufort Sea upper slope during the next century.

Alaska↗
USGS2011

A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa

Observations and simulations link anthropogenic greenhouse and aerosol emissions with rapidly increasing Indian Ocean sea surface temperatures (SSTs). Over the past 60 years, the Indian Ocean warmed two to three times faster than the central tropical Pacific, extending the tropical warm pool to the west by ~40° longitude (>4,000 km). This propensity toward rapid warming in the Indian Ocean has been the dominant mode of interannual variability among SSTs throughout the tropical Indian and Pacific Oceans (55°E–140°W) since at least 1948, explaining more variance than anomalies associated with the El Niño-Southern Oscillation (ENSO). In the atmosphere, the primary mode of variability has been a corresponding trend toward greatly increased convection and precipitation over the tropical Indian Ocean. The temperature and rainfall increases in this region have produced a westward extension of the western, ascending branch of the atmospheric Walker circulation. Diabatic heating due to increased mid-tropospheric water vapor condensation elicits a westward atmospheric response that sends an easterly flow of dry air aloft toward eastern Africa. In recent decades (1980–2009), this response has suppressed convection over tropical eastern Africa, decreasing precipitation during the ‘long-rains’ season of March–June. This trend toward drought contrasts with projections of increased rainfall in eastern Africa and more ‘El Niño-like’ conditions globally by the Intergovernmental Panel on Climate Change. Increased Indian Ocean SSTs appear likely to continue to strongly modulate the Warm Pool circulation, reducing precipitation in eastern Africa, regardless of whether the projected trend in ENSO is realized. These results have important food security implications, informing agricultural development, environmental conservation, and water resource planning.

Climate Dynamics↗
USGS2011

Effect of tidal fluctuations on transient dispersion of simulated contaminant concentrations in coastal aquifers

Variable-density groundwater models require extensive computational resources, particularly for simulations representing short-term hydrologic variability such as tidal fluctuations. Saltwater-intrusion models usually neglect tidal fluctuations and this may introduce errors in simulated concentrations. The effects of tides on simulated concentrations in a coastal aquifer were assessed. Three analyses are reported: in the first, simulations with and without tides were compared for three different dispersivity values. Tides do not significantly affect the transfer of a hypothetical contaminant into the ocean; however, the concentration difference between tidal and non-tidal simulations could be as much as 15%. In the second analysis, the dispersivity value for the model without tides was increased in a zone near the ocean boundary. By slightly increasing dispersivity in this zone, the maximum concentration difference between the simulations with and without tides was reduced to as low as 7%. In the last analysis, an apparent dispersivity value was calculated for each model cell using the simulated velocity variations from the model with tides. Use of apparent dispersivity values in models with a constant ocean boundary seems to provide a reasonable approach for approximating tidal effects in simulations where explicit representation of tidal fluctuations is not feasible.

Hydrogeology Journal↗
USGS1994

East Mariana Basin tholeiites: Cretaceous intraplate basalts or rift basalts related to the Ontong Java plume?

