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Big climate picture from tiny marine fossils

CARDIFF U. (UK) — Researchers are studying a unique 12,000-year fossil record of marine algae to learn more about past climate change in the western Antarctic Peninsula, one of the fastest warming regions on the planet today.

Scientists have debated the causes of the warming, particularly in light of recent instrumental records of both atmospheric and oceanic warming from the region.  As the atmosphere and ocean warm, the ice sheet—which holds an equivalent of 5 meters of global sea level rise, locked up in ice—becomes vulnerable to collapse.

Published in the journal Nature Geoscience, the new research used the record from microscopic fossils, which are half the width of a human hair, to trace glacial ice entering the ocean along the western Antarctic Peninsula. They found that the atmosphere had a more significant effect on warming along the western Antarctic Peninsula than oceanic circulation in the late Holocene (from 3,500 to 250 years ago).

This wasn’t the case before 3,500 years ago, and isn’t the case now.  The study has also shown that this late Holocene atmospheric warming was cyclic (400 to 500 year long cycles) and linked to the increasing strength of the El Niño Southern Oscillation phenomenon—a climate pattern centered in the low latitude Pacific Ocean—demonstrating an equatorial influence on high latitude climate.

“Our research is helping to understand the past dynamic behavior of the Antarctic Peninsula ice sheet,” says Jennifer Pike of the School of Earth and Ocean Sciences at Cardiff University. “The implications of our findings are that the modern observations of ocean-driven warming along the western Antarctic Peninsula need to be considered as part of a natural centennial timescale cycle of climate variability, and that in order to understand climate change along the Antarctic Peninsula, we need to understand the broader climate connections with the rest of the planet.”

Ice derived from land has a very distinctive ratio of oxygen isotopes. The research team used a technique to measure the oxygen isotope ratios of microscopic marine algae fossils (diatom silica).  When a large amount of glacial ice is discharged into the coastal ocean, it alters the oxygen isotope ratio of the sea water that the marine algae are living in.

This creates a clear imprint in the fossils that reveals the environmental conditions of the time.  The scientists used the oxygen isotope ratio of the fossils to reconstruct the amount of glacial ice entering the coastal ocean in the past 12,000 years, and to determine whether the variations in the amount of ice being discharged were the result of changes in the ocean or atmospheric environment.

The Natural Environment Research Council funded the research.

Source: Cardiff University

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