Publications
Following publications have been announced by our Institute of Coastal Systems – Analysis and Modeling. For further information please contact the marked authors of the publications:
León-FonFay, D., Barkhordarian, A., Feser, F., & Baehr, J. (2024): Sensitivity of Arctic marine heatwaves to half-a-degree increase in global warming: 10-fold frequency increase and 15-fold extreme intensity likelihood. Environ. Res. Lett. Vol 20, 014049, doi:10.1088/1748-9326/ada029
Abstract:
We utilize the 50-member MPI-ESM-LR Earth System model to investigate the projected changes in Arctic marine heatwaves‘ (MHWs) characteristics caused by an additional 0.5 ∘C increase in global warming, from 1.5 ∘C to 2 ∘C, with respect to pre-industrial levels. Our results indicate that this 0.5 ∘C increase in global warming triggers an intensified reaction in both the Arctic’s mean sea surface temperature (SST) and variability. In a 2 ∘C warmer world, one out of every four summer months would be warmer than the current climate. We detect a nonlinear increase of MHW intensity in a 2 ∘C world, which is characterized by a break in slope occurring around the year 2042 ± 2 (across 50 ensemble members of the SSP5-8.5 scenario). At the estimated post-break dates, the intensity rate roughly doubles, leading to MHWs in a 2 ∘C world with average cumulative heat intensity 100 ∘C*days higher than in a 1.5 ∘C world. Further results reveal that an extremely rare MHW with an intensity of 3.19 ∘C, classified as a 1-in-100-year event in a 1.5 ∘C world, is expected to transform into a 1-in-7-year event in a 2 ∘C world. This transition signifies a ∼15-fold increase in the likelihood of such events occurring due to a 0.5 ∘C increase in global warming. Likewise, a rare occurrence of years featuring 125 MHW days in a 1.5 ∘C world is projected to become a 1-in-10-year event in a 2 ∘C world, resulting in a 10-fold increase in occurrence probability. The main contributor to these changes is predominantly the rise in mean SST, with enhanced SST variability playing a minor role. These findings highlight that a 2 ∘C world could lead to a substantial escalation of the frequency and intensity of MHWs in the Arctic compared to a 1.5 ∘C world, transforming what are currently rare extreme events into more common events, with significant implications for global climate dynamics and the well-being of Arctic ecosystems and communities.
Yao, J., Chen, Z., Ge, J., & Zhang, W. (2024): Source-to-sink pathways of dissolved organic carbon in the river–estuary–ocean continuum: a modeling investigation. Biogeosciences, 21, 5435–5455, doi:10.5194/bg-21-5435-2024
Abstract:
Transport and cycling of dissolved organic carbon (DOC) are active in estuaries. However, a comprehensive understanding of the sources, sinks, and transformation processes of DOC throughout the river–estuary–ocean continuum is yet to be derived. Taking the Changjiang Estuary and adjacent shelf sea as a case study area, this study applies a physics–biogeochemistry coupled model to investigate DOC cycling in the river–estuary–ocean continuum. DOC is classified into two types depending on the origin, namely terrigenous DOC (tDOC) and marine DOC (mDOC). Simulation results were compared with observations and showed a satisfactory model performance. Our study indicates that in summer, the distribution of DOC in the Changjiang Estuary is driven by both hydrodynamics and biogeochemical processes, while in winter, it is primarily driven by hydrodynamics. The spatial transition from terrigenous-dominated DOC to marine-dominated DOC occurs mainly across the contour line of a salinity of 20 PSU. Additionally, the source–sink patterns in summer and winter are significantly different, and the gradient changes in chlorophyll a indicate the transition between sources and sinks of DOC. A 5-year-averaged budget analysis of the model results indicates that the Changjiang Estuary has the capability to export DOC, with tDOC contributing 31 % and mDOC accounting for 69 %. The larger proportion of mDOC is primarily attributed to local biogeochemical processes. The model offers a novel perspective on the distribution of DOC in the Changjiang Estuary and holds potential for its application in future organic carbon cycling of other estuaries.
