Abstract
Diatoms are the major marine primary producers in the Southern Ocean and a key component of the carbon and silicate biogeochemical cycle. Using 15 years of satellite-derived diatom concentration from September to April (1997–2012), we examine the mean patterns and the interannual variability of the diatom bloom phenology in the Southern Ocean. Mean spatial patterns of timing and duration of diatom blooms are generally associated with the position of the Southern Antarctic Circumpolar Current Front and of the maximum sea ice extent. In several areas the anomalies of phenological indices are found to be correlated with ENSO and SAM. Composite maps of the anomalies reveal distinct spatial patterns and opposite events of ENSO and SAM have similar effects on the diatom phenology. For example, in the Ross Sea region, a later start of the bloom and lower diatom biomass were observed associated with El Niño and negative SAM events; likely influenced by an increase in sea ice concentration during these events.
Highlights
Phytoplankton in many parts of the world ocean follows a distinct seasonal pattern, and the timing, or phenology, of events in that seasonal cycle, such as the spring bloom, strongly depends on physical influences, as the depth of the surface mixed layer, ice cover or temperature [1,2,3,4]
To further explore the interannual variability of the diatom phenology, we examined the relationship of the annual phenological indices with El Niño-SouthernOscillation (ENSO) and Southern Annular Mode (SAM)
We investigated the mean spatial and temporal patterns of diatom phenology and their interannual variability
Summary
Phytoplankton in many parts of the world ocean follows a distinct seasonal pattern, and the timing, or phenology, of events in that seasonal cycle, such as the spring bloom, strongly depends on physical influences, as the depth of the surface mixed layer, ice cover or temperature [1,2,3,4]. ENSO and SAM effects on bloom phenology may be amplified when El Niño (La Niña) and negative (positive) SAM events coincide The influence of these climate oscillations on the phytoplankton bloom phenology has been observed for example, in the Antarctic Peninsula [14,15]. Diatoms produce thick cell walls, spines and toxins to avoid grazers [24,25] and the rapid mass sinking events are considered a seeding strategy to overcome periods adverse to growth conditions [26,27] They shape the biogeochemistry of the oceans by being responsible for much of the vertical flux of carbon out of the surface layer [28,29]; specially in the Southern Ocean they dominate production almost everywhere [30]. Ocean by: (i) looking at the concentration of Chla in diatoms; (ii) examining the different characteristics of the phenology (iii) using a new merged satellite Chla product with improved spatial and temporal coverage than the data sets based only on one sensor; (iv) investigating trends and (v) investigating if the interannual variability of the diatom phenology could be modulated by the large scale climate oscillations ENSO and SAM
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