Scripps Institution Of Oceanography Research Articles

Resolution evaluation of the satellite altimetric gravity anomaly models with shipborne gravity data over the Cosmonaut Sea, East Antarctica (44–52° E)

AbstractSeveral satellite gravity anomaly models are freely available to calculate the free‐air gravity anomaly in areas where shipborne gravity measurements are scarce. Two models produced by the Technical University of Denmark (DTU17) and the Scripps Institution of Oceanography (SIOv32.1), respectively, were selected to compute the free‐air anomalies over the Cosmonaut Sea, East Antarctica. A statistical comparison analysis was performed to evaluate the resolution of satellite gravity anomaly models by comparing them with the shipborne surveying date. The radially averaged energy spectra of free‐air anomaly from different sources were calculated and compared over two selected regions to further evaluate the reliability of the data derived from satellite gravity anomaly models. The satellite gravity anomaly models have a better resolution in the ocean basin than in the area near the continental shelf. The comparison analysis revealed that the precision of both DTU17 and SIOv32.1 is close to the shipborne gravity data, but on average, SIOv32.1 is a little bit better than DTU17. The spectral analysis showed that the shipborne measurements may provide higher resolution than the satellite gravity anomaly model at wavelengths shorter than 20 km, and the free‐air data derived from SIOv32.1 have better resolution than the one from DTU17. These shipborne datasets will provide contributions for the updates of the Antarctic gravity anomaly and enable new high‐resolution combined Earth gravity models to be derived in Antarctica.

Multifrequency radar observations of marine clouds during the EPCAPE campaign

Abstract. The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) was a year-round campaign conducted by the US Department of Energy at the Scripps Institution of Oceanography in La Jolla, CA, USA, with a focus on characterizing atmospheric processes at a coastal location. The ground-based prototype of a new Ka-, W-, and G-band (35.75, 94.88, and 238.8 GHz) profiling atmospheric radar, named CloudCube, which was developed at the Jet Propulsion Laboratory, took part in the experiment during 6 weeks in March and April 2023. This article describes the unique data sets that were obtained during the field campaign from a variety of marine clouds and light precipitation. These are, to the best of the authors' knowledge, the first observations of atmospheric clouds using simultaneous multifrequency measurements including 238.8 GHz. These data sets therefore provide an exceptional opportunity to study and analyze hydrometeors with diameters in the millimeter- and submillimeter size range that can be used to better understand cloud and precipitation structure, formation, and evolution. The data sets referenced in this article are intended to provide a complete, extensive, and high-quality collection of G-band data in the form of Doppler spectra and Doppler moments. In addition, Ka-band and W-band reflectivity and Ka-, W-, and G-band reflectivity ratio profiles are included for several cases of interest on 6 different days. The data sets can be found at https://doi.org/10.5281/zenodo.10076227 (Socuellamos et al., 2024).

Geoheritage in the making: the discovery and vulnerability of deep-sea hydrothermal vents

Abstract Some significant geological sites are inaccessible. Among the most inaccessible sites are the hydrothermal vents and their associated biological communities located deep in the ocean. These prime geoheritage sites, hosting what may be the most primordial life on Earth, are vulnerable to mineral and fishing exploitation. Many lie in international waters, protected only by non-binding agreements with no clearly defined means of enforcement. The discovery of these vents in 1977 fundamentally altered scientists’ view of basic Earth processes and the extreme conditions under which life can exist. The discovery of the vents was a group effort and required technological accomplishments not available to previous generations of researchers. Often overlooked in the credits for this discovery was the persistence and determination of Kathleen Crane, a graduate student at Scripps Institution of Oceanography. Many women of her era faced significant challenges as they attempted to break into an often-unwelcoming field, marine geology. The challenges were not unique to geology; women were not welcomed in many other disciplines, both scientific and non-scientific. In spite of the obstacles, few people have made as remarkable a geoscience discovery as Dr Crane.

