ALBERT

Description: During the HALO-(AC)³ campaign in March-April 2022 airborne observations were performed with the High Altitude and LOng range research aircraft (HALO) covering the Fram Strait and north polar regions. The flight tracks covered open ocean areas, the marginal sea ice zone, and closed sea ice cover. Furthermore, cloud conditions were observed during air mass transformation events as marine cold air outbreaks and warm air intrusions. This data set summarizes the flight tracks of HALO and provides longitude, latitude, and altitude defined as position above WGS84. All data are measured by the Basic HALO Measurement and Data System (BAHAMAS) and resampled to 1 Hz temporal resolution.

Description: Ocean acidification may benefit algae that are able to capitalize on increased carbon availability for photosynthesis, but it is expected to have adverse effects on calcified algae through dissolution. Shifts in dominance between primary producers will have knock-on effects on marine ecosystems and will likely vary regionally, depending on factors such as irradiance (light vs. shade) and nutrient levels (oligotrophic vs. eutrophic). Thus experiments are needed to evaluate interactive effects of combined stressors in the field. In this study, we investigated the physiological responses of macroalgae near a CO2 seep in oligotrophic waters off Vulcano (Italy). The algae were incubated in situ at 0.2 m depth using a combination of three mean CO2 levels (500, 700-800 and 1200 µatm CO2), two light levels (100 and 70% of surface irradiance) and two nutrient levels of N, P, and K (enriched vs. non-enriched treatments) in the non-calcified macroalga Cystoseira compressa (Phaeophyceae, Fucales) and calcified Padina pavonica (Phaeophyceae, Dictyotales). A suite of biochemical assays and in vivo chlorophyll a fluorescence parameters showed that elevated CO2 levels benefitted both of these algae, although their responses varied depending on light and nutrient availability. In C. compressa, elevated CO2 treatments resulted in higher carbon content and antioxidant activity in shaded conditions both with and without nutrient enrichment--they had more Chla, phenols and fucoxanthin with nutrient enrichment and higher quantum yield (Fv/Fm) and photosynthetic efficiency (alpha ETR) without nutrient enrichment. In P. pavonica, elevated CO2 treatments had higher carbon content, Fv/Fm, alpha ETR, and Chla regardless of nutrient levels--they had higher concentrations of phenolic compounds in nutrient enriched, fully-lit conditions and more antioxidants in shaded, nutrient enriched conditions. Nitrogen content increased significantly in fertilized treatments, confirming that these algae were nutrient limited in this oligotrophic part of the Mediterranean. Our findings strengthen evidence that brown algae can be expected to proliferate as the oceans acidify where physicochemical conditions, such as nutrient levels and light, permit.

Description: Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400-500 ppm) and high CO2 (ca. 1200-1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5-3.0%) than that from oligotrophic waters (1.0-2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC50), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise.

Description: Sediment samples for measuring N2 production rates and for the characterization of the sediment system were taken in three seasons (winter, spring, summer) from sand and mud sediments of the Vistula Estuary and the open Bay of Gdansk at the Polish coast, Southern Baltic Sea. Sediment was sampled with a HAPS bottom corer (coarse sand), a Multicorer and a Boxcorer (fine sand, mud). Porosity was analyzed both from sediment slices and from entire core subsamples, which means that sediment in a sampling core (heights 15-20 cm, iD 2.3 cm) was mixed and sub sampled, assuming vertical homogeneity; sediment was dried overnight at 105°C and calculations followed Burdige (2006). Sediment organic matter content was analyzed as loss on ignition (LOI), for which dried sediment was combusted at 550°C for 4h. Sediment permeability was measured from pooled surface sediments (~1-2 cm homogeneous surface layer) with a permeameter cell following the constant head method for laminar flow of water through granular soil; calculations were derived from Darcy's Law. The oxygen penetration depth (OPD) was determined by manual (EMB 77, AL 449) and automated (EMB 123) profiling at bottom water temperature, electrode tip 100 µm: EMB 123, AL 449 (mud) and 250 µm: EMB 77, AL 449 (sand), EMB 123 (VE05, VE49). Denitrification rates were measured with the revised isotope pairing technique (r-IPT; Risgaard-Petersen et al. 2003, 2004) that accounts for the potential contribution of anammox (anaerobic ammonium oxidation) to total N2 production. Incubations were done in acrylic cores (heights 15-20 cm, iD 2.3 cm) in a concentration series of 30, 60, 90, 120 µM 15NO3- (n=3, EMB 77, AL 449) and 40 (n=4), 80 (n=4), 120 (n=12) µM 15NO3- for 3-5h at in situ bottom water temperature and darkness. In the presence of significant advective pore water flow, an advective incubation design was used. Dw gives denitrification of nitrate from the water column; Dn gives denitrification of nitrate from sediment nitrification (coupled nitrification-denitrification). If no contribution of anammox to total N2 production was found, columns hold a zero (0). The sediment silicate content (ASi =amorphous, biogenic Si (Na2CO3-extractable), Ca-Si = easily available Si (CaCl2-extractable), Ox-Si = oxide-bound Si (extractable by acid oxalate)) was analyzed from the top sediment layer.

