Ocean Station Research Articles

Proposed synergies between oceanography and metrology

Accurate and traceable measurements are required to understand ocean processes, to address pressing societal challenges, such as climate change and to sustainably manage marine resources. Although scientific and engineering research has resulted in advanced methods to measure Essential Ocean Variables (EOVs) there is a need for cross comparison of the techniques and traceability to recognized standards. Metrological laboratories are experienced in accredited methods and assessment of methodology. An EU INFRAIA-02-2020: Integrating Activities for Starting Communities project MINKE (Metrology for Integrated marine maNagement and Knowledge-transfer nEtwork https://minke.eu) brings European marine science and metrology Research Infrastructures together to identify synergies and create an innovative approach to Quality Assurance of oceanographic data. Quality depends both on the accuracy (that can be provided through the metrology component) and the completeness of the data sets. The collaboration between different Marine Research Infrastructures (RIs) places a fundamental role on assuring the completeness of the datasets, particularly at global scales. The MINKE project encourages enhancement through collaboration of national metrology laboratories and the oceanographic community. Metrological assessment of the accuracy and uncertainties within multidisciplinary ocean observations will provide data that are key to delivering policy information. Objectives across all the RIs are to facilitate ocean observation and build wider synergies. MINKE will investigate these synergies, then introduce metrology to the core of various EOV measurements. Currently the marine RIs cover laboratory and field operations, from the surface seafloor, coastal waters to deep sea, fixed ocean stations to ship and autonomous vehicle operations to ships of opportunity, and flux stations focusing on carbonate system variables. The nexus of these operations is the focal point for coordinated improvement of ocean observing methods. Measurement intercomparisons, traceability and uncertainty assessments should be at the core of the scientific observations. Specifically, MINKE will work with RIs and Metrology Institutes to improve the quality of dissolved oxygen, carbonate system, chlorophyll-fluorescence, ocean sound and current meter measurements, through access to metrology laboratories, Transnational Access and intercomparison studies across existing marine consortia and RIs. MINKE will also promote the development of absolute salinity observation, and improvements in marine litter measurements.

Emissions Assessment of Container Ships Sailing under Off-Design Conditions

Maritime transportation is the prevalent mode of transport for overseas freight, and it is frequently recognised as a relatively environmentally sustainable means of transport. However, shipping is still a substantial source of greenhouse gas emissions. We investigate the effect on fuel consumption and emissions when container ships are sailing below the design speed (i.e., slow steaming) as a strategy to minimise fuel consumption and costs. The estimation of ship fuel oil consumption is commonly based on the cubic speed‒power relation as a bottom-up approach. Nevertheless, the cubic relation could overestimate the impact of slow steaming on fuel consumption reduction and the emissions assessment. We compare real fuel consumption data and the consequent emissions with the results of assessing these parameters with the mentioned bottom-up approach. The analysis uses a set of container-ship slow steaming voyages, and the assessment is supported by speeds obtained from the Automatic Identification System (AIS). The exponential values obtained for the speed‒power relation range between 3.1 and 3.5, finding an overrating over 20% in all the cases analysed. Finally, we use a weather ship routing optimisation software to investigate additional emissions savings in the framework of ship-specific measures when weather ship routing and slow steaming are applied simultaneously.

Acoustical effects of extreme weather events

The transfer of water from evaporating regions to precipitating regions drives the global water cycle, and understanding its dynamics is essential in determining how weather patterns will respond to changes in global climate. An intensification of the global water cycle has been reported using 50-year sea surface salinity data (Durack and Wijffels, 2010, J. Climate) with the consequence of more frequent extreme weather events. However, data under extreme weather conditions over the ocean are rare and a lot of physics remains to be investigated. As part of the Ocean Climate Stations that NOAA is maintaining, the 1-year data presented here are from Ocean Station Papa (50°N, 145°W), including measurements of wind speed, rain rate, currents, wave height and direction, bubble plume spatial structure and dynamics, and ambient noise for wind speeds up to 25 m/s. This full suite of data enables the study of the statistical properties of bubble plumes, their relation to meteorological parameters, and how to take them into account in ambient noise prediction, especially under severe weather conditions. Knowledge gained through this unique dataset can be critical for understanding air–sea interaction, validating satellite rain products, and predicting the ambient noise field under extreme weather conditions.

