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The bio-physical feedback process between the marine ecosystem and the tropical climate system is investigated using both an ocean circulation model and a fully-coupled ocean–atmosphere circulation model, which interact with a biogeochemical model. We found that the presence of chlorophyll can have significant impact on the characteristics of the E...
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... The intermodel diversity in tropical Pacific SST can be attributed to various dynamic and thermodynamic mechanisms 9 . Biological feedback from marine phytoplankton has also been recognized recently as a potential contributing source in controlling tropical Pacific SST [10][11][12][13] . One notable aspect of this feedback is the bio-optical effect, whereby chlorophyll and related pigments in phytoplankton alter the heating of the ocean by reducing the penetration of shortwave radiation. ...
... Although the increase in chlorophyll concentrations in the TEP in BIO_on is expected to induce ocean surface warming due to the absorption of more shortwave radiation in the upper ocean (Fig. 3b), high chlorophyll in the TEP is known to have a cooling effect due to indirect ocean dynamic processes responding to the biologically induced shortwave heating 11,12 . That is, the upper-level shortwave heating caused by the increase in chlorophyll reinforces the stratification of the upper ocean, leads to the shallowing of the mixed layer and enhances poleward volume transport, thereby intensifying equatorial upwelling ( Fig. 3c; see Methods for further details), as shown in previous studies 11,33,34 . ...
The effects of bio-optical feedback through chlorophyll on future tropical cyclone (TC) activity are not well understood. Here we use Earth system model simulations with the biogeochemical feedback turned on and off to investigate the influence of chlorophyll changes on projections of TCs over the western North Pacific (WNP). An increase in chlorophyll in the tropical eastern Pacific and a decrease in the tropical western Pacific lead to a La Niña-like sea surface temperature warming. This pattern plays a crucial role in enhancing the genesis potential index over the southeastern WNP by 10.16% through strengthening of the Walker and local Hadley circulations. The enhanced genesis potential index is further supported by an additional higher-resolution atmospheric model experiment that shows a 71% increase in TC genesis over the southeastern WNP (from 2.00 to 3.43 yr⁻¹) and a 27.02% enhancement in TC landfall frequency in East Asia (from 4.33 to 5.50 yr⁻¹).
... Therefore, it is invaluable to fully understand ENSO-related mechanisms that control phytoplankton biomass and community composition under various climate scenarios. Meanwhile, ENSO can also be modulated by changes in marine ecosystems in the tropical Pacific through a direct warming effect and an indirect cooling effect, since chlorophyll in phytoplankton affects the absorption of shortwave radiation and subsequently the vertical and meridional heat gradient (Heinemann et al., 2011;Lengaigne et al., 2007;Nakamoto et al., 2001;Park et al., 2014;Shi et al., 2023;Tian et al., 2020;Zhang et al., 2009Zhang et al., , 2018. Though the overall effect of phytoplankton on ENSO remains uncertain, the facts of biologically induced changes in the physical environment are undeniable and have been proven to be a crucial factor in improving the accuracy of numerical models (Gnanadesikan et al., 2004;Manizza et al., 2005;Murtugudde et al., 2002). ...
The present study aims to investigate the influences of El Niño and Southern Oscillation (ENSO) events on chlorophyll biomass in the tropical Pacific under historical and RCP8.5 scenarios with simulations from the Community Earth System Model Large Ensemble (CESM‐LE) project. Large variance in surface chlorophyll concentrations is identified across the Peruvian Upwelling (PU), Equatorial Upwelling (EU), and Western Pacific (WP) regions within the tropical Pacific. Results suggest that responses of surface chlorophyll to ENSO in these regions are governed by different mechanisms. The increasing chlorophyll during La Niña is a consequence of increasing nutrients, influenced by local upwelling systems in the PU and EU regions, while the supplementary nutrients in the WP region arise from the eastern Pacific through stronger surface westward currents. Under RCP8.5 scenario, stronger water warming in the eastern equatorial Pacific leads to a remarkable reduction in the amplitudes of seasonal cycles and interannual variations of chlorophyll in both PU and EU regions. This results in less responsiveness of the chlorophyll biomass to El Niño and moderate La Niña compared to the historical period. However, though warming induces a decrease in chlorophyll concentrations in the WP region, the interannual variations of chlorophyll have shown an improvement in correlation with ENSO events. Meanwhile, despite the small phytoplankton‐dominated community being observed under future scenario, species dominance is likely to shift back to diatoms once extreme La Niña occurs, which is unseen in all El Niño and moderate La Niña cases.
