Copernicus Ocean State Report, issue 6

The 6th issue of the Copernicus OSR incorporates a large range of topics for the blue, white and green ocean for all European regional seas, and the global ocean over 1993–2020 with a special focus on 2020

The Arctic freshwater budget

In dieser Arbeit wird der Süßwasserhaushalt der Arktis mit all seinen Komponenten diskutiert. Dazu wird die Arktis in die Zweige Atmosphäre, Land und Ozean aufgeteilt und Haushaltsgleichungen für die drei Subsysteme aufgestellt. Die einzelnen Süßwasserkomponenten werden anschließend untersucht, wobei hauptsächlich das neuste ECMWF Reanalyseprodukt ERA5 verwendet wird. Die Parameter werden untersucht auf Saisonalität, zwischenjährliche Variabilität und Trends. So zeigt beispielsweise die mittlere Arktis einen leichten Zuwachs an Süßwasserzufuhr von der Atmosphäre zur Oberfläche, während Regionen wie die Karasee, Barentssee und Beaufortsee relativ beträchtliche Abnahmen verzeichnen. Die Größten Unstimmigkeiten zeigt der Süßwasser-Abfluss von den Landflächen in den Ozean. Während Daten von ERA5 starke Abfluss Abnahmen über die letzten Jahrzehnte zeigen, deuten Beobachtungen auf leichte Zunahmen hin. Da der Abfluss in ERA5-Land, der offline Simulation von ERA5, deutlich höhere Werte zeigt, liegt das Problem wohl am Datenassimilationssytsem und insbesondere an der Einführung eines neuen IMS Schneeprodukts in 2004.In this thesis the freshwater budget of the Arctic and all it's relevant components is discussed. Therefore the Arctic system is divided into it's three branches, the atmosphere, the land and the ocean, and budget equations for the subsystems are constructed. The individual hydrological components are then examined, using essentially the newest ECMWF reanalysis ERA5, and, if available, compared to other datasets and previous studies. The parameters are analysed on their spatial distribution, seasonalities, interannual variabilities and possible trends. Several hydrological variables exhibit significant changes over the past decades, e.g. the central Arctic indicates a slight increase of freshwater delivery from the atmosphere to the surface, while peripheral oceanic regions like Kara, Barents and Beaufort Sea show relatively strong decreases. The biggest inconsistencies were found concerning the hydrological land variable runoff, with values from ERA5 showing strong negative trends over the past decades and hence differing greatly from observed runoff values, that feature rather positive trends. As runoff from ERA5-Land, the offline simulation of ERA5, showed considerably higher values, the problem was attributed mainly to the data assimilation system and the introduction of a new IMS (Interactive Multi-sensor Snow and Ice Mapping System) snow cover product in 2004

Dichloromethane utilized by an anaerobic mixed culture: acetogenesis and methanogenesis

Dichloromethane (8.9 mg/l) was eliminated from industrially polluted, anaerobic groundwater in a fixed-bed reactor (43 m3) which was packed with activated charcoal and operated continuously for over three years. The elimination of dichloromethane over this period was some ten-fold in excess of the sorptive capacity of the charcoal, and the elimination (3.7 mg/h·[kg of charcoal]: residence time, 49 h) was tentatively attributed to dehalogenative microorganisms immobilized on the charcoal. Anaerobic enrichment cultures, with dichloromethane as the sole added source of carbon and energy, were inoculated with material from the reactor. Reproducibly complete substrate disappearance in subcultures was observed when traces of groundwater (1%) or yeast extract (0.01%) were supplied. Fed-batch experiments under an atmosphere of CO2 plus N2 led to the conversion in 11 days of 11 mM dichloromethane to 3 mM acetate and 2 mM methane, with a growth yield of 0.4 g of protein/mol of dichloromethane; insignificant amounts

Diagnostic evaluation of river discharge into the Arctic Ocean and its impact on oceanic volume transports

This study analyses river discharge into the Arctic Ocean using state-of-the-art reanalyses such as the fifth-generation European Reanalysis (ERA5) and the reanalysis component from the Global Flood Awareness System (GloFAS). GloFAS, in its operational version 2.1, combines the land surface model (Hydrology Tiled European Centre for Medium-Range Weather Forecasts – ECMWF – Scheme for Surface Exchanges over Land, HTESSEL) from ECMWF’s ERA5 with a hydrological and channel routing model (LISFLOOD). Furthermore, we analyse GloFAS' most recent version 3.1, which is not coupled to HTESSEL but uses the full configuration of LISFLOOD. Seasonal cycles as well as annual runoff trends are analysed for the major Arctic watersheds – Yenisei, Ob, Lena, and Mackenzie – where reanalysis-based runoff can be compared to available observed river discharge records. Furthermore, we calculate river discharge over the whole pan-Arctic region and, by combination with atmospheric inputs, storage changes from the Gravity Recovery and Climate Experiment (GRACE) and oceanic volume transports from ocean reanalyses, we assess closure of the non-steric water volume budget. Finally, we provide best estimates for every budget equation term using a variational adjustment scheme. Runoff from ERA5 and GloFAS v2.1 features pronounced declining trends induced by two temporal inhomogeneities in ERA5's data assimilation system, and seasonal river discharge peaks are underestimated by up to 50 % compared to observations. The new GloFAS v3.1 product exhibits distinct improvements and performs best in terms of seasonality and long-term means; however, in contrast to gauge observations, it also features declining runoff trends. Calculating runoff indirectly through the divergence of moisture flux is the only reanalysis-based estimate that is able to reproduce the river discharge increases measured by gauge observations (pan-Arctic increase of 2 % per decade). In addition, we examine Greenlandic discharge, which contributes about 10 % of the total pan-Arctic discharge and features strong increases mainly due to glacial melting. The variational adjustment yields reliable estimates of the volume budget terms on an annual scale, requiring only moderate adjustments of less than 3 % for each individual term. Approximately 6583±84 km3 of freshwater leaves the Arctic Ocean per year through its boundaries. About two-thirds of this is contributed by runoff from the surrounding land areas to the Arctic Ocean (4379±25 km3 yr−1), and about one-third is supplied by the atmosphere. However, on a seasonal scale budget residuals of some calendar months were too large to be eliminated within the a priori spreads of the individual terms. This suggests that systematical errors are present in the reanalyses and ocean reanalysis data sets, which are not considered in our uncertainty estimation