ALBERT

Description: We describe and test a new model of biological marine silicate cycling, implemented in the Kiel Marine Biogeochemical Model version 3 (KMBM3), embedded in the University of Victoria Earth System Climate Model (UVic ESCM) version 2.9. This new model adds diatoms, which are a key component of the biological carbon pump, to an existing ecosystem model. This new model combines previously published parameterizations of a diatom functional type, opal production and export with a novel, temperature-dependent dissolution scheme. Modelled steady-state biogeochemical rates, carbon and nutrient distributions are similar to those found in previous model versions. The new model performs well against independent ocean biogeochemical indicators and captures the large-scale features of the marine silica cycle to a degree comparable to similar Earth system models. Furthermore, it is computationally efficient, allowing both fully coupled, long-timescale transient simulations and “offline” transport matrix spinups. We assess the fully coupled model against modern ocean observations, the historical record starting from 1960 and a business-as-usual atmospheric CO2 forcing to the year 2300. The model simulates a global decline in net primary production (NPP) of 1.4 % having occurred since the 1960s, with the strongest declines in the tropics, northern midlatitudes and Southern Ocean. The simulated global decline in NPP reverses after the year 2100 (forced by the extended RCP8.5 CO2 concentration scenario), and NPP returns to 98 % of the pre-industrial rate by 2300. This recovery is dominated by increasing primary production in the Southern Ocean, mostly by calcifying phytoplankton. Large increases in calcifying phytoplankton in the Southern Ocean offset a decline in the low latitudes, producing a global net calcite export in 2300 that varies only slightly from pre-industrial rates. Diatom distribution moves southward in our simulations, following the receding Antarctic ice front, but diatoms are outcompeted by calcifiers across most of their pre-industrial Southern Ocean habitat. Global opal export production thus drops to 75 % of its pre-industrial value by 2300. Model nutrients such as phosphate, silicate and nitrate build up along the Southern Ocean particle export pathway, but dissolved iron (for which ocean sources are held constant) increases in the upper ocean. This different behaviour of iron is attributed to a reduction of low-latitude NPP (and consequently, a reduction in both uptake and export and particle, including calcite scavenging), an increase in seawater temperatures (raising the solubility of particulate iron) and stratification that “traps” the iron near the surface. These results are meant to serve as a baseline for sensitivity assessments to be undertaken with this model in the future.

Description: With this script, the Meridional Overturning Circulation (MOC) can be computed from NEMO ocean-model output for the whole globe or the Atlantic (AMOC), Indic (IMOC) and Pacific (PMOC) subbasins. The MOC is computable in z- and sigma coordinates. Moreover, for nested configurations, it is possible to combine data from both host and nest grids. Finally, it is possible to take into account of that the ORCA model grid is curvilinear north of 20°N: it is possible to compute the northward velocity component from the velocity field in x- and y- directions and to sum up the meridional flux over latitudional bands instead of in x-direction. When both steps are applied, the resulting MOC shows however strong variability in meridional direction. It needs to be clarified, whether this is realistic or not. The software is provided in the form of the jupyter notebook "MOC.ipynb" which includes more informations on the possibilites of the computations and an extensive appendix section with comparisons to computations with cdftools, as well as with details on the computation of the MOC including nest data and taking the curvilinearity of the grid into account. Necessary python modules are listed at the beginning of the document.

Description: CMSY++ is an advanced state-space Bayesian method for stock assessment that estimates fisheries reference points (MSY, Fmsy, Bmsy) as well as status or relative stock size (B/Bmsy) and fishing pressure or exploitation (F/Fmsy) from catch and (optionally) abundance data, a prior for resilience or productivity (r), and broad priors for the ratio of biomass to unfished biomass (B/k) at the beginning, an intermediate year, and the end of the time series. For the purpose of this User Guide, the whole package is referred to as CMSY++ whereas the part of the method that deals with catch-only data is referred to as CMSY (catch MSY), and the part of the method that requires additional abundance data is referred to as BSM (Bayesian Schaefer Model). Both methods are based on a modified Schaefer surplus production model (see paper cited above for more details). The main advantage of BSM, compared to other implementations of surplus production models, is the focus on informative priors and the acceptance of short and incomplete (i.e., fragmented, with missing years) abundance data. This document provides a simple step-by-step guide for researchers who want to apply CMSY++ to their own data.