... The conflicting results reported in the literature were mainly due to diverging bio-optical protocols among models rather than the inclusion of air-sea coupling. According to Park et al. (2014), atmosphere-ocean coupling amplifies the magnitude of PLF-induced changes without altering the sign of the response obtained in ocean-only simulations. Two main causes were put forward to explain the sign of the final heat perturbation: either an indirect dynamical response (Murtugudde et al., 2002;Löptien et al., 2009) or a direct thermal effect (Mignot et al., 2013;Hernandez et al., 2017). ...
... Hernandez et al. (2017) further distinguished a local from a remote thermal effect by highlighting the important role played by the advection of offshore CHL-induced cold anomalies in the Benguela upwelling waters. The interplay of these mechanisms is regionally variable (Park et al., 2014). Despite the diversity of modelled responses, a consensus emerges on the first-order effect of PLF on the ocean physics, which is to perturb the ocean thermal structure (Nakamoto et al., 2001;Murtugudde et al., 2002;Oschlies, 2004;Manizza et al., 2005Manizza et al., , 2008Anderson et al., 2007;Lengaigne et al., 2007;Gnanadesikan and Anderson, 2009;Löptien et al., 2009;Patara et al., 2012;Mignot et al., 2013;Hernandez et al., 2017). ...
... In some cases, the advection and upwelling of subsurface cold anomalies can lead to remote cooling effects (Hernandez et al., 2017;Echevin et al., 2022). Dynamical readjustment in response to perturbations in thermal structure has also been shown to have a cooling effect by increasing upwelling of cold water to the ocean surface (Manizza et al., 2005;Marzeion et al., 2005;Nakamoto et al., 2001;Löptien et al., 2009;Lengaigne et al., 2007;Park et al., 2014). Because these effects depend on upper-ocean stratification, an important role is attributed to modelled seasonal deepening of the mixed layer, as it determines the intensity of the underlying temperature anomaly and its vertical movement to the surface. ...
The phytoplankton–light feedback (PLF) describes the interaction between phytoplankton biomass and the downwelling shortwave radiation entering the ocean. The PLF allows the simulation of differential heating across the ocean water column as a function of phytoplankton concentration. Only one third of the Earth system models contributing to the 6th phase of the Coupled Model Intercomparison Project (CMIP6) include a complete representation of the PLF. In other models, the PLF is either approximated by a prescribed climatology of chlorophyll or not represented at all. Consequences of an incomplete representation of the PLF on the modelled biogeochemical state have not yet been fully assessed and remain a source of multi-model uncertainty in future projection. Here, we evaluate within a coherent modelling framework how representations of the PLF of varying complexity impact ocean physics and ultimately marine production of nitrous oxide (N2O), a major greenhouse gas. We exploit global sensitivity simulations at 1∘ horizontal resolution over the last 2 decades (1999–2018), coupling ocean, sea ice and marine biogeochemistry. The representation of the PLF impacts ocean heat uptake and temperature of the first 300 m of the tropical ocean. Temperature anomalies due to an incomplete PLF representation drive perturbations of ocean stratification, dynamics and oxygen concentration. These perturbations translate into different projection pathways for N2O production depending on the choice of the PLF representation. The oxygen concentration in the North Pacific oxygen-minimum zone is overestimated in model runs with an incomplete representation of the PLF, which results in an underestimation of local N2O production. This leads to important regional differences of sea-to-air N2O fluxes: fluxes are enhanced by up to 24 % in the South Pacific and South Atlantic subtropical gyres but reduced by up to 12 % in oxygen-minimum zones of the Northern Hemisphere. Our results, based on a global ocean–biogeochemical model at CMIP6 state-of-the-art level, shed light on current uncertainties in modelled marine nitrous oxide budgets in climate models.