High-precision 1′ × 1′ bathymetric model of Philippine Sea inversed from marine gravity anomalies

Abstract. The Philippine Sea, located at the edge of the northwestern Pacific Ocean, possesses complex seabed topography. Developing a high-precision bathymetric model for this region is of paramount importance, as it provides fundamental geoinformation essential for Earth observation and marine scientific research, including plate motion, ocean circulation, and hydrological characteristics. The gravity–geologic method (GGM), based on marine gravity anomalies, serves as an effective bathymetric prediction technique. To further strengthen the prediction accuracy of conventional GGM, we introduce the improved GGM (IGGM). The IGGM considers the effects of regional seafloor topography by employing weighted averaging to more accurately estimate the short-wavelength gravity component, along with refining the subsequent modeling of long-wavelength gravity component. In this paper, we focus on seafloor topography modeling in the Philippine Sea based on the IGGM, combining shipborne bathymetric data with the Scripps Institution of Oceanography (SIO) V32.1 gravity anomaly. To reduce computational complexity, the optimal parameter values required for IGGM are first calculated before the overall regional calculation, and then, based on the terrain characteristics and distribution of sounding data, we selected four representative local sea areas as the research objects to construct the corresponding bathymetric models using GGM and IGGM. The analysis indicates that the precision of the IGGM models in four regions is improved to varying degrees, and the optimal calculation radius is 2′. Based on the above finding, a high-precision 1′×1′ bathymetric model of the Philippine Sea (5–35° N, 120–150° E), known as the BAT_PS model, is constructed using IGGM. Results demonstrate that the BAT_PS model exhibits a higher overall precision compared to the General Bathymetric Chart of the Oceans (GEBCO), topo_25.1, and DTU18 models at single-beam shipborne bathymetric points.

Expected Precision of Gravity Gradient Recovered from Ka-Band Radar Interferometer Observations and Impact of Instrument Errors

Full tensor of gravity gradients contains extremely large amounts of information, which is one of the most important sources for research on recovery seafloor topography and underwater matching navigation. The calculation and accuracy of the full tensor of gravity gradients are worth studying. The Ka-band interferometric radar altimeter (KaRIn) of surface water and ocean topography (SWOT) mission enables high spatial resolution of sea surface height (SSH), which would be beneficial for the calculation of gravity gradients. However, there are no clear accuracy results for the gravity gradients (the gravity gradient tensor represents the second-order derivative of the gravity potential) recovered based on SWOT data. This study evaluated the possible precision of gravity gradients using the discretization method based on simulated SWOT wide-swath data and investigated the impact of instrument errors. The data are simulated based on the sea level anomaly data provided by the European Space Agency. The instrument errors are simulated based on the power spectrum data provided in the SWOT error budget document. Firstly, the full tensor of gravity gradients (SWOT_GGT) is calculated based on deflections of the vertical and gravity anomaly. The distinctions of instrument errors on the ascending and descending orbits are also taken into account in the calculation. The precision of the Tzz component is evaluated by the vertical gravity gradient model provided by the Scripps Institution of Oceanography. All components of SWOT_GGT are validated by the gravity gradients model, which is calculated by the open-source software GrafLab based on spherical harmonic. The Tzz component has the poorest precision among all the components. The reason for the worst accuracy of the Tzz component may be that it is derived by Txx and Tyy, Tzz would have a larger error than Txx and Tyy. The precision of all components is better than 6 E. Among the various errors, the effect of phase error and KaRIn error (random error caused by interferometric radar) on the results is greater than 2 E. The effect of the other four errors on the results is about 0.5 E. Utilizing multi-cycle data for the full tensor of gravity gradients recovery can suppress the effect of errors.

A Tribute to Richard W. Eppley

Richard W. Eppley (1931–2023), better known as “Dick,” was a tour de force in biological oceanography. Most of his research life was at Scripps Institution of Oceanography (Scripps), where he studied marine phytoplankton and their roles in biogeochemical processes. Over the course of his career, he influenced many people, not only in science but also as exemplar of integrity and fundamental curiosity about the ocean. His formidable contributions to phytoplankton physiology and biological oceanography were appreciatively reviewed shortly after his retirement (Weiler et al., 1990), and with added perspective after his death (Cullen and Eppley, 2024). What follows are tributes from several of his former students, postdocs, and colleagues.

