Sunlight drives countless photochemical and photobiological transformations that have far-reaching and significant consequences in freshwater, estuarine, and oceanic waters. They affect the surface microlayer and gas exchange, aquatic ecology, particulate, colloidal and dissolved organic matter, primary freshwater and marine aerosols, optics, remote sensing, trace element cycles, xenobiotics (e.g., plastics), and the atmosphere through the production of volatile gases in sunlit surface waters. Recent advances have led to a better understanding of freshwater and marine photochemical and photobiological processes, spanning molecular to global scales; and yet the full impact of climate change and anthropogenic inputs on mechanisms, linkages, and feedbacks that involve aquatic photo-processes are largely unexplored. We welcome submissions in all areas of aquatic photochemistry and photobiology, especially those exploring the potential role of climate change on these processes, their use in remediation and degradation of anthropogenic compounds, and their potential role in observed biogeochemical changes in lakes, rivers, coastal waters, and the ocean.
Lead Organizer: Joanna Kinsey, Quinnipiac University (joanna.kinsey@quinnipiac.edu)
Co-organizers:
David Kieber, State University of New York, College of Environmental Science and Forestry (djkieber@esf.edu)
William Miller, University of Georgia (bmiller@uga.edu)
Heather Reader, Memorial University of Newfoundland (hreader@mun.ca)
Presentations
03:00 PM
PHOTON-DOSE RESOLVED APPARENT QUANTUM YIELDS FOR THE TRANSFORMATION OF BIOLOGICALLY LABILE DISSOLVED ORGANIC MATTER (7208)
Primary Presenter: Heather Reader, Memorial University of Newfoundland (hereader@gmail.com)
Photochemical reactions play a complex role in the turnover of dissolved organic matter (DOM) in aquatic systems. While processes leading to the production or destruction of defined chemical species (i.e., CO, CO2, DMS) are relatively straightforward to quantify, photochemical reactions also lead to broad scale oxidation of the DOM pool and can alter its biological lability which can be challenging to to assess.The balance between photochemical enhancement and photochemical reduction of the lability of the DOM pool is a balance between the activity of photons and the activity of microbes. Experimental conditions that preclude the inclusion of microbes directly require high resolution and low photon doses in order to provide accurate assessments of the effect photochemistry has on biological substrates. Apparent quantum yields (AQYs) for the transformation of biologically labile DOM were calculated for three different total photon doses on a coastal water sample (Newfoundland, Canada). Samples were irradiated in a custom broadband irradiation set-up in quadruplicate 40-mL amber glass vials with 7 different long-pass cutoff filters. After irradiation, the samples were spiked with inorganic nutrients to induce carbon limitation, and an aliquot of the original microbial community was added. Biologically labile DOM was quantified as biological oxygen demand (BOD) over 14-days incubation using Winkler titrations. Results show the importance of high-resolution photon dose experiments with variable effects on spectral AQYs and total BOD as photon-dose increased.
03:15 PM
EXAMINING THE LIGHT-DEPENDENT REACTIVITY OF SUPEROXIDE IN SUNLIT WATERS (7119)
Primary Presenter: Leanne Powers, State University of New York College of Environmental Science and Forestry (lcpowers@esf.edu)
Superoxide dynamics in aquatic systems have been of interest for many years because superoxide participates in a suite of redox reactions critical in many biogeochemical cycles. Because superoxide can act as both an oxidant (producing hydrogen peroxide) and a reductant (returning to the dissolved oxygen pool), our understanding of its complex reactivity and fate in natural waters remains incomplete. The photoproduction of superoxide from chromophoric dissolved organic matter (CDOM) has been well studied, but most photoproduction estimates rely on measurements of superoxide steady-state concentrations and dark-decay decay rates. However, in sunlit waters, regardless of superoxide source (i.e., photochemistry or biology), superoxide may be impacted by reactions with short-lived photoproduced transients that are missed by solely examining superoxide decay in the dark. In this work, we investigated superoxide kinetics ‘in the light’ by monitoring the decay of nanomolar superoxide additions during irradiation experiments. Superoxide decayed more rapidly during irradiation when compared to superoxide decay in the dark, suggesting the presence of a light-dependent sink. A wavelength dependence of the light-dependent sink was also demonstrated, whereby superoxide decay rates decreased with increasing wavelength cut-off filter. Thus, understanding light-dependent sinks for superoxide should have significant impacts on the modeling of superoxide cycling in natural waters, especially those with significant penetration of solar radiation.
03:30 PM
MODELING MARINE HYDROGEN PEROXIDE PHOTOPRODUCTION GLOBALLY (7190)
Primary Presenter: David Kieber, State University of New York, College of Environmental Science and Forestry (djkieber@esf.edu)
Hydrogen peroxide (H2O2) is an important reactive oxygen species (ROS) in seawater, affecting water quality via participation in metal redox reactions and causing oxidative stress in marine ecosystems. While attempts have been made to better understand H2O2 dynamics in seawater, the relative importance of various H2O2 sources and losses remains uncertain. We developed a model to estimate photochemical H2O2 production rates using remotely sensed ocean color to characterize the ultraviolet (UV) radiation field in surface waters along with published apparent quantum yield (AQY) data for the photochemical formation of H2O2. Model inputs included temperature- and wavelength-dependent AQY, modeled solar irradiance, satellite-derived surface seawater temperature and UV optical properties; diffuse attenuation coefficients and dissolved organic matter absorption coefficients were estimated with remote sensing-based algorithms. The final model product, a monthly climatology of depth-resolved H2O2 photoproduction rates in the surface mixed layer, yields an integrated global estimate of ~21.1 Tmol yr-1 for photochemical H2O2 production. To evaluate our predictions of H2O2 photoproduction in surface waters, we compared modeled rates to measured rates from several stations in the NW Atlantic; comparative differences of 33% or less. This work has important implications for photo-redox reactions in seawater and improves our understanding of the role of solar irradiation on ROS cycling and the overall oxidation state in the oceans.
