Summertime Atmospheric Boundary Layer Gradients of O₂ and CO₂ over the Southern Ocean

Abstract

We present airborne observations of the vertical gradient of atmospheric oxygen (δ(O2/N2)) and carbon dioxide (CO2) through the atmospheric boundary layer (BL) over the Drake Passage region of the Southern Ocean, during the O2/N2 Ratio and CO2 Airborne Southern Ocean Study, from 15 January to 29 February 2016. Gradients were predominately anticorrelated, with excesses of δ(O2/N2) and depletions of CO2 found within the boundary layer, relative to a mean reference height of 1.7 km. Through analysis of the molar ratio of the gradients (GR), the behavior of other trace gases measured in situ, and modeling experiments with the Community Earth System Model, we found that the main driver of gradients was air‐sea exchange of O2 and CO2 driven by biological processes, more so than solubility effects. An exception to this was in the eastern Drake Passage, where positive GRs were occasionally observed, likely due to the dominance of thermal forcing on the air‐sea flux of both species. GRs were more spatially consistent than the magnitudes of the gradients, suggesting that GRs can provide integrated process constraints over broad spatial scales. Based on the model simulation within a domain bounded by 45°S, 75°S, 100°W, and 45°W, we show that the sampling density of the campaign was such that the observed mean GR (± standard error), −4.0± 0.8 mol O2 per mol CO2, was a reasonable proxy for both the mean GR and the mean molar ratio of air‐sea fluxes of O2 and CO2 during the O2/N2 Ratio and CO2 Airborne Southern Ocean Study.

Airborne measurements of oxygen concentration from the surface to the lower stratosphere and pole to pole

“…While airborne measurements of atmospheric O 2 come with many challenges, the potential for new scientific insights based on these measurements justifies meeting them. Airborne atmospheric O 2 measurements provide unique constraints on carbon cycle and physical climate processes (e.g., Bent, 2014;Nevison et al, 2015;Resplandy et al, 2016;Stephens et al, 2018;Asher et al, 2019;Morgan et al, 2019b). Precise, high resolution, global scale, seasonally resolved, profiling airborne measurements https://doi.org/10.5194/amt-2020-294 Preprint.…”

Atmospheric O2 and CO2 measurements at a single height provide weak constraint on surface carbon exchange

“…by flask sampling from aircraft. Although some studies have measured vertical profiles of O 2 and CO 2 , they primarily focused on well-mixed profiles or profiles over the ocean (Morgan et al, 2019;Stephens et al, 2021;Ishidoya et al, 2022b). Hence, careful consideration of the timing and location of the vertical measurements is important to advance our knowledge of the diurnal behaviour of ER atmos .…”

Observed APO Seasonal Cycles in the Pacific: Estimation of Autumn O2 Oceanic Emissions

“…In particular, joint observations of long-term atmospheric O2 and carbon dioxide (CO2) variations have been essential to assess the partitioning of fossil-fuel-derived CO2 sequestration between manuscript submitted to Global Biogeochemical Cycles the terrestrial biosphere and the ocean (Battle et al, 2000(Battle et al, , 2006Goto et al, 2017;Ishidoya, Morimoto et al, 2012;Keeling & Shertz, 1992;Manning & Keeling, 2006;Tohjima et al, 2019). Since the early studies, numerous campaigns for concurrent measurements of atmospheric O2 and CO2 have been conducted from diverse platforms, including ground stations (e.g., Heimann et al, 2022;Manning & Keeling, 2006;Tohjima et al, 2003), ships (e.g., Ishidoya et al, 2016;Pickers et al, 2017;Tohjima, Mukai et al, 2005), and aircraft (e.g., , Ishidoya et al, 2022Morgan et al, 2019;Stephens et al, 2021).…”