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The Southern Ocean is among the largest contemporary sinks of atmospheric carbon dioxide on our planet; however, remoteness, harsh weather and other circumstances have led to an undersampling of the ocean basin, compared with its northern hemispheric counterparts. While novel data interpolation methods can in part compensate for such data sparsity, recent studies raised awareness that we have hit a wall of unavoidable uncertainties in air–sea CO 2 flux reconstructions. Here, we present results from autonomous observing campaigns using a novel platform to observe remote ocean regions: sailboats. Sailboats are at present a free of charge environmentally friendly platform that recurrently pass remote ocean regions during round-the-globe racing events. During the past 5 years, we collected > 350 000 measurements of the sea surface partial pressure of CO 2 (p CO 2 ) around the globe including the Southern Ocean throughout an Antarctic circumnavigation during the Vendée Globe racing event. Our analysis demonstrates that the sailboat tracks pass regions where large uncertainty in the air–sea CO 2 flux reconstruction prevails, with regional oversaturation or undersaturation of the sea surface p CO 2 . Sailboat races provide an independent cross-calibration platform for autonomous measurement devices, such as Argo floats, ultimately strengthening the entire Southern Ocean observing system. This article is part of a discussion meeting issue ‘Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities’.

We evaluate the decadal evolution of ventilation and anthropogenic carbon (C-ant) in the Nordic Seas between 1982 and the 2010s. Ventilation changes on decadal timescale are identified by evaluating decadal changes in mean ages and apparent oxygen utilization in each of the four main basins of the Nordic Seas (the Greenland and Iceland Seas, and the Norwegian and Lofoten Basins). The ages are derived from the transient time distribution approach, based on the transient tracers chlorofluorocarbon-12 (CFC-12) and sulfur hexafluoride (SF6). The different decades show different phases in ventilation, with the 2000s being overall better ventilated than the 1990s in all basins. For the Greenland Sea, we also show that the 2010s are better ventilated than the 2000s, with a clear shift in hydrographic properties. The evolution of concentrations and inventory of C-ant is linked to the ventilation state. The deep waters get progressively older over the analyzed period, which is connected to the increased fraction of deep water from the Arctic Ocean.Plain Language Summary The ocean region between Greenland, Iceland, and Norway, called the Nordic Seas, is a main site of deep-water formation. This process produces dense waters and brings surface waters to larger depths, thereby ventilating the water below. This transports, among other things, man-made CO2 (anthropogenic carbon; C-ant) and oxygen from the atmosphere into the interior ocean, thereby reducing the amount of CO2 stored in the atmosphere. This study investigates how the ventilation has changed in the Nordic Seas from 1982 to the 2010s. We find that the ventilation has changed with time, from a rather well-ventilated state in 1982, to a reduced ventilation in the 1990s, and then a restrengthened ventilation from the 2000s.

Marine particles of different nature are found throughout the global ocean. The term “marine particles” describes detritus aggregates and fecal pellets as well as bacterioplankton, phytoplankton, zooplankton and nekton. Here, we present a global particle size distribution dataset obtained with several Underwater Vision Profiler 5 (UVP5) camera systems. Overall, within the 64 µm to about 50 mm size range covered by the UVP5, detrital particles are the most abundant component of all marine particles; thus, measurements of the particle size distribution with the UVP5 can yield important information on detrital particle dynamics. During deployment, which is possible down to 6000 m depth, the UVP5 images a volume of about 1 L at a frequency of 6 to 20 Hz. Each image is segmented in real time, and size measurements of particles are automatically stored. All UVP5 units used to generate the dataset presented here were inter-calibrated using a UVP5 high-definition unit as reference. Our consistent particle size distribution dataset contains 8805 vertical profiles collected between 19 June 2008 and 23 November 2020. All major ocean basins, as well as the Mediterranean Sea and the Baltic Sea, were sampled. A total of 19 % of all profiles had a maximum sampling depth shallower than 200 dbar, 38 % sampled at least the upper 1000 dbar depth range and 11 % went down to at least 3000 dbar depth. First analysis of the particle size distribution dataset shows that particle abundance is found to be high at high latitudes and in coastal areas where surface productivity or continental inputs are elevated. The lowest values are found in the deep ocean and in the oceanic gyres. Our dataset should be valuable for more in-depth studies that focus on the analysis of regional, temporal and global patterns of particle size distribution and flux as well as for the development and adjustment of regional and global biogeochemical models. The marine particle size distribution dataset (Kiko et al., 2021) is available at https://doi.org/10.1594/PANGAEA.924375.

