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USGS2017

Refining the formation and early evolution of the Eastern North American Margin: New insights from multiscale magnetic anomaly analyses

To investigate the oceanic lithosphere formation and early seafloor spreading history of the North Atlantic Ocean, we examine multiscale magnetic anomaly data from the Jurassic/Early Cretaceous age Eastern North American Margin (ENAM) between 31 and 40°N. We integrate newly acquired sea surface magnetic anomaly and seismic reflection data with publicly available aeromagnetic and composite magnetic anomaly grids, satellite-derived gravity anomaly, and satellite-derived and shipboard bathymetry data. We evaluate these data sets to (1) refine magnetic anomaly correlations throughout the ENAM and assign updated ages and chron numbers to M0–M25 and eight pre-M25 anomalies; (2) identify five correlatable magnetic anomalies between the East Coast Magnetic Anomaly (ECMA) and Blake Spur Magnetic Anomaly (BSMA), which may document the earliest Atlantic seafloor spreading or synrift magmatism; (3) suggest preexisting margin structure and rifting segmentation may have influenced the seafloor spreading regimes in the Atlantic Jurassic Quiet Zone (JQZ); (4) suggest that, if the BSMA source is oceanic crust, the BSMA may be M series magnetic anomaly M42 (~168.5 Ma); (5) examine the along and across margin variation in seafloor spreading rates and spreading center orientations from the BSMA to M25, suggesting asymmetric crustal accretion accommodated the straightening of the ridge from the bend in the ECMA to the more linear M25; and (6) observe anomalously high-amplitude magnetic anomalies near the Hudson Fan, which may be related to a short-lived propagating rift segment that could have helped accommodate the crustal alignment during the early Atlantic opening.

Journal of Geophysical Research B: Solid Earth↗

USGS2006

February 2003 marine atmospheric conditions and the bora over the northern Adriatic

A winter oceanographic field experiment provided an opportunity to examine the atmospheric marine conditions over the northern Adriatic. Mean February winds are from a northeasterly direction over most of the Adriatic and a more northerly direction along the western coast. Wind speeds are fastest in jets over the NE coast during bora events and weakest in the mid-northwestern Adriatic. Diurnal air temperature cycles are smallest on the NE coast and largest in the midwestern Adriatic. The maximum sea-air difference is +10??C on the eastern coast and near zero on the midwestern Adriatic. Boras are northeasterly (from) wind events that sweep off Croatia and Slovenia, bringing slightly colder and drier air over the northern Adriatic. The main bora season is December to March. Winter 2002-2003 was normal for bora events. Synoptic-scale temporal variations are correlated over the northern Adriatic. Fastest Bora winds and highest wind stress over the northern Adriatic is concentrated in four topographically controlled jets. The strongest is the Senj Jet, while the Trieste Jet extends across the entire northern Adriatic. Between each two jets is a weak wind zone. The greatest mean net heat loss is in bora jets in the NE Adriatic, where it was -438 W m-2 and is weakest in the midwestern northern Adriatic, where it was near zero. Wind stress is concentrated over the NE half of Adriatic in four bora jets, while wind stress is weak in the NW Adriatic. There is significant variation in wind stress mean and standard deviation structure over the northern Adriatic with each bora event. Copyright 2006 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗

USGS1976

Geothermal flux through palagonitized tephra, Surtsey, Iceland: The Surtsey temperature-data-relay experiment via Landsat-1

The net geothermal flux through palagonitized basaltic tephra rims of the Surtur I and Surtur II craters at Surtsey, Iceland, in 1972, is estimated at 780 ±325 μ cal cm -2 s -1 , indicating a decline since 1969 when a flux of 1,500 μ cal cm -2 s -1 was estimated. Heat flux in this range characterizes the postvolcanic environment on Surtsey in which the subaerial palagonitization of basaltic tephra is associated with mass transfer of hydrothermal vapor, either of meteoric or sea-water origin, only a few years after cessation of eruptive activity. The flux estimation is the result of the Surtsey data-relay experiment via Landsat-1 which was carried. out in several phases. Successful field installation and test transmissions demonstrated the feasibility of repetitive long-distance (that is, 4,800-km) data transmission and reception from a volcanic environment in Iceland via the Landsat Data Collection System. Temperature data were transmitted for a 38-day period in November and December 1972. A near-surface vertical gradient of 69.4 °C/m was obtained, suggesting a mixed mechanism of heat transfer, partitioned between conduction and convection. Comparison of four methods for estimating fluxes between 500 and 1,500 μ cal cm -2 s -1 , using temperature data derived from the Data Collection Platform, suggests that, where the only temperature available are from the surface and a depth of 1 m, methods of estimating the net geothermal flux from examination of spectral radiance are superior to methods that assume dominant convection or conduction. A computerized thermal-modeling technique to construct parametric diurnal surface-temperature curves is particularly applicable. Flux-estimation methods that assume dominant convection or conduction are limited by the lack of temperature data at greater depths and lack of knowledge of the exact energy partition.

