Effect of wind speed on the size distribution of gel particles in the sea surface microlayer: insights from a wind–wave channel experiment

Abstract. Gel particles, such as transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP), are important organic components in the sea surface microlayer (SML). Here, we present results on the effect of different wind speeds on the accumulation and size distribution of TEP and CSP during a wind wave channel experiment in the Aeolotron. Total areas of TEP (TEPSML) and CSP (CSPSML) in the surface microlayer were exponentially related to wind speed. At wind speeds < 6 m s−1, accumulation of TEPSML and CSPSML occurred, decreasing at wind speeds of > 8 m s−1. Wind speeds > 8 m s−1 also significantly altered the size distribution of TEPSML in the 2–16 µm size range towards smaller sizes. The response of the CSPSML size distribution to wind speed varied through time depending on the biogenic source of gels. Wind speeds > 8 m s−1 decreased the slope of CSPSML size distribution significantly in the absence of autotrophic growth. For the slopes of TEP and CSP size distribution in the bulk water, no significant difference was observed between high and low wind speeds. Changes in spectral slopes between high and low wind speed were higher for TEPSML than for CSPSML, indicating that the impact of wind speed on size distribution of gel particles in the SML may be more pronounced for TEP than for CSP, and that CSPSML are less prone to aggregation during the low wind speeds. Addition of an E. huxleyi culture resulted in a higher contribution of submicron gels (0.4–1 µm) in the SML at higher wind speed (> 6 m s−1), indicating that phytoplankton growth may potentially support the emission of submicron gels with sea spray aerosol.

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Effect of wind speed on the size distribution of biogenic gel particles in the sea surface microlayer: Insights from a wind wave channel experiment

10.5194/bg-2017-419 ◽

2017 ◽

Cited By ~ 1

Author(s):

Cui-Ci Sun ◽

Martin Sperling ◽

Anja Engel

Keyword(s):

Wind Speed ◽

Size Distribution ◽

Wind Wave ◽

Sea Surface ◽

Surface Microlayer ◽

Wind Speeds ◽

Wave Channel ◽

Gel Particles ◽

Sea Surface Microlayer ◽

Physical And Chemical

Abstract. Biogenic gels particles, such as transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP), are important components in the sea-surface microlayer (SML). The accumulation of gel particles in the SML and their potential implications for gas exchange and emission of primary organic aerosols have generated considerable research interest in recent years. Changes in the particle-size distribution (PSD) can provide important information for the understanding of physical and chemical processes involving gel particles, such as aggregation, degradation or loss. So far, little is known regarding the influence of wind speed on the size distribution of marine gel particles in the surface microlayer. Here, we present results on the effect of different wind speeds on the PSD of TEP and CSP during a wind wave channel experiment in the Aeolotron. Total area of TEP and CSP were exponentially related to wind speed in the SML. At wind speeds 8 m s−1 also significantly altered the PSD slope of TEP in the 2–16 μm size range toward smaller size. Changes in spectral slopes at wind speeds > 8 m s−1 were more pronounced for TEP than for CSP indicating a high aggregation potential for TEP in the SML, potentially enhancing the export of TEP by aggregates settling out of the SML. Our experiment provided evidence for the control of wind speed on the accumulation of biogenic gel particles and their PSD changes, providing a useful insight into particle dynamics and biophysical processes at the interface between air and sea.

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Formation and distribution of sea-surface microlayers

Biogeosciences Discussions ◽

10.5194/bgd-7-5719-2010 ◽

2010 ◽

Vol 7 (4) ◽

pp. 5719-5755 ◽

Cited By ~ 4

Author(s):

O. Wurl ◽

E. Wurl ◽

L. Miller ◽

K. Johnson ◽

S. Vagle

Keyword(s):

Wind Speed ◽

Primary Production ◽

Sea Surface ◽

Surface Microlayer ◽

Average Wind Speed ◽

Wind Speeds ◽

Average Wind ◽

The Pacific ◽

Sea Surface Microlayer ◽

Natural Surfactants

Abstract. Results from a study of surfactants in the sea-surface microlayer (SML) in different regions of the ocean (subtropical, temperate, polar) suggest that this interfacial layer between the ocean and atmosphere covers the ocean's surface to a significant extent. Threshold values at which primary production acts as a significant source of natural surfactants have been derived from the enrichment of surfactants in the SML relative to underlying water and local primary production. Similarly, we have also derived a wind speed threshold at which the SML is disrupted. The results suggest that surfactant enrichment in the SML is typically greater in oligotrophic regions of the ocean than in more productive waters. Furthermore, the enrichment of surfactants persisted at wind speeds of up to 10 m s−1 without any observed depletion above 5 m s−1. This suggests that the SML is stable enough to exist even at the global average wind speed of 6.6 m s−1. Global maps of primary production and wind speed are used to estimate the ocean's SML coverage. The maps indicate that wide regions of the Pacific and Atlantic Oceans between 30° N and 30° S are more significantly affected by the SML than northern of 30° N and southern of 30° S due to higher productivity (spring/summer blooms) and wind speeds exceeding 12 m s−1 respectively.

