Soundscape and ambient noise levels of the Arctic waters around Greenland

A longer Arctic open water season is expected to increase underwater noise levels due to anthropogenic activities such as shipping, seismic surveys, sonar, and construction. Many Arctic marine mammal species depend on sound for communication, navigation, and foraging, therefore quantifying underwater noise levels is critical for documenting change and providing input to management and legislation. Here we present long-term underwater sound recordings from 26 deployments around Greenland from 2011 to 2020. Ambient noise was analysed in third octave and decade bands and further investigated using generic detectors searching for tonal and transient sounds. Ambient noise levels partly overlap with previous Arctic observations, however we report much lower noise levels than previously documented, specifically for Melville Bay and the Greenland Sea. Consistent seasonal noise patterns occur in Melville Bay, Baffin Bay and Greenland Sea, with noise levels peaking in late summer and autumn correlating with open water periods and seismic surveys. These three regions also had similar tonal detection patterns that peaked in May/June, likely due to bearded seal vocalisations. Biological activity was more readily identified using detectors rather than band levels. We encourage additional research to quantify proportional noise contributions from geophysical, biological, and anthropogenic sources in Arctic waters.

Spatio-Temporal Analysis of Summer Salinity Fronts in the Greenland Sea

Using daily average data from the global ocean eddy resolution reanalysis product (GLORYS12V1) from 1993 to 2018, sea surface salinity horizontal gradient is calculated to obtain the spatio-temporal distribution and the intensity characteristics of the salinity front in the Greenland Sea. Combined with the sea ice concentration data, the salinity front and sea ice relationship is also studied. There is a significant spatial relationship between the main position of the salinity front and the ice edge before the sea ice shrinks toward the continental shelf. In the climatological seasonal variation, the intensity of the salinity front beyond the continental shelf reaches its strongest (~0.22 psu/km) in July. The front area beyond the continental shelf reaches its peak value (~7.80×104 km2) in August. The interannual variation of sea ice extent averaged from July to August has a downward trend of 5.83×103 km2/year. Under the background of rapid change in sea ice, the intensity and area of the salinity front beyond the continental shelf are reducing at about 1.7×10-3 psu/km and 142 km2 /year, respectively.

Looking back to the future—micro- and nanoplankton diversity in the Greenland Sea

Anthropogenic perturbations and climate change are severely threatening habitats of the global ocean, especially in the Arctic region, which is affected faster than any other ecosystem. Despite its importance and prevailing threats, knowledge on changes in its micro- and nanoplanktonic diversity is still highly limited. Here, we look back almost two decades (May 1–26, 2002) in order to expand the limited but necessary baseline for comparative field observations. Using light microscopy, a total of 196 species (taxa) were observed in 46 stations across 9 transects in the Greenland Sea. Although the number of observed species per sample ranged from 12 to 68, the diversity as effective species numbers (based on Shannon index) varied from 1.0 to 8.8, leaving about 88% as rare species, which is an important factor for the resilience of an ecosystem. Interestingly, the station with the overall highest species number had among the lowest effective species numbers. During the field survey, both number of rare species and species diversity increased with decreasing latitude. In the southern part of the examined region, we observed indications of an under-ice bloom with a chlorophyll a value of 9.9 μg l−1 together with a nitrate concentration < 0.1 μM. Further, we recorded non-native species including the Pacific diatom Neodenticula seminae and the fish-kill associated diatom Leptocylindrus minimus. Our comprehensive dataset of micro- and nanoplanktonic diversity can be used for comparisons with more recent observations and continuous monitoring of this vulnerable environment—to learn from the past when looking towards the future.

Horizontal circulation across density surfaces contributes substantially to the long-term mean northern Atlantic Meridional Overturning Circulation

The Greenland Sea is often viewed as the northern terminus of the Atlantic Meridional Overturning Circulation. It has also been proposed that the shutdown of open-ocean deep convection in the Labrador or Greenland Seas would substantially weaken the Atlantic Meridional Overturning Circulation. Here we analyze Robust Diagnostic Calculations conducted in a high-resolution global coupled climate model constrained by observed hydrographic climatology to provide a holistic picture of the long-term mean Atlantic Overturning Circulation at northern high latitudes. Our results suggest that the Arctic Ocean, not the Greenland Sea, is the northern terminus of the mean Atlantic Overturning Circulation; open-ocean deep convection, in either the Labrador or Greenland Seas, contributes minimally to the mean Atlantic Overturning Circulation, hence it would not necessarily be substantially weakened by a shutdown of open-ocean deep convection; horizontal circulation across sloping isopycnals contributes substantially (more than 40%) to the maximum mean northeastern subpolar Atlantic Overturning Circulation.

Combined influence of oceanic and atmospheric circulations on Greenland sea ice concentration

The amount and spatial extent of Greenland Sea (GS) ice are primarily controlled by the sea ice export across the Fram Strait (FS) and by local seasonal sea ice formation, melting, and sea ice dynamics. In this study, using satellite passive microwave sea ice observations, atmospheric and a coupled ocean-sea ice reanalysis system, TOPAZ4, we show that both the atmospheric and oceanic circulation in the Nordic Seas (NS) act in tandem to explain the SIC variability in the south-western GS. Northerly wind anomalies associated with anomalously low sea level pressure (SLP) over the NS reduce the sea ice export in the south-western GS due to westward Ekman drift of sea ice. On the other hand, the positive wind stress curl strengthens the cyclonic Greenland Sea Gyre (GSG) circulation in the central GS. An intensified GSG circulation may result in stronger Ekman divergence of surface cold and fresh waters away from the south-western GS. Both of these processes can reduce the freshwater content and weaken the upper-ocean stratification in the south-western GS. At the same time, warm and saline Atlantic Water (AW) anomalies are recirculated from the FS region to the south-western GS by a stronger GSG circulation. Under weakly stratified conditions, enhanced vertical mixing of these subsurface AW anomalies can warm the surface waters and inhibit new sea ice formation, further reducing the SIC in the south-western GS.

