Patra PK, Dlugokencky EJ, Elkins JW, Dutton GS, Tohjima Y, Sasakawa M, Ito A, Weiss RF, Manizza M, Krummel PB, et al. Forward and Inverse Modelling of Atmospheric Nitrous Oxide Using MIROC4-Atmospheric Chemistry-Transport Model. Journal of the Meteorological Society of Japan. Ser. II [Internet]. 2022. Publisher's VersionAbstract
Atmospheric nitrous oxide (N2O) contributes to global warming and stratospheric ozone depletion, so reducing uncertainty in estimates of emissions from different sources is important for climate policy. Here, we simulate atmospheric N2O using an atmospheric chemistry-transport model (ACTM), and the results are first compared with the in situ measurements. Five combinations of known (a priori) N2O emissions due to natural soil, agricultural land, other human activities and sea-air exchange are used. The N2O lifetime is 127.6 ± 4.0 yr in the control ACTM simulation (range indicate interannual variability). Regional N2O emissions are optimised by Bayesian inverse modelling for 84 partitions of the globe at monthly intervals, using measurements at 42 sites around the world covering 1997-2019. The best estimate global land and ocean emissions are 12.99 ± 0.22 and 2.74 ± 0.27 TgN yr−1, respectively, for 2000-2009, and 14.30 ± 0.20 and 2.91 ± 0.27 TgN yr−1, respectively, for 2010-2019. On regional scales, we find that the most recent ocean emission estimation, with lower emissions in the Southern Ocean regions, fits better with that predicted by the inversions. Marginally higher (lower) emissions than the inventory/model for the tropical (extra-tropical) land regions is estimated and validated using independent aircraft observations. Global land and ocean emission variabilities show statistically significant correlation with El Niño Southern Oscillation (ENSO). Analysis of regional land emissions shows increases over America (Temperate North, Central, Tropical), Central Africa, and Asia (South, East and Southeast) between the 2000s and 2010s. Only Europe as a whole recorded a slight decrease in N2O emissions due to chemical industry. Our inversions suggest revisions to seasonal emission variations for 3 of the 15 land regions (East Asia, Temperate North America and Central Africa), and the Southern Ocean region. The terrestrial ecosystem model (VISIT) is able to simulate annual total emissions in agreement with the observed N2O growth rate since 1978, but the lag-time scales of N2O emissions from nitrogen fertiliser application may need to be revised.
Cram JA, Fuchsman CA, Duffy ME, Pretty JL, Lekanoff RM, Neibauer JA, Leung SW, Huebert KB, Weber TS, Bianchi D, et al. Slow particle remineralization, rather than suppressed disaggregation, drives efficient flux transfer through the Eastern Tropical North Pacific Oxygen Deficient Zone. Global Biogeochemical Cycles [Internet]. 2022;36 (1) :e2021GB007080. Publisher's VersionAbstract

Models and observations suggest that particle flux attenuation is lower across the mesopelagic zone of anoxic environments compared to oxic environments. Flux attenuation is controlled by microbial metabolism as well as aggregation and disaggregation by zooplankton, all of which shape the relative abundance of differently sized particles. Observing and modeling particle spectra can provide information about the contributions of these processes. We measured particle size spectrum profiles at one station in the oligotrophic Eastern Tropical North Pacific Oxygen Deficient Zone (ETNP ODZ) using an underwater vision profiler (UVP), a high-resolution camera that counts and sizes particles. Measurements were taken at different times of day, over the course of a week. Comparing these data to particle flux measurements from sediment traps collected over the same time-period allowed us to constrain the particle size to flux relationship, and to generate highly resolved depth and time estimates of particle flux rates. We found that particle flux attenuated very little throughout the anoxic water column, and at some time points appeared to increase. Comparing our observations to model predictions suggested that particles of all sizes remineralize more slowly in the ODZ than in oxic waters, and that large particles disaggregate into smaller particles, primarily between the base of the photic zone and 500 m. Acoustic measurements of multiple size classes of organisms suggested that many organisms migrated, during the day, to the region with high particle disaggregation. Our data suggest that diel-migrating organisms both actively transport biomass and disaggregate particles in the ODZ core.