Stanev, E.V., Gramcianinov, C.B., Staneva, J., & Slabakova, V. (2024): Thermohaline intrusions as seen by Argo floats: The case of the Black Sea. Journal of Geophysical Research: Oceans, 129, e2024JC021762, doi:10.1029/2024JC021762
Abstract:
Understanding the dynamics of thermohaline intrusions is crucial for predicting changes in water masses and their impact on marine ecosystems, especially in highly stratified semi-enclosed seas and other coastal environments. We use high-resolution (up to 1–2 m) Argo profiling float data collected over 15 years in the Black Sea, an excellent test area for studying thermohaline intrusions. Our analysis challenges the conventional view of stagnant intermediate and deep waters, revealing active mixing processes that reshape the thermohaline structure. We identified two main mechanisms driving these intrusions, related to dense water inflows from the Marmara Sea and boundary mixing enhanced by frontal instabilities. Argo data also allowed us to identify areas with favorable conditions for double-diffusive processes. The variability of intrusions is due to changes in the thermohaline state of the upper ocean as well as to quasi-periodic changes in the inflow caused by local conditions. Trends in the intensity and frequency of intrusions indicate shifts in water mass properties that are likely to be associated with climate variability and extreme weather events. Such trends can affect nutrient cycling, oxygen distribution and the overall stability of the water column, thereby affecting biogeochemical cycles and the resilience of marine ecosystems. Similar ventilation mechanisms may operate in other highly stratified marine systems, such as the Baltic Sea and the Arctic Ocean, so our findings may have wider implications for understanding climate-induced changes in water masses at regional and global scales.
Ho-Hagemann, H.T.M., Maurer, V., Poll, S., & Fast, I. (2024): Coupling the regional climate model ICON-CLM v2.6.6 to the Earth system model GCOAST-AHOI v2.0 using OASIS3-MCT v4.0. Geosci. Model Dev., 17, 7815–7834, doi:10.5194/gmd-17-7815-2024
Abstract:
Interactions and feedback between components of the Earth system can have a significant impact on local and regional climate and its changes due to global warming. These effects can be better represented by regional Earth system models (RESMs) than by traditional stand-alone atmosphere and ocean models. Here, we present the RESM Geesthacht Coupled cOAstal model SysTem (GCOAST)-AHOI v2.0, which includes a new atmospheric component, the regional climate model Icosahedral Nonhydrostatic (ICON)-CLM, which is coupled to the Nucleus for European Modelling of the Ocean (NEMO) and the hydrological discharge model HD via the OASIS3-MCT coupler. The GCOAST-AHOI model has been developed and applied for climate simulations over the EURO-CORDEX domain. Two 11-year simulations from 2008 to 2018 of the uncoupled ICON-CLM and GCOAST-AHOI give similar results for seasonal and annual means of near-surface air temperature, precipitation, mean sea level pressure, and wind speed at a height of 10 m. However, GCOAST-AHOI has a cold sea surface temperature (SST) bias of 1–2 K over the Baltic and North seas that is most pronounced in the winter and spring seasons. A possible reason for the cold SST bias could be the underestimation of the downward shortwave radiation at the surface of ICON-CLM with the current model settings. Despite the cold SST bias, GCOAST-AHOI was able to capture other key variables well, such as those mentioned above. Therefore, GCOAST-AHOI can be a useful tool for long-term climate simulations over the EURO-CORDEX domain. Compared to the stand-alone NEMO3.6 forced by ERA5 and ORAS5 boundary forcing, GCOAST-AHOI has positive biases in sea ice fraction and salinity but negative biases in runoff, which need to be investigated further in the future to improve the coupled simulations. The new OASIS3-MCT coupling interface OMCI implemented in ICON-CLM adds the possibility of coupling ICON-CLM to an external ocean model and an external hydrological discharge model using OASIS3-MCT instead of the YAC (Yet Another Coupler). Using OMCI, it is also possible to set up a RESM with ICON-CLM and other ocean and hydrology models possessing the OASIS3-MCT interface for other regions, such as the Mediterranean Sea.
