Sea-suface microlayer (SML) and underlying water (ULW) samples focusing on CDOM spectral characteristics during METEOR cruise M91

• Main Authors: Galgani, Luisa, Engel, Anja
• Format: Dataset
• Language: English
• Published: PANGAEA 2016
• Subjects: #1778; Absorption coefficient; colored dissolved organic matter at 325 nm; Amino acids; dissolved hydrolyzable; Bacteria; BIOACID; Biological Impacts of Ocean Acidification; Carbon; organic; dissolved; particulate; Comment; Coomassie stainable particles; abundance; Date/Time of event; Event label; Fluorescence; dissolved organic matter; component; Humification index; LATITUDE; LONGITUDE; M91; M91_#1778; M91_S1; M91_S10_1; M91_S10_2; M91_S10_3; M91_S10_4; M91_S11; M91_S12_1; M91_S12_2; M91_S12_3; M91_S13_1; M91_S13_2; M91_S13_3; M91_S14_1; M91_S14_2; M91_S15_1; M91_S15_2; M91_S15_3; M91_S16_1; M91_S16_2; M91_S16_3; M91_S17_1; M91_S17_2; M91_S19; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.861947; https://doi.org/10.1594/PANGAEA.861947

The coastal upwelling system off the coast of Peru is characterized by high biological activity and a pronounced subsurface oxygen minimum zone, as well as associated emissions of atmospheric trace gases such as N2O, CH4 and CO2. From 3 to 23 December 2012, R/V Meteor (M91) cruise took place in the Peruvian upwelling system between 4.59 and 15.4°S, and 82.0 to 77.5°W. During M91 we investigated the composition of the sea-surface microlayer (SML), the oceanic uppermost boundary directly subject to high solar radiation, often enriched in specific organic compounds of biological origin like chromophoric dissolved organic matter (CDOM) and marine gels. In the SML, the continuous photochemical and microbial recycling of organic matter may strongly influence gas exchange between marine systems and the atmosphere. We analyzed SML and underlying water (ULW) samples at 38 stations focusing on CDOM spectral characteristics as indicator of photochemical and microbial alteration processes. CDOM composition was characterized by spectral slope (S) values and excitation-emission matrix fluorescence (EEMs), which allow us to track changes in molecular weight (MW) of DOM, and to determine potential DOM sources and sinks. Spectral slope S varied between 0.012 to 0.043 1 nm-1 and was quite similar between SML and ULW, with no significant differences between the two compartments. Higher S values were observed in the ULW of the southern stations below 15°S. By EEMs, we identified five fluorescent components (F1-5) of the CDOM pool, of which two had excitation/emission characteristics of amino-acid-like fluorophores (F1, F4) and were highly enriched in the SML, with a median ratio SML : ULW of 1.5 for both fluorophores. In the study region, values for CDOM absorption ranged from 0.07 to 1.47 m-1. CDOM was generally highly concentrated in the SML, with a median enrichment with respect to the ULW of 1.2. CDOM composition and changes in spectral slope properties suggested a local microbial release of DOM directly in the SML as a ...