Global Seismic Networks Operated by the U.S. Geological Survey

Abstract The U.S. Geological Survey (USGS) Global Seismographic Network (GSN) Program operates two thirds of the GSN, a network of state-of-the-art, digital seismological and geophysical sensors with digital telecommunications. This network serves as a multiuse scientific facility and a valuable resource for research, education, and monitoring. The other one third of the GSN is funded by the National Science Foundation (NSF), and the operations of this component are overseen by EarthScope. This collaboration between the USGS, EarthScope, and NSF has allowed for the development and operations of the GSN to be a truly multiuse network that provides near real-time open access data, facilitating fundamental discoveries by the Earth science community, supporting the earthquake hazards mission of the USGS, benefitting tsunami monitoring by the National Oceanic and Atmospheric Administration, and contributing to nuclear test monitoring and treaty verification. In this article, we describe the installation and evolution of the seismic networks operated by the USGS that ultimately led to the USGS portion of the GSN (100 stations under network codes IU, IC, and CU) as they are today and envision technological advances and opportunities to further improve the utility of the network in the future. This article focuses on the USGS-operated component of the GSN; a companion article on the GSN stations funded by the NSF and operated by the Cecil and Ida Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California at San Diego by Davis et al. (2023) appears in this volume.

West Antarctica’s contribution to sea level rise as Earth’s climate warms

West Antarctica’s contribution to sea level rise as Earth’s climate warms Dr Dan Lubin, Researcher at the Scripps Institution of Oceanography, explores the contribution of West Antarctica to sea level rise as Earth’s climate warms. Sea level rise (SLR) is one of the most pressing concerns with greenhouse gas-induced climate warming. Over one-third of the human population, including nearly two-thirds of the global urban population, lives within 100 km of the sea. SLR increases flooding from storm surges and high tides, deterioration of infrastructure, shoreline erosion, contamination of agriculture, and numerous other hardships. Climate warming causes SLR in two primary ways: the melting of polar ice sheets and glaciers and the thermal expansion of the ocean as it warms. The two largest contributors to SLR from the steadily warming polar regions are the Greenland Ice Sheet (GIS) and the West Antarctic Ice Sheet (WAIS), at approximately 280 and 160 gigatons of ice per year, respectively. The GIS and WAIS have contrasts in the details of their ice mass loss.

Museum specimens and occurrences of Glottidia audebarti, Discradisca strigata and other brachiopods (Brachiopoda) in the Pacific of Costa Rica

Introduction: Lamp shells or brachiopods have a rich fossil record but only about 400 extant species. Their diversity on the Eastern Pacific is poorly known and only eight species are reported for the Pacific of Costa Rica. Objective: To list the specimens from Costa Rica and provide a distribution map along its Pacific coast. Methods: We checked collections at the University of Costa Rica (MZ-UCR) and Scripps Institution of Oceanography. Results: We found 22 records at MZ-UCR and 10 at Scripps, both include unidentified specimens, as well as Glottidia audebarti and Discradisca strigata, which are frequently collected intertidally. Conclusion: The study of Eastern Pacific living brachiopods is at an early stage; ecological studies could focus on the more easily accessed intertidal species.

Using Marine Data to Estimate the Accuracy of Free Air Gravity Anomaly Models Derived From Satellite Altimetry

AbstractGlobal gravity models from satellite altimetry missions have widely contributed to the improvement of the knowledge over the oceans. However, few models are available with a validated accuracy model, as the most recent models V21 to V32 from Scripps Institution of Oceanography (SIO). The aim of this paper is to propose a method to estimate the accuracy of any free air gravity anomaly model derived from satellite altimetry from validated marine data sets. The main idea is to correlate the error of the model to the mean roughness of the free air gravity anomaly on precise marine measurement areas. The relationship obtained is then generalized to each point of the model. This error grid is eventually combined with the grid provided by the satellite models, reflecting the errors related to the technology of the different altimetry satellites used. The method has been successfully applied to successive versions of SIO gravity anomaly models (from V18 to V31) to produce continuous accuracy grids over the North Atlantic Ocean. Validation of the results from independent marine data shows that the proposed approach allows to strongly improve the estimation of the used models' accuracy which converges, whatever the tested versions, toward a minimal value of 0.9 mGal over flat areas.

