The biological pump is a major driver of carbon export from the atmosphere into the upper mixed layer and down to the deep ocean, where carbon is sequestered for several centuries. Plankton- and nekton-mediated processes affect the magnitude of gravitational and active carbon fluxes, controlling a plethora of key mechanisms such as ocean acidification, trophic transfer, and bentho-pelagic coupling. Carbon export efficiency varies significantly depending on the magnitude of photoautotrophic production, the influence of species composition and food web structure at different depths and trophic levels. Both primary and secondary producers are thus major drivers of biogeochemical feedbacks to global change. In recent years, a significant effort was put in motion to promote integrative ocean science connecting countries along and across the Atlantic Ocean, building from the initial impulses given by the Galway and Belém Statements signed by the European Union and Atlantic partners. Important research efforts within this framework investigate Atlantic ecosystems, their microbiome and metazoan communities, the different components of the biological pump and related biogeochemical cycles, and strategies to manage the Atlantic ecosystems in the context of expected global change. The application of novel molecular and imaging tools, in concert with seascape and connectivity studies and modelling approaches, drive recent progress in understanding the pelagic ecosystems of the Atlantic. Questions that now can be addressed also include the resilience and recovery potential of the biological pump and trophic transfer towards global change and human perturbations. This session invites contributions that represent new advances in understanding overall ecosystem functioning and carbon fluxes from the surface to the deep ocean. These could range from process studies over contributions from observational efforts to modelling approaches demonstrating how novel data and analytical tools can improve our understanding of plankton- and nekton-mediated carbon fluxes in the Atlantic during times of global change.
Lead Organizer: Rubens Lopes, University of Sao Paulo (rubens@usp.br)
Co-organizers:
Rainer Kiko, GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel (rkiko@geomar.de)
Helena Hauss, NORCE Norwegian Research Centre, Norway (heha@norceresearch.no)
Lars Stemmann, Institut de la Mer de Villefranche (IMEV) (lars.stemmann@imev-mer.fr)
Presentations
06:30 PM
Flow-topography interactions drive zooplankton abundance and carbon export to depth along the Vitoria-Trindade Seamount Chain (SW Atlantic) (7177)
Primary Presenter: Rubens Lopes, University of Sao Paulo (rubens@usp.br)
The interaction between mesoscale eddies and seamounts modifies water circulation and affect the transport of nutrients and the abundance of organisms. The impact of these processes on zooplankton communities has not been fully explored. This study investigates how the interaction between the seamounts and the Vitoria Eddy (VE) influences zooplankton abundance and particulate organic carbon (POC) vertical flux along the Vitoria-Trindade Seamount Chain (VTC), Southwestern Atlantic Ocean. Vertical profiles using the UVP5 were performed along two transects (32 stations) near the VTC, during the summer of 2017. Rhizaria was dominant in all stations, contributing up to 65% to the zooplankton total abundance. Highest zooplankton abundances and POC fluxes occurred at stations simultaneously influenced by the shallow seamounts and the VE activity, as well as at stations only influenced by the VE. The combination of the seamount topography and the VE circulation increased local productivity and the accumulation and entrapment of particles, increasing zooplankton abundance and POC flux. Our results suggest that the energetic VE amplified the flow-topography effects of the shallow seamounts in the euphotic layer. The seamount-eddy interaction provides a substantial rise in the potential of carbon export to depth in the Southwestern Atlantic Ocean oligotrophic waters, making the VTC and other seamount chains potential carbon export hotspots.
06:30 PM
Particulate Carbon Export using 234Th-238U disequilibrium along the Atlantic Equatorial line (5434)
Primary Presenter: Wokil Bam, Woods Hole Oceanographic Institution (wokil.bam@whoi.edu)
The Transatlantic Equatorial Cruise II (TRATLEQ-II) conducted in April – May 2022 was focused on upwelling conditions in the tropical Atlantic, its physical forcing, its importance for biological production, and plankton communities, associated chemical cycles, and the downward particulate organic carbon (POC) export. To achieve this goal, precise observations of POC export are needed. Here, we used the naturally occurring radiotracer 234Th-238U pair to estimate the magnitude of POC export and dynamics in the euphotic zone. The disequilibrium between this isotope pair allows estimating the POC export from the upper water column integrated over monthly time scales. The profiles of 234Th in the upper 500 m of the water column at 33 stations were obtained along the equator between 2°E and 44°W. Th-234 deficit was observed in the upper water column indicating the export of POC. Integration of 234Th deficit relative to 238U, observed in the productive surface layer yields 234Th flux, from which POC flux can be estimated by using the POC/234Th ratio on sinking particles. Particulate samples were collected at 10 stations, evenly distributed every 5° longitude between using in-situ pumps deployed at 6 depths per station to determine the POC/234Th ratio. The particulate organic carbon export from the euphotic zone and remineralization along the Equator determined using this approach will be presented and compared to estimates based on Underwater Vision Profiler data, also obtained during the cruise.
