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The inflow of warm and saline Atlantic water to the Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of volume transport and is associated with a large transport of heat towards the Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry, a method that has been calibrated by in situ observations gathered over 2 decades. Monthly averaged surface velocity anomalies calculated from SLA data were strongly correlated with anomalies measured by moored acoustic Doppler current profilers (ADCPs) with consistently higher correlations when using the reprocessed SLA data released in December 2021 rather than the earlier version. In contrast to the earlier version, the reprocessed data also had the correct conversion factor between sea level slope and surface velocity required by geostrophy. Our results show that the IF inflow crosses the IFR in two separate branches. The Icelandic branch is a jet over the Icelandic slope with average surface speed exceeding 20 cm s -1 , but it is narrow and shallow with an average volume transport of less than 1 Sv (10 6 m 3 s -1). Most of the Atlantic water crosses the IFR close to its southernmost end in the Faroese branch. Between these two branches, water from the Icelandic branch turns back onto the ridge in a retroflection with a recirculation over the northernmost bank on the IFR. Combining multi-sensor in situ observations with satellite SLA data, monthly mean volume transport of the IF inflow has been determined from January 1993 to December 2021. The IF inflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which is expected to weaken under continued global warming. Our results show no weakening of the IF inflow. Annually averaged volume transport of Atlantic water through the monitoring section had a statistically significant (95 % confidence level) increasing trend of (0.12±0.10) Sv per decade. Combined with increasing temperature, this caused an increase of 13 % in the heat transport, relative to 0 ∘ C, towards the Arctic of the IF inflow over the 29 years of monitoring. The near-bottom layer over most of the IFR is dominated by cold water of Arctic origin that may contribute to the overflow across the ridge. Our observations confirm a dynamic link between the overflow and the Atlantic water flow above. The results also provide support for a previously posed hypothesis that this link may explain the difficulties in reproducing observed transport variations in the IF inflow in numerical ocean models, with consequences for its predictability under climate change. [ABSTRACT FROM AUTHOR]

The gridded sea ice thickness (SIT) climate data record (CDR) produced by the European Space Agency (ESA) Sea Ice Climate Change Initiative Phase 2 (CCI-2) is the longest available, Arctic-wide SIT record covering the period from 2002 to 2017. SIT data are based on radar altimetry measurements of sea ice freeboard from the Environmental Satellite (ENVISAT) and CryoSat-2 (CS2). The CCI-2 SIT has previously been validated with in situ observations from drilling, airborne remote sensing, electromagnetic (EM) measurements and upward-looking sonars (ULSs) from multiple ice-covered regions of the Arctic. Here we present the Laptev Sea CCI-2 SIT record from 2002 to 2017 and use newly acquired ULS and upward-looking acoustic Doppler current profiler (ADCP) sea ice draft (VAL) data for validation of the gridded CCI-2 and additional satellite SIT products. The ULS and ADCP time series provide the first long-term satellite SIT validation data set from this important source region of sea ice in the Transpolar Drift. The comparison of VAL sea ice draft data with gridded monthly mean and orbit trajectory CCI-2 data, as well as merged CryoSat-2–SMOS (CS2SMOS) sea ice draft, shows that the agreement between the satellite and VAL draft data strongly depends on the thickness of the sampled ice. Rather than providing mean sea ice draft, the considered satellite products provide modal sea ice draft in the Laptev Sea. Ice drafts thinner than 0.7 m are overestimated, while drafts thicker than approximately 1.3 m are increasingly underestimated by all satellite products investigated for this study. The tendency of the satellite SIT products to better agree with modal sea ice draft and underestimate thicker ice needs to be considered for all past and future investigations into SIT changes in this important region. The performance of the CCI-2 SIT CDR is considered stable over time; however, observed trends in gridded CCI-2 SIT are strongly influenced by the uncertainties of ENVISAT and CS2 and the comparably short investigation period. [ABSTRACT FROM AUTHOR]

• First results from the Holyrood Subsea Observatory. • Marked change in benthic community during spring phytoplankton bloom. • Psolus cf. phantapus emerged after increased seafloor chlorophyll- a and temperature. • High frequency data collection enabled in situ study of behavioural phenology. Sub-Arctic seafloor communities rely on seasonal phytoplankton blooms for food, revealing a tight benthic-pelagic coupling. To maximize resource availability for offspring, organisms such as snow crabs, sea stars, and sea cucumbers synchronize their reproductive and feeding behaviours with spring blooms. Due to climate change, spring blooms are occurring earlier in sub-Arctic regions, leading to a possible mismatch between timing of resource availability and important life-history behaviours. Here, we utilize high-frequency time-series observations from the Holyrood Subsea Observatory, a new cabled seafloor observatory deployed in Conception Bay, Newfoundland. We use hourly data collected from environmental sensors (Conductivity-Temperature-Depth, Acoustic Doppler Current Profiler, fluorometer), a near-surface mooring (fluorometer), and a video camera to identify and quantify abundance and diversity of benthic megafauna, and to determine how community composition changed from pre-bloom to full bloom conditions. Data analysis revealed striking temporal changes in benthic activity, with the notable emergence of Psolus cf. phantapus sea cucumbers (up to 289.9 indiv./m2) coinciding with increased chlorophyll- a concentration and seawater temperature. At least three dense schools of forage fish, two Atlantic herring (79 and 144 indiv. frame−1) and one capelin (91 indiv. frame−1), were observed during the main bloom between May 5 and June 16. This study provides the first high-frequency in situ observations of benthic community response to seasonal food input in the region. The high temporal resolution made it possible to record the precise timing of the of Psolus cf. phantapus emergence in relation to the timing of food input to the seafloor, which will provide a baseline to monitor phenology as climate change progresses. Changes to the timing of spring blooms have implications for sub-Arctic fisheries productivity and ecosystem functioning, making continuous long-term monitoring of seafloor communities essential. [ABSTRACT FROM AUTHOR]