Studies of seafloor magnetic anomaly patterns suggest the presence of Jurassic oceanic crust in a large area in the western Pacific that includes the East Mariana, Nauru and Pigafetta Basins. Sampling of the igneous crust in this area by the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) allows direct evaluation of the age and petrogenesis of this crust. ODP Leg 129 drilled a 51 m sequence of basalt pillows and massive flows in the central East Mariana Basin. 40 Ar 39 Ar "> 40Ar39Ar ages determined in this study for two Leg 129 basalts average 114.6 ± 3.2 Ma. This age is in agreement with the Albian-late Aptian paleontologic age of the overlying sediments, but is distinctively younger than the Jurassic age predicted by magnetic anomaly patterns in the basin. Compositionally, the East Mariana Basin basalts are uniformly low-K tholeiites that are depleted in highly incompatible elements compared to moderately incompatible ones, which is typical of mid-ocean ridge basalts (MORB) erupted near hotspots. The Sr, Nd and Pb isotopic compositions of the tholeiites ( 87 Sr 86 Sr init = 0.70360–0.70374 "> 87Sr86Srinit= 0.70360–0.70374 ; 143 Nd 144 Nd init = 0.512769–0.512790 "> 143Nd144Ndinit= 0.512769–0.512790 ; 206 Pb 204 Pb meas = 18.355–18.386 "> 206Pb204Pbmeas= 18.355–18.386 ) also overlap with some Indian Ocean Ridge MORB, although they are distinct from the isotopic compositions of Jurassic basalts drilled in the Pigafetta Basin, the oldest Pacific MORB. The isotopic compositions of the East Mariana Basin tholeiites are also similar to those of intraplate basalts, and in particular, to the isotopic signature of basalts from the nearby Ontong Java and Manihiki Plateaus. The East Mariana Basin tholeiites also share many petrologic and isotopic characteristics with the oceanic basement drilled in the Nauru Basin at DSDP Site 462. In addition, the new 110.8 ± 1.0 Ma 40 Ar 39 Ar "> 40Ar39Ar age for two flows from the bottom of Site 462 in the Nauru Basin is indistinguishable from the age of the East Mariana Basin flows. Thus, while magnetic anomaly patterns predict that the igneous basement in the Nauru and East Mariana Basins is Jurassic in age, the geochemical and chronological results discussed here suggest that the basement formed during a Cretaceous rifting event within the Jurassic crust. This magmatic and tectonic event was created by the widespread volcanism responsible for the genesis of the large oceanic plateaus of the western Pacific.

Earth and Planetary Science Letters↗
USGS1987

North American nonmarine climates and vegetation during the Late Cretaceous

Analyses of physiognomy of Late Cretaceous leaf assemblages and of structural adaptations of Late Cretaceous dicotyledonous woods indicate that megathermal vegetation was an open-canopy, broad-leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year, with a moderate increase at about 40–45°N. Many dicotyledons were probably large, massive trees, but the tallest trees were evergreen conifers. Megathermal climate extended up to paleolatitude 45–50°N. Mesothermal vegetation was at least partially an open, broad-leaved evergreen woodland (perhaps a mosaic of woodland and forest), but the evapotranspirational stress was less than in megathermal climate. Some dicotyledons were large trees, but most were shrubs or small trees; evergreen conifers were the major tree element. Some mild seasonality is evidenced in mesothermal woods; precipitational levels probably varied markedly from year to year. Northward of approximately paleolatitude 65°N, evergreen vegetation was replaced by predominantly deciduous vegetation. This replacement is presumably related primarily to seasonality of light. The southern part of the deciduous vegetation probably existed under mesothermal climate. Comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational-climatic patterns suggested from North American data. Limited data from equatorial regions suggest low rainfall. Late Cretaceous climates, except probably those of the Cenomanian, had only moderate change through time. Temperatures generally appear to have warmed into the Santonian, cooled slightly into the Campanian and more markedly into the Maastrichtian, and then returned to Santonian values by the late Maastrichtian. The early Eocene was probably warmer than any period of the Late Cretaceous. Latitudinal temperature gradients were lower than at present. For the Campanian and Maastrichtian, a gradient of about 0.3°C/1° latitude is inferred. Equability was high: a mean annual range of temperature of about 8°C is inferred for paleolatitude 51–56°N during the Campanian. Most Late Cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation. A brief, low-temperature excursion and a major, long-lasting increase in precipitation occurred at the Cretaceous-Tertiary boundary. In megathermal climates, these events selected for plants that could exist in rainforest environments. In mesothermal climates, deciduousness and contamitant structural adaptations were selected. The events at the Cretaceous-Tertiary boundary had a major and long-lasting impact on the evolution of land plants and their ecosystems. Low precipitation at low to middle Late Cretaceous latitudes is suggested to be the result of high levels of atmospheric CO 2 , which, in turn, are probably related to inability of warm, saline oceans to store large amounts of carbon. Conditions appear to have rapidly changed at the Cretaceous-Tertiary boundary, when oceanic circulation and stratification may have been fundamentally altered. After the boundary, the oceans were apparently able to store much greater amounts of carbon, and the oceans withdrew large amounts of CO 2 from the atmosphere. In turn, more precipitation fell at low to middle latitudes; the resulting high-biomass vegetation formed a second major carbon reservoir to keep atmospheric CO 2 low relative to the Late Cretaceous. Changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean-atmosphere system.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1979

