Search for: All records

The biologically productive Northern Gulf of Alaska (NGA) continental shelf receives large inputs of freshwater from surrounding glaciated and non-glaciated watersheds, and a better characterization of the regional salinity spatiotemporal variability is important for understanding its fate and ecological roles. We here assess synoptic to seasonal distributions of freshwater pathways of the Copper River discharge plume and the greater NGA continental shelf and slope using observations from ship-based and towed undulating conductivity-temperaturedepth (CTD) instruments, satellite imagery, and satellite-tracked drifters. On the NGA continental shelf and slope we find low salinities not only nearshore but also 100–150 km from the coast (i.e. average 0–50 m salinities less than 31.9, 31.3, and 30.8 in spring, summer, and fall respectively) indicating recurring mid-shelf and shelfbreak freshwater pathways. Close to the Copper River, the shelf bathymetry decouples the spreading river plume from the direct effects of seafloor-induced steering and mixing, allowing iron- and silicic acid-rich river outflow to propagate offshore within a surface-trapped plume. Self-organized mapping analysis applied to true color satellite imagery reveals common patterns of the turbid river plume. We show that the Copper River plume is sensitive to local wind forcing and exerts control over water column stratification up to ~100 km from the river mouth. Upwelling-favorable wind stress modifies plume entrainment and density anomalies and plume width. Baroclinic transport of surface waters west of the river mouth closely follow the influence of alongshore wind stress, while baroclinic transport east of the river mouth is additionally modified by a recurring or persistent gyre. Our results provide context for considering the oceanic fate of terrestrial discharges in the Gulf of Alaska. 

Ballast water released from ships into coastal environments has been identified as a mechanism that introduces contaminants of concern into coastal ecosystems. 

This dataset includes the concentrations and conditional stability constants of iron-binding organic ligands in samples collected during an extension study of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) project and measured by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV). These samples originated from a spring melt field campaign conducted in Utqiaġvik, Alaska. This campaign was designed when the MOSAiC expedition could no longer accommodate spring melt trace metal work. The melt season was a key period of our effort during MOSAiC and necessary for addressing our proposed hypotheses. Using facilities in Utqiaġvik hosted by Ukpeaǵvik Iñupiat Corporation (UIC), we studied sea ice processes during the spring melt cycle from April – June of 2021. Four UAF Scientists participated in the field campaign. During that time, sea ice, snow and water samples were obtained from homogenous, flat, landfast ice at high (2-3 times a week) temporal resolution. 

The international GEOTRACES program was developed to enhance knowledge about the distribution of trace elements and their isotopes (TEIs) in the ocean and to reduce the uncertainty about their sources, sinks, and internal cycling. Recognizing the importance of intercalibration from the outset, GEOTRACES implemented intercalibration efforts early in the program, and consensus materials were generated that included the full range of TEIs dissolved in seawater, in suspended particles, and from aerosols. The GEOTRACES section cruises include “crossover station(s)” that are occupied by two or more sections and whereby all aspects of sample collection, preservation, and processing can be compared and intercalibrated. Once datasets are generated, an international intercalibration committee reviews intercalibration reports and works with the community to address issues and provide intercalibrated data for intermediate data products. This process has resulted in a highly cooperative community that shares advances in protocols to strengthen capacity building and GEOTRACES outcomes, including an unprecedented oceanic atlas of TEIs, with data quality that is state-of-the-art. This article outlines the development and implementation of the successful GEOTRACES intercalibration process. 

Using facilities in Utqiaġvik hosted by Ukpeaǵvik Iñupiat Corporation (UIC), we studied sea ice processes during the spring melt cycle from April – June of 2021. During that time, sea ice, snow and water samples were obtained from homogenous, flat, landfast ice. The dataset produced from this campaign is also unique in that its temporal coverage of the spring melt is higher resolution than any other biogeochemical sampling conducted in this region previously (2-3 times a week for all parameters sampled). The datasets herein include sea ice macronutrients, salinity, temperature, and density; sea ice micronutrients; and bottom ice chlorophyll. 