... Specifically, ENSO amplitude is slightly increased with the standard deviation increasing by 0.16 • C when CHL effect is included into a fully coupled general circulation model (Lengaigne et al., 2007). Park, Kug, Seo, and Bader (2014) found that the effects of CHL on ENSO enhance the positive skewness, which may be attributed to the thermocline feedback. In addition, Zhang et al. (2009) pointed out that interannual CHL effects act to decrease the Niño 3 SST variability and shorten the time scales of ENSO, compared with a case in which only the effect of climatological CHL is taken into account in a hybrid coupled atmosphere and ocean model. ...
... 3 of 24 approach is to represent the three-dimensional (3-D) CHL field in full water depth range (Marzeion et al., 2005;Patara et al., 2012;Wetzel et al., 2006). For instance, Park, Kug, Seo, and Bader (2014) coupled the MOM4 with a biogeochemical model, TOPAZ, and can simulate 3-D CHL field well, finding that higher CHL concentration gives rise to cooler SST in the eastern Pacific and increase the ENSO skewness because of intensified ocean dynamical adjustment. Notably, revealed that the different prescriptions of CHL field averaged in various depth ranges tend to cause different SST changes (see their Figure 7b). ...
... Both the changes in STD and the distribution of correlation coefficient prove that the amplitude of SSTA in the central equatorial Pacific increases with the inclusion of the DCM effects. The surface CHL field shows a similar but smaller effect on SSTA (Figures 9d-9f), which may be attributed to the damping effect of net surface heat flux; the smaller changes in zonal gradient of the thermocline depth also indicate smaller ENSO amplification, consistent with the thermocline feedback theory (Park, Kug, Seo, & Bader, 2014). ...
A coupled ocean general circulation model (OGCM)‐ocean ecosystem model is used to investigate the effects of the deep chlorophyll maximum (DCM) on the ocean state in the equatorial Pacific Ocean. Climatological and interannual three‐dimensional (3‐D) chlorophyll (CHL) fields are captured well in control runs using the coupled ocean physics‐ecosystem model forced by prescribed atmospheric fields. Further sensitivity experiments are performed to assess the effects of 3‐D CHL structure using the OGCM with the prescribed CHL fields taken from the control runs: CHL clim and are runs in which climatological DCM effect is included or only surface CHL effect is included; CHL inter and are runs with interannually varying DCM effects included or not. The differences in the simulated ocean conditions are analyzed to explore DCM effects on sea surface temperature (SST) and amplitude of El Niño‐Southern Oscillation (ENSO). Two competing mechanisms responsible for the DCM effects are revealed: an ocean biology‐induced direct heating (OBH) effect, and an indirect cooling effect due to dynamic processes associated with vertical mixing and shallow meridional overturning circulation. There are three major findings: (a) DCM acts to reduce mean SST by around 0.2°C in the eastern equatorial Pacific, being larger than the surface CHL effects. (b) DCM interannual variability increases the ENSO amplitude to a comparable degree as the surface CHL effects. (c) The total net impact of vertical mixing, currents, and net surface heat flux makes SST drop more under the DCM effect than the surface CHL effect in the eastern Pacific. These findings provide a new insight into the feedback mechanisms for the bioclimate interactions.
... teleconnections patterns, frequency, amplitude, and aspects of ENSO diversity (Wittenberg et al., 2006;Kug et al., 2010;Dunne et al., 2012;Dunne et al., 2020). Extension of these efforts to ESMs has furthermore revealed skillful depictions of ENSO-driven chlorophyll evolution, including chlorophyll feedbacks on ocean temperature and climate (Anderson et al., 2009;Park et al., 2014b;Park et al., 2018). Less attention, however, has been paid to post-El Niño chlorophyll rebound, with studies suggesting under-representation in ESMs (Park et al., 2018). ...
Plain Language Summary
In the tropical Pacific, year‐to‐year changes in chlorophyll, a proxy for the phytoplankton base of ocean food webs, is dominated by the El Niño–Southern Oscillation. El Niño, triggered by westerly wind anomalies and subsequent redistributions of upper ocean heat content, can sharply reduce the regional supply of nutrients limiting phytoplankton growth. A new Earth System Model captures not only the onset and extent of chlorophyll anomalies during El Niño events, but also a pronounced post‐El Niño “chlorophyll rebound” that produces positive equatorial Pacific chlorophyll anomalies in the summer following El Niño events. This post‐El Niño chlorophyll rebound is primarily driven by positive iron anomalies propagated from the subsurface western Pacific to the surface eastern Pacific cold tongue via the Equatorial Undercurrent. High post‐El Niño dust deposition anomalies arising from dry land conditions in Central and South America augment the post‐El Niño chlorophyll rebound. This post‐El Niño chlorophyll rebound provides a key source of resilience to marine ecosystems in the equatorial Pacific.
