Western North Atlantic Research Articles

A high-resolution coupled circulation-wave model for regional dynamic downscaling of water levels and wind waves in the western North Atlantic ocean

Reanalysis datasets provide temporally/spatially continuous data for sea level and wind wave climate studies but often lack the resolution to resolve the complex coastal physical processes. To address this issue, a high-resolution coupled circulation-wave model (ADCIRC + SWAN) is applied to dynamically downscale storm tides (tide + surge + wave setup) and waves in the western North Atlantic Ocean. The model is forced at its sea surface boundary with hourly surface pressure and wind fields, and its open boundary with water levels and direction-frequency wave spectrum from the ERA5 reanalysis dataset. The sensitivity of the model is evaluated for different combinations of internal tide energy conversion, quadratic friction coefficients, and wave physics packages. For the best model setup, the results show an RMSE range of 0.114 m–0.295 m for storm tide, 0.176 m–0.298 m for non-tidal residual, 0.143 m–0.39 m for significant wave height, and 0.42 s–1.04 s for mean wave period. Incorporating the direction-frequency wave spectrum as an open boundary condition improves the model's accuracy, reducing the RMSE for significant wave heights by up to 7% and for the mean wave period by up to 30% over a one-month simulation period.

Three new species of wood-boring bivalves (Mollusca: Xylophagaidae) from the deep Northwest Atlantic Ocean

Ruth Turner’s studies of xylophagaids, wood-boring bivalves, documented the very existence of wood-borers in the deep sea and made the northwestern Atlantic fauna among the best known. However, her work focused on specimens from less than 2000 m depth. Here study of specimens from depths over 2000 m deposited in the Smithsonian collections extends our knowledge of this fauna. Despite the lack of molecular data, three species, Xylophaga microdactylus n. sp., Xylophaga platyplax n. sp. and Xylophaga lambula n. sp. are described; only X. lambula n. sp. pertains to Xylophaga s.s. Turton. Additional records of the known species, Xyloredo nooi Turner, Xylonora atlantica (Richards), Abditoconus cf. anselli (Harvey), Xylophaga clenchi Turner & Culliney, Feaya dostwous (Voight), and Xylopholas cf. altenai Turner are provided, with some supplemental information on morphological characters. The presence of Xylophaga microdactylus n. sp., which is remarkably similar to X. microchira Voight, suggests a close relationship between the xylophagaids of the deep northwestern Atlantic and northeastern Pacific. The depth distributions of northwest Atlantic species are detailed with supplemental data from the literature to explore potential patterns of distribution.

Microplastic abundance and accumulation patterns in eelgrass (Zostera marina L.) meadows throughout coastal Massachusetts, USA.

Microplastics are fast-emerging as another potential threat to already globally declining seagrass ecosystems, but there is a paucity of in situ surveys showing their accumulations. Here, we surveyed multiple Zostera marina L. meadows in 2020 and 2021 across Massachusetts, USA, for microplastic contamination, as well as identified factors related to patterns of accumulation. We found that microplastics were ubiquitous throughout all sites regardless of proximity to human development, with fibers being the most common microplastic type. In addition, we showed that accumulation of microplastics within seagrass meadows was related to epiphytic cover on leaves, plant morphology, and bulk-density in sediments. The results of this study provide the first in situ baseline microplastic concentrations on Z. marina plants and sediments for the temperate western North Atlantic. Additionally, we identify specific biotic and abiotic factors related to patterns of microplastic accumulation in these ecosystems.