Surtsey↗

USGS2020

Acute toxicity of the lampricides TFM and niclosamide: Effects on a vascular plant and a chironomid species

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide have been used for about 60 years to control sea lamprey (Petromyzon marinus) in the Great Lakes Basin and Lake Champlain. To register these chemicals as pesticides in North America, their environmental effects must be reviewed on a periodic basis. As a part of this effort, toxicity of TFM and niclosamide to duckweed (Lemna gibba), and of niclosamide to aquatic midge (Chironomus tentans), was assessed. Results of these studies suggest that for both lampricides, the no-observable and lowest observable effects concentrations (NOEC and LOEC) exceed expected environmental concentrations, with effects only in the highest concentrations tested and the longest exposure times. Duckweed exposed to TFM indicated 7-day LOECs ≥ 4.88 mg/L for average specific growth rate and yield, with the EC50 > 9.74 mg/L. For duckweed exposed to niclosamide, 7-day LOECs for average specific growth rate and yield ranged from 0.271 to 0.569 mg/L, with the IC50 0.725 mg/L or greater depending on the parameter measured. For midge larvae exposed to niclosamide-dosed sediment, the LOEC values based on survival and growth were 26.2 mg/kg and > 82.1 mg/kg, respectively, and the EC50 based on survival was 49.6 mg/kg. Based on these data, deleterious effects on aquatic plants and benthic invertebrates are unlikely to result from use of TFM and niclosamide for lamprey control, given that the effect concentrations are in excess of the expected environmental concentrations.

Great Lakes Basin, Lake Champlain↗

USGS2008

Coarse-clast ridge complexes of the Caribbean: A preliminary basis for distinguishing tsunami and storm-wave origins

Coastal gravel-ridge complexes deposited on islands in the Caribbean Sea are recorders of past extreme-wave events that could be associated with either tsunamis or hurricanes. The ridge complexes of Bonaire, Jamaica, Puerto Rico (Isla de Mona), and Guadeloupe consist of polymodal clasts ranging in size from sand to coarse boulders that are derived from the adjacent coral reefs or subjacent rock platforms. Ridge-complex morphologies and crest elevations are largely controlled by availability of sediments, clast sizes, and heights of wave runup. The ridge complexes are internally organized, display textural sorting and a broad range of ages including historical events. Some display seaward-dipping beds and ridge-and-swale topography, and some terminate in fans or steep avalanche slopes. Together, the morphologic, sedimentologic, lithostratigraphic, and chronostratigraphic evidence indicates that shore-parallet ridge complexes composed of gravel and sand that are tens of meters wide and several meters thick are primarily storm-constructed features that have accumulated for a few centuries or millennia as a result of multiple high-frequency intense-wave events. They are not entirely the result of one or a few tsunamis as recently reported. Tsunami deposition may account for some of the lateral ridge-complex accretion or boulder fields and isolated blocks that are associated with the ridge complexes. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗

USGS2007

Bora event variability and the role of air-sea feedback

A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS??) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS?? is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ???12% over the northern Adriatic during both bora compared with a one-way coupled simulation. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research C: Oceans↗

USGS1998

Reproductive potential and fecundity of lake trout strains in southern and eastern waters of Lake Ontario, 1977-1994

