Chromophoric and fluorescent dissolved organic matter in and above the oxygen minimum zone off Peru

Abstract

As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a key role in microbial respiration and carbon cycling, but little is known on DOM distribution and cycling in the ETSP. DOM optical properties give important insights on DOM sources, structure and biogeochemical reactivity. Here, we present data and a conceptual view on distribution and cycling of chromophoric (CDOM) and fluorescent (FDOM) DOM in and above the oxygen minimum zone (OMZ) off Peru. Five fluorescent components were identified during PARAFAC analysis. Highest intensities of CDOM and of the amino acid‐like fluorescent component (C3) occurred above the OMZ and coincided with maximum chl a concentrations, suggesting phytoplankton productivity as major source. High intensities of a marine humic‐like fluorescent component (C1), observed in subsurface waters, indicated in situ microbial reworking of DOM. FDOM release from inner shelf sediment was determined by seawater analysis and continuous glider sensor measurement and included a humic‐like component (C2) with a signature typical for terrestrially derived humic acids. Upwelling supplied humic‐like substances to the euphotic zone. Photo‐reactions were likely involved in the production of a humic‐like fluorescent component (C5). Our data show that variable biological and physical processes need to be considered for understanding DOM cycling in a highly dynamic coastal upwelling system like the ETSP off Peru.

Characteristics of chromophoric and fluorescent dissolved organic matter in the Nordic Seas

“…In situ fluorometry provided an opportunity to study FDOM distribution in greater detail and commercially available FDOM fluorometers are usually built to detect humic substances Belzile et al, 2006;Kowalczuk et al, 2010;Aiken et al, 2011;Loginova et al, 2016). In this study we simultaneously measured three different FDOM components, and the most interesting feature observed with the use of this new instrument was very significant spatial coupling between I CH3 and I FChla .…”

Hydrological and Biogeochemical Controls on Absorption and Fluorescence of Dissolved Organic Matter in the Northern South China Sea

“…C1 displayed two excitation maxima at 250 and 365 nm and one emission maxima at 456 nm. Similar fluorescence signatures are initially categorized as representing a mixture of terrestrial humic‐like fluorescence peaks A and C (Coble, ) but have also been widely observed in oceanic waters (Catalá et al, ; Guéguen et al, ; Jørgensen et al, ; Kowalczuk et al, ; Loginova, Thomsen, & Engel, ; Yamashita et al, ). C2 had excitation/emission maxima at 250, 330/388 nm, consistent with marine humic‐like fluorescence (peak M; Coble, ), which has been characterized as representing microbially altered DOM (Stedmon & Markager, ; Yamashita et al, ).…”

Metabolic potential and in situ activity of marine Marinimicrobia bacteria in an anoxic water column

“…Genes encoding peptidases are also highly represented in both PN262000N21 and ARCTIC96B-7 (51 and 37 in each respectively), presumably for use in hydrolysing primary or secondary production available as dissolved or particulate organic matter. The organic matter pool in OMZ environments has not been extensively characterized (Loginova et al, 2016). However, subeuphotic marine areas are often enriched in semi-labile dissolved organic matter (Moran et al, 2016).…”