Catherine E. Cosca

CO2 distributions in the equatorial Pacific during the 1991–1992 ENSO event

Abstract As part of the U.S. JGOFS Equatorial Pacific Process Study, measurements of CO2 species concentrations were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992. Surface water fCO2 data indicate significant differences between the springtime El Nino conditions and the autumn post-El Nino conditions. The autumn fugacity (ΔfCO2) maxima were approximately 15–55 μatm higher than in the spring. The lower surface ΔfCO2 values in the spring data set were the result of: (i) advection of CO2-depleted water from the west at the equator near 170°W; and (ii) reduced upwelling and lower ΔfCO2 distributions as consequence of lighter zonal winds in the eastern Pacific from 140°W to 110°W. Assuming the springtime data are representative of the El Nino conditions and the autumn data are representative of the post-El Nino conditions, it is estimated that the net annual C02 flux during the 1991–1992 ENSO period is 0.3 Gt C. Over 60% of this flux occurred during the 4-month period in the autumn when ΔfCO2 values were close to normal. The net annual reduction of the ocean-atmosphere CO2 flux during the 1991–1992 El Nino is estimated to be on the order of 0.5–0.7 Gt C.

North Pacific Ocean CO2 disequilibrium for spring through summer, 1985–1989

Extensive measurements of CO2 fugacity in the North Pacific surface ocean and overlying atmosphere during the years 1985–1989 are synthesized and interpreted to yield a basin-wide estimate of ΔfCO2. The observations, taken from February through early September, suggest that the subtropical and subarctic North Pacific is a small sink for atmospheric CO2 (0.07 to 0.2 Gton C (half year)−1 for the region north of 15°N). Objective analysis techniques are used to estimate uncertainty fields resulting from constructing basin-wide contours of oceanic fCO2 on the basis of individual cruise transects. The uncertainties are significant and imply that future sampling programs need to recognize that estimating oceanic uptake of anthropogenic CO2 from ship-transect observations of oceanic fCO2 alone will require very extensive sampling.

Annual sea‐air CO2 fluxes in the Bering Sea: Insights from new autumn and winter observations of a seasonally ice‐covered continental shelf

High-resolution data collected from several programs have greatly increased the spatiotemporal resolution of pCO2(sw) data in the Bering Sea, and provided the first autumn and winter observations. Using data from 2008 to 2012, monthly climatologies of sea-air CO2 fluxes for the Bering Sea shelf area from April to December were calculated, and contributions of physical and biological processes to observed monthly sea-air pCO2 gradients (?pCO2) were investigated. Net efflux of CO2 was observed during November, December, and April, despite the impact of sea surface cooling on ?pCO2. Although the Bering Sea was believed to be a moderate to strong atmospheric CO2 sink, we found that autumn and winter CO2 effluxes balanced 65% of spring and summer CO2 uptake. Ice cover reduced sea-air CO2 fluxes in December, April, and May. Our estimate for ice-cover corrected fluxes suggests the mechanical inhibition of CO2 flux by sea-ice cover has only a small impact on the annual scale (<2%). An important data gap still exists for January to March, the period of peak ice cover and the highest expected retardation of the fluxes. By interpolating between December and April using assumptions of the described autumn and winter conditions, we estimate the Bering Sea shelf area is an annual CO2 sink of ?6.8 Tg C yr?1. With changing climate, we expect warming sea surface temperatures, reduced ice cover, and greater wind speeds with enhanced gas exchange to decrease the size of this CO2 sink by augmenting conditions favorable for greater wintertime outgassing.