Calvin W. Mordy

In recent decades, evidence has emerged of phytoplankton growing beneath Arctic sea ice, in some cases forming massive blooms. Observed and predicted changes in the cryosphere highlight the need to better understand the development and progression of under‐ice blooms. During June and July 2023, as a part of the Tale of Three Systems (ToTS) field program, we characterized the environmental conditions that led to the initiation, peak, and decline of a substantial under‐ice phytoplankton bloom in the Chukchi Sea. By sampling two transects 7–8 times over a period of approximately 6 weeks, we are able to describe spatial and temporal patterns in hydrography, nutrient distributions, and phytoplankton biomass, allowing for a thorough analysis of a generally understudied phenomenon. Along both transects, phytoplankton biomass was five times higher under consolidated sea ice (maximum 661 mg Chl a m ⁻² ) than they were in open water (114 ± 135 mg Chl a m ⁻² ). Nitrate (NO ₃ ⁻ ) was the limiting nutrient and controlling factor of the magnitude of the bloom. The under‐ice environment also exhibited much greater surface water NO ₃ ⁻ depletion and dissolved oxygen (O ₂ ) supersaturation than in open water. The bloom was dominated by Thalassiosira spp., a large chain‐forming diatom, and much of the organic matter produced at the surface was exported below the mixed layer, suggesting tight benthic‐pelagic coupling. In the absence of widespread melt ponds, leads appeared to be the most important factor in alleviating light limitation of phytoplankton growth. An increasingly dynamic ice pack could therefore have important impacts on phytoplankton and the broader ecosystem.

The eastern Bering Sea has recently experienced multiple years of pronounced warm temperature anomalies, facilitated by low winter sea‐ice extent. Although ice cover is well‐understood as a driver of temperature variations in this region, the ability for spring and summer forcing to modify anomalies present after ice retreat has been less explored. In this study, moored observations are used to investigate temperature balances, stratification, and mixing on the southern Bering Sea middle shelf, during spring‐summer 2017–2019. These results are discussed in context with surface temperature maxima observed at this site from 1995 to 2024. Surface heat flux and inferred mixing dominated the surface temperature tendency in the 2017–2019 deployments. In the bottom layer, weaker mixing was at times overwhelmed by horizontal advection. Inferred residual mixing in both balances correlates with simple scalings of flux and diffusivity in stratified turbulence. Anomalous warm surface temperatures in summer 2019 were associated with warm end‐of‐winter temperatures, strong shortwave heat input, and a lack of strong summer mixing, thus heat accumulation in a narrower layer. These factors are found to explain a majority of the variance in annual maximum surface temperature at this site from 1995 to 2024. Results illustrate in detail the contrast between vertical layers after restratification, and provide a simple framework for understanding surface maxima in the ice‐influenced portion of the southern Bering Sea middle shelf. Evidence for a lengthening warming season since 1995 warrants continued investigation, due to implications for maximum temperatures, stratification, and shelf ecosystem timing.

To better understand ecosystem dynamics in the Gulf of Alaska, Bering Sea, and Chukchi Sea, researchers at the U.S. National Oceanic and Atmospheric Administration’s (NOAA’s) Pacific Marine Environmental Laboratory and Alaska Fisheries Science Center have been conducting hydrographic and biological surveys in Alaska waters for decades. This article describes a new data compendium (“ACOD”) that assembles data sets from select NOAA programs into a single-point-of-access quality-controlled product. Included are 29717 vertical profiles of temperature and salinity (1974–2021), and 7016 profiles of dissolved inorganic macronutrients (nitrate, nitrite, ammonium, orthosilicic acid, and phosphate) at discrete depths (2001–2021). This value-added product includes systematic quality control of metadata, salinity, and nutrient data – in addition to creating a single point of access for data from 495 cruises across a nearly 50-year time period. ACOD files are archived at the Dryad Research Data Repository and will include annual or biennial updates. File types include netCDF (profiles and nutrients) and csv (nutrients), and a table with metadata from each cruise.

The Bering Sea is a highly productive subarctic ecosystem with some of the most valuable commercial fisheries in the United States. This seasonally ice‐covered sea has been rapidly changing due to ocean warming with impacts to the ecosystem structure and fisheries. The long‐term effects of these shifts on primary producers, however, are still unknown. Continuous monitoring of primary productivity in the Bering Sea is critical, yet observations that capture the ephemeral nature of plankton are challenging to sustain. To address this gap, high temporal resolution primary productivity rates were quantified at a mooring site (M2) in the southeastern Bering Sea in 2021. From a suite of sensors at M2 (fluorescence, dissolved oxygen, temperature, and total dissolved gas pressure), we calculated gross primary productivity (GPP), net primary productivity (NPP), and net community productivity (NCP), the latter based on net biological oxygen saturation using dissolved oxygen/nitrogen (O ₂ /N ₂ ) ratios. These estimates elucidate weekly patterns from the spring bloom through fall, when the water column becomes well‐mixed. In 2021, we observed average productivity during the spring bloom, yet wind patterns and mixing dynamics during the spring contributed to low productivity during summer and fall. The 2021 productivity metrics (GPP, NPP, and NCP) were compared across the growing season and contrasted with seasonal productivity estimates at M2 in previous years with consideration given to variability of ice conditions (warm/cold years) and wind stress.