Seismic refraction study of the continental edge off the eastern United States

Three long, strike-parallel, seismic-refraction profiles were made on the continental shelf edge, slope and upper rise off New Jersey during 1975. The shelf edge line lies along the axis of the East Coast Magnetic Anomaly (ECMA), while the continental rise line lies 80 km seaward of the shelf edge. Below the unconsolidated sediments (1.7–3.6 km/sec), high-velocity sedimentary rocks (4.2–6.2 km/sec) were found at depths of 2.6–8.2 km and are inferred to be cemented carbonates. Although multichannel seismic-reflection profiles and magnetic depth-to-source data predicted the top of oceanic basement at 6–8 km beneath the shelf edge and 10–11 km beneath the rise, no refracted events occurred as first arrivals from either oceanic basement (layer 2, approximately 5.5 km/ sec) or the upper oceanic crust (layer 3A, approximately 6.8 km/sec). Second arrivals from 10.5 km depth beneath the shelf edge are interpreted as events from a 5.9 km/sec refractor within igneous basement. Other refracted events from either layers 2 or 3A could not be resolved within the complex second arrivals. A well-defined crustal layer with a compressional velocity of 7.1–7.2 km/sec, which can be interpreted as oceanic layer 3B, occurred at 15.8 km depth beneath the shelf and 12.9 km beneath the upper rise. A well-reversed mantle velocity of 8.3 km/sec was measured at 18–22 km depth beneath the upper continental rise. Comparison with other deep-crustal profiles along the continental edge of the Atlantic margin off the United States, specifically in the inner magnetically quiet zone, indicates that the compressional wave velocities and layer depths determined on the U.S.G.S. profiles are very similar to those of nearby profiles. This suggests that the layers are continuous and that the interpretation of the oceanic layer 3B under the shelf edge east of New Jersey implies progradation of the shelf outward over the oceanic crust in that area. This agrees with magnetic anomaly evidence which shows the East Coast Magnetic Anomaly landward of the shelf edge off New Jersey and with previous seismic reflection data which reveal extensive outbuilding of the shelf edge during the Jurassic and Lower Cretaceous, probably by carbonate bank-margin accretion.

East Coast Magnetic Anomaly↗
USGS2011

Waves and tides responsible for the intermittent closure of the entrance of a small, sheltered tidal wetland at San Francisco, CA

Crissy Field Marsh (CFM; http://www.nps.gov/prsf/planyourvisit/crissy-field-marsh-and-beach.htm ) is a small, restored tidal wetland located in the entrance to San Francisco Bay just east of the Golden Gate. The marsh is small but otherwise fairly typical of many such restored wetlands worldwide. The marsh is hydraulically connected to the bay and the adjacent Pacific Ocean by a narrow sandy channel. The channel often migrates and sometimes closes completely, which effectively blocks the tidal connection to the ocean and disrupts the hydraulics and ecology of the marsh. Field measurements of waves and tides have been examined in order to evaluate the conditions responsible for the intermittent closure of the marsh entrance. The most important factor found to bring about the entrance channel closure is the occurrence of large ocean waves. However, there were also a few closure events during times with relatively small offshore waves. Examination of the deep-water directional wave spectra during these times indicates the presence of a small secondary peak corresponding to long period swell from the southern hemisphere, indicating that CFM and San Francisco Bay in general may be more susceptible to long period ocean swell emanating from the south or southwest than the more common ocean waves coming from the northwest. The tidal records during closure events show no strong relationship between closures and tides, other than that closures tend to occur during multi-day periods with successively increasing high tides. It can be inferred from these findings that the most important process to the intermittent closure of the entrance to CFM is littoral sediment transport driven by the influence of ocean swell waves breaking along the CFM shoreline at oblique angles. During periods of large, oblique waves the littoral transport of sand likely overwhelms the scour potential of the tidal flow in the entrance channel.