06:30 PM
Investigating organic carbon fluxes in a coastal system using the natural tracer thorium-234 (6697)
Primary Presenter: Madeline Healey, Dalhousie University (mhealey@dal.ca)
The ocean’s biological carbon pump plays a large role in the global carbon cycle. A fraction of the photosynthetically fixed organic carbon produced in the sunlit zone of the upper ocean is exported to depth as particulate organic carbon (POC). Here, we investigate seasonal changes in POC export in Bedford Basin, a semi-restricted coastal basin located on the east coast of Canada using the 238U-234Th radioisotope system. This isotope system is widely used in the open ocean, however, it’s application in complex coastal regimes is still relatively new. Results from sampling in 2019 and 2021 indicate general agreement between water column fluxes of 234Th and excess 234Th in the uppermost sediment layers of the basin. In addition, observations of 234Th fluxes in spring of 2021 show an increase in 234Th activity in the water column, and thus a smaller deficit with respect to 238U, compared to spring of 2019. The smaller deficit suggests a reduction in POC export to depth in spring 2021 compared to spring 2019. If confirmed, this reduction in POC flux during spring is likely driven by the ongoing warming of the basin and the related reduction in water column mixing during the winter. Data from this study will be incorporated into a model to validate steady-state assumptions in the basin. Continued advances in the application of the 234Th-238U method in coastal zones will improve our understanding and quantification of marine carbon fluxes and thus, open the door for addressing other complex questions and environmental concerns that face coastal areas in the Anthropocene.
06:30 PM
Biogeochemical Composition of Suspended and Sinking Marine Snow in the Northwest Atlantic (7178)
Primary Presenter: Carolina Cisternas-Novoa, Memorial University of Newfoundland (acisternasno@mun.ca)
The downward flux of marine snow particles is critical for the ocean's carbon sequestration, although a significant fraction of the organic carbon carried in marine snow is remineralized in the mesopelagic zone. Canonically, a positive correlation between aggregate size and sinking velocities is assumed; however, recent studies concluded that aggregate composition is crucial to constrain sinking velocity-size relationships. In May 2022, we collected intact marine snow-sized aggregates (ESD > 0.5 mm) in the Northwest Atlantic by deploying Marine Snow Catchers (MSC) below the mixed layer (between 80 and 160 m) at eight stations dominated by different phytoplankton communities. Here we show the concentrations of particulate organic carbon and nitrogen (POC/N), amino acids, and exopolymeric particles associated with suspended, slow- and fast-sinking particles and assessed aggregate size and shape. We found that more than 80% of the POC pool was suspended at all the stations and depths. POC concentrations of fast-sinking particles were 60% to 90% higher than those of slow-sinking particles, increasing with depth, except at stations characterized by a Phaeocystis bloom. The POC concentration at those stations was twice that at non-bloom stations, and the contribution of suspended and slow-sinking particles increased with depth. Fast-sinking particles contributed 17% of the POC concentration at 80 m but only 2% at 500 m. This data set allows us to explore compositional differences between suspended and sinking marine snow.
06:30 PM
Quantifying the biological carbon pump efficiency in the Labrador Sea during a Phaeocystis bloom (5409)
Primary Presenter: Montserrat Roca-Martí, Universitat Autònoma de Barcelona (montserrat.roca.marti@uab.cat)
The biological carbon pump (BCP) is principally mediated by the sinking of particulate organic carbon (POC) from the upper ocean to depth and varies strongly across regions and time. Here we present results from the most comprehensive study to quantify the BCP efficiency in the Labrador Sea to date. The Labrador Sea is a globally significant region for deep-water formation, playing a critical role in biogeochemical cycles. Field work was conducted in the Eastern Labrador Sea during a Phaeocystis bloom for a 15-day period in May-June 2022 capturing the bloom to senescence period of production. POC export fluxes are quantified using high vertical and spatial resolution measurements of Th-234 in the upper 500 m of the water column (15 depths, 15 stations), combined with the collection of particles obtained using large volume filtration pumps and marine snow catchers. POC flux estimates are used along with net primary production (NPP) rates to quantify the magnitude of POC export at the base of the euphotic zone relative to NPP (export efficiency), and the efficiency by which POC fluxes are transferred throughout the upper twilight zone (transfer efficiency). These assessments allow us to quantify the efficiency of the BCP in the Labrador Sea, put it into context of other oceanic regions, and better understand the impact of Phaeocystis blooms on POC export. This study will enhance our understanding of the BCP in the Labrador Sea and, in turn, improve future predictions of carbon cycling in the Northwest Atlantic and beyond.
