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The Little Ice Age and 20th-century deep Pacific cooling

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Science  04 Jan 2019:
Vol. 363, Issue 6422, pp. 70-74
DOI: 10.1126/science.aar8413
  • Fig. 1 Simulated interior ocean response to Common Era surface temperature anomalies.

    (A) Global average (black line) and regionally averaged (colored lines) surface temperature time series θb, for a simulation initialized from equilibrium in 15 CE (EQ-0015). Regional variations are plotted for the Antarctic (ANT), North Atlantic (NATL), sub-Antarctic (SUBANT), and North Pacific (NPAC). Prior to globally available instrumental surface temperatures beginning in 1870 CE, global changes are prescribed according to estimates from paleoclimate data. (B) Time evolution of the Pacific-average potential temperature profile from EQ-0015. (C) Similar to (B) but for the Atlantic-average profile. Atlantic and Pacific averages are taken north of 35°S and 45°S, respectively, and color shading has a 2.5-cK interval from –35 to 35 cK. Note the expanded time axis after 1750 CE.

  • Fig. 2 Observed and simulated deep-ocean temperature changes.

    Observed ocean temperature changes are diagnosed by differencing WOCE and Challenger temperature measurements. WOCE temperatures are linearly interpolated to the location of Challenger temperatures, and differences are plotted after averaging between 1800 and 2600 m depth (colored markers). Simulated temperature changes for the same depth interval are diagnosed from OPT-0015. Color scaling is equivalent for observed and simulated temperature changes.

  • Fig. 3 Vertical profiles of temperature change.

    Difference between WOCE and Challenger temperatures is shown as a function of depth with 95% confidence intervals averaged over the Pacific (blue) and Atlantic (red). Features of the WOCE-Challenger temperature difference are reproduced in a simulation initialized from equilibrium at 15 CE (EQ-0015, dashed curves) and an inversion constrained by the observations (OPT-0015, solid curves). WOCE-Challenger temperature differences are calculated using a weighted average that accounts for the covariance of ocean temperatures and their uncertainties based on the expected effects of high-frequency oceanic variability (markers and error bars with darker colors). For comparison, a simple average for each basin and depth level is also shown with uncertainties that are empirically estimated (lighter colors).

  • Fig. 4 Regional surface temperature variations and changes in ocean heat content over the Common Era.

    (A) Surface temperature time series after adjustment to fit the HMS Challenger observations (OPT-0015), including four major surface regions (colored lines) and the global area-weighted average (black line). (B) Time series of global oceanic heat content anomalies relative to 1750 CE from OPT-0015 as decomposed into upper (cyan, 0 to 700 m), mid-depth (blue, 700 to 2000 m), and deep (black, 2000 m to the bottom) layers. Heat content anomalies calculated from an equilibrium simulation initialized at 1750 (EQ-1750, dashed lines) diverge from the OPT-0015 solution in deeper layers. (C) Similar to (B) but for the Pacific. Heat content anomaly is in units of zettajoules (1 ZJ = 1021 J).

Supplementary Materials

  • The Little Ice Age and 20th-century deep Pacific cooling

    G. Gebbie and P. Huybers

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Table S1
    • Figs. S1 to S9
    • Caption for movie S1
    • References

    Images, Video, and Other Media

    Movie S1
    2,000-year evolution of potential temperature anomaly at 2500 meters depth from OPT-0015. Black contour lines are indicated from –95 cK to 95 cK at intervals of 10 cK

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