The organic matter (OM) in the ocean, due to its sensitivity to natural and anthropogenic environmental variations, provides key information for the characterization of actual and past sedimentary environments. The OM is principally formed of two pools, particulate organic matter (POM) and dissolved organic matter (DOM). From these two pools, DOM represents one of the largest active pools of organic carbon in the global carbon cycle, and its composition and potential reactivity have implications for the carbon balance, nutrient cycling and CO2 degassing.
In coastal upwelling areas, the high production and consumption of OM cause, in combination with other factors such as topography and oceanic circulation, the depletion of dissolved oxygen. Therefore aerobic degradation processes in the water column, and bioturbation and benthic respiration in the sediment are limited, thus favoring anaerobic processes. The Humboldt upwelling system off Peru is one of the areas around the world with the highest rates of primary productivity and an intense oxygen minimum zone (OMZ). Although many studies have been performed regarding the characterization of suspended and sedimentary POM, information about the composition and dynamics of DOM is scarce.
The aim of this project is to assess the dynamics of the DOM pool in coastal upwelling waters off central Peru under different conditions of productivity and intensity of the oxygen minimum zone. For this purpose, samples of DOM from water column and pore water from two different seasons (summer and winter) will be analyzed in terms of their molecular composition. In addition to this, degradation processes of POM to DOM will be studied by leaching experiments using particulate material from sediments and sediment traps. Chemical analyses of the molecular composition of DOM will be performed applying state-of-the art analytical techniques. Ultrahigh resolution mass spectrometry via Fourier-transform ion cyclotron resonance (FT-ICR-MS) enables the simultaneous detection of several tens of thousands of exact molecular masses within the complex mixture of DOM. Ultra performance liquid chromatography (UPLC) will be used for the compound-specific quantification of amino acids, carbohydrates and black carbon. The combination of these analytical approaches yields a most detailed characterization of the molecular composition of DOM, providing a novel data base for the understanding of DOM dynamics in this important high productivity region.
This project involves logistical cooperation and scientific exchange with the Instituto del Mar del Perú (IMARPE) in Callao, that will also provide the necessary sampling platform for the study. In this way, this project will strengthen the ongoing scientific cooperation between Germany and Peru, and will also help to create a link between IMARPE and the Research Group for Marine Geochemistry at the ICBM Oldenburg and MPI Bremen.