Jens Daniel Müller

and 13 more

Rik Wanninkhof

and 5 more

Monthly global sea-air CO2 flux estimates from 1998-2020 are produced by extrapolation of surface water fugacity of CO2 (fCO2w) observations using an Extra-trees (ET) machine learning technique. This new product (AOML_ET) is one of the eleven observation-based submissions to the second REgional Carbon Cycle Assessment and Processes (RECCAP2) effort. The target variable fCO2w is derived using the predictor variables including date, location, sea surface temperature, mixed layer depth, and chlorophyll-a. A monthly resolved sea-air CO2 flux product on a 1˚ by 1˚ grid is created from this fCO2w product using a bulk flux formulation. Average global sea-air CO2 fluxes from 1998-2020 are -1.7 Pg C yr-1 with a trend of 0.9 Pg C decade-1. The sensitivity to omitting mixed layer depth or chlorophyll-a as predictors is small but changing the target variable from fCO2w to air-water fCO2 difference has a large effect, yielding an average flux of -3.6 Pg C yr-1 and a trend of 0.5 Pg C decade-1. Substituting a spatially resolved marine air CO2 mole fraction product for the commonly used zonally invariant marine boundary layer CO2 product yield greater influx and less outgassing in the Eastern coastal regions of North America and Northern Asia but with no effect on the global fluxes. A comparison of AOML_ET for 2010 with an updated climatology following the methods of Takahashi et al. (2009), that extrapolates the surface CO2 values without predictors, shows overall agreement in global patterns and magnitude.

Fabian A Gomez

and 3 more

In the northern Gulf of Mexico shelf, the Mississippi-Atchafalaya River System (MARS) impacts the carbonate system by delivering freshwater with a distinct seasonal pattern in both total alkalinity (Alk) and dissolved inorganic carbon (DIC), and promoting biologically-driven changes in DIC through nutrient inputs. However, how and to what degree these processes modulate the interannual variability in calcium carbonate solubility have been poorly documented. Here, we use an ocean-biogeochemical model to investigate the impact of MARS’s discharge and chemistry on interannual anomalies of aragonite saturation state (ΩAr). Based on model results, we show that the enhanced mixing of riverine waters with a low buffer capacity (low Alk-to-DIC ratio) during high-discharge winters promotes a significant ΩAr decline over the inner-shelf. We also show that increased nutrient runoff and vertical stratification during high-discharge summers promotes strong negative anomalies in bottom ΩAr, and less intense but significant positive anomalies in surface ΩAr. Therefore, increased MARS discharge promotes an increased frequency of suboptimal ΩAr levels for nearshore coastal calcifying species. Additional sensitivity experiments further show that reductions in the Alk-to-DIC ratio and nitrate concentration from the MARS significantly modify the simulated ΩAr spatial patterns, weakening the positive surface ΩAr anomalies during high-discharge summers or even producing negative surface ΩAr anomalies. Our findings suggest that riverine water carbonate chemistry is a main driver of interannual variability in ΩAr over river dominated ocean margins.

Christopher Sabine

and 2 more

Significant advancements have been made over the past four decades in understanding and quantifying the stocks and flows of carbon between the reservoirs. However, knowledge of the complex oceanic processes influencing the carbon cycle has been largely compartmentalized into physico-chemical and biological studies. The connections between coastal and open-ocean carbon processes have also been understudied. To fully appreciate the ocean carbon cycle, and its anticipated changes in the future, a holistic and integrated approach to ocean carbon cycle research is needed. In particular, a greater quantitative understanding of how biological processes interact with the physical and chemical drivers in the open ocean and in coastal waters is needed. Moreover, the carbon cycle needs to be understood in the current socio-economic context and large anticipated changes in the next decades. To address these issues, the Integrated Ocean Carbon Research (IOC-R), a formal IOC working group, was formed in 2018. The working group is a response to the UN Decade of Ocean Science for Sustainable Development 2021-2030, “the Decade”. The IOC-R will contribute to the science elements of an overarching Implementation Plan for the Decade. The Implementation Plan is a high-level framework to guide actions by which ocean science can more effectively deliver its contribution to achieving the societal outcomes outlined for the Decade. The IOC-R focusses the ocean carbon cycle component of the Implementation Plan by addressing key issues in ocean carbon research through a combined strategy of research and observational goals. The research will be framed by four key questions that were formulated at the inaugural Expert Workshop on Integrated Ocean Carbon Research at the IOC-UNESCO Headquarters in Paris, France on Oct. 28-30, 2019: 1) Will the ocean uptake of anthropogenic carbon dioxide (CO2) continue as primarily an abiotic process? 2) What is the role of biology in the ocean carbon cycle? 3) What are the exchanges of carbon between the land-ocean continuum and how are they evolving over time? 4) How are humans altering the ocean carbon cycle, and what are the feedbacks?