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USGS2023

United States Gulf of Mexico waters provide important nursery habitat for Mexico’s green turtle nesting populations

Resolving natal populations for juvenile green turtles is challenging given their potential for extensive dispersal during the oceanic stage and ontogenetic shifts among nursery habitats. Mitochondrial DNA markers have elucidated patterns of connectivity between green turtle nesting populations (rookeries) and juvenile foraging aggregations. However, missing rookery baseline data and haplotype sharing among populations have often impeded inferences, including estimating origins of Gulf of Mexico juveniles. Here, we assessed genetic structure among seven foraging aggregations spanning southern Texas (TX) to southwestern Florida (SWFL), including Port Fourchon, Louisiana (LA); a surface-pelagic aggregation (SP) offshore of Louisiana and Florida; Santa Rosa Island, Florida (SRI); St. Joseph Bay, Florida (SJB); and the Big Bend region, Florida (BB). We estimated source contributions to aggregations with novel genetic data (excluding SP and BB) using a Bayesian many-to-one mixed stock analysis (MSA) approach. Haplotype frequencies for western (TX, LA, SP, SRI) and eastern (SJB, BB, SWFL) aggregations were significantly differentiated. The largest shift in haplotype frequencies between proximal nursery sites occurred between SRI and SJB, separated by only 150 km, highlighting the lack of a geographic yardstick for predicting genetic structure. In contrast to previous MSA results, there was no signal of Florida juveniles at any foraging site. Mexican contributions dominated in all aggregations, with strong connectivity between western Bay of Campeche (Tamaulipas/Veracruz) rookeries and western foraging aggregations. MSA indicated more diverse Mexican origins for eastern aggregations, with larger inputs from the eastern Bay of Campeche (Campeche/Yucatán), Campeche Bank, and Quintana Roo rookeries. These results demonstrate the significance of the Gulf of Mexico coast and offshore waters of the United States as important nursery habitat for green turtles of Mexican origin and highlight the need for international coordination for management of these populations.

Alabama, Florida, Louisiana, Mississippi, Texas↗

USGS2018

Quaternary sea-level history and the origin of the northernmost coastal aeolianites in the Americas: Channel Islands National Park, California, USA

Along most of the Pacific Coast of North America, sand dunes are dominantly silicate-rich. On the California Channel Islands, however, dunes are carbonate-rich, due to high productivity offshore and a lack of dilution by silicate minerals. Older sands on the Channel Islands contain enough carbonate to be cemented into aeolianite. Several generations of carbonate aeolianites are present on the California Channel Islands and represent the northernmost Quaternary coastal aeolianites on the Pacific Coast of North America. The oldest aeolianites on the islands may date to the early Pleistocene and thus far have only been found on Santa Cruz Island. Aeolianites with well-developed soils are found on both San Miguel Island and Santa Rosa Island and likely date to the middle Pleistocene. The youngest and best-dated aeolianites are located on San Miguel Island and Santa Rosa Island. These sediments were deposited during the late Pleistocene following the emergence of marine terraces that date to the last interglacial complex (~ 120,000 yr to ~ 80,000 yr). Based on radiocarbon and luminescence dating, the ages of these units correspond in time with marine isotope stages [MIS] 4, 3, and 2. Sea level was significantly lower than present during all three time periods. Reconstruction of insular paleogeography indicates that large areas to the north and northwest of the islands would have been exposed at these times, providing a ready source of carbonate-rich skeletal sands. These findings differ from a previously held concept that carbonate aeolianites are dominantly an interglacial phenomenon forming during high stands of sea. In contrast, our results are consistent with the findings of other investigators of the past decade who have reported evidence of glacial-age and interstadial-age aeolianites on coastlines of Australia and South Africa. They are also consistent with observations made by Darwin regarding the origin of aeolianites on the island of St. Helena, in the South Atlantic Ocean, more than a century and a half ago.