Description: MSM89 – Bridgetown/Barbados – Bridgetown/Barbados 2. Wochenbericht – MARIA S. MERIAN - MSM89 20.-26.01.2020

Description: MSM89 – Bridgetown/Barbados – Bridgetown/Barbados 1. Wochenbericht – MARIA S. MERIAN - MSM89 14.-19.01.2020

Description: MSM89 – Bridgetown/Barbados – Bridgetown/Barbados 3. Wochenbericht – MARIA S. MERIAN - MSM89 27.01.-02.02.2020

Description: Remobilization of soil carbon as a result of permafrost degradation in the drainage basin of the major Siberian rivers combined with higher precipitation in a warming climate potentially increase the flux of terrestrial derived dissolved organic matter (tDOM) into the Arctic Ocean. The Laptev (LS) and East Siberian Seas (ESS) receive enormous amounts of tDOM-rich river water, which undergoes at least one freeze-melt cycle in the Siberian Arctic shelf seas. To better understand how freezing and melting affect the tDOM dynamics in the LS and ESS, we sampled sea ice, river and seawater for their dissolved organic carbon (DOC) concentration and the colored fraction of dissolved organic matter. The sampling took place in different seasons over a period of 9 years (2010–2019). Our results suggest that the main factor regulating the tDOM distribution in the LS and ESS is the mixing of marine waters with freshwater sources carrying different tDOM concentrations. Of particular importance in this context are the 211 km3 of meltwater from land-fast ice from the LS, containing ~ 0.3 Tg DOC, which in spring mixes with 245 km3 of river water from the peak spring discharge of the Lena River, carrying ~ 2.4 Tg DOC into the LS. During the ice-free season, tDOM transport on the shelves takes place in the surface mixed layer, with the direction of transport depending on the prevailing wind direction. In winter, about 1.2 Tg of brine-related DOC, which was expelled from the growing land-fast ice in the LS, is transported in the near-surface water layer into the Transpolar Drift Stream that flows from the Siberian Shelf toward Greenland. The actual water depth in which the tDOM-rich brines are transported, depends mainly on the density stratification of the LS and ESS in the preceding summer and the amount of ice produced in winter. We suspect that climate change in the Arctic will fundamentally alter the dynamics of tDOM transport in the Arctic marginal seas, which will also have consequences for the Arctic carbon cycle.

Description: FS Alkor Reise 556, Fahrtabschnitt 14.05. - 22.05.2021 Die Ostsee hat im Rahmen des Klimawandels und wachsender anthropogener Nutzung in den letzten 50 Jahren tiefgreifende und im globalen Vergleich besonders schnell ablaufende Veränderungen, wie Erwärmung, Versauerung, Eutrophierung, zunehmenden Sauerstoffmangel, Überfischung, und die Ausbreitung invasiver Arten, erfahren. Die ökologischen und ökonomischen Konsequenzen dieser langfristigen Veränderungen sind durch kurzfristige Projekte nur schwer zu verfolgen. Umso wichtiger sind Langzeitdatenreihen, die auch dekadische Muster abbilden. Das Hauptziel der Ausfahrt AL556 ist es, durch Probennahmen und hydrographische Messungen eine der besten verfügbaren Langzeitdatenreihen für die pelagische Ostsee fortzusetzen. So wurden seit 1986 in den tiefen Becken der Ostsee mit Hauptfokus auf dem Bornholmbecken mit konsistenter Methodik pelagische Schleppnetzfischerei und Fischprobennahmen, Beprobungen des pelagischen Nahrungsnetzes (Phyto- und Zooplankton einschließlich Ichthyo- und gelatinösem („Quallen“) Plankton), ozeanographische/hydrographische Messungen und Hydroakustikaufnahmen durchgeführt. Diese Arbeiten werden während der AL556 weitergeführt, wobei die Ausfahrt aufgrund einer Corona-bedingten Unterbrechung der Langzeitdatenreihe in 2020 von besonderer Bedeutung ist. Die gewonnenen Proben und Daten sind dabei für verschiedene Projekte und internationale Kollaborationen der Abteilung „Marine Evolutionary Ecology“ am GEOMAR relevant. Dazu gehören insbesondere das Projekt "Fischereiindizierte Evolution" im Rahmen der DFG-Graduiertenschule TransEvo (CAU /GEOMAR), und das EU Horizon 2020 Projektes GoJelly. Sonderprojekte in 2021 sind zudem die Isolation von marinen Viren und der Phytoyplanktonart Ostreococcus für das Projekt Marine Mikroben und Viren der Ostsee unter dem Einfluß des Klimawandels und Probennahmen für die Untersuchung der Nahrungsökologie von Fischlarven und planktivoren adulten Fischen mit Hilfe molekularbiologischer Ansätze („Metabarcoding“).

Description: Global models show generally a large model-data misfit with regard to oxygen. One of the most intense OMZs is located in the Arabian Sea. The scripts serve to give an overview of the main model deficiencies in the Indian Ocean with a detailed comparison of the historical state of ten climate models from the 5th coupled model intercomparison project (CMIP5) that present our present-day understanding of physical and biogeochemical processes.

Description: Modern digital scientific workflows - often implying Big Data challenges - require data infrastructures and innovative data science methods across disciplines and technologies. Diverse activities within and outside HGF deal with these challenges, on all levels. The series of Data Science Symposia fosters knowledge exchange and collaboration in the Earth and Environment research community.