03:45 PM
CAROTENOID STRUCTURE IS LINKED TO LIFE STRATEGY IN PHYTOPLANKTON (5002)
Primary Presenter: Bruno Cremella, Université de Sherbrooke (brunocremella@gmail.com)
Phytoplankton exhibit a high diversity of carotenoids, yet most of them are broadly labeled as photoprotective and antioxidants indistinctly, constituting somewhat of a paradox. Comparative photochemistry of carotenoids has revealed structural trade-offs linked to specialized cellular roles that vary in prevalence across life strategies such as the CSR: organisms with co-adapted traits optimized to forcings of competition for resources (Competitive, C), constraints on production (Stress-tolerants, S), and disturbances (Ruderals, R). Here, we hypothesize that different life strategies of phytoplankton prioritize different structure-derived cellular roles of carotenoids: Ruderals with carotenoids that efficiently redirect and dissipate the energy flux (NPQ) in the large light gradient of mixed water columns; Stress-tolerants with high 3chl and 1O2 (oxidative excited states) quenching carotenoids to minimize photodamage under nutrient depletion; and Competitors with free radical quenching carotenoids to deal with the oxidative conditions of high light driven photosynthesis. We classified the carotenoids into cellular roles based on structure and tested their link to life strategies in lake phytoplankton and cultures. R-strategists had elevated NPQ and light harvesting carotenoid fractions; S-strategists had more 1O2 and 3chl quenchers; free radical quenchers were present in C-cultures and CSR-balanced lakes; and 3chl quenchers were predominant in C-strategists. Overall, we found support that the carotenoid groups reflect the organismal life strategies relationship to light.
04:00 PM
PHOTOSENSITIVITY OF FLUORESCENT DISSOLVED ORGANIC MATTER ACROSS THE ARCTIC OCEAN (6476)
Primary Presenter: Urban Wuensch, Technical University of Denmark (urbw@aqua.dtu.dk)
The Arctic Ocean exports a large amount of terrestrial dissolved organic matter (tDOM) to the Nordic seas. Climate change is projected to increase the supply of tDOM but sea ice retreat might lead to a simultaneous loss of tDOM due to intensifying photodegradation. While the DOM abundance can be estimated quickly via optical properties, quantifying DOM photodegradation requires experiments that last between one and ten days. Here, we simulated sunlight exposures of samples from the Siberian Shelf, Central Arctic Ocean, and Fram Strait. On average, 51 % of peak C fluorescence and 33 % of absorbance (350 nm) was lost due to photobleaching while no photomineralization was detectable. A N-way partial least squares model was trained to predict the proportion of photodegradable DOM fluorescence (“photosensitivity index”, PI) from the unexposed fluorescence landscapes. The prediction root mean squared error was 0.03 (4.8 % of the average PI). We then applied the model to > 1500 samples spanning from the Lena River plume to the East Greenland Shelf and observed an accumulation of photosensitive DOM (high PI) at depth. DOM in the mixed layer was often distinctly photobleached (low PI). The photosensitivity of tDOM in polar surface water did not change significantly until the material was exported to Fram Strait. Our findings indicate that fluorescence-based estimates of photobleaching offer valuable insights into the occurrence of photodegradation.
04:15 PM
THE PHOTOPHYSIOLOGICAL FINGERPRINTS OF LONG-TERM CHANGE: PHYTOPLANKTON ACCLIMATION ALONG A WARMING WEST ANTARCTIC PENINSULA (5444)
Primary Presenter: Quintin Diou-Cass, Rutgers University (qpd1@marine.rutgers.edu)
The West Antarctic Peninsula (WAP) provides an ideal natural laboratory to observe how climate change will alter biophysical interactions in the upper ocean. Namely, the coastal WAP exhibits some of the most rapid warming on Earth, headlined by accelerated melting of glaciers and profound disturbance of seasonal sea ice cycles. These changes are in turn associated with distinct, cascading perturbations throughout the food web from algae to penguins. Using two decades of time series data collected by the Palmer Long Term Ecological Research (LTER) program, we assessed if there were any trended changes in the photobiology and growth of phytoplankton communities associated with interdecadal change in the WAP. Our findings reveal a distinct, ecosystem-wide shift in algal photobiology, with a significant increase in the proportion of accessory pigments over 25 years. Most notably, we quantified a near doubling of photoprotective carotenoids in the algal community since 1995, coincident with a shoaling of surface ocean mixed layer depths and a boost in algal biomass and productivity. Our time series shows a persistent shallowing of the upper mixed layer that is accompanied by widespread photoacclimation of the resident phytoplankton communities towards a more high-light adapted state. This implies a beneficial shift in the prevailing biophysical conditions of the region, likely with far-reaching implications for the ecosystem’s biogeochemical function, and supports other studies that suggest light limitation as a primary driver of primary productivity in this region.
SS108 Impacts of Aquatic Photochemistry and Photobiology in a Changing World
Description
Time: 3:00 PM
Date: 5/6/2023
Room: Sala Palma