Description: Ocean warming and acidification are two important environmental drivers affecting marine organisms. Organisms living at high latitudes might be especially threatened in near future, as current environmental changes are larger and occur faster. Therefore, we investigated the effect of hypercapnia on thermal tolerance and physiological performance of sub-Arctic Mytilus edulis from the White Sea. Mussels were exposed (2 weeks) to 390 µatm (control) and 1,120 µatm CO2 (year 2100) before respiration rate (MO2), anaerobic metabolite (succinate) level, haemolymph acid-base status, and intracellular pH (pHi) were determined during acute warming (10-28°C, 3°C over night). In normocapnic mussels, warming induced MO2 to rise exponentially until it levelled off beyond a breakpoint temperature of 20.5°C. Concurrently, haemolymph PCO2 rose significantly 〉19°C followed by a decrease in PO2 indicating the pejus temperature (TP, onset of thermal limitation). Succinate started to accumulate at 28°C under normocapnia defining the critical temperature (TC). pHi was maintained during warming until it dropped at 28°C, in line with the concomitant transition to anaerobiosis. At acclimation temperature, CO2 had only a minor impact. During warming, MO2 was stimulated by CO2 resulting in an elevated breakpoint of 25.8°C. Nevertheless, alterations in haemolymph gases (〉16°C) and the concomitant changes of pHi and succinate level (25°C) occurred at lower temperature under hypercapnia versus normocapnia indicating a downward shift of both thermal limits TP and TC by CO2. Compared to temperate conspecifics, sub-Arctic mussels showed an enhanced thermal sensitivity, exacerbated further by hypercapnia, indicating their potential vulnerability to environmental changes projected for 2100.

Description: Coralline algae (Rhodophyta) play a key role in promoting settlement of other benthic organisms, being the food source for herbivores, being involved in the stabilization of reef networks, and in carbonate production. They are considered a vulnerable group to ocean acidification due to the potential dissolution of their high-Mg calcite skeleton at lower pH. Nevertheless, different species of coralline algae showed different responses to low-pH/high-pCO2 environment. Here, we studied the physiological response of Jania rubens to the pH condition predicted for the year 2100. We used a natural CO2 vent system as natural laboratory to transplant J. rubens from pH 8.1–7.5 for 3 weeks. Maximal PSII photochemical efficiency showed a significant reduction in transplanted thalli at low pH (7.5-T) compared to other conditions; consistent with that result, also the pigments involved in the light-harvesting spectrum of J. rubens (i.e., chlorophylls, carotenoids, and phycobilins), exhibited a significant decrease under water acidification, highlighting the strong sensitivity of this species to the environmental change. A major understanding of the response of coralline algae at high CO2 will go through the impact of OA on benthic ecosystems in the next future. This contribution is the written, peer-reviewed version of a paper presented at the Conference “Changes and Crises in the Mediterranean Sea” held at Accademia Nazionale dei Lincei in Rome on October 17, 2017.

