the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
NorESM-bcoi-v1: A bias-corrected reanalysis of ocean biogeochemistry at >40° N, 1980–2020, based on a global ocean model hindcast
Abstract. Accurate and gap-free historical datasets of oceanic nutrient concentrations, dissolved oxygen, and carbonate chemistry, are needed for the analysis of anthropogenic impacts and development of predictive models, including as boundary conditions for regional ocean models. We developed low-bias, quasi-optimal 4D interpolations of observed values at latitudes >40° N, excluding Mediterranean and Black Seas, for years 1980–2020 inclusive. Our approach used output from the NorESM-OCv1.2 ocean model hindcast as a basis for kernel-smoothing bias correction and optimal interpolation of anomalies, obtaining monthly reanalysis data at NorESM grid points (30–90 km spatial resolution) and all model depth levels. Based on cross-validation tests with spatially-separated training and test subset locations, the resulting products showed equal or better interpolative accuracy compared to standard climatological products from the World Ocean Atlas 2023 and GLODAPv2, and also compared to existing non-climatological products from machine learning and biogeochemical reanalysis/hindcast datasets from CMEMS/Copernicus. The new products showed skill in tracking smooth seasonal and interannual variations not included in the standard climatologies, and improved spatial coverage and detail resolution in northern/Arctic regions, compared to all tested alternatives. Significant uncertainties remained, however, largely due to sparse observational coverage in seasonal and permanent ice-covered regions, and limited resolution in coastal regions. The NorESM-bcoi-v1 reanalysis data, as well as the associated quality-controlled in situ observational compilations (NORBGCv1) and code used to develop the reanalysis, can be downloaded from https://doi.org/10.5281/zenodo.14525787 (Wallhead et al., 2024).
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Status: open (until 26 May 2025)
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RC1: 'Comment on essd-2025-76', Anonymous Referee #1, 08 Apr 2025
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NorESM-bcoi-v1: A bias-corrected reanalysis of ocean biogeochemistry at >40° N,
1980–2020, based on a global ocean model hindcast, by Philip J. Wallhead and colleagues
This paper describes what looks like an extremely useful data product for usage in regional modelling as boundary and initial conditions, to evaluate model hindcasts, or to provide forcing for biological models. The data product is available in a Zenodo address provided by the authors.
I strongly recommend the publication of this paper.
I made some comments directly on the manuscript. There is a question I have to the authors about the usage of a product based on a training dataset (NorESM-bcoi-v1(tr)) and the complete product based on the whole dataset (NorESM-bcoi-v1). I wonder why showing the results of both products, when the latter is the one of most interest to potential users, given its lower bias? I understand that when evaluating a model, we want to use a dataset that was not used for calibrating/learning the model, but this is not a case of model validation – here the goal is to get a dataset with the minimum possible bias. Therefore, it is not entirely clear to me the usefulness of adding both products in the paper.
The authors present Root Mean Square Errors to compare the performance of the developed products with other products and they show that NorESM-bcoi-v1 performs better for the selected biogeochemical variables. They also present time series to show that this new product captures seasonal variability as well as long-term trends. Finally, they make comparisons with climatological data. So, I think they make a relatively in-depth assessment of their results. I would suggest the usage of Taylor diagrams to compare different products based on their bias, correlation with observations and variability. I am not implying that this “must” be done, but I am just suggesting them to consider doing it.
My comments here and directly on the manuscript imply merely a minor revision.
Data sets
NorESM-bcoi-v1 reanalysis data for ocean biogeochemistry at >40° N, 1980-2020, and basis compilations of quality-controlled observations (NORBGCv1). Philip Wallhead et al. https://doi.org/10.5281/zenodo.14525787
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