ALBERT

Description: Algal pigment concentrations were retrieved from meltponds and leads, during Leg 4 and 5 of the MOSAiC expedition (Multidisciplinary drifting Observatory for the Study of Arctic Climate) in 2020. The summer increase in meltpond area and open lead water in the Arctic associated with increased light availability is of specific significance for biological production within the Arctic system (Smith et al. 2023). Over a period of 3.5 months, 46 samples have been collected and analysed. After extraction in 90 % acetone, samples were analysed using high-performance liquid chromatography (HPLC) on a Waters system. Algal pigments contain a multiple set of information. Firstly, pigment concentrations can show the presence of algal biomass in the various water masses sampled. Secondly, marker pigments can reveal seasonal and temporal dynamics in algal community structure, by discerning specific algal classes like diatoms, cryptophytes, haptophytes and chlorophytes that have specific roles in biogeochemical cycles. Thirdly, certain pigments are indicative of the (photo)-physiological state of micro-algae and fourth, degradation products of the main chlorophyll a pigment further give an indication about senescence and grazing in the various habitats.

Description: The distribution of diazotrophs and the magnitude of N2 fixation along with the input of new N through this process remains poorly constrained globally, but particularly in the Southern Pacific Ocean. Here we present a high-resolution dataset (every 0.5° latitude) describing the different N-cycling pathways which control the fixation and sequestration of carbon in the surface waters along a 7000 km transect in the South Pacific Ocean. Key oceanographic features along the P15S GO-SHIP transect from the Antarctic ice edge to the equator, included crossing of the subtropical front (STF), from the sub-Antarctic waters towards the oligotrophic tropics, and the equatorial upwelling region. We show how the natural isotopic abundance of particulate organic matter relate to different biogeochemical transformations in the N-cycle across four oceanic provinces. At all stations we measured N2 fixation rates. In the cold and nutrient rich waters of the Southern Ocean we found measurable N2 fixation rates (〉0.2 nmol L-1.d-1), which increased after the subtropical front, and remained at about 15 nmol L-1.d-1 until the equator. In the subtropical and tropical waters, the input of new nitrogen through N2 fixation could fuel on average 13±19% of the net primary productivity. Our data analysis showed that nitrifying organisms, from bacterial and archaeal genera such as Nitrospina, Nitrospinaceae, Nitrosopumilus, Nitrosopelagicus and Nitrosoarchaeum, prevailed in the Southern Ocean and within the STF. Nitrification rates ranged up to 60 nmol L-1.d-1 within the mixed layer depth in the Southern Ocean. Our results suggest that nitrification above the pycnoclines is an important component of the N cycle in the Southern Ocean. Our data has given us a better understanding of how the different N-cycling pathways relate to primary productivity in the South Pacific Ocean, as well as insights into the potential geographical N pathway shifts in light of the rapidly changing climate.

Description: Concentrations of Chlorophyll a and phaeopigments from CTD-rosette casts during the MOSAiC (PS122) drift expedition in the central Arctic Ocean. 2-4L of water were filtered onto precombusted GF/F filters (nominal pore size 0.7µm) and frozen at -80°C. Samples were subsequently extracted in 90°C acetone,homogenized using a cell mill, and meaured on the following day using a Turner flourometer, followed by an acidification step to determine pheopigments (see Knap et al. 1994 for details and calculations). Samples were collected roughly once per week from end of October 2019 to beginning of October 2020.

Description: We present sea ice temperature and salinity data from first-year ice (FYI) and second-year ice (SYI) relevant to the temporal development of sea ice permeability and brine drainage efficiency from the early growth phase in October 2019 to the onset of spring warming in May 2020. Our dataset was collected in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Expedition in 2019 to 2020. MOSAiC was an international transpolar drift expedition in which the German icebreaker RV Polarstern anchored into an ice floe to gain new insights into Arctic climate over a full annual cycle. In October 2019, RV Polarstern moored to an ice floe in the Siberian sector of the Arctic at 85 degrees north and 137 degrees east to begin the drift towards the North Pole and the Fram Strait via the Transpolar Drift Stream. The data presented here were collected during the first three legs of the expedition, so all the coring activities took place on the same floe. The end dates of legs 1, 2, and 3 were 13 December, 24 February, and 4 June, respectively. The dataset contributed to a baseline study entitled, Deciphering the properties of different Arctic ice types during the growth phase of the MOSAiC floes: Implications for future studies. The study highlights downward directed gas pathways in FYI and SYI by inferring sea ice permeability and potential brine release from several time series of temperature and salinity measurements. The physical properties presented in this paper lay the foundation for subsequent analyses on actual gas contents measured in the ice cores, as well as air-ice and ice-ocean gas fluxes. Sea ice cores were collected with a Kovacs Mark II 9 cm diameter corer. To measure ice temperatures, about 4.5 cm deep holes were drilled into the core (intervals varied by site and leg) . The temperatures were measured by a digital thermometer within minutes after the cores were retrieved. The ice cores were placed into pre-labelled plastic sleeves sealed at the bottom end. The ice cores were transported to RV Polarstern and stored in a -20 degrees Celsius freezer. Each of the cores was sub-sampled, melted at room temperature, and processed for salinity within one or two days. The practical salinity was estimated by measuring the electrical conductivity and temperature of the melted samples using a WTW Cond 3151 salinometer equipped with a Tetra-Con 325 four-electrode conductivity cell. The practical salinity represents the the salinity estimated from the electrical conductivity of the solution. The dataset also contains derived variables, including sea ice density, brine volume fraction, and the Rayleigh number.