Methylmercury (MeHg) is a neurotoxin that bioaccumulates to potentially harmful concentrations in Arctic and Subarctic marine predators and those that consume them. Monitoring and modeling MeHg bioaccumulation and biogeochemical cycling in the ocean requires an understanding of the mechanisms behind net mercury (Hg) methylation. The key functional gene pair for Hg methylation,hgcAB, is widely distributed throughout ocean basins and spans multiple microbial phyla. While multiple microbially mediated anaerobic pathways for Hg methylation in the ocean are known, the majority ofhgcAhomologs have been found in oxic subsurface waters, in contrast to other ecosystems. In particular, microaerophilicNitrospina, a genera of nitrite-oxidizing bacteria containing ahgcA-like sequence, have been proposed as a potentially important Hg methylator in the upper ocean. The objective of this work was therefore to examine the potential of nitrifiers as Hg methylators and quantify total Hg and MeHg across three Arctic and Subarctic seas (the Gulf of Alaska, the Bering Sea and the Chukchi Sea) in regions whereNitrospinaare likely present. In Spring 2021, samples for Hg analysis were obtained with a trace metal clean rosette across these seas. Mercury methylation rates were quantified in concert with nitrification rates using onboard incubation experiments with additions of stable isotope-labeled Hg and NH₄⁺. A significant correlation between Hg methylation and nitrification was observed across all sites (R²= 0.34,p< 0.05), with the strongest correlation in the Chukchi Sea (R²= 0.99,p< 0.001).Nitrospina-specifichgcA-like genes were detected at all sites. This study, linking Hg methylation and nitrification in oxic seawater, furthers understanding of MeHg cycling in these high latitude waters, and the ocean in general. Furthermore, these studies inform predictions of how climate and human interactions could influence MeHg concentrations across the Arctic in the future. 

Abstract A 25‐year (1996–2020) hindcast from a coupled physical‐biogeochemical model is evaluated with nutrients, phytoplankton and zooplankton field data and is analyzed to identify mechanisms controlling seasonal and interannual variability of the northern Gulf of Alaska (NGA) planktonic food web. Characterized by a mosaic of processes, the NGA is a biologically complex and productive marine ecosystem. Empirical Orthogonal Function (EOF) analysis combining abiotic and biotic variables averaged over the continental shelf reveals that light intensity is a main driver for nanophytoplankton variability during spring, and that nitrate availability is a main driver for diatoms during spring and for both phytoplankton during summer. Zooplankton variability is a combination of carry‐over effects from the previous year and bottom‐up controls from the current year, with copepods and euphausiids responding to diatoms and microzooplankton responding to nanophytoplankton. The results also demonstrate the effect of nitrate availability and phytoplankton community structure on changes in biomass and energy transfers across the planktonic food web over the entire growing season. In particular, the biomass of large copepods and euphausiids increases more significantly during years of higher relative diatom abundance, as opposed to years with higher nitrate availability. Large microzooplankton was identified as the planktonic group most sensitive to perturbations, presumably due to its central position in the food web. By quantifying the combined variability of several key planktonic functional groups over a 25‐year period, this work lays the foundation for an improved understanding of the long‐term impacts of climate change on the NGA shelf. 

First-year sea-ice thickness, draft, salinity, temperature, and density were measured during near-weekly surveys at the main first-year ice coring site (MCS-FYI) during the MOSAiC expedition (legs 1 to 4). The ice cores were extracted either with a 9-cm (Mark II) or 7.25-cm (Mark III) internal diameter ice corers (Kovacs Enterprise, US). This data set includes data from 23 coring site visits and were performed from 28 October 2019 to 29 July 2020 at coring locations within 130 m to each other in the MOSAiC Central Observatory. During each coring event, ice temperature was measured in situ from a separate temperature core, using Testo 720 thermometers in drill holes with a length of half-core-diameter at 5-cm vertical resolution. Ice bulk practical salinity was measured from melted core sections at 5-cm resolution using a YSI 30 conductivity meter. Ice density was measured using the hydrostatic weighing method (Pustogvar and Kulyakhtin, 2016) from a density core in the freezer laboratory onboard Polarstern at the temperature of –15°C. Relative volumes of brine and gas were estimated from ice salinity, temperature and density using Cox and Weeks (1983) for cold ice and Leppäranta and Manninen (1988) for ice warmer than –2°C.The data contains the event label (1), time (2), and global coordinates (3,4) of each coring measurement and sample IDs (13, 15). Each salinity core has its manually measured ice thickness (5), ice draft (6), core length (7), and mean snow height (22). Each core section has the total length of its top (8) and bottom (9) measured in situ, as well estimated depth of section top (10), bottom (11), and middle (12). The depth estimates assume that the total length of all core sections is equal to the measured ice thickness. Each core section has the value of its practical salinity (14), isotopic values (16, 17, 18) (Meyer et al., 2000), as well as sea ice temperature (19) and ice density (20) interpolated to the depth of salinity measurements. The global coordinates of coring sites were measured directly. When it was not possible, coordinates of the nearby temperature buoy 2019T66 were used. Ice mass balance buoy 2019T66 installation is described in doi:10.1594/PANGAEA.938134. Brine volume (21) fraction estimates are presented only for fraction values from 0 to 30%. Each core section also has comments (23) describing if the sample is from a false bottom, from rafted ice or has any other special characteristics.Macronutrients from the salinity core, and more isotope data will be published in a subsequent version of this data set.