Oceanic carbon cycling plays a major role in determining global atmospheric CO₂. A better understanding of dissolved organic matter and its constituents in the water column and how it affects marine carbon cycling is sought after. This study successfully measured osmolytes, low molecular zwitterionic compounds derived from amino acids, in depth profiles from the surface to 300 meters in the Sargasso Sea. Dimethylsulfionopropionate (DMSP), glycine betaine, and TMAo are three osmolytes that have been extensively studied. This study identified seven additional osmolytes in seawater for the first time: alanine betaine, propionobetaine, trigonelline, L-proline betaine, betonicine, butyrobetaine, and L-carnitine. We found that these compounds reached a maximum at different depths in the water column. Osmolyte concentrations were in the picomolar (pM) range, and fluctuated depending on time of day, suggesting a relationship to photosynthetic activity. Total osmolytes reached a maximum between 250 and 400 pM at the deep chlorophyll maximum at 80 to 120 meters below surface waters during all sampling times. In addition to these environmental measurements, experiments with cultured photosynthetic organisms were used to investigate the production of osmolytes in extracellular organic matter released by cells. These experiments yielded evidence of the production in culture of many of the osmolytes we had detected in seawate
