Climate change is rapidly altering aquatic ecosystems worldwide, from pristine headwater streams to the abyssal plain. The resulting shifts in ecosystem structure and function can, in turn, exert a reciprocal influence (feedback) on environmental chemistry and climate by amplifying or dampening the impact of the initial perturbation. At the global scale, aquatic ecosystems can alter climate by varying (1) albedo, (2) greenhouse gas fluxes, and (3) carbon stocks through short- to long-term reservoirs. These biogeochemical feedbacks have the potential to profoundly influence the rate of warming and other physical/chemical changes, and to determine ‘tipping points’ i.e., inflections in these rates. Yet, despite their probable importance, most biogeochemical feedbacks remain poorly constrained and, in some cases, even the directionality of their effect on the initial stimulus (amplifying or dampening) is unknown. Consequently, biogeochemical feedbacks represent an area of major uncertainty in Earth Systems Models, when they are included at all. This session will take the pulse of biogeochemical feedbacks in aquatic ecosystems, addressing the question: “How will ecosystem shifts (e.g., changes in diversity, productivity, trophic structure, size structure, stoichiometry, metabolic rates) driven by climate change-related stressors (e.g., warming, deoxygenation, acidification, sea level rise) alter Earth’s climate system?” We welcome presentations from modelers, experimentalists, and observationalists alike. The goal of this session is to improve our understanding of climate feedbacks driven by ecosystem dynamics in aquatic systems.
Lead Organizer: Richard LaBrie, McGill (richard.labrie@mcgill.ca)
Co-organizers:
Corday Selden, Rutgers University (crselden@marine.rutgers.edu)
Laura Ganley, New England Aquarium (lganley@neaq.org)
Presentations
09:00 AM
Is our understanding of aquatic ecosystems sufficient to quantify ecologically-driven climate feedbacks? (8945)
Tutorial/Invited: Invited
Primary Presenter: Laura Ganley, New England Aquarium (lganley@neaq.org)
The Earth functions as an integrated system—its current habitability to complex life is an emergent property dependent on interactions among biological, chemical and physical components. As global warming affects ecosystem structure and function, so too will the biosphere affect climate by altering atmospheric gas composition and planetary albedo. Constraining these ecosystem-climate feedbacks is essential to accurately predicting future change and developing mitigation strategies; however, interplay among ecosystem processes complicates assessment of their impact. Here, we explore the state of knowledge on how ecological and biological processes (e.g., competition, trophic interactions, metabolism, adaptation) affect the directionality and magnitude of feedbacks between ecosystems and climate, using illustrative examples from the aquatic sphere. We argue that, despite ample evidence for the likely significance of many, our present understanding of the combinatorial effects of ecosystem dynamics precludes the robust quantification of most ecologically-driven climate feedbacks. Constraining these effects must be prioritized within the ecological sciences for only by studying the biosphere as both subject and arbiter of global climate can we develop a sufficiently holistic view of the Earth system to accurately predict Earth’s future and unravel its past.
09:15 AM
Effects of short-term warming on surface ocean productivity: A case study across nitrogen- to iron-limited waters of the South Atlantic and Southern Ocean (9346)
Primary Presenter: Corday Selden, Rutgers University (crselden@marine.rutgers.edu)
Synergistic effects among ecosystem stressors introduce significant uncertainty in efforts to model biogeochemical climate feedbacks. In theory, future ocean warming should increase metabolic rates, with implications for productivity and biological carbon sequestration; however, nutrient limitation has the potential to severely dampen the realized effects of warming. This study investigated the effects of short-term warming on nutrient acquisition and net community production under distinct nutrient limitation regimes. Seven experiments were carried out across Fe-limited waters of the Southern Ocean to N-limited waters of the South Atlantic gyre. While N plays myriad roles in cells, Fe is used primarily in catalysis, meaning that Fe demand may decrease with warming given gains in enzymatic efficiency. Water was collected using a trace metal-clean sampling approach and incubated at ambient temperature, +2ºC, and +4ºC. At 72 h, 15N substrates were added to determine nitrate and ammonium uptake rates; endpoint samples were collected at 78 h. We quantified change per degree warming in nutrient and particulate organic carbon/N (POC/PON) concentrations, which generally scaled linearly with temperature. POC and PON increased by 10-30% of standing stock per degree warming in Fe-limited waters south of the Subantarctic Front and in co-limited waters at the Subtropical Front. North of the Subantarctic Front, gains increased by <6% per degree warming. Our results suggest that Fe-limited communities in the Southern Ocean may respond more strongly to warming events, with implications for climate feedbacks associated with the biological carbon pump.