06:30 PM
EVALUATION OF BIOLOGICAL CARBON PUMP METRICS IN THE SUBTROPICAL GULF OF AQABA, NORTHERN RED SEA (6040)
Primary Presenter: Stephanie Kienast, Dalhousie University (stephanie.kienast@dal.ca)
The efficiency of the biological carbon pump in the ocean and its response to continuously warming temperatures are of great importance to future projections of global change. Here, we investigate a time series of organic carbon fluxes from a monthly resolved sediment trap mooring in the Gulf of Aqaba (GOA), northern Red Sea, between 2014 and 2016. We evaluate the attenuation of sinking organic carbon in the context of the seasonally changing euphotic zone and provide the first estimates of biological pump efficiency in this region. The base of the euphotic zone changed seasonally as the system transitioned from oligotrophic and stratified conditions in summer to mesotrophic conditions during the winter mixing period. Carbon attenuation assessed using a power law fit yields an average coefficient of b = 0.80 ± 0.37, lower than expected based on the warm temperatures in the GOA. Estimates of export efficiency decreased from 40% in summer to 20% in winter, and show the opposite seasonal pattern as transfer efficiencies, which increased from 50% in summer to 95% in winter. Overall, the efficiency of the carbon pump was close to 20% in both seasons. These observations challenge the notion of a globally uniform positive correlation between increasing temperature and increasing carbon attenuation in the ocean and imply that warm subtropical ecosystems can support moderately enhanced carbon pump efficiencies, possibly also related to increased, dust-driven, mineral ballasting in low latitude regions such as the GOA
06:30 PM
QUANTIFYING THE BIOLOGICAL CARBON PUMP PATHWAYS AROUND THE IBERIAN PENINSULA (4962)
Primary Presenter: Maria Couret, Instituto de Oceanografía y Cambio Global (mariacouhuertas@gmail.com)
Diel Vertical Migration (DVM) of zooplankton and micronekton is a characteristic behavioral pattern in which their vertical distribution varies over the day as a response to predation avoidance. These organisms transport carbon from the surface to the deep layers, thus enhancing the efficiency of the biological carbon pump and sustaining the metabolic requirements of mesopelagic communities. Zooplankton active flux has been addressed in different studies, supporting fluxes equivalent up to 10-30% of particle export. However, the role of micronekton in the active flux is scarcely known, and the capacity of both communities to export carbon is still poorly studied. Here, we show the results of both active (zooplankton and micronekton) and passive fluxes from the Mediterranean Sea to the Atlantic Ocean around the Iberian Peninsula. Passive flux showed that particulate organic carbon (POC) was rather low even in the most productive zones of the Atlantic side. Regarding the active flux, we obtained a close relationship between migrant biomass and respiratory flux for both communities. Zooplankton total flux decreased in the northern Atlantic stations while micronekton flux increased, reaching more than two-times POC values. These results evidence the need to increase active flux estimations by both zooplankton and micronekton communities to better assess the role of the pelagic fauna in the biological carbon pump.
06:30 PM
EFFECT OF ZOOPLANKTON COMMUNITY STRUCTURE ON THE BIOLOGICAL PUMP IN ARCTIC (7362)
Primary Presenter: Marja Koski, Technical University of Denmark (mak@aqua.dtu.dk)
Zooplankton influence the biological pump in multiple ways, including production of sinking particles through fecal pellets, degradation of sinking particles through fragmentation and consumption, and by active carbon transport by daily and seasonal vertical migrations. The importance of these processes varies, depending on the behavioral and metabolic traits of organisms, so that a community dominated by large vertically migrating herbivorous copepods would increase the vertical flux, whereas a community dominated by small aggregate-feeding copepods would contribute to flux attenuation. We investigated the vertical distribution, fecal pellet production and aggregate feeding of large primarily herbivorous calanoids and small aggregate-colonizing copepods in the west coast of Greenland and Davis Strait in summer. We sampled zooplankton at 35 stations, using a Multinet with a 50 µm mesh, and conducted incubations to measure pellet production and aggregate feeding rates. Although the small copepods always dominated zooplankton abundance, the ratio of small vs. large copepods varied by 8-fold between the stations as did the pellet production and feeding rates. Our preliminary results indicate large differences both in proportional abundances of species and pellet production rates between the stations, suggesting that changing environment influences the effect of zooplankton on the biological pump, both through its effect on community composition and through its effect on the metabolic rates of copepods.
