Paleoceanographic Insights on Recent Oxygen Minimum Zone Expansion: Lessons for Modern Oceanography

Abstract

Climate-driven Oxygen Minimum Zone (OMZ) expansions in the geologic record provide an opportunity to characterize the spatial and temporal scales of OMZ change. Here we investigate OMZ expansion through the global-scale warming event of the most recent deglaciation (18-11 ka), an event with clear relevance to understanding modern anthropogenic climate change. Deglacial marine sediment records were compiled to quantify the vertical extent, intensity, surface area and volume impingements of hypoxic waters upon continental margins. By integrating sediment records (183-2,309 meters below sea level; mbsl) containing one or more geochemical, sedimentary or microfossil oxygenation proxies integrated with analyses of eustatic sea level rise, we reconstruct the timing, depth and intensity of seafloor hypoxia. The maximum vertical OMZ extent during the deglaciation was variable by region: Subarctic Pacific (~600-2,900 mbsl), California Current (~330-1,500 mbsl), Mexico Margin (~330-830 mbsl), and the Humboldt Current and Equatorial Pacific (~110-3,100 mbsl). The timing of OMZ expansion is regionally coherent but not globally synchronous. Subarctic Pacific and California Current continental margins exhibit tight correlation to the oscillations of Northern Hemisphere deglacial events (Termination IA, Bølling-Allerød, Younger Dryas and Termination IB). Southern regions (Mexico Margin and the Equatorial Pacific and Humboldt Current) exhibit hypoxia expansion prior to Termination IA (~14.7 ka), and no regional oxygenation oscillations. Our analyses provide new evidence for the geographically and vertically extensive expansion of OMZs, and the extreme compression of upper-ocean oxygenated ecosystems during the geologically recent deglaciation.

Sedimentary pyrite δ34S differs from porewater sulfide in Santa Barbara Basin: Proposed role of organic sulfur

“…This analysis yields MSR rates that are comparable with those of Reimers et al in the upper 10 cm but slower in deeper sediments. We convert sediment depths to approximate ages using an age model based on density profiles and varve counts from Schimmelmann et al (1990; Basin bottom waters (<10 µM, (Sholkovitz, 1973;Moffitt et al, 2015)), we attribute the majority of this DIC to the respiration of organic carbon by MSR with potential smaller contributions from anaerobic heterotrophy using nitrate, iron, or manganese (porewater nitrate concentrations are <80µM, (Reimers et al, 1996)) and fermentation. Surface sediments also contain 228 ± 23 µmol/g solid-phase reduced sulfur, including pyrite, Estimates of minimum MSR rates in zone 1 (at the multicore site) of >2.6 mM/yr are consistent with prior estimates of 2 to 10 mM/yr (Reimers et al, 1996).…”

The Ecological Physiology of Earth's Second Oxygen Revolution

“…OMZs intersect the seafloor over large areas of continental margins (Helly & Levin 2004) and thus provide natural oxygen gradients that can be used to study how animal communities respond to different oxygen levels. The major OMZs are geologically long-lasting features (Levin 2003, Jacobs et al 2004, so the animals that inhabit them are well adapted to low-oxygen conditions (locally, OMZs are dynamic on glacial-interglacial timescales; Moffitt et al 2015).…”

Response of seafloor ecosystems to abrupt global climate change

“…S4). During this time, ocean and climate changes led to abrupt reorganization of the vertical zonation of ecosystems on the continental margin through the expansion of the OMZ (20,44,45). Long-term (>1,000 y) ecosystem recovery is demonstrated in the Younger Dryas oxygenation reversal, wherein differences in trophic structures and physiological adaptations, from chemosynthetic extremophiles to motile carnivores and deposit feeders, determine the successional process and its timing.…”