California↗
USGS2017

Rare earth element behavior during groundwater – seawater mixing along the Kona Coast of Hawaii

Groundwater and seawater samples were collected from nearshore wells and offshore along the Kona Coast of the Big Island of Hawaii to investigate rare earth element (REE) behavior in local subterranean estuaries. Previous investigations showed that submarine groundwater discharge (SGD) is the predominant flux of terrestrial waters to the coastal ocean along the arid Kona Coast of Hawaii. Groundwater and seawater samples were filtered through 0.45 μm and 0.02 μm pore-size filters to evaluate the importance of colloidal and soluble (i.e., truly dissolved ionic species and/or low molecular weight [LMW] colloids) fractions of the REEs in the local subterranean estuaries. Mixing experiments using groundwater collected immediately down gradient from a wastewater treatment facility (WWTF) proximal to the Kaloko-Hanokohau National Historic Park, and more “pristine” groundwater from a well constructed in a lava tube at Kiholo Bay, were mixed with local seawater to study the effect of solution composition (i.e., pH, salinity) on the concentrations and fractionation behavior of the REEs as groundwater mixes with seawater in Kona Coast subterranean estuaries. The mixed waters were also filtered through 0.45 or 0.02 μm filters to ascertain the behavior of colloidal and soluble fractions of the REEs across the salinity gradient in each mixing experiment. Concentrations of the REEs were statistically identical (two-tailed Student t -test, 95% confidence) between the sequentially filtered sample aliquots, indicating that the REEs occur as dissolved ionic species and/or LMW colloids in Kona Coast groundwaters. The mixing experiments revealed that the REEs are released to solution from suspended particles or colloids when Kona Coast groundwater waters mix with local seawater. The order of release that accompanies increasing pH and salinity follows light REE (LREE) > middle REE (MREE) > heavy REE (HREE). Release of REEs in the mixing experiments is driven by decreases in the free metal ion activity in solution and the concomitant increase in the amount of each REE that occurs in solution as dicarbonato complexes [i.e., Ln(CO 3 ) 2 - ] as pH increases across the salinity gradient. Input-normalized REE patterns of Kona Coast groundwater and coastal seawater are nearly identical and relatively flat compared to North Pacific seawater, indicating that SGD is the chief source of these trace elements to the ocean along the Kona Coast. Additionally, REE concentrations of the coastal seawater are between 10 and 50 times higher than previously reported open-ocean seawater values from the North Pacific, further demonstrating the importance of SGD fluxes of REEs to these coastal waters. Taken together, these observations indicate that large-scale removal of REEs, which characterizes the behavior of REEs in the low salinity reaches of many surface estuaries, is not a feature of the subterranean estuary along the Kona Coast. A large positive gadolinium (Gd) anomaly characterizes groundwater from the vicinity of the WWTF. The positive Gd anomaly can be traced to the coastal ocean, providing further evidence of the impact of SGD on the coastal waters. Estimates of the SGD fluxes of the REEs to the coastal ocean along the Kona Coast (i.e., 1.3 – 2.6 mmol Nd day -1 ) are similar to recent estimates of SGD fluxes of REEs along Florida’s east coast and to Rhode Island Sound, all of which points to the importance of SGD as significant flux of REEs to the coastal ocean.

Hawaii↗
USGS2016

Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

Lake sediment oxygen isotope records (calcium carbonate-δ 18 O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ 18 O records along with a new compilation of lake water δ 18 O and δ 2 H that are used to characterize lake sediment sensitivity to precipitation-δ 18 O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ 18 O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ 18 O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ 18 O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ 18 O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ 18 O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ 18 O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive regional precipitation-δ 18 O responses to Pacific ocean–atmosphere variability, which in turn, will lead to a better understanding of internal Pacific ocean–atmosphere variability and its response to external climate forcing mechanisms.