First evidence of white sharks, Carcharodon carcharias, in the tongue of the ocean, central Bahamas

The white shark, Carcharodon carcharias, is an iconic apex predator, playing an important ecological role across its range. Persistent bycatch and overfishing led to white shark declines, but recent studies in the North Western Atlantic (NWA) revealed evidence for regional recovery, and highlighted the importance of Southeastern Florida and the Gulf of Mexico as overwintering grounds for maturing white sharks. However, despite its proximity to Florida and comparably productive habitats, records of white sharks in The Bahamas are extremely rare, with a comprehensive survey of sightings and captures describing only one white shark between 1800 - 2010. Here, we reveal acoustic tracking detections of ten white sharks from 2020 - 2024 along the western edge of the Tongue of the Ocean off Central Andros Island, The Bahamas. White sharks were originally tagged off the coast of the United States and Canada, and detected off Andros Island, The Bahamas from November-May. White sharks were detected along the drop-off zone of the reef at ca. 25 m, exclusively between dusk and dawn, with the number of detections suggesting transient behavior. These findings expand our knowledge of white shark distribution in the NWA, highlighting data gaps in The Bahamas and underlining the importance of collaborative protective measures for species recovery.

New middle Eocene radiolarian species (Rhizaria, Polycystinea) from Blake Nose, subtropical western North Atlantic Ocean

Abstract Diverse and well-preserved radiolarian assemblages were recovered from the middle Eocene sedimentary sequences drilled at Ocean Drilling Program Site 1051 (Leg 171B; western subtropical Atlantic). In addition to biostratigraphically important species, several unknown morphotypes were observed in this material, leading to the description of three new spumellarian species and 18 new nassellarian species. Described herein are: Periphaena petrushevskayae n. sp. (Phacodiscidae), Stylodictya oligodonta n. sp. (Trematodiscidae), Excentrosphaerella delicata n. sp. (Heliodiscidae), Eucyrtidium granatum n. sp. (Eucyrtidiidae), Dictyoprora echidna n. sp., Spirocyrtis matsuokai n. sp. (Artostrobiidae), Elaphospyris cordiformis n. sp., Elaphospyris quadricornis n. sp. (Cephalospyrididae), Ceratocyrtis oconnori n. sp. (Lophophaenidae), Botryocella? alectrida n. sp., Pylobotrys? bineti n. sp. (Pylobotrydidae), Lychnocanium cheni n. sp., Lychnocanium cingulatum n. sp., Lychnocanium croizoni n. sp., Lychnocanium forficula n. sp. (Lithochytrididae), Apoplanius hyalinus n. sp., Apoplanius cryptodirus n. sp. (Lophocyrtiidae), Albatrossidium messiaeni n. sp., Phormocyrtis microtesta n. sp., Cryptocarpium? judoka n. sp. (Pterocorythidae), and Thyrsocyrtis kamikuri n. sp. (Theocotylidae). Biostratigraphic information is provided for each new species. In addition, we re-describe and illustrate the morphological variability of a remarkable Pterocyrtidium species formerly published by Bütschli (1882a). UUID: http://zoobank.org/a01f7f03-73b0-458a-af7b-b85dc4666cc2

Detailed characterization of the complete mitochondrial genome of the oceanic whitetip shark Carcharhinus longimanus (Poey, 1861)

BackgroundThe oceanic whitetip shark Carcharhinus longimanus (family Carcharhinidae) is one of the largest sharks inhabiting all tropical and subtropical oceanic regions. Due to their life history traits and mortality attributed to pelagic longline fishing practices, this species is experiencing substantial population decline. Currently, C. longimanus is considered by the IUCN Red List of Threatened Species as “vulnerable” throughout its range and “critically endangered” in the western north Atlantic. This study sequences and describes the complete mitochondrial genome of C. longimanus in detail.Methods and resultsThe mitochondrial genome of C. longimanus was assembled through next-generation sequencing and then analyzed using specialized bioinformatics tools. The circular, double-stranded AT-rich mitogenome of C. longimanus is 16,704 bp long and contains 22 tRNA genes, 2 rRNA genes, 13 protein coding genes and a 1,065 bp long control region (CR). Out of the 22 tRNA genes, only one (tRNA-Ser1) lacked a typical ‘cloverleaf’ secondary structure. The prevalence of TTA (Leu), ATT (Ile) and CTA (Leu) codons in the PCGs likely contributes to the AT-rich nature of this mitogenome. In the CR, ten microsatellites were detected but no tandem repeats were found. Stem-and-loop secondary structures were common along the entire length of the CR. Ka/Ks values estimated for all PCGs were < 1, indicating that all the PCGs experience purifying selection. A phylomitogenomic analysis based on translated PCGs confirms the sister relationship between C. longimanus and C. obscurus. The analysis did not support the monophyly of the genus Carcharhinus.ConclusionsThe assembled mitochondrial genome of this pelagic shark can provide insight into the phylogenetic relationships in the genus Carcharhinus and aid conservation and management efforts in the Central Pacific Ocean.

