ALBERT

Description: Past sea ice conditions and open water phytoplankton production were reconstructed from a sediment core taken in Disko Bugt, West Greenland, using the sea ice biomarker IP~25~ and other specific phytoplankton biomarker (i.e., brassicasterol, dinosterol, HBI III) records. Our biomarker record indicates that Disko Bugt experienced a gradual expansion of seasonal sea ice during the last 2.2 kyr. Maximum sea ice extent was reached during the Little Ice Age around 0.2 kyr BP. Superimposed on this longer term trend, we find short-term oscillations in open water primary production and terrigenous input, which may be related to the Atlantic Multidecadal Oscillation and solar activity changes as potential climatic trigger mechanisms. A direct sample-to-sample multiproxy comparison of our new biomarker record with microfossil (i.e., benthic foraminifera, dinocysts, and diatoms) and other geochemical records (i.e., alkenone biomarkers) indicates that different proxies are influenced by the complex environmental system with pronounced seasonal changes and strong oceanographic gradients, e.g., freshwater inflow from the Greenland Ice Sheet. Differences in sea ice reconstructions may indicate that the IP~25~ record reflects only the relatively short sea ice season (spring), whereas other microfossil reconstructions may reflect a longer (spring–autumn) interval.

Description: Using a microprofiler and electrochemical oxygen sensors after Revsbech (1989) in situ oxygen profiles measurements were conducted with a spatial resolution if 100 µm and a temporal resolution of 30 seconds at three stations in Potter Cove in austral summer 2015.

Description: This is a dataset from an in situ experiment at station S2 from the LTER monitoring site HAUSGARTEN, performed in June-July 2013 during Maria S Merian expedition MSM29. The in situ responses of Arctic deep-sea benthos to input of phytodetritus of a diatom (Thalassiosira sp.) as opposed to a coccolithophorid (Emiliania huxleyi) were investigated in incubation chambers of benthic landers. Using 13C and 15N labelled phytodetritus harvested from cultures of these species, we traced the fate of the respective phytodetritus into different parts of the food web (respiration, assimilation by bacteria and infauna 〉250 µm), in a short (4d) and long (14d) term experiment. The benthic landers were lowered to the sea floor, where they enclosed ~ 20cm of sediment and ~10 cm of overlying water. During respectively 4d and 14d, the temperature and concentrations of O2, DIC, 13C-DIC, NHx, NOx, 15N-NH4, 15N-NOx were measured. Upon recovery of the landers, the sediment was retrieved and subsampled in vertical horizons to measure pigment, TOC and TN, 13C-POC and 15N-PN concentrations, pore water concentrations of DIC, 13C-DIC, NHx, NOx, 15N-NH4 and 15N-NOx and the assimilation of 13C in bacterial fatty acids (iC15:0 and aiC15:0) and in fauna 〉 250 µm

Description: We present the first field application of a N2O-based approach to correct for vertical mixing in the estimation of net community production (NCP) from mixed layer O2 measurements. Using new ship-based observations of N2O and biological oxygen saturation anomalies (DeltaO2/Ar) from the Subarctic Northeast Pacific, we provide refined mixed layer NCP estimates across contrasting hydrographic regimes and a comprehensive assessment of the methodological considerations and limitations of the approach. Increased vertical mixing coefficients at the base of the mixed layer, derived using N2O measurements, corresponded with periods of heightened wind speed and coastal upwelling. Corrections were most significant in coastal regions where the vertical supply of low-O2 water can otherwise falsely imply net heterotrophy from negative DeltaO2/Ar measurements. After correcting for the mixing flux, all coastal stations showed autotrophic signatures, with maximum NCP exceeding 100 mmol O2 m-2 day-1 in the spring and summer. Vertical fluxes were lower in off-shelf waters, but often contributed more than 50 % to corrected NCP. At some oceanic stations, however, the co-occurrence of N2O minima and O2 maxima resulted in biased (over-estimated) N2O corrections. Evaluating vertical fluxes in these regions remains a challenge for ship-based studies. Nonetheless, our refined NCP estimates show better coherence with surface chlorophyll, temperature, and mixed layer depth than uncorrected values. Potential mixed layer N2O production introduces some uncertainty in the approach, but errors are likely to be small. Ultimately, this work provides rationale for the adoption of the N2O correction to refine NCP estimates, particularly in coastal waters. Data in this submission include the ancillary components required to replicate all calculations, and conclusions made in the main manuscript.