North American Rocky Mountain↗
USGS2014

Phanerozoic continental growth and gold metallogeny of Asia

The Asian continent formed during the past 800 m.y. during late Neoproterozoic through Jurassic closure of the Tethyan ocean basins, followed by late Mesozoic circum-Pacific and Cenozoic Himalayan orogenies. The oldest gold deposits in Asia reflect accretionary events along the margins of the Siberia, Kazakhstan, North China, Tarim–Karakum, South China, and Indochina Precambrian blocks while they were isolated within the Paleotethys and surrounding Panthalassa Oceans. Orogenic gold deposits are associated with large-scale, terrane-bounding fault systems and broad areas of deformation that existed along many of the active margins of the Precambrian blocks. Deposits typically formed during regional transpressional to transtensional events immediately after to as much as 100 m.y. subsequent to the onset of accretion or collision. Major orogenic gold provinces associated with this growth of the Asian continental mass include: (1) the ca. 750 Ma Yenisei Ridge, ca. 500 Ma East Sayan, and ca. 450–350 Ma Patom provinces along the southern margins of the Siberia craton; (2) the 450 Ma Charsk belt of north-central Kazakhstan; (3) the 310–280 Ma Kalba belt of NE Kazakhstan, extending into adjacent NW Xinjiang, along the Siberia–Kazakhstan suture; (4) the ca. 300–280 Ma deposits within the Central Asian southern and middle Tien Shan (e.g., Kumtor, Zarmitan, Muruntau), marking the closure of the Turkestan Ocean between Kazakhstan and the Tarim–Karakum block; (5) the ca. 190–125 Ma Transbaikal deposits along the site of Permian to Late Jurassic diachronous closure of the Mongol–Okhotsk Ocean between Siberia and Mongolia/North China; (6) the probable Late Silurian–Early Devonian Jiagnan belt formed along the margin of Gondwana at the site of collision between the Yangtze and Cathaysia blocks; (7) Triassic deposits of the Paleozoic Qilian Shan and West Qinling orogens along the SW margin of the North China block developed during collision of South China; and (8) Jurassic(?) ores on the margins of the Subumusu block in Myanmar and Malaysia. Circum-Pacific tectonism led to major orogenic gold province formation along the length of the eastern side of Asia between ca. 135 and 120 Ma, although such deposits are slightly older in South Korea and slightly younger in the Amur region of the Russian Southeast. Deformation related to collision of the Kolyma–Omolon microcontinent with the Pacific margin of the Siberia craton led to formation of 136–125 Ma ores of the Yana–Kolyma belt (Natalka, Sarylakh) and 125–119 Ma ores of the South Verkhoyansk synclinorium (Nezhdaninskoe). Giant ca. 125 Ma gold provinces developed in the Late Archean uplifted basement of the decratonized North China block, within its NE edge and into adjacent North Korea, in the Jiaodong Peninsula, and in the Qinling Mountains. The oldest gold-bearing magmatic–hydrothermal deposits of Asia include the ca. 485 Ma Duobaoshan porphyry within a part of the Tuva–Mongol arc, ca. 355 Ma low-sulfidation epithermal deposits (Kubaka) of the Omolon terrane accreted to eastern Russia, and porphyries (Bozshakol, Taldy Bulak) within Ordovican to Early Devonian oceanic arcs formed off the Kazakhstan microcontinent. The Late Devonian to Carboniferous was marked by widespread gold-rich porphyry development along the margins of the closing Ob–Zaisan, Junggar–Balkhash, and Turkestan basins (Amalyk, Oyu Tolgoi); most were formed in continental arcs, although the giant Oyu Tolgoi porphyry was part of a near-shore oceanic arc. Permian subduction-related deformation along the east side of the Indochina block led to ca. 300 Ma gold-bearing skarn and disseminated gold ore formation in the Truong Son fold belt of Laos, and along the west side to ca. 250 Ma gold-bearing skarns and epithermal deposits in the Loei fold belt of Laos and Thailand. In the Mesozoic Transbaikal region, extension along the basin margins subsequent to Mongol–Okhotsk closure was associated with ca. 150–125 Ma formation of important auriferous epithermal (Balei), skarn (Bystray), and porphyry (Kultuminskoe) deposits. In northeastern Russia, Early Cretaceous Pacific margin subduction and Late Cretaceous extension were associated with epithermal gold-deposit formation in the Uda–Murgal (Julietta) and Okhotsk–Chukotka (Dukat, Kupol) volcanic belts, respectively. In southeastern Russia, latest Cretaceous to Oligocene extension correlates with other low-sulfidation epithermal ores that formed in the East Sikhote–Alin volcanic belt. Other extensional events, likely related to changing plate dynamics along the Pacific margin of Asia, relate to epithermal–skarn–porphyry districts that formed at ca. 125–85 Ma in northeastmost China and ca. 105–90 Ma in the Coast Volcanic belt of SE China. The onset of strike slip along a part of the southeastern Pacific margin appears to correlate with the giant 148–135 Ma gold-rich porphyry–skarn province of the lower and middle Yangtze River. It is still controversial as to whether true Carlin-like gold deposits exist in Asia. Those deposits that most closely resemble the Nevada (USA) ores are those in the Permo-Triassic Youjiang basin of SW China and NE Vietnam, and are probably Late Triassic in age, although this is not certain. Other Carlin-like deposits have been suggested to exist in the Sepon basin of Laos and in the Mongol–Okhotsk region (Kuranakh) of Transbaikal.