California↗

USGS1971

Distribution and age of high-grade blueschists, associated eclogites, and amphibolites from Oregon and California

Isolated blocks of high-grade blueschist and amphibolite facies metamorphic rocks occur within the Jurassic and Cretaceous eugeosynclinal deposits of the Coast Ranges of southwestern Oregon and California. The blocks range in size from individual rock masses commonly 5 to 1,000 ft in diameter to a few larger masses as much as 7 mi long and 2 mi wide. The high-grade blocks are predominantly basaltic in composition and include glaucophane schists, eclogites, and gneissic rocks of the amphibolite facies. Field relationships indicate that the blocks are closely associated with serpentine, that high-grade blueschist and amphibolite blocks, lower grade blueschists, volcanic rocks, and cherts occupy disturbed zones that may be related to thrusting, and that there is no exposed in situ provenance for the high-grade blueschists, eclogites, and amphibolites. Potassium-argon mineral ages of white mica and actinolite from the blueschists and of hornblende from the amphibolites indicate that these minerals crystallized approximately 150 m.y. ago, but the ages measured on glaucophane from the blueschist blocks are commonly younger. These data suggest that the high-grade blue-schist and amphibolite blocks represent fragments of a cryptic metamorphic terrane of pre-Tithonian age that have been tectonically mixed with younger rocks of the Franciscan Formation in California and Otter Point Formation in Oregon. The younger ages for glaucophane probably reflect metamorphic episodes in which lower grade in situ blueschist facies mineral assemblages were developed in the blocks after their emplacement within the Franciscan Formation. This pre-Tithonian cryptic metamorphic terrane probably developed as a result of interaction between oceanic and continental plates. The occurrence of tectonic blocks of this terrane within mélange zones in Oregon and California may be related to later plate interaction.

California, Oregon↗

USGS2020

The field trip that changed the course of my career

After gobbling down a breakfast of sliced papaya, scrambled eggs, refried beans, and soft flour tacos, we gathered our gear and loaded it into the red zodiac that the station manager had assigned to us. My colleagues and I were headed to a pair of islands off the coast of Belize called Twin Cays, occupied by a unique group of tropical plants and animals adapted to a wet and saline habitat. Our ride from Carrie Bow Cay, home of the Smithsonian Institution’s field station, took about twenty minutes because of the choppy water. As we crossed the three-kilometer stretch from Carrie Bow to Twin Cays, I struggled to keep my seat on the bouncing pontoon and was soon soaked by salt spray. As we neared Twin Cays, the deep blue of the lagoon gave way to the turquoise and pale green colors of the shallow sand flats in the lee of the archipelago. Finally, the zodiac slowed, and we pulled into the calm channel separating the two islands. On either side of the channel was an intimidating tangle of tree trunks, branches, leaves, and aerial roots. The trees leaned out over the water and appeared poised to topple into the sea. However, they were perfectly still in the humid morning air and anchored solidly in place by arching prop roots. I sensed that I had entered an alien world, a waterlogged Terra Incognita that looked, smelled, and sounded like nothing I had ever experienced. As we slowly motored along, I peered more closely at the trees that fringed the shoreline. They had gnarled trunks and twisted branches that supported a canopy of dark green leaves. These trees were red mangroves or Rhizophora mangle, their scientific name, and were the dominant vegetation here. These oceanic mangrove islands were intertidal, which means that the trees were inundated twice a day by the sea. Their intimate relationship with the sea, however, was most apparent along the water’s edge. Long, drop roots plunged from the canopy to dangle in the crystal-clear water. Encrusted on the submerged portions of the mangrove roots were yellow and orange sponges, white and pink anemones, sharp-edged oysters, and feathery-green algae. The mangroves, it turned out, provided the only solid substrate for these sessile creatures. There were also mobile animals that I glimpsed as I leaned over the pontoon to peer into the pellucid water. Tiny fish flashed among the partially submerged roots as each one briefly flipped its body sideways to catch the sun glinting through the water. A school of mangrove snappers swam past the boat and disappeared under the overhanging creekbank, which created a shadowy haven from predators. Ribbons of turtlegrass, uprooted from the nearby reef flat, were draped on mangrove prop roots like green and brown tinsel. As the zodiac floated closer to shore, I spotted a mangrove tree crab, which stealthily crept up a tree trunk. In the distance, I could hear the hectoring cry of an osprey, as well as the periodic cheep-cheep of a mangrove warbler deeper in the forest. A soft breeze carried the faint odor of rotten eggs, which was caused by the microbially mediated production of hydrogen sulfide in the waterlogged soil. This was my first close-up view of Belize’s mangroves. The year was 1985. The movie “Back to the Future” had just premiered, PLO terrorists had hijacked the Italian cruise ship Achille Lauro, five people had died after ingesting cyanide-laced Tylenol, and Microsoft had just released Windows 1.0. I had recently gotten a Macintosh personal computer with 128k of memory (seemed like a lot back then) and was learning how to use Cricket Graph, my first software program. Until that point, I had been creating graphs by hand with ink-filled drawing pens, T-squares, and Letraset dry-transfer sheets. This was a time when the world seemed to be on the verge of dramatic changes—many that would impact me and my career as a scientist.

