Preprints
https://doi.org/10.5194/cp-2023-80
https://doi.org/10.5194/cp-2023-80
09 Oct 2023
 | 09 Oct 2023
Status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

Eccentricity forcing on Tropical Ocean Seasonality

Luc Beaufort and Anta Clarisse Sarr

Abstract. The amount of radiative energy received at the Earth's surface depends on two factors: Earth-Sun distance and sunlight angle. Because of the former factor, high eccentricity cycles can induce the appearance of seasons in the tropical ocean. In this paper, we use the Earth System model IPSL-CM5A2 to investigate the response of the low-latitude oceans to variations in Earth's orbital eccentricity. Sea Surface Temperature (SST) and Primary Production (PP) were simulated under six precession configurations at high eccentricity and two configurations with low eccentricity, representing extreme configurations observed over the past million years. Results show that high eccentricity leads to increased seasonality in SST, with an annual thermal amplitude of approximately 2.2 °C in low latitude ocean surface waters (vs. 0.5 °C at low eccentricity). PP, which already exhibits inherent seasonality under low eccentricity conditions, sees its seasonality largely increased under high eccentricity. As a consequence, we show that on long time scales the intensity of SST seasonality exhibits only the eccentricity frequency, whereas that of PP additionally follows precession dynamics. Furthermore, the seasonal variations in both SST and PP at high eccentricities are influenced by the annual placement of perihelion with its direct impact of radiative energy received in tropical regions. This leads to a gradual and consistent transition of seasons within the calendar. We introduce the concept of "eccentriseasons," referring to distinct annual thermal differences observed in tropical oceans under high eccentricity conditions, which shift gradually throughout the calendar year. These findings have implications for understanding low latitude climate phenomena such as El Niño-Southern Oscillation and monsoons in the past.

Luc Beaufort and Anta Clarisse Sarr

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-80', Anonymous Referee #1, 12 Nov 2023
    • AC1: 'Reply on RC1', Luc Beaufort, 10 Feb 2024
  • RC2: 'Comment on cp-2023-80', Anonymous Referee #2, 18 Dec 2023
    • AC2: 'Reply on RC2', Luc Beaufort, 10 Feb 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-80', Anonymous Referee #1, 12 Nov 2023
    • AC1: 'Reply on RC1', Luc Beaufort, 10 Feb 2024
  • RC2: 'Comment on cp-2023-80', Anonymous Referee #2, 18 Dec 2023
    • AC2: 'Reply on RC2', Luc Beaufort, 10 Feb 2024
Luc Beaufort and Anta Clarisse Sarr
Luc Beaufort and Anta Clarisse Sarr

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Short summary
At present, under low eccentricity, the tropical ocean experiences a limited seasonality. Based on 8 climate simulations of sea surface temperature and primary production, we show that during high eccentricity times, significant seasons existed in the tropics due to annual changes in the Earth-Sun distance. Those tropical seasons are slowly shifting on the calendar year that is distinct from classical seasons. Their past dynamics should have influenced phenomena like ENSO and monsoons.