Gondwana Research↗
USGS2013

A 600-ka Arctic sea-ice record from Mendeleev Ridge based on ostracodes

Arctic paleoceanography and sea-ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core (HLY0503-06JPC, 800 m water depth) located on the Mendeleev Ridge, Western Arctic Ocean. The calcareous microfaunal record (ostracodes and foraminifers) covers several glacial/interglacial cycles back to estimated Marine Isotope Stage 13 (MIS 13, ∼500 ka) with an average sedimentation rate of ∼0.5 cm/ka for most of the stratigraphy (MIS 5–13). Results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in MIS 11 dominated by a temperate-water species Turborotalita egelida show that extreme interglacial warmth, high surface ocean productivity, and possibly open ocean convection characterized MIS 11 and MIS 13 (∼400 and 500 ka, respectively). A major shift in western Arctic Ocean environments toward perennial sea ice occurred after MIS 11 based on the distribution of an ice-dwelling ostracode Acetabulastoma arcticum . Spectral analyses of the ostracode assemblages indicate sea ice and mid-depth ocean circulation in western Arctic Ocean varied primarily at precessional (∼22 ka) and obliquity (∼40 ka) frequencies.

Quaternary Science Reviews↗
USGS2009

Anthropogenic molecular markers: Tools to identify the sources and transport pathways of pollutants

The activities of modern civilization have released to the oceans a wide variety of both mobilized natural compounds and synthetic compounds not found prior to modern times. Many of these compounds provide a means of identifying sources of inputs and pathways of movement of chemicals through oceanic ecosystems and serve as molecular markers of human activities. A coastal ocean (Tokyo Bay) and a deep ocean (Deep Water Dump Site 106 in the Western North Atlantic Ocean) example are presented. In the deep ocean study, the correlation between potential sewage marker, i.e. linear alkylbenzenes (LABs), and polychlorinated biphenyls (PCBs) concentrations indicates a contribution of sewage sludge PCBs to the dump site sediments.

ACS Symposium Series↗
USGS2018

Rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow

Submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment, yet few studies have investigated spatially distributed groundwater fluxes in deep‐ocean environments such as continental slopes. Heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity. These assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations. Here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow, ocean temperature changes, and seabed thermal conductivity variations on deep‐ocean sediment temperature profiles. Temperature observations from the sediment and bottom ocean water on the Scotian Slope off eastern Canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid. The spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper‐middle slope and discharge on the lower slope. We speculate that the downward groundwater flow inferred on the Scotian Slope is due to density‐driven processes arising from underlying salt domes, in contrast with upward slope systems driven by geothermal convection. Improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis, including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length.