Description: Arctic treelines are facing a strong temperature increase as a result of recent global warming, causing possible changes in forest extent, which will alter vegetation-climate feedbacks. However, the mode and strength of the response is rather unclear, as potential changes are happening in areas that are very remote and difficult to access, and empirical data are still largely lacking. Here, we assessed the current population structure and genetic differentiation of Larix Mill. tree stands within the northernmost latitudinal treeline reaching ~72° N in the southern lowlands of the Taymyr Peninsula (~100° E). We sampled 743 individuals belonging to different height classes (seedlings, saplings, trees) at eleven locations along a gradient from 'single tree' tundra over 'forest line' to 'dense forest' stands and conducted investigations applying eight highly polymorphic nuclear microsatellites. Results suggest a high diversity within subpopulations (HE=0.826-0.893), coupled, however, with heterozygote deficits in all subpopulations, but pronounced in 'forest line' stands. Overall, genetic differentiation of subpopulations is low (FST=0.005), indicating a region-wide high gene flow, although 'forest line' stands harbour few rare and private alleles, likely indicating greater local reproduction. 'Single tree' stands, located beyond the northern forest line, are currently not involved in treeline expansion, but show signs of a long-term refuge, namely asexual reproduction and change of growth-form from erect to creeping growth, possibly having persisted for thousands of years. The lack of differentiation between the subpopulations points to a sufficiently high dispersal potential, and thus a rapid northward migration of the Siberian arctic treeline under recent global warming seems potentially unconstrained, but observations show it to be unexpectedly slow.

Description: Ground-based spectroscopy measurements acquired systematically within the Toolik Vegetation Grid in the 2015 and 2016 growing seasons and within the Imnavait Vegetation Grid in the 2016 growing season. Data were collected in 68 distinct 1 x 1 m long-term monitoring plots representing five distinct vegetation communities. Spectral measurements were acquired two times throughout the season in 2015 representing peak and late season and three times in 2016 representing early, peak and late season. Data were acquired using a GER 1500 field spectrometer (350-1050 nm; 512 bands, spectral resolution 3 nm, spectral sampling 1.5 nm, and 8! field of view). Spectra were collected under clear weather conditions at the highest solar zenith angle between 10:00 and 14:00 local time. Data were collected at nadir approximately 1 m off the ground resulting in a Ground Instantaneous Field of View (GIFOV) of approximately 15 cm in diameter. Nine point measurements of upwelling radiance (Lup) were collected in 1 x 1 m plots representative of the five vegetation communities and averaged to characterize the spectral variability and to reduce noise. Downwelling radiance (Ldown) was measured as the reflectance from a white Spectralon© plate. Surface reflectance (R) was processed as Lup/Ldown x 100 (0-100%). Reflectance spectra were preprocessed with a Savitzky-Golay smoothing filter (n = 11) and subset to 400-985 nm to remove sensor noise at the edges of the radiometer detector.

