Abstract
Abstract. We present a newly developed upper-thermocline, open-ocean biogeochemical flux model that is complex and flexible enough to capture open-ocean ecosystem dynamics but reduced enough to incorporate into highly resolved numerical simulations and parameter optimization studies with limited additional computational cost. The model, which is derived from the full 56-state-variable Biogeochemical Flux Model (BFM56; Vichi et al., 2007), follows a biological and chemical functional group approach and allows for the development of critical non-Redfield nutrient ratios. Matter is expressed in units of carbon, nitrogen, and phosphate, following techniques used in more complex models. To reduce the overall computational cost and to focus on upper-thermocline, open-ocean, and non-iron-limited or non-silicate-limited conditions, the reduced model eliminates certain processes, such as benthic, silicate, and iron influences, and parameterizes others, such as the bacterial loop. The model explicitly tracks 17 state variables, divided into phytoplankton, zooplankton, dissolved organic matter, particulate organic matter, and nutrient groups. It is correspondingly called the Biogeochemical Flux Model 17 (BFM17). After describing BFM17, we couple it with the one-dimensional Princeton Ocean Model for validation using observational data from the Sargasso Sea. The results agree closely with observational data, giving correlations above 0.85, except for chlorophyll (0.63) and oxygen (0.37), as well as with corresponding results from BFM56, with correlations above 0.85, except for oxygen (0.56), including the ability to capture the subsurface chlorophyll maximum and bloom intensity. In comparison to previous models of similar size, BFM17 provides improved correlations between several model output fields and observational data, indicating that reproduction of in situ data can be achieved with a low number of variables, while maintaining the functional group approach. Notable additions to BFM17 over similar complexity models are the explicit tracking of dissolved oxygen, allowance for non-Redfield nutrient ratios, and both dissolved and particulate organic matter, all within the functional group framework.
Highlights
Biogeochemical (BGC) tracers and their interactions with upper-ocean physical processes, from basin-scale circulations to millimeter-scale turbulent dissipation, are critical for understanding the role of the ocean in the global carbon cycle
With a minimal increase in the number and complexity of the model equations, such as those associated with tracking phosphate in addition to carbon and nitrate, and by including both particulate and dissolved organic nutrient budgets, we anticipate that a significant increase in model accuracy and applicability might be achieved over previous models of similar complexity
Field data for calibration and validation of Biogeochemical Flux Model 17 (BFM17) are taken from the Bermuda Atlantic Time-series Study (BATS) (Steinberg et al, 2001) and the Bermuda Testbed Mooring (BTM) (Dickey et al, 2001) sites, which are located in the Sargasso Sea (31◦40 N, 64◦10 W) in the North Atlantic subtropical gyre
Summary
Biogeochemical (BGC) tracers and their interactions with upper-ocean physical processes, from basin-scale circulations to millimeter-scale turbulent dissipation, are critical for understanding the role of the ocean in the global carbon cycle. We note that other complex BGC models have been calibrated using data from the Sargasso Sea, such as those developed in Levy et al (2005), Ayata et al (2013), Spitz et al (2001), Doney et al (1996), Fasham et al (1990), Fennel et al (2001), Hurtt and Armstrong (1996), Hurtt and Armstrong (1999), and Lawson et al (1996) Each of these models employs less than 10 species and none use a CFF approach or include oxygen, a tracer that is historically difficult to predict. Results from an initial 0-D test of BFM17 are provided in Appendix B
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