Chromophoric Dissolved Organic Matter (CDOM) Naperian Absorption Coefficients from the Gulf of Finland from June to July 2019 (MODIE project)

These data are chromophoric dissolved organic matter (CDOM) Naperian absorption coefficients from the LightCycle DOM photodegradation experiments conducted in the western Gulf of Finland, Baltic Sea. The LightCycle experiments were conducted as a part of the AQUACOSM JOMEX project: Systems Responses to A Pulse of Dissolved Organic Carbon, at the Tvärminne Mesocosm Facility (TMF, Tvärminne Zoological Station (TZS), University of Helsinki).

The JOMEX experiment ran from 26 June to 10 July 2019 and the mesocosms were divided into three treatment groups: 1) three control mesocosms with no humic substances or nutrients added, 2) three humic-amended mesocosms with only humic substances added to a final concentration of 2 mg L−1 in each mesocosm and three humic+nutrients-amended mesocosms with humic substances (2 mg L−1 final concentration), and 3) three humic+nutrients-amended mesocosms with humic substances (2 mg L−1 final concentration) and NH4Cl and KH2PO4 (80 μg L−1 N and 20 μg L−1 P final concentrations) added.

Surface (1 m) water samples for the LightCycle experiments were collected from one each of control, humic-amended and humic+nutrients-amended mesocosms, immediately after the amendment (day 1) and 2, 5, 7, 9 and 12 days after the amendment (days 3, 6, 8, 10 and 13). These water samples were filtered with 0.2μm filters and irradiated under a solar simulator.

CDOM absorbance at different irradiation time points were measured for these experiments using a Shimadzu UV-2501PC UV-VIS recording spectrophotometer or an Agilent 8453 UV-visible Spectrophotometer, and converted to Naperian absorption coefficients.

The measurements of CDOM absorption and the subsequent calculation of CDOM fading (decrease in absorption) offered clues to the degradation of CDOM, and provided insights into the potential of photochemistry to remove added terrestrial dissolved organic matter (DOM) and the interactions of DOM photochemistry with eutrophication in this Baltic Sea system, where there are increasing concerns that climate change and anthropogenic activities can lead to increased terrestrial input of humic substances to surface waters and browning of surface waters.

These data were collected by Kun Ma and Jay Brandes of the Skidaway Institute of Oceanography, Department of Marine Sciences, University of Georgia.