Foraminifera-sponge interactions – commensalism to parasitism in the Norwegian-Greenland Sea

&lt;p&gt;&lt;span&gt;This is the first study on the interactions between foraminifera and sponges. Although &lt;/span&gt;&lt;span&gt;&lt;em&gt;Cibicides&lt;/em&gt;&lt;/span&gt;&lt;span&gt; and &lt;/span&gt;&lt;span&gt;&lt;em&gt;Hyrrokin&lt;/em&gt;&lt;/span&gt;&lt;span&gt; are regarded as parasites on siliceous sponges, it is not yet clarified whether foraminifera specifically colonize sponges or are accidentally sucked in during the pelagic stage. To better elucidate these relationships, 12 sponges of different genera were examined and their foraminiferal communities analyzed. In 2018, the sponges for this study were collected with a ROV in water depths of 223 to 625 m in the Norwegian-Greenland Sea. Sponge parts were preserved in ethanol (96 %) and stained with Rose Bengal (2g l&lt;/span&gt;&lt;sup&gt;&lt;span&gt;-1&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;) to allow a differentiation between the living and dead foraminiferal fauna. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Each sponge sample contained several hundred live and dead foraminiferal individuals of up to 60 different species. Even on &lt;/span&gt;&lt;span&gt;&lt;em&gt;Geodia baretti,&lt;/em&gt;&lt;/span&gt;&lt;span&gt; which is able to release barettin to avoid colonalisation of other organisms, few foraminiferal individuals were observed. On all sponges, the most abundant genus was &lt;/span&gt;&lt;span&gt;&lt;em&gt;Cibicides, &lt;/em&gt;&lt;/span&gt;&lt;span&gt;with&lt;/span&gt;&lt;span&gt;&lt;em&gt; Cibicides lobatulus&lt;/em&gt;&lt;/span&gt;&lt;span&gt; and&lt;/span&gt;&lt;span&gt;&lt;em&gt; Cibicides refulgens &lt;/em&gt;&lt;/span&gt;&lt;span&gt;as the most common taxa. Other very common species were &lt;/span&gt;&lt;span&gt;&lt;em&gt;Discorbinella bertheloti&lt;/em&gt;&lt;/span&gt;&lt;span&gt; or &lt;/span&gt;&lt;span&gt;&lt;em&gt;Epistominella nipponica&lt;/em&gt;&lt;/span&gt;&lt;span&gt;. Also, &lt;/span&gt;&lt;span&gt;&lt;em&gt;Hyrrokkin&lt;/em&gt;&lt;/span&gt; &lt;span&gt;&lt;em&gt;sarcophaga&lt;/em&gt;&lt;/span&gt;&lt;span&gt; was found on different sponges and following its lifestyle, penetrating the sponge surfaces. The fact that besides adult foraminifera splendid juvenile stages were found indicate that foraminifera reproduced while inside the sponges. This reproduction might be stimulated/triggered by enhanced food availability by the pumping sponge.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;In summary, sponges are a special habitat for a high number of foraminiferal taxa. Their interaction ranges from parasitic lifestyle up to reproduction purposes. All these aspects highlight the importance of foraminifera-sponge interactions.&lt;/span&gt;&lt;/p&gt;

Mixed layers along the Atlantic water path in the Nordic seas in HighResMIP models

&lt;p&gt;Atlantic water flows over the Greenland-Iceland-Scotland Ridge into the Norwegian Sea. Along its path towards the Arctic, the Atlantic water is cooled by strong air-sea fluxes. Deep winter mixed layers modify the stratification and properties of the Atlantic water and precondition its flow into the Arctic, thus influencing Arctic sea ice and climate. Atlantic water also recirculates in the Greenland sea where deep water formation contributes to the dense limb of the Atlantic Meridional Overturning Circulation. It is thus of paramount importance to represent mixed layer deepening and lateral heat exchanges processes in the Nordic Seas in climate models.&lt;/p&gt;&lt;p&gt;Heat exchanges in the Nordic Seas are influenced by narrow current branches, instabilities and eddies, which are not accurately represented in low resolution climate model (with grid ~ 50-100km). &amp;#160;Here we examine the mixed layer dynamics and heat exchanges using the latest generation of European high resolution global coupled models in the framework of HighResMip (5-15km grids in the Nordic Seas). We investigate in detail the effect of model resolution on the mixed layer depth and water mass formation in relation with the Atlantic water circulation and modification between the Norwegian and the Greenland Sea. First results show an increased northward ocean heat transport, a more realistic representation of the ocean current system in the Nordic Seas, and consequently an improved spatial distribution of the turbulent surface heat flux compared to standard resolution CMIP6 models. The mixed layer depth itself however varies strongly between different HighResMIP models. Summarizing, our assessment of the high resolution coupled simulations of the historical period demonstrates that future climate projections at high resolution have a huge potential, but also limitations.&lt;/p&gt;