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Iceberg influx into Atlantic during last ice age raised tropical methane emissions

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Posted May 30, 2015

Scientists at Oregon State University have conducted a study, which shows that influxes of fresh water into the North Atlantic Ocean from icebergs calving off North America during the last ice age increased the production of methane in the tropical wetlands.

Scientists reached such surprising results by analysing ice core using new method. They detected methane fingerprints from the Southern Hemisphere and reached a conclusion that iceberg influx in the North Atlantic had impact of methane emission in the Tropics (Image courtesy of Oregon State University).

Scientists reached such surprising results by analysing ice core using new method. They detected methane fingerprints from the Southern Hemisphere and reached a conclusion that iceberg influx in the North Atlantic had impact of methane emission in the Tropics (Image courtesy of Oregon State University).

These are unexpected findings as it was believe that methane levels were increased by warming temperature in the Northern Hemisphere rather than interval of cold. Such findings are very important for understanding how the Earth responds to changes in climate.

Rachael Rhodes, lead author on the study, explained the process like this – “Essentially what happened was that the cold water influx altered the rainfall patterns at the middle of the globe”. When the icebergs entered the North Atlantic, they caused exceptional cooling. Rainfall belt was condensed into the Southern Hemisphere and caused tropical wetland expansion and abrupt spikes in atmospheric methane.

In that time, during the last ice age, much of North America was covered by a giant ice sheet. It, as many scientists believe, underwent several catastrophic collapses and many huge pieces of ice ended up in the North Atlantic. The process is now called Heinrich events, but scientists still do not know for sure when they took place and how long they lasted.

Scientists reached such results by analysing the highly detailed West Antarctic Ice Sheet Divide ice core. Using new method they were able to make extremely detailed measurements of the air trapped in the ice. It allowed them to develop a nearly 60,000-year record of methane and measure a broad range of other chemical parameters on the same small sample of ice. New method not only allowed this record to be ultra-high-resolution, but also made possible to study piece of ice more efficiently and inexpensively than in ice core studies in the past.

Using such high-resolution records team of scientists was able to detect methane fingerprints from the Southern Hemisphere that do not match temperature records from Greenland ice cores. Even though cooling caused by piece of ice floating in the ocean was regional, impact on the climate was much broader. It pushed the rain belts to the south, intensified the rainfall and lengthened the wet season. This demonstrates how interconnected climate processes are – processes in polar areas can bring significant changes to the climate of the tropics. Not only that, but it also demonstrated how quickly these changes can happen. Scientists say that only about a decade passed between the iceberg intrusion and a resulting impact in the tropics.

These new findings will also help scientists to have better understanding about climate of the Earth today. As such seemingly local events as iceberg breaking off can change global climate in about a decade, we will have to evaluate processes that are happening today. Impact of activities of humans and natural events may have much more rapid results than previously believed.

Source: Oregon State University

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