Air-sea CO₂fluxes above the stratified oxygen minimum zone in the coastal region off Mexico

Abstract

Oxygen minimum zones (OMZs) are important sources of CO 2 to the atmosphere when physical forces bring subsurface water with high dissolved inorganic carbon (DIC) to the surface. This study examines, for the first time, the influence of the OMZ of the coastal North Eastern Tropical Pacific off Mexico on surface CO 2 fluxes. We use variations in the oxycline depth and subsurface water masses to discern physical oceanographic influences. During two cruises, in November 2009 and August 2010, DIC and total alkalinity (TA) measurements were used to estimate pCO 2 and air-sea CO 2 fluxes. At the OMZ layer, Subtropical Subsurface Water (StSsW) was found to have high pCO 2 values (1290 6 70 latm). Due to strong vertical stratification, however, the relationship between DpCO 2 at the air-sea interface and the oxycline/StSsW upper limit depth was weak. During November, the region was a weak source of CO 2 to the atmosphere (up to 2.5 mmol C m ) prevented subsurface mixing of water from the OMZ to the upper layer; particularly in November 2009 which was during an El Niño event. Results suggest that advection of surface water masses, reinforced by strong vertical stratification, controlled surface pCO 2 , and air-sea CO 2 fluxes.

Reconstruction of super-resolution ocean <i>p</i>CO<sub>2</sub> and air–sea fluxes of CO<sub>2</sub> from satellite imagery in the southeastern Atlantic

“…These methods make use of phenomenological descriptions of fully developed turbulence (FDT) in nonlinear physics, motivated by the values taken on by the Reynolds number in ocean dynamics. As predicted from the theory and also observed in the ocean, in a turbulent flow the coherent vortices (eddies) interact with each other stretching and folding the flow, generating smaller eddies or small-scale filaments and transition fronts characterized by strong tracer gradients (Frisch, 1995). This results in a cascade of energy from large to smaller scales.…”

“…could be higher in the oxygen minimum zones (OMZ) of the eastern boundary upwelling systems (EBUSs) due to the extreme regional variability in these areas (Paulmier et al, 2008;Franco et al, 2014). Indeed, this supports the design of proper methodologies to infer fluxes at high resolution from presently available satellite image data in order to improve current estimates of gas exchanges between the ocean and the atmosphere.…”

“…Geometrical organization of the flow linked to the energy cascade allows for the study of its properties from the geometrical properties of any tracer for which the advection is the dominant process. The relationships between the cascade and the multifractal organization of FDT has been set up either with canonical (Arneodo et al, 1995;Frisch, 1995) or microcanonical (Turiel et al, 2005;Bouchet and Venaille, 2012) descriptions. Within the microcanonical framework (MMF) the singularity exponents unlock the geometrical realization of the multifractal hierarchy.…”

“…In the ocean, the turbulence causes the formation of unsteady eddies on many scales which interact with each other (Frisch, 1995). Most of the kinetic energy of the turbulent motion is contained in the large-scale structures.…”

Influence of post‐Tehuano oceanographic processes in the dynamics of the CO2 system in the Gulf of Tehuantepec, Mexico

“…In the Gulf of Tehuantepec, water masses in the upper 500 m are composed primarily of Tropical Surface Water (TSW) and Subtropical Subsurface Water (StSsW) [ Barton et al ., ; Fiedler and Talley , ]. StSsW (Table ) contains part of the oxygen minimum layer (OML) and the maximum dissolved inorganic carbon (>2200 µmol kg −1 ) [ Franco et al ., ]. The upper depth limit of this water mass ranges between 70 and 100 m; therefore, it could have a significant influence on the biogeochemical processes in GoT surface waters when mesoscale structures, heavy mixing, or upwelling occur.…”