ALBERT

Description: Despite impressive results achieved by many on‐land visual mapping algorithms in the recent decades, transferring these methods from land to the deep sea remains a challenge due to harsh environmental conditions. Images captured by autonomous underwater vehicles, equipped with high‐resolution cameras and artificial illumination systems, often suffer from heterogeneous illumination and quality degradation caused by attenuation and scattering, on top of refraction of light rays. These challenges often result in the failure of on‐land Simultaneous Localization and Mapping (SLAM) approaches when applied underwater or cause Structure‐from‐Motion (SfM) approaches to exhibit drifting or omit challenging images. Consequently, this leads to gaps, jumps, or weakly reconstructed areas. In this work, we present a navigation‐aided hierarchical reconstruction approach to facilitate the automated robotic three‐dimensional reconstruction of hectares of seafloor. Our hierarchical approach combines the advantages of SLAM and global SfM that are much more efficient than incremental SfM, while ensuring the completeness and consistency of the global map. This is achieved through identifying and revisiting problematic or weakly reconstructed areas, avoiding to omit images and making better use of limited dive time. The proposed system has been extensively tested and evaluated during several research cruises, demonstrating its robustness and practicality in real‐world conditions.

Description: The Arctic Ocean plays an important role in the regulation of the earth's climate system, for instance by storing large amounts of carbon dioxide within its interior. It also plays a critical role in the global thermohaline circulation, transporting water entering from the Atlantic Ocean to the interior and initializing the southward transport of deep waters. Currently, the Arctic Ocean is undergoing rapid changes due to climate warming. The resulting consequences on ventilation patterns, however, are scarce. In this study we present transient tracer (CFC-12 and SF6) measurements, in conjunction with dissolved oxygen concentrations, to asses ventilation and circulation changes in the Eurasian Arctic Ocean over three decades (1991–2021). We constrained transit time distributions of water masses in different areas and quantified temporal variability in ventilation. Specifically, mean ages of intermediate water layers in the Eurasian Arctic Ocean were evaluated, revealing a decrease in ventilation in each of the designated areas from 2005 to 2021. This intermediate layer (250–1,500 m) is dominated by Atlantic Water entering from the Nordic Seas. We also identify a variability in ventilation during the observation period in most regions, as the data from 1991 shows mean ages comparable to those from 2021. Only in the northern Amundsen Basin, where the Arctic Ocean Boundary Current is present at intermediate depths, the ventilation in 1991 is congruent to the one in 2005, increasing thereafter until 2021. This suggests a reduced ventilation and decrease in the strength of the Boundary Current during the last 16 years. Key Points Temporal variability of ventilation in the Eurasian Arctic Ocean during the past 30 years is estimated by observations of transient tracers We found a slow down of the ventilation between 2005 and 2021 in the intermediate waters Evidence of multidecadal variability of ventilation in the intermediate waters of the Eurasian Arctic Ocean is present Plain Language Summary The Eurasian Arctic Ocean, the region of the Arctic Ocean connected to the European and Asian continents, is an important pathway for recently ventilated water from the Nordic Seas. These waters are exported back to the North Atlantic following their travel through the Arctic Ocean. Ventilation describes the process of surface waters being transported into the interior ocean due to increasing density, which affects the underlying water masses. In this study we investigate how the ventilation patterns have evolved in the Eurasian Arctic Ocean over the past three decades, using transient tracer (CFC-12 and SF6) measurements. We observed a significant change in the intermediate layer (250–1,500 m) with older waters found in measurements in 1991 and 2021 compared to 2005 and 2015. Moreover, our data suggest a slowdown in ventilation throughout the three decades in the northern Amundsen Basin, implying a decrease in the circulation time-scale of the Arctic Ocean Boundary Current over the past 16 years. This has potentially important implications for the transport of, for example, heat, salt or oxygen from the Atlantic Ocean around the Arctic Ocean, and back.

Description: Freshwater input from Greenland ice sheet melt has been increasing in the past decades from warming temperatures. To identify the impacts from enhanced meltwater input into the subpolar North Atlantic from 1997 to 2021, we use output from two nearly identical simulations in the eddy-rich model VIKING20X (1/20°) only differing in the freshwater input from Greenland: one with realistic interannually varying runoff increasing in the early 2000s and the other with climatologically (1961–2000) continued runoff. The majority of the additional freshwater remains within the boundary current enhancing the density gradient toward the warm and salty interior waters yielding increased current velocities. The accelerated boundary current shows a tendency to enhanced, upstream shifted eddy shedding into the Labrador Sea interior. Further, the experiments allow to attribute higher stratification and shallower mixed layers southwest of Greenland and deeper mixed layers in the Irminger Sea, particularly in 2015–2018, to the runoff increase in the early 2000s. Key Points The West Greenland Current (WGC) freshens and cools with the observed recent increase in meltwater runoff from Greenland The density gradient across the boundary current intensifies, strengthening the WGC and increasing local eddy formation Enhanced meltwater runoff contributed to an eastward shift in deep convection towards the Irminger Sea (2015–2018) Plain Language Summary Global warming has accelerated the melting of the Greenland ice sheet over the past few decades resulting in enhanced freshwater input into the North Atlantic. The additional freshwater can potentially inhibit deep water formation and have future implications on ocean circulation. To determine the influence from Greenland melt, we compare two high-resolution model experiments all with the same forcing but differing input of Greenland freshwater fluxes from 1997 to 2021. We find that in the experiment with realistically increasing Greenland meltwater, the water becomes fresher and cooler along the continental shelf and boundary of the subpolar gyre. The density difference between the shelf and interior increases with more freshwater, resulting in faster West Greenland Current speeds and enhanced eddy formation. Deeper mixed layers are found in the eastern Irminger Sea, particularly in 2015–2018. From 2009 to 2013, there were shallower mixed layers in the Labrador Sea where less Greenland meltwater was mixed downwards and spread eastward, causing mixed layers to deepen in the Irminger Sea.