Book chapter↗

USGS2017

Persistent shoreline shape induced from offshore geologic framework: Effects of shoreface connected ridges

Mechanisms relating offshore geologic framework to shoreline evolution are determined through geologic investigations, oceanographic deployments, and numerical modeling. Analysis of shoreline positions from the past 50 years along Fire Island, New York, a 50 km long barrier island, demonstrates a persistent undulating shape along the western half of the island. The shelf offshore of these persistent undulations is characterized with shoreface-connected sand ridges (SFCR) of a similar alongshore length scale, leading to a hypothesis that the ridges control the shoreline shape through the modification of flow. To evaluate this, a hydrodynamic model was configured to start with the US East Coast and scale down to resolve the Fire Island nearshore. The model was validated using observations along western Fire Island and buoy data, and used to compute waves, currents and sediment fluxes. To isolate the influence of the SFCR on the generation of the persistent shoreline shape, simulations were performed with a linearized nearshore bathymetry to remove alongshore transport gradients associated with shoreline shape. The model accurately predicts the scale and variation of the alongshore transport that would generate the persistent shoreline undulations. In one location, however, the ridge crest connects to the nearshore and leads to an offshore-directed transport that produces a difference in the shoreline shape. This qualitatively supports the hypothesized effect of cross-shore fluxes on coastal evolution. Alongshore flows in the nearshore during a representative storm are driven by wave breaking, vortex force, advection and pressure gradient, all of which are affected by the SFCR.

New York↗

USGS2005

Wave spectral energy variability in the northeast Pacific

The dominant characteristics of wave energy variability in the eastern North Pacific are described from NOAA National Data Buoy Center (NDBC) buoy data collected from 1981 to 2003. Ten buoys at distributed locations were selected for comparison based on record duration and data continuity. Long‐period (LP) [ T > 12] s, intermediate‐period [6 ≤ T ≤ 12] s, and short‐period [ T < 6] s wave spectral energy components are considered separately. Empirical orthogonal function (EOF) analyses of monthly wave energy anomalies reveal that all three wave energy components exhibit similar patterns of spatial variability. The dominant mode represents coherent heightened (or diminished) wave energy along the West Coast from Alaska to southern California, as indicated by composites of the 700 hPa height field. The second EOF mode reveals a distinct El Niño‐Southern Oscillation (ENSO)‐associated spatial distribution of wave energy, which occurs when the North Pacific storm track is extended unusually far south or has receded to the north. Monthly means and principal components (PCs) of wave energy levels indicate that the 1997–1998 El Niño winter had the highest basin‐wide wave energy within this record, substantially higher than the 1982–1983 El Niño. An increasing trend in the dominant PC of LP wave energy suggests that storminess has increased in the northeast Pacific since 1980. This trend is emphasized at central eastern North Pacific locations. Patterns of storminess variability are consistent with increasing activity in the central North Pacific as well as the tendency for more extreme waves in the south during El Niño episodes and in the north during La Niña.

Journal of Geophysical Research C: Oceans↗

USGS2013

Galveston Bay: Chapter D in Emergent wetlands status and trends in the northern Gulf of Mexico: 1950-2010

The Galveston Bay estuary is located on the upper Texas Gulf coast (Lester and Gonzalez, 2002). It is composed of four major sub-bays - Galveston, Trinity, East, and West Bays. It is Texas’ largest estuary on the Gulf Coast with a total area of 155,399 hectares (384,000 acres) and 1,885 km (1,171 miles) of shoreline (Burgan and Engle, 2006). The volume of the bay has increased over the past 50 years due to subsidence, dredging, and sea level rise. Outside of ship channels, the maximum depth is only 3.7 m (12 ft), with the average depth ranging from 1.2 m (4 ft) to 2.4 m (8 ft) - even shallower in areas with widespread oyster reefs (Lester and Gonzalez, 2002). The tidal range is less than 0.9 m (3 ft), but water levels and circulation are highly influenced by wind. The estuary was formed in a drowned river delta, and its bayous were once channels of the Brazos and Trinity Rivers. Today, the watersheds surrounding the Trinity and San Jacinto Rivers, along with many other smaller bayous, feed into the bay. The entire Galveston Bay watershed is 85,470 km 2 (33,000 miles 2 ) large (Figure 1). Galveston Island, a 5,000 year old sand bar that lies at the western edge of the bay’s opening into the Gulf of Mexico, impedes the freshwater flow of the Trinity and San Jacinto Rivers into the Gulf, the majority of which comes from the Trinity. The Bolivar Peninsula lies at the eastern edge of the bay’s opening into the Gulf. Water flows into the Gulf at Bolivar Roads, 1 U.S. Geological Survey National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, LA 70506 2 Harte Research Institute for Gulf of Mexico Studies, Texas A&M University - Corpus Christi, 6300 Ocean Drive, Unit 5869, Corpus Christi, Texas 78412 2 Galveston Pass, between Galveston Island and Bolivar Peninsula, and at San Luis Pass, between the western side of Galveston Island and Follets Island.

