Variability Off Research Articles

Internal Tide Variability Off Central California: Multiple Sources, Seasonality, and Eddying Background

AbstractTwo moorings deployed for 75 days in 2019 and long‐term satellite altimetry data reveal a spatially complex and temporally variable internal tidal field at the Surface Water and Ocean Topography (SWOT) Cal/Val site off central California due to the interference of multiple seasonally‐variable sources. These two data sets offer complementary insights into the variability of internal tides in various time scales. The in situ measurements capture variations occurring from days to months, revealing ∼45% coherent tides. The north mooring displays stronger mode‐1 M2 with an amplitude of ∼5.1 mm and exhibits distinct time‐varying energy and modal partitioning compared to the south mooring, which is only 30‐km away. The 27‐year altimetry data unveils the mean and seasonal variations of internal tides. The results indicate that the complex internal tidal field is attributed to multiple sources and seasonality. Mode‐1 tides primarily originate from the Mendocino Ridge and the 36.5–37.5°N California continental slope, while mode‐2 tides are generated by local seamounts and Monterey Bay. Seasonality is evident for mode‐1 waves from three directions. The highest variability of energy flux is found in the westward waves (±22%), while the lowest is in the southward waves (±13%). The large variability observed from the moorings cannot be solely explained by seasonality; additional factors like mesoscale eddies also play a role. This study emphasizes the importance of incorporating the seasonality and spatial variability of internal tides for the SWOT internal tidal correction, particularly in regions characterized by multiple tidal sources.

Intra-tidal upwelling variability off Zhoushan Islands, East China Sea

The coastal upwelling that takes place off the Zhoushan Islands is of great importance in the transport of nutrients, nourishing local fisheries and exerting a substantial environmental influence. While it is known that tides play a central role in triggering and controlling the Zhoushan upwelling, its short-term variability within the tidal cycle remains uncertain, thereby constituting the primary focus of this study, which relies on the analysis of high-resolution Sea Surface Temperature (SST) satellite images and in-situ data. In a tidal cycle, cold upwelling patches exhibit a westward shift during the flood tide and an eastward shift during the ebb tide. The extent of cold upwelling patches is greatest during maximum flood and ebb periods. At maximum ebb, the core temperature within the cold patches notably decreases, which indicates intensified upwelling. At the same time, a similar pattern of sudden increases is also observed throughout the entire water column in the upwelling region. The strong ebb current swiftly transports the upper water mass during maximum ebb, facilitating the compensation of lower water and augmenting the intensity of the upwelling. The calculated vertical velocity within the study area ranged from −9.04 × 10−4 m/s to 12.66 × 10−4 m/s during the observational period, when upwelling showed a significant congruence with low-temperature phenomena. Alternating upwelling and downwelling phases were discernible within a tidal cycle, with upwelling being prevalent. The influence of surface heat flux on seawater below the thermocline and night-time SST was negligible. Furthermore, compared to the vertical velocity, the calculated wind-induced upwelling velocity was much lower, reaching just 3.38 × 10−6 m/s during the observed tidal cycle, which suggests that wind does not exert a primary influence on upwelling within the tidal cycle. This study contributes to an enhanced understanding of upwelling variability under the influence of tides, a topic of paramount importance in the marine environment.

Early sea ice decline off East Antarctica at the last glacial-interglacial climate transition.

Antarctic climate warming and atmospheric CO2 rise during the last deglaciation may be attributed in part to sea ice reduction in the Southern Ocean. Yet, glacial-interglacial Antarctic sea ice dynamics and underlying mechanisms are poorly constrained, as robust sea ice proxy evidence is sparse. Here, we present a molecular biomarker-based sea ice record that resolves the spring/summer sea ice variability off East Antarctica during the past 40 thousand years (ka). Our results indicate that substantial sea ice reduction culminated rapidly and contemporaneously with upwelling of carbon-enriched waters in the Southern Ocean at the onset of the last deglaciation but began at least ~2 ka earlier probably driven by an increasing local integrated summer insolation. Our findings suggest that sea ice reduction and associated feedbacks facilitated stratification breakup and outgassing of CO2 in the Southern Ocean and warming in Antarctica but may also have played a leading role in initializing these deglacial processes in the Southern Hemisphere.

