Contributed Session.
Lead Organizer: Margaret Baker, Rice University (mb203@rice.edu)
Co-organizers:
Jasmine Saros, University of Maine (jasmine.saros@maine.edu)
Presentations
04:30 PM
Long term changes in a rapidly warming polar pelagic ecosystem (9210)
Primary Presenter: Oscar Schofield, Rutgers University, COOL (oscar@marine.rutgers.edu)
Polar systems have been experiencing accelerating change with increasing wind, melting glaciers and declining sea ice. These changes are rippling through the WAP ecology and biogeochemistry of the system. The Palmer LTER has for over three decades been tracking how these changes are now rippling through the food web. Results have shown that the food web is tightly coupled and that changes in the base of the food web rapidly cascades up from a highly productive diatom system through keystone species (Antarctic krill) to penguins and whales. The food web cascade is a temporally lagged response and appears tightly coupled to the wind and sea ice observed in the winter prior to the austral spring and summer. Over the time series, initially the high inter-annual variability in system responses was driven by competing forcing from cyclical climate forcing (El Nino, Southern Annual Mode, Pacific Decadal Oscillation) overlaid on global anthropogenic changes. While the early variability in the time series appeared to be dominated by the shorter climate forcing, recent observed changes indicate a large-scale shift in the Southern Ocean system. We will focus discussion on assessing the response of the food web in the anomalously warm low sea in the last three years embedded within the longer-term dynamics illuminated within the time series of the Palmer LTER.
04:45 PM
INSHORE-OFFSHORE DIVERGENCE IN THE LONG-TERM EFFECTS OF MIXED LAYER SHOALING ON SUMMER PHYTOPLANKTON COMMUNITIES ALONG THE WEST ANTARCTIC PENINSULA (9588)
Primary Presenter: Quintin Diou-Cass, Rutgers University (dioucass@gmail.com)
The West Antarctic Peninsula (WAP) provides an ideal setting to study long-term trends in Southern Ocean phytoplankton ecology under rapidly changing conditions. Over recent decades, shoaling of summer mixed layers on the WAP have been linked to increased surface phytoplankton productivity and CO2 drawdown via increased light supply to light-limited communities. However, the link between light-dependent physiology and shallowed mixing, as well as responses in offshore iron-limited regions, remains unclear. Using two decades of pigment data from the Palmer Long Term Ecological Research (LTER) program, we analyzed trends in photophysiology, biomass, productivity, and mixing across the WAP to assess the long-term responses of phytoplankton communities to physical change, both in total and between physiochemical regions. We found a doubling of photoprotective carotenoid (PPC) proportions on the WAP, correlated with shallower mixed layers, increased productivity, and increased production efficiency. However, biophysical trends showed notable inshore-offshore gradients, where coastal regions displayed weak changes in mixing and PPC but the highest biomass gains, while slope regions had stronger shoaling and high PPC but minimal change in biomass. These results suggest that while light boosts surface production, iron availability has significantly constrained long-term biomass gains in offshore regions. Our findings support a light-regulated model of productivity for the WAP as a whole, but highlight that growth remains severely dampened offshore.
05:00 PM
INVISIBLE INHABITANTS: MICROBIOTA ON THE SURFACE OF DORMANT ZOOPLANKTON EMBRYOS (9727)
Primary Presenter: Hunter Arrington, University of North Carolina Wilmington (hba4881@uncw.edu)
Dormant zooplankton embryos in inland water and estuarine sediment can remain viable for years in a state of extreme metabolic suppression. How these embryos resist microbial attack with limited metabolic capacity for immune defense or repair is unknown. An active defense against microbes requires metabolic activity, which they lack. Evaluating surface colonization of the Antarctic freshwater copepod, Boeckella poppei, was conducted as a first step in assessing resistance to microbial attack in dormant zooplankton. Scanning electron microscopy and microbiome analysis using the 16S ribosomal subunit gene and internal transcribed spacer (ITS) region, demonstrate the presence of a diverse microbial community on the embryo surface. Coverage of embryos with microbial life varies from a sparse population with individual microbes to complete coverage by a thick biofilm. Prokaryotes and diatoms with diverse physical structure are present. Putative fungal hyphae and amoeboid-like organisms were also observed. Frequent observation of bacterial fission indicates that the biofilm is viable in stored sediments. Extracellular polymeric substance binds debris and provides a structural element for the microbial community. Unexpectedly, previously undescribed layers of the cyst wall in B. poppei were identified. These outer layers fragment and create a complex environment for microbial colonization. The absence of damage to the underlying third layer after years of storage indicates that it is resistant to degradation by microbial enzymes, which should be of interest to material scientists.