Texas↗

USGS2013

California State Waters Map Series: Offshore of Carpinteria, California

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Offshore of Carpinteria map area lies within the central Santa Barbara Channel region of the Southern California Bight. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and the region is presently undergoing north-south shortening. The small city of Carpinteria is the most significant onshore cultural center in the map area; the smaller town of Summerland lies west of Carpinteria. These communities rest on a relatively flat coastal piedmont that is surrounded on the north, east, and west by hilly relief on the flanks of the Santa Ynez Mountains. El Estero, a salt marsh on the coast west of Carpinteria, is an ecologically important coastal estuary. Southeast of Carpinteria, the coastal zone is narrow strip containing highway and railway transportation corridors and a few small residential clusters. Rincon Point is a well-known world-class surf break, and Rincon Island, constructed for oil and gas production, lies offshore of Punta Gorda. The steep bluffs backing the coastal strip are geologically unstable, and coastal erosion problems are ongoing in the map area; most notably, landslides in 2005 struck the small coastal community of La Conchita, engulfing houses and killing ten people. The Offshore of Carpinteria map area lies in the central part of the Santa Barbara littoral cell, whose littoral drift is to the east-southeast. Drift rates have been estimated to be about 400,000 tons/yr at Santa Barbara Harbor (about 15 km west of Carpinteria). At the east end of the littoral cell, eastward-moving sediment is trapped by Hueneme and Mugu Canyons and then transported to the deep-water Santa Monica Basin. Sediment supply to the western and central part of the littoral cell is largely from relatively small transverse coastal watersheds, which have an estimated cumulative annual sediment flux of 640,000 tons/yr. The much larger Ventura and Santa Clara Rivers, the mouths of which are about 25 to 30 km southeast of Carpinteria, yield an estimated 3.4 million tons of sediment annually, the coarser sediment load generally moving southeast, down the coast, and the finer sediment load moving both upcoast and offshore. The offshore part of the map area consists of a relatively flat and shallow continental shelf, which dips so gently (about 0.4° to 0.5°) that water depths at the 3-nautical-mile limit of California’s State Waters are 40 to 45 m. This part of the Santa Barbara Channel is relatively well protected from large Pacific swells from the north and northwest by Point Conception and from the south and southwest by offshore islands and banks. Fair-weather wave base is typically shallower than 20-m water depth, but winter storms are capable of resuspending fine-grained sediments in 30 m of water, and so shelf sediments in the map area probably are remobilized on an annual basis. The shelf is underlain by variable amounts of upper Quaternary shelf, estuarine, and fluvial sediments that thicken to the south. Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft sediment and isolated areas of rocky habitat that support kelp-forest communities nearshore and rocky-reef communities in deep water. The potential marine benthic habitat types mapped in the Offshore of Carpinteria map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie within the Shelf (continental shelf) megahabitat, dominated by a flat seafloor and substrates formed from deposition of fluvial and marine sediment during sea-level rise. This fairly homogeneous seafloor provides promising habitat for groundfish, crabs, shrimp, and other marine benthic organisms. The only significant interruptions to this homogeneous habitat type are the exposures of hard, irregular, and hummocky sedimentary bedrock and coarse-grained sediment where potential habitats for rockfish and related species exist.