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land-use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data-products. The terrestrial CO2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gases inventories, supporting the assessment of collective countries’ climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr−1 (9.3 ± 0.5 GtC yr−1 when the cement carbonation sink is included), ELUC was 0.9 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission of 10.2 ± 0.8 GtC yr−1 (37.4 ± 2.9 GtCO2). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), SOCEAN was 3.0 ± 0.4 GtC yr−1 and SLAND was 2.9 ± 1 GtC yr−1, with a BIM of −0.8 GtC yr−1. The global atmospheric CO2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021, suggest a rebound in EFOS relative to 2020 of +4.9 % (4.1 % to 5.7 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows: (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra- tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set (Friedlingstein et al., 2020; Friedlingstein et al., 2019; Le Quéré et al., 2018b, 2018a, 2016, 2015b, 2015a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).

The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface-to-bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2022 is an update of the previous version, GLODAPv2.2021 (Lauvset et al., 2021). The major changes are as follows: data from 96 new cruises were added, data coverage was extended until 2021, and for the first time we performed secondary quality control on all sulfur hexafluoride (SF6) data. In addition, a number of changes were made to data included in GLODAPv2.2021. These changes affect specifically the SF6 data, which are now subjected to secondary quality control, and carbon data measured on board the RV Knorr in the Indian Ocean in 1994–1995 which are now adjusted using certified reference material (CRM) measurements made at the time. GLODAPv2.2022 includes measurements from almost 1.4 million water samples from the global oceans collected on 1085 cruises. The data for the now 13 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, chlorofluorocarbon-11 (CFC-11), CFC-12, CFC-113, CCl4, and SF6) have undergone extensive quality control with a focus on systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but converted to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For the present annual update, adjustments for the 96 new cruises were derived by comparing those data with the data from the 989 quality-controlled cruises in the GLODAPv2.2021 data product using crossover analysis. SF6 data from all cruises were evaluated by comparison with CFC-12 data measured on the same cruises. For nutrients and ocean carbon dioxide (CO2) chemistry comparisons to estimates based on empirical algorithms provided additional context for adjustment decisions. The adjustments that we applied are intended to remove potential biases from errors related to measurement, calibration, and data handling practices without removing 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 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (f CO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon and Acidification Data System of NOAA NCEI (https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oceans/GLODAPv2_2022/, last access: 15 August 2022). 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/10.25921/1f4w-0t92 (Lauvset et al., 2022). These bias-adjusted product files also include significant ancillary and approximated data, which were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2022 methods and provides a broad overview of the secondary quality control procedures and results., Earth System Science Data, 14 (12), ISSN:1866-3516, ISSN:1866-3508

The neodymium isotopic composition (εNd) of seawater is one of the most important geochemical tracers to investigate water mass provenance, which can also serve as a proxy to reconstruct past variations in ocean circulation. Nd isotopes have recently also been used to reconstruct past circulation changes in theMediterranean Sea on different time scales. However, the modern seawater ε Nd dataset for the Mediterranean Sea, which these reconstructions are based on, is limited and up to now only 160 isotopic measurements are available for the entire basin. The lack of present-day data also limits our understanding of the processes controlling the Nd cycle and Nd isotopic distribution in this semi-enclosed basin. Here we present new εNd data from 24 depth profiles covering all Mediterranean sub-basins, which significantly increases the available dataset in the Mediterranean Sea. The main goal of our study is to better characterize the relationship between the dissolved Nd isotope distributions and major water masses in the Mediterranean Sea and to investigate the impact and relative importance of local non-conservative modifications, which include input of riverine particles and waters, aeolian-derived material and exchange with the sediments at continental margins . This comprehensive εNd dataset reveals a clear εNd – salinity correlation and a zonal and depth gradient with εNd systematically increasing from the western to the eastern Mediterranean basin (average εNd = −8.8 ± 0.8 and −6.7 ± 1 for the entire water column, respectively), reflecting the large-scale basin circulation. We have evaluated the conservative εNd behaviour in theMediterranean Sea and quantified the non-conservative components of the ε Nd signatures by applying an Optimum Multiparameter (OMP) analysis and results from the Parametric Optimum Multiparameter (POMP) analysis of Jullion et al. (2017). The results of the present study combined with previously published Nd isotope values indicate that dissolved εNd behaves overall conservatively in the open Mediterranean Sea and show that its water masses are clearly distinguishable by their Nd isotope signature. However, misfits between measured and OMP- and POMP-derived εNd values exist in almost all sub-basins, especially in the eastern Levantine Basin and Alboran Sea at intermediate-deep depths, which can be explained by the influence of detrital lithogenic εNd signatures through interaction with highly radiogenic Nile sourced volcanic fractions and unradiogenic sediments, respectively. The radiogenic signature acquired in the eastern Levantine Basin is carried by the Levantine Intermediate Water and transferred conservatively to the entire Mediterranean at intermediate depths. Our measured εNd values and OMP- and POMP-derived results indicate that non-conservative contributions originating from sediment sources are then propagated by water mass circulation (with distinct preformed εNd) along the Mediterranean Sea through advection and conservative mixing. Mediterranean εNd effectively traces the mixing between the different water masses in this semi-enclosed basin and is a suitable water mass tracer.

