ALBERT

Description: Connectivity between the terrestrial and marine environment in the Artic is changing as a result of climate change, influencing both freshwater budgets and the supply of carbon to the sea. This study characterizes the optical properties of dissolved organic matter (DOM) within the Lena Delta region and evaluates the behavior of DOM across the fresh water-marine gradient. Six fluorescent components (four humic-like; one marine humic-like; one protein-like) were identified by Parallel Factor Analysis (PARAFAC) with a clear dominance of allochthonous humic-like signals. Colored DOM (CDOM) and dissolved organic carbon (DOC) were highly correlated and had their distribution coupled with hydrographical conditions. Higher DOM concentration and degree of humification were associated with the low salinity waters of the Lena River. Values decreased towards the higher salinity Laptev Sea shelf waters. Results demonstrate different responses of DOM mixing in relation to the vertical structure of the water column, as reflecting the hydrographical dynamics in the region. Two mixing curves for DOM were apparent. In surface waters above the pycnocline there was a sharper decrease in DOM concentration in relation to salinity indicating removal. In the bottom water layer the DOM decrease within salinity was less. We propose there is a removal of DOM occurring primarily at the surface layer, which is likely driven by photodegradation and flocculation.

Description: In this study organic mater fluorescence is characterized by excitation-emission matrix spectroscopy on alkaline extracted DOM from a Baltic Sea sediment core that spanned 8500 years and fluctuating levels of hypoxia. Our results showed that three underlying components had strong correlations with carbon, nitrogen content and δ15N. Our results demonstrate that optical properties of extracted OM from sediments reveal information about OM quality and quantity similar to those of biomarkers, which can be a useful additional tool for investigating OM deposition.

Description: We evaluated the role of microzooplankton (sensu latto, grazers 〈500 µm) in determining the fate of phytoplankton production (PP) along a glacier-to-open sea transect in the Greenland subarctic fjord, Godthabfjord. Based on the distribution of size fractionated chlorophyll a (chl a) concentrations we established 4 zones: (1) Fyllas Bank, characterized by deep chl a maxima (ca. 30 to 40 m) consisting of large cells, (2) the mouth and main branch of the fjord, where phytoplankton was relatively homogeneously distributed in the upper 30 m layer, (3) inner waters influenced by glacial melt water and upwelling, with high chl a concentrations (up to 12 µg/l) in the 〉10 µm fraction within a narrow (2 m) subsurface layer, and (4) the Kapisigdlit branch of the fjord, ice-free, and characterized with a thick and deep chl a maximum layer. Overall, microzooplankton grazing impact on primary production was variable and seldom significant in the Fyllas Bank and mouth of the fjord, quite intensive (up to 〉100% potential PP consumed daily) in the middle part of the main and Kapisigdlit branches of the fjord, and rather low and unable to control the fast growing phytoplankton population inhabiting the nutrient rich waters in the upwelling area in the vicinity of the glacier. Most of the grazing impact was on the 〈10 µm phytoplankton fraction, and the major grazers of the system seem to be 〉20 µm microzooplankton, as deducted from additional dilution experiments removing this size fraction. Overall, little or no export of phytoplankton out of the fjord to the Fyllas Bank can be determined from our data.

Description: Increased oceanic uptake of atmospheric carbon dioxide (CO2) is a threat to marine organisms and ecosystems. Among the most dramatic consequences predicted to date are behavioural impairments in marine fish which appear to be caused by the interference of elevated CO2 with a key neurotransmitter receptor in the brain. In this study, we tested the effects of elevated CO2 on the foraging and shelter-seeking behaviours of the reef-dwelling epaulette shark, Hemiscyllium ocellatum. Juvenile sharks were exposed for 30 d to control CO2 (400 µatm) and two elevated CO2 treatments (615 and 910 µatm), consistent with medium- and high-end projections for ocean pCO2 by 2100. Contrary to the effects observed in teleosts and in some other sharks, behaviour of the epaulette shark was unaffected by elevated CO2. A potential explanation is the remarkable adaptation of H. ocellatum to low environmental oxygen conditions (hypoxia) and diel fluctuations in CO2 encountered in their shallow reef habitat. This ability translates into behavioural tolerance of near-future ocean acidification, suggesting that behavioural tolerance and subsequent adaptation to projected future CO2 levels might be possible in some other fish, if adaptation can keep pace with the rate of rising CO2 levels.

