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Colored and fluorescent DOM in the sea-surface microlayer: response to a phytoplankton bloom and photodegradation in a mesocosm study.

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Title: Colored and fluorescent DOM in the sea-surface microlayer: response to a phytoplankton bloom and photodegradation in a mesocosm study.
Authors: Thölen, Claudia1 (AUTHOR) claudia.thoelen@uni-oldenburg.de, Wollschläger, Jochen1 (AUTHOR), Novak, Michael G.2 (AUTHOR), Röttgers, Rüdiger2 (AUTHOR), Zielinski, Oliver2,3 (AUTHOR)
Source: Biogeosciences. 2026, Vol. 23 Issue 11, p3697-3721. 25p.
Subject Terms: *Sea surface microlayer, *Algal blooms, *Environmental sciences, *Fluorophores, *Photodegradation, *Organic compounds, *Ocean-atmosphere interaction, *Dissolved organic matter
Abstract: A month-long mesocosm study at the Institute for Chemistry and Biology of the Marine Environment (Wilhelmshaven, Germany) examined how a phytoplankton bloom and photodegradation influence the composition of colored and fluorescent dissolved organic matter (CDOM and FDOM, respectively) in the sea-surface microlayer (SML) and underlying water (ULW). The SML, a thin (<1000 µ m) interface between ocean and atmosphere, plays a key role in air-sea exchange processes, but temporal mechanisms behind organic matter enrichment remain unclear. To isolate biogeochemical processes from environmental variability, daily SML and ULW samples were analyzed using spectral fluorometric and photometric methods, with supporting data e.g. on irradiance, temperature, and chlorophyll- a. The study covered bloom onset, peak, and decay of two partially overlying phytoplankton blooms. Samples were taken alternatively in the morning and in the afternoon, varying the exposure time to UV-light. Changes in composition and quality of organic matter were tracked using CDOM/FDOM derived metrics. Changes in the FDOM component composition were investigated using PERMANOVA. The significant influence of the bloom phases and the layer (SML or ULW) on the component composition was confirmed, however, their interaction was not significant. Protein-like FDOM components increased in both layers during bloom progression, while humic-like FDOM components decreased throughout the study. It is likely that the change in FDOM component composition is a joint result of the influences of the phytoplankton bloom and photodegradation effects. Based on the slope ratio (SR) of CDOM absorption slopes S275–295 and S350–400 , photodegradation was identified as the dominant sink of organic matter over microbial activity. While some CDOM/FDOM derived metrics indicated stronger photodegradation effects in the SML, a consistently enhanced photodegradation signal could not be conclusively confirmed due to co-occurring enrichment, passive accumulation, and degradation processes. [ABSTRACT FROM AUTHOR]
Database: Energy & Power Source
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  Data: Colored and fluorescent DOM in the sea-surface microlayer: response to a phytoplankton bloom and photodegradation in a mesocosm study.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Th&#246;len%2C+Claudia%22&quot;&gt;Th&#246;len, Claudia&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; claudia.thoelen@uni-oldenburg.de&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Wollschl&#228;ger%2C+Jochen%22&quot;&gt;Wollschl&#228;ger, Jochen&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Novak%2C+Michael&#160;G%2E%22&quot;&gt;Novak, Michael&#160;G.&lt;/searchLink&gt;&lt;relatesTo&gt;2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22R&#246;ttgers%2C+R&#252;diger%22&quot;&gt;R&#246;ttgers, R&#252;diger&lt;/searchLink&gt;&lt;relatesTo&gt;2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Zielinski%2C+Oliver%22&quot;&gt;Zielinski, Oliver&lt;/searchLink&gt;&lt;relatesTo&gt;2,3&lt;/relatesTo&gt; (AUTHOR)
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  Data: &lt;searchLink fieldCode=&quot;JN&quot; term=&quot;%22Biogeosciences%22&quot;&gt;Biogeosciences&lt;/searchLink&gt;. 2026, Vol. 23 Issue 11, p3697-3721. 25p.