Spatial and temporal variation of dissolved iodine in the eastern Arabian Sea

Here we report the seasonal and spatial variation of iodide (I−) and total dissolved iodine (TI) along a transect covering the oxygen minimum zone (OMZ) in the Arabian Sea (AS). This data is generated after a gap of more than two decades since the US-Joint Global Ocean Flux Study (JGOFS) reported observations of iodine speciation in the region. Also, this is the first study to report on iodine speciation from the coastal region of the west coast of India. Here the water samples were collected along the meridional transect (68°E) during spring inter-monsoon (SIM), southwest monsoon (SWM), and fall inter-monsoon (FIM), and from the coastal Goa transect during late SWM and FIM. In addition, sediment porewater was also collected from the coastal Goa transect during late SWM. Iodide was found to be dominant in the OMZ, whereas TI was majorly represented by iodate below the OMZ. The I− and TI concentrations were higher around the 15°N stations during all three seasons sampled. Seasonal variability was observed in the study, with high I− and TI during the SWM and FIM as compared to SIM. The coastal region was observed to have high I− values during seasonal anoxia in FIM as compared to the late SWM. This may be due to the release of I− from the sediments which are extremely rich in I−. The porewater showed extremely high I− (up to 4545 nM) at the shelf stations, which is 10 times higher than what is measured in the overlying waters. The US-JGOFS study reported iodide values as high as 953 nM in the AS OMZ with excess iodine (difference between the measured TI and the predicted TI) of 400 nM and attributed this to the input from the shelf sediments. In the present study TI values up to 811 nM were observed in the AS. To ascertain the source of excess iodine, porewater extracted from the sediments covering shelf and open ocean stations along the Goa transect was studied for iodine speciation. The diffusive flux of I− calculated from the surface sediments ranged between 14 and 43 μmol I− m−2 d−1 from the shelf stations off Goa, which is high enough to explain the excess iodine concentrations seen in the OMZ. Apart from the seasonality observed in iodine concentrations, our study infers that the shelf sediments along the west coast of India act as a source of iodine to the AS OMZ.

Spatio-Temporal Distributions of the Natural Non-Sea-Salt Aerosol Over the Southern Ocean and Coastal Antarctica and Its Potential Source Regions

More than 40 years of aerosol data including concentrations of particle number and of nine major ions collected over the Southern Ocean and coastal stations have been aggregated and filtered with back trajectories to reduce the risk of influence from adjacent continents. That provided a rich dataset including latitudinal distribution and seasonality of physical and chemical aerosol parameters that allow insights into aerosol sources over the Southern Ocean. These data together with statistics of back trajectory paths of high (75% percentile) and low (25% percentile) concentrations of the studied aerosol parameters were used to identify potential source regions of the respective compounds. For particle number concentrations, MSA, and the non-sea-salt fractions of Ca and potassium the most prominent source regions were found in high DMS-areas close to Antarctica, whereas the potential source regions of NH4 and the non-sea-salt fraction of Mg were located in part further north over the Southern Ocean. These geographical differences would reflect differences in the marine biota.

Deconvolving mechanisms of particle flux attenuation using nitrogen isotope analyses of amino acids

AbstractParticulate organic matter settling out of the euphotic zone is a major sink for atmospheric carbon dioxide and serves as a primary food source to mesopelagic food webs. Degradation of this organic matter encompasses a suite of mechanisms that attenuate flux, including heterotrophic metabolic processes of microbes and metazoans. The relative contributions of microbial and metazoan heterotrophy to flux attenuation, however, have been difficult to determine. We present results of compound specific nitrogen isotope analysis of amino acids of sinking particles from sediment traps and size‐fractionated particles from in situ filtration between the surface and 500 m at Ocean Station Papa, collected during NASA EXPORTS (EXport Processes in the Ocean from RemoTe Sensing). With increasing depth, we observe: (1) that, based on the δ15N values of threonine, fecal pellets dominate the sinking particle flux and that attenuation of downward particle flux occurs largely via disaggregation in the upper mesopelagic; (2) an increasing trophic position of particles in the upper water column, reflecting increasing heterotrophic contributions to the nitrogen pool and the loss of particles via remineralization; and (3) increasing δ15N values of source amino acids in submicron and small (1–6 μm) particles, reflecting microbial particle solubilization. We further employ a Bayesian mixing model to estimate the relative proportions of fecal pellets, phytodetritus, and microbially degraded material in particles and compare these results and our interpretations of flux attenuation mechanisms to other, independent methods used during EXPORTS.

