Abstract
AbstractWe report the first measurements of surfactant activity (SA) in the sea surface microlayer (SML) and in subsurface waters (SSW) at the ocean basin scale, for two Atlantic Meridional Transect from cruises 50°N to 50°S during 2014 and 2015. Northern Hemisphere (NH) SA was significantly higher than Southern Hemisphere (SH) SA in the SML and in the SSW. SA enrichment factors (EF = SASML/SASSW) were also higher in the NH, for wind speeds up to ~13 m s−1, questioning a prior assertion that Atlantic Ocean wind speeds >12 m s−1 poleward of 30°N and 30°S would preclude high EFs and showing the SML to be self‐sustaining with respect to SA. Our results imply that surfactants exert a control on air‐sea CO2 exchange across the whole North Atlantic CO2 sink region and that the contribution made by high wind, high latitude oceans to air‐sea gas exchange globally should be reexamined.
Highlights
The physics and biogeochemistry of the sea surface microlayer (SML) afford it a unique role in global element cycling and in the production and removal of climate active gases [Upstill-Goddard et al, 2003; Cunliffe et al, 2013; Carpenter and Nightingale, 2015]
We report the first measurements of surfactant activity (SA) in the sea surface microlayer (SML)
Given that the two transects differed by up to 13° of longitude between ~40°N and 20°S, AMT25 proceeding further into the North Atlantic Gyre between 20°N and 40°N and somewhat more easterly between the equator and 20°S (Figure 1), it appears that longitudinal SA gradients are comparatively small across a substantial part of the Atlantic Ocean and that surfactant distributions remain relatively constant between consecutive years
Summary
The physics and biogeochemistry of the sea surface microlayer (SML) afford it a unique role in global element cycling and in the production and removal of climate active gases [Upstill-Goddard et al, 2003; Cunliffe et al, 2013; Carpenter and Nightingale, 2015]. Open ocean surfactants include polysaccharides, lipids and proteins [Allan et al, 1972; Myklestad, 1974; Sakugawa and Handa, 1985], transparent exopolymer particles [Wurl and Holmes, 2008], and chromophoric dissolved organic matter [Tilstone et al, 2010] They are mainly biologically derived, from phytoplankton [Ẑutić et al, 1981], via zooplankton grazing [Kujawinski et al, 2002] and from bacteria [Kurata et al, 2016], with additional small components of terrestrial [Frew et al, 2002] origin and from the in situ photochemical reworking of preexisting organics [Tilstone et al, 2010]. We present the first comprehensive measurements of total surfactant activity (SA) in the SML and SSW across large spatial scales and up to high wind speeds, from two Atlantic Meridional Transect (AMT) cruises between 50°N and 50°S: AMT (2014) and AMT (2015)
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