Category: GEOF338

Icebergs are chunks of ice, which break off from marine terminating glaciers. They mostly stem from the Greenlandic and Antarctic Ice Sheets but can also be found in other areas in polar regions. They are a crucial feature of our oceans, since some major shipping tracks cross paths of larger icebergs. This poster looks at the shapes of icebergs and melt processes depending on the properties of the surrounding water.

In general icebergs have different shapes and can be separated into tabular (like a flat sheet) and non-tabular (other types of structures) icebergs. They also come in different sizes, with the smallest being 5 m tall and 15 m wide and the largest being 3900 km², which is larger than the Spanish island of Mallorca. The icebergs melt due to multiple processes. These are surface melting due to solar radiation and wind, wave erosion on the side, convective melting at the submarine sides and basal melting at the bottom. These processes create different freshwater plumes depending on the background flow strength.

Coastal polynyas are persistent open-water areas surrounded by sea ice, predominantly found along the Antarctic coast. These polynyas form primarily due to strong offshore katabatic winds that continuously remove newly formed sea ice, exposing ocean water to extremely cold atmospheric conditions. Such rapid and continuous ice formation leads to significant brine rejection, a process where salt is expelled from freezing seawater, increasing the salinity and density of the water below. This denser water mass is termed Dense Shelf Water (DSW) and sinks (cascades) down the continental slope, directly contributing to the formation of Antarctic Bottom Water (AABW). AABW is the densest and coldest water mass circulating in the global ocean. Using the Weddell Sea as a key example, this poster explores the essential role of Antarctic coastal polynyas as critical ice-production sites and their significant impact on deep ocean circulation.

Arctic sea-ice leads, gaps in the sea-ice cover, serve as critical windows for energy and mass exchange between the ocean and atmosphere. While typically small in area, these openings dominate wintertime heat fluxes and influence cloud formation, new ice growth, and seasonal melt patterns. This poster presents a summary of recent research on the formation, climatic impact, satellite detection, and model representation of Arctic sea-ice leads.

Field and satellite observations show that turbulent heat fluxes over leads can be up to 100 times greater than over adjacent sea ice. Lead activity varies regionally and seasonally and plays a measurable role in sea-ice dynamics. By accounting for the intensified energy exchange through leads, climate models achieve better agreement with observed Arctic surface temperatures and ice thickness patterns. Increased lead formation in winter and spring is strongly associated with increased summer sea-ice loss, underscoring the role of leads in seasonal Arctic ice dynamics. As global warming drives Arctic sea-ice retreat and thinning, accurately detecting and representing leads remains essential for understanding polar feedback mechanisms and forecasting Arctic climate evolution.

Fram Strait, located between Svalbard and Greenland, is dominated by two major currents: The West Spitsbergen Current brings saline and warm Atlantic water northwards, and the East Greenland Current brings fresh and cold Arctic water southwards. These mesoscale variabilities in temperature and salinity cause significant fluctuations within the water layers in Fram Strait. It is challenging to measure salinity and temperature in this area because of the presence of sea ice and depth-range limitations of in-situ measurements, making it challenging to create accurate ocean models.

This poster shows how ocean acoustics can be used to improve temperature estimates. The sound speed of acoustic waves, which can travel hundreds of kilometers, depends on temperature and salinity. The propagation and travel times of acoustic rays can be computed using ray tracing. The travel times of these acoustic waves can then be processed to provide large-scale temperature maps. Acoustic data from two experiments has been processed and is presented showing temperature maps in Fram Strait over distances of hundreds of kilometers. The first experiment shows that temperature errors are about 20m^oC. In the second experiment data assimilation was used to integrate the temperature measurements into a regional ocean circulation model, giving improved ocean temperature estimates. This shows that acoustic data can be used to improve temperature estimates in ocean models and thereby contribute to a better understanding of climate changes in Fram Strait.

The Arctic Ocean, though the smallest of the world’s oceans, plays a crucial role in regulating global ecosystems and biogeochemical cycles through its currents and water masses. Nitrogen is the key element responsible for limiting phytoplankton growth and annual primary production in the Arctic Ocean. Climate-induced reductions in sea ice extent and volume are altering the growth conditions for marine phytoplankton, with consequences for the Arctic marine ecosystem.

Obtaining high quality data in this region is challenging and autonomous instruments have become essential tools for long-term and continuous monitoring. The Submersible Ultraviolet Nitrate Analyser (SUNA) can measure chemical-free nitrate in fresh, brackish and salt water and is based on In-Situ Ultraviolet Spectroscopy. However, in natural waters, the conditions for SUNA to measure nitrate can be challenging, reducing its accuracy and precision. Nevertheless, with post-processing algorithms and routines it is possible to obtain high quality datasets. SUNA nitrate measurements can thus contribute to the understanding of future changes in the Arctic Ocean and their global implications.

The Greenland Sea has undergone a fundamental transformation over the past several decades - from a major site of deep-water formation to a stratified basin with more shallow convection. Historically, wintertime convection in the region, driven by brine rejection during sea-ice formation, enabled dense surface waters to sink and drive vertical deep ocean mixing. This process plays a key role in supporting the lower branch of the Atlantic Meridional Overturning Circulation (AMOC).

However, recent research on the Greenland Sea reveals a marked decline in deep convection over time. Increasing freshwater input from sea-ice melt and Arctic outflow has enhanced upper-ocean stratification, reducing surface density and limiting vertical mixing. This has shifted the stratification from a haline-controlled (β-ocean) to thermally controlled (α-ocean), with a clear shift identified around 1998. Since then, only intermediate water formation has been observed, and the thermobaric mechanism for deep convection has been effectively shut down. This shift has large consequences. Reduced formation of dense water in the Greenland Sea could weaken the lower branch of the AMOC, with potential impacts on global heat distribution, carbon uptake, and regional climate. The future evolution of the Greenland Sea—and feedbacks from changes in sea ice cover, freshwater fluxes, and atmospheric forcing—will be crucial in determining whether deep convection can resume or whether stratification will intensify and further weaken the AMOC.

The Arctic is currently undergoing fundamental changes that are gradually dissolving its unique polar character. Significant features of global climate change in recent decades are the main reasons for sea-ice decline and the warming of the Arctic atmosphere and ocean. These changes have far-reaching climatological consequences. A central process of this upheaval is the so-called "Atlantification", characterized by the increasing inflow of warmer and saltier Atlantic Water (AW). Atlantification manifests physically as a weakening of the cold halocline layer and a shoaling (upward shift) of the AW layer, enhancing vertical mixing and the upward heat flux from the AW to the surface. This enhanced oceanic heat release has become a major contributor to the observed rapid loss of sea ice in the eastern Eurasian Basin.

The resulting reduction in winter sea ice formation is significant but this ongoing physical reorganization also drives profound ecological changes, often referred to as Borealization. Boreal species such as Atlantic cod, capelin, and herring are expanding northward, while Arctic species like polar cod are declining. The loss of sea ice habitat also impacts associated organisms, and a related shoaling of the nutricline increases nutrient availability in the upper ocean with possible consequences for primary production. Atlantification thus represents an essential step towards a new Arctic climate state with major implications for both physical climate feedbacks and the marine ecosystem structure.