Guiet J, Bianchi D, Maury O, Barrier N, Kessouri F. Movement shapes the structure of fish communities along a cross-shore section in the California Current. Frontiers in Marine Science [Internet]. 2022;9. Publisher's VersionAbstract

Pelagic fish communities are shaped by bottom-up and top-down processes, transport by currents, and active swimming. However, the interaction of these processes remains poorly understood. Here, we use a regional implementation of the APex ECOSystem Model (APECOSM), a mechanistic model of the pelagic food web, to investigate these processes in the California Current, a highly productive upwelling system characterized by vigorous mesoscale circulation. The model is coupled with an eddy-resolving representation of ocean currents and lower trophic levels, and is tuned to reproduce observed fish biomass from fisheries independent trawls. Several emergent properties of the model compare realistically with observations. First, the epipelagic community accounts for one order of magnitude less biomass than the vertically migratory community, and is composed by smaller species. Second, the abundance of small fish decreases from the coast to the open ocean, while the abundance of large fish remains relatively uniform. This in turn leads to flattening of biomass size-spectra away from the coast for both communities. Third, the model reproduces a cross-shore succession of small to large sizes moving offshore, consistent with observations of species occurrence. These cross-shore variations emerge in the model from a combination of: (1) passive offshore advection by the mean current, (2) active swimming toward coastal productive regions to counterbalance this transport, and (3) mesoscale heterogeneity that reduces the ability of organisms to return to coastal waters. Our results highlight the importance of passive and active movement in structuring the pelagic food web, and suggest that a representation of these processes can help to improve the realism in simulations with marine ecosystem models.

Le Mézo P, Guiet J, Scherrer K, Bianchi D, Galbraith E. Global nutrient cycling by commercially-targeted marine fish. Biogeosciences Discussions. 2021 :1–37.
Bianchi D, Carozza DA, Galbraith ED, Guiet J, DeVries T. Estimating global biomass and biogeochemical cycling of marine fish with and without fishing. Science advances [Internet]. 2021;7 (41) :eabd7554. Publisher's VersionAbstract
The biomass and biogeochemical roles of fish in the ocean are ecologically important but poorly known. Here, we use a data-constrained marine ecosystem model to provide a first-order estimate of the historical reduction of fish biomass due to fishing and the associated change in biogeochemical cycling rates. The pre-exploitation global biomass of exploited fish (10 g to 100 kg) was 3.3 ± 0.5 Gt, cycling roughly 2% of global primary production (9.4 ± 1.6 Gt year−1) and producing 10% of surface biological export. Particulate organic matter produced by exploited fish drove roughly 10% of the oxygen consumption and biological carbon storage at depth. By the 1990s, biomass and cycling rates had been reduced by nearly half, suggesting that the biogeochemical impact of fisheries has been comparable to that of anthropogenic climate change. Our results highlight the importance of developing a better mechanistic understanding of how fish alter ocean biogeochemistry.
Tittensor DP, Novaglio C, Harrison CS, Heneghan RF, Barrier N, Bianchi D, Bopp L, Bryndum-Buchholz A, Britten GL, Büchner M, et al. Next-generation ensemble projections reveal higher climate risks for marine ecosystems. Nature climate change [Internet]. 2021;11 (11) :973–981. Publisher's VersionAbstract
Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth system model outputs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to provide insights into how projected climate change will affect future ocean ecosystems. Compared with the previous generation CMIP5-forced Fish-MIP ensemble, the new ensemble ecosystem simulations show a greater decline in mean global ocean animal biomass under both strong-mitigation and high-emissions scenarios due to elevated warming, despite greater uncertainty in net primary production in the high-emissions scenario. Regional shifts in the direction of biomass changes highlight the continued and urgent need to reduce uncertainty in the projected responses of marine ecosystems to climate change to help support adaptation planning.
Kessouri F, McLaughlin K, Sutula M, Bianchi D, Ho M, McWilliams JC, Renault L, Molemaker J, Deutsch C, Leinweber A. Configuration and validation of an oceanic physical and biogeochemical model to investigate coastal eutrophication in the Southern California Bight. Journal of Advances in Modeling Earth Systems. 2021;13 (12) :e2020MS002296.
