ALBERT

Description: Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open‐ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13C values of 0.8‰–2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel‐derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13C‐rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota.

Description: A global dataset of carbon stable isotope (δ13C) values from yellowfin, bigeye, and albacore tuna muscle tissue (n = 4275) was used to develop a novel tool to infer broad-scale movement and residency patterns of these highly mobile marine predators. This tool was coupled with environmental models and lipid content (C:N ratio) of tuna muscle tissues to examine ocean warming impacts on tuna ecology and bioenergetic condition across Longhurst provinces. Over a 16-year study period (2000–2015), latitudinal gradients in tuna δ13C values were consistent, with values decreasing with increasing latitude. Tuna δ13C values, reflecting modelled global phytoplankton δ13C landscapes (“isoscapes”), were largely related to spatial changes in oxygen concentrations at depth and temporal changes in sea surface temperature. Observed tuna isoscapes (δ13CLScorr), corrected for lipid content and the Suess effect (oceanic changes in CO2 over time), were subtracted from model-predicted baseline isoscapes (Δ13Ctuna-phyto) to infer spatial movement and residency patterns of the different tuna species. Stable isotope niche width was calculated for each Longhurst province using Δ13Ctuna-phyto and baseline-corrected nitrogen isotope (δ15Ntuna-phyto) values to further quantify isotopic variability as evidence of movements across isoscapes. A high degree of movement—defined as the deviation from the expected range of Δ13Ctuna-phyto values— was evident in three Longhurst provinces: Guinea current coast, Pacific equatorial divergence, and the North Pacific equatorial counter current. The highest level of population dispersal (variability in Δ13Ctuna-phyto values) was observed in Longhurst provinces within the western and central Pacific Oceans and in the Guinea current coast. While lipid content was low in yellowfin and bigeye, high and variable lipid stores in albacore muscle were consistent with seasonal movements between productive foraging and oligotrophic spawning habitats. Our ability to characterize tuna movement patterns without ambiguity remains challenged by uncertainty in trophic discrimination factors and ecological (e.g. diet variability) processes. However, this study illustrates that model-corrected δ13C values are a valuable, relatively cost-effective tool for identifying potential areas of mixing across management zones, particularly when electronic tagging studies are limited or absent. Stable isotope analyses of tuna tissues can therefore be an additional tool for guiding spatial stock assessments on top predator movement, dispersal patterns, and how they may be altered under a changing climate.

Description: Marine particulate organic carbon-13 stable isotope ratios (δ13CPOC) provide insights in understanding carbon cycling through the atmosphere, ocean, and biosphere. They have been used to trace the input of anthropogenic carbon in the marine ecosystem due to the distinct isotopically light signature of anthropogenic emissions. However, δ13CPOC is also significantly altered during photosynthesis by phytoplankton, which complicates its interpretation. For such purposes, robust spatio-temporal coverage of δ13CP OC observations is essential. We collected all such available data sets, merged and homogenized them to provide the largest available marine δ13CPOC data set (Verwega et al., 2021). The data set consists of 4732 data points covering all major ocean basins beginning in the 1960s. We describe the compiled raw data, compare different observational methods, and provide key insights in the temporal and spatial distribution that is consistent with previously observed patterns. The main different sample collection methods (bottle, intake, net, trap) are generally consistent with each other when comparing within regions. An analysis of 1990s mean δ13CP OC values in an meridional section accross the Atlantic Ocean shows relatively high values (≥ −22 ‰) in the low latitudes (〈 30°) trending towards lower values in the Arctic Ocean (∼ −24 ‰) and Southern Ocean (≤ −28 ‰). The temporal trend since the 1960s shows a decrease of mean δ13CPOC by more than 3 ‰ in all basins except for the Southern Ocean which shows a weaker trend but contains relatively poor multi-decadal coverage.

Description: Global anthropogenic mercury (Hg) emissions to the atmosphere since industrialization are widely considered to be responsible for a significant increase in surface ocean Hg concentrations. Still unclear is how those inputs are converted into toxic methylmercury (MeHg) then transferred and biomagnified in oceanic food webs. We used a unique long-term and continuous dataset to explore the temporal Hg trend and variability of three tropical tuna species (yellowfin, bigeye, and skipjack) from the southwestern Pacific Ocean between 2001 and 2018 (n = 590). Temporal trends of muscle nitrogen (δ15N) and carbon (δ13C) stable isotope ratios, amino acid (AA) δ15N values and oceanographic variables were also investigated to examine the potential influence of trophic, biogeochemical and physical processes on the temporal variability of tuna Hg concentrations. For the three species, we detected significant inter-annual variability but no significant long-term trend for Hg concentrations. Inter-annual variability was related to the variability in tuna sampled lengths among years and to tuna muscle δ15N and δ13C values. Complementary AA- and model-estimated phytoplankton δ15N values suggested the influence of baseline processes with enhanced tuna Hg concentrations observed when dinitrogen fixers prevail, possibly fuelling baseline Hg methylation and/or MeHg bioavailability at the base of the food web. Our results show that MeHg trends in top predators do not necessary capture the increasing Hg concentrations in surface waters suspected at the global oceanic scale due to the complex and variable processes governing Hg deposition, methylation, bioavailability and biomagnification. This illustrates the need for long-term standardized monitoring programs of marine biota worldwide.

