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Decadal Sea Level Changes in the 50-Year GECCO Ocean Synthesis

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  • 1 Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Hamburg, Germany
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Abstract

An estimate of the time-varying ocean circulation, obtained over the period 1952–2001, is analyzed here with respect to its decadal and longer-term changes in sea level. The estimate results from a synthesis of most of the ocean datasets available during this 50-yr period with the Estimating the Circulation and Climate of the Ocean/Massachusetts Institute of Technology (ECCO/MIT) ocean circulation model. Over the period 1992 through 2001, the increase in thermosteric sea level rise on average amounts to 1.2 mm yr−1 over the top 750 m and 1.8 mm yr−1 over the total water column. This corresponds to an increase in upper-ocean heat content of 1.5 × 1022 J yr−1 and is in agreement with the estimates of Willis et al. However, over the period 1962 through 2001 the global net thermosteric sea level rise is estimated as 0.66 mm yr−1 over the top 750 m, which is twice the recent estimate from Antonov et al. (0.33 mm yr−1). The corresponding trend over the total water column of 0.92 mm yr−1 is also about twice their value for the layer of 0–3000 m (0.40 mm yr−1). For the last decade, the global heat flux into the ocean of 1.5 W m−2 is twice as large as the recent estimate by Willis et al. due to the heat content change in deeper layers. Regional changes in sea level are predominantly associated with an intensification of the subtropical gyre circulation and a corresponding redistribution of heat. The horizontal advection of heat due to an increase in wind stress curl is found to explain a major fraction of the estimated regional sea level trends over the last 40 years. However, the mechanisms appear different during the last decade when in some regions changes in surface heat flux may explain as much as 50% of the sea level changes.

Corresponding author address: Armin Köhl, Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Bundesstr. 53, D-20146, Hamburg, Germany. Email: armin.koehl@zmaw.de

Abstract

An estimate of the time-varying ocean circulation, obtained over the period 1952–2001, is analyzed here with respect to its decadal and longer-term changes in sea level. The estimate results from a synthesis of most of the ocean datasets available during this 50-yr period with the Estimating the Circulation and Climate of the Ocean/Massachusetts Institute of Technology (ECCO/MIT) ocean circulation model. Over the period 1992 through 2001, the increase in thermosteric sea level rise on average amounts to 1.2 mm yr−1 over the top 750 m and 1.8 mm yr−1 over the total water column. This corresponds to an increase in upper-ocean heat content of 1.5 × 1022 J yr−1 and is in agreement with the estimates of Willis et al. However, over the period 1962 through 2001 the global net thermosteric sea level rise is estimated as 0.66 mm yr−1 over the top 750 m, which is twice the recent estimate from Antonov et al. (0.33 mm yr−1). The corresponding trend over the total water column of 0.92 mm yr−1 is also about twice their value for the layer of 0–3000 m (0.40 mm yr−1). For the last decade, the global heat flux into the ocean of 1.5 W m−2 is twice as large as the recent estimate by Willis et al. due to the heat content change in deeper layers. Regional changes in sea level are predominantly associated with an intensification of the subtropical gyre circulation and a corresponding redistribution of heat. The horizontal advection of heat due to an increase in wind stress curl is found to explain a major fraction of the estimated regional sea level trends over the last 40 years. However, the mechanisms appear different during the last decade when in some regions changes in surface heat flux may explain as much as 50% of the sea level changes.

Corresponding author address: Armin Köhl, Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Bundesstr. 53, D-20146, Hamburg, Germany. Email: armin.koehl@zmaw.de

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