Effects of ultraviolet B radiation on (not so) transparent exopolymer particles

Abstract

Abstract. Transparent exopolymer particles (TEP) are the most ubiquitous gel particles in the ocean and form abiotically from dissolved precursors. Although these particles can accumulate at the ocean surface, being thus exposed to intense sunlight, the role of solar radiation for the assembly and degradation of TEP is unknown. In this study, we experimentally determined the effects of visible and ultraviolet B (UVB) radiation on (1) TEP degradation (photolysis experiments), (2) TEP assembly from dissolved polymers (photoinhibition experiments) and (3) TEP release by microorganisms. Solar radiation, particularly in the UVB range, caused significant TEP photolysis, with loss rates from 27 to 34% per day. Dissolved polysaccharides did not increase in parallel. No TEP were formed under UVB, visible or dark conditions, indicating that light does not promote TEP assembly. UVB radiation enhanced TEP release by microorganisms, possibly due to cell deaths, or as a protective measure. Increases in UVB may lead to enhanced TEP photolysis in the ocean, with further consequences for TEP dynamics and, ultimately, sea-air gas exchange.

Protein and Carbohydrate Exopolymer Particles in the Sea Surface Microlayer (SML)

“…Wurl et al (2011) found that 10 ± 4% of the TEP in bulk seawater stuck to the inside of the inside of glass bottles. Similarly, Ortega-Retuerta et al (2009) found that 11 ± 3% of TEP model compounds (using (alginic acid and gum xanthan) stuck to the inside of borosilicate glass bottles. Wurl et al (2011) noted that TEP also sticks to the glass plates used to collect SML samples, but that the plates became "conditioned" once they have been dipped in the water a few times and did not take up any more TEP.…”

“…Work over the last 20 years has shown that TEP are ubiquitous and play an important role in particle dynamics and carbon cycling in the ocean (see reviews by Passow, 2002a;Burd and Jackson, 2009;Verdugo, 2012). Ultraviolet light enhances TEP production by microorganisms (Ortega-Retuerta et al, 2009), indicating that the high concentrations of microorganisms in the SML may be a significant source of TEP. However, the effects of ultraviolet light are complex as it also causes TEP photolysis (Ortega-Retuerta et al, 2009).…”

“…Ultraviolet light enhances TEP production by microorganisms (Ortega-Retuerta et al, 2009), indicating that the high concentrations of microorganisms in the SML may be a significant source of TEP. However, the effects of ultraviolet light are complex as it also causes TEP photolysis (Ortega-Retuerta et al, 2009). Another source of exopolymers to the SML is the accumulation of surface-active material on bubbles rising through the water column (Wurl and Holmes, 2008).…”

Variation in transparent exopolymer particles in relation to biological and chemical factors in two contrasting lake districts

“…Solid regression line is shown for a significant relationship considering all data for inland waters, while a dashed line is shown for nonsignificant relationship considering all data for marine waters. Data were obtained as follows: this study (Table 1) Corzo et al (2005) and Bhaskar and Bhosle (2008) The higher incident solar radiation in the Mediterranean in comparison to north temperate region could promote the release of TEP by bacteria as a solar protection screen, since TEP effectively absorb in the ultraviolet range (Ortega-Retuerta et al 2009b).…”

Long-term acclimation to elevated p CO 2 alters carbon metabolism and reduces growth in the Antarctic diatom Nitzschia lecointei

“…Sea ice algae are known to excrete high amounts of extracellular polymeric substances (EPS) that constitute a substantial fraction of the DOC pool in sea ice [12,13]. EPS are produced as a normal cell function and used for motility, aggregation, desiccation, cryoprotection and protection against ultraviolet radiation [13][14][15]. The release of DOC is an important nutrient source for heterotrophic bacteria and may therefore affect microbial ecology and biogeochemistry [16].…”