• Energy Research

AbstractThe Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience a continuous increase in seawater temperature and glacial melt while sea‐ice cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species diversity were quantified at the study site Hansneset, Kongsfjorden (W‐Spitsbergen) in order to identify potential changes over time. In 2021, we repeated the earlier studies by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0, 2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2 at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the depth transect in 2021 was not significantly different compared to 2012/2013, the digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed into an Alaria esculenta‐dominated kelp forest. Consequently, a pronounced shift in kelp forest structure occurred over time as we demonstrate that biomass allocation to thallus parts is kelp species‐specific. Over the past decade, kelp demography changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth limits of all dominant brown algae declined noticeably over the last 25 years while the red algal flora abundance remained unchanged at depth. We propose that the major factor driving the observed changes in the macroalgal community are alterations in underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance since 2012 and 2017, respectively. As a consequence, the interplay between kelp forest retreat to lower depth levels caused by coastal darkening and potential macroalgal biomass gain with increasing temperatures will possibly intensify in the future with unforeseen consequences for melting Arctic coasts and fjord ecosystem services.

Surveys were performed for macroalgae fresh biomass, dry biomass, leaf area index and kelp morphometry at Hansneset, Blomstrand in Kongsfjorden, Svalbard, from the infralittoral fringe down to 15 m depth in June - August 2021. This dataset is part of a time series currently spanning over 25 years and complements the studies conducted in 1996/98 (Hop et al., 2012, doi:10.1515/bot-2012-0097) and 2012-14 (Bartsch et al., 2016, doi:10.1007/s00300-015-1870-1). The aim was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period, alterations were observed in the seaweed community, especially kelps as major coastal foundation species.The data file contains a range of standard morphometric measurements of individual kelps (and associated seaweeds) by depth, quadrat (replicate), and species. The taxonomic 'Class' of the species is provided, as well as a 'Category' that shows if the species is a kelp, or was found in the understory of the kelp forest. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata. In some rare cases, the leaf area and/or Total FW and Total DW were measured together for multiple specimens (especially juveniles together with others). When this was done, a comment can be found for that row of data.

A survey of age class distribution and density of kelps was performed at Hansneset, Blomstrand in Kongsfjorden, Svalbard, at depths of 2.5, 5 and 10m in June - August 2021. This dataset is part of a time series and complements the investigations conducted in 2013 (Bartsch et al., 2016; doi:doi:10.1007/s00300-015-1870-1). The goal was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period alterations in kelp demography were observed.The data contains counts of individual kelps by depth, quadrat (replicate), species, and age class. Kelps younger than 1 year are classed as 'Juveniles', rather than '0years'. The 'Total_Individuals' value is the sum of all kelps of the same species, at the same depth and within the same quadrat (replicate). Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata, whereas here they have been classified simply as Laminariales.

Surveys of C:N ratios, carbon and nitrogen content in the blades of adult kelps at Hansneset, Blomstrand in Kongsfjorden, Svalbard, were performed along a depth transect down to 10m in June - August 2021. As major coastal foundation species, kelps contribute substantially to the coastal carbon cycle. The kelp forest at the sampling site changed substantially over the last 25 years and serves as a case study to document changes in Arctic kelp forest dynamics in an Arctic fjord system influenced by Arctic warming and glacial melt. The study showed that carbon and nitrogen allocation strategies significantly vary between the three prevailing kelps: A. esculenta, S. latissima, and 'Digitate Kelps' (i.e. the visually similar Laminaria digitata and Hedophyllum nigripes). Species dominance relationships in the kelp forest changed over time, which implies consequences for the coastal carbon budget and biological carbon sequestration in the fjord system. The data contains the percent of Nitrogen (N [%]), Carbon ([%]), and the ratio between the two (C:N [ratio]) found within the blades of kelps by depth, quadrat (replicate), and species. Up to five individuals were taken from each quadrat when possible. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible here. Historically these kelps were considered Laminaria digitata.