Evaluation of new and net community production estimates by multiple ship-based and autonomous observations in the Northeast Pacific Ocean

New production (NP) and net community production (NCP) measurements are often used as estimates of carbon export potential from the mixed layer of the ocean, an important process in the regulation of global climate. Diverse methods can be used to measure NP and NCP, from research vessels, autonomous platforms, and remote sensing, each with its own set of benefits and uncertainties. The various methods are rarely applied simultaneously in a single location, limiting our ability for direct comparisons of the resulting measurements. In this study, we evaluated NP and NCP from thirteen independent datasets collected via in situ, in vitro, and satellite-based methods near Ocean Station Papa during the 2018 Northeast Pacific field campaign of the NASA project EXport Processes in the Ocean from RemoTe Sensing (EXPORTS). Altogether, the datasets indicate that carbon export potential was relatively low (median daily averages between −5.1 and 12.6 mmol C m−2 d−1), with most measurements indicating slight net autotrophy in the region. This result is consistent with NCP estimates based on satellite measurements of sea surface temperature and chlorophyll a. We explored possible causes of discrepancies among methods, including differences in assumptions about stoichiometry, vertical integration, total volume sampled, and the spatiotemporal extent considered. Results of a generalized additive mixed model indicate that the spatial variation across platforms can explain much of the difference among methods. Once spatial variation and temporal autocorrelation are considered, a variety of methods can provide consistent estimates of NP and NCP, leveraging the strengths of each approach.

Carbon budgets of Scotia Sea mesopelagic zooplankton and micronekton communities during austral spring

Zooplankton form an integral component of epi- and mesopelagic ecosystems, and there is a need to better understand their role in ocean biogeochemistry. The export and remineralisation of particulate organic matter at depth plays an important role in controlling atmospheric CO2 concentrations. Pelagic mesozooplankton and micronekton communities may influence the fate of organic matter in a number of ways, including: the consumption of primary producers and export of this material as fast-sinking faecal pellets, and the active flux of carbon by animals undertaking diel vertical migration (DVM) into the mesopelagic. We present day and night vertical biomass profiles of mesozooplankton and micronekton communities in the upper 500 m during three visits to an ocean observatory station (P3) to the NW of South Georgia (Scotia Sea, South Atlantic) in austral spring, alongside estimates of their daily rates of ingestion and respiration throughout the water column. Day and night community biomass estimates were dominated by copepods >330 μm, including the lipid-rich species, Calanoides acutus and Rhincalanus gigas. We found little evidence of synchronised DVM, with only Metridia spp. and Salpa thompsoni showing patterns consistent with migratory behaviour. At depths below 250 m, estimated community carbon ingestion rates exceeded those of metabolic costs, supporting the understanding that food quality in the mesopelagic is relatively poor, and organisms have to consume a large amount of food in order to fulfil their nutritional requirements. By contrast, estimated community rates of ingestion and metabolic costs at shallower depths were approximately balanced, but only when we assumed that the animals were predominantly catabolising lipids (i.e. respiratory quotient = 0.7) and had relatively high absorption efficiencies. Our work demonstrates that it is possible to balance the metabolic budgets of mesopelagic animals to within observational uncertainties, but highlights the need for a better understanding of the physiology of lipid-storing animals and how it influences carbon budgeting in the pelagic.

