Revaluating ocean warming impacts on global phytoplankton

Behrenfeld, Michael J.; O’Malley, Robert T.; Boss, Emmanuel; Westberry, T. K.; Graff, Jason R.; Halsey, Kimberly H.; Milligan, Allen J.; Siegel, David A.; Brown, Matthew B.

doi:10.1038/nclimate2838

Cited by 289 publications

(309 citation statements)

References 44 publications

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“…Our findings suggest that the steep chlorophyll gradients across the coastal transition zone are mainly driven by the nutrient gradients, but they are first amplified by the acclimative capacity, and then further by higher Chl : C ratios at the coastal waters. The large variations in simulated Chl : C ratios within the SNS, both in space and time, indicate that ignoring photoacclimation can lead to potentially flawed estimates for primary production or phytoplankton biomass as was recently pointed out by Arteaga et al (2014) and Behrenfeld et al (2015), based on the variability of Chl : C ratios at global scales. Here we show that this warning applies especially in the coastal environments characterized by steep resource gradients, which may be critical, given the increasing recognition of the role of coastal-shelf systems in the global carbon and nutrient cycling (Fennel, 2010;Bauer et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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Abstract. Ecosystem models often rely on heuristic descriptions of autotrophic growth that fail to reproduce various stationary and dynamic states of phytoplankton cellular composition observed in laboratory experiments. Here, we present the integration of an advanced phytoplankton growth model within a coupled three-dimensional physicalbiogeochemical model and the application of the model system to the southern North Sea (SNS) defined on a relatively high resolution ( ∼ 1.5-4.5 km) curvilinear grid. The autotrophic growth model, recently introduced by Wirtz and Kerimoglu (2016), is based on a set of novel concepts for the allocation of internal resources and operation of cellular metabolism. The coupled model system consists of the General Estuarine Transport Model (GETM) as the hydrodynamical driver, a lower-trophic-level model and a simple sediment diagenesis model. We force the model system with realistic atmospheric and riverine fluxes, background turbidity caused by suspended particulate matter (SPM) and open ocean boundary conditions. For a simulation for the period 2000-2010, we show that the model system satisfactorily reproduces the physical and biogeochemical states of the system within the German Bight characterized by steep salinity; nutrient and chlorophyll (Chl) gradients, as inferred from comparisons against observation data from long-term monitoring stations; sparse in situ measurements; continuous transects; and satellites. The model also displays skill in capturing the formation of thin chlorophyll layers at the pycnocline, which is frequently observed within the stratified regions during summer. A sensitivity analysis reveals that the vertical distributions of phytoplankton concentrations estimated by the model can be qualitatively sensitive to the description of the light climate and dependence of sinking rates on the internal nutrient reserves. A non-acclimative (fixed-physiology) version of the model predicted entirely different vertical profiles, suggesting that accounting for physiological flexibility might be relevant for a consistent representation of the vertical distribution of phytoplankton biomass. Our results point to significant variability in the cellular chlorophyll-to-carbon ratio (Chl : C) across seasons and the coastal to offshore transition. Up to 3-fold-higher Chl : C at the coastal areas in comparison to those at the offshore areas contribute to the steepness of the chlorophyll gradient. The model also predicts much higher phytoplankton concentrations at the coastal areas in comparison to its non-acclimative equivalent. Hence, findings of this study provide evidence for the relevance of physiological flexibility, here reflected by spatial and seasonal variations in Chl : C, for a realistic description of biogeochemical fluxes, particularly in the environments displaying strong resource gradients.

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Section: Discussionmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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“…To a phytoplankton cell, these biomolecular triggers mimic those experienced when PSII is under pressure from excess light, and signals cold-acclimated cells to down-regulate chlorophyll synthesis (Behrenfeld et al, 2016) and cell volume declines to compensate for pigment packaging effects (Raven, 1984;Kirk, 1994). As temperature rises, cells appear to require more light to saturate photosynthesis despite light conditions remaining constant.…”

