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At least 1,063 records · Page 59Linked to original sources

USGS2020

Planktic foraminiferal test size and weight response to the late Pliocene environment

Atmospheric carbon dioxide ( p CO 2 atm ) is impacting the ocean and marine organisms directly via changes in carbonate chemistry and indirectly via a range of changes in physical parameters most dominantly temperature. To assess potential impacts of climate change on carbonate production in the open ocean, we measured size and weight of planktic foraminifers during the late Pliocene at p CO 2 atm concentrations comparable to today and global temperatures 2 to 3 °C warmer. Size of all foraminifers was measured at Atlantic Ocean Deep Sea Drilling Project (DSDP) Site 610, Ocean Drilling Program (ODP) Site 999, and Integrated Ocean Drilling Program (IODP) Site U1313. Test size was smaller during the Pliocene than in modern assemblages under the same environmental conditions. During the cold marine isotope stage (MIS) M2, size increased at Site 999, potentially linked to intensified stratification of the surface ocean in response to the closure of the Central American Seaway. At Site U1313, test size tracks the warming throughout the late Pliocene. Size-normalized weight (SNW) of Globigerina bulloides at Site U1313 decreased during warmer temperature intervals. SNW of Globigerinoides ruber (white) at Site 999 displays high-frequency variability not correlated to temperature. Yet during the glacial period within MIS M2, test weight was higher during higher temperatures. Our results support studies in the modern ocean, which challenge the view that carbonate chemistry is the primary driver for calcification. To better understand processes driving changes in SNW, computer tomography was used to quantify calcite to volume ratios. During interglacial periods, lower calcite volume but higher test volume suggests less suitable conditions for calcification. As this signal is not evident in SNW, subtle changes in calcification might not be observed by the weight-based method.

Paleoceanography and Paleoclimatology↗

USGS2014

Potential fitness benefits of the half-pounder life history in Klamath River steelhead

Steelhead Oncorhynchus mykiss from several of the world's rivers display the half-pounder life history, a variant characterized by an amphidromous (and, less often, anadromous) return to freshwater in the year of initial ocean entry. We evaluated factors related to expression of the half-pounder life history in wild steelhead from the lower Klamath River basin, California. We also evaluated fitness consequences of the half-pounder phenotype using a simple life history model that was parameterized with our empirical data and outputs from a regional survival equation. The incidence of the half-pounder life history differed among subbasins of origin and smolt ages. Precocious maturation occurred in approximately 8% of half-pounders and was best predicted by individual length in freshwater preceding ocean entry. Adult steelhead of the half-pounder phenotype were smaller and less fecund at age than adult steelhead of the alternative (ocean contingent) phenotype. However, our data suggest that fish of the half-pounder phenotype are more likely to spawn repeatedly than are fish of the ocean contingent phenotype. Models predicted that if lifetime survivorship were equal between phenotypes, the fitness of the half-pounder phenotype would be 17–28% lower than that of the ocean contingent phenotype. To meet the condition of equal fitness between phenotypes would require that first-year ocean survival be 21–40% higher among half-pounders in freshwater than among their cohorts at sea. We concluded that continued expression of the half-pounder phenotype is favored by precocious maturation and increased survival relative to that of the ocean contingent phenotype.

California↗

USGS1964

Igneous rocks of the East Pacific Rise

The apical parts of large volcanoes along the East Pacific Rise (islands and seamounts) are encrusted with rocks of the alkali volcanic suite (alkali basalt, andesine- and oligoclase-andesite, and trachyte). In contrast, the more submerged parts of the Rise are largely composed of a tholeiitic basalt which has low concentrations of K, P, U, Th, Pb, and Ti. This tholeiitic basalt is either the predominant or the only magma generated in the earth's mantle under oceanic ridges and rises. It is at least 1000-fold more abundant than the alkali suite, which is probably derived from tholeiitic basalt by magmatic differentiation in and immediately below the larger volcanoes. Distinction of oceanic tholeiites from almost all continental tholeiites is possible on the simple basis of total potassium content, with the discontinuity at 0.3 to 0.5 percent K 2 O by weight. Oceanic tholeiites also are readily distinguished from some 19 out of 20 basalts of oceanic islands and seamount cappings by having less than 0.3 percent K 2 O by weight and more than 48 percent SiO 2 . Deep drilling into oceanic volcanoes should, however, core basalts transitional between the oceanic tholeiites and the presumed derivative alkali basalts. The composition of the oceanic tholeiites suggests that the mantle under the East Pacific Rise contains less than 0.10 percent potassium oxide by weight; 0.1 part per million of uranium and 0.4 part of thorium; a potassium: rubidium ratio of about 1200 and a potassium: uranium ratio of about 10 4 .