Simulation of spatiotemporal interannual variability of oceanic subsurface temperature off East Africa

The oceanic subsurface variability off East Africa in the tropical western Indian Ocean plays a crucial role in ocean dynamics and living resources as well as weather and climate variability. A regional ocean model is applied to understand the oceanic subsurface interannual variability off East Africa. The region with the highest sea surface temperature (SST) variability in the offshore region lies adjacent to strong subsurface temperature variations located between 30 and 130 m corresponding with strong variations in the thermocline depth. The weakest SST variations in the Tanzanian shelf waters lie over the subsurface waters with the smallest temperature variations in the upper 200 m with weak variations in the thermocline depth. Such signals are associated with induced forcings from the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) in both regions with different intensity and peaking times. The IOD-induced forcings are weaker, evolving in October and November-December in the region with the weakest and strongest SST variations, respectively. However, relatively stronger ENSO-induced forcings occur in both regions with stronger signals in the region with the strongest SST variations throughout the years except in August, and it peaks in January. The ENSO-induced forcings occur in January to May peaking in March and April in the region with the weakest SST. Consequently, anomalous Rossby waves as well as local Ekman downwelling and upwelling associated with both large-scale modes occur in the region leading to the subsurface temperature variations.

Slope and Shelf Flow Anomalies Off Oregon Influenced by the El Niño Remote Oceanic Mechanism in 2014–2016

AbstractOutputs of the regional ocean circulation model are analyzed to demonstrate the measurable impact of the El Niño remote oceanic forcing mechanism along the US West Coast during the major heat wave period of 2014–2016. The 2‐km horizontal resolution model, based on the Regional Ocean Modeling System (ROMS), was run for the period of 2009–2018. Though the model does not assimilate observations, it performs well by comparison with time series data explaining observed variability on temporal scales from several days to seasonal and interannual. The El Niño‐related oceanic anomalies provided by a global state estimate are introduced in the regional model at the southern boundary at 24N. These propagate alongshore with coastally trapped waves (CTWs) and influence the variability off Oregon (41°–46°N). In particular, CTWs are evident in the subsurface along‐slope current, vs, and in the depth of the 26.5 kg m−3 isopycnal surface over the slope, z26.5. In summer 2014 and 2015, vs anomalies are positive (northward) and z26.5 anomalies are negative (deeper) along the US West Coast. In addition to the CTW patterns, z26.5 anomalies also exhibit slow‐moving features associated with undercurrent widening, separation, and subsurface eddy variability. Over the Oregon shelf, El Niño conditions contributed to the sharp weakening of the southward alongshore current throughout the water column in July 2014 and 2015, despite the near‐average southward, upwelling‐favorable winds.

A decadal sea-level variability in Port-Said Harbour (Egypt)

This paper used hourly data from the sea-level recorder installed in Port-Said Harbour on the Eastern Egyptian Mediterranean Coast. The data covered one decade (2002–2011) and were used to describe the temporal sea-level variability off Port Said including; its mean sea level (MSL), annual rate trend, seasonal behaviour, main tidal features, and the different water levels. The T_TIDE program was applied to obtain the astronomical constituents and the residual elevations. Throughout the period of study, the MSL was 69.1 cm; reaching its minimum (63.5 cm) in 2007 and its maximum (74.5 cm) in 2006. Tides were mixed mainly semidiurnal, and the sea level had an increasing rate of 2.1 mm/yr. The Principal Lunar constituent (M2) had the largest astronomical amplitude of 13.4 cm, and the spring to neap ratio was 1.4. The sea level displayed seasonal alterations with the lowest values in spring and highest in summer. The residual heights varied between 11.60 and 110 cm with an average of 67.5 cm. Results revealed that the astronomical tide contributed with 2.3% in the observed sea level, while the surge contributed with 97.7%. The correlation between the sea-level fluctuations with the meteorological conditions in the vicinity of Port Said needs further investigation.