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Formation and global distribution of sea-surface microlayers

Biogeosciences ◽

10.5194/bg-8-121-2011 ◽

2011 ◽

Vol 8 (1) ◽

pp. 121-135 ◽

Cited By ~ 138

Author(s):

O. Wurl ◽

E. Wurl ◽

L. Miller ◽

K. Johnson ◽

S. Vagle

Keyword(s):

Wind Speed ◽

Primary Production ◽

Trophic Levels ◽

Sea Surface ◽

Surface Microlayer ◽

Average Wind Speed ◽

Wind Speeds ◽

The Pacific ◽

Sea Surface Microlayer ◽

Natural Surfactants

Abstract. Results from a study of surfactants in the sea-surface microlayer (SML) in different regions of the ocean (subtropical, temperate, polar) suggest that this interfacial layer between the ocean and atmosphere covers the ocean's surface to a significant extent. New, experimentally-derived threshold values at which primary production acts as a significant source of natural surfactants to the microlayer are coupled with a wind speed threshold at which the SML is presumed to be disrupted, and the results suggest that surfactant enrichment in the SML is greater in oligotrophic regions of the ocean than in more productive waters. Furthermore, surfactant enrichments persisted at wind speeds of up to 10 m s−1, without any observed depletion above 5 m s−1. This suggests that the SML is stable enough to exist even at the global average wind speed of 6.6 m s−1. Using our observations of the surfactant enrichments at various trophic levels and wind states, global maps of primary production and wind speed allow us to extrapolate the ocean's SML coverage . The maps indicate that wide regions of the Pacific and Atlantic Oceans between 30° N and 30° S may be more significantly covered with SML than north of 30° N and south of 30° S, where higher productivity (spring/summer blooms) and wind speeds exceeding 12 m s−1 may prevent extensive SML formation.

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The organic sea-surface microlayer in the upwelling region off the coast of Peru and potential implications for air–sea exchange processes

Biogeosciences ◽

10.5194/bg-13-989-2016 ◽

2016 ◽

Vol 13 (4) ◽

pp. 989-1007 ◽

Cited By ~ 47

Author(s):

Anja Engel ◽

Luisa Galgani

Keyword(s):

Amino Acids ◽

Organic Matter ◽

Wind Speed ◽

Coastal Upwelling ◽

Sea Surface ◽

Surface Microlayer ◽

Close Coupling ◽

Exchange Processes ◽

Sea Surface Microlayer ◽

Almost All

Abstract. The sea-surface microlayer (SML) is at the uppermost surface of the ocean, linking the hydrosphere with the atmosphere. The presence and enrichment of organic compounds in the SML have been suggested to influence air–sea gas exchange processes as well as the emission of primary organic aerosols. Here, we report on organic matter components collected from an approximately 50 µm thick SML and from the underlying water (ULW), ∼  20 cm below the SML, in December 2012 during the SOPRAN METEOR 91 cruise to the highly productive, coastal upwelling regime off the coast of Peru. Samples were collected at 37 stations including coastal upwelling sites and off-shore stations with less organic matter and were analyzed for total and dissolved high molecular weight (> 1 kDa) combined carbohydrates (TCCHO, DCCHO), free amino acids (FAA), total and dissolved hydrolyzable amino acids (THAA, DHAA), transparent exopolymer particles (TEP), Coomassie stainable particles (CSPs), total and dissolved organic carbon (TOC, DOC), total and dissolved nitrogen (TN, TDN), as well as bacterial and phytoplankton abundance. Our results showed a close coupling between organic matter concentrations in the water column and in the SML for almost all components except for FAA and DHAA that showed highest enrichment in the SML on average. Accumulation of gel particles (i.e., TEP and CSP) in the SML differed spatially. While CSP abundance in the SML was not related to wind speed, TEP abundance decreased with wind speed, leading to a depletion of TEP in the SML at about 5 m s−1. Our study provides insight to the physical and biological control of organic matter enrichment in the SML, and discusses the potential role of organic matter in the SML for air–sea exchange processes.

