Humic-like dissolved organic matter (DOM) holds significant importance in marine sediment pore waters as a major component of DOM. Due to its complex molecular structures and extended presence in natural environments, it is generally considered refractory. However, the bio-reactivity of humic-like DOM has not been adequately investigated, particularly in depositional settings where organic matter availability varies. This knowledge gap hinders our understanding of its role in sustaining deep life and regulating long-term carbon cycling in the ocean.
Marine sediment pore waters harbor humic-like DOM, which arises from various sources such as decaying plants, microbial activity, and river runoff. Its intricate molecular composition and resistant nature contribute to its persistence over time. Scientists have recognized these characteristics and often categorized humic-like DOM as refractory, assuming that it remains chemically unaltered and biologically inert in marine ecosystems.
Nevertheless, recent research efforts aim to unravel the bio-reactive potential of humic-like DOM and explore its significance in supporting deep-sea life forms. Depositional environments exhibit variations in the availability of organic matter, creating microhabitats with different nutrient concentrations. These distinct conditions can influence the reactivity of humic-like DOM and its interactions with associated microbial communities.
Understanding the role of humic-like DOM in deep-sea ecosystems is crucial because it can serve as a potential energy source for microorganisms residing in oxygen-depleted sediments. Despite the limited availability of labile organic matter in these environments, previous studies have suggested that microorganisms can access and utilize refractory DOM through enzymatic breakdown processes. The bioavailability of humic-like DOM under varying organic matter availability scenarios remains an intriguing area of investigation.
Furthermore, the intricate relationship between humic-like DOM and long-term oceanic carbon cycling necessitates further exploration. The cycling of carbon in the ocean involves the exchange of carbon dioxide (CO2) between the atmosphere and seawater, with DOM playing an essential role in this process. Understanding the fate and reactivity of humic-like DOM is crucial for accurately estimating carbon budgets and predicting the long-term impacts of climate change on the global carbon cycle.
In summary, while humic-like dissolved organic matter is often considered refractory due to its complex molecular structures and extended residence time, its bio-reactivity remains poorly understood. Investigating its roles in supporting deep-sea life and regulating long-term oceanic carbon cycling is vital for comprehending the complexities of marine ecosystems and predicting the effects of environmental changes. Further research in depositional settings with varying organic matter availability will shed light on the bioavailability and reactivity of humic-like DOM, ultimately contributing to our understanding of the intricate relationships within the marine environment.