Optimum Multiparameter Analysis of Water Mass Structure off Western Guangdong during Spring Monsoon Transition

Water masses and their variability play vital roles in regulating ocean circulation, material exchanges and biogeochemical processes. However, there is still a lack of quantitative analysis of water mass distributions in coastal waters of the South China Sea. Here, two oceanographic cruise observations in April and May 2016 are used to quantify water mass distributions, pathways and mixture, and their intraseasonal variability off western Guangdong during the spring monsoon transition. Temperature and salinity observations qualitatively reveal that there are three types of water masses: the Pearl River diluted water (PRDW, salinity (S) = 22 psu, potential temperature (θ) = 25 °C), the South China Sea surface water (SCSSW, S = 34 psu, θ = 28 °C) and the South China Sea subsurface water mass (SCSSUW, S = 34.5 psu, θ = 17 °C). Their relative contributions and intraseasonal variability are quantified using the Optimum Multiparameter (OMP) method. The PRDW is largely confined to the upper 10 m layer in shallow nearshore waters (depths < 30 m), with a maximum contribution >90% near the Pearl River Estuary. The SCSSW mainly dominates the rest of the surface layer above 20 m, with a contribution >50% in offshore regions. The layer below 20 m is primarily composed of ~60% SCSSW and ~40% SCSSUW. A comparison between the two different observations suggests that the PRDW tends to expand southwestward and the SCSSUW spreads offshore, whereas the SCSSW moves landward and is situated underneath the surface fresh PRDW. These characteristics are very likely associated with the wind transition from weak southeasterly in April to strong northeasterly in May, which enhances the southwestward coastal current and the onshore surface Ekman transport from offshore waters.

Evidence for anthropogenic, climatic and oceanographic variability off southwestern Morocco during the last three millennia

In order to obtain a better knowledge of oceanic changes in the Canary Upwelling region during the Late Holocene, marine surface samples and two sediment cores retrieved off southwestern Morocco, GeoB8601–3 and GeoB4223–1, were investigated for organic-walled dinoflagellate cysts (dinocysts). The results were compared with pollen, microcharcoal particles, geochemical records, stable hydrogen and carbon isotope composition (δ 2 H and δ 13 C) of plant-waxes of the same material. The dinocyst results indicate active upwelling prior to 750 BCE and a longer upwelling season between 750 BCE and 950 CE, which is attributed to increased northeast trade winds. After 950 CE, a marked increase of Lingulodinium machaerophorum and Gymnodinium species indicates high fluvial input probably due to a combination of climate (possibly negative NAO) and anthropogenic (terrestrial erosion related to Early Arab conquest) impacts. • We present a new compilation of modern dinocyst distribution off southwestern Morocco. • We investigate Late Holocene dinocyst records from two marine sediment cores. • We employ a multiproxy approach with pollen, microcharcoal and geochemical records. • An interplay of climate and anthropogenic controls were demonstrated.

Seasonal Variability of Sea Surface Salinity in the NW Gulf of Guinea from SMAP Satellite

The advent of satellite-derived sea surface salinity (SSS) measurements has boosted scientific study in less-sampled ocean regions such as the northwestern Gulf of Guinea (NWGoG). In this study, we examine the seasonal variability of SSS in the NWGoG from the Soil Moisture Active Passive (SMAP) satellite and show that it is well-suited for such regional studies as it is able to reproduce the observed SSS features in the study region. SMAP SSS bias, relative to in-situ data comparisons, reflects the differences between skin layer measurements and bulk surface measurements that have been reported by previous studies. The study results reveal three broad anomalous SSS features: a basin-wide salinification during boreal summer, a basin-wide freshening during winter, and a meridionally oriented frontal system during other seasons. A salt budget estimation suggests that the seasonal SSS variability is dominated by changes in freshwater flux, zonal circulation, and upwelling. Freshwater flux, primarily driven by the seasonally varying Intertropical Convergence Zone, is a dominant contributor to salt budget in all seasons except during fall. Regionally, SSS is most variable off southwestern Nigeria and controlled primarily by westward extensions of the Niger River. Anomalous salty SSS off the coasts of Cote d’Ivoire and Ghana especially during summer are driven mainly by coastal upwelling and horizontal advection.