Description: Ocean warming and acidification act concurrently on marine ectotherms with the potential for detrimental, synergistic effects; yet, effects of these stressors remain understudied in large predatory fishes, including sharks. We tested for behavioural and physiological responses of blacktip reef shark (Carcharhinus melanopterus) neonates to climate change relevant changes in temperature (28 and 31 °C) and carbon dioxide partial pressures (pCO2; 650 and 1050 µatm) using a fully factorial design. Behavioural assays (lateralisation, activity level) were conducted upon 7–13 days of acclimation, and physiological assays (hypoxia tolerance, oxygen uptake rates, acid–base and haematological status) were conducted upon 14–17 days of acclimation. Haematocrit was higher in sharks acclimated to 31 °C than to 28 °C. Significant treatment effects were also detected for blood lactate and minimum oxygen uptake rate; although, these observations were not supported by adequate statistical power. Inter-individual variability was considerable for all measured traits, except for haematocrit. Moving forward, studies on similarly 'hard-to-study' species may account for large inter-individual variability by increasing replication, testing larger, yet ecologically relevant, differences in temperature and pCO2, and reducing measurement error. Robust experimental studies on elasmobranchs are critical to meaningfully assess the threat of global change stressors in these data-deficient species.

Description: Here, we present a comprehensive, seasonal observation of chromophoric dissolved organic matter (CDOM) as well as dissolved organic carbon (DOC) in the Central Arctic Ocean (CAO) including ocean water column samples and Lead water samples based on the year round (November 2019 - September 2020) expedition “Multidisciplinary Drifting Observatory for the Study of Arctic Climate” (MOSAiC). Ocean water samples taken from the CTD/rosette on Polarstern or the one based on the ice floe ('Ocean City', Rabe et al., 2022) were filtered through pre-combusted (450 °C, 5 h) glass fiber filters (Whatman; GF/F), subsequently for DOC and total dissolved nitrogen (TDN), as well as absorbance and fluorescence excitation-emission matrices (EEMs) measurements. Lead water samples were collected using the peristatic pump (Master flex E/S portable sampler) between August 25th and September 4th 2020 in summer in the Amundsen Basin, then filtered through an in line 0.2 µm pore size Sterivex cartridge filter (polyethersulfone membrane) and subsequently for DOC and TDN, as well as absorbance and EEMs measurements. Salinity for Lead water samples was measured with a hand-held multi parameter meter (Cond 340i, WTW). DOC and TDN were determined by high temperature catalytic oxidation (HTCO) and non dispersive infrared spectroscopy and chemiluminescence detection (TOC VCPN, Shimadzu; for details see Ksionzek et al., 2018). EEMs were measured using a spectrofluorometer (Aqualog, Horiba) equipped with a charge-coupled device (CCD) detector. CDOM absorbance spectra were acquired by a spectrophotometer (UV2700, Shimadzu) in a quartz cuvette with an optical path length of 10. To inventive the influence of the transpolar drift (TPD) on the MOSAiC expedition, we compared the MOSAiC ocean water columns with the ocean water columns in the western Nansen Basin and Yermak Plateau from the Norwegian young sea ICE (N ICE2015) expedition (January to June 2015; Granskog et al., 2018), and the ocean water columns in the Bering Strait, Laptev Sea, and East Siberian Sea that were acquired during the expedition TA19_4 (September to October 2019, Hölemann et al., 2021). The EEMs combined with parallel factor analysis (PARAFAC) model based on MOSAiC, N ICE2015 and TA19_4 expeditions were processed by the staRdom package in R studio (Version 3.5.1; Pucher et al., 2019). Five PARAFAC components were determined, subsequently we named as C475, C440, C395, C340, and C320 according to their fluorescence emission maxima.