Ocean chlorophyll response to two types of El Niño events in an ocean‐biogeochemical coupled model

Kie‐Woung Lee,Sang‐Wook Yeh,Jong‐Seong Kug,Jong‐Yeon Park

doi:10.1002/2013jc009050

Abstract

AbstractBased on a long‐term simulation of an ocean‐biogeochemical coupled model, we investigate the biogeochemical response to the two types of El Niño events, a Cold Tongue (CT)‐El Niño and a Warm Pool (WP)‐El Niño, in which a local maximum of anomalous sea surface temperature (SST) is located in the eastern and central tropical Pacific. Our model is able to reasonably simulate the characteristics of the biological variables in a way comparable to the observations. During the developing period, anomalous low chlorophyll appears in the eastern Pacific, while it appears in the central Pacific in the WP‐El Niño. The difference in the spatial‐temporal response of chlorophyll for the two types of El Niño events is mainly due to the eastward zonal advection of upper ocean currents, which plays a role in bringing nutrient‐poor water from the western Pacific. During the decaying period of the WP‐El Niño, anomalous high chlorophyll appears concurrently with anomalous low SST in the eastern Pacific. Conversely, anomalous high chlorophyll appears in the central Pacific prior to the decaying period of the CT‐El Niño. In particular, the anomalous low sea level from the northwestern Pacific shifts to the southern equatorial region during the decaying period of the CT‐El Niño. This drives anticyclonic boundary currents which enhance the Equatorial Undercurrent, playing a role in the supply of nutrients to the central equatorial Pacific, resulting in an increase in chlorophyll concentration in the same region.

Highlights

Phytoplankton are one of the primary producers in the ecosystem via carbon fixation, producing nearly half of the world’s oxygen through photosynthesis
The ENSO plays a key role in influencing the variability of chlorophyll in the tropical Pacific ecosystem
~o events using a long-term ocean-biogeoexamined the chlorophyll response to the two types of El Nin chemical coupled model simulation that utilizes GFDL MOM4p1, which is forced by the historical wind stress forcing from the years 1951 to 2010

Summary

Introduction

Phytoplankton are one of the primary producers in the ecosystem via carbon fixation, producing nearly half of the world’s oxygen through photosynthesis. They assist in recycling elements such as carbon, phosphorus, and nitrogen, which are required by other organisms [Field et al, 1998; Behrenfeld et al, 2001]. An understanding of how the variability of chlorophyll is associated with the changes in the physical properties of the upper ocean sheds light on many topics. The concentration of chlorophyll is determined by the light, temperature, and nutrients available [Tilman et al, 1982; Cullen, 1991]. The Equatorial Pacific region is characterized by richer light and temperature, but less of the nutrients that are needed for the growth of phytoplankton. The supply of nutrients including iron and nitrate is important for the increase of chlorophyll in the equatorial

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Results

Conclusion