The U.S. Long Term Ecological Research (LTER) network expanded in 2017 to encompass four marine sites with a pelagic focus, complementing existing time-series maintained by NSF, NOAA, and multiple international funding agencies and enhancing our ability to document multidecadal ecosystem responses to climate variability and change across a global gradient. The four LTER sites span a range in terms of physical environment, geography, bathymetry, and terrestrial influence. Palmer LTER, on the western Antarctic Peninsula and extending 200 km offshore, is dominated by seasonal changes in sea ice cover and light availability. The California Current Ecosystem LTER is an eastern boundary upwelling regime and primarily an open ocean site with minor terrestrial inputs. The Northeast U.S. Shelf and Northern Gulf of Alaska LTER sites extend from the continental shelf into the open ocean, with significant terrestrial influences. All of the sites are associated with productive fisheries, and all are experiencing warming trends in surface air temperatures with associated impacts on mixed layer temperature and depth, and/or sea ice cover. This session will showcase ongoing studies of ecological responses at the LTER sites in terms of primary production, community composition and structure, carbon and nutrient cycling, and disturbance. We strongly encourage submissions related to these topics from other (non-LTER) national and international pelagic time-series sampling programs. Recent cross-LTER site synthesis efforts will also be highlighted.
Lead Organizer: Katherine Barbeau, Scripps Institution of Oceanography, UC San Diego (kbarbeau@ucsd.edu)
Co-organizers:
Russ Hopcroft, University of Alaska Fairbanks (rrhopcroft@alaska.edu)
Heidi Sosik, Woods Hole Oceanographic Institution (hsosik@whoi.edu)
Oscar Schofield, Rutgers University (oscar@marine.rutgers.edu)
Presentations
02:30 PM
MARINE PLANKTON SIZE SPECTRA AND TROPHIC TRANSFER EFFICIENCY AT PELAGIC LONG-TERM ECOLOGICAL RESEARCH (LTER) SITES ACROSS A LATITUDINAL GRADIENT (9043)
Primary Presenter: Deborah Steinberg, Virginia Institute of Marine Science (debbies@vims.edu)
Plankton size spectra are an empirical way to study trophic transfer efficiency in marine ecosystems. The slopes of size spectra have been related to abiotic factors such as nutrient concentration and temperature, as well as primary productivity, fish biomass, and carbon export, with flatter slopes suggesting more efficient transfer of carbon from smaller to larger organisms. As part of the pelagic Long-Term Ecological Research (LTER) synthesis working group, the four oceanic LTER sites spanning a latitudinal gradient from the Northern Gulf of Alaska to the Northeast U.S. Shelf, California Current, and Antarctic Peninsula, standardized carbon-based biomass measurements for planktonic organisms from heterotrophic bacteria (<1 micron) through phytoplankton to macrozooplankton (as large as 50 mm). The range in the normalized biomass size spectrum (NBSS) spans seven orders of magnitude and is similar across sites. Interesting nonlinear features in size spectra slopes are likely related to characteristics of planktonic community structure, such as the relatively low biomass of heterotrophic bacteria and high biomass of macrozooplankton at Palmer LTER on the western Antarctic Peninsula, which are well-described phenomena in the Southern Ocean. Other deviations from linearity appear to be related to undersampling of certain size classes and variation in methodologies; knowledge that will help inform future synthesis efforts across these diverse programs. Finally, we discuss how size spectra relate to environmental drivers and ecosystem function at these sites.
02:45 PM
INVESTIGATING TROPHIC AMPLIFICATION AT LONG-TERM MARINE TIME-SERIES SITES (9398)
Primary Presenter: Michael Stukel, Florida State University (mstukel@fsu.edu)
The trophic amplification hypothesis suggests that climate-driven alterations at the base of marine ecosystems (i.e,. phytoplankton) will be amplified by food-web processes. Thus decreases (or increases) in net primary production will lead to proportionally greater decreases (or increases) in higher trophic levels and fisheries production. The trophic amplification hypothesis is supported by modeling results and analyses of inter-regional variability in the spatial organization of marine foodwebs. However, due to a paucity of long-term, multi-trophic level pelagic studies, it has not been thoroughly tested with time series data. In this project we bring together long-term datasets from the four marine pelagic long-term ecological research (LTER) sites (Palmer LTER in the Western Antarctic Peninsula, California Current Ecosystem LTER, Northeast U.S. Shelf LTER, and Northern Gulf of Alaska LTER), as well as other long-term pelagic time-series to test aspects of the trophic amplification hypothesis. Specifically, we 1) investigate whether interannual variability increases at higher trophic levels, 2) test whether successive trophic levels are positively correlated and 3) investigate impacts of food web structural variability in ecosystems spanning tropical, temperate and polar seas. Preliminary results show support for the trophic amplification hypothesis at some, but not all locations.
