Long-term ocean oxygen depletion in response to carbon dioxide emissions from fossil fuels

Climate sensitivity measures the response of Earth's surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth's climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO 2 solubility, which in turn leads to higher atmospheric CO 2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000-165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO 2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene-Eocene Thermal Maximum.

“…My results suggest a longer lifetime of human-induced future warming than previous studies (15,(38)(39)(40)(41) (Fig. 2B).…”

Section: Resultscontrasting

confidence: 55%

Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions

Zeebe

2013

“…Models have predicted their expansion in response to global warming, both as a result of reduced oxygen solubility at higher temperatures and from an increased water-column stratification resulting from stronger temperature gradients in the upper waters (69,70). Examination of a 50-y dissolved oxygen database suggests such an expansion (12), which should continue well into the future (13). The increasing deposition of atmospheric anthropogenically fixed nitrogen on the open ocean (71) is also expected to contribute to AMZ expansion and intensification, and eventually to the development of sulfidic conditions.…”

Section: Amzs In the Anthropocenementioning

confidence: 99%

“…Climate-induced warming of the upper ocean appears to have already contributed to deoxygenation of the global ocean (10,11) and to an expansion of OMZ waters (12). This trend is expected to increase into the future (13), expanding the AMZ area and influencing rates of fixed nitrogen loss from the oceans.…”

mentioning

confidence: 99%

Microbial oceanography of anoxic oxygen minimum zones

Ulloa

Canfield

DeLong

et al. 2012

386

403

Vast expanses of oxygen-deficient and nitrite-rich water define the major oxygen minimum zones (OMZs) of the global ocean. They support diverse microbial communities that influence the nitrogen economy of the oceans, contributing to major losses of fixed nitrogen as dinitrogen (N 2 ) and nitrous oxide (N 2 O) gases. Anaerobic microbial processes, including the two pathways of N 2 production, denitrification and anaerobic ammonium oxidation, are oxygen-sensitive, with some occurring only under strictly anoxic conditions. The detection limit of the usual method (Winkler titrations) for measuring dissolved oxygen in seawater, however, is much too high to distinguish low oxygen conditions from true anoxia. However, new analytical technologies are revealing vanishingly low oxygen concentrations in nitriterich OMZs, indicating that these OMZs are essentially anoxic marine zones (AMZs). Autonomous monitoring platforms also reveal previously unrecognized episodic intrusions of oxygen into the AMZ core, which could periodically support aerobic metabolisms in a typically anoxic environment. Although nitrogen cycling is considered to dominate the microbial ecology and biogeochemistry of AMZs, recent environmental genomics and geochemical studies show the presence of other relevant processes, particularly those associated with the sulfur and carbon cycles. AMZs correspond to an intermediate state between two "end points" represented by fully oxic systems and fully sulfidic systems. Modern and ancient AMZs and sulfidic basins are chemically and functionally related. Global change is affecting the magnitude of biogeochemical fluxes and ocean chemical inventories, leading to shifts in AMZ chemistry and biology that are likely to continue well into the future.

“…Past changes in OMZ intensity (45) and the resulting effects on seafloor benthic biodiversity provide an interpretive precedent to understand the capacity for substantial and long-term ecosystem disturbance to accompany future oceanic oxygen loss (1,2). Previous deoxygenation events dwarf modern scales of ecological disturbance (42) and illustrate the nonanalog nature of environmental disturbance in the recent geologic past.…”

Section: Mv0811-15jc Biotic Recordmentioning

confidence: 99%

“…The global ocean inventory of oxygen is predicted to decline between 1% and 7% by the year 2100, and modeling predictions reveal extensive oceanic deoxygenation, on thousand-year timescales, under "business-as-usual" carbon emission scenarios (2). Modern oceanographic time series already document rapid loss of [O 2 ] in interior ocean waters over the last 4 decades (3,4), although this trend is complicated in regions where [O 2 ] demand is decreased through the slackening of trade winds (5).…”

mentioning

confidence: 99%

Response of seafloor ecosystems to abrupt global climate change

Moffitt

Hill

Roopnarine

et al. 2015

Anthropogenic climate change is predicted to decrease oceanic oxygen (O 2 ) concentrations, with potentially significant effects on marine ecosystems. Geologically recent episodes of abrupt climatic warming provide opportunities to assess the effects of changing oxygenation on marine communities. Thus far, this knowledge has been largely restricted to investigations using Foraminifera, with little being known about ecosystem-scale responses to abrupt, climate-forced deoxygenation. We here present high-resolution records based on the first comprehensive quantitative analysis, to our knowledge, of changes in marine metazoans (Mollusca, Echinodermata, Arthropoda, and Annelida; >5,400 fossils and trace fossils) in response to the global warming associated with the last glacial to interglacial episode. The molluscan archive is dominated by extremophile taxa, including those containing endosymbiotic sulfur-oxidizing bacteria (Lucinoma aequizonatum) and those that graze on filamentous sulfur-oxidizing benthic bacterial mats (Alia permodesta). This record, from 16,100 to 3,400 y ago, demonstrates that seafloor invertebrate communities are subject to major turnover in response to relatively minor inferred changes in oxygenation (>1.5 to <0.5 mL·L −1 [O 2 ]) associated with abrupt (<100 y) warming of the eastern Pacific. The biotic turnover and recovery events within the record expand known rates of marine biological recovery by an order of magnitude, from <100 to >1,000 y, and illustrate the crucial role of climate and oceanographic change in driving long-term successional changes in ocean ecosystems.seafloor ecosystems | abrupt climate change | deglaciation | oxygen minimum zone | metazoans O ceanic deoxygenation is a predictable, fundamental, and long-lasting property of anthropogenic climate change (1). The global ocean inventory of oxygen is predicted to decline between 1% and 7% by the year 2100, and modeling predictions reveal extensive oceanic deoxygenation, on thousand-year timescales, under "business-as-usual" carbon emission scenarios (2). Modern oceanographic time series already document rapid loss of [O 2 ] in interior ocean waters over the last 4 decades (3, 4), although this trend is complicated in regions where [O 2 ] demand is decreased through the slackening of trade winds (5). As oxygen levels in the ocean decrease and the already extensive oxygen minimum zones (OMZs) expand, the volumetric habitat for aerobic respiration is reduced, presumably resulting in a fundamental reorganization of marine communities. Past events of climate warming and OMZ expansion, including the recent deglaciation from 18 to 11 ka, provide a case study for understanding the effects on marine ecosystems of abrupt temperature and oxygenation changes.Paleoceanographic records clearly demonstrate that OMZ strength changed in response to