Oceanographic sampling has traditionally been based on pre-planned or deterministic sampling stations and depths, offering little possibility to track instantaneous and local conditions; this can in turn lead to under-sampling of important features in the water column.

Intelligent underwater vehicles search for plankton

Autonomous underwater vehicles, AUVs, are propeller-driven unmanned vehicles, and they offer the potential to deliver high-resolution targeted samples of the ocean interior. Normally, AUV trajectories are pre-scripted missions, where the vehicle follows a deterministic path. In adaptive path planning, the mission is continuously updated based on what the vehicle is sensing.

In a recent study, Nansen Legacy scientists have now demonstrated that programming underwater robots to continuously adapt their sampling strategy to local features will render a more accurate representation of the ocean and the processes therein. The team used a light autonomous underwater vehicle (LAUV) to survey the edges of predefined water volumes. The resulting data allowed the robot to identify interior areas with high concentrations of subsurface chlorophyll a for additional, detailed sampling. The results from the LAUV survey were so confirmed with data from remote sensing and shipboard samples.

The study demonstrates that the combination of real-time data analysis and accurate, adaptive robotic sampling will help improve our understanding of marine food webs and their dynamic, heterogeneous environments.

Read more about this publication on Forskning.no or the original article:

The inflow of warm Atlantic water to the Arctic Ocean is relevant for what happens to the sea ice and the ecosystem, and studying the processes that regulate Atlantic water inflow is therefore important in order to understand the observed changes. Nansen Legacy scientists have investigated processes related to warm Atlantic water inflow in three recently published studies:

Large inflow of warm Atlantic water keeps the ocean north of Svalbard ice free well into winter

A large area of ice-free water has become a concurrent feature north of Svalbard. Based on timeseries of hydrography and velocity of the Atlantic water current north of Svalbard, Nansen Legacy scientists document in a recent study that large inflow of warm water in autumn and early winter prohibits sea ice formation in that area. This, combined with recent years’ reduction in sea ice coverage and thickness also in the central Arctic Ocean, results in less freshwater input from the north, weakening the isolating colder meltwater layer at the ocean surface. As a consequence, the warm Atlantic-origin water extends all the way up to the surface for major parts of the year,creating the large ice-free area north of Svalbard. Only when the wind blows more sea ice and fresh water from the interior Arctic Ocean or from the east, a proper sea ice cover may establish over the Atlantic inflow area north of Svalbard.

Read more about this publication on ScienceNordic.comForskning.no or the original article:

Upstream regulation of inflow to the Arctic Ocean

A sea ice and ocean model that resolves eddy (circular current of water) formation was used to investigate oceanographic conditions that promote flow over the Yermak Plateau, a topographic obstacle which warm water in the West Spitsbergen Current must pass on its way to the Arctic Ocean. The results of the study show that strong pulses of inflow were associated with a warmer and faster West Spitsbergen Current. This increases the potential vorticity in the outer part of the current, which acts as a barrier and guides the flow onto the Plateau. This implies that if the temperature of the current flowing toward the Arctic Ocean increases, and a larger fraction of the ocean current is likely to be steered into the Arctic Ocean.

The role of Atlantic heat transport in future Arctic winter sea ice loss

During recent decades Arctic sea ice variability and retreat during winter have largely been a result of variable ocean heat transport. In a recent study, Nansen Legacy modellers used the Community Earth System Model (CESM) large ensemble simulation to disentangle internally and externally forced winter Arctic sea ice variability, and to assess to what extent future winter sea ice variability and trends are driven by Atlantic heat transport. The major findings of the study are:

1. Ocean heat transport remains a good predictor for the winter sea ice extent. More heat, less sea ice. Both for the Barents Sea and the Arctic Ocean beyond; for warming trend and year-to-year fluctuations. (The relation weaken as the Barents Sea becomes largely ice-free.)

2. Future periods of increasing winter sea ice extent are not impossible, but increasingly unlikely the longer the period considered.

3. The northern branch into the Nordic Seas strengthens through the 21st century even as the large-scale Atlantic circulation (AMOC) is projected to weaken.

(Photos successively from the top: colourbox.com, David Fierstein & Arild Hareide, Ola Reibo & Arild Sundfjord)

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