Abstract
Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) are gel-like particles, ubiquitous in the ocean, that affect important biogeochemical processes including organic carbon cycling by planktonic food webs. Despite much research on both groups of particles (especially TEP) over many years, whether they exist as distinctly stainable fractions of the same particles or as independent particles, each with different driving factors, remains unclear. To address this question, we examined the temporal dynamics of TEP and CSP over 2 complete seasonal cycles at 2 coastal sites in the Northwestern Mediterranean Sea, the Blanes Bay Microbial Observatory (BBMO) and the L’Estartit Oceanographic Station (EOS), as well as their spatial distribution along a coast-to-offshore transect. Biological, chemical, and physical variables were measured in parallel. Surface concentrations (mean ± standard deviation [SD]) of TEP were 36.7 ± 21.5 µg Xanthan Gum (XG) eq L–1 at BBMO and 36.6 ± 28.3 µg XG eq L–1 at EOS; for CSP, they were 11.9 ± 6.1 µg BSA eq L–1 at BBMO and 13.0 ± 5.9 µg BSA eq L–1 at EOS. Seasonal variability was more evident at EOS, where surface TEP and CSP concentrations peaked in summer and spring, respectively, and less predictable at the shore-most station, BBMO. Vertical distributions between surface and 80 m, monitored at EOS, showed highest TEP concentrations within the surface mixed layer during the stratification period, whereas CSP concentrations were highest before the onset of summer stratification. Phytoplankton were the main drivers of TEP and CSP distributions, although nutrient limitation and saturating irradiance also appeared to play important roles. The dynamics and distribution of TEP and CSP were uncoupled both in the coastal sites and along the transect, suggesting that they are different types of particles produced and consumed differently in response to environmental variability.
Highlights
IntroductionZamanillo et al: Seasonality of Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) in the Mediterranean Sea can ascend through the upper water column, accumulate in the sea surface microlayer (SML), and influence air–sea gas exchanges (Calleja et al, 2009; Wurl et al, 2016; Jenkinson et al, 2018)
The ocean, which currently absorbs ca. 30% of the anthropogenic CO2, contains a vast amount of carbon in the formEdith Cowan University, Joondalup, WA, AustraliaArt. 9(1) page 2 of 23Zamanillo et al: Seasonality of Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) in the Mediterranean Sea can ascend through the upper water column, accumulate in the sea surface microlayer (SML), and influence air–sea gas exchanges (Calleja et al, 2009; Wurl et al, 2016; Jenkinson et al, 2018)
At the shore-most site, the Blanes Bay Microbial Observatory (BBMO), we followed TEP and CSP concentrations near the surface; at the offshore site, the L’Estartit Oceanographic Station (EOS), which presents a conspicuous deep chlorophyll maximum (DCM) between 20 and 80 m, we examined the seasonal variations in the vertical distribution of TEP and CSP
Summary
Zamanillo et al: Seasonality of TEP and CSP in the Mediterranean Sea can ascend through the upper water column, accumulate in the sea surface microlayer (SML), and influence air–sea gas exchanges (Calleja et al, 2009; Wurl et al, 2016; Jenkinson et al, 2018) They can be released to the atmosphere, contributing to organic aerosols (Aller et al, 2005) and impacting the Earth’s radiative budget (Brooks and Thornton, 2018). TEP precursors, which generally are acidic polysaccharides, are released mostly by phytoplankton (Decho, 1990) and assembled abiotically into TEP through ionic bonding (Alldredge et al, 1993; Thornton, 2004) Such assembly is presumably the case for CSP (Cisternas-Novoa et al, 2015), but this process has not yet been tested directly. Owing to the lack of similar studies with CSP, only nutrient availability is known to affect CSP production (Radic et al, 2006), while physiological stress did not enhance CSP production by diatoms and cyanobacteria in culture (Thornton and Chen, 2017)
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