Decrease of dissolved oxygen after the mid‐1980s in the western North Pacific subtropical gyre along the 137°E repeat section

Takatani, Yusuke; Sasano, Daisuke; Nakano, Toshiya; Midorikawa, Takashi; Ishii, Masayoshi

doi:10.1029/2011gb004227

Cited by 39 publications

(64 citation statements)

References 65 publications

(82 reference statements)

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“…Over the mid-latitudes, patterns of projected changes in subsurface O 2 are broadly consistent with observations collected over the past several decades (Helm et al, 2011;Stendardo and Gruber, 2012;Takatani et al, 2012). Yet there is no such model-data agreement over most of the tropical oceans.…”

Section: General Descriptionsupporting

confidence: 66%

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

et al. 2013

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Abstract. Ocean ecosystems are increasingly stressed by human-induced changes of their physical, chemical and biological environment. Among these changes, warming, acidification, deoxygenation and changes in primary productivity by marine phytoplankton can be considered as four of the major stressors of open ocean ecosystems. Due to rising atmospheric CO 2 in the coming decades, these changes will be amplified. Here, we use the most recent simulations performed in the framework of the Coupled Model Intercomparison Project 5 to assess how these stressors may evolve over the course of the 21st century. The 10 Earth system models used here project similar trends in ocean warming, acidification, deoxygenation and reduced primary productivity for each of the IPCC's representative concentration pathways (RCPs) over the 21st century. For the "businessas-usual" scenario RCP8.5, the model-mean changes in the 2090s (compared to the 1990s) for sea surface temperature, sea surface pH, global O 2 content and integrated primary productivity amount to +2.73 (±0.72) • C, −0.33 (±0.003) pH unit, −3.45 (±0.44) % and −8.6 (±7.9) %, respectively. For the high mitigation scenario RCP2.6, corresponding changes are +0.71 (±0.45) • C, −0.07 (±0.001) pH unit, −1.81 (±0.31) % and −2.0 (±4.1) %, respectively, illustrating the effectiveness of extreme mitigation strategies. Although these stressors operate globally, they display distinct regional patterns and thus do not change coincidentally. Large decreases in O 2 and in pH are simulated in global ocean intermediate and mode waters, whereas large reductions in primary production are simulated in the tropics and in the North Atlantic. Although temperature and pH projections are robust across models, the same does not hold for projections of subsurface O 2 concentrations in the tropics and global and regional changes in net primary productivity. These high uncertainties in projections of primary productivity and subsurface oxygen prompt us to continue intermodel comparisons to understand these model differences, while calling for caution when using the CMIP5 models to force regional impact models.

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Section: General Descriptionsupporting

confidence: 66%

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

et al. 2013

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“…Observational studies indicate a mostly negative trend in the oxygen content over recent decades in different basins of the world's ocean (Stramma et al, 2008;Chan et al, 2008;Whitney et al, 2007;Mecking et al, 2006;Emerson et al, 2004;Joos et al, 2003;Keeling et al, 2010;Takatani et al, 2012). A recent global-scale observational study (Helm et al, 2011) supports the evidence of a widespread ocean O 2 decrease between the 1970s and the 1990s.…”

Section: Cocco Et Al: Oxygen and Indicators Of Stress In Multi-momentioning

confidence: 48%

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

et al. 2013

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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

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“…The non-anthropogenic CO 2 contribution dominantly accounted for the enhanced acidification of intermediate water rather than anthropogenic CO 2 uptake, but our value might be an overestimate. This is because the long-term trends and bi-decadal oscillations of AOU in subsurface waters in the northwestern subarctic Pacific Ocean have been reported (ex., Ono et al, 2001;Osafune and Yasuda, 2006;Watanabe et al, 2008, Takatani et al, 2012. In our data, collected during 1997-2011, AOU varies on a shorter than bi-decadal cycle and the AOU increase on 26.9σ θ (1.8 ± 0.4 µmol kg −1 yr −1 ) was twice that from 1968 to 1998 in the Oyashio region near the western subarctic gyre (0.8 ± 0.3 µmol kg −1 yr −1 ) (Ono et al, 2001).…”

Section: +063(16/170aou)mentioning

confidence: 73%

Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

et al. 2013

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Abstract. Rising atmospheric CO 2 contents have led to greater CO 2 uptake by the oceans, lowering both pH due to increasing hydrogen ions and CaCO 3 saturation states due to declining carbonate ion (CO 2− 3 ). Here we used previously compiled data sets and new data collected in 2010 and 2011 to investigate ocean acidification of the North Pacific western subarctic gyre. In winter, the western subarctic gyre is a source of CO 2 to the atmosphere because of convective mixing of deep waters rich in dissolved inorganic carbon (DIC). We calculated pH in winter mixed layer from DIC and total alkalinity (TA), and found that it decreased at the rate of −0.0011 ± 0.0004 yr −1 from 1997 to 2011. This decrease rate is slower than that expected under the condition of seawater/atmosphere equilibration, and it is also slower than the rate in the subtropical regions (−0.002 yr −1 ). The slow rate is caused by a reduction of CO 2 emission in winter due to an increase in TA. Below the mixed layer, the calcite saturation horizon (∼ 185 m depth) shoaled at the rate of 2.9 ± 0.9 m yr −1 as the result of the declining CO 2− 3 concentration (−0.03 ± 0.01 µmol kg −1 yr −1 ). Between 200 m and 300 m depth, pH decline during the study period (−0.0051 ± 0.0010 yr −1 ) was larger than ever reported in the open North Pacific. This enhanced acidification rate below the calcite saturation horizon reflected not only the uptake of anthropogenic CO 2 but also the increase in the decomposition of organic matter evaluated from the increase in AOU, which suggests that the dissolution of CaCO 3 particles increased.

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Decrease of dissolved oxygen after the mid‐1980s in the western North Pacific subtropical gyre along the 137°E repeat section

Cited by 39 publications

References 65 publications

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

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

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

Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

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