... Atmospheric CO 2 Korean Meteorological Society absorbed by the ocean can be converted to O 2 through photosynthesis by phytoplankton, the ocean's primary producer, or can be stored in the ocean through the biological pump that controls the amount of CO 2 in the atmosphere (Reid et al. 2009). In addition, marine phytoplankton can change ENSO or Arctic warming through marine environmental and geophysical feedbacks (Park et al. 2014a(Park et al. , 2014b(Park et al. , 2015(Park et al. , 2017Kang et al. 2017;Lim et al. 2018) and can release dimethyl sulfide (DMS) into the atmosphere that acts as cloud condensation nuclei and can affect climate through cloud albedo feedback (Charlson et al. 1987;Kim et al. 2018). Thus, ocean biogeochemical processes can influence various climate-related factors, including ocean physics and atmospheric chemistry, through direct and indirect feedback mechanisms, thereby consequently affecting the climate. ...
... Previous studies have confirmed that marine environmental simulation results obtained from ESMs, including ocean biogeochemical processes, vary from those of other models (Kang et al. 2017;Park et al. 2017Park et al. , 2019Lim et al. 2018;Ham et al. 2020). Park et al. (2014b) determined that the direct and indirect effects of chlorophyll affect the amplitude and asymmetry of ENSO in the Geophysical Fluid Dynamics Laboratory (GFDL) model results. In addition, using the Community ESM of the National Center for Atmospheric Research (NCAR CESM), Kang et al. (2017) showed that a model with chlorophyll feedback simulated the ENSO amplitude better than a model without this feedback. ...
... Figure 3 shows the differences in chlorophyll concentrations (a proxy for phytoplankton biomass) simulated for 1870-1919 using the UKESM-TOPAZ and UKESM1 models, as well as the SeaWiFS satellite data from 1998 to 2008. Considering that the SeaWiFS data include chlorophyll concentrations at the sea surface and in the upper part of the mixed layer, the average of 12 vertical levels from 0 to 20 m was used (Jochum et al. 2009;Park et al. 2014b;Jung et al. 2020). The models correctly simulated the chlorophyll concentrations, which are high at the equator and high latitudes and low in the subtropical gyres (Fig. 3a, c, d). ...
Earth system models (ESMs) comprise various Earth system components and simulate the interactions between these components. ESMs can be used to understand climate feedbacks between physical, chemical, and biological processes and predict future climate. We developed a new ESM, UKESM-TOPAZ, by coupling the UK ESM (UKESM1) and the Tracers of Phytoplankton with Allometric Zooplankton (TOPAZ) biogeochemical module. We then compared the preliminary simulated biogeochemical variables, which were conducted over a period of 70 years, using observational and existing UKESM1 model data. Similar to UKESM1, the newly developed UKESM-TOPAZ closely simulated the relationship between the El Niño-Southern Oscillation and chlorophyll concentration anomalies during the boreal winter. However, there were differences in the chlorophyll distributions in the eastern equatorial Pacific between the two models, which were due to dissolved iron, as this value was higher in UKESM-TOPAZ than in UKESM1. In a mean field analysis, the distributions of the major marine biogeochemical variables in UKESM-TOPAZ (i.e., nitrate, silicate, dissolved oxygen, dissolved inorganic carbon, and alka-linity) were not significantly different from those of UKESM1, likely because the models share the same initial conditions. Our results indicate that TOPAZ has a simulation performance that does not lag behind UKESM1's basic biogeochemical model (Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration, and Acidification; MEDUSA). The UKESM-TOPAZ model can simulate the variability of the observed Niño 3.4 and 4 indices more closely than UKESM1. Thus, the UKESM-TOPAZ model can be used to deepen our understanding of the Earth system and to estimate ESM uncertainty.