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Assessing the potential for DMS enrichment at the sea-surface and its influence on air–sea flux

10.5194/os-2016-26 ◽

2016 ◽

Author(s):

C. F. Walker ◽

M. J. Harvey ◽

M. J. Smith ◽

T. G. Bell ◽

E. S. Saltzman ◽

...

Keyword(s):

Sea Surface ◽

Gas Transfer ◽

Surface Microlayer ◽

Surface Seawater ◽

Biological Factors ◽

Near Surface ◽

Wind Speeds ◽

Factors Influencing ◽

Sea Surface Microlayer ◽

High Enrichment

Abstract. The flux of dimethylsulfide (DMS) to the atmosphere is generally inferred using water sampled at or below 2 m depth, thereby excluding any concentration anomalies at the air–sea interface. Two independent techniques were used to assess the potential for near-surface DMS enrichment to influence DMS emissions and also identify the factors influencing enrichment. DMS measurements in productive frontal waters over the Chatham Rise, east of New Zealand, did not identify any significant DMS gradients between 0.01 and 6 m in sub-surface seawater, whereas DMS enrichment in the sea-surface microlayer was variable, with a mean enrichment factor (EF; the concentration ratio between DMS in the SSM and in sub-surface water) of 1.7. Physical and biological factors influenced sea-surface microlayer DMS concentration, with high enrichment (EF > 1.3) only recorded in a dinoflagellate-dominated bloom, and associated with low to medium wind speeds and near-surface temperature gradients. On occasion, high DMS enrichment preceded periods when the air–sea DMS flux, measured by eddy covariance, exceeded the flux calculated using COARE parameterised gas transfer velocities and measured sub-surface seawater DMS concentrations. The results of these two independent approaches suggest that air–sea emissions may be influenced by near-surface DMS production under certain conditions, and highlights the need for further study to constrain the magnitude and mechanisms of DMS production in the sea surface microlayer.

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A Comparative Assessment of Surface Wind Speed and Sea Surface Temperature over the Indian Ocean by TMI, MSMR, and ERA-40

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech2021.1 ◽

2007 ◽

Vol 24 (6) ◽

pp. 1131-1142 ◽

Cited By ~ 23

Author(s):

Anant Parekh ◽

Rashmi Sharma ◽

Abhijit Sarkar

Keyword(s):

Wind Speed ◽

Indian Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Microwave Radiometer ◽

Surface Wind ◽

Surface Wind Speed ◽

Sea Surface ◽

Wind Speeds ◽

Low Wind Speeds

A 2-yr (June 1999–June 2001) observation of ocean surface wind speed (SWS) and sea surface temperature (SST) derived from microwave radiometer measurements made by a multifrequency scanning microwave radiometer (MSMR) and the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) is compared with direct measurements by Indian Ocean buoys. Also, for the first time SWS and SST values of the same period obtained from 40-yr ECMWF Re-Analysis (ERA-40) have been evaluated with these buoy observations. The SWS and SST are shown to have standard deviations of 1.77 m s−1 and 0.60 K for TMI, 2.30 m s−1 and 2.0 K for MSMR, and 2.59 m s−1 and 0.68 K for ERA-40, respectively. Despite the fact that MSMR has a lower-frequency channel, larger values of bias and standard deviation (STD) are found compared to those of TMI. The performance of SST retrieval during the daytime is found to be better than that at nighttime. The analysis carried out for different seasons has raised an important question as to why one spaceborne instrument (TMI) yields retrievals with similar biases during both pre- and postmonsoon periods and the other (MSMR) yields drastically different results. The large bias at low wind speeds is believed to be due to the poorer sensitivity of microwave emissivity variations at low wind speeds. The extreme SWS case study (cyclonic condition) showed that satellite-retrieved SWS captured the trend and absolute magnitudes as reflected by in situ observations, while the model (ERA-40) failed to do so. This result has direct implications on the real-time application of satellite winds in monitoring extreme weather events.

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The organic sea surface microlayer in the upwelling region off Peru and implications for air–sea exchange processes

Biogeosciences Discussions ◽

10.5194/bgd-12-10579-2015 ◽

2015 ◽

Vol 12 (13) ◽

pp. 10579-10619 ◽

Cited By ~ 4

Author(s):

A. Engel ◽

L. Galgani

Keyword(s):