Observations of Surface Currents and Tidal Variability Off of Northeastern Taiwan from Shore-Based High Frequency Radar

A network of high-frequency radars (HFRs) has been deployed around Taiwan. The wide-area data coverage is dedicated to revealing near real-time sea-surface current information. This paper investigates three primary objectives: (1) describing the seasonal current synoptic variability; (2) determining the influence of wind forcing; (3) describing the tidal current field pattern and variability. Sea surface currents derived from HFR data include both geostrophic components and wind-driven components. This study explored vector complex correlations between the HFR time series and wind, which was sufficient to identify high-frequency components, including an Ekman balance among the surface currents and wind. Regarding the characteristics of mesoscale events and the tidal field, a year-long high-resolution surface dataset was utilized to observe the current–eddy–tide interactions over four seasons. The harmonic analysis results derived from surface currents off of northeastern Taiwan during 2013 are presented. The results agree well with the tidal parameters estimated from tide-gauge station observations. The analysis shows that this region features a strong, mixed, mainly semidiurnal tide. Continued monitoring by a variety of sensors (e.g., satellite and HFR) would improve the understanding of the circulation in the region.

Air‐Sea Interaction in the Western Tropical Pacific and its Impact on Asymmetry of the Ningaloo Niño/Niña

AbstractNingaloo Niño/Niña is the dominant interannual sea surface temperature (SST) variability off Western Australia with the former typically stronger than the latter. Although a recent study suggested that oceanic teleconnections from the Pacific partly contribute to the amplitude asymmetry, this seems counterintuitive as La Niña, which often induces the Ningaloo Niño, is generally weaker than El Niño. Here, mechanisms of the amplitude asymmetry in the oceanic teleconnection are investigated by analyzing reanalysis data and conducting ocean model simulations. Sensitivity experiments using a linear continuously stratified model reveal that stronger easterly wind anomalies in the western equatorial Pacific contribute to the stronger oceanic teleconnection during the Ningaloo Niño. Furthermore, a mixed layer heat budget analysis with a regional ocean model shows that negatively skewed SST anomalies in the central equatorial Pacific related to the skewed wind anomalies in the western equatorial Pacific, are mainly induced by vertical advection/diffusion and entrainment.

Upper ocean variability off NE Greenland (79°N) since the last glacial maximum reconstructed from stable isotopes in planktic foraminifer morphotypes

We report on stable oxygen and carbon isotope data obtained on two different morphotypes of polar planktic foraminifers, i.e., fully encrusted and minor encrusted Neogloboquadrina pachyderma, from a sediment core taken on the NE Greenland continental margin. These morphotypes are supposed to live at different water depths of the upper water column in the area which today is strongly stratified, with a low-saline, cold-water layer at the surface. The paired isotopic data sets inform on temporal variations of past water salinity and temperature in the preferred water depth ranges of the investigated morphotypes and allow conclusions on the stratification of the upper water column. The radiocarbon-dated sediment core covers the time interval from 21 to 4 cal-ka, but the early part of the deglacial interval (18.5–12.7 cal-ka) is not represented, probably due to intense erosion by bottom currents. In sediments from the late last glacial maximum, oxygen isotope differences between thin-shelled and thick-shelled N. pachyderma are low and point at a weaker stratification with less freshwater than today near the surface. The carbon isotopes indicate a dense, perennial sea ice cover, very limited bioproduction, and the presence of a subsurface Atlantic Water layer. In the late deglaciation until ∼10.3 cal-ka, the stable isotope values of both analyzed morphotypes are considerably lower, with significantly stronger amplitudes in the record of thin-shelled specimens than later on. The high-amplitude record stems from a laminated sediment sequence whose older part was deposited within just a few decades. The data are evidence of a strong freshwater event in the research area that probably started before 12.7 ka and may have reduced sea surface salinities by 4–5 practical salinity units. As freshwater sources we discuss both the disintegration of NE Greenland shelf ice and export from the Arctic Ocean interior. The event may have contributed to the weakening of the Atlantic meridional overturning circulation during the Younger Dryas cold event. For the early and mid-Holocene (10-4 cal-ka), the isotope data suggest a structure of the upper water column similar to today, with a well-developed halocline separating low-saline near-surface waters from the underlying Atlantic Water layer. A seasonally disintegrated sea ice cover allowed for a considerable planktic bioproduction.

