Arctic Ocean

The Arctic Ocean plays a fundamental role in the global ocean-atmosphere-climate system. The presence or absence of snow and ice influences the global heat distribution through its effect on the albedo. Furthermore the Arctic seas are the source of dense, cold bottom waters which influence the thermohaline circulation in the world oceans. Therefore the Arctic Ocean represents a sensitive indicator for Global Change and it is essential to investigate the Arctic climate, tectonic evolution and controlling processes. Key aspects of Arctic scientific drilling as determined in the ODP Program Planning Group "Arctic's Role in Global Change" include:

The knowledge of the initiation of perennial ice cover in the Arctic Ocean would permit correlation to global climate changes and thus a clearer understanding of the climate system. In this regard important questions are: When did perennial ice develop? Under what boundary conditions did it develop, and disappear? Were the fluctuations in sea-ice cover linked to the growth and decay of continental ice? What is the climatic feedback of an evolving sea-ice cover related to intensifying polar cooling by increasing albedo and restricting ocean-atmosphere heat transfer?
In order to accomplish these objectives, the ridges in the central Arctic Ocean need to be cored, especially in areas where sedimentation rates might be high (>1 cm/kyr). While seasonal ice would occur in the periphery of the Arctic Ocean, only the central Arctic would record perennial pack-ice.

Variations in Water Mass Evolution The series of interconnected basins comprising the Nordic Seas contain about 0.7% of the volume of the world ocean, excluding the Amerasian Basin of the Arctic Ocean. Despite the small volume of these areas, they act as a primary source of a large portion of deep, ventilated waters in the world ocean. Also, the export of ventilated deep waters to the Atlantic via the Fram Strait is compensated by a corresponding import of relatively warm and saline surface waters of Atlantic origin. The Arctic Ocean is hence commonly described as one of the lungs of the deep global ocean (the other being the Weddell Sea). The tectonic development and opening of the Fram Strait has determined the history of water mass exchange between the Arctic Ocean and the World Ocean, as the strait represents the only deep connection between the Arctic and all other oceans. The initial opening of the Fram Strait may have occurred as early as late Eocene, some 35 million years ago. An understanding of the exchange of water masses between the Arctic Ocean and the world ocean is an essential element in modelling the change in global oceanographic conditions over the past ~40 million years. Such models require knowledge about the onset of bottom water formation in the Arctic, the variation of chemical and physical characteristics of the water mass through time, and the cause and relationships which are governed the development of the Arctic water masses.

Gas Hydrates in the Arctic The distribution of gas hydrate in marine Arctic environments is poorly documented. Occurrence of gas hydrate is associated with permafrost on the submerged continental shelves of the circum-arctic sedimentary basins. Gas hydrate may also be present in deep marine Arctic basins, as suggested by the recent observation of bottom-simulating reflectors (BSR) on seismic lines crossing the Lomonosov and Alpha Ridges. The amount of methane that is trapped in gas hydrate is perhaps 3,000 times the amount contained in the atmosphere. A large portion of this methane reservoir is located on the Arctic continental shelf associated with permafrost. The exact link between global warming and gas hydrate dissociation is still debated. A unique site to document the on-going process of methane release from gas hydrate dissociation is the Arctic continental shelf. The process of methane release to the atmosphere may have been active on the extensive Arctic continental shelf since the end of the Pleistocene glaciations, when submergence of the shelf considerably increased the temperature at the sediment surface.

Permafrost and Climate in the Arctic The processes leading to the development of permafrost on the Arctic continental shelf have received little attention. Fit-to-mission drilling platforms and technologies should be used to investigate these permafrost zones that contain high latitude climate (glacial and interglacial) records. Establishing long-term observatories in permafrost regions of these margins will provide important monitoring of the current impact of global warming and its influence on degradation of permafrost and gas hydrates. Other biogeochemical cycles, such as the silica cycle, should also be investigated in context of regional and global climate change. Very little is known about the nutrient flux in the Arctic Ocean.

Figure 1: Permafrost discovered in sediment core from the Laptev Sea. The core was recovered during an expedition with the Russian vessel Kimberlit.