Description: Our data, as part of the OISO (Ocean Indien Service d'Observation) campaign, contributes to a better understanding of the physical and biological factors controlling N2 fixation in the Southern Indian Ocean and the French Southern and Antarctic lands during Austral summer January and February 2017. We measured N2 and C fixation as well as NH4+ and NO3- assimilation in 3-6 replicates per station. Additionally, we measured diagnostic pigment concentrations to evaluate phtosynthetic community composition. For pigment analysis 4L water was filtered through 25mm Whatman GF/F filters (pressure drop 〈10kPa). Samples were stored at -80°C until analysis. Pigments were analysed using High Performance Liquid Chromatography (HPLC). Pigment concentration were calculated according to Kilias et al (2013, doi:10.1111/jpy.12109). N2 fixation experiments were carried out in three to six replicates for each station. Incubations were done in pre-acid washed polycarbonate bottles on deck with ambient light conditions. All polycarbonate incubation bottles were rinsed with deionized water, and seawater prior to incubation. We used the combination of the bubble approach (Montoya et al., 1996) and the dissolution method (Mohr et al., 2010, doi:10.1371/journal.pone.0012583) proposed by Klawonn et al. (2015, doi:10.3389/fmicb.2015.00769). Bottles were filled up to capacity to avoid air contamination. Incubations were initialized by adding a 10 ml 15-15N gas bubble. Bottles were gently rocked for 15 minutes. Finally, the remaining bubble was removed to avoid equilibration between gas and aqueous phase. after 24 hours a water subsample was taken to a 12 ml exetainer and preserved with 100 µl HgCl2 solution for later determination of exact 15N-15N concentration. Natural 15N2 was determined using Membrane Inlet Mass Spectrometry (MIMS; GAM200, IPI) for each station. Analysis of 15N2 incorporated was carried out by the Isotopic Laboratory at the UC Davis, California campus. We used stable isotope tracers (15N) to measure dissolved inorganic nitrogen (DIN) assimilation rates. Experiments were initiated by adding a known concentration of 0.05 of K15NO3 and 15NH4Cl for oligotrophic waters of the IO and 0.625 µmol L-1 for HNLC regions in the ACC and PF (Knap et al., 1994, Waite et al., 2007, doi:10.1016/j.dsr2.2006.12.010) to one litre polycarbonate bottles. For C assimilation experiments, we added 20 µmol L-1 of NaH13CO3 to one of each of N2 fixation, NH4+ and NO3- assimilation experiment bottles. For incubation, we followed the same procedure as for N2 fixation experiments. Findings reveal that N2 fixation occurs throughout the whole sampling area up to 55°S latitude. In addition, variations of N2 fiaxation rates between replicates were relatively high indicating a great heterogeneity of the French Southern and Antarctic waters. References: Montoya 1996: Montoya, Joseph P., et al. "A Simple, High-Precision, High-Sensitivity Tracer Assay for N (inf2) Fixation." Applied and environmental microbiology 62.3 (1996): 986-993. Knap et al 1994: Knap, A., Michaels, A., Close, A., Ducklow, H. & Dickson, A. 1994. Protocols for the Joint Global Ocean Flux Study (JGOFS) Core Measurements, JGOFS, Reprint of the IOC Manuals and Guides No. 29. UNESCO, 19, 1.

Description: Lithogenic material such as Saharan dust can be incorporated into organic aggregates and act as ballast, potentially enhancing the marine carbon export via increased sinking velocities of aggregates. We studied the ballasting effects of Saharan dust on the aggregate dynamics in the upwelling region off Cape Blanc (Mauritania). Aggregate formation from a natural plankton community exposed to Saharan dust deposition resulted in higher abundance of aggregates with higher sinking velocities compared to aggregate formation with low dust. This higher aggregate abundance and sinking velocities potentially increased the carbon export 10-fold when the aggregates were ballasted by Saharan dust. After aggregate formation in the surface waters, subsequent sinking through suspended Saharan dust minerals had no influence on aggregate sizes, abundance, and sinking velocities. We found that aggregates formed in the surface ocean off Mauritania were already heavily ballasted with lithogenic material and could therefore not scavenge any additional minerals during their descent. This suggests that carbon export to the deep ocean in regions with high dust deposition is strongly controlled by dust input to the surface ocean while suspended dust particles in deeper water layers do not significantly interact with sinking aggregates.