Gait variability is linked to the atrophy of the Nucleus Basalis of Meynert and is resistant to STN DBS in Parkinson's disease

Parkinson's disease (PD) is a systemic brain disorder where the cortical cholinergic network begins to degenerate early in the disease process. Readily accessible, quantitative, and specific behavioral markers of the cortical cholinergic network are lacking. Although degeneration of the dopaminergic network may be responsible for deficits in cardinal motor signs, the control of gait is a complex process and control of higher-order aspects of gait, such as gait variability, may be influenced by cognitive processes attributed to cholinergic networks. We investigated whether swing time variability, a metric of gait variability that is independent from gait speed, was a quantitative behavioral marker of cortical cholinergic network integrity in PD.Twenty-two individuals with PD and subthalamic nucleus (STN) deep brain stimulation (PD-DBS cohort) and twenty-nine age-matched controls performed a validated stepping-in-place (SIP) task to assess swing time variability off all therapy. The PD-DBS cohort underwent structural MRI scans to measure gray matter volume of the Nucleus Basalis of Meynert (NBM), the key node in the cortical cholinergic network. In order to determine the role of the dopaminergic system on swing time variability, it was measured ON and OFF STN DBS in the PD-DBS cohort, and on and off dopaminergic medication in a second PD cohort of thirty-two individuals (PD-med). A subset of eleven individuals in the PD-DBS cohort completed the SIP task again off all therapy after three years of continuous DBS to assess progression of gait impairment.Swing time variability was significantly greater (i.e., worse) in PD compared to controls and greater swing time variability was related to greater atrophy of the NBM, as was gait speed. STN DBS significantly improved cardinal motor signs and gait speed but did not improve swing time variability, which was replicated in the second cohort using dopaminergic medication. Swing time variability continued to worsen in PD, off therapy, after three years of continuous STN DBS, and NBM atrophy showed a trend for predicting the degree of increase. In contrast, cardinal motor signs did not progress. These results demonstrate that swing time variability is a reliable marker of cortical cholinergic health, and support a framework in which higher-order aspects of gait control in PD are reliant on the cortical cholinergic system, in contrast to other motor aspects of PD that rely on the dopaminergic network.

Mid to late-Holocene sea-surface temperature variability off north-eastern Newfoundland and its linkage to the North Atlantic Oscillation

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1–2°C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2–4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic.

PH variability off Goa (eastern Arabian Sea) and the response of sea urchin to ocean acidification scenarios

AbstractThe increasing atmospheric CO2 concentration in the last few decades has resulted in a decrease in oceanic pH. In this study, we assessed the natural variability of pH in coastal waters off Goa, eastern Arabian Sea. pHT showed large variability (7.6–8.1) with low pH conditions during south‐west monsoon (SWM), and the variability is found to be associated with upwelling rather than freshwater runoff. Considering that marine biota inhabiting dynamic coastal waters off Goa are exposed to such wide range of natural fluctuations of pH, an acidification experiment was carried out. We studied the impact of low pH on the local population of sea urchin Stomopneustes variolaris (Lamarck, 1816). Sea urchins were exposed for 210 days to three treatments of pHT: 7.96, 7.76 and 7.46. Our results showed that S. variolaris at pHT 7.96 and 7.76 were not affected, whereas the ones at pHT 7.46 showed adverse effects after 120 days and 50% mortality by 210 days. However, even after exposure to low pH for 210 days, 50% organisms survived. Under low pH conditions (pHT 7.46), the elemental composition of sea urchin spines exhibited deposition of excess Sr2+ as compared to Mg2+ ions. We conclude that although the sea urchins would be affected in future high CO2 waters, at present they are not at risk even during the south‐west monsoon when low pH waters reside on the shelf.