We assessed the reproductive potential of various genetic strains of hatchery lake trout ( Salvelinus namaycush ) in southern and eastern Lake Ontario from indices of fecundity and indices of male abundance. Indices were constructed from catches of mature lake trout in gill nets during September 1980 to 1994 after correcting for mortality from sea lampreys ( Petromyzon marinus ) which occurred between September sampling and late fall spawning. Strain and age were assigned to individual lake trout based on clipped fins and maxillary bones or coded wire tags. Fecundity-length relationships for fish of the same age, determined from mature females collected in 1977 to 1981 and 1994, were not different (P > 0.05) among genetic strains. For all strains combined, fecundity-length relationships in 1977 to 1981 were not different among fish of various ages but in 1994, age-5 and -6 fish had fewer eggs (P < 0.003) than age-7 fish, and age-7 fish had fewer eggs (P < 0.003) than fish of age 8, 9, or 10. Annual indices of fecundity varied 19 fold and indices of mature males varied 11 fold; both indices were low in the early 1980s, increased sharply in the mid 1980s, and peaked in 1993. The strain which dominated fecundity and mature male indices shifted during the study from Seneca Lake strain to Lake Superior strain and then back to Seneca Lake strain. However, changes in either reproductive potential or genotypes do not appear responsible for the abrupt appearance of naturally-produced yearling lake trout throughout southern and eastern Lake Ontario in 1994–1995, the first widespread occurrence of juveniles produced by hatchery lake trout in Lake Ontario.

Journal of Great Lakes Research↗

USGS1968

Rehabilitation of lake trout in the Apostle Islands region of Lake Superior

Marked success of rehabilitation of lake trout in Lake Superior has been due principally to the control of the sea lamprey and closure of the lake trout fishery in 1962 and large-scale plantings of yearling lake trout in 1959-66. After the sea lamprey became established in the late 1940s, spawning stocks of lake trout began to decrease and were almost nonexistent by 1960-61. After control of the sea lamprey and closure of the commercial fishery for lake trout in 1962, the abundance of spawning stocks began to rise and reached the highest levels on record in 1964-66. Successful spawning in 1964 and 1965 was demonstrated by catches of age-0 lake trout in 1965 and 1966, the first evidence of natural reproduction since 1959. Plantings of hatchery-reared lake trout in Wisconsin waters of Lake Superior began in 1952. The percentage of hatchery-reared fish in catches of juvenile lake trout increased almost steadily from 1953 to 1965 (when nearly all were of hatchery origin). The abundance of juvenile fish increased from 1959 to 1962 and remained nearly constant in 1962-66. The success of lake trout plantings was highest in 1959-61 but generally declined after 1961; the success of the plantings was inversely related to the abundance of older lake trout. Annual increments of growth of hatchery-reared lake trout varied from 1.1 to 5.0 inches after planting. The average lengths of fish of identical age-groups varied according to gear of capture, depth of water, and season. More than 65% of the season's growth of age-III lake trout took place after September. The findings indicate that the present rate of stocking lake trout may be higher than necessary to maintain optimum abundance.

Journal of the Fisheries Research Board of Canada↗

USGS2014

Ice sheet load cycling and fluid underpressures in the Eastern Michigan Basin, Ontario, Canada

Strong fluid underpressures have been detected in Paleozoic strata in the eastern Michigan Basin, with hydraulic heads reaching ~400 m below land surface (~4 MPa underpressure) and ~200 m below sea level in strata where unusually low permeabilities (~10 −20 –10 −23  m 2 ) were measured in situ. Multiple glaciations, including three with as much as 3 km of ice cover at the site in the last 120 ka, suggest a causal link with the underpressures. We examined this possibility using a one-dimensional groundwater flow model incorporating mechanical loading from both ice weight and lithospheric flexure. Because hydrologic and mechanical changes during glaciation are not well characterized and subsurface properties are imperfectly known, the model was used inversely to estimate flexural loads and loosely constrained permeabilities by matching observed pressures. Acceptable matches were obtained for a surprisingly wide range of scenarios with permeabilities close to measured values and plausible flexural loads. Matches were not obtained when too many parameters were preselected, or when permeabilities were constrained to be significantly larger than measured values. In successful model runs groundwater expulsion under glacial-mechanical loads caused the underpressuring, and flexural loads were important if aquifer and sub-glacial pressures were significantly elevated during glaciation. Simulated fluid pressures in the low-permeability strata fluctuated by 30–40 MPa during glacial cycles but resulted in advective transport of only tens of meters or less. Although other mechanisms cannot be ruled out, we conclude that glacial-mechanical forcing of a water-saturated system can explain the observed underpressures.

