The Role of Boundary Mixing for Diapycnal Oxygen Fluxes in a Stratified Marine System

Abstract

Over the past decades, the occurrence of suboxic and anoxic zones has significantly increased worldwide with major implications for the affected ecosystems (Conley et al., 2011; Diaz & Rosenberg, 2008, and others). The generation of anoxic water masses in stratified marine systems is related to unbalanced rates of oxygen consumption, production, and transport. Especially in shallow marine and limnic systems, organic matter degradation and in turn oxygen depletion is largely determined by benthic processes and resuspension in the turbulent bottom boundary layer (Glud, 2008). In such systems, turbulent vertical transport of oxygen toward the sediment becomes a key factor in regulating deep-water oxygen dynamics. Lack of sufficient transport mechanisms may lead to permanent anoxia with well-known examples including the Black Sea, the Baltic Sea, and the Cariaco Basin (Astor et al., 2003;Konovalov et al., 2005;Reissmann et al., 2009). For understanding the oxygen dynamics in stratified marine systems, it is thus mandatory to identify and understand the physical transport mechanisms.Recent research has made considerable progress in identifying and quantifying both oxygen transport processes and oxygen consumption rates. For example, benthic consumption processes, especially relevant in shallow marine systems and lakes, have been studied in various settings using chamber landers, oxygen microprofilers, eddy-covariance techniques, and other approaches (

Oxygen dynamics in a deep‐silled fjord: Tight coupling to the open shelf

“…Important components of the oxygen dynamics in winter are still uncertain. For example, Holtermann et al (2022) found that boundary mixing was a major source of oxygen into the deep part of the Baltic Sea. If that was true across this fjord system, then one would expect deep oxygen to behave similarly at KSK1 and FOC1.…”