Optical model for the Baltic Sea with an explicit CDOM state variable: a case study with Model ERGOM (version 1.2)

Thomas Neumann,Mikko Kervinen,Sakari Väkevä,Jenni Attila,Petra Philipson,Pasi Ylöstalo,Carsten Brockmann,Susanne Thulin,Kari Kallio,Dagmar Müller,Constant Mazeran,Sampsa Koponen

doi:10.5194/gmd-14-5049-2021

Abstract

Abstract. Colored dissolved organic matter (CDOM) in marine environments impacts primary production due to its absorption effect on the photosynthetically active radiation. In coastal seas, CDOM originates from terrestrial sources predominantly and causes spatial and temporal changing patterns of light absorption which should be considered in marine biogeochemical models. We propose a model approach in which Earth Observation (EO) products are used to define boundary conditions of CDOM concentrations in an ecosystem model of the Baltic Sea. CDOM concentrations in riverine water derived from EO products serve as forcing for the ecosystem model. For this reason, we introduced an explicit CDOM state variable in the model. We show that the light absorption by CDOM in the model can be improved considerably in comparison to approaches where CDOM is estimated from salinity. The model performance increases especially with respect to spatial CDOM patterns due to the consideration of single river properties. A prerequisite is high-quality CDOM data with sufficiently high spatial resolution which can be provided by the new generation of ESA satellite sensor systems (Sentinel 2 MSI and Sentinel 3 OLCI). Such data are essential, especially when local differences in riverine CDOM concentrations exist.

Highlights

Colored dissolved organic matter (CDOM) is a major light absorption constituent in the marine environment and especially in coastal seas
We show that the light absorption by CDOM in the model can be improved considerably in comparison to approaches where CDOM is estimated from salinity
We present the implementation of a CDOM state variable in the biogeochemical model ERGOM (Ecological ReGional Ocean Model, Leibniz Institute for Baltic Sea Research, 2015) and the generation of CDOM boundary data with the aid of satellite imagery, and we discuss the effect of the proposed model extension on the Baltic Sea ecosystem

Summary

Introduction

Colored dissolved organic matter (CDOM) is a major light absorption constituent in the marine environment and especially in coastal seas. The shortwave light absorption is located in the upper water column increasing the temperature, while in clear water a thicker layer is warmed but to a lesser degree (Jolliff and Smith, 2014). This process impacts the sea surface temperature (SST) in particular. Model studies show an SST increase up to 2 K in coastal regions when colored organic materials are considered (Gnanadesikan et al, 2019)

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