California↗

USGS1996

Cadmium in the California Current system: Tracer of past and present upwelling

Over 100 samples were collected off the west coast of North America during 1991–1993 to determine the relation between wind‐driven upwelling and nearshore concentrations of dissolved silicate (Si), phosphate (P), and cadmium (Cd). Highly enriched in deep water offshore, these constituents are sensitive indicators of upwelling. Coastal water was sampled from the shore in January and June 1992 at 12 sites distributed between 36° and 48°N latitude. In January the composition of nearshore water along this transect was fairly uniform: 5–15 μmol/kg for Si, 0.5 to 1.0 μmol/kg for P, and 0.1–0.3 nmol/kg for Cd. In June, elevated concentrations of Si (30 μmol/kg), P (2.0 μmol/kg), and Cd (0.6 nmol/kg) revealed a region of intense upwelling between 38° and 40°N. The pattern is broadly consistent with meridional gradients in coastal upwelling calculated from the long‐term mean of alongshore winds compiled from ship reports. Nearshore water was also collected biweekly to monthly at two sites 3 km apart near San Francisco Bay (37.5°N) during 1991–1993. The variability seen in the time series suggests that the composition of nearshore water integrates the effect of alongshore winds over timescales of several weeks. Seasonal variations in Si (5–50 μmol/kg), P (0.5–2.5 μmol/kg), and Cd (0.1–0.8 nmol/kg) concentrations were consistent with upwelling during spring and summer. Maximum Si, P, and Cd concentrations reached in May 1991 were consistent with advection to the very nearshore region from a depth of about 300 m relative to a vertical profile at a distance of 200 km from the coast. Nearshore Si, P, and Cd concentrations were reduced relative to 1991 in 1992, and, to a lesser extent, in 1993 due to weaker upwelling linked to the warm phase of the El Niño‐Southern Oscillation. During periods of weaker upwelling or downwelling, variations in P, Si, and Cd concentrations became uncoupled. There is a good correlation between the coastal Cd time series near San Francisco Bay (37.5°N) and a second order polynomial function of the upwelling index of Bakun [1975] at 36°N, filtered with a 30‐day running mean ( r 2 = 0.71, n = 39). The index is a daily estimate of coastal upwelling calculated from 6‐hourly mean atmospheric pressure distributions at 36°N. From this function and a record of daily upwelling indices, we infer a range of annually averaged coastal Cd concentrations of at least 0.3–0.5 nmol/kg since 1967. Cd/Ca ratios in shells of foraminifera from San Francisco Bay suggest that average coastal Cd concentrations 3500–4500 years ago were at the upper end of this range.

Journal of Geophysical Research C: Oceans↗

USGS2013

A twenty-first century California observing network for monitoring extreme weather events

During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. In order to improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, is required. Here we describe how California is addressing their most important and costliest environmental issue – water management – in part, by installing a state-of-the-art observing system to better track the area’s most severe wintertime storms.

California↗

USGS1980

Intrusions and intrusive complexes in an ophiolite near San Luis Obispo; a chemical and petrologic study

The San Luis Obispo ophiolite is a sequence of mafic and ultramafic rocks that lie as a thrust-like slice on top of Franciscan melange in the southern California Coast Range. The ophiolite comprises the classic Steinmann Trinity of basal serpentinized ultramafic rocks overlain sequentially by spilitized pillow lavas and cherts. The ophiolite is intruded by numerous diabasic dikes and several large intrusive complexes that contain peridotite, gabbro, diabase and felsic rocks. Field relations indicate that this ophiolite originated as a sequence of submarine volcanic flows and breccia units extruded onto an ultramafic basement. Later the volcanic and ultramafic rocks were intruded along their contact by mafic magma that crystallized as a stratiform complex of cumulate peridotite and gabbro. Next, this stratiform complex was intruded by diorite and albite-granite (trondhjemite) sills, which may have been produced by partial melting of gabbros in the upper levels of the stratiform complex. Finally all earlier units were intruded by diabasic sills and dikes that probably were late feeders for the pre-existing volcanic unit. All the ophiolite rocks underwent subsequent highly localized brecciation, under greenschist-facies conditions, in which felsic rocks were incipiently melted by frictional heating. The host rocks and intrusions were metamorphosed at low temperature and the mafic rocks were altered by Na- and Si-metasomatism. Despite this pervasive alteration, evidences of the formational stages of the ophiolite are preserved in disequilibrium mineral assemblages, primarily within mafic and ultramafic rocks of the intrusive complexes. Whole-rock analyses of the ophiolite suite indicate that alteration has obscured but not obliterated the original chemical character of the mafic rocks. The ophiolite diabases and basalts contain up to 6 weight percent Na 2 0 and 58 percent Si0 2 , in contrast to normal Si0 2 contents of 50 percent or less and Na 2 0 contents of less than 3 percent for unaltered oceanic and continental tholeiite basalts. However, the low K 2 0 contents (less than 0.8 percent) of all units in the ophiolite suite indicate that these rocks are not part of an alkalic kindred, but rather are altered tholeiites. Compositions of relict amphibole and plagioclase in the mafic rocks indicate that the ophiolite formed in a high-temperature environment and the deep seated rocks were metamorphosed under amphibolite-facies conditions. A later change in the environmental conditions allowed subsequent low-temperature (greenschist facies) metamorphism and metasomatism. The structure and chemistry of the San Luis Obispo ophiolite support the hypothesis that this body may represent a fragment of oceanic crust and mantle. The volcanic rocks and the intrusive complexes probably formed at a mid-ocean ridge, where conditions of high heat-flow provided the requisite high-temperature environment and promoted the production of mafic magmas. The change to low-temperature conditions probably was due to inception or acceleration of crustal spreading at that portion of the ridge where this ophiolite formed. The nature of brecciation in the ophiolite indicates that the low-temperature environment also was one of greater tectonic disturbance, relative to conditions at the ridge. This tectonically active environment probably corresponds to an island arc where the ophiolite-bearing plate was subducted in an adjacent trench. The absence of a high-pressure mineral assemblage in the San Luis Obispo ophiolite suggests that this segment of ocean-crust and upper mantle was not buried in a subduction zone, but rather was rafted on top of subduction melange (Franciscan Formation) into its present position.