Water Resources Research↗
USGS2010

Comparison of deep structure along three transects of the western North American continental margin

Similarities in geology and potential field data that have in the past been noted among the regions of southern Alaska, southern Vancouver Island, and central California are now seen to be accompanied by similarities in deep crustal structure. A number of tectonic elements have been identified in the deep structure along transects in these three regions, although not all elements are present along each transect. These elements are (A) an actively subducting oceanic plate and (B) an overriding continental plate that consists of (1) a Cenozoic accretionary prism, (2) a Mesozoic accretionary prism, (3) a backstop to the Mesozoic prism, (4) a tectonically underplated body of oceanic rocks, and (5) a crustal root. The Mesozoic prism is in some cases an underthrust body (type 2a) but in other cases forms the principal component of a landward verging tectonic wedge (type 2b). The technically underplated body of oceanic rocks extends landward from the fault contact between the Cenozoic and Mesozoic prisms to a point beneath the backstop. The crustal root lies beneath the backstop and landward of the underplated body. All of these elements are interpreted to be present along the Alaskan and Vancouver Island transects. In Alaska the underplated body is interpreted to be fragments of the Kula plate; the same may be true at Vancouver Island. These two transects appear to differ in that, in Alaska, the Mesozoic prism, in one interpretation, is the principal component of a tectonic wedge (type 2b), whereas at Vancouver Island, it is an underthrust body (type 2a). Along the central California transect, active subduction is no longer taking place, and the San Andreas fault has removed the Cenozoic prism from this region of the North American plate. On the North American plate (i.e., east of the San Andreas fault), the Mesozoic prism, interpreted as the main component of a tectonic wedge (type 2b), and the backstop to the Mesozoic prism are present. There is, however, no clear evidence of tectonically underplated oceanic rocks, and the crust is thin (no root). In both Alaska and Vancouver Island, the Mesozoic prisms above the underplated bodies experienced low-pressure/high-temperature metamorphism at about the time of tectonic underplating; no such metamorphism is currently exposed in California. The metamorphism may have been caused by the underplating of young, hot oceanic crust, or, alternatively, by subduction of an oceanic ridge. The presence of a tectonic wedge (type 2b) in Alaska and California and the absence of such a wedge at Vancouver Island could arise either from the fact that in the former two locations the Mesozoic prisms were more voluminous, owing to either more rapid trench sedimentation or more rapid convergence, or to the possibility that at the latter location the Mesozoic prism was juxtaposed with the backstop primarily by strike-slip faulting.

Alaska, California↗
USGS2019

Ross Ice Shelf response to climate driven by the tectonic imprint on seafloor bathymetry

Ocean melting has thinned Antarctica's ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and new ocean simulations, to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean-atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet.

Nature Geoscience↗
USGS2024

A phylogeographical study of the discontinuously distributed Harlequin Duck (Histrionicus histrionicus)

Species distributions are often indicative of historical biogeographical events and contemporary spatial biodiversity patterns. The Harlequin Duck Histrionicus histrionicus is a sea duck of conservation concern that has a disjunct distribution, with discrete portions of its range associated with northern Pacific and Atlantic Ocean basins. Movement data indicate migratory connectivity within regions of each ocean basin but not cross-continent dispersal, suggesting that genetic structuring could exist at multiple spatial scales. Little is known regarding the impacts of past vicariance events on the species phylogeographical structure and historical demography, or rates of gene flow at different spatial scales. We used data from microsatellite loci and mitochondrial DNA (mtDNA) sequences to quantify levels of genetic diversity within, and the extent of spatial genetic differentiation among locations sampled at multiple spatial scales across the species range. Samples were collected at nonbreeding locations, which represent groupings appropriate for characterizing genetically differentiated subgroups at regional and continental scales. Collectively, genetic data and coalescence modelling suggested that individuals colonized regions currently occupied within both ocean basins in the Holocene from a single refuge in the Atlantic. Further, it seems likely there was secondary contact with lineages derived from populations in Asia, based on the shallow species-wide mtDNA phylogeny and high incidence of recently derived private mtDNA haplotypes. Estimates of inter-location variance in microsatellite allele and mtDNA haplotype frequency were moderate and significant between western (Pacific – North America) and eastern (Atlantic – North America, Greenland and Iceland) ocean basins and among sampling groups within each ocean basin. Genetic differentiation among sampling groups was particularly evident at the species distributional margins in the Atlantic (Iceland) and the Pacific (Shemya Island) Ocean basins. Coalescent modelling results suggest that contemporary spatial genetic patterns in the species arose through the combined influences of secondary contact, shared ancestry and gene flow after the last glacial maxima.

