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Ocean warming-acidification synergism undermines dissolved organic matter assembly.

Chen CS, Anaya JM, Chen EY, Farr E, Chin WC - PLoS ONE (2015)

Bottom Line: The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C).We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5.If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering, University of California Merced, Merced, California, United States of America.

ABSTRACT
Understanding the influence of synergisms on natural processes is a critical step toward determining the full-extent of anthropogenic stressors. As carbon emissions continue unabated, two major stressors--warming and acidification--threaten marine systems on several scales. Here, we report that a moderate temperature increase (from 30°C to 32°C) is sufficient to slow--even hinder--the ability of dissolved organic matter, a major carbon pool, to self-assemble to form marine microgels, which contribute to the particulate organic matter pool. Moreover, acidification lowers the temperature threshold at which we observe our results. These findings carry implications for the marine carbon cycle, as self-assembled marine microgels generate an estimated global seawater budget of ~1016 g C. We used laser scattering spectroscopy to test the influence of temperature and pH on spontaneous marine gel assembly. The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C). We then tested the hypothesis that temperature and pH have a synergistic influence on marine gel dispersion. We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5. If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected.

Show MeSH
Decreased microgel equilibrium size (black circles) and bound Ca2+ (blue triangles) with concomitant increase in hydrophobicity (red squares).The non-linear rate of declining microgel size with increased temperature indicates potential cooperativity; around 32˚C all three parameters experienced the most pronounced associative effect—a major drop in microgel size and bound Ca2+, with a concomitant rise in hydrophobicity.
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pone.0118300.g004: Decreased microgel equilibrium size (black circles) and bound Ca2+ (blue triangles) with concomitant increase in hydrophobicity (red squares).The non-linear rate of declining microgel size with increased temperature indicates potential cooperativity; around 32˚C all three parameters experienced the most pronounced associative effect—a major drop in microgel size and bound Ca2+, with a concomitant rise in hydrophobicity.

Mentions: To probe the mechanism of gel assembly changes, we studied microgels using spectrofluorophotometry. Two major mechanisms of DOM cross-linking have been demonstrated: Ca2+ cross-linking and hydrophobic binding [1]. Divalent ion (Ca2+) cross-linking has been identified as a major driving mechanism for DOM microgel formation [1,4]. We used chlortetracycline (CTC) to quantify bound Ca2+ on DOM polymers to assess the relative contribution of Ca2+ cross-linking [4,21,22]. The CTC fluorescence intensity of heated DOM decreased ~50%, which indicated fewer bound Ca2+ ions on polymer surfaces (Fig. 4). Thus, decreased levels of bound Ca2+ on DOM polymers associated with increased temperatures would explain smaller equilibrium sizes of forming gels.


Ocean warming-acidification synergism undermines dissolved organic matter assembly.

Chen CS, Anaya JM, Chen EY, Farr E, Chin WC - PLoS ONE (2015)

Decreased microgel equilibrium size (black circles) and bound Ca2+ (blue triangles) with concomitant increase in hydrophobicity (red squares).The non-linear rate of declining microgel size with increased temperature indicates potential cooperativity; around 32˚C all three parameters experienced the most pronounced associative effect—a major drop in microgel size and bound Ca2+, with a concomitant rise in hydrophobicity.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340923&req=5

pone.0118300.g004: Decreased microgel equilibrium size (black circles) and bound Ca2+ (blue triangles) with concomitant increase in hydrophobicity (red squares).The non-linear rate of declining microgel size with increased temperature indicates potential cooperativity; around 32˚C all three parameters experienced the most pronounced associative effect—a major drop in microgel size and bound Ca2+, with a concomitant rise in hydrophobicity.
Mentions: To probe the mechanism of gel assembly changes, we studied microgels using spectrofluorophotometry. Two major mechanisms of DOM cross-linking have been demonstrated: Ca2+ cross-linking and hydrophobic binding [1]. Divalent ion (Ca2+) cross-linking has been identified as a major driving mechanism for DOM microgel formation [1,4]. We used chlortetracycline (CTC) to quantify bound Ca2+ on DOM polymers to assess the relative contribution of Ca2+ cross-linking [4,21,22]. The CTC fluorescence intensity of heated DOM decreased ~50%, which indicated fewer bound Ca2+ ions on polymer surfaces (Fig. 4). Thus, decreased levels of bound Ca2+ on DOM polymers associated with increased temperatures would explain smaller equilibrium sizes of forming gels.

Bottom Line: The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C).We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5.If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected.

View Article: PubMed Central - PubMed

Affiliation: School of Engineering, University of California Merced, Merced, California, United States of America.

ABSTRACT
Understanding the influence of synergisms on natural processes is a critical step toward determining the full-extent of anthropogenic stressors. As carbon emissions continue unabated, two major stressors--warming and acidification--threaten marine systems on several scales. Here, we report that a moderate temperature increase (from 30°C to 32°C) is sufficient to slow--even hinder--the ability of dissolved organic matter, a major carbon pool, to self-assemble to form marine microgels, which contribute to the particulate organic matter pool. Moreover, acidification lowers the temperature threshold at which we observe our results. These findings carry implications for the marine carbon cycle, as self-assembled marine microgels generate an estimated global seawater budget of ~1016 g C. We used laser scattering spectroscopy to test the influence of temperature and pH on spontaneous marine gel assembly. The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C). We then tested the hypothesis that temperature and pH have a synergistic influence on marine gel dispersion. We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5. If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected.

Show MeSH