Description: Ground-based spectroscopy measurements acquired systematically within the Toolik Vegetation Grid in the 2016 growing season. All data were collected in a subset of 1 x 1 m long-term monitoring plots representing three distinct vegetation communities three times representing early, peak and late season. Spectral data were acquired using a GER 1500 field spectrometer (350-1050 nm; 512 bands, spectral resolution 3 nm, spectral sampling 1.5 nm, and 8! field of view). Spectra were collected under clear weather conditions at the highest solar zenith angle between 10:00 and 14:00 local time. Data were collected at nadir approximately 1 m off the ground resulting in a Ground Instantaneous Field of View (GIFOV) of approximately 15 cm in diameter. Nine point measurements of upwelling radiance (Lup) were collected in each plot and averaged to characterize the spectral variability and to reduce noise. Downwelling radiance (Ldown) was measured as the reflectance from a white Spectralon© plate. Surface reflectance (R) was processed as Lup/Ldown x 100 (0-100%). Reflectance spectra were preprocessed with a Savitzky-Golay smoothing filter (n = 11) and subset to 400-985 nm to remove sensor noise at the edges of the radiometer detector. Digital camera data were acquired using a consumer-grade camera (Panasonic DM3 LMX, Japan) approximately 1 m off the ground with a white frame for registration of off nadir images. For detailed definitions of the RGB indices see metadata.docx. Leaves and stems of the dominant vascular species in a subset of the sampled plots were collected at early, peak, and late season for chlorophyll and carotenoid analysis.Samples were placed in porous tea bags and preserved in a silica gel desiccant in an opaque container for up to 3 months until pigment extraction (Esteban et al. 2009, doi:10.1007/s11120-009-9468-5). Each sample was homogenized by grinding with a mortar and pestle. Approximately 1.00 mg (+/- 0.05 mg) of homogenized sample was placed into a vial with 2 ml of dimethylformamide (DMF). Vials were then wrapped in aluminum foil to eliminate any degradation of pigments due to UV light and stored in a fridge (4C) for 24 hrs. Samples were measured into a cuvette prior to spectrophotometric analysis. Bulk pigments concentrations were then estimated using a spectrophotometer measuring absorption at 646.8, 663.8 and 480 nm (Porra et al. 1989, doi:10.1016/S0005-2728(89)80347-0) . Absorbance (A) values at specific wavelengths were transformed into µg/mg concentrations of chlorophyll a, Chla, chlorophyll b, Chlb, total chlorophyll, Chl, carotenoids, Car (for equations see metadata.docx). Pigment concentration was calculated as the average concentration of the dominant species in each plot. mean_"pigment" represents the mean of all biomass from each vegetation community and sd_"pigment" represents the standard deviation of each vegetation community.

Description: Seasonal variations in fluxes of isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and the estimated temperatures based on TEX86 are examined in sinking particles collected using moored sediment traps in the eastern Atlantic upwelling regions. In the equatorial Guinea Basin, GDGT fluxes show a correlation with opal fluxes, implying that GDGTs are mainly transported via aggregation with diatoms. The flux-weighted TEXH86 temperatures derived from particles collected both at 853 m and 3,921 m depth correspond to the water temperature (24.1 °C) of ca. 50 m depth, where nitrate concentration starts to increase, potentially as a consequence of nitrification by Thaumarchaeota. This suggests that nutrient concentrations may affect the depth habitat of Thaumarchaeota, and it determines at which water depth the TEXH86 temperature is recorded. In the coastal upwelling off Namibia, TEXH86 temperatures are similar to satellite-derived sea surface temperature (SST) during the warm season, but the record derived from the trap is delayed relative to the SST by approximately 26 days. Warm biases, however, occur during the cold season, similar to what has previously been observed in the filamentous upwelling region off Cape Blanc. In both coastal upwelling regions, oxygen minimum zones (OMZs) are a common feature, and higher TEX86 values have been found within the OMZs in the water column off Cape Blanc and elsewhere. Thus, contributions from GDGTs produced in OMZs might explain the warmer temperature estimates during the cold season in both regions. We thus conclude that in the eastern Atlantic upwelling system, TEXH86 temperature estimates are influenced by non-thermal factors such as nutrient depth distributions and GDGTs produced in the OMZ. In paleoenvironmental records of TEX86, non-thermal signals have to be considered on regional scales.

