Scientists drill cores in ocean sediment because this mud contains evidence of past climatic fluctuations. Layers within these cores are radio-carbon dated, and the data gleaned between layers provides proxy evidence for the climatic conditions that occurred within different periods of time. Scientists have recently drilled cores at various sites in the Arctic Ocean. One site at Lomonosov Ridge yielded a 428 meter core, revealing a 56 million year record of Arctic Circle climate.
Map of the Lomonosov Ridge. Sediment cores taken from this formation reveal 56 million years of Arctic climate history.
The presence in sediment cores of certain biological proxies helps scientists determine past climatic conditions. These include plant material such as diatoms, algae, and pollen; and micro-invertebrates such as foraminifera and ostracods. Some species are only found in warm ice free waters, while others occur in environments with ice. The species composition and abundance within a layer provides evidence for the climatic conditions of that time period. Moreover, the chemical composition of foraminifera shells can be analyzed to determine the average annual temperatures when the tiny creatures were alive. Scientists also use larger biological proxies. The presence of driftwood in ancient extinct arctic beaches is evidence of an ice-advancing phase because driftwood eventually becomes water-logged and sinks, but ice can carry the driftwood forward. The presence of certain species of mollusks, such as blue mussels (Mytilus edulis), is evidence of ice free summers because they require beach environments that don’t exist adjacent to perennially ice-covered water. Fossil remains of bowhead whales, narwhals, walruses, and polar bears indicates the presence of ice edge habitat. The presence of their bones helps scientists determine the former boundaries of polar ice.
Epistominella exigua. The presence of this species of foraminifera in dated sediment is evidence of ice free summers in the arctic.
Acetabulastoma hyperboreum. The presence of A. articum, a species of ostracod that looks just like this, in dated sediment is evidence of ice covered ocean.
Skeletal evidence of bowhead whales is evidence of ice edge habitat.
Presently (and for the last 6000 years), much of the Arctic Ocean retains a layer of sea ice all year long. But there have been many climatic phases when the north polar ice cap mostly melted during summers. The early Pliocene from 5 million years BP-3 million years BP probably had long ice free summers in the Arctic. The mid-Pleistocene and several interglacials during the late Pleistocene, most notably phases known as Marine Isotope Stage 11 and MIS 5, had seasonally ice free Arctic waters. The most recent phase of seasonally ice free Arctic summers occurred during the early Holocene from 11,700 BP-6000 BP. Proxy evidence suggests average temperatures in the Arctic were 5-8 degrees F warmer during the early Holocene than they are today. Scientists believe this was caused by orbitally forced insolation. Higher latitudes received more solar radiation due to cyclical changes in the timing of the precession of equinoxes. This is a 21,000 year orbital cycle. A feedback mechanism was also involved. Year round snow and ice reflected a fraction of solar radiation (albedo), but when this melted during summers more solar heat was absorbed by the darker ocean water. Scientists think the recent increase in polar ice cap melting is driven more by anthropogenic greenhouse gas emissions than by solar radiation because orbitally driven insolation is at a cyclical minimum.
The dark green represents proxy evidence that summers in the Arctic were mostly ice free between 11,700 BP-6000 BP.
A recent study (cited below) has determined the dissolution of the north polar ice cap is not a threat to marine mammals. Genetic and fossil evidence suggests polar bears, ringed seals, harbor seals, and walruses survived many climate phases of seasonally ice-free summers in the Arctic. Most recently, they survived the early Holocene phase mentioned above.
Remember Al Gore (the rapist Vice President) and his comically inaccurate film, An Inconvenient Truth? The film shows a stupid cartoon of a polar bear drowning because it can’t find an ice floe upon which to rest. A polar bear could easily return to land, if it couldn’t find a floating ice pack. But it would never swim blindly into the ocean because they can smell ice floes from many miles away. Most politicians are dumb and Al Gore is no exception. It always annoys me when dumb politicians and political pundits in the media talk about science. Liberals make fun of conservatives when the latter ridiculously cite blizzards as evidence that there is no global warming. Liberals ask, “don’t conservatives understand the difference between weather and climate?” Then these same snarky liberals will turn around and blame every storm and drought on anthropogenic-driven climate change. I would like to ask them, “don’t you understand the difference between weather and climate?” I wish both sides would shut up and leave the science discussions to scientists.
Al Gore’s stupid cartoon of a polar bear drowning.
Cronin, Thomas; and Matthew Cronin
“Biological Responses to Climate Change in the Arctic Ocean: the View from the Past”
Polyak, Leonid; et. al.
“History of Sea Ice in the Arctic”
Quaternary Science Reviews 2010
Strannhe, Christian; Martin Jakobsson, and Goran Bjork
“Arctic Ocean Perennial Sea Ice Breakdown during the Early Holocene Insolation Maximum”
Quaternary Science Reviews May 2014