Influence of amino acids on bacterioplankton production, biomass and community composition at Ocean Station Papa in the subarctic Pacific

Bacterioplankton play a central role in carbon cycling, yet their relative contributions to carbon production and removal can be difficult to constrain. As part of the Export Processes in the Ocean from RemoTe Sensing (EXPORTS) program, this study identifies potential influences of bacterioplankton community and dissolved organic matter (DOM) composition on carbon cycling at Ocean Station Papa in August 2018. Surface (5–35 m) bacterioplankton production rates and stocks spanned a 2- to 3-fold range over the 3-week cruise and correlated positively with the DOM degradation state, estimated using the mole proportion of total dissolved amino acids. When the DOM was more degraded, 16S rRNA gene amplicon data revealed a less diverse bacterioplankton community with a significant contribution from members of the Flavobacteriaceae family. Over the course of 7–10 d, as the DOM quality improved (became less degraded) and bacterioplankton productivity increased, the responding bacterioplankton community became more diverse, with increased relative contributions from members of the SAR86, SAR11 and AEGEAN-169 clades. The cruise mean for mixed layer, depth-integrated bacterioplankton carbon demand (gross bacterioplankton production) was 5.2 mmol C m−2 d−1, representing 60% of net primary production, where the difference between net primary production and bacterioplankton carbon demand was less than sinking flux at 50 m. The concentrations of dissolved organic carbon (cruise average of 58.5 µM C) did not exhibit a systematic change over the cruise period. Therefore, we hypothesize that carbon supplied from gross carbon production, values that were 2- to 3-fold greater than net primary production, provided the carbon necessary to account for the sinking flux and bacterioplankton carbon demand that were in excess of net primary production. These findings highlight the central contributions of bacterioplankton to carbon cycling at Ocean Station Papa, a site of high carbon recycling.

Lithospheric Imaging Through Reverberant Layers: Sediments, Oceans, and Glaciers

AbstractThe Earth, in large portions, is covered in oceans, sediments, and glaciers. High‐resolution body wave imaging in such environments often suffers from severe reverberations, that is, repeating echoes of the incoming scattered wavefield trapped in the reverberant layer, making interpretation of lithospheric layering difficult. In this study, we propose a systematic data‐driven approach, using autocorrelation and homomorphic analysis, to solve the twin problem of detection and elimination of reverberations without a priori knowledge of the elastic structure of the reverberant layers. We demonstrate, using synthetic experiments and data examples, that our approach can effectively identify the signature of reverberations even in cases where the recording seismic array is deployed in complex settings, for example, using data from (a) a land station sitting on Songliao basin, (b) an ocean bottom station in the fore‐arc setting of the Alaska amphibious community seismic experiment, and (c) a station deployed on ice‐sediment strata in the glaciers of Antarctica. The elimination of the reverberation is implemented by a frequency domain filter whose parameters are automatically tuned using seismic data alone. On glaciers where the reverberating sediment layer is sandwiched between the lithosphere and an overlying ice layer, homomorphic analysis is preferable in detecting the signature of reverberation. We expect that our technique will see wide application for high‐resolution body wave imaging across a wide variety of conditions.

COVID-19 Containment Measures—a Step Back for Walking Mobility? A 2-Year, 60-Country Analysis of the Apple Mobility Data

COVID-19 containment measures curb viral spread but may hamper walking mobility. As a low daily step count is associated with increased noncommunicable diseases and mortality, assessing the relationship between pandemic responses and walking mobility can help trade-off public health measures. We investigated the association between containment stringency and walking mobility across 60 countries in the period between January 21, 2020 and January 21, 2022 and modeled how this could impact mortality hazard. Walking mobility was measured through the Apple Mobility Trends, containment measures stringency index through the Oxford COVID-19 response tracker (which considers local policies on closures, healthcare, and economy), and meteorological data by National Oceanic and Atmospheric Administration weather stations. Walking mobility was regressed over stringency in a mixed-effect model with weather variables as covariates. The impact of stringency on all-cause mortality due to reduced mobility was modeled based on regression results, prepandemic walking mobility, and the association between step count and all-cause mortality hazard. Across the 60 countries, the average stringency was 55 (9) (mean [SD]) out of 100. Stringency was negatively associated with walking mobility; a log-linear model fitted data better than a linear one, with a regression coefficient for stringency on ln (walking mobility) (95% confidence interval) of -1.201 × 10-2 (-1.221 × 10-2 to -1.183 × 10-2). Increasing stringency, thus decreasing walking mobility, nonlinearly incremented the modeled all-cause mortality hazard by up to ∼40%. In this study, walking mobility was negatively associated with containment measures stringency; the relationship between stringency, mobility, and the subsequent impact on health outcomes may be nonlinear. These findings can help in balancing pandemic containment policies.