Description: Recently, Ponto-Caspian species (i.e. area of Azov, Black and Caspian Seas) have invaded brackish and freshwater habitats of the North and Baltic Seas and the Laurentian Great Lakes in much higher numbers than expected based on shipping frequency and environmental conditions among these regions. Therefore, it has been hypothesized that Ponto-Caspian species may have inherent advantages over other species in colonizing new habitats, or that they are of freshwater origin. To test these hypotheses, we conducted artificial selection experiment on Ponto-Caspian amphipod Pontogammarus maeoticus collected from 10 PSU to evaluate adaptation capacity of this species to different salinities. Our results indicated that selection to lower salinity than that of population's ambient salinity is possible. Though, generation time in lower salinity conditions took slightly longer. On the contrary, selection to higher salinity was unsuccessful. Taking into account the results from this and previous studies and the geological history of the Ponto-Caspian region, we suggest that majority of the Ponto-Caspian relict fauna might be of freshwater origin and lack necessary genetic background for adaptation to fully marine conditions. Further selection studies using more species and populations, as well as molecular techniques, should be conducted to confirm this hypothesis on a broader scale. Consequently, if Ponto-Caspian relict species are of freshwater origin, the perception that they are better colonizers than species from other regions might be inclined by the fact that areas with biggest introduction frequency of nonindigenous species (i.e., shipping ports) are environmentally variable habitats which often include freshwater conditions.

Description: The Kara Sea is an important area for paleo-climatic research since sea ice and brine formation take place on its shelf-two processes inducing supra-regional climatic implications and thereby connecting regional environmental variability with global climatic conditions. To gain information about past sea ice coverage and variations, three sediment cores distributed in the southern and central parts of the marginal Sea were investigated. By applying the sea ice biomarker IP25 and the PIP25 index [phytoplankton biomarker (dinosterol)-IP25 index] post-glacial sea ice variability could be detected in the central Kara Sea (Core BP00-36/4), with most intense sea ice cover between 12.4 and 11.8 ka coinciding with the Younger Dryas (12.9-11.6 ka), and reduced sea ice cover between 10 and 8 ka during the Holocene Thermal Maximum. During the last ~7 ka, increasing sea ice indicators might indicate a Holocene cooling trend, probably induced by declining summer insolation. Furthermore, temporal changes in the fast ice?polynya distribution in the southern Kara Sea were detected: expanding fast ice during the late Holocene and a cyclic short-term Holocene climate variability documented by abrupt changes in the sea ice coverage at the BP00-07/7 core site. Core BP99-04/7 from the Yenisei estuary recorded consistently seasonal sea ice cover since ~9.3 ka, apart from five short phases of fast ice expansion to the core site. The strong influence of river run-off as well as estuary processes might prevent the detection of (short-term) climatic signals at this study site.

Description: Ocean acidification causes an accumulation of CO2 in marine organisms and leads to shifts in acid-base parameters. Acid-base regulation in gill breathers involves a net increase of internal bicarbonate levels through transmembrane ion exchange with the surrounding water. Successful maintenance of body fluid pH depends on the functional capacity of ion-exchange mechanisms and associated energy budget. For a detailed understanding of the dependence of acid-base regulation on water parameters, we investigated the physiological responses of the shore crab Carcinus maenas to 4 weeks of ocean acidification [OA, P(CO2)w = 1800 µatm], at variable water bicarbonate levels, paralleled by changes in water pH. Cardiovascular performance was determined together with extra-(pHe) and intracellular pH (pHi), oxygen consumption, haemolymph CO2 parameters, and ion composition. High water P(CO2) caused haemolymph P(CO2) to rise, but pHe and pHi remained constant due to increased haemolymph and cellular [HCO3-]. This process was effective even under reduced seawater pH and bicarbonate concentrations. While extracellular cation concentrations increased throughout, anion levels remained constant or decreased. Despite similar levels of haemolymph pH and ion concentrations under OA, metabolic rates, and haemolymph flow were significantly depressed by 40 and 30%, respectively, when OA was combined with reduced seawater [HCO3-] and pH. Our findings suggest an influence of water bicarbonate levels on metabolic rates as well as on correlations between blood flow and pHe. This previously unknown phenomenon should direct attention to pathways of acid-base regulation and their potential feedback on whole-animal energy demand, in relation with changing seawater carbonate parameters.