Northern copepod mitochondria can't beat the heat

How hot is too hot and why is it too hot? Unravelling the physiology of how animals cope with warming environments can tell us a lot about their evolutionary history as well as their current (and future) habitats. One possible mechanism by which an animal's physiology could limit its heat tolerance is if high temperatures interfered with routine but important metabolic processes such as making energy, ATP, by the mitochondria. Copepods, which often live in splash pools above the high tide line, adapt to the peculiarities of their particular pools. The copepod Tigriopus californicus has made its home in rock pools from balmy Mexico to chilly northern California, and has adapted its mitochondria to the vastly differing climes. With beakers of these copepods, descended from various populations, available in the lab, Tim Healy and Ron Burton from the Scripps Institution of Oceanography, USA, compared how quickly the mitochondria from different populations of copepods made ATP when in warm water and how that related to each populations’ natural habitat to find out whether their mitochondria influenced what temperatures they tolerated and, in doing so, their natural habitat ranges.For each population, the researchers isolated mitochondria from several individuals and provided them with all the materials they needed to make ATP. The team then compared how quickly the mitochondria did this at a range of temperatures from 20°C to a scorching 36°C, and found that the mitochondria from copepods from cold climates generally made ATP faster than those from warm climates, especially at temperatures below 25°C; although that was not surprising, because some animals such as copepods can counteract the natural slowing effect of cold temperatures on their metabolism. However, the northern population's mitochondria were also much more sensitive to high temperatures, as their ability to make ATP declined sharply when the temperature was above the mid-30s. Meanwhile, the mitochondria from southern copepods resisted the heat and happily made ATP at temperatures hot enough to hinder making ATP in the northern populations. Taken together, this suggested that the mitochondria of each population are best adjusted to make ATP at the temperatures that they would naturally encounter in the wild. Healy and Burton then turned their attention to figuring out whether the differences in mitochondrial physiology uncovered in the lab contributed to differences in heat tolerance in the wild.The duo compared the temperature at which each population of copepods made ATP half as fast as normal with the temperature at which they stopped swimming, a sign that it was too hot for them, and discovered that the southern populations, whose mitochondria could churn out decent amounts of ATP at relatively high temperatures, also tended to keep swimming at hotter temperatures, supporting the idea that copepods hit their upper temperature limit when their mitochondria stop performing well. This suggested that having ‘southern style’ or ‘northern style’ mitochondria not only impacted which temperatures the copepods could make the most ATP, but also which temperatures they could survive in the wild.Taken together, it is clear that northern populations of copepods like the cold, while southern populations like the heat, and how fast mitochondria can make ATP at these temperatures underlies at least some of this variation. But how copepod mitochondria react to heat does more than distinguish different populations – it also seems to set the maximum temperature where different populations can survive. As animals scramble to respond to the looming threat of climate change, understanding what sets the temperatures an animal can tolerate will be key to understanding why animals live where they do in the present and where they might live in the future.

The cell surface of a diatom from the bacterial perspective

Journal of PhycologyVolume 59, Issue 2 p. 307-308 ALGAE HIGHLIGHT The cell surface of a diatom from the bacterial perspective Emma E. George, Corresponding Author Emma E. George [email protected] Scripps Institution of Oceanography, Integrative Oceanography Division, University of California, La Jolla, California, USA Correspondence Emma E. George, Scripps Institution of Oceanography, Integrative Oceanography Division, University of California, San Diego, La Jolla, California, USA. Email: [email protected]Search for more papers by this author Emma E. George, Corresponding Author Emma E. George [email protected] Scripps Institution of Oceanography, Integrative Oceanography Division, University of California, La Jolla, California, USA Correspondence Emma E. George, Scripps Institution of Oceanography, Integrative Oceanography Division, University of California, San Diego, La Jolla, California, USA. Email: [email protected]Search for more papers by this author First published: 12 April 2023 https://doi.org/10.1111/jpy.13319Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume59, Issue2April 2023Pages 307-308 RelatedInformation

Kimberly Prather wins Esselen Award

The 36th Gustavus John Esselen Award for Chemistry in the Public Interest has been awarded to Kimberly A. Prather , distinguished chair in atmospheric chemistry at the Scripps Institution of Oceanography, University of California San Diego. The Esselen Award recognizes chemists whose scientific and technical achievements have contributed to the public good and enhanced the public’s perception of chemistry. Prather is being honored for her use of mass spectrometry to characterize individual aerosols in the atmosphere. Her discoveries have clarified the impact of aerosols on climate, air pollution, water quality, and disease transmission. Most recently, in media interviews and briefings with public health and other leaders, Prather has spotlighted the importance of acknowledging aerosol transmission to reduce the spread of COVID-19. Prather will receive her award during a ceremony at Harvard University on April 14, after which she will deliver a public lecture titled “Tiny Critters, Huge Impacts: How Microbes

