Biogeochemical versus ecological consequences of modeled ocean physics

Abstract

Abstract. We present a systematic study of the differences generated by coupling the same ecological-biogeochemical model to a 1 • , coarse-resolution, and 1/6 • , eddy-permitting, global ocean circulation model to (a) biogeochemistry (e.g., primary production) and (b) phytoplankton community structure. Surprisingly, we find that the modeled phytoplankton community is largely unchanged, with the same phenotypes dominating in both cases. Conversely, there are large regional and seasonal variations in primary production, phytoplankton and zooplankton biomass. In the subtropics, mixed layer depths (MLDs) are, on average, deeper in the eddy-permitting model, resulting in higher nutrient supply driving increases in primary production and phytoplankton biomass. In the higher latitudes, differences in winter mixed layer depths, the timing of the onset of the spring bloom and vertical nutrient supply result in lower primary production in the eddy-permitting model. Counterintuitively, this does not drive a decrease in phytoplankton biomass but results in lower zooplankton biomass. We explain these similarities and differences in the model using the framework of resource competition theory, and find that they are the consequence of changes in the regional and seasonal nutrient supply and light environment, mediated by differences in the modeled mixed layer depths. Although previous work has suggested that complex models may respond chaotically and unpredictably to changes in forcing, we find that our model responds in a predictable way to different ocean circulation forcing, despite its complexity. The use of frameworks, such as resource competition theory, provides a tractable way to explore the differences and similarities that occur. As this model has many similarities to other widely used biogeochemical models that also resolve multiple phytoplankton phenotypes, this study provides important insights into how the results of running these models under different physical conditions might be more easily understood.

Dimensions of marine phytoplankton diversity

“…Meso-and sub-mesoscale features give rise to temporal increases in nutrient supplies (see e.g. Clayton et al, 2017), and, according to our results, this suggests temporal increases in size classes during such events. Sub-and mesoscale mixing in frontal regions will also enhance species richness in hot spots (Clayton et al, 2013) but also result in a general increase in species richness (Lévy et al, 2014).…”

“…Only recently have studies incorporated diversity from a genomic perspective (e.g. de Vargas et al, 2015). Genomic diversity tends to capture a much higher diversity than other methods, with a long tail of rare species not captured by other measurements (Busseni, 2018).…”

Biogeography of zooplankton feeding strategy

“…5). This tendency is known from previous applications of the model configuration providing the basis for our setup (Follows et al 2007;Prowe et al 2012a), and might partly be caused by the relatively coarse, non-eddy-permitting spatial resolution underestimating vertical transport of nutrients (Clayton et al 2017). Coarse resolution simulations furthermore tend to overestimate phytoplankton production and biomass in the temperate latitudes, which also occurs in our simulations.…”

“…5), driven by upwelling of nutrient-rich deep waters. This would lead to the p-c-A food chain dominating in the model, or, as discussed above, to a trophic link currently not resolved between large phytoplankton and C. In our simulation, the coarse resolution of the model likely hinders the upwelling of nutrients and thereby PP (Clayton et al 2017).…”

Mesoscale Effects on Carbon Export: A Global Perspective

“…Adding a biogeochemical model requires additional computational effort and has been reported in only a few studies. Clayton et al (2013Clayton et al ( , 2017) report on the changes in biodiversity and biogeochemistry between an eddy permitting (1/6 ∘ ) and coarser-resolution (1 ∘ ) ESM with a many-plankton ecosystem biogeochemistry model. Like previous regional models, they find increases in mixed layer depth (MLD) across the tropics and subtropics, corresponding to increases in vertical nitrate flux, driving greater primary production and plankton biomass.…”