Non-stationary low flow frequency analysis under climate change

Analysis of low river flows provides important information for effective management of water resources in a region. Despite the critical importance of understanding low flow dynamics, there is a gap in the literature regarding the use of non-stationary models to analyze low flow data under climate change in Turkey. In this research, low flow series from 80 measuring stations in Turkey are investigated by employing both stationary and non-stationary models based on the Generalized Additive Models for Location, Scale and Shape (GAMLSS). For constructing non-stationary models, 31 explanatory variables consisting of time, precipitation, temperature and atmospheric oscillation indices were used to model the parameters of the chosen distributions. The results show that stationary models are more successful at 7 stations, while non-stationary models are more successful at 73 stations. Comparisons between non-stationary models showed that for most stations, the best performing models were non-stationary models with annual precipitation as covariates. In addition, successful results were obtained when Western Mediterranean Oscillation and North Atlantic Oscillation indices were used as explanatory variables. Additionally, this study investigated 20 and 50-year return levels by fitting the non-stationary frequency distribution models for low flows over historical and projection periods under SSP2-4.5 and SSP5-8.5 climate scenarios. GAMLSS incorporated annual total precipitation, which is the most effective explanatory variable for low flows, as a covariate, and thus changes in low flows were analyzed. The results show that decreases are expected in low flows, except for the stations in the upper Euphrates basin compared to the historical period.

Western Atlantic regionalization based on distributional congruence patterns of Scleractinian corals

Coral reefs represent a source of ecosystem services relevant for the permanence of coastal human communities. Given the importance of zooxanthellate scleractinian corals (ZSC) in these ecosystems, information on the presence and distribution of this group is valuable for studying the biodiversity and establishing management strategies to ensure their permanence over time. Despite being a highly studied biological group in the Western Atlantic, records of ZSC presence are heterogeneous and are distributed mainly in the Caribbean Sea. One way to analyze the distribution of biota at large spatial scales is through biogeographic regionalizations. To identify the distribution patterns of ZSC in the Western Atlantic and propose a biogeographic regionalization based in this biological group, we performed a Parsimony Analysis of Endemism (PAE) at ecoregion scale using Species Distribution Models (SDM) to fill the gaps in data on the distribution of these corals. Through these analyses, we identified the presence of two main biogeographic provinces: Northwestern Atlantic Tropical Province and Tropical Southwestern Atlantic. According to Jaccard Index, this regionalization is highly similar to those performed with multitaxa by other authors, which demonstrates that for these purposes this taxa can be considered as a surrogate group. In terms of management, this study highlights the importance of establishing preservation and conservation measures that address this biological group, in order to guarantee both the permanence of other taxa and the ecosystem goods and services they provide.

Multidisciplinary characterisation of the biodiversity, geomorphology, oceanography and glacial history of Bowditch Seamount in the Sargasso Sea

