Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool

Abstract

Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are ∼23 W m−2 and are a large fraction of the climatological mean net air‐sea heat flux (∼40 W m−2). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst, in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W m−2 at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13°C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.

Estimating downwelling solar irradiance at the surface of the tropical Atlantic Ocean: A comparison of PIRATA measurements against several re-analyses and satellite-derived data sets

“…The net downward surface energy is positive and accumulates within the ocean with a resulting northward meridional transport of heat in the Atlantic Ocean (Liu et al, 2017). The DSIS influences the vertical structure at more rapid time scales with local impact on physics and plankton (Siegel et al, 1995).…”

“…The solar radiation impinging at the ocean surface is known to be an essential variable in the ocean-climate system (Budyko, 1969;Manabe, 1969;Siegel et al, 1995;Lean and Rind, 1998). The density of power received from the sun on a horizontal surface at ground level and per unit surface is called the downwelling solar irradiance at surface and is here abbreviated in DSIS.…”

Radiant heating of the western equatorial Pacific during TOGA‐COARE

“…For shallower depths a greater portion of the solar spectrum must be included [e.g, Siegel et al, 1995a;Ohlmann et al, 1996). Solar transmission variations within the top few meters are presently being examined with the use of a full spectral radiative transfer model.…”

Effects of Ocean Biology on the Penetrative Radiation in a Coupled Climate Model

“…Observational evidence for a significant role of phytoplankton concentration for the upper-ocean heat budget in the equatorial Pacific is reported by Siegel et al (1995), Chavez et al (1998), and Strutton and Chavez (2004). Murtugudde et al (2002) have tested possible effects on the upper tropical ocean circulation in an ocean general circulation model (GCM).…”