“…the limits of the unknown had to recede step by step before the ever-increasing yearning after light and knowledge of the human mind, till they made a stand in the north at the threshold of Nature’s great Ice Temple…”
–Dr. Fridjof Nansen, Farthest North
This morning we awoke to the news that we had spent much of the night being chased off station by floating icebergs. As the sun rose, it glinted off of more than a dozen icebergs within easy reach and later, as we scanned the seafloor for good sites to take sediment cores, we had to stray from our search lines to avoid colliding with the floating giants.
Despite the fact that they are literally putting kinks in our plans, I have to admit to being thrilled by the sight of these gleaming sculptures of ice. Not only do they make for spectacular photographs, they’re also the modern analogue of the phenomenon I’m studying aboard the Royal Research Ship Discovery.
My name is Allison Jacobel and I’m a postdoctoral research scientist from Columbia University’s Lamont-Doherty Earth Observatory. Together with Grace Cushman, an undergraduate at Barnard College, I am studying the record of Earth’s past climate preserved in marine sediments. They may not look like much, but these layers of sediment, from deep below the waves, tell us about the ocean’s past temperature, salinity, productivity and how it moved heat around the planet.
Grace and I are particularly interested in the record of rocks and other terrestrial debris deposited by icebergs. These pieces of ice rafted debris were picked up by glaciers on land and as the icebergs melted at sea they deposited their load of pebbles (and sometimes even boulders) in the sediments below. Just as the icebergs floating outside our portholes are a consequence of ice melt from Greenland, the record of icebergs in the marine sediments indicates past melt.
Twenty thousand years ago, Long Island sat at the foot of an enormous glacier fed by an ice sheet that covered the greater part of North America. This was the Last Glacial Maximum, the most recent ice age. Our transition from the LGM, when Boston was covered by almost a mile of ice, to the warm climate of the present was not a smooth one. Research has shown that the transition was punctuated by catastrophic floods of icebergs that disrupted ocean circulation. Studying the history of iceberg melt is thus a valuable way to help us understand abrupt changes in climate and to shed light on the sensitivity of the climate system to additions of freshwater.
Today the Arctic is experiencing a rate of warming faster than any other place on Earth. Dramatic ice loss is occurring from the Greenland Ice Sheet and from the mountain glaciers that surround the Arctic. Although our work on the RRS Discovery is focused on past changes, our results are also important for modern climate prediction efforts. Models are currently equivocal about the future of the ocean’s overturning circulation and understanding how past inputs of meltwater affected circulation is critical to improving these models and climate forecasts.
The early 20th century polar expeditions of Nansen and other famous explorers were dedicated to expanding our geographic knowledge of the poles. Today, we know the shape of the coastlines and the safest routes for travel, but we are still working to push back the limits of the unknown. Not only are we learning the details of modern productivity regimes and deep-sea habitats, we are also using Earth’s own records to uncover its history, in the hope that we might help protect what remains of Nature’s great Ice Temple.
A handful of the icebergs we have observed off of coastal southwest Greenland. (Photo credit: Marcus Badger)
An iceberg transferring debris to the ocean. (Photo credit: Allison Jacobel)
A Mega Corer, housing 8 sediment cores collected from the seafloor. (Photo credit: Allison Jacobel)
A sediment core in the process of being sliced for geochemical analyses. (Photo credit: Grace Cushman)