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Gas exchange between the atmosphere and ocean interior profoundly impacts global climate and biogeochemistry. However, our understanding of the relevant physical processes remains limited by a scarcity of direct observations. Dissolved noble gases in the deep ocean are powerful tracers of physical air-sea interaction due to their chemical and biological inertness, yet their isotope ratios have remained underexplored. Here, we present high-precision noble gas isotope and elemental ratios from the deep North Atlantic (~32°N, 64°W) to evaluate gas exchange parameterizations using an ocean circulation model. The unprecedented precision of these data reveal deep-ocean undersaturation of heavy noble gases and isotopes resulting from cooling-driven air-to-sea gas transport associated with deep convection in the northern high latitudes. Our data also imply an underappreciated and large role for bubble-mediated gas exchange in the global air-sea transfer of sparingly soluble gases, including O 2 , N 2 , and SF 6 . Using noble gases to validate the physical representation of air-sea gas exchange in a model also provides a unique opportunity to distinguish physical from biogeochemical signals. As a case study, we compare dissolved N 2 /Ar measurements in the deep North Atlantic to physics-only model predictions, revealing excess N 2 from benthic denitrification in older deep waters (below 2.9 km). These data indicate that the rate of fixed N removal in the deep Northeastern Atlantic is at least three times higher than the global deep-ocean mean, suggesting tight coupling with organic carbon export and raising potential future implications for the marine N cycle. 

Assessment of the global budget of the greenhouse gas nitrous oxide ( ${\mathrm{N}}_2$O) is limited by poor knowledge of the oceanic ${\mathrm{N}}_2$O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatological ${\mathrm{N}}_2$O emissions from the ocean by training a supervised learning algorithm with over 158,000 ${\mathrm{N}}_2$O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots of ${\mathrm{N}}_2$O flux and reveals a vigorous global seasonal cycle. We estimate an annual mean ${\mathrm{N}}_2$O flux of 4.2 ± 1.0 Tg N $\cdot {\mathrm{y}}^{-1}$, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. This ${\mathrm{N}}_2$O flux ranges from a low of 3.3 ± 1.3 Tg N $\cdot {\mathrm{y}}^{-1}$in the boreal spring to a high of 5.5 ± 2.0 Tg N $\cdot {\mathrm{y}}^{-1}$in the boreal summer. Much of the seasonal variations in global ${\mathrm{N}}_2$O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the global ${\mathrm{N}}_2$O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmospheric ${\mathrm{N}}_2$O budget. 

Abstract. Marine diazotrophs convert dinitrogen (N2) gas intobioavailable nitrogen (N), supporting life in the global ocean. In 2012, thefirst version of the global oceanic diazotroph database (version 1) waspublished. Here, we present an updated version of the database (version 2),significantly increasing the number of in situ diazotrophic measurements from13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cellabundance, and nifH gene copy abundance have increased by 184 %, 86 %, and809 %, respectively. Version 2 includes two new data sheets for the nifH genecopy abundance of non-cyanobacterial diazotrophs and cell-specific N2fixation rates. The measurements of N2 fixation rates approximatelyfollow a log-normal distribution in both version 1 and version 2. However,version 2 considerably extends both the left and right tails of thedistribution. Consequently, when estimating global oceanic N2 fixationrates using the geometric means of different ocean basins, version 1 andversion 2 yield similar rates (43–57 versus 45–63 Tg N yr−1; rangesbased on one geometric standard error). In contrast, when using arithmeticmeans, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1 (mean ± standard error; same hereafter) compared to version 1(74±7 Tg N yr−1). Specifically, substantial rate increases areestimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics,and for the North Atlantic Ocean (40±9 versus 10±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in theIndian Ocean to be 35±14 Tg N yr−1, which could not be estimatedusing version 1 due to limited data availability. Furthermore, a comparisonof N2 fixation rates obtained through different measurement methods atthe same months, locations, and depths reveals that the conventional15N2 bubble method yields lower rates in 69 % cases compared tothe new 15N2 dissolution method. This updated version of thedatabase can facilitate future studies in marine ecology andbiogeochemistry. The database is stored at the Figshare repository(https://doi.org/10.6084/m9.figshare.21677687; Shao etal., 2022). 

Abstract. In the current era of rapid climate change, accuratecharacterization of climate-relevant gas dynamics – namely production,consumption, and net emissions – is required for all biomes, especially thoseecosystems most susceptible to the impact of change. Marine environmentsinclude regions that act as net sources or sinks for numerous climate-activetrace gases including methane (CH4) and nitrous oxide (N2O). Thetemporal and spatial distributions of CH4 and N2O are controlledby the interaction of complex biogeochemical and physical processes. Toevaluate and quantify how these mechanisms affect marine CH4 andN2O cycling requires a combination of traditional scientificdisciplines including oceanography, microbiology, and numerical modeling.Fundamental to these efforts is ensuring that the datasets produced byindependent scientists are comparable and interoperable. Equally critical istransparent communication within the research community about the technicalimprovements required to increase our collective understanding of marineCH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB)was organized to enhance dialogue and collaborations pertaining tomarine CH4 and N2O. Here, we summarize the outcomes from theworkshop to describe the challenges and opportunities for near-futureCH4 and N2O research in the marine environment. 

Abstract Dinitrogen (N₂) fixation is an important source of biologically reactive nitrogen (N) to the global ocean. The magnitude of this flux, however, remains uncertain, in part because N₂fixation rates have been estimated following divergent protocols and because associated levels of uncertainty are seldom reported—confounding comparison and extrapolation of rate measurements. A growing number of reports of relatively low but potentially significant rates of N₂fixation in regions such as oxygen minimum zones, the mesopelagic water column of the tropical and subtropical oceans, and polar waters further highlights the need for standardized methodological protocols for measurements of N₂fixation rates and for calculations of detection limits and propagated error terms. To this end, we examine current protocols of the¹⁵N₂tracer method used for estimating diazotrophic rates, present results of experiments testing the validity of specific practices, and describe established metrics for reporting detection limits. We put forth a set of recommendations for best practices to estimate N₂fixation rates using¹⁵N₂tracer, with the goal of fostering transparency in reporting sources of uncertainty in estimates, and to render N₂fixation rate estimates intercomparable among studies.