More Like this

1. Observations of biological production and light transmittance with warming and sea ice decline across the Pacific Arctic Distributed Biological Observatory

   Frey, Karen E (December 2024, American Geophysical Union 2024 Fall Meeting)

   Recent low sea ice extents across Distributed Biological Observatory (DBO) sites in the northern Bering, Chukchi, and Beaufort seas of the Pacific Arctic region have been due to both later fall/winter freeze-up and earlier spring breakup, which in turn have important cascading impacts on the physical, biological, and biogeochemical state of the overall marine environment throughout this region. Satellite observations of the DBO sites that span across a large latitudinal gradient (~62–72°N) include sea surface temperature (SST), sea ice concentration, annual sea ice persistence and the timing of sea ice breakup/formation, chlorophyll-a concentrations, and primary productivity. While we observe significant trends in SST, sea ice, and chlorophyll-a/primary productivity throughout the year, the most significant and synoptic trends for the DBO sites have been those during late summer and autumn (warming SST during October/November, later shifts in the timing of sea ice formation, and increases in chlorophyll-a/primary productivity during August/September). Measurements of the transmittance of solar radiation through the ocean water column is also one of the critical elements for understanding the potential implications of these recent shifts in sea ice, including impacts on primary production, damaging effects of UV radiation on phytoplankton, photodegradation of dissolved organic matter, and upper ocean heating. Field-based observations of downwelling irradiance and upwelling radiance profiles in the top ~30-50 meters of ocean waters are also presented, collected at discrete stations across DBO sites 1–5 in the northern Bering and Chukchi Seas. Profiles were collected during July 2018, 2019, 2021, 2022, and 2023 as part of the DBO program onboard the Canadian Coast Guard Ship (CCGS) Sir Wilfrid Laurier, and represent a first time series of optical measurements across these DBO sites. Continued monitoring of the transmittance of solar radiation through the water column at these DBO sites will be crucial for understanding changes in the underwater light field as the duration of the open water season continues to lengthen with declining seasonal sea ice cover. 

   more » « less
2. Seasonal and interannual changes in a coastal Antarctic zooplankton community

   https://doi.org/10.3354/meps14256  

   Conroy, JA; Steinberg, DK; Thomas, MI; West, LT (February 2023, Marine Ecology Progress Series)

   Seasonal fluctuations are key features of high-latitude marine ecosystems, where zooplankton exhibit a wide array of adaptations within their life cycles. Repeated, sub-seasonal sampling of Antarctic zooplankton is rare, even along the West Antarctic Peninsula (WAP), where multidecadal changes in sea ice and phytoplankton are well documented. We quantified zooplankton biomass, size structure, and composition at 2 coastal time-series stations in the northern WAP over 3 field seasons (November-March) with different sea-ice, temperature, and phytoplankton conditions. Seasonal peaks in zooplankton biomass followed weeks after phytoplankton blooms. Biomass of mesozooplankton (0.2-2 mm) was consistent and low, while high biomass of macrozooplankton (>2 mm) occasionally resulted in a size distribution dominated by krill and salps, which appears to be a characteristic phenomenon of the Southern Ocean. Zooplankton composition and size changed between years and from spring to summer as the water column warmed after sea-ice breakup. Seasonal succession was apparent typically in decreasing zooplankton size and a shift to species that are less dependent upon phytoplankton. Mean central abundance dates varied by 54 d across 14 taxa, and specific feeding preferences and life-history traits explained the different seasonal abundance patterns. In all 3 yr, the dominant euphausiid species switched from Euphausia superba in spring to Thysanoessa macrura in late summer. Various taxa shifted their phenology between years in response to the timing of sea-ice breakup and the onset of phytoplankton productivity, a level of natural environmental variability to which they appear resilient. Nevertheless, the limits to this resilience in response to climate change remain uncertain. 

   more » « less
3. Chemical and biological vertical distributions within central Arctic (>82°N) sea ice during late summer

   https://doi.org/10.3354/meps14213  

   Torstensson, A; Showalter, GM; Margolin, AR; Shadwick, EH; Deming, JW; Smith, WO (January 2023, Marine Ecology Progress Series)

