Production of tyrosine-like fluorescence and labile chromophoric dissolved organic matter (DOM) and low surface accumulation of low molecular weight-dominated DOM in a productive Antarctic sea

Abstract

The Antarctic seas play critical roles in global carbon cycling. Yet, little is known about the dissolved organic matter (DOM) characteristics and the dynamics there. Here, we conducted an extensive study on the seawater DOM in the Amundsen Sea in the Pacific sector of the Southern Ocean. We found that low molecular weight fractions quantitatively dominated the DOM composition at the surface of the highly productive Amundsen Sea Polynya with the relative abundance reaching up to ~89%. Moreover, CDOM and tyrosine-like fluorescence generation were observed, with the average values of~2.4？2.6m？1 (a254) and ~0.3 RU, respectively. While there is a net positive accumulation of dissolved organic carbon (DOC) at the ocean's surface, the net accumulation was negative for the chromophoric DOM (CDOM), which suggests a labile nature for the freshly produced CDOM. The estimated net DOC production ratio was only ~9 ± 6%, which was less than the global level (~17%). This finding signified a low surface accumulation of DOM in the austral summer, which is potentially explained by its nonlimiting nutrients, photo- and/or bio-labile nature of produced DOM, and long water residence time.