The first multidisciplinary characterisation of Bowditch Seamount in the Sargasso Sea was conducted to provide new baseline knowledge of the biodiversity, geomorphology, oceanography and glacial history of this seamount. A dropframe camera transect 1483–1562 m deep on the seamount documented 77 megafaunal taxa including Vulnerable Marine Ecosystem indicator taxa such as sponges, cold-water corals, and stalked crinoids. Seabed terrain analysis of multibeam echosounder data showed species varied significantly along this transect in response to local geomorphological variability (R2adj = 31%, p < 0.0001), with changes in seafloor relief and substrata driving species composition over the seamount. 14C-calibrated and 230Th-ages of fossil corals (Desmophyllum dianthus) collected by Van Veen grabs 1517 m deep showed corals thrived on the seamount ∼24 ka BP and ∼17 ka BP. Abrupt excursions between higher and lower radiogenic εNd-composition values of the skeletons suggested that D. dianthus persisted on the seamount over times of southern source water input and detrital sediments from the melting Laurentide Ice Sheet, respectively. In agreement with other studies from the western North Atlantic, living D. dianthus were absent in the contemporary setting at these depths, and suggest a significant re-organisation of the seamount community since the deglacial when ice-rafted debris of carbonates likely resulted in a lower aragonite compensation depth allowing D. dianthus to proliferate at deeper depths. New conductivity-depth-temperature profiling revealed the seamount at these depths is now bathed by highly oxygenated Labrador Sea Water (LSW) formed at high latitudes. Co-analysis of a newly constructed 70-year long time series of temperature and salinity for the Labrador Sea and Bermuda regions revealed a 10-year transit time from high latitudes to Bowditch Seamount. This multidisciplinary approach shows how geomorphology drives local biodiversity patterns, but also how upstream climatic forcing in subpolar regions may influence Bermuda's subtropical seamount ecosystem.

Age validation of yellowfin and bigeye tuna using post-peak bomb radiocarbon dating confirms long lifespans in the western and central Pacific Ocean

Abstract Age-reading protocols for tuna species using annual growth zones in thin-cut transverse otolith sections have produced greater age estimates than previous methods. Lifespan estimates for yellowfin (YFT) and bigeye (BET) tuna (Thunnus albacares and T. obesus) were validated up to 16–18 years in the western North Atlantic Ocean using bomb 14C dating and the current study extends the approach to YFT and BET of the western and central Pacific Ocean (WCPO). Archived otoliths from young-of-the-year (YOY) tuna caught in the WCPO were analysed for 14C to establish a reference chronology covering 30 years (1989–2019). This YOY 14C time series exhibited strong concordance with existing coral-otolith 14C references for the tropical-subtropical Pacific Ocean and was combined as a single chronology. Otolith cores from YFT aged 1–14 years and BET aged 1–13 years from presumed annual counts were analysed for 14C. These measurements aligned with the reference chronology for the calculated hatch years for both species. These findings provide strong evidence that growth zones in thin-sectioned otoliths are deposited annually for YFT and BET of the WCPO and that age interpretation is correct using the current age reading protocol with little to no bias.

Machine learning with taxonomic family delimitation aids in the classification of ephemeral beaked whale events in passive acoustic monitoring.

Passive acoustic monitoring is an essential tool for studying beaked whale populations. This approach can monitor elusive and pelagic species, but the volume of data it generates has overwhelmed researchers' ability to quantify species occurrence for effective conservation and management efforts. Automation of data processing is crucial, and machine learning algorithms can rapidly identify species using their sounds. Beaked whale acoustic events, often infrequent and ephemeral, can be missed when co-occurring with signals of more abundant, and acoustically active species that dominate acoustic recordings. Prior efforts on large-scale classification of beaked whale signals with deep neural networks (DNNs) have approached the class as one of many classes, including other odontocete species and anthropogenic signals. That approach tends to miss ephemeral events in favor of more common and dominant classes. Here, we describe a DNN method for improved classification of beaked whale species using an extensive dataset from the western North Atlantic. We demonstrate that by training a DNN to focus on the taxonomic family of beaked whales, ephemeral events were correctly and efficiently identified to species, even with few echolocation clicks. By retrieving ephemeral events, this method can support improved estimation of beaked whale occurrence in regions of high odontocete acoustic activity.

