93 research outputs found
Export of organic carbon by ocean biological pump from GYRE ocean model
No full text<p>Model data of the biological pump of organic carbon computed from the idealized ocean model GYRE used in: Resplandy, Lévy and McGillicuddy (2019). Effects of eddy-driven subduction on ocean biological carbon pump. Global Biogeochemical Cycles. Readme file describes the data.</p>LR is funded by NASA EXPORTS awards 80NSSC17K0555 and NNX16AR50G. DJM gratefully acknowledges support of NSF and NASA grant NNX16AR50G. ML is supported by Centre National d'Etudes Spatiales (CNES) and by the French Agence Nationale de la Recherche award SOBUMPS ANR-16-CE01-0014
ESM2025 Research Highlight - Modelling carbon fluxes from the land to the open ocean: a journey along inland waters, estuaries, tidal wetlands and the coastal ocean
No full textA research highlight about the modelling of land-to-ocean aquatic continuum carbon fluxes. Based on the publication:
Regnier, P., Resplandy, L., Najjar, R.G. et al. (2022) The land-to-ocean loops of the global carbon cycle. Nature 603, 401–410 . https://doi.org/10.1038/s41586-021-04339-
How does dynamical spatial variability impact 234Th-derived estimates of organic export?
No full textIn this study we first evaluate the small-scale spatial variability of particulate export, using a set of synoptic thorium-234 activity observations sampled within a one-degree radius. These data show significant variability of surface thorium activity on scales of the order of 100 km (?270–550 dpm m?3). This patchiness of export potentially affects the robustness of point observations and our interpretation of them. Motivated by these observations we subsequently couple an explicit model of thorium-234 dynamics to a coupled physical–biogeochemical basin model capable of resolving these small-scales. The model supports the observations in displaying marked thorium variability on spatial scales of the order of 100 km and smaller, with highest values in the regions of large eddy kinetic energy and large primary productivity. The model is also used to quantify the impact of small-scale variability on export estimates. Our model shows that the primary source of error associated with the presence of small-scale spatial variability is related to the standard assumptions of steady state and non-steady state (>40% during bloom condition). The non-steady state method can misinterpret variations due to patchiness in thorium activity as temporal changes and lead to errors larger than those introduced by the simpler steady state approach. We show that the non-steady state approach could improve the flux estimates in some cases if the sampling was conducted in a Lagrangian framework. Undersampling the spatial variability results in further bias (>20%) that can be reduced when the sampling density is increased. Finally, errors due to the dynamical transport of thorium associated with small-scale structures are relatively low (<20%) except in regions of high eddy kinetic energy
Hydrological cycle amplification imposes spatial patterns on the climate change response of ocean pH and carbonate chemistry
No full textOcean CO2 uptake and acidification in response to human activities are driven primarily by the rise in atmospheric CO2 but are also modulated by climate change. Existing work suggests that this “climate effect” influences the uptake and storage of anthropogenic carbon and acidification via the global increase in ocean temperature, although some regional responses have been attributed to changes in circulation or biological activity. Here, we investigate spatial patterns in the climate effect on surface ocean acidification (and the closely related carbonate chemistry) in an Earth system model under a rapid CO2-increase scenario and identify a different driving process. We show that the amplification of the hydrological cycle, a robustly simulated feature of climate change, is largely responsible for the spatial patterns in this climate effect at the sea surface. This “hydrological effect” can be understood as a subset of the total climate effect, which includes warming, hydrological cycle amplification, circulation, and biological changes. We demonstrate that it acts through two primary mechanisms: (i) directly diluting or concentrating dissolved ions by adding or removing freshwater and (ii) altering the sea surface temperature, which influences the solubility of dissolved inorganic carbon (DIC) and acidity of seawater. The hydrological effect opposes acidification in salinifying regions, most notably the subtropical Atlantic, and enhances acidification in freshening regions such as the western Pacific. Its single strongest effect is to dilute the negative ions that buffer the dissolution of CO2, quantified as alkalinity. The local changes in alkalinity, DIC, and pH linked to the pattern of hydrological cycle amplification are as strong as the (largely uniform) changes due to warming, explaining the weak increase in pH and DIC seen in the climate effect in the subtropical Atlantic Ocean.</p
Observed small spatial scale and seasonal variability of the CO<sub>2</sub> system in the Southern Ocean
No full textThe considerable uncertainties in the carbon budget of the Southern
Ocean are largely attributed to unresolved variability, in particular
at a seasonal timescale and small spatial scale
(~ 100 km). In this study, the variability of surface
pCO2 and dissolved inorganic carbon (DIC) at seasonal and small spatial scales is
