Phenological Responses to ENSO in the Global Oceans

Abstract

Phenology relates to the study of timing of periodic events in the life cycle of plants or animals as influenced by environmental conditions and climatic forcing. Phenological metrics provide information essential to quantify variations in the life cycle of these organisms. The metrics also allow us to estimate the speed at which living organisms respond to environmental changes. At the surface of the oceans, microscopic plant cells, so-called phytoplankton, grow and sometimes form blooms, with concentrations reaching up to 100 million cells per litre and extending over many square kilometres. These blooms can have a huge collective impact on ocean colour, because they contain chlorophyll and other auxiliary pigments, making them visible from space. Phytoplankton populations have a high turnover rate and can respond within hours to days to environmental perturbations. This makes them ideal indicators to study the first-level biological response to environmental changes. In the Earth's climate system, the El Niño-Southern Oscillation (ENSO) dominates large-scale inter-annual variations in environmental conditions. It serves as a natural experiment to study and understand how phytoplankton in the ocean (and hence the organisms at higher trophic levels) respond to climate variability. Here, the ENSO influence on phytoplankton is estimated through variations in chlorophyll concentration, primary production and timings of initiation, peak, termination and duration of the growing period. The phenological variabilities are used to characterise phytoplankton responses to changes in some physical variables: sea surface temperature, sea surface height and wind. It is reported that in oceanic regions experiencing high annual Surv Geophys (2017) 38:277-293 DOI 10.1007 variations in the solar cycle, such as in high latitudes, the influence of ENSO may be readily measured using annual mean anomalies of physical variables. In contrast, in oceanic regions where ENSO modulates a climate system characterised by a seasonal reversal of the wind forcing, such as the monsoon system in the Indian Ocean, phenologybased mean anomalies of physical variables help refine evaluation of the mechanisms driving the biological responses and provide a more comprehensive understanding of the integrated processes.

Contrasting ENSO Types With Satellite‐Derived Ocean Phytoplankton Biomass in the Tropical Pacific

“…The Chl-a EOF patterns are consistent with Radenac et al (2012) except for the magnitudes, which can be explained by the improved algorithms used to derive Chl-a. Biomass and Chl-a anomalies are lognormally distributed, as biological indices can span up to 3 orders of magnitude (Racault et al, 2016).…”

“…The maximum SST anomalies confined in the central-eastern equatorial and dominantly in the central equatorial tropical Pacific region contrast the EPEN and CPEN, respectively. Multiple studies have focused on distinguishing EPEN and CPEN using SST (Ashok et al, 2007), sea surface salinity (Ashok et al, 2007;Singh et al, 2011), precipitation (Feng & Li, 2011Zhang et al, 2011), and subsurface temperature (Yu & Kim, 2010), while a couple of new studies discuss the impacts of EPEN and CPEN based on satellite-derived Chl-a (Messié & Chavez, 2013;Radenac et al, 2012;Turk et al, 2011) and primary production (PP) and phytoplankton growth (Racault et al, 2016(Racault et al, , 2017. However, no study has characterized different types of El Niño using backscattering-based phytoplankton biomass.…”

Impact of El Niño Variability on Oceanic Phytoplankton

“…In this region, ENSO is recognized as the main driver of inter-annual phytoplankton variability. Tropical, as well as extra-tropical, influences of ENSO and ENSO Modoki have been demonstrated using statistical analyses based on a range of indices applied to ocean-color remotesensing observations (Yoder and Kennelly, 2003;Behrenfeld et al, 2006;Chavez et al, 2011;Vantrepotte and Mélin, 2011;Chavez, 2012, 2013;Racault et al, 2012Racault et al, , 2017Couto et al, 2013;Raitsos et al, 2015). One of the most widely-used environmental indices to characterize influence of ENSO on ocean biology is the Multivariate ENSO Index (MEI).…”

Adaptation to temperature stress by Vibrio fischeri facilitates this microbe's symbiosis with the Hawaiian bobtail squid ( Euprymna scolopes )

“…; Racault et al. ). Even single strains have been able to cross entire ocean basins (González‐Escalona et al.…”

“…Although the Vibrionaceae can freely adopt a planktonic lifestyle, they also are highly proficient at forming biofilms, which permits microbial dispersal via rafting (Theil and Gutow 2005;. These characteristics greatly facilitate the Vibrionaceae's ability to disseminate throughout the world's oceans, a feature that will be immensely heightened with climate change (Martinez-Urtaza et al 2016;Racault et al 2016). Even single strains have been able to cross entire ocean basins (González-Escalona et al 2015;Martinez-Urtaza et al 2017).…”