Long‐Term Trends in Aerosols, Low Clouds, and Large‐Scale Meteorology Over the Western North Atlantic From 2003 to 2020

AbstractA continuous decrease in aerosols over the Western North Atlantic Ocean (WNAO) on a decadal timescale provides a long‐term benchmark to evaluate how various natural and anthropogenic processes affect the manifestation of aerosol‐cloud interactions in this region. Furthermore, the WNAO serves as a natural laboratory with diverse aerosol sources, marine boundary layer clouds more variable than those in marine stratocumulus deck regions, and unique flow regimes established by the Gulf Stream and the semi‐permanent Bermuda High. We investigate how satellite‐retrieved macrophysical and microphysical properties of low clouds and the surface shortwave irradiance changed from 2003 to 2020, in tandem with this aerosol decrease. The decadal changes in large‐scale meteorology related to the North Atlantic Oscillation (NAO) are also examined. We find a reduction in low‐cloud optical thickness, accompanied by fewer and larger cloud droplets, yet observe no significant changes in low‐cloud fraction and liquid water path. Despite the reduction in low‐cloud optical thickness together with aerosol decrease, a corresponding increase in the trends of surface shortwave irradiance, also known as surface brightening, is lacking. This absence of brightening is potentially related to concomitant changes found in large‐scale meteorology associated with NAO—Bermuda High strengthening, sea surface warming, and atmospheric moistening— as well as an increase in high‐level cloud fraction that can counteract the surface brightening. Ultimately, our findings suggest that spatial patterns of decadal meteorological variability introduce complexities in the surface cloud radiative effect over the WNAO, thereby complicating the isolation and examination of aerosol‐cloud interactions.

Stable isotope evidence for resource partitioning in extinct marine carnivores

Living pinnipeds play essential roles in marine ecosystems and display divergent lineage-specific foraging and habitat preferences. The origin of these ecological strategies remains unclear. We analyzed original (n = 22) and published (n = 93) stable carbon (δ13C) and oxygen (δ18O) isotope compositions of tooth enamel from fossil pinnipeds and coeval marine and terrestrial mammals from the late Early Miocene to early Middle Miocene Temblor Formation, the early Middle Miocene Round Mountain Silt Formation at Sharktooth Hill Bonebed, the Middle Miocene of lower levels of the Monterey Formation, and the late Middle Miocene Santa Margarita Formation from the eastern North Pacific Ocean; and original (n = 43) δ13C and δ18O values from the Early Pliocene Yorktown Formation in the western North Atlantic. As expected for aquatic mammals, pinnipeds and control marine mammals had low δ18O variability relative to coeval terrestrial mammals, indicating minimal diagenetic alteration. Among late Early Miocene and Middle Miocene pinnipeds, Allodesmus had lower δ13C values than coeval taxa indicating offshore foraging, in agreement with predictions based on skeletal morphology. However, Allodesmus from the late Middle Miocene Santa Margarita Formation had overlapping δ13C values with co-occurring cetaceans and pinnipeds suggesting preferential nearshore habitat. The stem otariid Pithanotaria had higher enamel δ13C values than co-occurring pinnipeds, indicating nearshore foraging. The stem odobenid Neotherium had intermediate δ13C values supporting foraging between nearshore and offshore predators. Conversely, the stem odobenid cf. Imagotaria had lower enamel δ18O but comparable δ13C values to coexisting pinnipeds, suggesting the exploitation of estuarine resources. At least two ecologically distinct pinniped groups also occurred in the Yorktown Formation. In this unit, the odobenid Ontocetus and some monachinae phocids were predominantly nearshore foragers, with higher enamel δ13C and δ18O values than simultaneously occurring marine mammals. The second group was exclusively composed of phocids, which had comparatively low δ13C and δ18O values, compatible with northward foraging movements along the western North Atlantic coast. The paleoecological profiles of fossils bear strong similarities to the life modes of extant pinniped communities, implying that extant foraging modes appeared early in pinniped evolution and that resource partitioning contributed to their community structure over time.