Description: Aim Seamounts are conspicuous geological features with an important ecological role and can be considered vulnerable marine ecosystems (VMEs). Since many deep‐sea regions remain largely unexplored, investigating the occurrence of VME taxa on seamounts is challenging. Our study aimed to predict the distribution of four cold‐water coral (CWC) taxa, indicators for VMEs, in a region where occurrence data are scarce. Location Seamounts around the Cabo Verde archipelago (NW Africa). Methods We used species presence–absence data obtained from remotely operated vehicle (ROV) footage collected during two research expeditions. Terrain variables calculated using a multiscale approach from a 100‐m‐resolution bathymetry grid, as well as physical oceanographical data from the VIKING20X model, at a native resolution of 1/20°, were used as environmental predictors. Two modelling techniques (generalized additive model and random forest) were employed and single‐model predictions were combined into a final weighted‐average ensemble model. Model performance was validated using different metrics through cross‐validation. Results Terrain orientation, at broad scale, presented one of the highest relative variable contributions to the distribution models of all CWC taxa, suggesting that hydrodynamic–topographic interactions on the seamounts could benefit CWCs by maximizing food supply. However, changes at finer scales in terrain morphology and bottom salinity were important for driving differences in the distribution of specific CWCs. The ensemble model predicted the presence of VME taxa on all seamounts and consistently achieved the highest performance metrics, outperforming individual models. Nonetheless, model extrapolation and uncertainty, measured as the coefficient of variation, were high, particularly, in least surveyed areas across seamounts, highlighting the need to collect more data in future surveys. Main Conclusions Our study shows how data‐poor areas may be assessed for the likelihood of VMEs and provides important information to guide future research in Cabo Verde, which is fundamental to advise ongoing conservation planning.

Description: At the end of the summer 2021, an increase in CO2 emissions at Vulcano brought to an increase in the alert level and, as a consequence, to the upgrade of the monitoring activities by increasing the number of instruments deployed and the rate of the surveys. One of the new devices installed was a geodetic GNSS mobile network for a Real-Time and High-Frequency monitoring of ground deformation, to increase the detail with respect to the existing permanent network. The whole dataset provided here, consists of 1022 files for a total of 13GB of GNSS RINEX raw data. The GNSS data archive is organized in 4 folders, one for each station, named with the site abbreviation (namely, VCAM, VCOA, VCST and VPRT). Within each folder, there are all the raw data files for that station, one for each day of acquisition. Names of the files are structured following the RINEX 3 standard, the first 4 digits being the station code, that is an S and the last 3 digits of the receiver serial number. The date of acquisition is given by the 11 digits in the central part of the name, in the format YYYYDDDHHMM; namely, 4 digits for the year, followed by 3 digits for the day of the year (from 1 to 365 or 366 for leap years) and then 2 digits for the hour and 2 for the minute of the starting time.

Description: Here we present the concentrations of inorganic nutrients, dissolved organic carbon, nitrogen and phophorus and dissolved inorganic carbon (DIC) from discrete water samples collected with a CTD-rosette during the European Iron Fertilization Experiment (EIFEX). The experiment was carried out from February 11 to March 20, 2004 in the 60-km diameter, rotating core of an eddy, formed by a meander of the Antarctic Polar Front (centred at around 49°10' S and 2°10' E). Samples were taken within the eddy inside and outside the fertilized patch, and in a few cases outside the eddy. Inorganic nutrients (silicate, phosphate, nitrate, nitrite and ammonium) were measured with a Technicon Autoanalyser II system using standard methods. Dissolved organic carbon (DOC) was determined by high temperature combustion using a TOC-VCPH/CPN (Shimadzu) according to Skoog et al. (1997). Dissolved organic nitrogen (DON) was measured on an Evolution continuous flow analyser (Alliance Instruments) after Valderrama (1981). Dissolved inorganic carbon was measured by coulometric titration (Johnson et al., 1987) using a SOMMA system with gas loop calibration with a reproducibility of 2 mmol/kg. DIC was calibrated against certified reference materials from Andrew Dickson at Scripps Institution of Oceanography (SIO).