Description: Nitrogen and carbon stable isotope data sets are commonly used to assess complex population to ecosystem responses to natural or anthropogenic changes at regional to global spatial scales, and monthly to decadal timescales. Measured in the tissues of consumers, nitrogen isotopes (delta N-15) are primarily used to estimate trophic position while carbon isotopes (delta C-13) describe habitat associations and feeding pathways. Models of both delta N-15 and delta C-13 values and their associated variance can be used to estimate likely dietary contributions and niche width and provide inferences about consumer movement and migration. Stable isotope data have added utility when used in combination with other empirical data sets (e.g., stomach content, movement tracking, bioregionalization, contaminant, or fisheries data) and are increasingly relied upon in food web and ecosystem models. While numerous regional studies publish tables of mean delta N-15 and delta C-13 values, limited individual records have been made available for wider use. Such a deficiency has impeded full utility of the data, which otherwise would facilitate identification of macroscale patterns. The data provided here consist of 4,498 records of individuals of three tuna species, Thunnus alalunga, T. obesus, and T. albacares sampled from all major ocean basins from 2000 to 2015. For each individual tuna, we provide a record of the following: species name, sampling date, sampling location, tuna length, muscle bulk and baseline corrected delta N-15 values, and muscle bulk and, where available, lipid corrected delta C-13 values. We provide these individual records to support comparative studies and more robust modeling projects seeking to improve understanding of complex marine ecosystem dynamics and their responses to a changing environment. There are no copyright restrictions for research and/or teaching purposes. Users are requested to acknowledge their use of the data in publications, research proposals, websites, and other outlets following the citation instructions in Class III, Section B.

Description: While research on ocean acidification (OA) impacts on coral reefs has focused on calcification, relatively little is known about effects on coral photosynthesis and respiration, despite these being among the most plastic metabolic processes corals may use to acclimatize to adverse conditions. Here, we present data collected between 2016 and 2018 at three natural CO2 seeps in Papua New Guinea where we measured the metabolic flexibility (i.e. in hospite photosynthesis and dark respiration) of 12 coral species. Despite some species-specific variability, metabolic rates as measured by net oxygen flux tended to be higher at high pCO2 (ca 1200 µatm), with increases in photosynthesis exceeding those of respiration, suggesting greater productivity of Symbiodiniaceae photosynthesis in hospite, and indicating the potential for metabolic flexibility that may enable these species to thrive in environments with high pCO2. However, laboratory and field observations of coral mortality under high CO2 conditions associated with coral bleaching suggests that this metabolic subsidy does not result in coral higher resistance to extreme thermal stress. Therefore, the combined effects of OA and global warming may lead to a strong decrease in coral diversity despite the stimulating effect on coral productivity of OA alone.

Description: A new version (2022) is available: https://doi.org/10.1594/PANGAEA.946915 Marine particulate organic carbon-13 stable isotope ratios (δ13CPOC) provide additional constraints and insights on the cycling of carbon from dissolved pools to the marine ecosystem including anthropogenic contributions. For such purposes, robust spatio-temporal coverage of δ13CPOC observations is essential. We collected all such available known data sets, merged and uniformed them to provide – to the best of our knowledge – the largest available marine δ13CPOC data set. The data set consists of 4732 data points covering all major ocean basins from the 1960s to 2010s. We provide the data in twenty-one different files for best direct application on specific research purposes: a csv file including the 4732 δ13CPOC measurements, their anomalies relative to their mean −23.96 ‰ as well as all available meta-information a NetCDF file including an interpolation onto the 1°x1°-resolution grid based on the World Ocean Atlas (WOA18) data product of all δ13CPOC measurements with full spatio-temporal metadata, averaging all observations from each year together, each year accounting for a time increment on the time axis twelve NetCDF files - one for each month of the year - including an interpolation onto the 1°x1°-resolution grid based on the World Ocean Atlas (WOA18) data product of all δ13CPOC measurements with full spatio-temporal metadata, averaging only observations from the respective month, each year accounting for a time increment on the time axis a NetCDF file including an interpolation onto a 1.8°x3.6°-resolution grid of a δ13CPOC simulating model of all δ13CPOC measurements with full spatial metadata six NetCDF files – one for each decade between the 1960s and 2010s – including an interpolation onto the 1.8°x3.6°-resolution grid of a δ13CPOC simulating model of all δ13CPOC measurements with full spatial metadata and available sample year information

Description: Marine particulate organic carbon-13 stable isotope ratios (δ13C-POC) provide additional constraints and insights into the cycling of carbon from dissolved pools to marine ecosystems including anthropogenic contributions. For such purposes, a robust spatio-temporal coverage of δ13C-POC observations is essential. In this data product, we collected and merged two large data compilations (Close and Henderson, 2020; St John Glew et al., 2021) into our previous version (Verwega et al., 2021) to provide the largest available marine δ13C-POC data set. Additionally, we have incorporated more meta information including if the samples were acidified before measuring the isotope ratio. The data set consists of 6952 data points covering the global ocean from year 1966 to 2019. We provide the data in the following two formats for best application on specific research purposes: (1) A spreadsheet file including all collected individual data and meta-information; (2) Network Common Data Form (NetCDF) files that only include acidified samples (6633 total data points) interpolated onto a global ocean grid (1°x1° horizontal resolution, 33 vertical levels based on World Ocean Atlas 2009) for each month individually and all months combined, with each file covering the temporal range from year 1966 to 2019.