ALBERT

Description: Oceanic upwelling velocities are too small to be measured directly. The surface disequilibrium of the 3He/4He ratio provides an indirect method to infer vertical velocities at the base of the mixed layer. Samples of helium isotopes were taken from two coastal upwelling regions, off Peru on cruise M91, and off Mauritania on 3 cruises. The helium-3 flux into the mixed layer also depends on the diapycnal mixing. Direct observations of the vertical diffusivity have been performed on all 4 cruises and are also used in this study. The resulting upwelling velocities in the coastal regions vary between 1.1 × 10−5 and 2.8 × 10−5 m s−1 for all cruises. Vertical velocities off the equator can also be inferred from the divergence of the wind driven Ekman transport. In the coastal regimes, the agreement between wind and helium derived upwelling is fairly good at least for the mean values. Further offshore, the helium derived upwelling still reaches 1 × 10−5 m s−1, whereas the wind driven upwelling from Ekman suction is smaller by at least one order of magnitude. One reason for this difference might be eddy induced upwelling. Both advective and diffusive nutrient fluxes into the mixed layer are calculated based on the helium derived vertical velocities and the measured vertical diffusivities. The advective part of these fluxes makes up at least 50 % of the total. The nutrient flux into the mixed layer in the coastal upwelling regimes is equivalent to a net community production (NCP) of 1.3 g C m2 d−1 off Peru and 1.6–1.9 g C m2 d−1 off Mauritania.

Description: Upwelling is an important process, bringing gases and nutrients into the ocean mixed layer. The upwelling velocities, however, are too small to be measured directly. Here we use the surface disequilibrium of the 3He / 4He ratio measured in two coastal upwelling regions off Peru in the Pacific ocean and off Mauritania in the Atlantic ocean to calculate the regional distribution of vertical velocities. To also account for the fluxes by diapycnal mixing, microstructure-based observations of the vertical diffusivity have been performed on all four cruises analysed in this study. The upwelling velocities in the coastal regions vary between 1.1 ± 0.3 × 10−5 and 2.8 ± 1.5 × 10−5 m s−1 for all cruises. Vertical velocities are also inferred from the divergence of the wind-driven Ekman transport. In the coastal regimes, both methods agree within the error range. Further offshore, the helium-derived vertical velocity still reaches 1 × 10−5 m s−1, whereas the wind-driven upwelling from Ekman suction is smaller by up to 1 order of magnitude. One reason for this difference is ascribed to eddy-induced upwelling. Both advective and diffusive nutrient fluxes into the mixed layer are calculated based on the helium-derived vertical velocities and the vertical diffusivities. The advective part of these fluxes makes up at about 50 % of the total. The nutrient flux into the mixed layer in the coastal upwelling regimes is equivalent to a net community production (NCP) of 1.3 ± 0.3 g C m2 d−1 off Peru and 1.6–2.1 ± 0.5 g C m2 d−1 off Mauritania.

Description: The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of water samples. GLODAPv2.2020 is an update of the previous version, GLODAPv2.2019. The major changes are: data from 106 more cruises added, extension of time coverage until 2019, and the inclusion of available discrete fugacity of CO2 (fCO2) values in the merged product files. GLODAPv2.2020 includes measurements from more than 1.2 million water samples from the global oceans collected on 946 cruises. The data for the 12 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, CFC-11, CFC-12, CFC-113, and CCl4) have undergone extensive quality control, especially systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but updated to WOCE exchange format and (ii) as a merged data product with adjustments applied to minimize bias. These adjustments were derived by comparing the data from the 106 new cruises with the data from the 840 quality-controlled cruises of the GLODAPv2.2019 data product. They correct for errors related to measurement, calibration, and data handling practices, while taking into account any known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 μmol kg−1 in dissolved inorganic carbon, 4 μmol kg−1 in total alkalinity, 0.01–0.02, depending on region, in pH, and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete fCO2 were not subjected to bias comparison or adjustments. The original data, their documentation and doi codes are available at the Ocean Carbon Data System of NOAA NCEI (https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2020/, last access: 22 June 2020). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/2c8h-sa89 (Olsen et al., 2020). The bias corrected product files also include significant ancillary and approximated data. These were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2020 methods and provides a broad overview of the secondary quality control procedures and results.