On performance of vertical gravity gradient determined from CryoSat-2 altimeter data over Arabian Sea

SUMMARYHigh-precision and high-resolution satellite altimetry data from CryoSat-2 are widely utilized for marine gravity inversion. The vertical gravity gradient is a crucial parameter of the Earth's gravity field. To evaluate the performance of vertical gravity gradient determined from CryoSat-2 altimeter data, the pre-processed along-track sea surface heights (SSHs) are obtained through error correction. The study area focused on the Arabian Sea and its surrounding region, where the along-track geoid was derived by subtracting the mean dynamic topography of the ocean from the along-track SSH of CryoSat-2. The residual along-track geoidal gradients were obtained by adjusting the along-track geoid gradients calculated from CryoSat-2 altimeter data using the remove-restore method. This was done by subtracting the geoid gradients calculated by the gravity field model XGM2019e_2159. After obtaining the residual along-track geoidal gradients, the residual gridded deflections of the vertical (DOV) are calculated using the least-squares collocation (LSC) method. The residual gridded DOV are then used to compute the residual gridded gravity anomaly gradients in the study area using the finite-difference method. After restoring the gravity anomaly gradients computed by the XGM2019e_2159 model, a high-resolution gravity anomaly gradient model with a resolution of 1′ ×1′ is obtained for the Arabian Sea and its surrounding area. To evaluate the accuracy of the gravity anomaly gradient model derived from CryoSat-2, it was compared with the SIO V32.1 gravity anomaly gradient model released by the Scripps Institution of Oceanography. The comparison showed that the root mean square (RMS) of the differences between the two models is 7.69E, demonstrating the high accuracy and precision of the vertical gravity gradient determined from CryoSat-2 altimeter data.

Scripps Argo Trajectory-Based Velocity Product: Global Estimates of Absolute Velocity Derived from Core, Biogeochemical, and Deep Argo Float Trajectories at Parking Depth

Abstract Global estimates of absolute velocities can be derived from Argo float trajectories during drift at parking depth. A new velocity dataset developed and maintained at Scripps Institution of Oceanography is presented based on all Core, Biogeochemical, and Deep Argo float trajectories collected between 2001 and 2020. Discrepancies between velocity estimates from the Scripps dataset and other existing products including YoMaHa and ANDRO are associated with quality control criteria, as well as selected parking depth and cycle time. In the Scripps product, over 1.3 million velocity estimates are used to reconstruct a time-mean velocity field for the 800–1200 dbar layer at 1° horizontal resolution. This dataset provides a benchmark to evaluate the veracity of the BRAN2020 reanalysis in representing the observed variability of absolute velocities and offers a compelling opportunity for improved characterization and representation in forecast and reanalysis systems. Significance Statement The aim of this study is to provide observation-based estimates of the large-scale, subsurface ocean circulation. We exploit the drift of autonomous profiling floats to carefully isolate the inferred circulation at the parking depth, and combine observations from over 11 000 floats, sampling between 2001 and 2020, to deliver a new dataset with unprecedented accuracy. The new estimates of subsurface currents are suitable for assessing global models, reanalyses, and forecasts, and for constraining ocean circulation in data-assimilating models.

Altimetry‐Derived Gravity Gradients Using Spectral Method and Their Performance in Bathymetry Inversion Using Back‐Propagation Neural Network

AbstractVariations in bathymetry produce gravity gradients; therefore, gravity gradients should be suitable for inverting bathymetry. However, classical bathymetry inversion methods often use gravity anomalies. Studies wherein gravity gradients are employed always use only vertical gravity gradients, ; however, the remaining five gravity gradients also contain bathymetric information. This study presents a spectral method of inverting gravity gradients from altimetry‐derived deflection of the vertical. The accuracy of derived gravity gradients is first evaluated by Laplace's equation. Results show that, except the Arctic region, the mean and standard deviation (STD) of the Laplace operator are, respectively, less than 0.001 and 0.06 E in the Atlantic, Indian and Pacific oceans. Computed was compared with from Scripps Institution of Oceanography. The differences have means and STDs smaller than 0.06 and 6.7 E, respectively, in all study areas, except the Arctic which registered an STD of 13.81 E. All six tensors were then fed into a back‐propagation neural network to predict bathymetries of each study area. The resultant bathymetries compare well with reference models from ship‐borne depths, SRTM15+V2 and GEBCO_2021. Relative to ship‐borne depths, the Atlantic, Pacific, Indian and Arctic study areas yielded mean errors, error STDs and correlation coefficients of 5.40, 3.28, 0.92, 3.07 m; 110.03, 76.23, 104.58, 132.41 m; and 0.9861, 0.9615, 0.9760, 0.9803; respectively. The bathymetries were inverted again, however, with each gravity gradient component omitted. Analysis showed that was not the most influential component across the study regions; rather, each gravity gradient component can significantly contribute to bathymetry inversion.