examined using a data set of surface drifters including ~ 80 000
measurements at high spatiotemporal resolution. On spatial scales of
100 km, we find gradients ranging from 5 to 50 μatm
for pCO2 and 2 to 30 μmol kg−1 for DIC,
with highest values in energetic and frontal regions. This result is
supported by a second estimate obtained with sea surface temperature (SST) satellite images and
local DIC–SST relationships derived from drifter observations. We
find that dynamical processes drive the variability of DIC at small
spatial scale in most regions of the Southern Ocean and the cascade of
large-scale gradients down to small spatial scales, leading to
gradients up to 15 μmol kg−1 over
100 km. Although the role of biological activity is more
localized, it enhances the variability up to 30 μmol kg−1
over 100 km. The seasonal cycle of
surface DIC is reconstructed following Mahadevan et al. (2011), using an
annual climatology of DIC and a monthly climatology of mixed layer
depth. This method is evaluated using drifter observations and proves
to be a reasonable first-order estimate of the seasonality in the
Southern Ocean that could be used to validate model simulations. We
find that small spatial-scale structures are a non-negligible source
of variability for DIC, with amplitudes of about a third of the
variations associated with the seasonality and up to 10 times the
magnitude of large-scale gradients. The amplitude of small-scale
variability reported here should be kept in mind when inferring
temporal changes (seasonality, interannual variability, decadal
trends) of the carbon budget from low-resolution observations and models
Concentrations, ratios, and sinking fluxes of major bioelements at Ocean Station Papa
No full text© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Roca-Marti, M., Benitez-Nelson, C. R., Umhau, B. P., Wyatt, A. M., Clevenger, S. J., Pike, S., Horner, T. J., Estapa, M. L., Resplandy, L., & Buesseler, K. O. Concentrations, ratios, and sinking fluxes of major bioelements at Ocean Station Papa. Elementa: Science of the Anthropocene, 9(1), (2021): 00166, https://doi.org/10.1525/elementa.2020.00166.Fluxes of major bioelements associated with sinking particles were quantified in late summer 2018 as part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign near Ocean Station Papa in the subarctic northeast Pacific. The thorium-234 method was used in conjunction with size-fractionated (1–5, 5–51, and >51 μm) concentrations of particulate nitrogen (PN), total particulate phosphorus (TPP), biogenic silica (bSi), and particulate inorganic carbon (PIC) collected using large volume filtration via in situ pumps. We build upon recent work quantifying POC fluxes during EXPORTS. Similar remineralization length scales were observed for both POC and PN across all particle size classes from depths of 50–500 m. Unlike bSi and PIC, the soft tissue–associated POC, PN, and TPP fluxes strongly attenuated from 50 m to the base of the euphotic zone (approximately 120 m). Cruise-average thorium-234-derived fluxes (mmol m–2 d–1) at 120 m were 1.7 ± 0.6 for POC, 0.22 ± 0.07 for PN, 0.019 ± 0.007 for TPP, 0.69 ± 0.26 for bSi, and 0.055 ± 0.022 for PIC. These bioelement fluxes were similar to previous observations at this site, with the exception of PIC, which was 1 to 2 orders of magnitude lower. Transfer efficiencies within the upper twilight zone (flux 220 m/flux 120 m) were highest for PIC (84%) and bSi (79%), followed by POC (61%), PN (58%), and TPP (49%). These differences indicate preferential remineralization of TPP relative to POC or PN and larger losses of soft tissue relative to biominerals in sinking particles below the euphotic zone. Comprehensive characterization of the particulate bioelement fluxes obtained here will support future efforts linking phytoplankton community composition and food-web dynamics to the composition, magnitude, and attenuation of material that sinks to deeper waters.The authors would like to acknowledge support from the National Aeronautics and Space Administration as part of the EXport Processes in the Ocean from RemoTe Sensing program awards 80NSSC17K0555 and 80NSSC17K0662. They also acknowledge the funding from the Woods Hole Oceanographic Institution’s Ocean Twilight Zone study for MRM and KOB, the National Science Foundation Graduate Research Fellowship Program for AMW, and the Ocean Frontier Institute for MRM
Impacts biogéochimiques des processus de haute fréquence à l'échelle régionale et saisonnière
No full textL objectif de ce travail était l'étude de l'impact de processus de haute fréquence (1-90 jours ; 10-100 km) sur l'évolution saisonnière et la distribution grande échelle de la production primaire dans l'océan. La nature et l'effet de ces processus sur la biogéochimie dépendent fortement du contexte régional dynamique. Afin d'obtenir une vision d'ensemble de ces mécanismes de couplage, trois régimes dynamiques caractéristiques des basses et moyennes latitudes ont été considérés : une région d'upwelling côtier dont l'intensité et les échanges côte-large sont modulés par une forte activité tourbillonnaire ; une région oligotrophe sous influence de coups de vent permettant les échanges entre surface et subsurface ; et enfin une région de bloom printanier où la dynamique saisonnière de la couche mélangée est modulée par la sub-mésoéchelle typique de l'océan ouvert.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
Natural variability of CO 2 and O 2 fluxes: What can we learn from centuries-long climate models simulations?