Section: Temperature Driven Changes In Fitness and Other Functional Tmentioning

confidence: 99%

Thermal Performance Curves of Functional Traits Aid Understanding of Thermally Induced Changes in Diatom-Mediated Biogeochemical Fluxes

et al. 2016

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How the functional traits (FTs) of phytoplankton change with temperature is important for understanding the impacts of ocean warming on phytoplankton mediated biogeochemical fluxes. This study quantifies the thermal performance curves (TPCs) of FTs in the cosmopolitan model diatom, Thalassiosira pseudonana, to advance understanding of trade-offs between physiological (photoacclimation, carbon fixation, nitrate, phosphate, and silicate uptake) and morphological traits (cell volume and frustule silicification). We show that each FT has substantial phenotypic plasticity and exhibits a unique TPC, varying in both shape and thermal optimum, and diverging from the growth response. The TPC for growth was symmetric with a thermal optimum (T opt ) of 18 • C. In comparison, the TPC for primary productivity was warm-skewed with a T opt around 21 • C, whereas frustule silicification decreased linearly with increasing temperature. Together, this suggests that the optimal temperature for overall fitness is a balance of trade-offs in the underlying functional traits. Moreover, these results demonstrate that growth is not necessarily an accurate estimate of overall biogeochemical performance and that temperature change will likely influence elemental fluxes such as carbon and silicon. Finally, we show that temperature-driven changes in individual traits e.g., photoacclimation, can mimic responses experienced under other environmental stressors (high light) and so a multi-trait assessment is essential for accurate interpretation of the cellular impact of warming. This study also reveals that multi-trait analysis, in the context of TPCs, provides insight into the cellular physiology regulating the whole cell response and has the potential to provide better estimates of how diatom-mediated biogeochemical fluxes are likely to be impacted in the context of ocean warming. Analyzing the response of multiple traits more comprehensively over other environmental gradients may therefore provide a useful framework to advance understanding of how taxon-specific functional traits will respond to multifaceted ocean change.

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“…However, this has never been truly demonstrated due to the absence of sufficient data at the proper spatio-temporal scales in the water column. Furthermore, recent studies conducted in various oligotrophic environments, also suggest that [CHL] variability in the surface layer may primarily reflect changes in intracellular pigment concentration, rather than biomass variability (Behrenfeld et al, 2016;Halsey and Jones, 2015;Jakobsen and Markage, 2016;Siegel et al, 2013). Hence, the main processes involved in the seasonal variability of surface chlorophyll in the GOM have not yet been resolved.…”

Section: Introductionmentioning

confidence: 99%

Temporal variability of chlorophyll distribution in the Gulf of Mexico: bio-optical data from profiling floats

et al. 2017

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Abstract. Chlorophyll concentration is a key oceanic biogeochemical variable. In the Gulf of Mexico (GOM), its distribution, which is mainly obtained from satellite surface observations and scarce in situ experiments, is still poorly understood. In 2011-2012, eight profiling floats equipped with biogeochemical sensors were deployed for the first time in the GOM and generated an unprecedented dataset that significantly increased the number of chlorophyll vertical distribution measurements in the region. The analysis of these data, once calibrated, permits us to reconsider the spatial and temporal variability of the chlorophyll concentration in the water column. At a seasonal scale, results confirm the surface signal seen by satellites, presenting maximum concentrations in winter and low values in summer. It is shown that the deepening of the mixed layer is the primary factor triggering the chlorophyll surface increase in winter. In the GOM, a possible interpretation is that this surface increase corresponds to a biomass increase. However, the present dataset suggests that the basin-scale climatological surface increase in chlorophyll content results from a vertical redistribution of subsurface chlorophyll and/or photoacclimation processes, rather than a net increase of biomass. One plausible explanation for this is the decoupling between the mixed-layer depth and the deep nutrient reservoir since mixed-layer depth only reaches the nitracline in sporadic events in the observations. Float measurements also provide evidence that the depth and the magnitude of the deep chlorophyll maximum is strongly controlled by the mesoscale variability, with higher chlorophyll biomass generally observed in cyclones rather than anticyclones.

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Revaluating ocean warming impacts on global phytoplankton

Cited by 289 publications

References 44 publications

The acclimative biogeochemical model of the southern North Sea

The acclimative biogeochemical model of the southern North Sea

Thermal Performance Curves of Functional Traits Aid Understanding of Thermally Induced Changes in Diatom-Mediated Biogeochemical Fluxes

Temporal variability of chlorophyll distribution in the Gulf of Mexico: bio-optical data from profiling floats

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