The ocean is currently rapidly losing oxygen. In the open ocean, this change is mostly attributed to global warming and associated circulation changes, whereas in coastal waters, anthropogenic eutrophication is typically the key driver. Ocean deoxygenation has major impacts on marine life and on the cycling of bio-active elements such as carbon, nitrogen, phosphorus, sulfur and trace metals, that, in turn, can feed back on ocean deoxygenation. Thus, for example, oxygen loss can reduce the habitat of pelagic and benthic animals and can greatly enhance rates of marine nitrogen removal and amplify phosphorus recycling. Strongest effects have so far been reported for Oxygen Minimum Zones and coastal systems that are naturally sensitive to hypoxia linked to water column stratification, which might be affected by sampling biases in the heavily undersampled ocean. Ocean deoxygenation has frequently occurred in Earth’s past, thereby also impacting the evolution of marine organisms. In this session, we invite presentations related to all aspects of deoxygenation in the past, present and future ocean. Hence, we invite modeling, field and laboratory studies on the drivers and consequences of loss of oxygen in marine waters on all spatial and temporal scales. This includes, for example, observational studies in the modern coastal and open ocean, results of Earth System Modeling and reports on the development and application of redox proxies for all relevant periods of Earth’s history (e.g. Oceanic Anoxic Events).
Lead Organizer: Caroline P. Slomp, Utrecht University (c.p.slomp@uu.nl)
Co-organizers:
Marilaure Grégoire, University of Liege (mgregoire@ulg.ac.be)
Andreas Oschlies, GEOMAR Helmholtz Centre for Ocean Research Kiel (aoschlies@geomar.de)
Peter Croot, University of Galway (peter.croot@nuigalway.ie)
Presentations
06:30 PM
Scaling deoxygenation impacts from individual fish consumption, activity, and metabolism (5843)
Primary Presenter: Jonathan Eric Falciani, Technical University of Denmark (jonathan.e.falciani@gmail.com)
Projections place the decline in the global ocean dissolved oxygen inventory at 1 to 7% by 2100, threatening marine community structure, species distributions, and biogeochemical cycling. Previous studies have used species assemblages to mechanistically predict the physiological and biogeographical effects of ocean oxygen limitation. However, this limits predictions to species whose hypoxic tolerance has been characterized in relation to temperature and oxygen concentration. Our study establishes a systematic metabolic relationship between oxygen demand, carbon consumption, and traits associated with functional fish guilds across species. This allows us to assess the energy and respiration contributing to size-at-age, reproduction, and activity for fish communities in a warming, deoxygenating seascape. We aim to scale these individual oxygen and carbon budgets using a size- and trait-based fish community model to resolve emergent community properties under ocean deoxygenation projections. We expect the results to show ocean deoxygenation reduces average individual size and compresses available vertical and geographic habitat.
06:30 PM
Oxygen variability off Southern California Bight: Correlated structures with season, climate indies, and linear trend (4661)
Primary Presenter: Sung Yong Kim, Korea Advanced Institute of Science and Technology (syongkim@kaist.ac.kr)
A coastal ocean climatology of oxygen in the Southern California Bight is estimated from oxygen sample profiles collected by historical California Cooperative Oceanic Fisheries Investigation (CalCOFI) cruises (1950–2009; quarterly after 1984) off southern California and quarterly/monthly nearshore CTD surveys (within 30 km from the coast except for the surfzone; 1999–2009) off San Diego and Los Angeles. The oxygen time series are decomposed into linear combinations of an annual cycle and its five harmonics, as well as three standard climate indices (El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO)), the Scripps Pier temperature time series, and a mean and linear trend without time lags. Following the multivariate regression in Kim and Cornuelle [2015], the basis functions are prepared with successively orthogonalized to eliminate ambiguity and overlapped variance in the identification of the contributed variance of each component. The regression coefficients are used to examine the near-shore and offshore variability of oxygen and consistency in a view of vertical transects.
06:30 PM
THE INFLUENCE OF REMINERALIZATION ON THE EQUATORIAL PACIFIC ODZ IN THE NASA-GISS MODEL E2.1 (5430)
Primary Presenter: Paul Lerner, Columbia University (pedmondlerner@gmail.com)
Global warming has resulted in the inventory of marine dissolved oxygen declining by ~2% over the past several decades (Schmidtko et al., 2017; Oschlies et al., 2018), and this decline is projected to continue throughout the 21st century (Kwiatkowski et al., 2020). This deoxygenation has resulted in an expansion of tropical oxygen deficient zones (ODZs; Stramma et al., 2008), potentially altering both the habitable zones of marine organisms and rates of biogeochemical transformations. Remineralization is a key process controlling the volume of the ODZs. Remineralization is represented in all CMIP6 models, but the actual parameterizations, as well as their magnitudes, are widely varying. Here we examine the sensitivity to remineralization of the equatorial Pacific in the NASA-GISS climate model. We find a near-linear, negative relationship between ODZ volume, onset depth, and thickness and remineralization rate. These sensitivities are driven by (i) an increase in biological oxygen consumption and decrease in vertical oxygen convergence in the upper-ocean, and (ii) a decrease in biological oxygen consumption in the deep ocean, with increasing remineralization. On the other hand, the ODZ area has a more complex, non-monotonic relationship with maximum remineralization rate. These findings may suggest that models with higher remineralization rates should expect ODZs that are shallower but of reduced volume and thickness, though the relative importance of remineralization vs. other physical parameterizations remains to be established.
06:30 PM
Past ocean deoxygenation – Lessons from the Mesozoic Oceanic Anoxic Events (5456)
Primary Presenter: Fanny Monteiro, University of Bristol (f.monteiro@bristol.ac.uk)
The ocean has experienced intense deoxygenations over the last 250 million years, with evidence of global anoxia during the Mesozoic, called Oceanic Anoxic events (OAEs). OAEs are characterised by widespread depositions of organic-carbon-rich sediments and are associated with increased volcanic activity (causing high atmospheric CO2, warming and eutrophication via enhanced weathering). Due to biogeochemical interactions, these past ocean deoxygenations impacted the nutrient cycles and marine ecosystem, strongly influencing the ocean nitrogen system. Estimating OAEs triggers and potential consequences can help us understand the impact of global warming on ocean oxygen levels and their coupling with other biogeochemical and ecological processes. Here, we apply an Earth System Model of intermediate complexity (cGEnIE) to 1) reconstruct the state of ocean deoxygenation during OAEs, 2) quantify the triggers of global anoxia (comparing temperature versus nutrient effect), and 3) assess the OAEs impact on the ocean nitrogen cycle and its ecology. We compare model sensitivity experiments with paleo-observations to accurately reconstruct the ocean state in oxygen and nutrient levels and contrast the OAEs with modern climate and other key paleo-ocean events. We conclude that OAEs were associated with dramatic changes in marine nutrients, oxygen and ecology, revealing stronger (while slower) perturbations than predicted in the future.
SS015P Deoxygenation in the Past, Present and Future Ocean
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine