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Abstract Natural decadal climate variability in the Pacific, such as the Pacific decadal oscillation (PDO) or the interdecadal Pacific oscillation (IPO), plays a powerful role in evolving global hydroclimate on decadal time scales. Recent generations of general circulation models (GCMs) have been found to simulate the spatial pattern of the PDO well but struggle to capture temporal variability on decadal time scales. To use GCMs to project future climate, we must understand the degree to which climate models can successfully reproduce historical PDO and IPO spatial patterns, temporal behavior, and influence on hydroclimate. We calculate PDO and IPO spatial patterns and time series using 16 models within the CMIP6 archive, all with large (n≥ 10) ensembles, and compare them to observations in an integrated assessment of models’ ability to represent Pacific decadal variability spatiotemporally. All models underestimate decadal variability in the PDO and IPO and have a westward bias in their PDO and IPO North Pacific SST anomalies. We also evaluate hydroclimate teleconnections of the PDO and IPO in models using PDO- and IPO-associated precipitation, circulation, low-cloud, and vapor pressure deficit anomalies. We show that models’ underpowered decadal variability in the Pacific is consistent with their inability to reproduce large-amplitude decadal swings in precipitation in southwestern North America and that models are virtually unable to produce a 30-yr precipitation trend in the southwest of the magnitude observed from 1982 to 2011. We emphasize the importance of model fidelity in simulating Pacific decadal variability for accurate representation of decadal-scale hydroclimate change in Pacific-teleconnected land regions.
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Mechanisms of Low‐Frequency Oxygen Variability in the North Pacific
This study investigates the mechanisms of interannual and decadal variability of dissolved oxygen (O2) in the North Pacific using historical observations and a hindcast simulation using the Community Earth System Model. The simulated variability of upper ocean (200 m) O2is moderately correlated with observations where sampling density is relatively high. The dominant mode of O2variability explains 24.8% of the variance and is significantly correlated with the Pacific Decadal Oscillation (PDO) index (r = 0.68). Two primary mechanisms are hypothesized by which the PDO controls upper ocean O2variability. Vertical movement of isopycnals (“heave”) drives O2variations in the deep tropics; isopycnal surfaces are depressed in the eastern tropics under the positive (El Niño‐like) phase of PDO, leading to O2increases in the upper water column. In contrast to the tropics, changes in subduction are the primary control on extratropical O2variability. These hypotheses are tested by contrasting O2anomalies with the heave‐induced component of variability calculated from potential density anomalies. Isopycnal heave is the leading control on O2variability in the tropics, but heave alone cannot fully explain the amplitude of tropical O2variability, likely indicating reinforcing changes from the biological O2consumption. Midlatitude O2variability indeed reflects ocean ventilation downstream of the subduction region where O2anomalies are correlated with the depth of winter mixed layer. These mechanisms, synchronized with the PDO, yield a basin‐scale pattern of O2variability that are comparable in magnitude to the projected rates of ocean deoxygenation in this century under “unchecked” emission scenario.
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- Award ID(s):
- 1737188
- PAR ID:
- 10453573
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 33
- Issue:
- 2
- ISSN:
- 0886-6236
- Page Range / eLocation ID:
- p. 110-124
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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