The last few decades have seen dramatic changes in the hydrography and biogeochemistry of the Mediterranean Sea. The complex bathymetry and highly variable spatial and temporal scales of atmospheric forcing, convective and ventilation processes contribute to generate complex and unsteady circulation patterns and significant variability in biogeochemical systems. Part of the variability of this system can be influenced by anthropogenic contributions. Consequently, it is necessary to document details and to understand trends in place to better relate the observed processes and to possibly predict the consequences of these changes. In this context we report data from an oceanographic cruise in the Mediterranean Sea on the German research vessel Maria S. Merian (MSM72) in March 2018. The main objective of the cruise was to contribute to the understanding of long-term changes and trends in physical and biogeochemical parameters, such as the anthropogenic carbon uptake and to further assess the hydrographical situation after the major climatological shifts in the eastern and western part of the basin, known as the Eastern and Western Mediterranean Transients. During the cruise, multidisciplinary measurements were conducted on a predominantly zonal section throughout the Mediterranean Sea, contributing to the Med-SHIP and GO-SHIP long-term repeat cruise section that is conducted at regular intervals in the Mediterranean Sea to observe changes and impacts on physical and biogeochemical variables. The data can be accessed at https://doi.org/10.1594/PANGAEA.905902 (Hainbucher et al., 2019), https://doi.org/10.1594/PANGAEA.913512 (Hainbucher, 2020a) https://doi.org/10.1594/PANGAEA.913608, (Hainbucher, 2020b) https://doi.org/10.1594/PANGAEA.913505, (Hainbucher, 2020c) https://doi.org/10.1594/PANGAEA.905887 (Tanhua et al., 2019) and https://doi.org/10.25921/z7en-hn85 (Tanhua et al, 2020).

4 pages, 1 figure.-- This article is licensed under a Creative Commons Attribution 4.0 International License, The ocean is mitigating global warming by absorbing large amounts of excess carbon dioxide from human activities. To quantify and monitor the ocean carbon sink, we need a state-of-the-art data resource that makes data submission and retrieval machine-compatible and efficient, This effort has been supported by EU Horizon 2020 through the EuroSea action (grant no. 862626), the Helmholtz Association through “Digital Earth” (grant no. ZT-0025), L.C.C. acknowledges the UERJ/Prociencia grant (2018-2021), M.H. acknowledge EU Horizon 2020 action SO-CHIC (grant N°821001). B.C., R.A.F., E.B., K.O’.B., and R.W. were supported by NOAA/OAR and NOAA/GOMO (fund ref. 100007298), B.T. was partly supported by Australia’s Integrated Marine Observing System (IMOS), S.K.L. acknowledges internal strategic funding from NORCE Climate, M.T. acknowledges support from the US NSF grant OCE-1840868 to SCOR. The PMEL and CICOES contributions are 5253 and 2020-1141, respectively

19 pages, 7 tables, 11 figures.-- Open access, Global climatologies of the seawater CO2 chemistry variables are necessary to assess the marine carbon cycle in depth. The climatologies should adequately capture seasonal variability to properly address ocean acidification and similar issues related to the carbon cycle. Total alkalinity (AT) is one variable of the seawater CO2 chemistry system involved in ocean acidification and frequently measured.We used the Global Ocean Data Analysis Project version 2.2019 (GLODAPv2) to extract relationships among the drivers of the AT variability and AT concentration using a neural network (NNGv2) to generate a monthly climatology. The GLODAPv2 qualitycontrolled dataset used was modeled by the NNGv2 with a root-mean-squared error (RMSE) of 5.3 μmol kg1. Validation tests with independent datasets revealed the good generalization of the network. Data from five ocean time-series stations showed an acceptable RMSE range of 3–6.2 μmol kg1. Successful modeling of the monthly AT variability in the time series suggests that the NNGv2 is a good candidate to generate a monthly climatology. The climatological fields of AT were obtained passing through the NNGv2 the World Ocean Atlas 2013 (WOA13) monthly climatologies of temperature, salinity, and oxygen and the computed climatologies of nutrients from the previous ones with a neural network. The spatiotemporal resolution is set by WOA13: 1 1 in the horizontal, 102 depth levels (0–5500 m) in the vertical and monthly (0–1500 m) to annual (1550–5500 m) temporal resolution. The product is distributed through the data repository of the Spanish National Research Council (CSIC; https://doi.org/10.20350/digitalCSIC/8644, Broullón et al., 2019), This research has been supported by the H2020 Food (AtlantOS, grant no. 633211); the Ministerio de Educación, Cultura y Deporte (grant no. FPU15/06026); the Ministerio de Economía y Competitividad, Consejo Superior de Investigaciones Científicas (grant no. CTM2016-76146-C3-1-R); and the Ministerio de Economía y Competitividad, Salvador de Madariaga (grant no. PRX18/00312)