Epidermal Microbiomes of Leopard Sharks (Triakis semifasciata) Are Consistent across Captive and Wild Environments.

Characterizations of shark-microbe systems in wild environments have outlined patterns of species-specific microbiomes; however, whether captivity affects these trends has yet to be determined. We used high-throughput shotgun sequencing to assess the epidermal microbiome belonging to leopard sharks (Triakis semifasciata) in captive (Birch Aquarium, La Jolla California born and held permanently in captivity), semi-captive (held in captivity for <1 year in duration and scheduled for release; Scripps Institute of Oceanography, San Diego, CA, USA) and wild environments (Moss Landing and La Jolla, CA, USA). Here, we report captive environments do not drive epidermal microbiome compositions of T. semifasciata to significantly diverge from wild counterparts as life-long captive sharks maintain a species-specific epidermal microbiome resembling those associated with semi-captive and wild populations. Major taxonomic composition shifts observed were inverse changes of top taxonomic contributors across captive duration, specifically an increase of Pseudoalteromonadaceae and consequent decrease of Pseudomonadaceae relative abundance as T. semifasciata increased duration in captive conditions. Moreover, we show captivity did not lead to significant losses in microbial α-diversity of shark epidermal communities. Finally, we present a novel association between T. semifasciata and the Muricauda genus as Metagenomes associated genomes revealed a consistent relationship across captive, semi-captive, and wild populations. Since changes in microbial communities is often associated with poor health outcomes, our report illustrates that epidermally associated microbes belonging to T. semifasciata are not suffering detrimental impacts from long or short-term captivity. Therefore, conservation programs which house sharks in aquariums are providing a healthy environment for the organisms on display. Our findings also expand on current understanding of shark epidermal microbiomes, explore the effects of ecologically different scenarios on benthic shark microbe associations, and highlight novel associations that are consistent across captive gradients.

Blue whale heart rate immortalised in motion sensor trace

Scientists have been attaching motion sensors to penguins, whales and other marine animals for decades, recording their flipper and fluke beats and every twist and turn to learn about their extraordinary aquatic lifestyles. But could other details about these animals’ lives also be preserved in the jagged acceleration traces they recorded? ‘Last July, James Fahlbusch and I were going through tag data from a blue whale with a fine-toothed comb looking for night-time breathing behaviour’, says Max Czapanskiy from Stanford University, USA, when the duo stumbled across something unexpected. ‘We noticed repetitive, gentle noise in the accelerometry record during resting dives’, Czapanskiy recalls. And when the pair measured the time between the barely perceptible peaks in the noisy traces, they realised that it correlated with the period between each of the mighty beast's heart beats. Could the motion sensors have inadvertently measured the iconic creature's heart rate? Czapanskiy sent a quick screenshot to Paul Ponganis (Scripps Institution of Oceanography, USA) and Jeremy Goldbogen (Stanford University), who confirmed that his hunch could be correct. But, before they could be sure, the team needed to test their theory on killer whales at SeaWorld of California, USA, where they could simultaneously measure the animal's heart rate while recording its manoeuvres.Working with Todd Schmitt (SeaWorld) the team attached an ECG monitor and motion sensor to a killer whale and recorded the animal's heart beats and movements. Then, Czapanskiy and Ponganis analysed a 14 s portion of the killer whale's acceleration trace when the animal was stationary to search for any sign of a pulse. After months of patient investigation, the duo successfully revealed the soft throbbing motion as the animal's body gently recoiled in response to its heartbeat. And when they compared the movement trace with the killer whale's ECG record, they found the two corresponded perfectly. It is possible to extract heart rate records from the acceleration traces recorded by motion sensors when the animal is static, but could the team apply their novel technique to the manoeuvres of freely roaming wild whales?The researchers returned to the movement data collected by the motion sensor located behind the blue whale's flipper, close to its heart, as the animal dived to rest repeatedly at ∼20 m. Sure enough, the accelerations generated by the whale's mighty movements overwhelmed the gentle body jiggle produced by the animal's powerful heartbeat, so the team focused on 30 s to 2 min segments when the whale was clearly resting at the bottom of its dive. Czapanskiy and Ponganis were able to identify the gentle shuttling motion of the whale's body in response to its heartbeat, recording a heart rate ranging from 4 to 8 beats min−1, in agreement with the only ECG ever recorded from a blue whale. And when the team plotted the animal's heart rate over several dives, it increased gradually from ∼4.1 beats min−1 when the animal began its descent, to ∼8.3 beats min−1 as the whale returned to the surface.‘As accelerometer tags have been deployed on many cetacean species for multiple decades, this method may be applied to mine existing datasets and better understand how heart rate scales with body size and other biological factors’, says Czapanskiy. And the team suggests that the technique could help researchers and conservationists better understand the impact of human noise pollution on these sensitive animals. One thing is sure, there is already a treasure trove of heart rate measurements buried in the movement traces of whales, dolphins and other aquatic mammals waiting to be unearthed by scientists to learn more about the physiology of these depth-defying animals.