Description: Anthropogenic nutrient enrichment is changing the structure and the function of coastal ecosystems. These coastal zones are transitions between freshwater and marine systems where multiple biogeochemical processes remove, produce and transform organic matter. The extent to which the coastal zone is merely a conduit for terrestrial (allochthonous) organic matter, versus a distinct source of autochthonous organic matter fueled by eutrophication, is unclear. To address this issue, we characterized the freshwater and marine dissolved organic matter (DOM) pools in an eutrophic estuary with a long water residence time (Roskilde Fjord, Denmark) over an annual cycle. We combined elemental, optical (absorbance and fluorescence) and isotopic analyses to obtain insight about the bulk properties of the DOM pool during this period. We also used sediment traps to analyze the changes related to the exchange of organic matter between the particulate (POM) and dissolved (DOM) fractions. The results showed that labile autochthonous DOM from in situ primary production was rapidly transformed to more recalcitrant DOM that accumulated in the estuary despite continuous exchange with the open sea. Also, parts of the POM pool were degraded rapidly (within 24h) and transformed into the DOM pool. Accumulated DOM was characterized by relatively low molecular size and stable carbon isotopic value, and by high protein-like fluorescence. These results indicate that autotrophic material can be a major source of specific recalcitrant DOM in eutrophic coastal waters, contributing significantly to the flux of organic carbon to the ocean.

Description: The high-relief catchment of the Tavignanu River (Corsica Island, France) with an elevation range from sea level to 2622 m above sea level was investigated from January 2016 to April 2017 for its on-site parameters (T, pH, EC, TA), riverine carbon budget (TCO2) and stable carbon isotopes (d13C). Partial pressure of CO2 (pCO2) and annual carbon flux across the air-water boundary (FCO2) were calculated from analytical results. This data set contains the supplementary analytical data of the related publication.

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2016P18 drifting on Antarctic sea ice. The buoy was deployed on multi year ice without drogue during POLARSTERN cruise ANT-XXXI/2 (PS96). The time series describes the position and additional parameters of the buoy between 18 Jan 2016 and 22 Aug 2017 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2015P12 drifting on Arctic sea ice. The buoy was deployed on first year ice without drogue during POLARSTERN cruise ARK-XXIX/3 (PS94). The time series describes the position and additional parameters of the buoy between 02 Sep 2015 and 12 Sep 2017 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2017P24 drifting on Arctic sea ice. The buoy was deployed on first year ice without drogue during POLARSTERN cruise ARK-XXXI/1 (PS106). The time series describes the position and additional parameters of the buoy between 07 Jun 2017 and 21 Jun 2017 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2016P20 drifting on Antarctic sea ice. The buoy was deployed on multi year ice without drogue during POLARSTERN cruise ANT-XXXI/2 (PS96). The time series describes the position and additional parameters of the buoy between 18 Jan 2016 and 09 Jul 2017 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2015P21 drifting on Antarctic sea ice. The buoy was deployed on multi year ice without drogue during POLARSTERN cruise ANT-XXXI/2 (PS96). The time series describes the position and additional parameters of the buoy between 02 Sep 2015 and 12 Sep 2017 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift was measured by Surface Velocity Profiler 2017P38 drifting on Arctic sea ice. The buoy was deployed without drogue during POLARSTERN cruise ARK-XXXI/1 (PS106). The time series describes the position of the buoy between 12 Jun 2017 and 26 Jun 2017 in sample intervals of 5 minutes. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift was measured by Surface Velocity Profiler 2017P39 drifting on Arctic sea ice. The buoy was deployed without drogue during POLARSTERN cruise ARK-XXXI/1 (PS106). The time series describes the position of the buoy between 12 Jun 2017 and 12 Jul 2017 in sample intervals of 5 minutes. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: Sea ice drift was measured by Surface Velocity Profiler 2016P46 drifting on Arctic sea ice. The buoy was deployed on second year ice without drogue during POLARSTERN cruise ARK-XXX/3 (PS101). The time series describes the position of the buoy between 29 Sep 2016 and 30 May 2017 in sample intervals of 30 minutes. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: In permafrost areas, seasonal freeze-thaw cycles of active layer result in upward and downward movements of the ground. Additionally, relatively uniform thawing of the ice-rich layer at the permafrost table can contribute to net long-term surface lowering. We use a simple method to quantify surface lowering (subsidence) and uplift in a yedoma area of the Lena River Delta, Siberian Arctic (Kurungnakh Island), using reference rods (metal pipes and fiberglass rods) installed deeply in permafrost. The metal pipes were 2 m long and 3 cm in diameter and were anchored at least 1 m below the typical active layer. The fiberglass rods were 2 m long and 1 cm in diameter and were anchored at least 70 m below the typical active layer. We assume, therefore, that the rods were motionless relative to the permafrost. The plexiglass plate with a size of 10 by 10 cm was fixed in its horizontal position by the rod but could move freely with the surface vertically along the rod. We repeatedly measured distance between the top of a rod and a plexiglass plate resting on the ground surface. Several distance measurements around each rod were taken at each visit and averaged. Altogether 12 metal pipes were installed at the study site in April 2013 and 19 fiberglass rods were installed in April 2014. Measurements were conducted during field campaigns from spring 2013 to summer 2017 with some gaps. We provide here the measured distances between the top of a rod and a plexiglass plate. To obtain the ground displacement, the user have to define the period of interest and calculate the displacement.