03:00 PM
LATITUDINAL VARIABILITY AND LONG-TERM RESPONSES OF PELAGIC COMMUNITY STRUCTURE TO CLIMATE FORCING ACROSS FOUR MARINE LTER SITES (9444)
Primary Presenter: Alexandra Cabanelas, Woods Hole Oceanographic Institution (acabanelas@whoi.edu)
Pelagic marine ecosystems exhibit varied responses to both stochastic and long-term environmental changes, but the mechanisms driving these responses are not fully understood. Long-Term Ecological Research (LTER) sites provide invaluable long-term data across a latitudinal gradient. Here, we analyze pelagic populations across four marine LTER sites—Northeast U.S. Shelf, California Current Ecosystem (CCE), Northern Gulf of Alaska, and Palmer Antarctica—to investigate how zooplankton respond to climate forcing. We tested whether mechanisms observed in the CCE, in particular the Double-Integration Hypothesis, apply to other marine ecosystems and help explain distinct patterns in community composition and structure across varying timescales. This hypothesis suggests that cumulative integrations of noisy atmospheric forcing drive long-term population variability. Using time-series data spanning 25-75 year duration for taxa encompassing copepods, euphausiids, and pteropods, we find varying degrees of support for the Double-Integration Hypothesis across sites, considering indices such as the Pacific Decadal Oscillation, the El Niño-Southern Oscillation, and the Gulf Stream Index. This work reveals both similarities and unique responses, highlighting the importance of a cross-system perspective in understanding marine ecosystem responses to physical climate forcing. Understanding how pelagic populations respond to changing conditions and the drivers of long-term variability is crucial for effective ecosystem management due to the central role of plankton in marine ecosystems.
03:15 PM
SURFACE AND SUBSURFACE PHYTOPLANKTON BIOMASS AND STOICHIOMETRY AT STATION ALOHA OVER THREE DECADES (8867)
Primary Presenter: Johannes Viljoen, University of Exeter (j.j.viljoen@exeter.ac.uk)
Marine phytoplankton contribute approximately half of Earth’s primary production, fuelling marine ecosystems and playing a key role in global climate regulation. However, uncertainties remain regarding their response to climate variability, particularly with respect to vertical distribution patterns. While previous research has advanced our understanding of surface or column-integrated phytoplankton biomass, vertical structuring has received less attention. Recent research in a seasonally stratified region of the subtropics has shown contrasting seasonal and temporal trends in surface and subsurface phytoplankton. In this study, we apply a similar conceptual modelling tool that divides the vertical profile of phytoplankton biomass into two distinct communities—one in the surface mixed layer and another in the subsurface layer—to over 30 years of chlorophyll-a, particulate organic carbon (POC) and particulate organic nitrogen (PON) data from Station ALOHA. Preliminary analyses reveal contrasting seasonal trends between these communities, with surface phytoplankton appearing to adjust their carbon-to-chlorophyll ratio, potentially reflecting photoacclimation processes, while subsurface ratios remain relatively stable. Longer-term trends in these patterns, along with the roles of photoacclimation and changing stoichiometry are examined in the context of ocean warming. Given that satellite remote sensing only captures surface signals, sustained in situ measurements of subsurface phytoplankton are essential for understanding their response to climate change.
03:30 PM
Patterning of zooplankton communities as revealed by 25 years of observations along the Seward Line in the Northern Gulf of Alaska (8991)
Primary Presenter: Russell Hopcroft, University of Alaska - Fairbanks (rrhopcroft@alaska.edu)
The northern Gulf of Alaska zooplankton communities have been well sampled for the past quarter century. Here we illustrate the major environmental gradients present in this time series: season, cross-shelf, depth, and year. Spring and summer/fall occupy separate and distinct multi-dimensional space. Stations typically display a distinct multi-dimensional cross-shelf patterning as do depth layers (when data is available). Year introduces scatter along these gradients. We will explore what species are most influential in establishing these patterns, and the degree to which environmental factors explain the variability manifested by year. Establishing these connections will facilitate predictions of community structure that may be expected under future environmental settings.
SS27A - Long-term perspectives in marine pelagic ecosystem research
Description
Time: 2:30 PM
Date: 30/3/2025
Room: W207AB