06:30 PM
Decreasing the uncertainty in Particulate Organic Carbon (POC) distribution and budgets in the North Atlantic mesopelagic layer (6726)
Primary Presenter: Mª Andrea Orihuela-García, Barcelona Supercomputing Center (andrea.orihuela@bsc.es)
The mesopelagic layer (200-1000m) plays a fundamental role in oceanic carbon sequestration. It also hosts a massive biomass of zooplankton and small fish that feed on sinking detritus (i.e., POC). However, scientific understanding of mesopelagic POC is still underdeveloped due to the numerous processes involved (gravitational sinking, horizontal transport, biological transformations by bacteria and zooplankton…). The objective of this study is to quantify the terms dominating the spatiotemporal variability of the mesopelagic POC budget in different regions of the North Atlantic. The choice of these regions is based on dynamical and biogeochemical criteria. Our analyses are based on numerical simulations performed with the ocean dynamical model NEMO4 (Madec et al. 2008) coupled to the biogeochemical model PISCES-v2 (Aumont et al. 2017). Compared to observations, our model shows biases in mesopelagic POC distribution and fluxes (from spatially distributed bioArgo floats and the sediment trap time series at BATS). Those biases can arise from uncertainties in POC supply from the surface layer and from the representation in mesopelagic processes in the model equations. Improving the model performance at the surface, we expect improving the model performance in the mesopelagic layer. For that, we develop a model sub-routine that allows constraining the model to follow satellite observations, in terms of small and large phytoplankton carbon biomass at the sea surface. Eventually, this enables us to reduce the uncertainty in mesopelagic POC distribution and budget.
06:30 PM
MODEL PARAMETERS THAT CONTROL MESOPELAGIC POC BUDGETS: CONSTRAINTS FROM HIGH RESOLUTION BGC-ARGO DATA AND IMPACT ON POC BUDGETS IN THE LABRADOR SEA (4964)
Primary Presenter: Martí Galí, ICM, CSIC (marti.gali.tapias@gmail.com)
Understanding mesopelagic carbon budgets is central to answering pressing ecological, climatic, and economic questions: from the oceans’ role in carbon sequestration to the transfer of primary production to higher trophic levels. However, biogeochemical models used to simulate and predict mesopelagic carbon budgets still suffer from large uncertainties, which arise in part from poorly constrained parameters. Global ocean biogeochemistry models are typically optimized using climatological fields (e.g., nutrients, oxygen, export fluxes) as observational targets, therefore tuning them to reproduce the long-term mean state of the ocean. Our working hypothesis is that model parameters can be further constrained using high-resolution profiles from biogeochemical (BGC-) Argo floats, using particulate backscattering as a proxy for particulate organic carbon (POC). To test this hypothesis, we selected single-float coherent annual time series in the Labrador Sea (subpolar North Atlantic) and matched them to 1D biogeochemical model simulations (NEMO4-PISCESv2_RC). We then identified the model parameters that control mesopelagic POC budgets to (i) run comprehensive sensitivity analyses via parameter perturbations, (ii) optimize the most sensitive parameters against BGC-Argo observations using a genetic algorithm, and (iii) quantify the impact of parameter optimization on tridimensional POC fluxes. Our approach sheds new light on elusive mesopelagic POC budgets and their modulation by intense events in productive high-latitude oceans.
06:30 PM
Phytoplankton communities vary by depth across a subducted eddy front in the eastern North Atlantic (6097)
Primary Presenter: Katherine Roche, University of Rhode Island (kmroche@uri.edu)
Carbon export following the North Atlantic spring bloom is driven by biological and physical processes. Plankton-derived carbon can be exported from the surface through sinking of cells, aggregates, or fecal pellets. Alternatively, subduction occurring at eddy perimeters transports particulate carbon to depth by physical advection. As part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) North Atlantic field campaign, a coordinated biological, chemical, and physical sampling event took place across the edge of a mesoscale eddy to examine the contribution of eddy subduction to carbon export. During this event, we characterized phytoplankton community composition at varying depths and positions across the eddy front. High throughput sequencing of the eukaryotic 18S rDNA V4 region and a diatom-targeted 18S rDNA region were used to delineate both phytoplankton and diatom community composition in the context of physical water mass properties. Phytoplankton and diatom diversity increased with depth to around 200 m. The highest phytoplankton diversity occurred within a water mass physically characterized as subducted chlorophyll-a. The community composition in this water mass was unique, driven by a higher proportion of sequencing reads from the two diatom genera Chaetoceros and Bacteriastrum. Ongoing integration of the biological and physical datasets will help to reveal whether these taxa were transported via sinking or subduction from the surface, providing a better understanding of carbon export processes in the North Atlantic.
SS087P Biological Pump Dynamics and Trophic Transfer in Pelagic Ecosystems of the Atlantic
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine