Quo Vadis Seas – Tropical Pacific Sea Level DROPPED From 1958 – 2007, New Study Shows

Tuvalu is saved! What follows is a press release from the Leibniz Institute for Marine Science (IFM-GEOMAR) on a new paper appearing in the GRL, which shows sea level changes are far more complex than first thought. It’s back to the drawing board for climate and sea level modellers.

Quo Vadis Sea Levels? New Study Shows Ocean Currents Lead To Strong Regional Fluctuations

Dr. Andreas Villwock

Scientists of the Leibniz Institute for Marine Science (IFM-GEOMAR) have now shown that there are large regional variations when it comes to sea level change. The causes are due to changes in ocean currents, which lead to varying sea levels, especially in the tropical Pacific and Indian Oceans.

Chart above: Sea level fluctuations caused by wind and ocean currents (relative to mean global sea level rise) for the period 1958-2007 (in cm). The model simulation shows regions with sunken sea level (blue) in the tropical Pacific and Indian Ocean. Graphic from IFM-GEOMAR.

Why has the sea level in some regions of the tropical Indian Ocean and Pacific risen strongly over the last 15 years, while in the decades before the sea levels at these locations dropped? The ocean scientists from Kiel are uncovering why by using computer simulations. A paper now appearing in the Geophysical Research Letters shows that fluctuations in ocean currents, caused by trade winds in the tropical Pacific, play an important role.

The impact of wind and ocean currents are prevalent in the tropical Pacific especially in the wake of the El Niño phenomena. “The associated swashing back and forth of the warm surface water leads to a continuous rise and drop in sea level of up to 20 cm within just a few years“, explains oceanographer Franziska Schwarzkopf of the Leibniz Institute for Marine Science (IFM-GEOMAR) and author of the study.

While these short term fluctuations are well documented by modern satellite measurements, little was known about the long-term pattern of changes. “Our computer simulations which use current models show that regional water levels also over time periods of several decades are affected by wind changes and ocean currents“, says Professor Claus Böning, director of Kiel Ocean-Modelling and co-author of the study. A surprising finding from the scientists in Kiel:

"In the middle of the last 50 years, some areas in the tropical Pacific and Indian Ocean experienced a drop in sea levels, contrary to the global trend.”

These new results on sea level rise of the last decades mean an additional challenge for climate modeling. “Whether a group of islands has to reckon with a greater increase in sea level with respect to the average, or can reckon with a temporary drop over the next decades depends decisively on the development of the wind systems and ocean currents“, says Böning. “Future research programs will put increasing focus on the regional fluctuations in the oceans.“

The paper: Schwarzkopf, F.U. and C.W. Böning, 2011: Contribution of Pacific wind stress to multi-decadal variations in upper-ocean heat content and sea level in the tropical south Indian Ocean. Geophysical Research Letters, 38, L12602, doi: 10.1029/2011GL047651.


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