Understanding the physical mechanisms behind the deformation of pack ice floes is important for understanding the dynamics of the local ice regime, and for the calibration and validation of ice dynamics models. In April 2017, six Iridium satellite-tracking beacons were deployed on six pack ice floes in the Barents Sea south of Svalbard in the Norwegian Arctic. The ice tracker deployment was performed as part of an offshore research expedition carried out onboard the Research Vessel (RV) Polarsyssel to characterize the local sea ice environment. In addition to the ice tracker deployments, an anemometer beacon, a wave beacon, and an Acoustic Doppler Current Profiler (ADCP) were deployed on a drifting ice floe to which the vessel was moored for nearly three days, and extensive thickness, salinity, and density measurements were made. The wave beacon recorded the vertical acceleration of the floe so that wave forcing on the floe drift could be estimated. The in-situ wind, ocean current, wave, and ice thickness and density measurements permitted the estimation of met-ocean forcings on the acceleration of the ice floe. On April 28, two days after the last ice tracker was deployed on April 26, the six tracked ice floes rapidly dispersed just to the west-southwest of Hopen Island. The dispersion of the ice floes was dominated by strong shearing within the local ice pack, coinciding with a rapid increase in the speeds of the local tidal currents, which was soon followed by a rapid increase in the wave energy. Each of the six tracked ice floes increased their observed drift speeds in sync with the increase in the local tidal current speeds at different times for each floe, but at approximately the same decrease in water depth as they reached the northern edge of Spitsbergen Bank. The rapid increase in the tidal currents was linked to the topographic enhancement of tidal motion near Hopen Island in the shallower waters of Spitsbergen Bank. The wind and wave measurements made by the anemometer and wave beacons and ice tracker left on the ice floe to which the vessel was moored allowed for an estimate of the relative strength of the wind, tidal, and wave forcings on the local ice field. The results showed that the tidal currents initially dominated the dynamic response of the local ice field compared to the wind, which led to the conclusion that the enhanced tidal current was ultimately the dominant cause of the initial dispersion of the local pack ice field on April 28, and the dispersion was then further enhanced by the increase in wave energy. • Six tracking beacons were deployed on pack ice floes in the Barents Sea west of Hopen Island during April 2017. • Floes showed strong deformation due to increase in tidal current speed, followed by increase in wave energy at pack edge. • Increase in tidal current speeds and floe drift speeds caused by shallow water, which enhanced tidal motion. [ABSTRACT FROM AUTHOR]

Acoustic Doppler current profilers (ADCP) are quasi-remote sensing instruments widely used in oceanography to measure velocity profiles continuously. One of the applications is the quantification of land–ocean exchange, which plays a key role in the global cycling of water, heat, and materials. This exchange mostly occurs through estuaries, lagoons, and bays. Studies on the subject thus require that observations of total volume or mass transport can be achieved. Alternatively, numerical modeling is needed for the computation of transport, which, however, also requires that the model is validated properly. Since flows across an estuary, lagoon, or bay are usually non-uniform and point measurements will not be sufficient, continuous measurements across a transect are desired but cannot be performed in the long run due to budget constraints. In this paper, we use a combination of short-term transect-based measurements from a vessel-mounted ADCP and relatively long-term point measurements from a moored ADCP at the bottom to obtain regression coefficients between the transport from the vessel-based observations and the depth-averaged velocity from the bottom-based observations. The method is applied to an Arctic lagoon by using an ADCP mounted on a buoyant platform towed by a small inflatable vessel and another ADCP mounted on a bottom deployed metal frame. The vessel-based measurements were performed continuously for nearly 5 h, which was sufficient to derive a linear regression between the datasets with an R2-value of 0.89. The regression coefficients were in turn applied to the entire time for the moored instrument measurements, which are used in the interpretation of the subtidal transport variations. [ABSTRACT FROM AUTHOR]

• Acoustic surveys indicate favorable feeding conditions in Hinlopen Trough. • Hinlopen Trough receives topographically steered inflow of Atlantic Water. • Troughs are special habitats where the Atlantic domain is extended onto the shelf. Atlantic Water (AW) flowing along the western and northern Svalbard shelf-break extends the Atlantic domain into the Arctic and is the region's major source of heat, nutrients and advected plankton. We investigated the inflow and recirculation of AW into four major troughs that cut into the Svalbard shelf, the Isfjorden, Kongsfjorden, Hinlopen and Kvitøya Troughs, and related the circulation patterns to acoustic backscatter observed with echosounders and Acoustic Doppler Current Profilers. The acoustic observations showed higher levels of backscatter from fish in the Hinlopen Trough compared to the shelf and shelf-break north of Svalbard. This coincides with a steady inflow of nutrients, biomass and heat into the trough with the AW. Trough circulation was characterized using output from a high-resolution regional ocean model and particle tracking simulations. All four troughs experience topographically steered recirculation (in-and-outflow) of AW, but the troughs on the western Svalbard shelf showed a stronger seasonality than the troughs on the northern shelf. The Hinlopen Trough receives the strongest AW inflow and the most direct inflow from the shelf-break boundary current. The troughs form hybrid habitats between the shelf and shelf-break that extend the Atlantic advective domain closer to the Svalbard coastline. [ABSTRACT FROM AUTHOR]