The relationship between gas exchange and wind speed is used extensively for estimating bulk fluxes of atmospheric gases across the air‐sea interface. Here, I provide an update on the frequently used ...method of Wanninkhof (1992). The update of the methodology reflects advances that have occurred over the past two decades in quantifying the input parameters. The general principle of obtaining a relationship constrained by the globally integrated bomb‐14CO2 flux into the ocean remains unchanged. The improved relationship is created using revised global ocean 14C inventories and improved wind speed products. Empirical relationships of the Schmidt number, which are necessary to determine the fluxes, are extended to 40°C to facilitate their use in the models. The focus is on the gas exchange of carbon dioxide, but the suggested functionality can be extended to other gases at intermediate winds (≈4−15 m s−1). The updated relationship, expressed as k = 0.251 (Sc/660)−0.5 where k is the gas transfer velocity, is the average squared wind speed, and Sc is the Schmidt number, has a 20% uncertainty. The relationship is in close agreement with recent parameterizations based on results from gas exchange process studies over the ocean.
The reinvigoration of the Southern Ocean carbon sink Landschützer, Peter; Gruber, Nicolas; Haumann, F. Alexander ...
Science (American Association for the Advancement of Science),
09/2015, Volume:
349, Issue:
6253
Journal Article
Peer reviewed
Open access
Several studies have suggested that the carbon sink in the Southern Ocean—the ocean's strongest region for the uptake of anthropogenic CO2—has weakened in recent decades. We demonstrated, on the ...basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012 the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized.
Although the Southern Ocean is thought to account for a significant portion of the contemporary oceanic uptake of carbon dioxide (CO2), flux estimates in this region are based on sparse observations ...that are strongly biased toward summer. Here we present new estimates of Southern Ocean air‐sea CO2 fluxes calculated with measurements from biogeochemical profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling project during 2014–2017. Compared to ship‐based CO2 flux estimates, the float‐based fluxes find significantly stronger outgassing in the zone around Antarctica where carbon‐rich deep waters upwell to the surface ocean. Although interannual variability contributes, this difference principally stems from the lack of autumn and winter ship‐based observations in this high‐latitude region. These results suggest that our current understanding of the distribution of oceanic CO2 sources and sinks may need revision and underscore the need for sustained year‐round biogeochemical observations in the Southern Ocean.
Plain Language Summary
The Southern Ocean absorbs a great deal of carbon dioxide from the atmosphere and helps to shape the climate of Earth. However, we do not have many observations from this part of the world, especially in winter, because it is remote and inhospitable. Here we present new observations from robotic drifting buoys that take measurements of temperature, salinity, and other water properties year‐round. We use these data to estimate the amount of carbon dioxide being absorbed by the Southern Ocean. In the open water region close to Antarctica, the new estimates are remarkably different from the previous estimates, which were based on data collected from ships. We discuss some possible reasons that the float‐based estimate is different and how this changes our understanding of how the ocean absorbs carbon dioxide.
Key Points
Measurements from biogeochemical profiling floats were used to estimate air‐sea fluxes of carbon dioxide
Significant annual net outgassing of carbon dioxide was observed in the high‐latitude Antarctic‐Southern Zone
In this region, a large difference with previous estimates was found in winter when ship‐based sampling is sparse
GLODAPv2.2019 – an update of GLODAPv2 Olsen, Are; Lange, Nico; Key, Robert M ...
Earth system science data,
09/2019, Volume:
11, Issue:
3
Journal Article
Peer reviewed
Open access
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. This update of GLODAPv2, v2.2019, adds data from 116 cruises to the previous version, extending its coverage in time from 2013 to 2017, while also adding some data from prior years. GLODAPv2.2019 includes measurements from more than 1.1 million water samples from the global oceans collected on 840 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 116 new cruises with the data from the 724 quality-controlled cruises of the GLODAPv2 data product. They correct for errors related to measurement, calibration, and data handling practices, taking into account any known or likely time trends or variations. 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, and 5 % in the halogenated transient tracers. The compilation also includes data for several other variables, such as isotopic tracers. These were not subjected to bias comparison or adjustments. The original data, their documentation and DOI codes are available in the Ocean Carbon Data System of NOAA NCEI (https://www.nodc.noaa.gov/ocads/oceans/GLODAPv2_2019/, last access: 17 September 2019). 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/xnme-wr20 (Olsen et al., 2019). The product files also include significant ancillary and approximated data. These were obtained by interpolation of, or calculation from, measured data. This paper documents the GLODAPv2.2019 methods and provides a broad overview of the secondary quality control procedures and results.