Evaluation of WRF model configurations for dynamic downscaling of tropical cyclones activity over the North Atlantic basin for Lagrangian moisture tracking analysis in future climate

This study assessed five well-established physics suites of the Weather Research and Forecasting (WRF) model in operational forecasting systems in the North Atlantic (NATL) basin or from previous sensitive experiments for dynamic downscaling tropical cyclone (TC) activity. We performed long-term simulations for the 2020 TC season in the NATL and compared the WRF tracks against the HURDAT2 dataset from the US National Hurricane Center. Among the tested configurations, the analysis revealed that the Kain-Fritsch, Purdue Lin, BouLac and revised MM5 schemes for cumulus, microphysics, planetary boundary layer and surface layer, respectively (hereafter WT), outperformed all four others in terms of TC frequency, track density and intensity and showed good performance in the cyclone accumulated energy and TC landfalling locations. In addition, WT well-captured the spatial distribution of accumulated TC precipitation and moisture uptake patterns, although it overestimated the precipitation maxima. Likewise, it agreed on the relative moisture contribution from fixed moisture sources (i.e., Gulf of Mexico, Caribbean Sea, tropical NATL, and western NATL) in the NATL basin. Overall, this study highlighted the high potential of using the WT physics suite in WRF for downscaling TC activity over the NATL basin, which will be useful for TC Lagrangian moisture sources analysis in future climate.

Retrievals of aerosol optical depth over the western North Atlantic Ocean during ACTIVATE

Abstract. Aerosol optical depth was retrieved from two airborne remote sensing instruments, the Research Scanning Polarimeter (RSP) and Second Generation High Spectral Resolution Lidar (HSRL-2), during the National Aeronautics and Space Administration (NASA) Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE). The field campaign offers a unique opportunity to evaluate an extensive 3-year dataset under a wide range of meteorological conditions from two instruments on the same platform. However, a long-standing issue in atmospheric field studies is that there is a lack of reference datasets for properly validating field measurements and estimating their uncertainties. Here we address this issue by using the triple collocation method, in which a third collocated satellite dataset from the Moderate Resolution Imaging Spectroradiometer (MODIS) is introduced for comparison. HSRL-2 is found to provide a more accurate retrieval than RSP over the study region. The error standard deviation of HSRL-2 with respect to the ground truth is 0.027. Moreover, this approach enables us to develop a simple, yet efficient, quality control criterion for RSP data. The physical reasons for the differences in two retrievals are determined to be cloud contamination, aerosols near the surface, multiple aerosol layers, absorbing aerosols, non-spherical aerosols, and simplified retrieval assumptions. These results demonstrate the pathway for optimal aerosol retrievals by combining information from both lidars and polarimeters for future airborne and satellite missions.

Insights into the origin of precipitation moisture for tropical cyclones during rapid intensification process

In this study, we identified the moisture sources for the precipitation associated with tropical cyclones (TCs) during the rapid intensification (RI) process from 1980 to 2018 by applying a Lagrangian moisture source diagnostic method. We detected sixteen regions on a global scale for RI events distributed as follows: four in the North Atlantic (NATL), two in the Central and East Pacific Ocean (NEPAC), the North Indian Ocean (NIO) and South Indian Ocean (SIO), and three in the South Pacific Ocean (SPO) and the Western North Pacific Ocean (WNP). The moisture uptake (MU) mostly was from the regions where TCs underwent RI. The Western NATL, tropical NATL, Caribbean Sea, the Gulf of Mexico and the Central America and Mexico landmass supported ∼85.4% of the precipitating moisture in the NATL, while the latter source and the eastern North Pacific Ocean provided the higher amount of moisture in NEPAC (∼84.3%). The Arabian Sea, the Bay of Bengal and the Indian Peninsula were the major moisture sources in NIO, contributing approximately 81.3%. The eastern and western parts of the Indian Ocean supplied most of the atmospheric humidity in SIO (∼83.8%). The combined contributions (∼87.9%) from the western and central SPO and the Coral Sea were notably higher in SPO. Meanwhile, TCs in the WNP basin mostly received moisture from the western North Pacific Ocean, the Philippine Sea and the China Sea, accounting for 80.1%. The remaining moisture support in each basin came from the summed contributions of the remote sources. Overall, RI TCs gained more moisture up to 2500 km from the cyclone centre than those slow intensification (SI) and the total MU was approximately three times higher during RI than SI. Finally, the patterns of the MU differences respond to the typical pathways of moisture transport in each basin.