8 pages, 2 tables, 4 figures, We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO2 inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year−1 and represents 31 ± 4% of the global anthropogenic CO2 emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation, We are grateful to the many funding agencies in the various countries that financially supported the global ship-based surveys that underpin much of this work. In particular, we acknowledge funding from the U.S. National Science Foundation and from the National Oceanic and Atmospheric Administration (NOAA), and the GO-SHIP program together with the International ocean carbon coordination project (IOCCP), for their efforts to initiate and coordinate the repeat hydrography program. The work of N.G. and D.C. was supported by ETH and the FP7 projects CarboChange (264879) and Geocarbon (283080). S.v.H. also received support from CarboChange (264879). R.W., R.A.F., and B.R.C. acknowledge the support of Oceanic and Atmospheric Research NOAA and the U.S. Department of Commerce, including resources from the NOAA Global Ocean Monitoring and Observations Division (fund reference 100007298). This is contribution no. 4796 from the NOAA Pacific Marine Environmental Laboratory and JISAO contribution 2018-0185. M.I. acknowledges support from the Japan Meteorological Agency and MEXT KAKENHI grant no. 24121003 “NEOPS” and JP16H01594 “OMIX”. S.K.L. acknowledges support from the Research Council of Norway (214513). F.F.P. was supported by Ministerio de Economía y Competitividad through the ARIOS (CTM2016-76146-C3-1-R) project cofunded by the Fondo Europeo de Desarrollo Regional 2014-2020 (FEDER) and EU Horizon 2020 through the AtlantOS project (grant agreement 633211)

26 pages, 11 figures, 7 tables.-- This work is distributed under the Creative Commons Attribution 4.0 License, 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 seawater samples. GLODAPv2.2020 is an update of the previous version, GLODAPv2.2019. The major changes are data from 106 new cruises added, extension of time coverage to 2019, and the inclusion of available (also for historical cruises) discrete fugacity of CO2 (fCO2) values in the merged product files. GLODAPv2.2020 now 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 with a focus on 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 using crossover analysis. Comparisons to empirical algorithm estimates provided additional context for adjustment decisions; this is new to this version. The adjustments are intended to remove potential biases from errors related to measurement, calibration, and data-handling practices without removing 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 μmolkg-1 in dissolved inorganic carbon, 4 μmolkg-1 in total alkalinity, 0.01–0.02 in pH (depending on region), 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 and 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: 20 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). These bias-adjusted 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, Nico Lange was funded by EU Horizon 2020 through the EuroSea action (grant no. 862626). Leticia Cotrim da Cunha was supported by Prociencia/UERJ (grant no. 2019-2021). Marta Álvarez was supported by the IEO RADIALES and RADPROF projects. Peter J. Brown was partially funded by the UK Climate Linked Atlantic Sector Science (CLASS) NERC National Capability Long-term Single Centre Science Programme (grant no. NE/R015953/1). Anton Velo and Fiz F. Pérez were supported by the BOCATS2 Project (grant no. PID2019-104279GBC21) co-funded by the Spanish Government and the Fondo Europeo de Desarrollo Regional (FEDER). RikWanninkhof and Brendan R. Carter were supported by the NOAA Global Observations and Monitoring Division (fund reference 100007298) and the Office of Oceanic and Atmospheric Research of NOAA. Henry C. Bittig has been supported by the BONUS INTEGRAL project (grant no. 03F0773A). This research was also funded by the Initiative and Networking Fund of the Helmholtz Association through the project “Digital Earth” (grant no. ZT-0025)

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.