Ontario↗

USGS1976

Sedimentary depositional environments of uranium and petroleum host rocks of the Jackson Group, south Texas

Determination of depositional environments in rocks of the Jackson Group of late Eocene age aids in the exploration for uranium and petroleum in south Texas. During deposition of the Jackson Group, conditions were similar to those existing along the modern Gulf Coast of Texas except for a less arid climate and a greater supply of volcanic sediment. Sedimentary depositional environments recognized in both the modern coast and the Jackson rocks, in order from sea toward land, are: shoreface, beach, lagoon and bay, and paludal. Sediment deposited in these environments in places is interbedded with or transected by fluvial sediment. Both uranium and petroleum are found in the shoreface, beach, and fluvial facies. These facies are characterized by permeable well-sorted sandstone, which is commonly overlain and underlain by less permeable mudstone. A typical vertical sequence in ascending order through a unit containing a beach sandstone facies is (1) lagoonal or paludal clay stone and siltstone, (2) crossbedded fine-grained beach sandstone which contains Ophiomorpha burrows and, which, in places, is locally interbedded with lacustrine or lagoonal mudstone, (3) weakly laminated beach sandstone which contains root impressions at the top and Ophiomorpha , and (4) lagoonal or paludal claystone and siltstone. Gulfward, the beach sandstone apparently grades into highly burrowed, generally finer grained, more poorly sorted, less porous shoreface rocks. The beach facies may include barrier island beaches and mainland beaches, some of which were probably cheniers. Beach facies sandstone units extend many miles along the depositional strike, which nearly parallels the present outcrop strike, but extend only a mile or two (2-3 km) normal to the depositional strike into the subsurface. Recognition of the various facies in outcrops and drill holes is necessary for determination of true stratigraphic relations and for aid in exploration for beach and fluvial sandstone favorable for uranium and petroleum accumulations.

Texas↗

USGS2019

Separating sea and slow slip signals on the seafloor

Seafloor pressure measurements hold promise for estimating vertical displacements from transient slow slip events on submarine faults. We assess the accuracy of pressure offset estimates that evolve over days to weeks and the confidence with which they may be attributed to tectonic deformation or to the ocean water column. One common approach to resolve this ambiguity assumes water column pressures vary insignificantly over the study region and are represented by stable reference site pressures. Assessing the validity of this assumption requires independent evidence. Correlations between pressures and colocated temperatures collected during the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip experiment suggest temperatures might provide a useful independent proxy for water column pressures. We compared offsets estimated using several methods, with temperature and other proxies. The use of a temperature proxy was unsuccessful, because seafloor temperatures did not track the seasonal signal that contributes significantly to seafloor pressure changes over the slow slip event period. Regardless of the estimation method, offsets varied within a few cm around some uncertain reference level. Commonly used statistical measures are shown not to be reliable indicators of offset accuracy since offsets contribute minimally to the total variance. Offsets estimated using identical methods but with seafloor pressures simulated using a regional ocean model were larger than those derived from the data but had a similar pattern. Since the model simulates only water column processes, this suggests a significant fraction of the estimated pressure offsets are due to seasonal water column signal and are not of tectonic origin.

Journal of Geophysical Research- Solid Earth↗

USGS2025

Evaluation of a recovering lake trout population in Lake Champlain using close-kin mark-recapture and genetic strain assignment

Lake trout ( Salvelinus namaycush ) populations in many northern North American large lake systems have been substantially reduced or extirpated due to overfishing, habitat loss, and introduction of invasive species. Following reductions in fishing pressure and successful suppression of sea lamprey, attempts have been made to restore self-sustaining populations into most of these waters but success has been slow and limited. In contrast, lake-wide lake trout restoration occurred abruptly and rapidly in Lake Champlain after 40 years of stocking, with robust, widespread, and sustained wild recruitment observed from the 2012 cohort onwards. We sought to better understand the dynamics of the recovery success in Lake Champlain using a multi-year tissue dataset, in combination with a recently-designed genotyping panel and close-kin mark-recapture, to quantify the performance (i.e., survival and reproductive success) of stocking sources and strategies with an eye towards informing restoration programs in other systems. We also assessed the overall abundance of adult fish and parental dynamics associated with wild recruitment. Our results indicate that adult survival is remarkably high and overall abundance is low compared to other large lake systems in similar latitudes, with the vast majority of wild recruitment genetically traceable to the Seneca strain fish historically stocked by New York State. We observed little evidence of hybridization between the two strains and close-kin mark-recapture estimates indicated that approximately 20 % of the adult population was contributing to successful recruitment on a regular basis. Ultimately, our results point to a growing wild population that has the potential to become self-sustaining.