Clements DJ, Yang S, Weber TS, McDonnell AMP, Kiko R, Stemmann L, Bianchi D. A new estimate of Global Ocean Carbon Flux from In Situ Optical Observations and Supervised Learning. Earth and Space Science Open Archive ESSOAr [Internet]. 2021. Publisher's Version
Sutula M, Ho M, Sengupta A, Kessouri F, McLaughlin K, McCune K, Bianchi D. A baseline of terrestrial freshwater and nitrogen fluxes to the southern california bight, usa. Marine Pollution Bulletin [Internet]. 2021;170 :112669. Publisher's Version
Kessouri F, McWilliams JC, Bianchi D, Sutula M, Renault L, Deutsch C, Feely RA, McLaughlin K, Ho M, Howard EM. Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system. Proceedings of the National Academy of Sciences [Internet]. 2021;118 (21). Publisher's Version
Deutsch C, Frenzel H, McWilliams JC, Renault L, Kessouri F, Howard E, Liang J-H, Bianchi D, Yang S. Biogeochemical variability in the California Current system. Progress in Oceanography [Internet]. 2021 :102565. Publisher's Version
Moscoso JE, Stewart AL, Bianchi D, McWilliams JC. The Meridionally Averaged Model of Eastern Boundary Upwelling Systems (MAMEBUSv1.0). Geoscientific Model Development [Internet]. 2021;14 (2) :763–794. Publisher's Version
Sutula M, Ho M, Sengupta A, Kessouri F, McLaughlin K, McCune K, Bianchi D. Dataset of Terrestrial Fluxes of Freshwater, Nutrients, Carbon, and Iron to the Southern California Bight, U.S.A. Data in Brief [Internet]. 2021 :106802. Publisher's VersionAbstract
The Southern California Bight (SCB) is an upwelling-dominated, open embayment on the U.S. West Coast and receives discharges of anthropogenically-enhanced freshwater, nutrients, carbon, and other materials. These inputs include direct point sources discharged from wastewater treatment (WWT) plants via ocean outfalls and point, non-point, and natural sources discharged via coastal rivers. We assembled a daily time series over 1971-2017 of discharges from large WWT plants ≥ 50 million gallon per day (MGD) and 1997-2017 from small WWT plants and coastal rivers. Constituents include nitrogen, phosphorus, organic carbon, alkalinity, iron, and silica. Data from research studies, several government and non-government agency databases containing discharge monitoring reports, river flow gauges, and other collateral information were compiled to produce this dataset. Predictive models and expert analysis addressed unmonitored sources and data gaps. The time series of terrestrial discharge and fluxes are provided with location of coastal discharge point or tributary. The data are deposited in a repository found in Sutula et al. [1].
Kessouri F, McLaughlin K, Sutula MA, Bianchi D, Ho M, McWilliams JC, Renault L, Molemaker J, Deutsch CA, Leinweber A. Configuration and validation of an oceanic physical and biogeochemical model to investigate coastal eutrophication: case study in the Southern California Bight. [Internet]. 2020. Publisher's Version
Weber T, Bianchi D. Efficient Particle Transfer to Depth in Oxygen Minimum Zones of the Pacific and Indian Oceans. Frontiers in Earth Science [Internet]. 2020;8 :376. Publisher's VersionAbstract
The remineralization depth of sinking organic particles controls the efficiency of the biological carbon pump by setting the sequestration timescale of remineralized carbon in the ocean interior. Oxygen minimum zones (OMZs) have been identified as regions of elevated particle transfer and efficient carbon sequestration at depth, but direct measurements remain sparse in these regions and only provide snapshots of the particle flux. Here, we use remineralization tracers to reconstruct time-mean particle flux profiles in the OMZs of the Eastern Tropical Pacific and the Arabian Sea. Compared to the surrounding tropical waters, both OMZs exhibit slow flux attenuation between 100 and 1000 m where suboxic waters reside, and sequester carbon beneath 1000 m more than twice as efficiently. Using a mechanistic model of particle sinking, remineralization, and disaggregation, we show that three different mechanisms might explain the shape of the OMZ flux profiles: (i) a significant slow-down of remineralization when carbon oxidation transitions from aerobic to anaerobic respiration (e.g., denitrification); (ii) the exclusion of zooplankton that mediate disaggregation of large particles from suboxic waters, and (iii) the limitation of remineralization by the diffusive supply of oxidants (oxygen and nitrate) into large particles. We show that each mechanism leaves a unique signature in the size distribution of particles, suggesting that observations with optical instruments such as Underwater Vision Profilers hold great promise for understanding the drivers of efficient carbon transfer though suboxic water columns. In turn, this will allow more accurate prediction of future changes in carbon sequestration as the ocean loses oxygen in a warming climate.
