A wave of oceanographic articles published
During April and the first week of May, the oceanographic research unit at SMHI had no fewer than seven scientific articles published.
Itzel Ruvalcaba Baroni, Mehdi Pasha Karami, Per Pemberton, Bengt Karlson, Sam Fredriksson, Dorothée Vallot. Magnus Hieronymus, Lars Arneborg, Ye Liu, Germo Väli, Anders Torstensson.
“Sometimes lots of good news comes at once, and April and early May were really good for us,” says Sam Fredriksson, head of the SMHI’s oceanographic research unit.
“It shows that our research is of high quality, that it is in demand both nationally and internationally, and that it helps to lay a scientific foundation for SMHI’s activities,” continues Sam Fredriksson.
The studies show how small-scale ocean processes, changes in the atmosphere’s large-scale circulation, and variations in salinity and precipitation affect the Baltic Sea’s ecosystem, water exchange and climate sensitivity – knowledge that provides decision support in itself but can also improve our own and others’ ocean and climate models. The studies also contribute, among other things, to our understanding of plankton dynamics in the seas around Sweden and to improved models of Antarctic ice shelf melting. Altogether the studies provide a better basis for understanding and predicting the effects of climate change regionally and globally.
Submesoscale dynamics in the Baltic Sea – a review
Urmas Lips, et al. Authors from SMHI: Germo Väli, Lars Arneborg, Per Pemberton
This paper is an overview of the current knowledge on the so-called submesoscale (SMS) dynamics and processes in the Baltic Sea, i.e. eddies and circulation systems with lateral length scale less than 5-10 km. Different studies based on observations, numerical models and remote sensing are summarized, and a future outlook on needed research is given. The most important message is that SMS are present in different parts of the Baltic Sea, both in the surface and below surface with important contributions to the energy and matter exchange, and that improved understanding of these processes can therefore lead to enhanced model simulations of the Baltic Sea system.
Read more about "Submesoscale dynamics in the Baltic Sea – a review" External link.
Large-scale atmospheric circulation and its impact on the Baltic Sea region: controls, predictability and consequences
Florian Börgel et al. Authors from SMHI: Itzel Ruvalcaba Baroni, Magnus Hieronymus, Mehdi Pasha Karami
“This manuscript explains how natural climate cycles and large-scale atmospheric and oceanic forces influence the Baltic Sea's temperature, salinity, acidity, and capacity to support marine life. By reviewing past research and climate models, we explore how stormy winters or dry summers affect oxygen levels, ocean acidification, and the growth of microscopic algae at the base of the food web. While we have a good understanding of how weather changes the Baltic Sea's physical conditions, the exact chain of events and temporal scales leading to changes in water chemistry remains unclear. To better predict future changes and protect the Baltic ecosystem, we identify the most urgent scientific studies needed to fill these knowledge gaps.”
Baltic sea deep salinity: an initial and boundary value problem
Magnus Hieronymus
The salinity in the deeper part of the Baltic sea is a consequence of a balance between highly intermittent inflows of high saline waters from Kattegatt and a slow salt loss to the upper layers. The intermittent nature of the inflows give rise to a sizeable natural variability in salinity. This paper studies this natural variability and derives new results linking salinity changes both to inflows and the initial (pre inflow) salinity. An interesting result is that an inflow of a given magnitude can result in very different salinity changes depending on the initial salinity in the basin.
Read more about "Baltic sea deep salinity: an initial and boundary value problem" External link.
High throughput in situ imaging reveals widely occurring diel vertical migration among phytoplankton
Karin Garefelt et al. Authors from SMHI: Bengt Karlsson och Anders Torstensson.
We used high-throughput in situ imaging flow cytometry to investigate vertical migration of phytoplankton in the Skagerrak and the Baltic Sea. An Imaging FlowCytobot (IFCB) was deployed to continuously profile the vertical water column for ~10 weeks (August–October 2016) near a mussel farm in the Skagerrak. This revealed diel vertical migration e.g. among ciliates, dinoflagellates, and diatoms, shifting median depth by 2–6 m between night and day. Another IFCB was used at Utö in the Northern Baltic Proper, here also cyanobacteria were investigated. Migratory taxa accounted for 77 percent and 79 percent of total phytoplankton biomass (size range <10–150 μm) in the Skagerrak and Baltic Sea, respectively, underscoring the ecological significance of vertical migration. Most populations peaked near the surface at midday, although other patterns were also observed. This study highlights the prevalence of vertical migration in phytoplankton and showcases the power of automated, high-throughput imaging technologies to advance our understanding of plankton ecology.
Effects of subgrid-scale ice topography on the ice shelf basal melting simulated in NEMO-4.2.0
Dorothée Vallot
Ice shelves in Antarctica play an important role in the climate system by buttressing the continental ice shelf and therefore limiting sea level rise but also by releasing freshwater in the Southern Ocean at the ice-ocean interface, which can change circulation pattern. Understanding melt processes and apply a good parameterisation in ocean models is crucial to reduce uncertainties in future projections. Usually, the sub-shelf surface is considered flat and smooth in models but recent observations show that melt is slope dependent and this sub-grid topography is not taken into acount. In this study, we show that applying a variable roughness in the computation of the friction velocity can reduce vertical resolution dependency and show better results in crevassed areas. As ice shelves are projected to experience more damage (i.e. crevasses) in the future, it may have positive feedbacks that could be ignored if not taken into account.
Response of a semi-enclosed sea to perturbed freshwater and open ocean salinity forcing
Lars Arneborg, Magnus Hieronymus, Per Pemberton, Ye Liu, Sam T. Fredriksson
The Baltic Sea is a brackish sea where the marine ecosystems have adjusted to the prevailing low salinity during thousands of years and will be highly impacted by salinity changes, e.g. due to climate change. In this work we show that the Baltic Sea salinity is highly sensitive to changes in precipitation over the sea and catchment area as well as changes in North Sea salinity. The study also provides new understanding of this sensitivity: Basically, about half of the freshwater added to the Baltic Sea by increased precipitation will recirculate instead of leaving through the entrance area. This means that the inflow of saline water will decrease correspondingly since the input of water must balance the outflow over long time scales. Both of these processes lead to decreased Baltic Sea salinities, but this is further reinforced by reduced inflow salinities, since the inflow water is a mixture of two parts outflowing Baltic Sea water (with reduced salinity) and one part North Sea water.
Revisiting the parameterization of dense water plume dynamics in geopotential coordinates in NEMO v4.2.2
Robinson Hordoir et al. Authors from SMHI: Magnus Hieronymus, Per Pemberton
Bottom gravity currents, composed of dense waters flowing along sloping ocean bottoms, are important components of overturning circulations in many ocean basins. Such current are present, for example, in many fjords, the Baltic Sea and in the North Atlantic, as a part of the AMOC current system. Many ocean models struggle to represent these current owing to a multitude of factors. In this paper a simple recipe is introduced that can improve the migration of these currents in a certain class of models.