The extended multilinear regression method is used to determine the uptake and storage of anthropogenic carbon in the Atlantic Ocean based on repeat occupations of four cruises from 1989 to 2014 ...(A16, A20, A22, and A10), with an emphasis on the 2003–2014 period. The results show a significant increase in basin‐wide anthropogenic carbon storage in the North Atlantic, which absorbed 4.4 ± 0.9 Pg C decade−1 from 2003 to 2014 compared to 1.9 ± 0.4 Pg C decade−1 for the 1989–2003 period. This decadal variability is attributed to changing ventilation patterns associated with the North Atlantic Oscillation and increasing release of anthropogenic carbon into the atmosphere. There are small changes in the uptake rate of CO2 in the South Atlantic for these time periods (3.7 ± 0.8 Pg C decade−1 versus 3.2 ± 0.7 Pg C decade−1). Several eddies are identified containing ~20% more anthropogenic carbon than the surrounding waters in the South Atlantic demonstrating the importance of eddies in transporting anthropogenic carbon. The uptake of carbon results in a decrease in pH of ~0.0021 ± 0.0007 year−1 for surface waters during the last 10 years, in line with the atmospheric increase in CO2.
Key Points
Large decadal increase in the uptake of anthropogenic carbon in the North Atlantic
The pH in the surface waters has decreased by 0.0021 ± 0.0007 per year
Eddies significantly impact anthropogenic carbon inventories
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. GLODAPv2.2021 is an update of the previous version, GLODAPv2.2020 (Olsen et al., 2020). The major changes are as follows: data from 43 new cruises were added, data coverage was extended until 2020, all data with missing temperatures were removed, and a digital object identifier (DOI) was included for each cruise in the product files. In addition, a number of minor corrections to GLODAPv2.2020 data were performed. GLODAPv2.2021 includes measurements from more than 1.3 million water samples from the global oceans collected on 989 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 CCl.sub.4) 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 World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For this annual update, adjustments for the 43 new cruises were derived by comparing those data with the data from the 946 quality controlled cruises in the GLODAPv2.2020 data product using crossover analysis. Comparisons to estimates of nutrients and ocean CO.sub.2 chemistry based on empirical algorithms provided additional context for adjustment decisions in 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 with to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg.sup.-1 in dissolved inorganic carbon, 4 µmol kg.sup.-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 CO.sub.2 fugacity (fCO.sub.2 ), were not subjected to bias comparison or adjustments.
The past decade has seen a substantial amount of research on air-sea gas exchange and its environmental controls. These studies have significantly advanced the understanding of processes that control ...gas transfer, led to higher quality field measurements, and improved estimates of the flux of climate-relevant gases between the ocean and atmosphere. This review discusses the fundamental principles of air-sea gas transfer and recent developments in gas transfer theory, parameterizations, and measurement techniques in the context of the exchange of carbon dioxide. However, much of this discussion is applicable to any sparingly soluble, non-reactive gas. We show how the use of global variables of environmental forcing that have recently become available and gas exchange relationships that incorporate the main forcing factors will lead to improved estimates of global and regional air-sea gas fluxes based on better fundamental physical, chemical, and biological foundations.
The relationship between gas transfer velocity and wind speed was evaluated at low wind speeds by quantifying the rate of evasion of the deliberate tracer, SF6, from a small oligotrophic lake. ...Several possible relationships between gas transfer velocity and low wind speed were evaluated by using 1-min-averaged wind speeds as a measure of the instantaneous wind speed values. Gas transfer velocities in this data set can be estimated virtually equally well by assuming any of three widely used relationships between k600and winds referenced to 10-m height, U10: (1) a bilinear dependence with a break in the slope at$\sim\!3.7\>m\>s^{-1}$, which resulted in the best fit; (2) a power dependence; and (3) a constant transfer velocity for$U_{10} <\>\sim\!3.7\>m\>s^{-1}$, with a linear dependence on wind speed at higher wind speeds. The lack of a unique relationship between transfer velocity and wind speed at low wind speeds suggests that other processes, such as convective cooling, contribute significantly to gas exchange when the wind speeds are low. All three proposed relationships clearly show a strong dependence on wind for winds >3.7 m s-1which, coupled with the typical variability in instantaneous wind speeds observed in the field, leads to average transfer velocity estimates that are higher than those predicted for steady wind trends. The transfer velocities predicted by the bilinear steady wind relationship for$U_{10} <\>\sim\!3.7\>m\>s^{-1}$are virtually identical to the theoretical predictions for transfer across a smooth surface.
Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and ...Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO
(pCO
) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.
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