Ship weather routing featuring w-MOEA/D and uncertainty handling

The paper presents a new version of evolutionary multi-objective weather routing (WR) for ships taking into account uncertainties of weather forecasts in route optimization. The method applies authors’ w-MOEA/D algorithm: MOEA/D framework incorporating Decision Maker’s (DM) preferences by means of w-dominance relation. Owing to this, DM preferences are taken into account throughout optimization, allowing the process to focus on the part of vast objective’s space. Only the part of Pareto front being of interest to DM is generated, thus the process converges faster, without sacrificing quality of the final set. All of the above is essential for the WR method, which pursues three objectives while trying to meet multiple constraints and handling uncertainty of weather data. The final method has been implemented as a part of client–server system architecture, whose client part has been installed on board of a m/v Monte da Guia (MdG) vessel navigating between the Portuguese coast and the Azores. The method has then been verified in the course of computer simulations and its results have been compared with real MdG GPS routes. The comparison shows that the presented method is able to find routes that bring progress in terms of the objectives’ while satisfying the constraints.

An intelligent modeling framework to optimize the spatial layout of ocean moored buoy observing networks

This research is motivated by the practical requirements in the sustainable deployment of ocean moored buoy observing networks. Ocean moored buoys play an important role in the global marine environment monitoring. Ocean buoy station layout planning is a typical multiple-objective spatial optimization problem that aims to reduce the spatial correlation of buoy stations and improve their spatial monitoring efficiency. In this paper, we develop a multi-objective mathematical model for allocating ocean buoy stations (MOLMofOBS) based on Tobler’s first law of geography. A spatial neighborhood model based on a Voronoi diagram is built to represent the spatial proximity of distributed buoy stations and delimit the effective monitoring region of every station. Then, a heuristic method based on a multiple-objective particles swarm optimization (MOPSO) algorithm is developed to calculate the MOLMofOBS via a dynamic inertia weight strategy. Meanwhile, a series of experiments is conducted to verify the efficiency of the proposed model and algorithms in solving single- and multiple-buoy station location problems. Finally, an interactive portal is developed in the Cyberinfrastructure environment to provide decision-making services for online real-time planning of the ocean buoy station locations. The work reported in this paper will provide spatial decision-making support for the sustainable development of ocean buoy observing networks.

Particle size distribution at Ocean Station Papa from nanometers to millimeters constrained with intercomparison of seven methods

Particle size distribution (PSD) is a fundamental property that affects almost every aspect of the marine ecosystem, including ecological trophic interactions and transport of organic matter and trace elements. We measured PSDs using a suite of seven instruments in waters near Ocean Station Papa in the Northeast Pacific Ocean. These instruments and their sizing ranges are: Laser In-Situ Scattering and Transmissometer (LISST)-Volume Scattering Function meter (VSF) and Multispectral Volume Scattering Meter (MVSM), both sizing particles from 0.02 µm to 2000 µm; the LISST-100X, from 3 µm to 180 µm; the ViewSizer, from 0.3 µm to 2 µm; the Coulter Counter, from 2 µm to 40 µm; the Imaging Flow CytoBot (IFCB), from 5 µm to 100 μm; and the underwater vision profiler (UVP), from 100 µm to 2000 µm. Together, they cover an unprecedented size range spanning 5 orders of magnitude from 20 nm to 2 mm. The differences in size definition for the different instruments cause biases in comparing PSDs. The absolute differences in PSDs, after correcting for mean biases, were less than a factor of 3 among all the instruments, and within 50% among LISST-100X, LISST+MVSM, Coulter Counter and IFCB. We also found that particles of sizes <50 µm were not very porous; however, porosity must be considered for particles >50 µm. The merged PSDs, ranging from 0.02 µm to 2000 µm, showed little variation in the PSD slope in the upper 75 m of the water column even though the total number of particles decreased with depth. While submicrometer particles are numerically dominant, particles of sizes 1 µm to 100 µm account for 70–90% of the solid volume of particles. We expect that the results of this study will lead to improved estimates of mass and carbon flux in the study area.

