Accumulation of Ancient but Labile Dissolved Organic Matter in the Dead Sea

The global reservoir of dissolved organic carbon (DOC) equals the amount of atmospheric carbon, yet the mechanisms allowing its long-term persistence in aquatic systems remain poorly resolved. The hypersaline Dead Sea offers an extreme model for testing how environmental constraints affect organic matter cycling and microbial utilization. We analyzed dissolved organic matter (DOM) from the Dead Sea, its tributary springs, and surrounding aquifers using ¹⁴C dating and Fourier-transform ion cyclotron resonance mass spectrometry.  DOC concentrations in the Dead Sea were ~2000 µM, ~50-fold higher than in the deep ocean, with ¹⁴C ages of ~10,000 years. Dead Sea DOM was molecularly almost undistinguishable from submarine and coastal springs, indicating that the DOM originates mainly from groundwater and sedimentary inputs rather than in situ production. Despite its age, molecular indices revealed features typical of labile material, and in incubation experiments with a productive North Sea microbial community, Dead Sea DOM was readily consumed. DOC decreased by 15% and 800 molecular formulas were lost within 3 years, demonstrating that it remains biologically degradable under non-extreme conditions. Accordingly, the long-term accumulation of DOC in the Dead Sea is not due to intrinsic molecular recalcitrance but to environmental inhibition of microbial degradation caused by extreme salinity and ionic toxicity, redefining the concept of “refractory” DOM as a relative property, determined by local environmental and ecological constraints rather than chemical stability alone.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Danny Ionescu, Technische Universität Berlin (ionescu@tu-berlin.de)

Authors:

Sarah Bercovici, National Oceanography Centre, Southampton, UK;  (sarah.bercovici@noc.ac.uk)

Jutta Niggemann, University of Oldenburg, Germany  (jutta.niggemann@uni-oldenburg.de)

Christian Siebert, UFZ Halle/Saale, Germany  (christian.siebert@ufz.de)

Beatriz Noriega Ortega, University of Oldenburg, Germany  (beno23@gmail.com)

Timothy Eglinton, ETH Zurich, Switzerland  (timothye@retired.ethz.ch)

Franziska Lechleitner, ETH Zurich, Switzerland  (franziska.lechleitner@unibe.ch)

Cameron McIntyre, ETH Zurich, Switzerland  (Cameron.Mcintyre@glasgow.ac.uk)

Negar Haghipour, ETH Zurich, Switzerland  (negar.haghipour@eaps.ethz.ch)

Thorsten Dittmar, University of Oldenburg, Germany  (thorsten.dittmar@uni-oldenburg.de)