Oxygen and indicators of stress for marine life in multi-model global warming projections

Abstract

Decadal-to-century scale trends for a range of marine environmental variables in the upper mesopelagic layer (UML, 100–600 m) are investigated using results from seven Earth System Models forced by a high greenhouse gas emission scenario. The models as a class represent the observation-based distribution of oxygen (O2) and carbon dioxide (CO2), albeit major mismatches between observation-based and simulated values remain for individual models. By year 2100 all models project an increase in SST between 2 °C and 3 °C, and a decrease in the pH and in the saturation state of water with respect to calcium carbonate minerals in the UML. A decrease in the total ocean inventory of dissolved oxygen by 2% to 4% is projected by the range of models. Projected O2 changes in the UML show a complex pattern with both increasing and decreasing trends reflecting the subtle balance of different competing factors such as circulation, production, remineralization, and temperature changes. Projected changes in the total volume of hypoxic and suboxic waters remain relatively small in all models. A widespread increase of CO2 in the UML is projected. The median of the CO2 distribution between 100 and 600m shifts from 0.1–0.2 mol m−3 in year 1990 to 0.2–0.4 mol m−3 in year 2100, primarily as a result of the invasion of anthropogenic carbon from the atmosphere. The co-occurrence of changes in a range of environmental variables indicates the need to further investigate their synergistic impacts on marine ecosystems and Earth System feedbacks

Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models

“…For RCP8.5, this translates into a −9.03 (±1.15) Tmol O 2 or −6.13 (±0.78) mmol m −3 decrease in the 2090s relative to the 1990s, based on the reference global O 2 inventory from WOA 2009. This long-term decline in O 2 inventory is a consistent trend simulated in many coupled climate-marine biogeochemical models (e.g., Sarmiento et al, 1998) -2099 (compared to 1990-1999) simulated rates of deoxygenation in the CMIP5 models under RCP8.5 are quite similar to those reported in a previous model intercomparison study (−2 to −4 %) of seven models under the SRES-A2 scenario (Cocco et al, 2013). The model spread is limited (moderate uncertainty) largely because the global O 2 inventory is an integrated quantity with low interannual variability (Fig.…”

“…Apart from changes in the equatorial Pacific, these regional changes in subsurface O 2 are consistent across models under the RCP8.5 scenario (stippling in Fig. 5), and they are quite similar to those from a recent inter-model comparison of the previous generation of Earth system models (Cocco et al, 2013).…”

“…In a recent intercomparison of seven Earth system models, Cocco et al (2013) found that the oceanic O 2 inventory would decline by 2-4 % in 2100 under SRES-A2, an earlier IPCC scenario similar to the RCP8.5 scenario used here.…”

Time of emergence of trends in ocean biogeochemistry

“…We note that by also applying the linear trend from the 1970 to 1999 period in the future, any changes in trends are not explicitly accounted for. Changes in trends are likely to remain relatively small in the next few decades, but trends will differ considerably between business-as-usual and stringent mitigation scenarios by the end of this century (e.g., Steinacher et al, 2009;Cocco et al, 2013;Bopp et al, 2013). For N , the standard deviation (SD) over the entire simulation, 1870-1999, is used.…”

Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific oceans

“…Modeling results Cocco et al, 2013) predict that O 2 levels will decrease significantly over the next decades in response to climate change and eutrophication. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the possible expansion and intensification of tropical OMZs (Codispoti, 2010).…”