The Bering Sea and other high‐latitude systems are experiencing unprecedented changes related to climate warming and the consequent loss of sea ice. Understanding how such changes influence primary production is a pressing question. Here, we quantify primary production rates in the southeastern Bering Sea over 4 years (2016–2019) at daily to weekly time resolution. A moored high‐resolution Profiling Crawler was used in combination with in situ sampling to collect physical and biological data in the ocean's upper 50 m. We used dissolved oxygen (O₂) data to estimate gross and net primary production (NPP), and chlorophyll‐a (Chl‐a), temperature, and irradiance data to model NPP rates. We then assessed seasonal variation in phytoplankton production rates, phytoplankton community growth rates () and explored to what extent summer phytoplankton community growth rates may be influenced by nitrogen limitation. Our analyses revealed that the majority of gross primary production (GPP) and net community production occurs in association with the spring phytoplankton bloom. After the bloom, the water column generally experienced low GPP and net biological carbon consumption. Phytoplankton growth rates were commonly suppressed in late summer due to apparent nitrogen depletion. Using high temporal resolution vertically resolved measurements of O₂ and Chl‐a, our analyses provides important insight into how biogeochemical cycles, phytoplankton community growth rates, and carbon available for export vary seasonally in the southeastern Bering Sea.

In situ nutrient concentration data and salinity‐nutrient parameterizations established at Anadyr Strait from June 2017 to June 2018 are used to estimate monthly Pacific‐to‐Arctic fluxes of nitrate, phosphate, and silicate through Bering Strait over 1997–2019. In most months our estimates rely on measurements made from mooring‐based sensors and whole water samples, while over May–August the basis is shipboard hydrography. We find annually averaged Bering Strait fluxes of 16 ± 6, 1.5 ± 0.5, and 30 ± 11 kmol/s for nitrate, phosphate, and silicate, respectively, with inter‐annual variability ±30% of the mean. Maximum fluxes occur in April, exceeding the annual average by ∼50%, while minimum fluxes occur in December. Annually averaged fluxes estimated here are ∼50% higher than previous estimates. Significant (p < 0.05) increasing trends in phosphate and silicate fluxes are found over 1998–2018, but not nitrate. However, it is unclear if these trend results are due to differences in draw‐down or limitations of the salinity‐nutrient parameterizations.

Salinity in the Bering Sea is vital for the physical environment that is tied to the productive ecosystem and the properties of Pacific waters transported to the Arctic Ocean. Its salinity variability reflects many fundamental processes, including sea ice formation/melting and river runoff, but its spatial and temporal characteristics require better documentation. This study utilizes remote sensing products and in situ observations collected by saildrone missions to investigate Sea Surface Salinity (SSS) variability. All Satellite products resolve the large-scale pattern set up by the relatively salty deep basin and the fresh coastal region, but they can be inaccurate near the ice edge and near land. The SSS annual cycle exhibits seasonal maxima in winter to spring, and minima in summer to fall. The amplitude and timing of the seasonal cycle are variable, especially on the eastern Bering Sea shelf. SSS variability recorded by both saildrone, and satellite instruments provide unprecedented insights into short-term oceanic processes including sea ice melting, wind-driven currents during weather events, and river plumes etc. In particular, the Soil Moisture Active Passive (SMAP) satellite demonstrates encouraging skills in capturing the freshening signals induced by spring sea ice melting. The Yukon River plume is another source of intense SSS variability. Surface wind forcing plays an essential role in controlling the horizontal movement of plume water and thereby shaping the SSS seasonal cycle in local regions.

Photography can be a powerful instrument for change. Combining scientific research, new imaging technologies equipped with Artificial Intelligence, and underwater photography, we'll share near- to real-time changes of biodiversity in the Arctic and highlight these rapidly changing and unique environments. Through this project we will continually develop new ways of creating images and stories that both celebrate the sea yet also highlight environmental stress.Scientists often speak of a “new Arctic” to describe the region's rapidly changing landscape and marine systems. Temperatures are higher than before, sea ice is dwindling, and many experts believe the far north is quickly transforming into something unrecognizable.A new Arctic will be warmer, rainier, and substantially less frozen. Animals that used to be common may disappear, while new species may move in to take their place. Opportunities for hunting and fishing by sea ice are declining. And shipping in the region is already significantly increasing as the ice disappears. With this, planning for natural and human-made disasters is an increasingly daunting task.We want to take an Ocean-Shot and visually capture this change in a way that has never been done before. We want to transform the way in which science can be conducted.

The eastern Bering Sea Shelf is characterized by high biological productivity, seasonal sea ice, and commercially important fisheries. Enhanced productivity is often associated with small‐scale oceanographic features. Our objective was to use an autonomous underwater vehicle to examine features typically missed by ~20‐km spaced shipboard sampling. A coastal glider (Oculus) sampled ~3 dives hr⁻¹ with horizontal spacing of ~300 m per dive in August/September 2017. In the north‐south transition zone near St. Matthew Island, the glider sampled four eddy‐like features associated with weaker vertical stratification. These features had diameters of 15–20 km and were associated with higher surface chlorophyll. Shipboard data collected in the same region approximately a month later showed that a similar feature was associated with high concentrations of small copepods. Incorporating higher resolution sampling available with gliders into the Bering Sea observing network will improve our understanding of ecosystem response to patchiness in the system.