Description: Increasing concentrations of surface-seawater carbon dioxide (CO2) (ocean acidification) could favour seaweed species that currently are limited for dissolved inorganic carbon (DIC). Among them, those that are unable to use CO2-concentrating mechanisms (CCMs) to actively uptake bicarbonate (HCO3–) across the plasmalemma are most likely to benefit. Here, we assess how the DIC uptake and photosynthetic rates of three rhodophytes without CCMs respond to four seawater CO2 concentrations representing pre-industrial (280 μatm), present-day (400 μatm), representative concentration pathway (RCP) emissions scenario 8.5 2050 (650 μatm) and RCP 8.5 2100 (1000 μatm). We demonstrated that the photosynthetic rates of only one species increase between the preindustrial and end-of-century scenarios, but because of differing photosynthetic quotients (DIC taken up relative to O2 evolved), all three increase their DIC uptake rates from pre-industrial or present-day scenarios to the end-of-century scenario. These variable, but generally beneficial, responses highlight that not all species without CCMs will respond to ocean acidification uniformly. This supports past assessments that, on average, this group will likely benefit from the impacts of ocean acidification. However, more concerted efforts are now required to assess whether similar benefits to photosynthetic rates and DIC uptake are also observed in chlorophytes and ochrophytes without CCMs.

Description: Macroalgae such as kelp are important ecosystem engineers in the Polar Regions and potentially affected by freshening and ocean warming. The endemic Arctic kelp Laminaria solidungula might be particularly imperiled and become locally extinct from Arctic fjord systems in the future, since temperature increase is most pronounced in the Polar Regions. Additionally, increased temperatures cause glacier and sea ice melting and enhancing terrestrial run-off from snowfields, which eventually can result in hyposaline conditions in fjord systems. We conducted a multiple-stressor experiment at four temperatures (0, 5, 10, 15 °C) and two salinities (SA 25, 35) over 14 days to investigate the combined effects of increasing temperature and decreasing salinities on young L. solidungula sporophytes. The experiment was conducted with laboratory cultures (AWI culture number 3130) at Alfred Wegener Institute - Helmholtz Centre for Polar and Marine Research, Bremerhaven in February 2018. As physiological parameter, the maximum photosynthetic quantum yield of photosystem II (Fv/Fm; Imaging-PAM) was monitored every fourth day with an Imaging-PAM (Walz GmbH Mess- und Regeltechnik, Effeltrich, Germany). The total nitrogen, total carbon content was analyzed with an elemental analyzer and the C:N ratio calculated. Phlorotannins, mannitol as well as absolute pigment concentrations were analyzed using a HPLC and the deepoxydation state of the xanthophyll cycle (DPS) calculated.

Description: Ocean acidification (OA), the global decrease in surface water pH from absorption of anthropogenic CO2, may put many marine taxa at risk. However, populations that experience extreme localized conditions, and are adapted to these conditions predicted in the global ocean in 2100, may be more tolerant to future OA. By identifying locally adapted populations, researchers can examine the mechanisms used to cope with decreasing pH. One oceanographic process that influences pH, is wind driven upwelling. Here we compare two Californian populations of the coral Balanophyllia elegans from distinct upwelling regimes, and test their physiological and transcriptomic responses to experimental seawater acidification. We measured respiration rates, protein and lipid content, and gene expression in corals from both populations exposed to pH levels of 7.8 and 7.4 for 29 days. Corals from the population that experiences lower pH due to high upwelling, maintained the same respiration rate throughout the exposure. In contrast, corals from the low upwelling site had reduced respiration rates, protein content, and lipid‐class content at low pH exposure, suggesting they have depleted their energy reserves. Using RNA‐Seq, we found that corals from the high upwelling site upregulated genes involved in calcium ion binding and ion transport, most likely related to pH homeostasis and calcification. In contrast, corals from the low upwelling site downregulated stress response genes at low pH exposure. Divergent population responses to low pH observed in B. elegans highlight the importance of multi‐population studies for predicting a species' response to future OA.