An inter-comparison of autonomous in situ instruments for ocean CO2 measurements under laboratory-controlled conditions

Observations of the marine CO2 system are important for understanding ocean acidification, air-sea CO2 fluxes and the marine carbon cycle in general. A variety of autonomous in situ instruments have been developed and used towards this end. There is, however, a lack of inter-comparison studies of currently available sensor technologies. In this study, a total of 10 instruments including commercially available pH, partial pressure of CO2 (pCO2), and total alkalinity (AT) sensors were tested and compared in a 5000 L seawater tank located at Scripps Institution of Oceanography (SIO), California, USA. The test took place over ~12 days (August 16 to 28, 2016) where conditions in the tank were artificially varied to encompass a wide range of AT, pH and pCO2 as well as temperature and salinity. To assess accuracy, independent measurements of pH, pCO2, dissolved inorganic carbon (DIC) and AT were made using benchtop instrumentation. We also evaluated internal consistency, comparing the measured parameter from the sensors with the calculated parameter, e.g. pCO2 calculated from AT and pH compared with directly measured pCO2. DIC can be precisely derived (within ±5 μmol/kg) over a wide range of conditions from measured pH or pCO2 paired with AT. Sensor accuracy established by discrete samples is sufficient for short-term and seasonal dynamical studies, but their ability in determining long-term (e.g. climate) variability could not be evaluated because of the brevity of the study. These results provide insights into sensor performance and strategies for data quality control for future studies of ocean acidification and carbon cycling.

Improved Gravity-Geologic Method Reliably Removing the Long-Wavelength Gravity Effect of Regional Seafloor Topography: A Case of Bathymetric Prediction in the South China Sea

The conventional gravity-geologic method (GGM), as a widely used method for bathymetric prediction, is a single-point calculation method between the gravity anomaly and unknown bathymetry. To enhance the accuracy of bathymetric prediction, the improved GGM (IGGM) reliably removing the long-wavelength gravity effect of regional seafloor topography was proposed. The modeling of the long-wavelength gravity field was refined by calculating the short-wavelength gravity correction at the control points based on the weight parameters introduced into the Bouguer slab formulation. The IGGM bathymetric model for the experimental area (113°E-119°E, 12°N-19°N) in the South China Sea was constructed by combining shipborne bathymetry data from the National Centers for Environmental Information (NCEI) and the V31.1 gravity anomaly model from the Scripps Institution of Oceanography (SIO). The standard deviation of the difference between the IGGM model and shipborne bathymetry was approximately 103.46 m at iteration points, which was better than the DTU18, GEBCO_2021 and topo_23.1 bathymetric models. Compared with the accuracy of the model derived from the GGM, the accuracy of the model from IGGM was improved by about 27%. At checkpoints, the accuracy of IGGM was improved by approximately 17 m, and the improvement was larger in areas with complex terrain.