Abstract
Kelps have a major role in marine and atmospheric iodine cycling in the coastal zone of temperate regions, with potential wide-ranging impacts on ozone destruction in the coastal marine boundary layer. However, little is known about the impact of kelp forests on iodine speciation in coastal sea water. To address this, we examined iodide and iodate concentrations in seawater in and around a giant kelp forest near San Diego, CA, USA, and a nearby site that was not influenced by kelp biology. Our data shows that while both iodide and iodate concentrations remained unchanged during the year at the nearby site, these concentrations changed significantly in and around the kelp forest, and were strongly related to changes in kelp canopy biomass. In particular, iodide reached its highest concentration and iodate reached its lowest concentration during the summer when the kelp canopies were near their maximum, while the opposite pattern was observed during the winter and spring when the kelp canopies were near their minimum. Further, comparisons of these changes with corresponding changes in seawater temperature and wind speed indicated that these relationships were relatively small compared to those with changes in kelp biomass. Together, our data show a strong relationship between kelp biomass and iodine metabolism.
Highlights
Marine production of organic halogenated compounds has been proposed as an important link between ocean biology, atmospheric composition, and climate [1,2,3,4,5]
Monitoring seawater total reducible iodine (TRI), iodide and iodate concentrations at Scripps Pier monthly from January through July 2015 revealed that the concentrations of these species were essentially unchanged throughout the monitoring period (Regressions: iodide, F1,5 = 0.195, p = 0.677; iodate, F1,5 = 0.014, p = 0.908)
The concentration of Total reducible iodine (TRI) was, on average, 523 ± 36 nM, the concentration of iodide was, on average, 150 ± 11 nM, and iodate was, on average, 373 ± 43 nM (Fig 1). These values are in accord with other measurements taken in low latitude coastal waters [33]. These values were statistically unchanged as a function of sample month, there was slightly more relative temporal variation in iodate concentration (CV = 0.11) than iodide concentration (CV = 0.08) or TRI (CV = 0.07), and the temporal variation observed in TRI appeared more closely related to variation in iodate than iodide (Fig 1)
Summary
Marine production of organic halogenated compounds has been proposed as an important link between ocean biology, atmospheric composition, and climate [1,2,3,4,5]. The climate relevance of the link between ocean biology and atmospheric halogens (including iodine) was demonstrated by estimating the change in the ozone radiative forcing due to halogen-driven ozone loss using a climate model [7,8]. These halogenated compounds enter the stratosphere through rapid convection from the marine boundary layer (MBL) [9], and once there may be more efficient than.
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