Biochemical characteristics and bacterial community structure of the sea surface microlayer in the South Pacific Ocean

Abstract

Abstract. The chemical and biological characteristics of the surface microlayer were determined during a transect across the South Pacific Ocean in October-December 2004. Concentrations of particulate organic carbon (1.3 to 7.6-fold) and nitrogen (1.4 to 7-fold), and POC:PON ratios were consistently higher in the surface microlayer as compared to surface waters (5 m). The large variability in particulate organic matter enrichment was negatively correlated to wind speed. No enhanced concentrations of dissolved organic carbon were detectable in the surface microlayer as compared to 5 m, but chromophoric dissolved organic matter was markedly enriched (by 2 to 4-fold) at all sites. Based on pigment analysis and cell counts, no consistent enrichment of any of the major components of the autotrophic and heterotrophic microbial community was detectable. CE-SSCP fingerprints and CARD FISH revealed that the bacterial communities present in the surface microlayer had close similarity (>76%) to those in surface waters. By contrast, bacterial heterotrophic production ( 3 H-leucine incorporation) was consistently lower in the surface microlayer than in surface waters. By applying CARD-FISH and microautoradiography, we observed that Bacteroidetes and Gammaproteobacteria dominated leucine uptake in the surface microlayer, while in surface waters Bacteroidetes and Alphaproteobacteria were the major groups accounting for leucine incorporation. Our results demonstrate that the microbial community in the surface microlayer closely resembles that of the surface Correspondence to: I. Obernosterer (ingrid.obernosterer@obs-banyuls.fr)waters of the open ocean. Even a short residence in the surface microlayer influences leucine incorporation by different bacterial groups, probably as a response to the differences in the physical and chemical nature of the two layers.

High concentrations of mycosporine‐like amino acids and colored dissolved organic matter in the sea surface microlayer off the Iberian Peninsula

“…5B). Similarly, Obernosterer et al (2008) found particulate organic matter enrichment in the microlayer was negatively correlated with wind speed. The SSM at Sta.…”

Enrichment of microbial abundance in the sea-surface microlayer over a coral reef: implications for biogeochemical cycles in reef ecosystems

“…However, it should be noted that most of recent studies on bacterial abundance at the SML used flow cytometry (instead of microscopy) for cell counting (e.g. Agogué et al 2005a, Joux et al 2006, Obernosterer et al 2008, Stolle et al 2010, where inclined indiscriminate detection of particle-attached bacteria (Obernosterer et al 2005), may have resulted in lower EFs. Although to the best of our knowledge there are only 8 published studies that reported flagellate numbers in the SML, the EFs of hetero (HF)-and autotrophic flagellates (AF) in our HCC site (22.6 and 18.8, respectively) were the highest among the previous reports.…”

“…Extensive research has shown that the SML contains elevated concentrations of heterotrophic-and autotrophic micro organisms including bacteria, cyanobacteria, flagellates and algae (e.g. Taguchi & Nakajima 1971, Sieburth et al 1976, Harvey & Young 1980, Garabét-ian 1990, Agogué et al 2004, Obernosterer et al 2008, Santos et al 2011. Concentrations of these microorganisms are generally 1 to 10 times greater at the SML than in the sub-surface water (SSW) ( Table 1).…”

High-resolution variability of the enrichment of fluorescence dissolved organic matter in the sea surface microlayer of an upwelling region

“…Indeed, Tilstone et al (2010) suggested that microbial production of CDOM, including FDOM, occurs within a welldefined SML, and that CDOM may act as UV-protection for phytoplankton within the SML. Similarly, Obernosterer et al (2008), who performed their study in a nonupwelling region, reported constant CDOM enrichment in the SML at six stations in the tropical Pacific, providing additional evidence that continuous supply of CDOM to the SML, either from the bulk water or through microbial production in the SML, balances out losses due to photobleaching at extremely high solar and UV irradiance.…”

“…Organic materials are transported upward from bulk water to the SML through diffusion, positively buoyant particles (Azetsu-Scott and Passow, 2004), and rising air bubbles (Gershey, 1983). In addition to the direct net production of organic matter within the SML (Wurl et al, 2016), upward transport of organic matter from bulk water explains the typical enrichment of organic matter in the SML (Obernosterer et al, 2008). Our observations of elevated EFs during upwelling indicate the ability of upwelled water masses to capture by-products of biological processes from the euphotic zone of the water column.…”