Conserved molecular properties of dissolved organic matter during Weddell Sea Deep Water formation

Antarctic Bottom Water (AABW) is decreasing in volume due to climate change with potential consequences for abyssal carbon storage, where carbon is locked away from the atmosphere for centuries. Understanding the formation and export of dissolved organic matter (DOM) on the Antarctic shelf is therefore essential to determine how organic carbon enters this deep-sea reservoir. Here, we investigate solid-phase extractable DOM (SPE-DOM) transformations in the Weddell Sea, where half of AABW forms. Molecular and structural properties of SPE-DOM remain unchanged during dense-water formation. Shelf processes minimally affect exported organics into the deep-sea, likely due to remineralization to inorganic carbon enhanced by long residence times on the shelf. Consequently, the dominant SPE-DOM signature in Weddell Sea Deep Water (WSDW) is established before dense shelf waters mix with warmer off-shelf waters. We estimate that 0.155 ± 0.03 PgC are transferred annually from the Weddell Sea to AABW, and that its molecular composition is expected to remain conserved despite ongoing climate-driven weakening of AABW.