   We assessed the distribution of biota (autotrophs and heterotrophs) and associated carbonate chemistry variables in Arctic sea ice at latitudes >82°N during late summer and early autumn 2018. The sampled sea ice was relatively thick (average 1.4 m) with variable snow cover (mean 7 cm) and low bulk salinities throughout. Most measured variables, including carbonate chemistry parameters, were low in the upper half of the ice cores, but increased with depth. Measurements of particulate organic carbon (POC), chlorophyll a (chl a) , bacterial abundance, and particulate extracellular polysaccharide (pEPS) in the cores strongly suggested that detrital carbon was the major particulate organic pool. Near the ice-water interface, autotrophic material comprised ca. 50% of the total POC, whereas pEPS and bacterial carbon accounted for ca. 8 and 1% of the total POC, respectively. Under-ice water was nutrient poor, providing only a small input of nutrients to support autotrophic growth, at least during the time of our sampling. While the Arctic Ocean has substantial interannual variability in sea-ice concentration and thickness, these measurements enrich the available database and suggest that during years when autumn sea ice is >1 m thick, sea-ice biota are limited in activity and biomass. 

   more » « less
4. Sea‐ice microbial communities in the Central Arctic Ocean: Limited responses to short‐term pCO₂ perturbations

   https://doi.org/10.1002/lno.11690  

   Torstensson, Anders; Margolin, Andrew R.; Showalter, Gordon M.; Smith, Jr, Walker O.; Shadwick, Elizabeth H.; Carpenter, Shelly D.; Bolinesi, Francesco; Deming, Jody W. (January 2021, Limnology and Oceanography)

   Abstract The Arctic Ocean is more susceptible to ocean acidification than other marine environments due to its weaker buffering capacity, while its cold surface water with relatively low salinity promotes atmospheric CO₂uptake. We studied how sea‐ice microbial communities in the central Arctic Ocean may be affected by changes in the carbonate system expected as a consequence of ocean acidification. In a series of four experiments during late summer 2018 aboard the icebreakerOden, we addressed microbial growth, production of dissolved organic carbon (DOC) and extracellular polymeric substances (EPS), photosynthetic activity, and bacterial assemblage structure as sea‐ice microbial communities were exposed to elevated partial pressures of CO₂(pCO₂). We incubated intact, bottom ice‐core sections and dislodged, under‐ice algal aggregates (dominated byMelosira arctica) in separate experiments under approximately 400, 650, 1000, and 2000 μatm pCO₂for 10 d under different nutrient regimes. The results indicate that the growth of sea‐ice algae and bacteria was unaffected by these higher pCO₂levels, and concentrations of DOC and EPS were unaffected by a shifted inorganic C/N balance, resulting from the CO₂enrichment. These central Arctic sea‐ice microbial communities thus appear to be largely insensitive to short‐term pCO₂perturbations. Given the natural, seasonally driven fluctuations in the carbonate system of sea ice, its resident microorganisms may be sufficiently tolerant of large variations in pCO₂and thus less vulnerable than pelagic communities to the impacts of ocean acidification, increasing the ecological importance of sea‐ice microorganisms even as the loss of Arctic sea ice continues. 

   more » « less
5. Marine phytoplankton resilience may moderate oligotrophic ecosystem responses and biogeochemical feedbacks to climate change

   https://doi.org/10.1002/lno.12029  

   Martiny, Adam C.; Hagstrom, George I.; DeVries, Tim; Letscher, Robert T.; Britten, Gregory L.; Garcia, Catherine A.; Galbraith, Eric; Karl, David; Levin, Simon A.; Lomas, Michael W.; et al (February 2022, Limnology and Oceanography)

   Abstract Are the oceans turning into deserts? Rising temperature, increasing surface stratification, and decreasing vertical inputs of nutrients are expected to cause an expansion of warm, nutrient deplete ecosystems. Such an expansion is predicted to negatively affect a trio of key ocean biogeochemical features: phytoplankton biomass, primary productivity, and carbon export. However, phytoplankton communities are complex adaptive systems with immense diversity that could render them at least partially resilient to global changes. This can be illustrated by the biology of theProchlorococcus“collective.” Adaptations to counter stress, use of alternative nutrient sources, and frugal resource allocation can allowProchlorococcusto buffer climate‐driven changes in nutrient availability. In contrast, cell physiology is more sensitive to temperature changes. Here, we argue that biogeochemical models need to consider the adaptive potential of diverse phytoplankton communities. However, a full understanding of phytoplankton resilience to future ocean changes is hampered by a lack of global biogeographic observations to test theories. We propose that the resilience may in fact be greater in oligotrophic waters than currently considered with implications for future predictions of phytoplankton biomass, primary productivity, and carbon export. 

   more » « less