Abstract
Abstract. Transparent exopolymer particles (TEPs) are a major source for both organic matter (OM) and carbon transfer in the ocean and into the atmosphere. Consequently, understanding the vertical distribution of TEPs and the processes which impact their movement is important in understanding the OM and carbon pools on a larger scale. Additionally, most studies looking at the vertical profile of TEPs have focused on large depth scales from 5 to 1000 m and have omitted the near-surface environment. Results from a study of TEP enrichment in the sea surface microlayer (SML) in different regions (tropical, temperate) has shown that, while there is a correlation between TEP concentration and primary production (PP) on larger or seasonal scales, such relationships break down on shorter timescales and spatial scales. Using a novel small-scale vertical sampler, the vertical distribution of TEPs within the uppermost 2 m was investigated. For two regions with a total of 20 depth profiles, a maximum variance of TEP concentration of 1.39×106 µg XG eq2 L−2 between depths and a minimum variance of 6×102 µg XG eq2 L−2 was found. This shows that the vertical distribution of TEPs was both heterogeneous and homogeneous at times. Results from the enrichment of TEPs and Chl a between different regions have shown TEP enrichment in the SML to be greater in oligotrophic waters, when both Chl a and TEP concentrations were low, suggesting the importance of abiotic sources for the enrichment of TEPs in the SML. However, considering multiple additional parameters that were sampled, it is clear that no single parameter could be used as a proxy for TEP heterogeneity. Other probable biochemical drivers of TEP transport are discussed.
Highlights
The sea surface microlayer (SML), a thin layer 10 μm–1 mm thick, lays at the top of the ocean
We present data from three field campaigns which show the accumulation of transparent exopolymer particles (TEPs) in the upper 2 m and how they relate to water column stratification, primary production and sea surface conditions
The importance and influence of the SML has been thoroughly supported (Engel et al, 2017; Cunliffe et al, 2013; Wurl et al, 2011b; Liss and Duce, 1997; Hardy, 1982), and there is a need to better understand the biogeochemical cycling occurring in the near-surface water and how they relate to organic matter transfer to deeper water masses
Summary
The sea surface microlayer (SML), a thin layer 10 μm–1 mm thick, lays at the top of the ocean. The SML is further characterized by its gelatinous nature (Sieburth, 1983), being thoroughly permeated with extracellular polymeric substances, the largest faction of which are transparent exopolymer particles (TEPs) (Wurl and Holmes, 2008; Cunliffe and Murrell, 2009) These gel particles can form in two ways: abiotically via the collision of colloidal material by physical forces or biotically via the breakdown and secretion of precursor material from organisms, with phytoplankton being the largest source (Passow, 2002a).
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