Regional impacts of ocean color on tropical Pacific variability

Abstract

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

Impact of different solar penetration depths on climate simulations

“…The differences of MLD, D20 and averaged temperature over the upper oceans are largely consistent with SWAD differences between EX1 and EX2. A larger value of SWAD in the model produces a deeper MLD and D20, and higher temperatures at depths ranging from 30 to 300 m. These results are similar to previous studies such as Sweeney et al (2005), Anderson et al (2009) etc.…”

“…EX2 tends to damp El Nin˜o due to a deeper thermocline. This result is consistent with the conclusion of Anderson et al (2009). The differences in Nin˜o3.4 (58N to 58S, 1708W to 1208W) SSTA are generally less than 0.28C, and are highly correlated with the SST anomaly (correlation coefficient of 0.78): a large ENSO event often produces a large SSTA difference between experiments.…”

Interactions between marine biota and ENSO: a conceptual model analysis

“…Eventually, changes of radiant heating within the upper water column can lead to significant changes in the sea surface temperature (SST) in the tropical Pacific. Effects of biologically-induced heating on tropical Pacific climate were also found in simulations conducted with ocean models (Nakamoto et al, 2001;Murtugudde et al, 2002;Löptien et al, 2009), atmosphere-ocean hybrid coupled models (Marzeion et al, 2005;Ballabrera-Poy et al, 2007;Zhang et al, 2009), and coupled general circulation models (Manizza et al, 2005;Wetzel et al, 2006;Lengaigne et al, 2007;Anderson et al, 2007Anderson et al, , 2009; Gnanadesikan and Anderson, 2009).…”

Impact of bio-physical feedbacks on the tropical climate in coupled and uncoupled GCMs

“…Thus, the different results of the bio-physical feedbacks in previous studies might arise from other factors, such as different spatial patterns of chlorophyll simulated in different biogeochemical models, various settings to determine the attenuation depth used in control experiments, and the sensitivity of the oceanic response to the biologically-induced differential heating due to uncertainties in the parameterization of tropical convection. For example, given that the horizontal and vertical structure of chlorophyll is acknowledged to play a large role in the response to biological feedback (Lengaigne et al 2007;Anderson et al 2009;Gnanadesikan and Anderson 2009), differences in the chlorophyll distribution shown in previous studies may explain the diversity of the model responses. If this is the case, a realistic simulation of the 3-dimensional structure of chlorophyll should be precomputed and validated against the observed distribution.…”