The Arctic Ocean is particularly vulnerable to ocean acidification, a process that is mainly driven by the uptake of anthropogenic carbon (Cant) from the atmosphere. Although Cant concentrations cannot be measured directly in the ocean, they have been estimated using data‐based methods such as the transient time distribution (TTD) approach, which characterizes the ventilation of water masses with inert transient tracers, such as CFC‐12. Here, we evaluate the TTD approach in the Arctic Ocean using an eddying ocean model as a test bed. When the TTD approach is applied to simulated CFC‐12 in that model, it underestimates the same model's directly simulated Cant concentrations by up to 12%, a bias that stems from its idealized assumption of gas equilibrium between atmosphere and surface water, both for CFC‐12 and anthropogenic CO2. Unlike the idealized assumption, the simulated partial pressure of CFC‐12 (pCFC‐12) in Arctic surface waters is undersaturated relative to that in the atmosphere in regions and times of deep‐water formation, while the simulated equivalent for Cant is supersaturated. After accounting for the TTD approach's negative bias, the total amount of Cant in the Arctic Ocean in 2005 increases by 8% to 3.3 ± 0.3 Pg C. By combining the adjusted TTD approach with scenarios of future atmospheric CO2, it is estimated that all Arctic waters, from surface to depth, would become corrosive to aragonite by the middle of the next century even if atmospheric CO2 could be stabilized at 540 ppm., Key Points The amount of anthropogenic carbon in the Arctic Ocean appears to be underestimated by 7–12%A refined approach yields a new estimate of 3.3 ± 0.3 Pg C for year 2005All Arctic Ocean waters become corrosive to aragonite if atmospheric CO2 is held at 540 ppm

The occurrence of mesoscale eddies that develop suboxic environments at shallow depth (about 40–100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, with the use of moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). During the survey the eddy core showed oxygen concentrations as low as 5 µmol kg−1 with a pH of around 7.6 at approximately 100 m depth. Correspondingly, the aragonite saturation level dropped to 1 at the same depth, thereby creating unfavorable conditions for calcifying organisms. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate organic matter and dissolved organic matter (POM and DOM), generally showed elevated concentrations in the surface mixed layer (0–70 m), with DOM also accumulating beneath the oxygen minimum. With the use of reference data from the upwelling region where these eddies are formed, the oxygen utilization rate was calculated by determining oxygen consumption through the remineralization of organic matter. Inside the core, we found these rates were almost 1 order of magnitude higher (apparent oxygen utilization rate (aOUR); 0.26 µmol kg−1 day−1) than typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC), were around 0.19 to 0.23 g C m−2 day−1 at 100 m depth, clearly exceeding fluxes typical for an oligotrophic open-ocean setting. The observations support the view that the oxygen-depleted eddies can be viewed as isolated, westwards propagating upwelling systems of their own, thereby represent re-occurring alien biogeochemical environments in the ETNA.

The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo’s global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities., Sí

The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30 °N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66 °N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.

The Global Ocean Ship-Base Hydrographic Investigations Program (GO-SHIP) provides a globally coordinated network and oversight of repeat hydrography. Repeat Hydrography involves a number of core hydrographic sections that are repeated on a decadal time-scale (although a few are “high frequency lines with biennial, annual or bi-annual repeats). These sections are typically full depth CTD stations at high spatial resolution with measurements of a defined set of EOVs (the GO-SHIP level 1 variables), and goes from continent to continent, i.e. crossing ocean basins. AtlantOS have supported and improved the Atlantic GO-SHIP program in three main ways: 1) AtlantOS supported a coordination office located at JCOMMOPS in Brest, 2) AtlantOS supported the concept of European central laboratories for the observation of not-commonly measured EOVs that are core in GO-SHIP, and 3) by facilitating the observation and delivery of ocean current data from ship-based ADCP systems. The technical coordination of the program has enabled the GO-SHIP program to be visible on the JCOMMOPS network coordination site, facilitating the overall coordination and assessment of the ocean observing system. The coordination has also made significant progress in tracking the impact of the network in terms of scientific output and has supported the progress of key documentation and support. AtlantOS supported central facilities for measurements of key GO-SHIP EOVs that are not regularly measured on other platforms of observing systems. AtlantOS decided to support facilities for the inorganic carbon system and transient tracers. Both are EOVs, seldom measured by other networks, and are thus a challenge to maintain facilities for measurements of these in each country. The concept of central European facilities proved to be useful, and a concept that can be used in the future, but requires long-term funding commitments paired with expectation to support GO-SHIP lines. The improvement of software for processing ADCP data and support for a data management system for these data has showed large potential, and is now ready to deploy on a larger scale for the Atlantic GO-SHIP program.