New York, Vermont↗

USGS2014

Improving groundwater predictions utilizing seasonal precipitation forecasts from general circulation models forced with sea surface temperature forecasts

Recent studies have found a significant association between climatic variability and basin hydroclimatology, particularly groundwater levels, over the southeast United States. The research reported in this paper evaluates the potential in developing 6-month-ahead groundwater-level forecasts based on the precipitation forecasts from ECHAM 4.5 General Circulation Model Forced with Sea Surface Temperature forecasts. Ten groundwater wells and nine streamgauges from the USGS Groundwater Climate Response Network and Hydro-Climatic Data Network were selected to represent groundwater and surface water flows, respectively, having minimal anthropogenic influences within the Flint River Basin in Georgia, United States. The writers employ two low-dimensional models [principle component regression (PCR) and canonical correlation analysis (CCA)] for predicting groundwater and streamflow at both seasonal and monthly timescales. Three modeling schemes are considered at the beginning of January to predict winter (January, February, and March) and spring (April, May, and June) streamflow and groundwater for the selected sites within the Flint River Basin. The first scheme (model 1) is a null model and is developed using PCR for every streamflow and groundwater site using previous 3-month observations (October, November, and December) available at that particular site as predictors. Modeling schemes 2 and 3 are developed using PCR and CCA, respectively, to evaluate the role of precipitation forecasts in improving monthly and seasonal groundwater predictions. Modeling scheme 3, which employs a CCA approach, is developed for each site by considering observed groundwater levels from nearby sites as predictands. The performance of these three schemes is evaluated using two metrics (correlation coefficient and relative RMS error) by developing groundwater-level forecasts based on leave-five-out cross-validation. Results from the research reported in this paper show that using precipitation forecasts in climate models improves the ability to predict the interannual variability of winter and spring streamflow and groundwater levels over the basin. However, significant conditional bias exists in all the three modeling schemes, which indicates the need to consider improved modeling schemes as well as the availability of longer time-series of observed hydroclimatic information over the basin.

Georgia↗

USGS2021

Volcanic seismicity beneath Chuginadak Island, Alaska (Cleveland and Tana volcanoes): Implications for magma dynamics and eruption forecasting

Cleveland and Tana are remote volcanoes located in the central Aleutian volcanic arc on the eastern end of the Islands of Four Mountains (IFM). The persistently active Mount Cleveland volcano, on the western side of Chuginadak Island, is surrounded by several closely spaced Quaternary volcanic centers including Carlisle, Herbert, Kagamil, Tana, and Uliaga, and numerous small satellite vents on Chiginadak between Cleveland and Tana. The Alaska Volcano Observatory (AVO) installed two permanent broadband seismometers on Chuginadak Island in 2014, and we operated a temporary broadband network focused on the western side of the island in 2015–2016. Collectively, these stations provided the first seismic observations of this frequently active volcano and the surrounding Holocene-aged volcanic vents. During the study period (July 2014–January 2019), eruptive activity at Cleveland was characterized by small explosions separated by periods of lava effusion that formed small domes in the volcano's summit crater. We characterize seismicity beneath Chuginadak Island through automated analysis of event waveform frequency content, development of a one-dimensional P-wave velocity model, calculation of earthquake hypocenters, magnitudes, focal mechanisms, and identification of earthquake families. This analysis reveals the full range of seismic event types expected in a highly active volcanic environment and includes Volcano-Tectonic (VT) earthquakes, Long-Period (LP) events, and explosion signals. LP events appear to cluster at shallow depth beneath the active crater of Mount Cleveland and almost all of the explosions occur without identifiable short-term (hours to days) seismic precursors. VT earthquakes beneath Mount Cleveland occur at depths of 2 to 8 km below sea level (BSL) and range in magnitude from −0.2 to 1.8. VT focal mechanisms have horizontal P-axes that align with the regional axis of maximum stress. These observations, and a relatively slow one-dimensional seismic velocity model, are consistent with a shallow body of magma that is fed through a deeper conduit system. The time-history of VT earthquakes and shallow LP events suggest their occurrence may track the transfer of magma and fluids from the mid-crust to the shallow portions of the conduit system and may provide a means to anticipate future explosions and periods of dome growth. VT hypocenters also extend ~7 km northeast of Cleveland's summit at depths of 5 to 10 km BSL, under a group of Holocene-aged vents between Mount Cleveland and Tana. These earthquakes have vertically-oriented P-axes and a greater percentage occur in families. These observations, combined with observations of vent orientation and morphology and gas flux, suggest the area between Cleveland and Tana represents a zone of complicated volcano-tectonic interaction, similar to calderas elsewhere in the Aleutian arc. The presence of a larger volcanic system in the eastern IFM could influence magmatism and account for the multiple closely spaced volcanic centers in this region.