California↗

USGS2016

Forcing and variability of nonstationary rip currents

Surface wave transformation and the resulting nearshore circulation along a section of coast with strong alongshore bathymetric gradients outside the surf zone are modeled for a consecutive 4 week time period. The modeled hydrodynamics are compared to in situ measurements of waves and currents collected during the Nearshore Canyon Experiment and indicate that for the entire range of observed conditions, the model performance is similar to other studies along this stretch of coast. Strong alongshore wave height gradients generate rip currents that are observed by remote sensing data and predicted qualitatively well by the numerical model. Previous studies at this site have used idealized scenarios to link the rip current locations to undulations in the offshore bathymetry but do not explain the dichotomy between permanent offshore bathymetric features and intermittent rip current development. Model results from the month‐long simulation are used to track the formation and location of rip currents using hourly statistics, and results show that the direction of the incoming wave energy strongly controls whether rip currents form. In particular, most of the offshore wave spectra were bimodal and we find that the ratio of energy contained in each mode dictates rip current development, and the alongshore rip current position is controlled by the incident wave period. Additionally, model simulations performed with and without updating the nearshore morphology yield no significant change in the accuracy of the predicted surf zone hydrodyanmics indicating that the large‐scale offshore features (e.g., submarine canyon) predominately control the nearshore wave‐circulation system.

Journal of Geophysical Research C: Oceans↗

USGS2023

Bayesian hierarchical modeling for probabilistic estimation of tsunami amplitude from far-field earthquake sources

Evaluation of tsunami disaster risk for a coastal region requires reliable estimation of tsunami hazard, for example, wave amplitude close to the shore. Observed tsunami data are scarce and have poor spatial coverage, and for this reason probabilistic tsunami hazard analysis (PTHA) traditionally relies on numerical simulation of “synthetic” tsunami generation and propagation toward the coast. Such an approach has been extensively studied in the past and it is widely recognized as an important disaster-risk mitigation tool. PTHA can not only provide less uncertain and spatially coherent hazard estimates in comparison with classical empirical data analysis which is restricted at the tide gauge stations, but also local inundation information. In this paper, we explore a purely statistical alternative to traditional PTHA for evaluation of tsunami amplitude hazard. Here, we use tide gauge measurements of tsunami amplitude along the western United States, specifically California and Oregon, and develop a spatial Bayesian hierarchical model (BHM) to assess tsunami hazard from far-field earthquake sources at various recurrence intervals. The configuration of our model incorporates latent Gaussian fields that utilize information on the distance between tide gauges as well as on the continental shelf width, that is, a covariate linked to potential dissipative effects on wave energy as the tsunami travels over shallow water. Through our BHM, we produce spatially continuous probabilistic maps of far-field tsunami hazard which can aid comprehensive tsunami disaster risk reduction and management.

California, Oregon, Washington↗

USGS1993

Sediment export by ice rafting from a coastal Polynya, Arctic Alaska, U.S.A.