Surveys were performed of abundance and lower depth distribution of biomass dominant brown algae species at Hansneset, Blomstrand in Kongsfjorden, Svalbard, between 2 m and 20 m depth in June - August 2021. This dataset is part of a time series currently spanning over 25 years and complements the studies conducted in 1996/98 (Hop et al., 2012, doi:10.1515/bot-2012-0097) and 2012-14 (Bartsch et al., 2016, doi:10.1007/s00300-015-1870-1). The aim was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period alterations were observed in the seaweed community, especially kelps as major coastal foundation species.The depth distribution of biomass dominant brown algae was semi-quantitatively (visually) investigated by scientific divers in five parallel transects off the coastline covering the vertical gradient between 2 m and 20 m depth. For each replicate a 1x1 m quadrat divided into four 50 x 50 cm subquadrats was placed on the ground or above the kelps at every depth meter along the transect and species occurrence was documented as attached frequency within each subquadrat. This resulted in a relative frequency of 0 - 4 per replicate (Frequency count). Additionally, the visual presence of the species in the close surroundings of each replicate was documented 0 or 1 (Additional Presence). In summary this generates in a maximum presence score of 5 for each species per replicate. The target replication was five per depth but due to depth corrections to chart datum this resulted in n = 3–8 for each depth and species. The presence (1) or absence (0) of rocks, pebbles, and/or sand was all documented.

The main objective of this Sternfahrt-8, from 10th to 16th September 2021, was to assess the temporal variance of oceanographic real time data in the Elbe influence area of the German Bight (North Sea). Therefore, the participating Ships should repeat the same tracks for four days (see map). One ship (RV Uthörn) covered the western part between Cuxhaven and Heligoland, the second ship (RV Littorina) went to the northern part between Heligoland and Büsum and the third vessel (RV Ludwig Prandtl) should have covered the middle part of the study area, but due to vandalism damage it could not participate on the cruise. During the whole cruise chemical and physical data were recorded continuously along the tracks. Additionally, discrete water samples were taken on six stations along the way for further analysis in the laboratory. The latter data is not included in the present dataset, and can be accessed via https://doi.pangaea.de/10.1594/PANGAEA.963455. For more information about the MOSES campaign and the "Sternfahrten" cruises see article cited in references.

Macroalgal fresh biomass was surveyed at Hansneset, Blomstrand in Kongsfjorden, Svalbard, from the infralittoral fringe down to 15 m depth in summer 2012, 2013 and 2021. This dataset is part of a time series currently spanning over 25 years including the following three time points: 1996/98 (Hop et al., 2012; doi:10.1515/bot-2012-0097), 2012-14 (Bartsch et al., 2016; doi:10.1007/s00300-015-1870-1) and 2021 (Düsedau et al., in prep.). Our goal was to document changes in Arctic kelp forests dynamics in an Arctic fjord system influenced by glacial melt by repeatedly sampling the same site in a standardized manner. As ocean temperatures in the Arctic have risen substantially and underwater light climate continuously deteriorated over this time period we observed alterations in the seaweed community, especially kelps as major coastal foundation species.This data contains the mean fresh weight [kg/m²] of a number of species sampled within replicate quadrats (Replicate) at different water depths (Depth [m]) over different years at Hansneset, Kongsfjorden, Svalbard. Within the species column there is a 'Digitate kelps' value. This is due to the complication of the visual similarity of Laminaria digitata and Hedophyllum nigripes. Because these are field data, and the distinction between these species requires genetic lab work, the exact species identification is not possible so they are listed here with the WORMS code for Laminariales. Historically these kelps were considered Laminaria digitata.

Temperature is a major driver for the geographical distribution of organisms, such as the foundation kelp species Saccharina latissima. Globally rising sea surface temperatures and intensification of marine heatwaves have already led to local loss of kelp populations. We investigated temporal variations in the thermal susceptibility of S. latissima. Therefore, we assessed the stress responses of field sporophytes sampled from Helgoland (German Bight) to an experimental heat wave scenario in June 2018, August 2018, and August 2019. The experiment in June 2018 was conducted by Diehl et al. (2021a) and the respective dataset (Diehl et al. 2021b, https://doi.org/10.1594/PANGAEA.931637) was re-evaluated for this study. Treatment temperatures (18, 20, 22, 24 °C) were based on 18 °C summer mean sea surface temperature on Helgoland as control, and Δ+2, Δ+4, Δ+6 °C as temperature-amplitude treatments, mimicking marine heatwaves. After a three-days wound healing phase, seven days of temperature acclimation (day 0-7) and seven days of temperature treatment (day 8-14) followed. The survival, growth and maximum photosynthetic quantum yield (Fv/Fm; June 2018/August 2018: ImagingPAM, Walz Imaging PAM Maxi Version M-series; August 2019: Portable Chlorophyll Fluorometer PAM-2100, Heinz Walz GmbH, Effeltrich, Germany) were measured on day 0 and day 14. To highlight changes as response to the experimental heat wave, physiological parameters were shown as percentage of the initial values. Absolute concentrations of pigments were analyzed using a HPLC. Afterwards, accessory pigment (Acc) and xanthophyll cycle pigment (VAZ) concentration, as well as the de-epoxidation state of the xanthophyll cycle (DPS) and ratios were calculated.