Science↗

USGS2018

Paleoclimate Records: Providing context and understanding of current Arctic change

At present, the Arctic Ocean is experiencing changes in ocean surface temperature and sea ice extent that are unprecedented in the era of satellite observations, which extend from the 1980s to the present (see sections 5c,d). To provide context for current changes, scientists turn to paleoclimate records to document and study anthropogenic influence and natural decadal and multidecadal climate variability in the Arctic system. Paleoceanographic records extend limited Arctic instrumental measurements back in time and are central to improving our understanding of climate dynamics and the predictive capability of climate models. By comparing paleoceanographic records with modern observations, scientists can place the rates and magnitudes of modern Arctic change in the context of those inferred from the geological record. Over geological time, paleoceanographic reconstructions using, for instance, marine sediment cores indicate that the Arctic has experienced huge sea ice fluctuations. These fluctuations range from nearly completely ice-free to totally ice-covered conditions. The appearance of ice-rafted debris and sea ice-dependent diatoms in Arctic marine sediments indicate that the first Arctic sea ice formed approxi-mately 47 million years ago (St. John 2008; Stickley et al. 2009; Fig. SB5.1), coincident with an interval of declining atmospheric carbon dioxide (CO2) concentration, global climate cooling, and expansion of Earths cryosphere during the middle Eocene. The development of year-round (i.e., perennial) sea ice in the central Arctic Ocean, similar to conditions that exist today, is evident in sediment records as early as 1418 million years ago (Darby 2008). These records suggest that transitions in sea ice cover occur over many millennia and often vary in concert with the waxing and waning of circum-Arctic land ice sheets, ice shelves, and long-term fluctuations in ocean and atmospheric temperature and atmospheric CO2 concentrations (Stein et al. 2012; Jakobsson et al. 2014). Over shorter time scales, shallow sediment records from Arctic Ocean continental shelves allow more detailed, higher-resolution (hundreds of years resolution) reconstructions of sea ice history extending through the Holocene (11 700 years ago to present), the most recent interglacial period. A notable feature of these records is an early Holocene sea ice minimum, corresponding to a thermal maximum (warm) period from 11 000 to 5000 years ago, when the Arctic may have been warmer and had less summertime sea ice than today (Kaufman et al. 2004). However, it is not clear that the Arctic was ice-free at any point during the Holocene (Polyak et al. 2010). High-resolution paleosea ice records from the western Arctic in the Chukchi and East Siberian Seas indicate that sea ice concentrations increased through the Holocene in concert with decreasing summer solar insolation (sunlight). Sea ice extent in this region also varied in response to the volume of Pacific water delivered via the Bering Strait into the Arctic Basin (Stein et al. 2017; Polyak et al. 2016). Records from the Fram Strait (Mller et al. 2012), Laptev Sea (Hrner et al. 2016), and Canadian Arctic Archipelago (Vare et al. 2009) also indicate a similar long-term expansion of sea ice and suggest sea ice extent in these regions is modulated by the varying influx of warm Atlantic water into the Arctic Basin (e.g., Werner et al. 2013). Taken together, available records support a circum-Arctic sea ice expansion during the late Holocene. A notably high-resolution summer sea ice history (<5-year resolution) has been established for the last 1450 years using a network of terrestrial records (tree ring , lake sediment, and ice core records) located around the margins of the Arctic Ocean (Kinnard et al. 2011). Results summarized in Fig. SB5.2 indicate a pronounced decline in summer sea ice extent beginning in the 20th century, with exceptionally low ice extent recorded since the mid-1990s, consistent with the satellite record (see section 5d). While several episodes of reduced and expanded sea ice extent occur in association with climate anomalies such as the Medieval Climate Warm Period (AD 8001300) and the Little Ice Age (AD 14501850), the magnitude and pace of the modern decline in sea ice is outside of the range of natural variability and unprecedented in the 1450-year reconstruction (Kinnard et al. 2011). A radiocarbon-dated driftwood record of the Ellesmere ice shelf in the Canadian High Arctic, the oldest landfast ice in the Northern Hemisphere, also demonstrates a substantial reduction in ice extents over the 20th century (England et al. 2017). A supporting sediment record indicates that inflowing Atlantic water in Fram Strait has warmed by 2C since 1900, driving break up and melt of sea ice (Spielhagen et al. 2011). Complementary mooring and satellite observations show the Atlantification of the eastern Arctic due to enhanced inflow of warm saline water through Fram Strait (Nilsen et al. 2016) and nutrient-rich Pacific water via the Bering has increased by more than 50% (Woodgate et al. 2012), further driving sea ice melt and warming seas. Similar high-resolution proxy records from Arctic regions also indicate that the modern rate of increasing annual surface air temperatures has not been observed over at least the last 2000 years (McKay and Kaufman 2014). Scientists conclude that broad-scale sea ice variations recorded in the paleo record were dominantly driven by changes in basin-scale changes in atmospheric circulation patterns, fluctuations in air temperature, strength of incoming solar radiation, and changes in the inflow of warm water via Pacific and Atlantic inflows (Polyak et al. 2010). There is general consensus that ice-free Arctic summers are likely before the end of the 21st century (e.g., Stroeve et al. 2007; Massonnet et al. 2012), while some climate model projections suggest ice-free Arctic summers as early as 2030 (Wang and Overland 2009). Paleoclimate studies and observational time series attribute the decline in sea ice extent and thickness over the last decade to both enhanced greenhouse warming and natural climate variability. While understanding the interplay of these factors is critical for future projections of Arctic sea ice and ecosystems, most observational time series records cover only a few decades. This highlights the need for additional paleoceanographic reconstructions across multiple spatial and temporal domains to better understand the drivers and implications of present and future Arctic Ocean change.