Description: In permafrost areas, seasonal freeze-thaw cycles of active layer result in upward and downward movements of the ground. Additionally, relatively uniform thawing of the ice-rich layer at the permafrost table can contribute to net long-term surface lowering. We use a simple method to quantify surface lowering (subsidence) and uplift in a yedoma area of the Lena River Delta, Siberian Arctic (Kurungnakh Island), using reference rods (metal pipes and fiberglass rods) installed deeply in permafrost. The metal pipes were 2 m long and 3 cm in diameter and were anchored at least 1 m below the typical active layer. The fiberglass rods were 2 m long and 1 cm in diameter and were anchored at least 70 m below the typical active layer. We assume, therefore, that the rods were motionless relative to the permafrost. The plexiglass plate with a size of 10 by 10 cm was fixed in its horizontal position by the rod but could move freely with the surface vertically along the rod. We repeatedly measured distance between the top of a rod and a plexiglass plate resting on the ground surface. Several distance measurements around each rod were taken at each visit and averaged. Altogether 12 metal pipes were installed at the study site in April 2013 and 19 fiberglass rods were installed in April 2014. Measurements were conducted during field campaigns from spring 2013 to summer 2017 with some gaps. We provide here the measured distances between the top of a rod and a plexiglass plate. To obtain the ground displacement, the user have to define the period of interest and calculate the displacement.