Fatty acid composition in the endemic Humboldt Current krill, Euphausia mucronata (Crustacea, Euphausiacea) in relation to the phytoplankton community and oceanographic variability off Dichato coast in central Chile

Fatty acids (FA) have been used as diet biomarkers. They have proven to be a valuable method of defining food web relationships, trophic positioning, and the dietary behaviors of marine species. The endemic krill species of the Humboldt Current System (HCS), Euphausia mucronata, is the most abundant krill species over the continental shelf, usually associated with coastal upwelling zones. This study aimed to quantify the changes in the FA composition of E. mucronata in the coastal upwelling zone off Dichato in central Chile concerning the phytoplankton community and environmental variability. We hypothesized that E. mucronata changes its FA composition according to the functional species groups that structure the phytoplankton community as well as environmental variability. Krill, phytoplankton, and environmental datasets were analyzed using multivariate analyses, considering samplings from January 2013 to August 2014. The total concentration of FAs was 550.5 ng/g (n = 42) of which the 77% corresponded to six FAs: palmitoleic acid (16:1n7), palmitic acid (16:0), vaccenic acid (18:1), oleic acid (18:1n7), eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA, 22:6n3). FA composition did not change according to neither the season nor sampling date. Seasonal changes were observed in both community structure of the phytoplankton (i.e. species composition and functional groups) and sea temperature. EPA/DHA ratio, PUFA/SFA ratio and carnivory variability were seasonally different suggesting that E. mucronata had mostly a diatom-based herbivorous habit during austral spring and summer and, it could have omnivore or carnivore habits during austral autumn and winter. Diatom and ciliate abundances and, sea temperature were the best predictor variables explaining 64% of the total variation in the FA composition. This study suggests that, despite seasonal environmental variation (biotic and abiotic), this krill species fed mainly diatoms and could shift its trophic habit to carnivory according to season of the year.

Environmental variability off NE Greenland (western Fram Strait) during the past 10,600 years

To reconstruct the climatic and paleoceanographic variability offshore Northeast Greenland during the last ~10 ka with multidecadal resolution, sediment core PS93/025 from the outermost North-East Greenland continental shelf (80.5°N) was studied by a variety of micropaleontological, sedimentological and isotopic methods. High foraminiferal fluxes, together with high proportions of ice-rafted debris and high Ca/Fe ratios, indicate a maximum in bioproductivity until ~8 ka related to a low sea-ice coverage. Sortable silt values, planktic foraminifer associations, and stable isotope data of planktic and benthic foraminifers suggest a strong westward advection of relatively warm Atlantic Water by the Return Atlantic Current during this time, with a noticeable bottom current activity. This advection may have been facilitated by a greater water depth at our site, resulting from postglacial isostatic depression. For the following mid-Holocene interval (ca. 8–5 ka), isotope data, lower foraminiferal fluxes and a shift in grain size maxima point to a lasting but successively decreasing Atlantic Water inflow, a weakening productivity, and a growing sea-ice coverage which is also revealed by the PIIIIP25 index. A final stage in the environmental development was reached at ~5 ka with the establishment of pre-industrial conditions. Low Ca/Fe ratios, low foraminiferal fluxes, low sortable silt values and the sea-ice indicating PIIIIP25 index point to a limited productivity and a weak Atlantic Water inflow by the Return Atlantic Current to our research area, as well as a higher and/or seasonally more extended sea-ice coverage during the Late Holocene. Two intervals with somewhat enhanced Atlantic Water advection around 2.0 and 1.0 ka are indicated by slightly increased foraminiferal fluxes and the reoccurrence of subpolar foraminifers. These intervals may correlate with the Roman Warm Period and the Medieval Climate Anomaly, as defined in the North Atlantic region.

Cenozoic increase in subduction erosion during plate convergence variability along the convergent margin off Trujillo, Peru

Subduction erosion is a long-term, large-scale geological process that dominates the structural inventory of a large number of convergent margins. Along the Peruvian convergent margin, this process has controlled the structural deformation of the forearc as a consequence of spatio-temporal variations during the Cenozoic. However, the pace at which tectonic erosion occurred has not been linked to regional, subduction-related events. The aim of this study is to show that subduction erosion along the Central Peruvian convergent margin off Trujillo (7∘S–9∘S) was influenced by plate convergence variability since the Late Cretaceous. Drilling data, multi-channel seismic (MCS) data and subsidence analyses are used to investigate the long-term effect of subduction erosion on the tectonic evolution of the Peru margin. Our study shows that subduction erosion (1) did not occur between the Cretaceous and Early Eocene (110–56 Ma), (2) increased and fluctuated between the Eocene and Pliocene (56–5 Ma) with a maximum average trench retreat of 3 km.Myr−1 between the Middle Miocene and Late Miocene (20–5 Ma), and (3) has decreased since the Pliocene (5 Ma) (1 km.Myr−1 of average trench retreat). A remarkable finding is that shorter periods of faster subduction erosion coincide with or follow major plate reorganization events that were marked by changes in the velocity and direction of relative plate convergence as well as with well-known phases of Andean orogeny. Based on our analyses, we therefore conclude that convergence variability off Peru is a primary mechanism controlling the pace at which tectonic erosion occurred along the Trujillo Basin during the Cenozoic.