The lionfishes: Comparative development of Pterois volitans, Dendrochirus barberi, and D. hemprichi (Scorpaeniformes: Scorpaenidae: Pteroinae) and discrimination of their early life stages from non-pteroine scorpaenid genera in the Western North Atlantic

Despite the threat that lionfishes pose to non-native marine ecosystems worldwide, their early life stages (ELS) remain difficult to distinguish from morphologically similar taxa due to inadequate descriptions and poorly defined taxonomic characters. Two members of the Indo-Pacific marine assemblage commonly known as lionfishes, zebrafishes, firefishes, turkeyfishes, and butterfly-cods (Scorpaeniformes: Scorpaenidae: Pteroinae) are invasive in the Western North Atlantic (WNA). Here, we describe the ELS of Pterois volitans, Dendrochirus barberi, and two transforming larvae and an early juvenile of D. hemprichi; review the early development of D. zebra and a larva described as D. bellus; identify characteristics that distinguish P. volitans from the four members of Dendrochirus; and compile meristic and distribution data for all currently valid species of lionfishes worldwide based on recent revisions and updated nomenclature. We also briefly describe a small juvenile of two poorly known non-pteroine deep-water scorpaenids, and discuss characteristics that distinguish the five pteroines from non-pteroine scorpaenid genera in the WNA. Differences in relative length and elevation of the parietal and nuchal spines, and in pigmentation patterns distinguish P. volitans from the four members of Dendrochirus. Pterois volitans has parietal spines two or more times longer than the nuchals with both sets of spines oriented about 30° above the longitudinal axis of the head, whereas the four members of Dendrochirus have relatively short parietal and nuchal spines subequal in length that lay flatter against the cranium (i.e., elevation ≤15° above longitudinal axis of head). Transforming larvae of the four members of Dendrochirus also develop saddles of pigment along the dorsal and ventral margins of the body that P. volitans lacks at the sizes examined. One or more of the following suite of traits distinguish larvae of the five pteroines from those of non-pteroine scorpaenids and other morphologically similar taxa: the presence or absence of a “shield” of pigment over the dorsolateral margin of the visceral mass (may be reduced or augmented with scattered blotches of pigment in larger larvae of some taxa); the relative length, elevation, and placement of the parietal and nuchal spines; the presence or absence of a small slit behind the fourth gill arch; differences in pectoral-fin length, shape, and extent of pigmentation; the relative size, length, and placement of spines along the posterior shelf of the preopercle (PPO); and the presence or absence, number, and placement of spine(s) along the opercle.

Atmospheric and Oceanic Factors Related to the Increasing Summer High Temperature Extremes on the Tibetan Plateau under the Background of Global Warming

Abstract The related atmospheric and oceanic factors are investigated in this analysis to understand the natural attributes responsible for the significant increase of the high temperature extremes (HTEs) on the Tibetan Plateau (TP) in summer. It is found that a stronger-than-normal South Asian high (SAH) and corresponding weaker-than-normal East Asian jet, an anomalous anticyclone and intensified midlevel westerly wind over the TP, and a more extensive, stronger, farther westward- and northward-stretching western Pacific subtropical high motivate more occurrences of HTEs over the TP on the interannual time scale. From 1961 to 2021, these crucial circulation patterns show a significant changing trend favorable for the occurrence of HTEs and thus contribute to its great increase. Further, the significant warmings of sea surface temperature (SST) in the tropical western Indian, northern North Pacific, and western North Atlantic Oceans make great contributions through different air–sea interactive processes as the Matsuno–Gill response, zonal vertical circulation cell, and mid- to high-latitude teleconnection wave train, respectively. Meanwhile, the interdecadal variability plays an important role. A breakpoint at the early twenty-first century is detected in the occurrence of summer HTEs on the TP. Both the crucial circulation patterns and the SST anomalies in the key oceanic regions experienced significant interdecadal transition to favor the occurrence of HTEs. In particular, the Atlantic multidecadal oscillation (AMO) is significantly and positively correlated with the interdecadal variation of summer HTEs on the TP. The zonal teleconnection wave train triggered by AMO forms a stronger-than-normal SAH and strengthened midlevel westerly airflow over the TP, conducive to the increase of summer HTEs on the TP.