09:30 AM
Circulation and resource limitation control global pattern of phytoplankton diversity: Insights from a trait-based model (8779)
Primary Presenter: Guillaume Le Gland, Aix-Marseille Université (guillaume.le-gland@univ-amu.fr)
Diversity has been observed to decrease with latitude in many oceanic taxa, a pattern often explained by the positive kinetic effect of high temperature on metabolic rates, but whether this pattern also apply to phytoplankton remains debated. In order to disentangle the drivers of phytoplankton diversity, we developed a global 3D phytoplankton ecological dynamics model, coupled to the MIT general circulation model at a resolution of 1°, where ecotypes differing by their cell size, temperature niche, and solar irradiance niche, compete for the same nutrients and are transported by oceanic currents. The phytoplankton diversity pattern we simulate, validated by PhytoBase observations, is neither monotonic in latitude nor governed by temperature. Instead, we find that diversity is increased by vertical stratification and horizontal mixing, and depressed by nutrient and light limitations. Warm waters host local diversity maxima in upwelling regions, where permanent stratification allows each depth level to select a different community uniquely adapted to its environmental conditions, and minima in the nutrient-depleted centers of the subtropical gyres, where only the smallest cells have positive net growth rates. We also find maxima in the mid-latitudes, characterized by seasonality and meridional dispersal across strong temperature gradients, and minima in the well-mixed Southern Ocean south of 50°S. We conclude by some hypotheses on phytoplankton response to future changes in the physical environment, such as warming, mixed-layer shallowing or Gulf Stream weakening.
09:45 AM
Oxygen and carbon-based rates of production and respiration across the Equatorial and South Pacific Oceans (9447)
Primary Presenter: Robert Clegg, University of Hawaiʻi at Mānoa (rcleggrtc@gmail.com)
Accurately quantifying marine primary production is vital for understanding the global carbon cycle and the ocean's role in CO₂ sequestration. This study used in situ, ship-based measurements, including Winkler titrations, O₂/Ar ratios, optical proxies for carbon concentrations, as well as 18O and ¹⁴C incubations, across a 40 degree latitudinal gradient in the Equatorial and South Pacific ocean to assess primary production and respiration rates over the diel time scale. Macromolecular analyses of particulate organic carbon (POC) were used to investigate how biochemical compositions influence the photosynthetic quotient (PQ) and respiratory quotient (RQ). Results were compared to previous observations in the North Pacific, providing a basin-scale view of how metabolic balance changes with nutrient supply and particle compositions. These findings will improve predictive models of global carbon cycling and enhance the understanding of marine ecosystems' role in climate variability.
10:00 AM
Tracking coastal diatom carbon metabolic mechanisms and microbial networks with time-series -omics data (9212)
Primary Presenter: Arianna Krinos, Brown University (akrinos@vt.edu)
Diatoms are spring bloom formers and dominant contributors to coastal carbon cycling. In Cape Cod Bay, spring diatom blooms are common, but with high variability. For over 20 years, the Massachusetts Water Resources Authority and Provincetown Center for Coastal Studies have collected water samples for physico-chemical monitoring and plankton counts from a series of Cape Cod Bay sites, and we collected metatranscriptomic samples in 3 spring seasons. We captured spring blooms of Guinardia and Proboscia and a modest spring bloom of Thalassiosira in the metatranscriptomes. We also captured mid-summer growth of diatoms Dactyliosolen and Leptocylindrus. This diversity of abundant diatom taxa in different seasons, temperatures, and nutrient contexts enabled us to test our hypothesis that different diatom taxa would result in different dominant expressed carbon-related genes. We contextualized our metatranscriptomes with 18S and 16S rRNA gene data, evaluated genetic distance between diatoms observed in adjacent years, and constructed networks of environmental associations between phytoplankton and bacteria. We applied a k-mer clustering approach to the metatranscriptomic assemblies to annotate diatom sequences more precisely and identified carbon metabolism genes specific to diatoms, especially photorespiration and carbon concentrating mechanisms. We correlated expression of carbon pathway genes that produce less labile intermediates to bacterial abundance. Our results highlight how -omics approaches can illuminate aspects of diatom metabolism and their community context.
SS06A - Biogeochemical feedbacks in aquatic environments: On the role of ecology, evolution, and biological adaptation as drivers of Earth’s climate system
Description
Time: 9:00 AM
Date: 28/3/2025
Room: W207CD