Ibis↗
USGS2007

Associations of decadal to multidecadal sea-surface temperature variability with Upper Colorado River flow

The relations of decadal to multidecadal (D2M) variability in global sea-surface temperatures (SSTs) with D2M variability in the flow of the Upper Colorado River Basin (UCRB) are examined for the years 1906-2003. Results indicate that D2M variability of SSTs in the North Atlantic, North Pacific, tropical Pacific, and Indian Oceans is associated with D2M variability of the UCRB. A principal components analysis (with varimax rotation) of detrended and 11-year smoothed global SSTs indicates that the two leading rotated principal components (RPCs) explain 56% of the variability in the transformed SST data. The first RPC (RPC1) strongly reflects variability associated with the Atlantic Multidecadal Oscillation and the second RPC (RPC2) represents variability of the Pacific Decadal Oscillation, the tropical Pacific Ocean, and Indian Ocean SSTs. Results indicate that SSTs in the North Atlantic Ocean (RPC1) explain as much of the D2M variability in global SSTs as does the combination of Indian and Pacific Ocean variability (RPC2). These results suggest that SSTs in all of the oceans have some relation with flow of the UCRB, but the North Atlantic may have the strongest and most consistent association on D2M time scales. Hydroclimatic persistence on these time scales introduces significant nonstationarity in mean annual streamflow, with critical implications for UCRB water resource management. ?? 2007 American Water Resources Association.

Journal of the American Water Resources Associatio↗
USGS2010

Marine-target craters on Mars? An assessment study

Observations of impact craters on Earth show that a water column at the target strongly influences lithology and morphology of the resultant crater. The degree of influence varies with the target water depth and impactor diameter. Morphological features detectable in satellite imagery include a concentric shape with an inner crater inset within a shallower outer crater, which is cut by gullies excavated by the resurge of water. In this study, we show that if oceans, large seas, and lakes existed on Mars for periods of time, marine-target craters must have formed. We make an assessment of the minimum and maximum amounts of such craters based on published data on water depths, extent, and duration of putative oceans within “contacts 1 and 2,” cratering rate during the different oceanic phases, and computer modeling of minimum impactor diameters required to form long-lasting craters in the seafloor of the oceans. We also discuss the influence of erosion and sedimentation on the preservation and exposure of the craters. For an ocean within the smaller “contact 2” with a duration of 100,000 yr and the low present crater formation rate, only ˜1–2 detectable marine-target craters would have formed. In a maximum estimate with a duration of 0.8 Gyr, as many as 1400 craters may have formed. An ocean within the larger “contact 1-Meridiani,” with a duration of 100,000 yr, would not have received any seafloor craters despite the higher crater formation rate estimated before 3.5 Gyr. On the other hand, with a maximum duration of 0.8 Gyr, about 160 seafloor craters may have formed. However, terrestrial examples show that most marine-target craters may be covered by thick sediments. Ground penetrating radar surveys planned for the ESA Mars Express and NASA 2005 missions may reveal buried craters, though it is uncertain if the resolution will allow the detection of diagnostic features of marine-target craters. The implications regarding the discovery of marine-target craters on Mars is not without significance, as such discoveries would help address the ongoing debate of whether large water bodies occupied the northern plains of Mars and would help constrain future paleoclimatic reconstructions.

Meteoritics and Planetary Science↗