05:15 PM
Dynamics of diazotroph particle colonization in the Arctic Ocean (8928)
Primary Presenter: Arthur Coët, Mediterranean Institute of Oceanography (arthur.coet@mio.osupytheas.fr)
Arctic warming is melting sea ice, releasing nutrients and boosting primary productivity, which increases nitrogen demand. Diazotrophs, microorganisms that convert atmospheric nitrogen into bioavailable forms, are essential for maintaining nitrogen levels. With rising nitrogen consumption, diazotroph nitrogen fixation will become critical for sustaining productivity in future nutrient-poor oceans. Unlike cyanobacterial diazotrophs that photosynthesize, non-cyanobacterial diazotrophs (NCDs) rely on organic matter. Although NCDs dominate many ecosystems, their interactions with Arctic marine particles remain poorly understood. This study investigates the chemotactic behavior and colonization dynamics of diazotrophs in the Arctic Ocean using an adapted In Situ Chemotaxis Assay with alginate and agarose artificial particles. Seawater from the Barents Sea was analyzed via nifH and 16S rRNA gene sequencing. Gammaproteobacteria rapidly colonized alginate, showing strong attraction to algal polysaccharides, abundant in the Arctic, while non-diazotrophic bacteria showed no preference. These results reveal niche partitioning within the microbial community and highlight the potential for increased N₂ fixation associated with algal particles. As the ice cover retreats, organic matter from algal blooms and glacial runoff is poised to expand habitats for particle-associated diazotrophs, potentially reshaping nutrient cycling and boosting primary production. Grasping these interactions is pivotal for predicting the Arctic Ocean's response to climate change.
05:30 PM
TRACE ELEMENT DYNAMICS AND MICROBIAL SULFATE REDUCTION IN RESPONSE TO HISTORICAL CARBON PULSES IN AN ICE-COVERED HIGH ARCTIC LAKE (8918)
Primary Presenter: Florence Mercier, Université Laval (florence.mercier.3@ulaval.ca)
Arctic lakes, which remain ice-covered for most of the year, are highly sensitive to accelerating climate change and vulnerable to human impacts. Lake Meretta (NU, Canada, 74°42’N) offers a rare opportunity to study the impacts of human-induced nutrient loads in a High Arctic, ice-covered lake. Its upstream basin (A) received decades of elevated organic carbon inputs from sewage discharges, while the downstream basin (B) remained unaffected. In this study, we collected 40 cm sediment cores beneath a 1.8 m-thick ice cover and sampled both sediments and porewater from the two basins. We analyzed vertical profiles of nutrients (NH4+, PO43-), essential micronutrients (Fe, Mn, S, V, Mo, Co, Cu), sulfides (HS-), and potential contaminants (Cd, As, Pb) to assess trace element mobility and geochemical processes. Our findings show distinct geochemical dynamics between the two basins: (1) Porewater concentration gradients of NH4+ and PO43- indicate that sediments in both basins act as a source of NH4+, but only basin A continues to release PO43-; (2) Basin A exhibits elevated HS⁻ levels (up to 19.6 µM) and low Fe, pointing to sulfur-driven geochemistry, whereas basin B has high dissolved Fe (up to 274 µM) and comparatively lower HS-; (3) Dissolved trace element concentrations are generally much higher in basin A, with the exception of Mn and Co, which are more concentrated in basin B. Overall, our results suggest that historical carbon inputs have led to sustained sulfur-reducing conditions, which remain key drivers of nutrient and trace element mobility in the eutrophic basin A.
05:45 PM
MULTI-SCALAR APPROACH TOWARDS A HOLISTIC UNDERSTANDING OF LAKE LEVEL IN AN AGRICULTURAL, DROUGHT-PRONE SUB-ARCTIC LANDSCAPE (9178)
Primary Presenter: Amanda Gavin, University of Maine (amanda.gavin@maine.edu)
Although the disappearance of the Norse settlement in South Greenland has been a topic of interdisciplinary, scientific debate for decades, the impact of anthropogenic climate change on the past, present, and future of lakes that are critical for Inuit sheep farming communities in this area remain unexplored. Using lake level as a proxy for water availability, we evaluated the drivers of lake level at varying temporal frequencies to understand lake system response to an intensifying hydrological cycle. Indigenous Knowledge interwoven with paleolimnological and high-frequency lake level provide a holistic understanding of lake level, and hence water availability, across timescales. Semi-structured interviews with sheep farmers contributed to site selection, historical lake level observations, and lake level response to weather events. Diatom-inferred lake level and three-dimensional bathymetry modeling were used to reconstruct decadal trends in lake level that predate contemporary agricultural operations. High-frequency lake level sensors were used to quantify water availability drivers on a daily, seasonal, and interannual scale. Preliminary results show strong lake level coherence across a gradient of hydrological connectivity and lake level response to weather events that vary seasonally. As the Arctic experiences unprecedented warming and agricultural operations are expected to increase, understanding the interaction of climate change and managed landscapes in a sub-Arctic context is paramount.
CS15 - Polar Ecosystems
Description
Time: 4:30 PM
Date: 27/3/2025
Room: W205CD