Organic Matter ◽

Organic Compounds ◽

Coastal Upwelling ◽

Sea Surface ◽

Surface Microlayer ◽

Surface Ocean ◽

Gel Particles ◽

Exchange Processes ◽

Sea Surface Microlayer

Abstract. The sea surface microlayer (SML) is at the very surface of the ocean, linking the hydrosphere with the atmosphere, and central to a range of global biogeochemical and climate-related processes. The presence and enrichment of organic compounds in the SML have been suggested to influence air–sea gas exchange processes as well as the emission of primary organic aerosols. Among these organic compounds, primarily of plankton origin, are dissolved exopolymers, specifically polysaccharides and proteins, and gel particles, such as Transparent Exopolymer Particles (TEP) and Coomassie Stainable Particles (CSP). These organic substances often accumulate in the surface ocean when plankton productivity is high. Here, we report results obtained in December 2012 during the SOPRAN Meteor 91 cruise to the highly productive, coastal upwelling regime off Peru. Samples were collected from the SML and from ~ 20 cm below, and were analyzed for polysaccharidic and proteinaceous compounds, gel particles, total and dissolved organic carbon, bacterial and phytoplankton abundance. Our study provides insight to the physical and biological control of organic matter enrichment in the SML, and discusses the potential role of organic matter in the SML for air–sea exchange processes.

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A laboratory study of the minimum wind speed for wind wave generation

Journal of Fluid Mechanics ◽

10.1017/s0022112088001892 ◽

1988 ◽

Vol 192 ◽

pp. 339-364 ◽

Cited By ~ 42

Author(s):

Kimmo K. Kahma ◽

Mark A. Donelan

Keyword(s):

Wind Speed ◽

Shear Flow ◽

Wind Wave ◽

Flow Instability ◽

Wave Generation ◽

Wind Speeds ◽

Instability Theory ◽

Low Wind Speeds ◽

Shear Flow Instability ◽

The Waves

The minimum wind speed for wind wave generation has been investigated in a laboratory wind-wave flume using a sensitive slope gauge to measure the initial wavelets about 10 μm high. The growth at very low wind speeds was higher than predicted by the viscous shear-flow instability theory. Assuming that the growth is exponential, the inception wind speed at which the growth rate becomes positive can be defined. It occurred at (friction velocity) u* ≈ 2 cm/s, somewhat lower than the u* ≈ 4–5 cm/s predicted by shear-flow instability theory. However, the observed growth rates were close to the theory at higher wind speeds when the waves were higher than 1 mm. The effect of temperature on the wind speed at which the waves become readily visible is shown to be appreciable and in keeping with the temperature dependent viscous damping. Other sources of growth are discussed. Our estimates show that the Phillips resonance mechanism might be sufficiently effective to generate the observed growth at very low wind speeds.

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Assessing the potential for dimethylsulfide enrichment at the sea surface and its influence on air–sea flux

Ocean Science ◽

10.5194/os-12-1033-2016 ◽

2016 ◽

Vol 12 (5) ◽

pp. 1033-1048 ◽

Cited By ~ 8

Author(s):

Carolyn F. Walker ◽

Mike J. Harvey ◽

Murray J. Smith ◽

Thomas G. Bell ◽

Eric S. Saltzman ◽

...

Keyword(s):

Sea Surface ◽

Gas Transfer ◽

Surface Microlayer ◽

Surface Seawater ◽

Biological Factors ◽

Near Surface ◽

Wind Speeds ◽

Factors Influencing ◽

Sea Surface Microlayer ◽

High Enrichment

Abstract. The flux of dimethylsulfide (DMS) to the atmosphere is generally inferred using water sampled at or below 2 m depth, thereby excluding any concentration anomalies at the air–sea interface. Two independent techniques were used to assess the potential for near-surface DMS enrichment to influence DMS emissions and also identify the factors influencing enrichment. DMS measurements in productive frontal waters over the Chatham Rise, east of New Zealand, did not identify any significant gradients between 0.01 and 6 m in sub-surface seawater, whereas DMS enrichment in the sea-surface microlayer was variable, with a mean enrichment factor (EF; the concentration ratio between DMS in the sea-surface microlayer and in sub-surface water) of 1.7. Physical and biological factors influenced sea-surface microlayer DMS concentration, with high enrichment (EF > 1.3) only recorded in a dinoflagellate-dominated bloom, and associated with low to medium wind speeds and near-surface temperature gradients. On occasion, high DMS enrichment preceded periods when the air–sea DMS flux, measured by eddy covariance, exceeded the flux calculated using National Oceanic and Atmospheric Administration (NOAA) Coupled-Ocean Atmospheric Response Experiment (COARE) parameterized gas transfer velocities and measured sub-surface seawater DMS concentrations. The results of these two independent approaches suggest that air–sea emissions may be influenced by near-surface DMS production under certain conditions, and highlight the need for further study to constrain the magnitude and mechanisms of DMS production in the sea-surface microlayer.

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