... ocean-atmosphere coupled models to investigate the effect of ENSO dynamics (e.g., Park et al., 2014 for a review). While most models simulated a cooling of ∼0.5°C-1°C in the Peru upwelling region (e.g., Anderson et al., 2007;Lin et al., 2007;Manizza et al., 2005), a warming of the eastern Pacific (∼0.4°C) was produced in a fully coupled ocean-atmosphere-biogeochemical simulation (Lengaigne et al., 2007). ...
The influence of chlorophyll shading on ocean dynamics has been usually disregarded in eastern boundary upwelling systems modeling studies in spite of their very high primary productivity. Here, we study how this effect impacts on the Peru upwelling system using a regional mesoscale‐resolving physical biogeochemical coupled model. We show that the shading effect leads to a surface cooling of up to 1°C on the shelf due to subsurface cooling of the source waters during their transit toward the shelf. The shading effect leads to a more realistic subsurface stratification, a slowdown of the alongshore currents, and a shoaling of the oxycline. Impacts on the regional model biases show that the shading effect needs to be taken into account in both physical and coupled physical‐biogeochemical regional models of upwelling systems.
... Lengaigne et al., 2007;Park et al., 2014a;Park et al., 2014b). Nevertheless, in some circumstances, the presence of phytoplankton, as reported by (Nakamoto et al., 2001;Manizza et al., 2005;Park et al., 2014b), may lead to the cooling of the surface layer as well due to enhanced upwelling of cold subsurface water in the eastern equatorial Pacific. ...
... The effect of the spatial and temporal variability of a fully coupled marine ecosystem upon SWR attenuation in water (experiment INDB) leads to a cooling of the ocean waters compared to a reference INDJ experiment where a constant attenuation coefficient was set equal to 0.06 m -1 (Jerlov IB water type). Generally, taking into account the phytoplankton when calculating light extinction in the ocean leads to a warming of the upper ocean layer and cooling of sub-surface layers compared 480 to a 'no-bio' reference experiment (e.g., Nakamoto et al., 2000;Lengaigne et al., 2007;Park et al., 2014a;Park & Kug, 2012;Park et al., 2014). But, as emphasized in (Lengaigne et al., 2007), the sign of the effect is determined by the choice of the reference experiment. ...
We investigate the effect of variable marine biogeochemical light absorption on Indian Ocean sea surface temperature (SST) and how this affects the South Asian climate. In twin experiments with a regional Earth System Model, we found that the average SST is lower over most of the domain when variable marine biogeochemical light absorption is taken into account, compared to the reference experiment with a constant light attenuation coefficient equal to 0.06 m-1. The most significant deviations (more than 1 °C) in SST are observed in the summer period. A considerable cooling of subsurface layers occurs, and the thermocline shifts upward in the experiment with the activated biogeochemical impact. Also, the phytoplankton primary production becomes higher, especially during periods of winter and summer phytoplankton blooms. The effect of altered SST variability on climate was investigated by coupling the ocean models to a regional atmosphere model. We find the largest effects on the amount of precipitation, particularly during the monsoon season. In the Arabian Sea, the reduction of the transport of humidity across the equator leads to a reduction of the large-scale precipitation in the eastern part of the basin, reinforcing the reduction of the convective precipitation. In the Bay of Bengal, it increases the large-scale precipitation, countering convective precipitation decline. Thus, the key impacts of including the full biogeochemical coupling with corresponding light attenuation, which in turn depends on variable chlorophyll-a concentration, include the enhanced phytoplankton primary production, a shallower thermocline, decreased SST and water temperature in subsurface layers, with cascading effects upon the model ocean physics which further translates into altered atmosphere dynamics.
... Specifically, the impacts originate from ocean phytoplankton, which is the primary producer. Furthermore, the studies have shown that chlorophyll feedback by phytoplankton in the eastern equatorial Pacific Ocean affects El Niño-Southern Oscillation (Kang et al., 2017;Park et al., 2014;Park et al., 2017). The eastern equatorial Pacific Ocean is one of the high-nutrient, low-chlorophyll regions; moreover, iron limits the ocean primary production (Libes, 2009;Tagliabue et al., 2017;Williams and Follows, 2011). ...