Predictors of embolic complications during carotid stenting (TACTILE trial)

Background. In 30% to 87% patients undergoing carotid artery stenting (CAS), new ischaemic lesions (NILs) of the brain are detected on magnetic resonance imaging (MRI). According to some authors, in 60% cases who undergo CAS via transfemoral (TF) access, NILs are also found in the contralateral and other vascular pools of the brain that are not directly related to the target carotid artery, most likely a result of the endovascular manipulation of the catheter on the aortic arch. An alternative access site for CAS is transradial (TR) access. Theoretically, with TR access, the catheter’s contact with the aortic arch is reduced, particularly with an intervention on the right internal carotid artery, and the risk of embolic events is possibly reduced. However, this aspect has not yet been explored.Aim. The aim of this study was to identify the predictors of NILs of the brain in patients undergoing CAS via the TR and TF approaches.Methods. The study included 96 patients with indications for CAS. Patients were randomised in a 1:1 ratio to either the TR (n = 48) or TF (n = 48) groups. All patients underwent diffusion-weighted imaging MRI before and 12 to 24 hours after the procedure. Multiple logistic regression with step-by-step turning off of variables was used to determine the predictors of NIL.Results. A total of 40 clinical, demographic, instrumental and intraoperative variables were analysed. Based on the results of single regression analysis, 6 predictors (age, male sex, hypertension, history of percutaneous transluminal coronary angioplasty, intersection of the aortic arch and type II/III aortic arch) were included in the multivariate model. From the final multivariate analysis, it was found that age, intersection of the aortic arch and type II/III aortic arch are independent predictors of NILs after CAS.Conclusion. Patient age, type II/III aortic arch and need for a catheter to cross the aortic arch are independent predictors of NILs during carotid stenting. Received 9 January 2020. Revised 21 February 2020. Accepted 25 February 2020. Funding: The study did not have sponsorship. Conflict of interest: Authors declare no conflict of interest.

Effects of Variability in Ship Traffic and Whale Distributions on the Risk of Ships Striking Whales

Assessments of ship-strike risk for large whales typically use a single year of ship traffic data and averaged predictions of species distributions. Consequently, they do not account for variability in ship traffic or species distributions. Variability could reduce the effectiveness of static management measures designed to mitigate ship-strike risk. We explore the consequences of interannual variability on ship-strike risk using multiple years of both ship traffic data and predicted fin, humpback, and blue whale distributions off California. Specifically, risk was estimated in four regions that are important for ship-strike risk management. We estimated risk by multiplying the predicted number of whales by the cumulative distance travelled by ships. To overcome the temporal mismatch between the ship traffic and whale data available off California, we classified the time series of ship traffic data into nearshore and offshore traffic scenarios using the percentage of ship traffic travelling more than 24nmi from the mainland coast, which was the boundary of a clean fuel rule implemented in 2009 that altered ship traffic patterns. We found that risk for fin and humpback whale populations off California increased as these species recovered from whaling. We also found that broad-scale, northward shifts in blue whale distributions throughout the North Pacific, likely in response to changes in oceanographic conditions, were associated with increased ship-strike risk off northern California. The magnitude of ship-strike risk for fin, humpback, and blue whales was influenced by the ship traffic scenarios. Interannual variability in predicted whale distributions also influenced the magnitude of ship-strike risk, but generally did not change whether the nearshore or offshore traffic scenario had higher risk. The consistency in the highest risk from the traffic scenarios likely occurred because areas containing the highest predicted number of whales were generally the same across years. The consistency in risk from the traffic scenarios suggests that static spatial management measures (e.g., changing shipping lanes or creating areas to be avoided) can provide an effective means of mitigating risk resulting from ship traffic variability off California.