Eocene‐Oligocene Intensification of the Deep Western Boundary Current in the North Atlantic Ocean

AbstractThe role played by ocean circulation in major transitions in Earth's climate is debated. Here, we investigate the physical evolution of the Deep Western Boundary Current (DWBC) in the western North Atlantic Ocean through the late Eocene‐to‐mid Oligocene (35−26 Ma) using terrigenous grain size and geochemistry records of marine sediment cores. Our records cover the most pivotal transition in Cenozoic climate history, the Eocene‐Oligocene Transition (EOT; ∼33.7 Ma), when Earth first became sufficiently cool to sustain large ice sheets on Antarctica. To assess changes in deep‐water circulation in the northwest Atlantic across the EOT, we assembled sortable silt (10–63 μm) grain‐size and Nd, Hf, and Pb radiogenic isotope records at two Integrated Ocean Drilling Program (IODP) drill sites on the Newfoundland ridges (Sites U1406 and U1411). These records reveal an overall gradual increase in sortable silt abundance (SS%) at both sites with no change in sediment provenance. We interpret a steady, long‐term invigoration of the DWBC, likely driven by deepening of the Greenland‐Scotland Ridge and resultant enhanced inflow of waters sourced from deep‐water production sites in the Nordic Seas to the North Atlantic Ocean. Our results do not support abrupt and widespread invigoration of bottom current activity in the North Atlantic synchronous with accelerated cooling and Antarctic ice growth at the EOT. Instead, our records suggest that the DWBC started to intensify before this pivotal event in Cenozoic climate history (at ∼35 Ma) and then further strengthened gradually across the EOT (∼34 Ma) and through the early‐to‐mid Oligocene (∼34‒26 Ma).

A Comparative Study of Mercury Bioaccumulation in Bivalve Molluscs from a Shallow Estuarine Embayment.

In estuarine food webs, bivalve molluscs transfer nutrients and pollutants to higher trophic levels. Mercury (Hg) pollution is ubiquitous, but it is especially elevated in estuaries historically impacted by industrial activities, such as those in the U.S. Northeast. Monomethylmercury (MeHg), the organic form of Hg, is highly bioaccumulative and transferable in the food web resulting in the highest concentrations in the largest and oldest marine predators. Patterns of Hg concentrations in marine bivalve molluscs, however, are poorly understood. In this study, inorganic Hg (iHg), MeHg, and the total Hg (THg) in soft tissues of the northern quahogs (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), and ribbed mussels (Geukensia demissa) from eastern Long Island sound, a temperate estuary of the western North Atlantic Ocean was investigated. In all three species, concentrations of THg remained similar between the four sampling months (May, June, July, and September), and were mostly independent of animal size. In quahogs, MeHg and iHg displayed significant (p < 0.05) positive (iHg in May and June) and negative (MeHg in July and September) changes with shell height. Variability in concentrations of THg, MeHg, and iHg, both inter- and intra-specifically was high and greater in quahogs and oysters (THg: 37, 39%, MeHg: 28, 39%, respectively) than in mussels (THg: 13%, MeHg: 20%). The percentage of THg that was MeHg (%MeHg) was also highly variable in the three species (range: 10-80%), highlighting the importance of measuring MeHg and not only THg in molluscs.