... The annual surface chlorophyll concentration in the tropical Pacific Ocean of CTL was compared with those of SeaWiFS (Fig. 2) to analyze the default chlorophyll simulation performance of the NEMO-TOPAZ. The surface chlorophyll concentrations of the model experiments were averaged from the surface to 20 m because the SeaWiFS-based chlorophyll concentration mainly represents the surface value owing to light backscattering (Jochum et al., 2009, Jung et al., 2020, Park et al., 2014. Chlorophyll concentration was high on the coast of the eastern equatorial Pacific Ocean owing to the upwelling of nutrients (Williams and Follows, 2011). ...
Ocean biogeochemistry plays a crucial role in sustaining the marine ecosystem and global carbon cycle. To investigate the oceanic biogeochemical responses to iron parameters in the tropical Pacific, we conducted sensitivity experiments using the Nucleus for European Modelling of the Ocean-Tracers of Ocean Phytoplankton with Allometric Zooplankton (NEMO-TOPAZ) model. Compared to observations, the NEMO-TOPAZ model overestimated the concentrations of chlorophyll and dissolved iron (DFe). The sensitivity tests showed that with increasing (+50%) iron scavenging rates, chlorophyll concentrations in the tropical Pacific were reduced by approximately 16%. The bias in DFe also decreased by approximately 7%; however, the sea surface temperature was not affected. As such, these results can facilitate the development of the model tuning strategy to improve ocean biogeochemical performance using the NEMO-TOPAZ model.
... The cold SST anomalies induced by the presence of chlorophyll can be further amplified through large-scale ocean-atmosphere interaction (e.g. Park et al. 2014a;Lim et al. 2018), i.e. Bjerknes feedback (Bjerknes 1969). ...
... For example, the earlier studies tend to utilize OGCM without considering atmospheric feedback to investigate the effect of chlorophyll on the ocean (Nakamoto et al. 2001;Murtugudde et al. 2002;Sweeney et al. 2005;Löptien et al. 2009). When the coupled climate models are introduced to examine this effect, the chlorophyll-induced SST change in the eastern equatorial Pacific also exhibits diverse response under different coupling intensity, i.e., SST warming (e.g., Lengaigne et al. 2007;Patara et al. 2012) or cooling (e.g., Gnanadesikan and Anderson 2009;Park et al. 2014a). ...
... the large-scale ocean-atmosphere coupling is represented through the positive Bjerknes feedback, which has been found in a simulation using the GFDL-CM 2.1(e.g., Park et al. 2014a). However, in our HCM simulation, by taking α = 1.15, the presence of chlorophyll actually induces an SST warming in the eastern equatorial Pacific when the ocean-atmosphere coupling is explicitly taken into account (Fig. 3b), characterized by an El Niño-like pattern. ...
Phytoplankton pigments (e.g., chlorophyll-a) absorb solar radiation in the upper ocean and induce a pronounced radiant heating effect (chlorophyll effect) on the climate. However, the ocean chlorophyll-induced heating effect on the mean climate state in the tropical Pacific has not been understood well. Here, a hybrid coupled model (HCM) of the atmosphere, ocean physics and biogeochemistry is used to investigate the chlorophyll effect on sea surface temperature (SST) in the eastern equatorial Pacific; a tunable coefficient, α, is introduced to represent the coupling intensity between the atmosphere and ocean in the HCM. The modeling results show that the chlorophyll effect on the mean-state SST is sensitively dependent on α (the coupling intensity). At weakly represented coupling intensity (0 ≤ α < 1.01), the chlorophyll effect tends to induce an SST cooling in the eastern equatorial Pacific, whereas an SST warming emerges at the strongly represented coupling intensity (α ≥ 1.01). Thus, a threshold exists for the coupling intensity (about α = 1.01) at which the sign of SST responses can change. Mechanisms and processes are illustrated to understand the different SST responses. In the weak coupling cases, indirect dynamical cooling processes (the adjustment of ocean circulation, enhanced vertical mixing, and upwelling) tend to dominate the SST cooling. In the strong coupling cases, the persistent warming induced by chlorophyll in the southern subtropical Pacific tends to induce cross-equatorial northerly winds, which shifts to anomalous westerly winds in the eastern equatorial Pacific, consequently reducing the evaporative cooling and weakening indirect dynamical cooling; eventually, SST warming maintains in the eastern equatorial Pacific. These results provide new insights into the biogeochemical feedback on the climate and bio-physical interactions in the tropical Pacific.