Description: Differential SAR interferometry (DInSAR) uses the phase difference between two SAR signals acquired on two dates over the same area to measure small-scale ground motion. During the last decade the method has been adapted for monitoring permafrost-related ground motion. Here we perform DInSAR on TerraSAR-X data to assess its viability for seasonal thaw subsidence detection in a yedoma landscape of the Lena River Delta. TerraSAR-X is a right-looking SAR satellite launched in 2007, operating in the X-band (wavelength 3.1 cm, frequency 9.6 GHz), with a revisit time of eleven days. All data that we used were acquired in StripMap mode with HH polarization from a descending orbit at 08:34 local acquisition time (22:34 UTC). The incidence angle of the track we use is approximately 31 degrees. The scene size covered an area of approximately 18 km x 56 km. The slant range and azimuth pixel spacing were approximately 0.9 m and 2.4 m, respectively. Based on the ground temperature data we roughly estimated the beginning and the end of thaw season in 2013. The corresponding TerraSAR-X time series used for this study includes nine Single-Look Slant Range Complex (SSC) images taken between 7 June and 14 September 2013. The time span between the acquisitions that we used for interferometry was 11 days, with one exception when the time span was 22 days due to a missing acquisition. The data were processed using the Gamma radar software. The SSC data were converted to Gamma Single Look Complex (SLC) format and the SLC data were then consecutively co-registered with subpixel accuracy (typically better than 0.2 pixels) in such a way that the co-registered slave image became the master for the next image. This way of co-registering also ensures subpixel co-registration accuracy for all interferometric combinations of the nine images. Multilooking was performed with the factor 4 in the range and factor 3 in the azimuth directions to reduce the noise and obtain roughly square ground range pixels. The ground size of the multilooked pixel is approximately 7 m. We removed the topographic phase term using ArcticDEM that is a freely available high-resolution (5 m) circum-Arctic DEM produced from optical stereographic WorldView imagery acquired from 2012–2016. Obtained differential interferograms were then filtered with an adaptive filter based on the local fringe spectrum with the filtering window size of 128 pixels and an alpha exponent of 0.4. Interferograms, featuring especially low coherence, were additionally filtered with a window size of 64 pixels. For the phase unwrapping we used a branch-cut algorithm with the seeding point located approximately in the middle of the study area with relatively high coherence. We did not attempt to unwrap the areas, separated from the main study area by the river channels. The influence of atmospheric phase delays was evident in the unwarpped interferograms. In order to enhance the displacement signal and reduce atmospheric noise, all eight unwrapped interferograms were summed up in a time-continuous stack. Phase rate per day was calculated from the stack. A strong linear ramp was present across the phase rate map. To remove the trend, a 2D linear function was fit to the data and then subtracted from the phase rate map. The phase rate was then converted to vertical displacement rate in meters, under the assumption that the ground movement is purely vertical. The resulting displacement rate map was geocoded using ArcticDEM to the Universal Transverse Mercator (UTM) projection, zone 52N WGS84 with a pixel size of 5 m. The map was finally converted to the displacement magnitude by multiplying the rate by 99 days (from 7 June to 14 September 2013) and converted to centimeters. As opposed to the results, published in the related paper, here we did not start the unwrapping from the known bedrock position, as it was partly affected by low coherence as well as rather remote from the main area of interest and only weakly connected to the rest of the map over a small and noisy area of valid pixels. It means that the displacement map published here, features only displacement values relative to each other, without a fixed reference point. The spatial pattern of the signal, however, did not change with this alteration in processing. The DInSAR map showed a distinct subsidence in most of the thermokarst basins relative to the upland. Moreover, the spatial pattern of DInSAR signal was in high agreement with the surface wetness in the basins, identified with the near infra-red band of a high-resolution optical image. Drier parts of the basins were clearly separated from wetter parts that showed a prominent subsidence. In general, low coherence in combination with atmospheric effects as well as remoteness of a reference ground point were severe obstacles for the retrieval of a wide-area seasonal thaw subsidence map with TerraSAR-X data.

Description: Sea ice drift, surface temperature, and barometric pressure were measured by Surface Velocity Profiler 2017P23 drifting on Arctic sea ice. The buoy was deployed on first year ice without drogue during POLARSTERN cruise ARK-XXXI/1 (PS106). The time series describes the position and additional parameters of the buoy between 07 Jun 2017 and 11 Jul 2018 in sample intervals of 1 hour. The data set has been processed, including the removal of obvious inconsistencies (missing values).

Description: The copepod Calanus finmarchicus plays a crucial role in the north Atlantic food web. Its seasonal life cycle involves reproduction and development in surface waters before overwintering in diapause at depth. Although diapause has been studied for more than a century, the factors responsible for the initiation and termination of it are still unclear. Endogenous clocks have been identified as potent tools for photoperiod measurement and seasonal rhythmicity in many terrestrial species, but knowledge of these remains scarce in the marine realm. Focusing on the dominant CV copepodid stage, we sampled a population of C. finmarchicus from a Scottish sea loch to characterize population dynamics, several physiological parameters, and diel and seasonal expression rhythms of 35 genes representing different metabolic pathways, including the circadian clock machinery. This generated a detailed overview of the seasonal cycle of C. finmarchicus including the most extensive field dataset on circadian clock gene expression in a marine species to date. Gene expression patterns revealed distinct gene clusters upregulated at different phases of the copepod's seasonal cycle. While diel clock cycling was restricted to the active spring/summer phase, many clock genes exhibited the highest expression during diapause. Our results provide new insights into diapause on physiological and genetic levels. We suggest that photoperiod, in interaction with internal and external factors (lipid content, temperature, food availability) and the endogenous clock mechanism, plays an important role in the timing of diapause in C. finmarchicus.

Description: Added are 5 seismic reflection data sets of Store Glacier, a tide water glacier in West Greenland Uummannaq Fjord. Two crossing profiles were recorded, 20140513, along the ice flow and 20140514, across the ice flow.