Description: The CTD data on cruise M164 contain oceanic measurements of temperature, salinity, oxygen and pressure at 126 stations. The data were collected with the research vessel Meteor during cruise M164: Region: subpolar North Atlantic, 9°W-47°W, 45°N-53°N; Ports: Emden - Emden; Date: June 23 - July 31, 2020 . The data where collected by a CTD device of type SBE 9. The CTD was mounted to a metal frame with 22 water sample bottles, which was lowered from the sea surface down to 10 m above the seafloor. The sampling frequency was 24 Hz, the raw data were then interpolated on 1 dbar intervals. Salinity and oxygen data from the CTD were calibrated by comparison with samples from the water bottles. The bottle salinity was analysed by a salinometer of type Guildline Autosal 8400A, bottle oxygen samples by Winkler titration. The accuracy of the calibrated CTD measurements is: 1 dbar for pressure, 0.001 °C for temperature, 0.0025 for salinity, 3.0 µmol/kg for oxygen. Detailed information can be found in the cruise report: https://doi.org/10.48433/cr_m164.

Description: Raw data acquired by two thermosalinographs (SBE21, SeaBird GmbH) on board RV Polarstern were processed to yield a calibrated and validated data set of temperature, conductivity and salinity during expedition PS122/4. Both sensors were equipped with a more accurate external temperature sensor (SBE38, Sea-Bird GmbH). Data were downloaded from the DAVIS SHIP data base (https://dship.awi.de) with a resolution of 1 sec. The raw hex data were converted to temperature and conductivity while a sensor drift correction was applied using calibration coefficients from before and after the expedition. Salinity was calculated according to the instructions from the Practical Salinity Scale PSS-78, using the obtained (internal) temperature and conductivity data and a pressure of 11 dbar which represents the water depth of the inlet of the TSG system on Polarstern. Processed data are provided as 10min means of salinity and water temperature aligned with position data taken from master track of the respective cruise. A speed filter was not applied to the PS122 dataset because of the slow drift speed. This slow movement may lead to an overestimation of the mixed-layer temperature; in particular, small heat fluxes from the ship may raise the temperature in adjacent water in the lee, i.e. during times of drift in the direction opposite to the TSG inlet. The effect is expected to be small, but can potentially be higher than the accuracy of the temperature measurement. Further details and evaluation of the data is outlined in the data processing report found at the EPIC repository under URL (https://hdl.handle.net/10013/epic.7fffb528-06bd-48ae-8489-cea0444c4eab).

Description: Raw data acquired by two thermosalinographs (SBE21, SeaBird GmbH) on board RV Polarstern were processed to yield a calibrated and validated data set of temperature, conductivity and salinity during expedition PS122/2. Both sensors were equipped with a more accurate external temperature sensor (SBE38, Sea-Bird GmbH). Data were downloaded from the DAVIS SHIP data base (https://dship.awi.de) with a resolution of 1 sec. The raw hex data were converted to temperature and conductivity while a sensor drift correction was applied using calibration coefficients from before and after the expedition. Salinity was calculated according to the instructions from the Practical Salinity Scale PSS-78, using the obtained (internal) temperature and conductivity data and a pressure of 11 dbar which represents the water depth of the inlet of the TSG system on Polarstern. Processed data are provided as 10min means of salinity and water temperature aligned with position data taken from master track of the respective cruise. A speed filter was not applied to the PS122 dataset because of the slow drift speed. This slow movement may lead to an overestimation of the mixed-layer temperature; in particular, small heat fluxes from the ship may raise the temperature in adjacent water in the lee, i.e. during times of drift in the direction opposite to the TSG inlet. The effect is expected to be small, but can potentially be higher than the accuracy of the temperature measurement. Further details and evaluation of the data is outlined in the data processing report found at the EPIC repository under URL (https://hdl.handle.net/10013/epic.7fffb528-06bd-48ae-8489-cea0444c4eab).

Description: Raw data acquired by two thermosalinographs (SBE21, SeaBird GmbH) on board RV Polarstern were processed to yield a calibrated and validated data set of temperature, conductivity and salinity during expedition PS122/1. Both sensors were equipped with a more accurate external temperature sensor (SBE38, Sea-Bird GmbH). Data were downloaded from the DAVIS SHIP data base (https://dship.awi.de) with a resolution of 1 sec. The raw hex data were converted to temperature and conductivity while a sensor drift correction was applied using calibration coefficients from before and after the expedition. Salinity was calculated according to the instructions from the Practical Salinity Scale PSS-78, using the obtained (internal) temperature and conductivity data and a pressure of 11 dbar which represents the water depth of the inlet of the TSG system on Polarstern. Processed data are provided as 10min means of salinity and water temperature aligned with position data taken from master track of the respective cruise. A speed filter was not applied to the PS122 dataset because of the slow drift speed. This slow movement may lead to an overestimation of the mixed-layer temperature; in particular, small heat fluxes from the ship may raise the temperature in adjacent water in the lee, i.e. during times of drift in the direction opposite to the TSG inlet. The effect is expected to be small, but can potentially be higher than the accuracy of the temperature measurement. Further details and evaluation of the data is outlined in the data processing report found at the EPIC repository under URL (https://hdl.handle.net/10013/epic.7fffb528-06bd-48ae-8489-cea0444c4eab).