Howard EM, Frenzel H, Kessouri F, Renault L, Bianchi D, McWilliams JC, Deutsch C. Attributing Causes of Future Climate Change in the California Current System With Multimodel Downscaling. Global Biogeochemical Cycles [Internet]. 2020;34 (11) :e2020GB006646. Publisher's VersionAbstract
Abstract Coastal winds in the California Current System (CCS) are credited with the high productivity of its planktonic ecosystem and the shallow hypoxic and corrosive waters that structure diverse macrofaunal habitats. These winds thus are considered a leading mediator of climate change impacts in the CCS and other Eastern Boundary Upwelling systems. We use an eddy-permitting regional model to downscale the response of the CCS to three of the major distinct climate changes commonly projected by global Earth System Models: regional winds, ocean warming and stratification, and remote water chemical properties. An increase in alongshore winds intensifies spring upwelling across the CCS, but this response is muted by increased stratification, especially during summer. Despite the seasonal shift in regional wind-driven upwelling, basin-scale changes are the decisive factor in the response of marine ecosystem properties including temperature, nutrients, productivity, and oxygen. Downscaled temperature increases and dissolved oxygen decreases are broadly consistent with coarse resolution Earth System Models, and these projected changes are large and well constrained across the models, whereas nutrient and productivity changes are small compared to the intermodel spread. These results imply that global models with poor resolution of coastal processes nevertheless yield important information about the dominant climate impacts on coastal ecosystems.
McCoy D, Bianchi D, Stewart AL. Global observations of submesoscale coherent vortices in the ocean. Progress in Oceanography [Internet]. 2020;189 :102452. Publisher's VersionAbstract
Subsurface-intensified anticyclones are ubiquitous in the ocean, yet their impact on the large-scale transport of heat, salt and chemical tracers is poorly understood. These submesoscale coherent vortices (SCVs) can trap and advect waters thousands of kilometers away from the formation region, providing a transport pathway that is unresolved by low-resolution Earth System Models. However, knowledge of the importance of these eddies for the large scale circulation is hindered by the lack of systematic observations. Here, we take advantage of the global network of Argo floats to identify occurrences of these eddies, which appear as weakly stratified anomalous water masses with Gaussian-shaped vertical structures. We develop a general algorithm to detect subsurface eddies that have propagated away from their source region, and apply it to the database of Argo float profiles, resulting in roughly 4000 detections from more than 20 years of observations. We further group detections into regional populations to identify hot-spots of generation and mechanisms of formation. Analysis of regional SCV statistics reveals important sites of SCV generation in Eastern Boundary Upwelling Systems, marginal sea overflows, and mode water formation regions along major open-ocean fronts. Because of the heat and salt anomaly contained within their cores, SCV could leave a significant imprint on the hydrographic properties of water masses in regions of high SCV density.
Kessouri F, Bianchi D, Renault L, McWilliams JC, Frenzel H, Deutsch CA. Submesoscale Currents Modulate the Seasonal Cycle of Nutrients and Productivity in the California Current System. Global Biogeochemical Cycles [Internet]. 2020;34 (10) :e2020GB006578. Publisher's VersionAbstract
In the California Current, subduction by mesoscale eddies removes nutrients from the coastal surface layer, counteracting upwelling and quenching productivity. Submesoscale eddies are also ubiquitous in the California Current, but their biogeochemical role has not been quantified yet in the region. Here, we present results from a physical-biogeochemical model of the California Current run at a resolution of 1 km, sufficient to represent submesoscale dynamics. By comparing it with a coarser simulation run at 4 km resolution, we demonstrate the importance of submesoscale currents for the seasonal cycles of nutrients and organic matter and highlight the existence of different regimes along a cross-shore gradient. In the productive coastal region, submesoscale currents intensify quenching and reduce productivity, further counteracting wind-driven upwelling. In the offshore oligotrophic region, submesoscale currents enhance the upward transport of nutrients, fueling a dramatic increase in new production. These effects are modulated by seasonality, strengthening near the coast during upwelling and offshore in wintertime. The intensification of the transport by submesoscale eddies drives an adjustment of the planktonic ecosystem, with a reduction of plankton biomass, productivity, and size near the coast and an increase offshore. In contrast, organic matter export by sinking particles and subduction of detritus and living cells are enhanced nearly everywhere. Similar processes are likely important in other regions characterized by seasonal upwelling, for example, other eastern boundary upwelling systems.
Wilson ST, Al-Haj AN, Bourbonnais A, Frey C, Fulweiler RW, Kessler JD, Marchant HK, Milucka J, Ray NE, Suntharalingham P, et al. Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment. Biogeosciences [Internet]. 2020;17 (22) :5809–5828. Publisher's Version
Yang S, Chang BX, Warner MJ, Weber TS, Bourbonnais AM, Santoro AE, Kock A, Sonnerup RE, Bullister JL, Wilson ST, et al. Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle. Proceedings of the National Academy of Sciences. 2020;117 (22) :11954–11960.