Bulletin American Meteorological Society↗

USGS1991

Magmatic evolution of the Gulf of California rift

Magmatic events in the Baja peninsula-Gulf of California region are closely related to sequential tectonic regimes of: (1) late Tertiary subduction beneath the continental margin until ~16 to 12.5 Ma; and (2) continental to oceanic rifting that began about 13 Ma. Orogenic calcalkaline volcanic rocks formed subparallel belts of rhyolite ignimbrite of Oligocene age (~34 to 27 Ma) east of the Gulf in the Sierra Madre Occidental and andesite of Miocene age (~24 to 11 Ma) along the eastern Baja peninsula. Shutoff of the Miocene andesitic arc broadly corresponds to migration of the Pacific-Farallon (Guadalupe)-North America triple junction along the Baja peninsula. Orogenic andesitic volcanism ended at ~16 Ma in northern Baja, and at ~11 Ma in southern Baja, within ~1 to 2 Ma of cessation of subduction. Waning orogenic magmatism persisted along the southern Baja peninsula during the initial stages of rifting. Paleogeographic implications of the distribution of circum-Gulf volcanic rocks and their inferred easterly source areas suggest that, from about 13 to 8 Ma, the rift consisted of a narrow seaway along the eastern side of the present Gulf. By about 6 Ma, the Gulf had broadened westward to approximately its present width. The period from 13 to 10 Ma was a time of tectonic transition and magmatic diversity. During this interval, medium-K calcalkaline, high-K calcalkaline, alkalic, and tholeiitic magmas erupted from the central to southern part of the Baja peninsula-Gulf region, and from about 14 to 8 Ma, rhyolite ignimbrite erupted in the northern Gulf region. Since 10 Ma, volcanism on the western Baja peninsula has been dominated by alkalic magmas, the Gulf margins by calcalkaline magmas, and the Gulf by tholeiitic magmas. Postsubduction calcalkaline andesite to rhyolite erupted sporadically and locally along the northern Gulf margins from ~9 Ma through Holocene time. Alkalic magmas associated with rifting in the Gulf of California are unlike alkalic magmas from intraplate settings. They comprise nepheline- to quartz-normative, basaltic to andesitic rocks characterized by diverse trace element ratios. They are broadly similar to intraplate alkalic rocks in having high K, P, Ba, Sr and the light REE (rare earth elements), but have some trace element characteristics typical of orogenic magmas (low Nb and Ta relative to K, Ba, Sr, and La) that distinguish these alkalic rocks from intraplate or cratonic rift alkalic rocks. Rb abundances (mostly <25 ppm, as low as 5 ppm) are unusually low in these alkalic rocks, both in contrast to the high K (~1.7-4.1 wt% K 2 O), Ba (~800-2200 ppm), and Sr (~1000-3700 ppm), and in comparison to Rb abundances in mafic lavas in general; many samples have Rb at levels typically found in low-K tholeiites. The high K/Rb ratios, mostly ~1000 to 5000, are among the highest reported for any lavas. Samples ranging in SiO 2 from 48 to 61% have Mg’ ≥ 65, indicating that a broad range of compositions may represent primary melts. The generally high Mg’, and the low Rb, Th, Nb, and Ta in some lavas, suggest that depleted refractory mantle equivalent to a mid-ocean ridge basalt (MORB) source contributed to these melts. The distinctive trace element enrichments are attributed to the stabilization in the source of amphibole and apatite from metasomatic fluids related to prior subduction beneath the peninsula. In discrimination diagrams, these alkalic rocks typically cluster outside previously defined fields for various magma types. The common tectonic setting among these and geochemically similar alkalic suites is the occurrence in a continental margin that is undergoing extension, located along a recently or currently active convergent plate boundary. Tholeiitic basalts have erupted since the earliest stages of continental rifting through development of oceanic spreading centers. Gulf of California tholeiites exhibit an evolution distinguished particularly by differences in rare-earth-element (REE) abundances. Early-rift magmas are similar in trace element geochemistry to some intraplate tholeiites from ocean islands and continental flood basalts, and have convex-upward REE patterns. The most recent tholeiites from the East Pacific Rise in the mouth of the Gulf are equivalent to N-MORB (normal mid-ocean ridge basalt) from other mid-ocean rifts, and are depleted in the light-REE. The transition in tholeiite geochemistry from intraplate tholeiite to MORB is attributed to progressive fusion of more refractory mantle components. Incipient-rift tholeiites are derived from selective fusion of clinopyroxenite veins, and with continued melting, N-MORB are formed by fusion of peridotite. This tholeiite sequence reflects the evolution of mantle source regions in rifts that sustain an ensialic to oceanic transition.

Baja California, Baja California Sur↗

USGS1981

Origin of organic-carbon-rich mid-Cretaceous limestones, Mid-Pacific Mountains and southern Hess Rise

