Biology subjects

Kelly, T. B.

Publications and source records attributed to Kelly, T. B..

5 recordsLinked to original sources

bioRxiv2025

Analysis of environmental data during a lagrangian experiment: The influence of vertical movements.

Investigating the time evolution of physical and biochemical properties of the ocean with in situ sampling can follow two approaches: Eulerian and Lagrangian. In the Eulerian approach, repeated measurements are taken at fixed locations, whereas the sampling point moves with the displacement of a water parcel in the Lagrangian approach. During the BLOOFINZ-IO cruise off northwest Australia, four Lagrangian experiments ("cycles") were conducted with multidisciplinary sampling done at regular intervals for several days following a satellite tracked drifter with mixed-layer drogue. To test the Lagrangian nature of these experiments, we adapted the Bindoff and McDougall (1994) approach for decomposing observed changes between adjacent CTD profiles into components due to vertical movement (heaving) and those occurring along isopycnal surfaces. Profile depth variability was mainly driven by vertical displacements of isopycnals (internal waves), while temperature, chlorophyll, oxygen and salinity were relatively stable when observed on isopycnal surfaces across all casts within the same cycle, and different on average between cycles. Our analysis clearly indicated that density surface was a more appropriate vertical coordinate than physical depth for assessing real environmental variability during each cycle and confirmed the Lagrangian character of the experiments. While the BLOOFINZ cruise serves as a case study, the methodology can be readily extended to analyze other biochemical variables in different ocean regions.

ecology↗

bioRxiv2025

Sinking particle export within and beneath the euphotic zone in the eastern Indian Ocean

The eastern Indian Ocean is substantially under sampled with respect to the biological carbon pump - the suite of processes that transport the carbon fixed by phytoplankton into the deeper ocean. Using sediment traps and other ecosystem measurements, we quantified sinking organic matter flux and investigated the characteristics of sinking particles in waters overlying the Argo Abyssal Plain directly downstream of the Indonesian Throughflow off northwest Australia. Carbon export from the euphotic zone averaged 7.0 mmol C m-2 d-1, which equated to an average export efficiency (export / net primary production) of 0.17. Sinking particle flux within the euphotic zone (beneath the mixed layer, but above the deep chlorophyll maximum) averaged slightly higher than flux at the base of the euphotic zone, suggesting that the deep euphotic zone was a depth stratum of net particle remineralization. Carbon flux attenuation continued into the twilight zone with a transfer efficiency (export at euphotic depth + 100m / export at euphotic depth) of 0.62 and an average Martins b-value of 1.1. Within the euphotic zone, fresh phytoplankton (chlorophyll associated with sinking particles, possibly contained within appendicularian houses) were an important component of sinking particles, but beneath the euphotic zone the fecal pellets of herbivorous zooplankton (phaeopigments) were more important. Changes in carbon and nitrogen isotopic composition with depth further reflected remineralization processes occurring as particles sank. We show similarities with biological carbon pump functioning in a similar semi-enclosed oligotrophic marginal sea, the Gulf of Mexico, including net remineralization across the deep chlorophyll maximum. Submitted to: Deep-sea Research II HighlightsDespite low productivity, export efficiency was 17% of primary production Flux attenuation beneath the euphotic zone (EZ) was low for a tropical region Sinking particle flux from the upper to lower EZ exceeded export from lower EZ The deep EZ was a stratum of net particle remineralization (and net heterotrophy)

ecology↗

bioRxiv2023

Strong and efficient biological carbon pump in the Northern Gulf of Alaska during summer

Sinking marine particles, one pathway of the biological carbon pump, transport carbon to the deep ocean from the oceans surface, thereby contributing to atmospheric carbon dioxide modulation and benthic food supply. Few in situ measurements exist of sinking particles in the Northern Gulf of Alaska (NGA); therefore, regional carbon flux prediction is poorly constrained. In this study, we aim to (1) characterize the magnitude and efficiency of the biological carbon pump and (2) identify drivers of carbon flux in the NGA. We deployed drifting sediment traps to simultaneously collect bulk carbon and intact sinking particles in polyacrylamide gels and measured net primary productivity from deck-board incubations. Through deployments during the summer of 2019, we found high carbon flux magnitude, low attenuation with depth, and high export efficiency. We quantitatively attributed carbon flux between ten particle types, including various fecal pellet categories, dense detritus, and aggregates using polyacrylamide gels. The contribution of aggregates to total carbon flux (41 - 93%) and total carbon flux variability (95%) suggests that aggregation processes, not zooplankton repackaging, played a dominant role in carbon export during the summer of 2019 in the NGA. Furthermore, efficient export correlated significantly with the proportion of chlA > 20 {micro}m, total aggregate flux, and proportion aggregate flux. These results suggest that this stratified, small-cell-dominated ecosystem can have sufficient aggregation to allow for a strong and efficient biological carbon pump. These are the first measurements of carbon flux and the first integrative description of the BCP in this region. Significance StatementO_ST_ABSNovelty and significanceC_ST_ABSWe use a comprehensive approach that brings together sediment trap sampling and imaging, optically measured distribution of sinking and suspended particles, and incubations to make the first description of the biological carbon pump in the Northern Gulf of Alaska. We found high carbon flux magnitude, low attenuation with depth, and high export efficiency with a phytoplankton community consisting of mostly pico-and nanoplankton. Notably, just 25% of carbon flux out of the euphotic zone was as recognizable fecal pellets; instead, we demonstrate that aggregation processes were the main driver of carbon flux. Additionally, size-fractionated chlorophyll-a (> 20 {micro}m) strongly correlated with export efficiency across our region. These results lead us to question our expectations about what conditions and processes can create strong and efficient flux events in the Gulf of Alaska. Breadth of InterestThis study is the first description of the biological carbon pump in the Northern Gulf of Alaska and greatly improves biogeochemical constraints on this system. We report observed primary production, carbon flux, export ratio, carbon flux attenuation, and carbon flux by 10 particle types, which can be used to test regional climate models. This study builds on previous studies published in L&O: Strom et al. 2007; Ebersbach & Trull 2008; McDonnell & Buesseler 2010, 2012; and Durkin et al. 2016. Author contribution statementSO, SS, and AM: conceptualization, methodology, and investigation. SS, AM, GH: funding acquisition and project administration. SO, TK, AM: formal analysis. GH, TK, and AM: supervision. SO: visualization, writing-original draft preparation. SO, GH, TK, SS, and AM: writing-reviewing and editing.

biochemistry↗

bioRxiv2021

Taxon-specific phytoplankton growth, nutrient utilization, and light limitation in the oligotrophic Gulf of Mexico

The highly stratified, oligotrophic regions of the oceans are predominantly nitrogen limited in the surface ocean and light limited at the deep chlorophyll maximum (DCM). Hence, determining light and nitrogen co-limitation patterns for diverse phytoplankton taxa is crucial to understanding marine primary production throughout the euphotic zone. During two cruises in the deep-water Gulf of Mexico, we measured primary productivity (H13CO3-), nitrate uptake (15NO3-), and ammonium uptake (15NH4+) throughout the water column. Primary productivity declined with depth from the mixed-layer to the DCM, averaging 27.1 mmol C m-2 d-1. The fraction of growth supported by NO3- was consistently low, with upper euphotic zone values ranging from 0.01 to 0.14 and lower euphotic zone values ranging from 0.03 to 0.44. Nitrate uptake showed strong diel patterns (maximum during the day), while ammonium uptake exhibited no diel variability. To parameterize taxon-specific phytoplankton nutrient and light utilization, we used a data assimilation approach (Bayesian Markov Chain Monte Carlo) including primary productivity, nutrient uptake, and taxon-specific growth rate measurements. Parameters derived from this analysis define distinct niches for five phytoplankton taxa (Prochlorococcus, Synechococcus, diatoms, dinoflagellates, and prymnesiophytes) and may be useful for constraining biogeochemical models of oligotrophic open-ocean systems.

plant biology↗

bioRxiv2020

Plankton food webs of the Gulf of Mexico spawning grounds of Atlantic Bluefin tuna

We used linear inverse ecosystem modeling techniques to assimilate data from extensive Lagrangian field experiments into a mass-balance constrained food web for the Gulf of Mexico open-ocean ecosystem. This region is highly oligotrophic, yet Atlantic Bluefin Tuna (ABT) travel long distances from feeding grounds in the North Atlantic to spawn there. Our results show that the food web is dominated by the microbial loop (>80% of net primary productivity is respired by heterotrophic bacteria and protists that feed on them). In contrast, herbivorous food web pathways from phytoplankton to metazoan zooplankton process <4% of net primary production in the mixed layer. Nevertheless, ABT larvae feed preferentially on calanoid copepods and other suspension-feeding zooplankton that in turn derive much of their nutrition from diatoms and mixotrophic flagellates. This allows ABT larvae to maintain a comparatively low trophic level ([~]4.0 for pre-flexion larvae; [~]4.2 for post-flexion larvae) that increases trophic transfer from phytoplankton to larval fish.

ecology↗