Ocean ventilation is the integrated effect of various processes that exchange surface properties with the ocean interior and is essential for oxygen supply, storage of anthropogenic carbon and the heat budget of the ocean, for instance. Current observational methods utilise transient tracers, e.g. tritium, SF6, CFCs and 14C. However, their dating ranges are not ideal to resolve the centennial-dynamics of the deep ocean, a gap filled by the noble gas isotope 39Ar with a half-life of 269 years. Its broad application has been hindered by its very low abundance, requiring 1000 L of water for dating. Here we show successful 39Ar dating with 5 L of water based on the atom-optical technique Atom Trap Trace Analysis. Our data reveal previously not quantifiable ventilation patterns in the Tropical Atlantic, where we find that advection is more important for the ventilation of the intermediate depth range than previously assumed. Now, the demonstrated analytical capabilities allow for a global collection of 39Ar data, which will have significant impact on our ability to quantify ocean ventilation., The rare noble gas isotope 39Ar is the ideal tracer to investigate the ventilation of the deep ocean in the time range of 50 to 1000 years. Here the authors constrain transit time distributions in the eastern Tropical Atlantic with 39Ar-measurements done on a sample size of 5 L of water utilising modern atom-optical techniques.

The Mediterranean is a semi-enclosed sea characterized by high salinities, temperatures and densities. The net evaporation exceeds the precipitation, driving an anti-estuarine circulation through the Strait of Gibraltar, contributing to very low nutrient concentrations. The Mediterranean Sea has an active overturning circulation, one shallow cell that communicates directly with the Atlantic Ocean, and two deep overturning cells, one in each of the two main basins. It is surrounded by populated areas and is thus sensitive to anthropogenic forcing. Several dramatic changes in the oceanographic and biogeochemical conditions have been observed during the past several decades, emphasising the need to better monitor and understand the changing conditions and their drivers. During 2011 three oceanographic cruises were conducted in a coordinated fashion in order to produce base-line data of important physical and biogeochemical parameters that can be compared to historic data and be used as reference for future observational campaigns. In this article we provide information on the Mediterranean Sea oceanographic situation, and present a short review that will serve as background information for the special issue in Ocean Science on "Physical, chemical and biological oceanography of the Mediterranean Sea". An important contribution of this article is the set of figures showing the large-scale distributions of physical and chemical properties along the full length of the Mediterranean Sea.

17 pages, 24 figures, 1 table., Data on carbon and carbon-relevant hydrographic and hydrochemical parameters from previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged to a new database: CARINA (CARbon IN the Atlantic). These data have gone through rigorous quality control (QC) procedures to assure the highest possible quality and consistency. The data for most of the measured parameters in the CARINA data base were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions; Arctic, Atlantic and Southern Ocean. Out of a total of 188 cruise entries in the CARINA database, 98 were conducted in the Atlantic Ocean and of these, 75 cruises report alkalinity values. Here we present details of the secondary QC on alkalinity for the Atlantic Ocean part of CARINA. Procedures of quality control, including crossover analysis between cruises and inversion analysis of all crossover data are briefly described. Adjustments were applied to the alkalinity values for 16 of the cruises in the Atlantic Ocean region. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s. Based on our analysis we estimate the internal accuracy of the CARINA-ATL alkalinity data to be 3.3 μmol kg−1. The CARINA data are now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation., This work has been performed and funded as part of the EU project CarboOcean (Project 511176). Additional support from the International Ocean Carbon Coordination Project IOCCP (Maria Hood) and the Hanse Institute for Advanced Study (HWK Delmenhorst, Germany) are gratefully acknowledged. Additional support provided as follows: for A. Velo, F. F. Perez, PGIDIT05OXIC40203PM Xunta de Galicia and CTM200627116E/MAR MEC; P. J. Brown, Award NER/S/A/2004/12255; and R. M. Key, NOAA grant NA08OAR4320752 and NA08OAR4310820.

Ocean observations are analysed in the framework of Collaborative Research Center 754 (SFB 754) "Climate-Biogeochemistry Interactions in the Tropical Ocean" to study (1) the structure of tropical oxygen minimum zones (OMZs), (2) the processes that contribute to the oxygen budget, and (3) long-term changes in the oxygen distribution. The OMZ of the eastern tropical North Atlantic (ETNA), located between the well-ventilated subtropical gyre and the equatorial oxygen maximum, is composed of a deep OMZ at about 400 m in depth with its core region centred at about 20° W, 10° N and a shallow OMZ at about 100 m in depth, with the lowest oxygen concentrations in proximity to the coastal upwelling region off Mauritania and Senegal. The oxygen budget of the deep OMZ is given by oxygen consumption mainly balanced by the oxygen supply due to meridional eddy fluxes (about 60%) and vertical mixing (about 20%, locally up to 30%). Advection by zonal jets is crucial for the establishment of the equatorial oxygen maximum. In the latitude range of the deep OMZ, it dominates the oxygen supply in the upper 300 to 400 m and generates the intermediate oxygen maximum between deep and shallow OMZs. Water mass ages from transient tracers indicate substantially older water masses in the core of the deep OMZ (about 120–180 years) compared to regions north and south of it. The deoxygenation of the ETNA OMZ during recent decades suggests a substantial imbalance in the oxygen budget: about 10% of the oxygen consumption during that period was not balanced by ventilation. Long-term oxygen observations show variability on interannual, decadal and multidecadal timescales that can partly be attributed to circulation changes. In comparison to the ETNA OMZ, the eastern tropical South Pacific OMZ shows a similar structure, including an equatorial oxygen maximum driven by zonal advection but overall much lower oxygen concentrations approaching zero in extended regions. As the shape of the OMZs is set by ocean circulation, the widespread misrepresentation of the intermediate circulation in ocean circulation models substantially contributes to their oxygen bias, which might have significant impacts on predictions of future oxygen levels.

The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP's biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948–2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, CTabio and 14CTabio, to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols are founded on those from previous phases of the Ocean Carbon-Cycle Model Intercomparison Project. They have been merged and updated to reflect improvements concerning gas exchange, carbonate chemistry, and new data for initial conditions and atmospheric gas histories. Code is provided to facilitate their implementation.

Diapycnal diffusivity estimates from two Tracer Release Experiments (TREs) and microstructure measurements in the oxycline and core of the oxygen minimum zone (OMZ) in the eastern tropical North Atlantic are compared. For the first time, two TREs within the same area at different depths were realized: the Guinea Upwelling Tracer Release Experiment (GUTRE) initiated in 2008 in the oxycline at approximately 320 m depth, and the Oxygen Supply Tracer Release Experiment (OSTRE) initiated in 2012 in the core of the OMZ at approximately 410 m depth. The mean diapycnal diffusivity Dz was found to be insignificantly smaller in the OMZ core with (1.06 ± 0.24) × 10− 5 m2 s− 1 compared to (1.11 ± 0.22) × 10− 5 m2 s− 1 90 m shallower in the oxycline. Unexpectedly, GUTRE tracer was detected during two of the OSTRE surveys which showed that the estimated diapycnal diffusivity from GUTRE over a time period of seven years was within the uncertainty of the previous estimates over a time period of three years. The results are consistent with the Dz estimates from microstructure measurements and demonstrate that Dz does not vary significantly vertically in the OMZ within the depth range of 200–600 m and does not change with time. The presence of a seamount chain in the vicinity of the GUTRE injection region did not cause enhanced Dz compared to the smoother bottom topography of the OSTRE injection region, although the analysis of vertical shear spectra from ship ADCP data showed elevated internal wave energy level in the seamount vicinity. However, the two tracer patches covered increasingly overlapping areas with time and thus spatially integrated increasingly similar fields of local diffusivity, as well as the difference in local stratification counteracted the influence of roughness on Dz. For both experiments no significant vertical displacements of the tracer were observed, thus diapycnal upwelling within the ETNA OMZ is below the uncertainty level of 5 m yr− 1.

Transient tracer data (CFC-12 and SF6) from three oceanographic field campaigns to the Mauritanian Upwelling area conducted during winter, spring and summer from 2005 to 2007 is presented. The transient tracers are used to constrain a possible solution to the transient time distribution (TTD) along 18°N and to quantify the mean ages in vertical sections perpendicular to the coast. We found that an Inverse Gaussian distribution where the ratio of the moments δ and Γ equals 1.2 is a possible solution (δ/Γ=1.2) of the TTD. The transient tracers further show considerable under-saturation in the mixed layer during the winter and spring cruises that can only be maintained by mixing or upwelling by tracer-poor water from below the mixed layer. We use dissipation data from microstructure measurements and the tracer depth distribution to quantify the flux of tracers to the mixed layer by vertical diffusivity and wind data from the ship to quantify the air-sea flux. We then use the magnitude of the under-saturation in the mixed layer to estimate the advective upwelling velocity which is the balance the first two processes, in a steady state assumption. We find that the upwelling velocities range from less than 1 to 5.6×10-5ms-1 (

Water column data of carbon and carbon relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruises in the Arctic, Atlantic, and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic). The data have been subject to rigorous quality control (QC) in order to ensure highest possible quality and consistency. The data for most of the parameters included were examined in order to quantify systematic biases in the reported values, i.e. secondary quality control. Significant biases have been corrected for in the data products, i.e. the three merged files with measured, calculated and interpolated values for each of the three CARINA regions; the Arctic Mediterranean Seas (AMS), the Atlantic (ATL) and the Southern Ocean (SO). With the adjustments the CARINA database is consistent both internally as well as with GLODAP (Key et al., 2004) and is suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation. The Arctic Mediterranean Seas includes the Arctic Ocean and the Nordic Seas, and the quality control was carried out separately in these two areas. This contribution provides an overview of the CARINA data from the Nordic Seas and summarises the findings of the QC of the salinity data. One cruise had salinity data that were of questionable quality, and these have been removed from the data product. An evaluation of the consistency of the quality controlled salinity data suggests that they are consistent to at least 0.05.

Research article, The Mediterranean Sea is considered a “hot spot” for climate change, being characterized by oligotrophic to ultra-oligotrophic waters and rapidly increasing seasurface temperature and changing carbonate chemistry. Coccolithophores are considered a dominant phytoplankton group in these waters. As marine calcifying organisms they are expected to respond to the ongoing changes in seawater carbonate chemistry. We provide here a description of the springtime coccolithophore distribution in the Mediterranean Sea and relate this to a broad set of in situ-measured environmental variables. Samples were taken during the R/V Meteor (M84/3) oceanographic cruise in April 2011, between 0 and 100m water depth from 28 stations. Total diatom and silicoflagellate cell concentrations are also presented. Our results highlight the importance of seawater carbonate chemistry, especially [CO2􀀀� 3 ] but also [PO3􀀀� 4 ] in unraveling the distribution of heterococcolithophores, the most abundant coccolithophore life phase. Holo- and heterococcolithophores respond differently to environmental factors. For instance, changes in heterococcolithophore assemblages were best linked to the combination of [CO2􀀀� 3 ], pH, and salinity ( D0.57), although salinity might be not functionally related to coccolithophore assemblage distribution. Holococcolithophores, on the other hand, showed higher abundances and species diversity in oligotrophic areas (best fit, D0.32 for nutrients), thriving in nutrient-depleted waters. Clustering of heterococcolithophores revealed three groups of species sharing more than 65% similarities. These clusters could be assigned to the eastern and western basins and deeper layers (below 50 m), respectively. In addition, the species Gephyrocapsa oceanica, G. muellerae, and Emiliania huxleyi morphotype B/C are spatially distributed together and trace the influx of Atlantic waters into the Mediterranean Sea. The results of the present work emphasize the importance of considering holo- and heterococcolithophores separately when analyzing changes in species assemblages and diversity. Our findings suggest that coccolithophores are a main phytoplankton group in the entire Mediterranean Sea and can dominate over siliceous phytoplankton. They have life stages that are expected to respond differently to the variability in seawater carbonate chemistry and nutrient concentrations., 2,2930

Significant changes in the overturning circulation of the Mediterranean Sea has been observed during the last few decades, the most prominent phenomena being the Eastern Mediterranean Transient (EMT) in the early 1990s and the Western Mediterranean Transition (WMT) during the mid-2000s. During both of these events unusually large amounts of deep water were formed, and in the case of the EMT, the deep water formation area shifted from the Adriatic to the Aegean Sea. Here we synthesize a unique collection of transient tracer (CFC-12, SF6 and tritium) data from nine cruises conducted between 1987 and 2011 and use these data to determine temporal variability of Mediterranean ventilation. We also discuss biases and technical problems with transient tracer-based ages arising from their different input histories over time; particularly in the case of time-dependent ventilation. We observe a period of low ventilation in the deep eastern (Levantine) basin after it was ventilated by the EMT so that the age of the deep water is increasing with time. In the Ionian Sea, on the other hand, we see evidence of increased ventilation after year 2001, indicating the restarted deep water formation in the Adriatic Sea. This is also reflected in the increasing age of the Cretan Sea deep water and decreasing age of Adriatic Sea deep water since the end of the 1980s. In the western Mediterranean deep basin we see the massive input of recently ventilated waters during the WMT. This signal is not yet apparent in the Tyrrhenian Sea, where the ventilation seems to be fairly constant since the EMT. Also the western Alboran Sea does not show any temporal trends in ventilation.