Limestones of mid-Cretaceous age containing as much as 8.6 percent organic carbon were cored at one site (463) in the Mid-Pacific Mountains and at two sites (465, 466) on southern Hess Rise, central North Pacific Ocean, during Leg 62 of the Deep Sea Drilling Project. In the Mid-Pacific Mountains, three layers containing more than 2% organic carbon are associated with volcanic ash in silicified limestone of early Aptian age (—112-113 m.y. old), a time when the site was south of the equator and considerably shallower than at present (2525 m). The beds of laminated, organiccarbon-rich limestone, implying deposition in an oxygen-deficient environment, are interbedded with normal pelagic limestones. This sequence lies on interbedded pelagic limestones and clastic limestones containing locally derived shallow-water carbonate debris, and it is overlain by interbedded green, gray, and pink limestones. The organic-carbonrich strata on southern Hess Rise are dark-olive, laminated limestones with rare interbeds of altered volcanic ash of the late Aptian to early Cenomanian ( — 98 to 103 m.y. old), a time when the site was passing under the equatorial highproductivity zone and subsiding from shallow to intermediate water depths. The organic-carbon-rich limestone sequence overlies volcanic basement (trachyte) in this part of Hess Rise. The association of volcanogenic sediments with organic-carbon-rich strata on Hess Rise is not as striking as in the Mid-Pacific Mountains, but the occurrences do suggest a coincidence of mid-plate volcanic activity and accumulation of organic matter at intermediate water depths in the tropical North Pacific Ocean during the mid-Cretaceous. Pyrolysis assays indicate that most of the organic matter in the limestone on Hess Rise is composed of lipid-rich kerogen derived from marine organisms. Limestones from the Mid-Pacific Mountains contain lower concentrations of organic matter. Pyrolysis assays and extractable hydrocarbons indicate that the organic matter in samples from Hole 463 is also predominantly of marine origin, and that contributions of terrigenous organic matter were probably minor. Analyses of stable carbon isotopes indicate that the organic carbon in all analyzed samples is isotopically light (δ13C 24 to - 29‰) relative to most modern marine organic carbon (δ13C - 9 to - 30%), and that the lightest carbon (δ13C 28 to - 29‰) is also the most lipid-rich. The organic-carbon-rich mid-Cretaceous limestones on Hess Rise, the Mid-Pacific Mountains, and other elevated plateaus and seamounts in the Pacific Ocean are approximately equivalent in age (mid-Cretaceous, -85-120 m.y.) to organic-carbon-rich lithofacies elsewhere in the world ocean, particularly in the Atlantic Ocean and parts of the Indian Ocean. However, strata of equivalent age deposited in the Pacific Ocean at greater depths do not contain any carbon rich horizons. This observation, together with the evidence that the plateau sites were considerably shallower and close to the equator during the mid-Cretaceous, suggests that an expanded mid-water oxygen minimum, together with local restrictions in circulation, may have resulted in the preservation of organic matter in an oxygen-deficient environment where the oxygen minimum impinged on elevated platforms such as Hess Rise and the Mid-Pacific Mountains.

Initial reports of the Deep Sea Drilling Project↗