– Name: Subject
  Label: Subject Terms
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  Data: *&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Sea+surface+microlayer%22&quot;&gt;Sea surface microlayer&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Algal+blooms%22&quot;&gt;Algal blooms&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Environmental+sciences%22&quot;&gt;Environmental sciences&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Fluorophores%22&quot;&gt;Fluorophores&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Photodegradation%22&quot;&gt;Photodegradation&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Organic+compounds%22&quot;&gt;Organic compounds&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Ocean-atmosphere+interaction%22&quot;&gt;Ocean-atmosphere interaction&lt;/searchLink&gt;&lt;br /&gt;*&lt;searchLink fieldCode=&quot;DE&quot; term=&quot;%22Dissolved+organic+matter%22&quot;&gt;Dissolved organic matter&lt;/searchLink&gt;
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: A month-long mesocosm study at the Institute for Chemistry and Biology of the Marine Environment (Wilhelmshaven, Germany) examined how a phytoplankton bloom and photodegradation influence the composition of colored and fluorescent dissolved organic matter (CDOM and FDOM, respectively) in the sea-surface microlayer (SML) and underlying water (ULW). The SML, a thin (&lt;1000 &#181; m) interface between ocean and atmosphere, plays a key role in air-sea exchange processes, but temporal mechanisms behind organic matter enrichment remain unclear. To isolate biogeochemical processes from environmental variability, daily SML and ULW samples were analyzed using spectral fluorometric and photometric methods, with supporting data e.g. on irradiance, temperature, and chlorophyll- a. The study covered bloom onset, peak, and decay of two partially overlying phytoplankton blooms. Samples were taken alternatively in the morning and in the afternoon, varying the exposure time to UV-light. Changes in composition and quality of organic matter were tracked using CDOM/FDOM derived metrics. Changes in the FDOM component composition were investigated using PERMANOVA. The significant influence of the bloom phases and the layer (SML or ULW) on the component composition was confirmed, however, their interaction was not significant. Protein-like FDOM components increased in both layers during bloom progression, while humic-like FDOM components decreased throughout the study. It is likely that the change in FDOM component composition is a joint result of the influences of the phytoplankton bloom and photodegradation effects. Based on the slope ratio (SR) of CDOM absorption slopes S275–295 and S350–400 , photodegradation was identified as the dominant sink of organic matter over microbial activity. While some CDOM/FDOM derived metrics indicated stronger photodegradation effects in the SML, a consistently enhanced photodegradation signal could not be conclusively confirmed due to co-occurring enrichment, passive accumulation, and degradation processes. [ABSTRACT FROM AUTHOR]
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.5194/bg-23-3697-2026
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 25
        StartPage: 3697
    Subjects:
      – SubjectFull: Sea surface microlayer
        Type: general
      – SubjectFull: Algal blooms
        Type: general
      – SubjectFull: Environmental sciences
        Type: general
      – SubjectFull: Fluorophores
        Type: general
      – SubjectFull: Photodegradation
        Type: general
      – SubjectFull: Organic compounds
        Type: general
      – SubjectFull: Ocean-atmosphere interaction
        Type: general
      – SubjectFull: Dissolved organic matter
        Type: general
    Titles:
      – TitleFull: Colored and fluorescent DOM in the sea-surface microlayer: response to a phytoplankton bloom and photodegradation in a mesocosm study.
        Type: main
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            NameFull: Thölen, Claudia
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            NameFull: Wollschläger, Jochen
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            NameFull: Novak, Michael G.
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            NameFull: Röttgers, Rüdiger
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            NameFull: Zielinski, Oliver
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            – D: 01
              M: 06
              Text: 2026
              Type: published
              Y: 2026
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              Value: 11
          Titles:
            – TitleFull: Biogeosciences
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