Alaska↗

USGS2007

Evidence of lake whitefish spawning in the Detroit River: Implications for habitat and population recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish ( Coregonus clupeaformis ) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey ( Petromyzon marinus ) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m3 of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid- and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.

Michigan↗

USGS2013

Sr/Ca proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park

Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ~6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer-driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST + 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961-2008) and a 7-year Holocene (~6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ~0.3 and 0.5 mmol/mol. The amplitude of ~0.3 to 0.5 mmol/mol equates to a 10-15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s. The Holocene (~6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

Florida↗

USGS2021

Role of future reef growth on morphological response of coral reef islands to sea-level rise

Coral reefs are widely recognised for providing a natural breakwater effect that modulates erosion and flooding hazards on low‐lying sedimentary reef islands. Increased water depth across reef platforms due sea‐level rise (SLR) can compromise this breakwater effect and enhance island exposure to these hazards, but reef accretion in response to SLR may positively contribute to island resilience. Morphodynamic studies suggest that reef islands can adjust to SLR by maintaining freeboard (island crest elevation above still water level) through overwash deposition and island accretion, but the impact of different future reef accretion trajectories on the morphological response of islands remain unknown. Here we show, using a process‐based morphodynamic model, that, although reef growth significantly affects wave transformation processes and island morphology, it does not lead to decreased coastal flooding and island inundation. According to the model, reef islands evolve during SLR by attuning their elevation to the maximum wave runup and islands fronted by a growing reef platform attain lower elevations than those without reef growth, but have similar overwash regimes. The mean overwash discharge Q over across the island crest plays a key role in the ability of islands to keep up with SLR and maintain freeboard, with a Q over value of O (10 l m ‐1 s ‐1 ) separating island construction from destruction. Islands, therefore, can grow vertically to keep up with SLR via flooding and overwash if specific forcing and sediment supply conditions are met, offering hope for uninhabited and sparely populated islands. However, this physical island response will negatively impact infrastructure and assets on developed islands.

Journal of Geophysical Research--Earth Surface↗

USGS2024

Subduction zone geometry modulates the megathrust earthquake cycle: Magnitude, recurrence, and variability

Megathrust geometric properties exhibit some of the strongest correlations with maximum earthquake magnitude in global surveys of large subduction zone earthquakes, but the mechanisms through which fault geometry influences subduction earthquake cycle dynamics remain unresolved. Here, we develop 39 models of sequences of earthquakes and aseismic slip (SEAS) on variably-dipping planar and variably-curved nonplanar megathrusts using the volumetric, high-order accurate code tandem to account for fault curvature. We vary the dip, downdip curvature and width of the seismogenic zone to examine how slab geometry mechanically influences megathrust seismic cycles, including the size, variability, and interevent timing of earthquakes. Dip and curvature control characteristic slip styles primarily through their influence on seismogenic zone width: wider seismogenic zones allow shallowly-dipping megathrusts to host larger earthquakes than steeply-dipping ones. Under elevated pore pressure and less strongly velocity-weakening friction, all modeled fault geometries host uniform periodic ruptures. In contrast, shallowly-dipping and sharply-curved megathrusts host multi-period supercycles of slow-to-fast, small-to-large slip events under higher effective stresses and more strongly velocity-weakening friction. We discuss how subduction zones' maximum earthquake magnitudes may be primarily controlled by the dip and dimensions of the seismogenic zone, while second-order effects from structurally-derived mechanical heterogeneity modulate the recurrence frequency and timing of these events. Our results suggest that enhanced co- and interseismic strength and stress variability along the megathrust, such as induced near areas of high or heterogeneous fault curvature, limits how frequently large ruptures occur and may explain curved faults' tendency to host more frequent, smaller earthquakes than flat faults.

Journal of Geophysical Research: Solid Earth↗