Alfred Wegener Institute for Polar and Marine Research
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Simulating sea ice freezing using a continuum mechanical multi-phase and multi-component homogenization framework
Get PDFThe formation of porous sea ice in the polar oceans is a complex process influenced by the interaction between saline seawater and temperature. As ocean warming and environmental changes continue in these regions, a likely impact on the microstructure of sea ice is expected to occur, which in turn affects the biogeochemical processes associated with ice formation. To better understand and model the phase transition phenomena, this study presents a biphasic model that considers both solid ice and saline seawater within the framework of extended Theory of Porous Media (eTPM). This approach applies a continuum mechanical treatment on multiple phases and components associated with ice and seawater. The model captures phase transition between ice and brine using an interfacial mass transfer method, where the mass exchange is treated as a jump across an interface separating the two phases. This mass production is governed by factors such as heat flux, specific enthalpies, and the interfacial area. The resulting system of equations provides a high-fidelity representation of the ice-brine interactions and is solved using the Finite Element Method (FEM). To validate the approach, the study includes academic test cases as proof of concept
Processes and Palaeo‐Environmental Changes in the Arctic from Past to Present (PalaeoArc) – introduction
Get PDFCharacterizing Snowdrift Events at Bayelva Station, Spitsbergen
Get PDFSnow distribution is an important factor that controls the ground thermal regime and influences permafrost thaw and glacier mass loss, because snow is a very effective
insulator. These ground-snow dynamics are influenced on a microscale from redistribution of snow by wind, known as snowdrift, because it leads to heterogenous
snow accumulation. Nevertheless, snowdrift is poorly researched so that models rely on wind speed as a proxy. I addressed this research gap with a detailed characterization of snowdrift events and their drivers. For this, I used 30-minutes averaged snow flux data
from the acoustic FlowCapt4 sensor together with meteorological and snow data at Bayelva station from September 2024 to September 2025. I developed a quality assessment and defined snowdrift events. With this, I identified 73 snowdrift events in the season which have a great variety in their meteorological conditions, snow characteristics and their drivers. This demonstrates the complexity of snowdrift events in their drivers and frequency. Nevertheless, just one of these events accounts for 50% of the total snow transport during the whole season. The results emphasize that more integrated research is needed to further examine snowdrift events as well as evaluate their impact on the cryosphere
From eons to epochs: multifractal geological time and the compound multifractal - Poisson process
Get PDFGeological time is punctuated by events that define biostrata and the Geological Time Scale’s (GTS) hierarchy of eons, eras, periods, epochs, ages. Paleotemperatures and macroevolution rates, have already indicated that the range ≈ 1 Myr to (at least) several hundred Myrs is a scaling (hence hierarchical) “megaclimate” regime. We apply analysis techniques including Haar fluctuations, structure functions, trace moment and extended self-similarity to the temporal density of the boundary events (ρ(t)) of two global and four zonal series. We show that ρ(t) itself is a new paleoindicator and we determine the fundamental multifractal exponents characterizing the mean fluctuations, the intermittency and the degree of multifractality. The strong intermittency allows us to show that the (largest) megaclimate scale is at least ≈ 0.5 Gyr. We find that the tail of the probability distribution of the intervals (“gaps”) between boundaries is also scaling with an exponent qD ≈ 3.3 indicating huge variability with occasional very large gaps such that it’s third order statistical moment barely converges. The scaling in time implies that record incompleteness increases with its resolution (the “Resolution Sadler effect”), while scaling in probability space implies that incompleteness increases with sample length (the “Length Sadler effect”). The density description of event boundaries is only a useful characterization over time intervals long enough for there to be typically one or more events. In order to model the full range of scales and densities, we introduce a compound multifractal - Poisson process in which the subordinating multifractal process determines the probability of a Poisson event and that this new process is close to the observed statistics. Scaling changes our understanding of life and the planet and it is needed for unbiasing many statistical paleobiological and geological analyses, including unbiasing spectral analysis of the bulk of geodata that are derived from paleoclimatic and paleoenvironmental archives
The impact of measurement precision on the resolvable resolution of ice core water isotope reconstructions
Get PDFAbstract. Stable water isotopes in ice cores serve as a valuable proxy for the climate of the past hundreds of thousands of years. Over time, water isotope diffusion causes significant attenuation of the isotopic signal, exacerbated in deep ice due to extreme layer thinning and increased temperatures from geothermal heat flux. This damping affects higher frequencies to a greater extent, erasing information on the shortest timescales. It is possible to restore some of the attenuated variability through deconvolution, a method which reverses the effect of diffusion. However, since the measured isotopic signal always contains noise from the measurement process, deconvolution inevitably amplifies this measurement noise along with the isotopic signal. Thus the effectiveness of deconvolution depends on the precision of the measurements, with noisier data limiting the ability to restore otherwise resolvable frequencies. Here, we quantify the upper frequency limit introduced by the magnitude of the measurement noise analytically for different climate states, and offer a numerical example using the Beyond EPICA Oldest Ice Core (BE-OIC). We also demonstrate the qualitative significance of measurement noise on simulated Antarctic isotopic profiles. The general resolution improvement for firn or upper ice records is on the order of 1.5 times for a 10-fold reduction in measurement noise. Similarly, throughout the BE-OIC, we find the deconvolution of δ18O records with measurement error of 0.1 ‰ contributes a 1.5 times increase in the maximum resolvable frequency, which rises to a factor of 2 improvement after reducing the measurement noise to 0.01 ‰. While progress is continuously being made towards improving precision of stable isotope measurements, further improvements using longer integration times should be considered when analysing limited and precious deep ice in order to obtain the most faithful climate reconstructions possible