Efficient ship weather routing using probabilistic roadmaps

This paper introduces the probabilistic roadmap (PRM) concept in maritime transportation for solving the ship weather routing (SWR) problem. SWR is a path finding problem that seeks for the optimum route (path) for a ship moving from an initial port to a final desired port considering the weather conditions (winds, waves, sea currents). PRM is an old effective algorithm for robot motion planning based on a systematic use of a graph-based map which represents the robot's workspace. Using this map PRM explores feasible paths around the obstacles until finding a collision-free path between the starting and goal configurations of the robot. Considering the digital map of the ship's navigation area as well as forecasting data (updated every 3 h) concerning the weather conditions, a modified PRM algorithm is presented for tackling SWR. The proposed algorithm starts by taking random samples across the ship's navigation area which follow a particular distribution. Then, it uses a local planner to construct a large undirected graph (a roadmap) with nodes all the generated sample points connected with feasible (collision-free) edges (paths). Each path is related with a weight estimated by considering the weather conditions in the corresponding sea's region. Finally, given the departure and desired arrival ports, a modified Dijkstra's algorithm is applied to the resulting graph to search for the optimal path in terms of both fuel consumption and travel time that connects the two ports in the roadmap. The proposed algorithm operates in real-time determining the best solution within less than 1 min. Simulation simulations over the Aegean archipelagos as well as the Mediterranean Sea demonstrate the efficiency of the developed algorithm.

Sperm whale acoustic ecology investigations using Jeffrey Nystuen‘s Passive Aquatic Listeners

When Jeffrey Nystuen invented the Passive Aquatic Listener (PAL) for quantifying rainfall and wind speed using underwater sound spectra, he considered all biological sounds in the recordings as noise. Using this noise data, I built a doctoral thesis, comprised of three published papers. None of this would have happened without Jeff’s continuous encouragement and support. Here, we present results from analyzing (1) five years (2007–2012) of PAL recordings from Ocean Station PAPA (OSP) in the offshore Gulf of Alaska; and (2) 19 months of PAL data from two sites, Pylos and Athos Stations (in the Hellenic Trench and North Aegean Trough respectively), in the Greek Seas, investigating the acoustic ecology of sperm whales (Physeter macrocephalus). Results of the bioacoustic analysis revealed the year-round presence of sperm whales at OSP and the Ionian Sea, with higher detections during the warm seasons. The sperm whale time series from OSP was correlated with in situ and remotely-sensed oceanographic variables to improve our understanding of global-warming-driven changes in the pelagic ecosystem of the NE Subarctic Pacific. Results from the Hellenic Trench emphasize the risk from increased shipping noise and contribute to the conservation efforts for the small, endangered sperm whale population in an understudied region.

Listening to the raindrops from underwater for weather and climate

Jeffrey A. Nystuen is a pioneer in using the passive acoustic method to measure oceanic rainfall. Under Nystuen’s efforts, a self-contained passive acoustic recording device called the acoustic rain gauges were deployed all over the world, from a brackish pond in Florida, Carr inlet in Puget Sound, Crater Lake in Oregon, BioSphere II in Arizona, then to the South China Sea, the Pacific Ocean, the Taiwan strait, the Ionian Sea in Greece, the Aleutian Islands and ocean station Papa. This simple device records long-term spectra of sound pressure levels with minimum data screening, could detect the presence of oceanic rainfall, and provide estimates of rain rate and surface wind speed. Nystuen’s inspirational works over the past three decades set an example and path for future scientists and engineers to foster curiosity, pursue exploration and make discoveries.