USGS2004

Stratiform barite deposits in the Roberts Mountains allochthon, Nevada: A review of potential analogs in modern sea-floor environments

The United States is a net importer of barite, a critical mineral for the oil and gas industry; more than 80 percent of current domestic consumption of barite is imported from China. Nearly all of the domestic production of barite comes from stratiform deposits in Nevada. The 'modern analogs' approach adopted in this review can contribute to improving deposit models and the long-term resource picture in the United States. Massive barite deposits in Nevada are interlayered with deep-water siliceous sedimentary strata of Paleozoic age within the Roberts Mountains Allochthon. Although the barite deposits formed along the long-lived, tectonically active margin of western North America before the Antler orogeny, uncertainty still exists regarding key aspects of their genesis, especially with respect to tectonic setting and depositional processes. Proposed tectonic settings include a continental slope adjacent to an ocean basin, and a rifted basin formed on continental crust. A margin dominated by other stress configurations and strike-slip faulting may also have been present during the Paleozoic. Hypotheses for the genesis of sediment-hosted, stratiform barite deposits in Nevada can be grouped into two categories: (1) a synsedimentary hydrothermal model and (2) an ocean-circulation/productivity-zone model. Both models include a stage involving bacterial reduction of seawater sulfate. Disseminated, diagenetic, and hydrothermal barite deposits are widespread features of the modern ocean. In the Pacific Ocean, disseminated barite deposits (max 9 weight percent BaSO4) are forming below high-productivity zones (for example, in equatorial belts) and on the flanks of ocean ridges (as fallout of 'black smoker' particles). Massive barite deposits of diagenetic (in the subsea floor and at cold seeps) and hydrothermal origins are present in several sediment-covered tectonic settings, including ocean ridges (Escanaba Trough and Guaymas Basin), oceanic transform faults (Blanco Fracture Zone), marginal basins (Sea of Okhotsk), convergent margins (Peru, Oregon, Alaska), and transform margins (California Continental Borderland). Both hydrothermal and diagenetic barite deposits may be present in some environments (for example, the California California Borderland). On the basis of a consideration of tectonic settings and a comparison of deposit attributes (associated rock types, size, structure), mineralogy (BaSO4 content, SiO2 content), and geochemistry (S- and Sr-isotopic ratios) for modern and ancient massive barite deposits, cold seeps along transform margins (or, possibly, marginal basins) represent the most promising present-day metallogenetic analogs for stratiform barite. Hydrothermal systems can also produce high-grade barite, but the ubiquity of associated sulfide mineralization on the modern sea floor (and the paucity of sulfides in Nevada deposits) is problematic. On the basis of data from modern barite deposits, the presence of vent-specific faunas (tubeworms) and the variation in d34S values for barite (related to bacterial reduction of seawater sulfate) may not permit discrimination between a diagenetic or hydrothermal origin for ancient barite deposits.