Strong offshore winds in early 1989 produced a shore polynya that reached along the entire north coast of Alaska and eastward beyond the mouth of the Mackenzie River in Canada. From January through April, this open water periodically exposed the shelf to sediment entrainment by suspension freezing. This process requires turbulence and supercooled water, which results in the formation of frazil and anchor ice. The resulting granular, sediment-laden ice was observed to extend over 100 km seaward of the outer continental shelf after having been advected offshore. It was sampled to determine sediment type and to quantify the particle load. The particle size was mainly silt and clay, with local admixtures of as much as 27% sand and coarser clasts. Melted ice samples contained from 31 to nearly 600 mg L -1 of sediment. Combining these data with over 400 km of shipboard and aerial observations, photographs, and computer analysis of a summer Landsat image, we estimated the sediment load per unit area of sea ice. Seaward of the shelf, in regions of dense pack ice, a conservatively estimated sediment load was over 289 t km -2 . Using a westward summer drift rate of 3 cm s -1 , the sediment transport through a 1-km-long north-south segment is 67,418 t during 3 mo. In terms of regional sediment dynamics (littoral transport estimated at 10,000 t during the same period) and sediment budget (continental denudation estimated at 10 t km -2 during the same period), this number is very significant. Benthic microfossils indicate that bottom sediment incorporated in the ice came from water depths ranging from the inner neritic seaward to 50 m. The large load of shelf-derived sediment observed seaward of the continental shelf indicates that ice entrainment and transport cause shelf erosion. Nothing is known about sediment release over the Arctic Ocean Basin from these pulses of dirty ice that are periodically introduced into the Transpolar Drift.

Alaska↗

USGS2004

Quaternary tectonic setting of South-Central coastal California

Recent geodetic, geologic, and seismologic studies show that the south-central coast of California is a region of active Quaternary deformation. Northeast-directed crustal shortening is occurring in a triangular-shaped region between the Hosgri-San Simeon fault system on the west, the Southern Coast Ranges on the northeast, and the western Transverse Ranges on the south. We informally call this region the Los Osos domain. In this study, we conducted detailed geological, seismological, and geophysical investigations to characterize the nature and rates of deformation in the domain. Locations of active and potentially active faults and folds are compiled at a scale of 1:250,000 for the entire domain based primarily on onshore geologic data and offshore geophysical data. Crustal shortening in the domain is accommodated by a series of prominent northwest-trending reverse faults and localized folding. The reverse faults separate distinct structural blocks that have little or no internal deformation. Hangingwall blocks are being uplifted at rates of up to 0.2 mm/yr. Footwall blocks are either static or slowly subsiding at rates of 0.1 mm/yr or less, except for localized areas of concentrated subsidence directly adjacent to some faults. The cumulative rate of crustal shortening is about 1 to 2 mm/yr across the northern part of the domain based on observed geologic deformation. Cumulative shortening across the central and southern parts of the domain is poorly constrained by geologic data and may approach 2 to 3 mm/yr. Historical and instrumental seismicity generally are spatially associated with the uplifted blocks and bordering reverse faults to depths of about 10 km. Together with near-surface geological data and deeper crustal geophysical imaging that show high-angle faulting, the seismicity data indicate that the reverse faults probably extend to the base of the seismogenic crust. The base of the seismogenic crust may correspond with a mid-crustal detachment or decollement surface into which the reverse faults root. We speculate that the detachment may coincide, in part, with the top of a northeast-dipping slab of oceanic crust that extends beneath the western margin of the continent or with the brittle-ductile transition above the subducted slab. The Los Osos domain of north-northeast/south-southwest crustal shortening is structurally detached from the offshore Hosgri Fault Zones. Both the pattern and regional extent of deformation in the Los Osos domain contrast sharply with that of the offshore Santa Maria Basin. The basin is undergoing minor east-northeast/west-southwest crustal shortening at rates of less than 0.1 mm/yr and is moving northwestward at a rate of about 1 to 3 mm/yr relative to the Los Osos domain along the San Simeon and Hosgri Fault Zones. Geodetic data and the kinematics of north-northeast-directed crustal shortening of the Los Osos domain east of the Hosgri Fault Zone show that the rate and cumulative amount of right-slip along the Hosgri Fault Zone progressively decrease southward. Quaternary deformation within the Los Osos domain is related to distributed dextral simple shear associated with Pacific-North American plate motion. Paleomagnetic data show that clockwise rotation of the western Transverse Ranges has occurred along the southern boundary of the domain during the past 6 m.y. During this time, the Salinian crustal block, which forms the eastern boundary of the Los Osos domain, has remained relatively stable. Internal shortening of the Los Osos domain has accommodated the relative motions of these bordering crustal blocks, particularly the rotation of the western Transverse Ranges.