Pelagic calcium carbonate production and shallow dissolution in the North Pacific Ocean

Planktonic calcifying organisms play a key role in regulating ocean carbonate chemistry and atmospheric CO2. Surprisingly, references to the absolute and relative contribution of these organisms to calcium carbonate production are lacking. Here we report quantification of pelagic calcium carbonate production in the North Pacific, providing new insights on the contribution of the three main planktonic calcifying groups. Our results show that coccolithophores dominate the living calcium carbonate (CaCO3) standing stock, with coccolithophore calcite comprising ~90% of total CaCO3 production, and pteropods and foraminifera playing a secondary role. We show that pelagic CaCO3 production is higher than the sinking flux of CaCO3 at 150 and 200 m at ocean stations ALOHA and PAPA, implying that a large portion of pelagic calcium carbonate is remineralised within the photic zone; this extensive shallow dissolution explains the apparent discrepancy between previous estimates of CaCO3 production derived from satellite observations/biogeochemical modeling versus estimates from shallow sediment traps. We suggest future changes in the CaCO3 cycle and its impact on atmospheric CO2 will largely depend on how the poorly-understood processes that determine whether CaCO3 is remineralised in the photic zone or exported to depth respond to anthropogenic warming and acidification.

The lateral transport of zooplankton explains trophic and taxonomic similarities over the zonal gradient of central Chile

The highly productive upwelling zone in the Southeast Pacific provides inputs of C and N to the oceanic deep-water system via lateral transport, although the quality of this organic matter, the organisms being transported, and the controlling mechanisms are unclear. Here, we assessed whether the taxonomic and trophic structure of zooplankton over more oceanic offshore waters differ from that of zooplankton located in the upwelling zone, along with the characterization of the oceanographic processes and variables associated with the lateral transport. For this, epipelagic, mesopelagic, and bathypelagic zooplankton along with oceanographic variables and particulate organic matter (POM) were analyzed at the upwelling zone and adjacent oceanic stations off Central Chile (27–33°S), some of which were located over the Atacama trench, during September 2016. The community structure of size-fractioned zooplankton (<200 μm, 200–500 μm, 500–1000 μm, 1000–2000 μm, and >2000 μm size classes) was assessed by an automated method, along with the analysis of the isotopic niche computed from their δ 15 N and δ 13 C. The isotope signatures of POM indicated that diatoms contributed mostly to production of new organic C, being the main food source for small-sized zooplankton in coastal waters. The zooplankton community structure differed between the upwelling and oceanic areas, but their isotopic signature showed a large overlap (78%). Satellite-derived geostrophic flow and the depth of the mixed layer appeared as the main factors explaining the homogeneity in the isotopic and biogeochemical signatures of zooplankton between the upwelling zone and offshore waters. Cross-shelf advection is thus suggested as a key process promoting zooplankton export to the deep-water ecosystem, including the ultra-deep Atacama Trench. • The organic matter produced in the upwelling zone can be transported over the Atacama trench by strong offshore advection. • Isotopic niches of zooplankton from the Atacama Trench and the upwelling zone exhibit large overlapping (78%). • The upwelling systems acts as a C subsidiary for the offshore deep-sea ecosystem including the Atacama Trench.

A new method to retrieve rainfall intensity level from rain-contaminated X-band marine radar image

ABSTRACT In this study, a new methodcombining wave-number energy spectrum (WES) and Genetic algorithm-back propagation neural network (GA-BPNN) isproposed to retrieve the rainfall intensity level from rain-contaminated X-bandmarine radar image. Since the intensity of spatialrainfall can be reflected by the distribution of energy in the wavenumberfrequency domain, the obtained WES is divided into three wavenumber segments(low, medium and high wavenumber segments), and the ratio of the wavenumber ineach wavenumber segment to the total wavenumber is calculated separately as the characteristicparameters. Based on the excellent networkconvergence speed and data prediction accuracy of the GA-BPNN, these calculatedparameters are input into the constructed GA-BPNN for training to complete thetask of rainfall intensity level retrieval. The proposed method is tested usingdata collected at the ocean observation station of Haitan Island in PingtanCounty. Referring to the actual rainfallintensity synchronously recorded by the rain gauge, the retrieval accuracy ofthe proposed method is 97.4%, which is 4.3% higher than that of back propagation neural network (BPNN) not optimizedby Geneticalgorithm(GA). In addition, compared with theretrieval performance of the ratio of zero intensity to echo (RZE) method basedon the occlusion area of radar image, the retrievalaccuracy of the proposed method is improved by about 12.9%.