Spatially Varying Biogeochemical Parameter Estimation in a Global Ocean Model
Get PDFOcean biogeochemical (BGC) models are key tools for investigating ocean biogeochemistry and the global carbon cycle. These models contain many uncertain and often poorly known process parameters that are treated as constant values. This study addresses this limitation by estimating spatially and temporally varying parameters in the Regulated Ecosystem Model 2 (REcoM2) through the assimilation of satellite‐derived chlorophyll‐a data using an ensemble Kalman filter. Nine key BGC parameters were optimized, significantly improving the model's performance. Utilizing the optimized parameters in the model results in a 26% reduction in root mean square error for surface chlorophyll‐a concentrations compared to simulations with uniform parameters, with the spatial patterns of parameter estimates aligning well with observed distributions. These findings underscore the benefits of incorporating spatially and temporally varying parameters for enhancing model accuracy and understanding BGC variability
Seasonal and interannual variability on the chemical composition of the Svalbard surface snowpack
Get PDFAbstract. The Svalbard Archipelago, highly sensitive to rapid environmental changes, offers an ideal physical laboratory to investigate how environmental drivers can shape the seasonal chemical composition of snow in a warming climate. From 2018 to 2021, sampling campaigns at the Gruvebadet Snow Research Site in Ny-Ålesund, in the North-West of the Svalbard Archipelago, captured the interannual variability in ionic and elemental impurities within surface snow, reflecting seasonal differences in atmospheric and oceanic conditions. Notably, warmer conditions prevailed in 2018–2019 and 2020–2021, contrasting with the relatively colder season of 2019–2020. Our findings suggest that impurity concentrations in the 2019–2020 colder season are impacted by enhanced sea spray aerosol production, likely driven by a larger extent of sea ice, and drier, windy conditions. This phenomenon was particularly evident in March 2020, when extensive sea ice was present in Kongsfjorden and around Spitsbergen due to an exceptionally strong, cold stratospheric polar vortex and unusual Arctic Oscillation (AO) index positive phase. This study provides a detailed characterization of how snow chemistry in this area responds to major environmental conditions, with particular attention to sea-ice extent, atmospheric circulation, synoptic conditions, and Arctic climate variability
Modelling the Late Pliocene with AWI-CM3 as a contribution to PlioMIP3 core experiments
Get PDFThe Late Pliocene, particularly the Marine Isotope Stage KM5c (3.205 Ma BP) has been increasingly proposed as an analogue to future climate change, especially considering changes in the hydrological cycle, monsoon systems, and atmospheric and ocean warming above Pre-Industrial (1850 CE) and historical levels. The Pliocene Modelling Intercomparison Project (PlioMIP), now in its third phase (PlioMIP3), seeks to explore climate of the Pliocene based on a combination of climate model simulations and proxy data reconstructions. One of its goals is also to assess the analogy between past and future climates and to quantify climate sensitivity to Pliocene boundary conditions. This work shall help to improve climate models and their application for both past and future warm climates and to provide a paleoclimate-informed assessment of uncertainties in modelled warm climates. With this manuscript we present the PlioMIP3 core simulations for the pre-industrial control (PI) and the Late Pliocene (LP) based on the AWI Climate Model, Version 3 (AWI-CM3). This represents the first application of AWI-CM3 at tectonic timescales which necessitates more extensive adjustment of model setups than the application for recent climate. We therefore take advantage of the opportunity to also document more generally the methods we devised to generate AWI-CM3 model setups for paleoclimate research under geographies that differ from the modern reference state. AWI-CM3 simulates a Late Pliocene climate that is about 4 °C warmer than the pre-industrial reference, with land warming exceeding ocean warming by a factor of 1.2. Polar amplification is particularly pronounced, with Antarctic surface air temperature anomalies exceeding 6 °C while Arctic anomalies reach 4 °C to 5 °C. In comparison to the previous PlioMIP2, this places AWI-CM3 among the warmer ensemble members, consistent with a relatively high equilibrium climate sensitivity of
4 °C. Our simulations also display an intensified hydrological cycle, with global mean precipitation increasing by 0.31 mm d−1. The ocean surface warms globally to about 3.06 °C, accompanied by contrasting salinity trends, with salinization of the North Atlantic (+3 PSU) and freshening of the Arctic (–2.5 PSU) and Indian (–1 PSU) Oceans. Additionally, the meridional overturning circulation (MOC) reorganizes, with the Atlantic MOC strengthening by about 8 Sv, the Pacific MOC remaining inactive, and the global Antarctic Bottom Water cell being substantially reduced (11 Sv weaker relative to PI). We find reduced global sea-ice extent, that is halved with respect to PI in the Southern Hemisphere, and enhanced northward ocean heat transport in the North Atlantic. Overall, AWI-CM3 reproduces the large-scale climate features of the Late Pliocene inferred from proxy records and the PlioMIP2 ensemble, while highlighting key ocean–atmosphere feedbacks shaping this warm climate