Bulletin↗

USGS2012

Gauging state-level and user group views of oyster reef restoration activities in the northern Gulf of Mexico

Successful oyster reef restoration, like many conservation challenges, requires not only biological understanding of the resource, but also stakeholder cooperation and political support. To measure perceptions of oyster reef restoration activities and priorities for future restoration along the northern Gulf of Mexico coast, a survey of 1500 individuals representing 4 user groups (oyster harvesters, shrimpers, environmental organization members, professionals), across 5 states (Texas, Louisiana, Mississippi, Alabama, Florida) was conducted in 2011. All respondents highly supported reef restoration efforts, but there was a dichotomy in preferred restoration goals with commercial fishermen more likely to support oyster reef restoration for stock enhancement, while professionals and environmental organization members were more likely to support oyster reef restoration to enhance ecosystem services. All user groups identified enforcement, funding, and appropriate site selection as basic requirements for successful reef restoration. For management of restored oyster reefs, oyster harvesters and shrimpers were less likely to support options that restricted the use of reefs, including gear restrictions and permanent closures, but did support rotating annual reef closures, while other stakeholders were willing to consider all options, including annual reef closures and sanctuary reefs. Overall, there were clear differences in management and communication preferences across user groups, but few differences across states. Understanding these key differences in stakeholder support for, and willingness to accept specific management actions is critical in moving management and restoration forward while minimizing conflict.

Ocean and Coastal Management↗

USGS2019

Upper thermal tolerance and heat shock protein response of juvenile American shad (Alosa sapidissima)

Juvenile American shad ( Alosa sapidissima ) experience a wide range of temperatures in rivers before migrating to the ocean. Temperatures in these freshwater environments can vary greatly spatially, seasonally, year-to-year, and can be impacted by anthropogenic factors such as power plant discharge or climate change. Currently, there is uncertainty concerning juvenile American shad thermal tolerance due to a lack of a well-controlled study. Here, we report results of laboratory experiments to establish the upper thermal tolerance and heat shock protein response of juvenile American shad exposed to gradually increasing temperatures. Upper thermal tolerance was determined to be 35 °C (median; range = 34–36 °C) when fish were acclimated to 25 °C and temperatures were raised 1 °C day −1 . Heat shock protein response was indicated by changes in branchial mRNA abundance of the inducible heat shock protein 90 alpha ( hsp90α ), which was significantly elevated (more than 5-fold increase) at 30 °C, and highest in fish that had reached their upper thermal maximum between 34 and 36 °C. Our findings indicate a higher upper thermal tolerance than previously reported for juvenile American shad, and an onset temperature of hsp90α induction at 30 °C, a temperature juvenile American shad commonly experience during summer months.

Estuaries and Coasts↗

USGS2022

Defining oyster resource zones across coastal Louisiana for restoration and aquaculture

Eastern oysters ( Crassostrea virginica ) are a critical ecological and commercial resource in the northern Gulf of Mexico facing changing environmental conditions from river management and climate change. In Louisiana, USA, development of restored reefs, and off-bottom aquaculture would benefit from the identification of locations supportive of sustainable oyster populations ( i.e., metapopulations) and high consistent production. This study defines four oyster resource zones across coastal Louisiana based on environmental conditions known to affect oyster survival, growth, and reproduction. Daily data from 2015 to 2019 were interpolated to generate salinity and temperature profiles across Louisiana's estuaries, which were then used to classify zones based on monthly and annual salinity mean and variance. Zones were classified as supportive of (1) broodstock sanctuary reefs (i.e., support reproductive populations), (2) productive reefs during dry (salty) years, (3) productive reefs during wet (fresh) years, and (4) off-bottom aquaculture development. Of the 38,000 km 2 investigated, over 11,000 km 2 of potential oyster zone area was identified across the Louisiana coast. The Broodstock Sanctuary Zone was the smallest (∼540 km 2 ), as salinity variance limited this zone in many areas, as it is driven largely by riverine inputs across many estuaries. Located up-estuary (Dry Restoration Zone) and down-estuary (Wet Restoration Zone) of the Broodstock Sanctuary Zone, Dry and Wet Restoration Zone areas covered ∼2400 km 2 and ∼3900 km 2 , respectively. Mapped reefs in Louisiana currently exist largely within the Dry Restoration zones, suggesting a potential strategy to focus reef development in Wet Restoration zones to ensure reef network sustainability through years with high precipitation and river inflow. The off-bottom Aquaculture Zone was the largest (∼6400 km 2 ) zone identified, with much of this area located more down-estuary and off-shore. Accounting for variable water quality conditions enables the development of a network of reefs resilient to environmental variability, and more stable areas for consistent off-bottom aquaculture production. Spatial planning and identification of oyster resource zones reduces focus on individual reef success and supports management of oyster metapopulation outcomes, while identifying zones supportive of off-bottom aquaculture.

Louisiana↗