Nevada↗

USGS2011

Proceedings of a Coastal and Marine Spatial Planning Workshop for the Western United States

Recent scientific and ocean policy assessments demonstrate that a fundamental change in our current management system is required to achieve the long-term health of our ocean, coasts, and Great Lakes in order to sustain the services and benefits they provide to society. The present (2011) species- and sector-centric way we manage these ecosystems cannot account properly for cumulative effects, sustaining multiple ecosystem services, and holistically and explicitly evaluating the tradeoffs associated with proposed alternative and multiple human uses. A transition to an ecosystem-based approach to management and conservation of coastal and marine resources is needed. Competing uses and activities such as commerce, recreation, cultural practices, energy development, conservation, and national security are increasing pressure for new and expanded resource usage in coastal marine ecosystems. Current management efforts use a sector-by-sector approach that mostly focuses on a limited range of tools and outcomes [for example, oil and gas leases, fishery management plans, and Marine Protected Areas (MPAs)]. A comprehensive, ecosystem-based, and proactive approach to planning and managing these uses and activities is needed. Further, scientific understanding and information are essential to achieve an integrated decision-making process that includes knowledge of ecosystem services, existing and possible future conditions, and potential consequences of natural and anthropogenic events. Because no single government agency has executive authority for coastal or ocean resources, conflicting objectives around competing uses abound. In recent years, regional- and state-level initiatives in Coastal and Marine Spatial Planning (CMSP) have emerged to coordinate management activities. In some respects, the components and steps of the overall CMSP process are similar to how existing ocean resources are regulated and managed. For example, the Bureau of Ocean Energy Management Regulation and Enforcement (BOEMRE) uses spatial planning exercises in State Renewable Energy Task Force meetings to identify competing and conflicting ocean uses, and to delineate areas suitable for renewable energy development. Similarly terrestrial areas such as in national parks and national wildlife refuges managed by the Department of the Interior (DOI) prepare management plans for preservation and restoration of species and habitats of concern, some of which are protected by law. The analogy to CMSP is clear - multiple users and multiple expectations, resulting in the requirement to establish spatial plans for management of different resources and different ecosystem services. A two-day workshop on December 1-2, 2010, was convened for DOI representatives and several key non-DOI participants with roles in CMSP as a step toward clarifying national perspectives and consequences of the National Ocean Policy for the West (appendix 1). Discussions helped to develop an understanding of CMSP from the federal perspective and to identify regional priorities. An overarching theme was to promote a better understanding of current and future science needs. The workshop format included briefings by key Federal agencies on their understanding of the national focus followed by discussion of regional issues, including the needs for scientific information and coordination. The workshop also explored potential science contributions by Federal agencies and others; utilizing current capabilities, data, and information systems; and provided a foundation for possible future regional workshops focusing in turn on the West Coast Region (California, Oregon, and Washington), Pacific Islands (sometimes referred to as Oceania) and Alaska. Participants were asked to share information in the following areas, recognizing that the purpose would be to learn more about the national perspective (see appendixes 2-4): Explore how the Western U.S. (Alaska, Pacific Islands, and West Coast Region) migh