No full textInternational audienc
Impact of submesoscale variability in estimating the air-sea CO<sub>2</sub> exchange: Results from a model study of the POMME experiment
No full textInternational audienceA high-resolution ocean biogeochemical model is used to estimate oceanic pCO2 and air-sea CO2 flux in the NE Atlantic. The model is validated against shipboard and Carioca drifting float data acquired during the POMME experiment. Between winter and spring, the seasonal variability is characterized by a rapid drawdown of pCO2 of ~20 μatm associated with the phytoplankton bloom driving CO2 uptake by the ocean. The model reveals that this uptake propagates northward in response to the northward propagation of the bloom. More remarkably, this study demonstrates intense variability of the carbon system at the submesoscale. Our model predicts filamentary structures of pCO2 that show gradients of 25 μatm over 20 km, consistent with observations from Carioca drifting floats. This submesoscale variability is similar in magnitude to the mean seasonal drawdown. Lagrangian diagnostics suggest that pCO2 small-scale structures are shaped by horizontal stirring of large-scale gradients created by the bloom northward propagation. We compared air-sea flux derived from model pCO2 and from observed pCO2 and estimated the error due to data undersampling to ~15 to 30%. Results from a simulation at coarser resolution showed that the impact of model resolution on air-sea CO2 flux is only ~5%. This suggests that the submesoscale variability of pCO2, although large in amplitude, accounts for small modulation of the net air-sea CO2 flux in this region
iMarNet: an ocean biogeochemistry model intercomparison project within a common physical ocean modelling framework
No full textOcean biogeochemistry (OBGC) models span a wide variety of complexities, including highly simplified nutrient-restoring schemes, nutrient–phytoplankton–zooplankton–detritus (NPZD) models that crudely represent the marine biota, models that represent a broader trophic structure by grouping organisms as plankton functional types (PFTs) based on their biogeochemical role (dynamic green ocean models) and ecosystem models that group organisms by ecological function and trait. OBGC models are now integral components of Earth system models (ESMs), but they compete for computing resources with higher resolution dynamical setups and with other components such as atmospheric chemistry and terrestrial vegetation schemes. As such, the choice of OBGC in ESMs needs to balance model complexity and realism alongside relative computing cost. Here we present an intercomparison of six OBGC models that were candidates for implementation within the next UK Earth system model (UKESM1). The models cover a large range of biological complexity (from 7 to 57 tracers) but all include representations of at least the nitrogen, carbon, alkalinity and oxygen cycles. Each OBGC model was coupled to the ocean general circulation model Nucleus for European Modelling of the Ocean (NEMO) and results from physically identical hindcast simulations were compared. Model skill was evaluated for biogeochemical metrics of global-scale bulk properties using conventional statistical techniques. The computing cost of each model was also measured in standardised tests run at two resource levels. No model is shown to consistently outperform all other models across all metrics. Nonetheless, the simpler models are broadly closer to observations across a number of fields and thus offer a high-efficiency option for ESMs that prioritise high-resolution climate dynamics. However, simpler models provide limited insight into more complex marine biogeochemical processes and ecosystem pathways, and a parallel approach of low-resolution climate dynamics and high-complexity biogeochemistry is desirable in order to provide additional insights into biogeochemistry–climate interactions
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