Hernan E. Garcia

The change in oceanic O 2 inventory associated with recent global warming

Oceans general circulation models predict that global warming may cause a decrease in the oceanic O2 inventory and an associated O2 outgassing. An independent argument is presented here in support of this prediction based on observational evidence of the oceans biogeochemical response to natural warming. On time scales from seasonal to centennial, natural O2 flux/heat flux ratios are shown to occur in a range of 2 to 10 nmol of O2 per joule of warming, with larger ratios typically occurring at higher latitudes and over longer time scales. The ratios are several times larger than would be expected solely from the effect of heating on the O2 solubility, indicating that most of the O2 exchange is biologically mediated through links between heating and stratification. The change in oceanic O2 inventory through the 1990s is estimated to be 0.3 ± 0.4 × 1014 mol of O2 per year based on scaling the observed anomalous long-term ocean warming by natural O2 flux/heating ratios and allowing for uncertainty due to decadal variability. Implications are discussed for carbon budgets based on observed changes in atmospheric O2/N2 ratio and based on observed changes in ocean dissolved inorganic carbon.

World ocean atlas 2001. Volume 2, Salinity

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On the Global Oxygen Anomaly and Air-Sea Flux

We present a new climatology of monthly air-sea oxygen fluxes throughout the ice-free surface global ocean. The climatology is based on weighted linear least squares regressions using heat flux monthly anomalies for spatial and temporal interpolation of historical O2 data. The seasonal oceanic variations show that the tropical belt (20°S-20°N) is characterized by relatively small air-sea fluxes when compared to the middle to high latitudes (40°–70°). The largest and lowest seasonal fluxes occur during summer and winter in both hemispheres. By means of an atmospheric transport model we show that our climatology is in better agreement with the observed amplitude and phasing of the variations in atmospheric O2/N2 ratios because of seasonal air-sea exchanges at baseline stations in the Pacific Ocean than with previous air-sea O2 climatologies. Our study indicates that the component of the air-sea O2 flux that correlates with heat flux dominates the large-scale air-sea O2 exchange on seasonal timescales. The contribution of each major oceanic basin to the atmospheric observations is described. The seasonal net thermal (SNOT) and biological (SNOB) outgassing components of the flux are examined in relation to latitudinal bands, basin-wide, and hemispheric contributions. The Southern Hemispheres SNOB (∼0.26 Pmol) and SNOT (∼0.29 Pmol) values are larger than the Northern Hemispheres SNOB (∼0.15 Pmol) and SNOT (∼0.16 Pmol) values (1 Pmol = 1015 mol). We estimate a global extratropical carbon new production during the outgassing season of 3.7 Pg C (1 Pg = 1015 g), lower than previous estimates with air-sea O2 climatologies.

On the variability of dissolved oxygen and apparent oxygen utilization content for the upper world ocean: 1955 to 1998

exchange between the atmosphere and the ocean. We show that the basin-scale content variability in O2, AOU, and heat in this layer is characterized by relatively small linear trends superimposed on large decadal fluctuations. The magnitudes of the O2 and AOU trends are dependent on the starting and ending time periods chosen as reference endpoints indicating that the trends for one time period should not be extrapolated to other time periods. The observations indicate also that there is no obvious O2-to-heat content relation which unambiguously relates the trends in O2 content to the trends in heat content for all time periods. We hypothesize that both physical and biochemical processes which affect the upper-ocean O2 content vary in time and space.

Decadal‐scale chemical variability in the subtropical North Atlantic deduced from nutrient and oxygen data

In August 1992 the R/V Hesperides reoccupied a transatlantic section nominally along 24.5°N previously sampled in April 1957 and in August 1981. Observation of significant warming over the 35-year period has already been reported for the ocean layer between 800 and 2500 m depth (∼0.01°C yr−1). We examine decadal-scale variability in the nutrient and O2 measurements primarily comparing the 1981 and 1992 sections. The basin-scale water mass structure remained relatively unchanged from 1981 to 1992. Zonally averaged differences of the chemical data show that the layer of maximum increase in temperature and salinity at 1100 m is roughly coincident with an apparent decrease in O2 concentration of about 7 μmol kg−1. The O2 decrease is equivalent to an average rate of decrease of 0.6 μmol kg−1 yr−1. The vertically integrated water column O2 utilization rate is 0.9 mol m2 yr−1. This is equivalent to 23–33% of the new production rate estimates in the Sargasso Sea. The O2 decrease at 1100 m cannot be explained by using oxidative ratios relating regeneration of nutrients and O2 consumption. The O2 decrease is not highly correlated with zonally averaged changes in the nutrient measurements. The nutrients show small or insignificant changes near 1100 m over the 11-year period. Part of the O2 decrease might be explained by measurement error (30%) and changes in solubility (20%) due to warming. The chemical changes are likely caused by changes in the characteristics of the source waters entering 24.5°N near 700–1700 m depth.

World ocean atlas 2013. Volume 4, Dissolved inorganic nutrients (phosphate, nitrate, silicate)

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2013 World Ocean Atlas Aids High‐Resolution Climate Studies

Since 1982, the Levitus Climatological Atlas of the Worlds Ocean and each succeeding World Ocean Atlas have been used to provide initial and boundary conditions for modeling studies, as well as baselines for climate studies. However, there has been a broadening demand for ocean modeling on spatial scales finer than 1-degree resolution [e.g., Penduff et al., 2010]. Likewise, vertical resolution for isobaric coordinate models is important for realistic representation of ocean processes [Wang et al., 2008].