Photo by courtesy of H. Kassens, GEOMAR Kiel

Response of the Arctic during Periods of Extreme Warmth Another important challenge in paleoclimatology and paleoceanography is to develop a quantitative understanding of the mechanisms responsible for maintaining the extreme polar warmth of the Eocene and older as well as younger periods. In terms of intervals of extreme warmth, there are seven key time intervals to examine in the Arctic: the Aptian, Albian, Cenomanian, late Paleocene, early Eocene, middle Miocene, and early Pliocene. What was the climate of the Arctic during these periods? Studies of terrestrial floras suggest mean annual temperatures as high as 13°C during the Cenomanian greenhouse conditions. What was the circulation and fertility of this open basin? Was there sea-ice during the Neogene warm intervals? Perhaps the most extreme greenhouse interval is the Late Paleocene Thermal Maximum (LPTM). This event, which could have been caused by the release and oxidation of methane from clathrates, is characterized by as much as 8°C of warming in the high southern latitudes. What was the response of the Arctic to this warming event?

At present, the existing climate proxy data for the Arctic are at odds with paleoclimate simulations (general circulation models) that produce polar regions characterized by sub-freezing temperatures and significant seasonality. And yet, the fossil record suggests mild climates characterized by winters that rarely see sub-freezing conditions. Climatologists have focused on heat transport processes as well as the effects of greenhouse gases to explain the dynamics of extreme polar warmth. Simulations to test the effects of increased oceanic heat transport on high latitude climates have found to be inadequate for sustaining polar warmth. Along these lines, the heat capacity of a large body of water should have a major influence on high latitude temperature, daily and seasonal, although the impact of this requires additional quantitatively testing. One potential solution to the high-latitude warmth paradigm may involve methane in generating polar-stratospheric clouds that would cause an insulation of the poles.

Evolution of Polar Biota and Fertility What little we know about the composition of the Arctic floras and faunas is largely derived from isolated studies of the shallow-marine assemblages in the onshore sediments of Arctic Canada, Spitsbergen, the Pechora Basin, Eurasian Arctic, and a few piston cores from the Alpha Ridge. Mesozoic microfossils (mostly foraminifera and palynomorphs) have been studied from Siberia, Canada, and Spitsbergen. Cenozoic foraminifera and palynological assemblages have been studied in offshore exploration wells in the Beaufort-MacKenzie Basin. These areas provide at least some insight into the evolution of Arctic marine faunas.

The taxonomic composition of the Arctic marine faunas and floras is poorly known. A complete microfossil biochronology for the Arctic is needed for regional cross correlations and for age constrains for future drilling targets.

Figure 2: Onisimus glacialis - an amphipod living at the underside of Arctic sea ice.

Photo by courtesy of I. Werner, University Kiel

Tectonic History of the Arctic Ocean The environment of the Arctic Ocean changed dramatically during the Mesozoic/Cenozoic tectonic evolution. The Cenozoic opening of the gateways, especially the Fram Strait, favoured the formation of continental ice sheets and the sea-ice cover in the Arctic, perhaps changing the mean average temperature from 13 degrees Centigrade to the present day situation. Knowledge about this history can only be obtained by drilling and rock sampling.

The current models suggest that the oldest Arctic deep-sea basin (Canada Basin) opened in the Cretaceous. For most of the Mesozoic, the Arctic Ocean consisted of an isolated deep-sea area with no major deep-water connection to the world ocean. Although this model is widely accepted, details on the evolution of the Mesozoic Arctic are very limited. While the Cenozoic spreading at the Gakkel Ridge explains the opening of the Eurasian Basin and its relationship to the Lomonosov Ridge, the nature of the Alpha-Mendeleev Ridge in the Amerasian Basin as well as the age of the surrounding deep-sea basins is not known. For the Cenozoic history the most important question to be addressed is the timing of the opening of the Arctic gateways. For unravelling the geological history of the high-Arctic a number of key areas have to be investigated by drilling.

Key Areas for Arctic Scientific Drilling are (Fig.3):

Laptev Sea - Lomonosov - Gakkel Ridge Sediment Transect
Mackenzie Delta - Beaufort Sea Slope Sediment Transect
Alpha-Mendeleyev Ridge Depth Transect
Chuckchi Plateau Depth Transect
Lomonosov Ridge Depth Transect
Gakkel Ridge Depth Transect