DOI: 10.5281/zenodo.15131072
title: Improved air-sea CO2 flux estimates from sailboat measurements

description: This repository contains files and MATLAB scripts used to generate figures for the paper titled "Improved air-sea CO2 flux estimates from sailboat measurements". The study shows through an observing system simulation study with different sampling schemes how integrating sailboat data improves global air-sea CO2 flux estimates including analyses of measurement uncertainties and biases associated with sailboat data. 

Overview

We used fCO2 data sourced from HAMOCC (HAMburg Ocean Carbon Cycle model) model coupled to the ocean general circulation model MPIOM, contributing to GCB simulation at a monthly 1x1 degree resolution from 1982 until the end of 2021, along with other environmental variables. We used the model dataset as our starting point and applied different subsampling schemes to get pseudo-observations. We used SOCATv2022 tracks as well as the included tracks from the IMOCA 60 sailboats “Seaexplorer-Yacht Club de Monaco” (until 2019 “Malizia”) and “Newrest - Art & Fenêtres” (now “Nexans - Art & Fenêtres”) during offshore sailing and training events from 2018 to 2021, available via SOCATv2022 (www.socat.info). We applied the 2-step neural network method SOM-FFN (Landschützer et al., 2013) to reconstruct air-sea CO2 flux estimates. Several sets of air-sea CO2 flux estimates were reconstructed, each with 10-40 ensemble members to account for random errors in the neural network. These are the datasets used in this study:

Data X) - “truth”: Ground truth fCO2 values from the HAMOCC modelData A) - “existing sailboat”: Subsampled model fCO2 (X) generated using the SOCATv2022 sampling scheme, including sailboat data.Data B) - “without sailboat”: Subsampled model fCO2 (X) generated using the SOCATv2022 sampling scheme, excluding sailboat dataData C) - “3 circumnavigations”: Subsampled model fCO2 (X) generated using the SOCATv2022 sampling scheme including existing sailboat data and two additional Antarctic circumnavigations (Vendée Globe; 2012/13, 2016/17, 2020/21) (from which only the latter one is from the existing track and also included in A; the track of the Vendée Globe 2020/21, where fCO2 measurements were taken, was used to subsample the model data in earlier years when Vendée Globe races occurred without fCO2 measurements.)Data D) - “2 different circumnavigations”: Subsampled model fCO2 (X) generated using the SOCATv2022 sampling scheme including sailboat data and 2 different round-the-world races (Vendée Globe 2020/21 and the preliminary The Ocean Race 2017/18) (for the latter one we used existing tracks from 2023)Data E) - “3 circumnav + meas. uncert.”: Data C, but with an added random measurement uncertainty ranging from  ±5 µatmData F) - “3 circumnav + 5 offset”: Data C, but with an added + 5 µatm measurement offset to the data from sailboat tracksData G) - “3 circumnav – 5 offset”: Data C, but with an added – 5 µatm measurement offset to the data from sailboat tracksData H) - “3 circumnav + high uncert”: Data C, but with an added random measurement uncertainty ranging from ±10 µatm (higher end of what is expected from the measurement device) to the data from sailboat tracksData I) - “3 circumnav + 10 offset”: Data C, but with an added + 10 µatm measurement offset to the data from sailboat tracksData J) - “3 circumnav – 10 offset”: Data C, but with an added – 10 µatm measurement offset to the data from sailboat tracks

These air-sea CO2 flux density estimates are 4-dimensional, represented in mol C m-2 yr-1, with the following dimensions:- Ensemble size of flux reconstructions (10 or 40)- Time (months from 1982 to 2021, totaling 480 months)- Latitude (1-degree intervals, totaling 180 latitudes)- Longitude (1-degree intervals, totaling 360 longitudes)

There are the following folders and MATLAB codes in this repository:- figures (contains codes for generating the figures in the manuscript)- functions (contains functions needed for generating the figures)- mat-files (contains MATLAB files needed for generating the figures)- netcdf (contains NetCDF files needed for generating the figures)- scripts (contains codes to generate the MATLAB and NetCDF files needed for generating the figures)