Open-File Report↗

USGS2010

Analysis of the Shallow Groundwater Flow System at Fire Island National Seashore, Suffolk County, New York

Fire Island National Seashore (FIIS) occupies 42 kilometers of the barrier island for which it is named that lies off the southern shore of Suffolk County, N.Y. Freshwater in the highly permeable, sandy aquifer underlying Fire Island is bounded laterally by marine surface waters and at depth by saline groundwater. Interspersed throughout FIIS are 17 pre-existing residential communities that in summer months greatly increase in population through the arrival of summer residents and vacationers; in addition, the National Park Service (NPS) has established several facilities on the island to accommodate visitors to FIIS. The 2.2 million people estimated by the NPS to visit Fire Island annually impact groundwater quality through the release of waste-derived contaminants, such as nutrients, pathogens, and organic compounds, into the environment. Waste-contaminated groundwater can move through the aquifer and threaten the ecological health of the adjacent back-barrier estuaries to which much of the groundwater ultimately discharges. In 2004, the U.S. Geological Survey (USGS), in cooperation with the NPS, began a 3-year investigation to (1) collect groundwater levels and water-quality (nutrient) samples, (2) develop a three-dimensional model of the shallow (water-table) aquifer system and adjacent marine surface waters, and (3) calculate nitrogen loads in simulated groundwater discharges from the aquifer to back-barrier estuaries and the ocean. The hydrogeology of the shallow aquifer system was characterized from the results of exploratory drilling, geophysical surveying, water-level monitoring, and water-quality sampling. The investigation focused on four areas-the communities of Kismet and Robbins Rest, the NPS Visitor Center at Watch Hill, and the undeveloped Otis Pike Fire Island High Dune Wilderness. Thirty-five observation wells were installed within FIIS to characterize subsurface hydrogeology and establish a water-table monitoring network in the four study areas. A variable-density model of the shallow aquifer system and adjacent marine surface waters was developed to simulate groundwater flow patterns and rates. Nitrogen loads from the shallow aquifer system were calculated from representative total nitrogen (TN) concentrations and simulated groundwater discharges to back-barrier estuaries and the ocean. The model simulates groundwater directions, velocities, and discharge rates under 2005 mean annual conditions. Groundwater budgets were developed for recharge areas of similar land use that contribute freshwater to back-barrier estuaries, the ocean, and subsea-discharge zones. Total freshwater discharge from the shallow aquifer system is about 43,500 cubic meters per day (m3/d) (79.8 percent) to back-barrier estuaries and about 10,200 m3/d (18.7 percent) to the ocean; about 836 m3/d (1.5 percent) may exit the system as subsea underflow. The total contribution of fresh groundwater to shoreline discharge zones amounts to about 53,700 m3/d (98.5 percent). The median age of freshwater discharged to back-barrier estuaries and the ocean was 3.4 years, and the 95th-percentile age was 20 years. The TN concentrations and loads under 2005 mean annual conditions for areas that contribute fresh groundwater to back-barrier estuaries and the ocean were calculated for the principal land uses on Fire Island. The overall TN load from the shallow aquifer system to shoreline discharge zones is about 16,200 kilograms per year (kg/yr) (82.2 percent) to back-barrier estuaries and about 3,500 kg/yr (17.8 percent) to the ocean. The overall TN load to marine surface waters amounts to about 19,700 kg/yr-roughly 6 percent of the annual TN load from shallow groundwater entering the South Shore Estuary Reserve (SSER) from the Suffolk County mainland, which is about 345,000 kg/yr. In contrast to the TN load from shallow groundwater for the SSER watershed, which annually yields about 353 kilograms per square kilometer (kg/km2), the overall TN loa

Scientific Investigations Report↗

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↗