How sensitive is the oceanic conveyor belt to the influx of glacial melt water and/or decrease of seasonal ice formation in the Arctic Ocean/North Atlantic Ocean?

The impact of all other global warming issues may be minimized if there is a threshold of fresh water influx and/or decrease of seasonal ice formation which may soon be exceeded and thus dramatically slow or reverse the trend of global warming.

Will the Atlantic Meridional Overturning Circulation slow in the comming century and what will be the climate impacts due to this change?

The Atlantic Meridional Overturning Circulation (MOC) is the principal manifestation of the ocean’s response to earth’s net radiation budget. Its mean circulation and variability are linked to globally distributed climate phenomena e.g. European average temperatures and rainfall distribution. The MOC is predicted to slow under global warming. We first need to observe the meridional distribution and temporal characteristics of the MOC then model and predict future change.

What are the key processes that control the size and shape of the global ocean overturning circulation, and how will they combine to influence its future evolution?

The meridional overturning circulation (MOC) of the global ocean has a governing role over the Earth’s climate, a consequence of the enormous capacity of the ocean to store and redistribute heat, freshwater, carbon dioxide and other climatically-important tracers. This results in the MOC being arguably the most prominent feature of the climate system that transcends physical, chemical and biological processes, linking atmosphere-ocean-ice interactions with the carbon cycle and other biogeochemical processes, including ocean acidification. The MOC is known to exhibit variability on timescales from months to millennia, and has the potential to induce abrupt change in climate, most pertinently in the region of the North Atlantic.

The mechanisms governing the strength, shape and variability of the overturning circulation are not fully understood, but include wind forcing, buoyancy forcing and mixing. It has been postulated that the polar regions, where global climate change impacts are predicted to occur earliest and with largest amplitude, play a disproportionately important role in these. A combination of theoretical studies, model simulations and observational analysis (including monitoring of the present state and assessment of paleo conditions) is essential to better understand these mechanisms and to predict future changes.

Can we quantify the meridional overturning circulation (MOC) as a function of space and time?

The MOC moves 90% of the heat and dissolved gases around the planet yet it is very poorly quantified in space and time.

The MOC is changing markedly as the drivers in the polar regions change ever faster (sea ice formation, ice-shelf distribution, temperature and salinity changes etc.).

Understanding and quantification is very low at present, partly because it has been very difficult and expensive to measure but new technology provides important new opportunities to establish an appropriate long term monitoring network. Data from such a global network would offer fundamental improvements to models and hence increase the accuracy of projections.

How will cryospheric changes at the poles impact polar terrestrial and marine ecosystems and the Earth’s climate?

Global climate change is heavily noticed at the poles. Sea ice diminishes, ice shelves collapse and ice sheets shrinking as ice melts and glaciers accelerate. Consequences are manifold:

A large subglacial hydrological system exists beneath the Greenland and Antarctic Ice Sheet. Across this system the ice and water interacts with the underlying lithosphere and biochemical processes mobilizing nutrients which are subsequently transported to the ocean. Hidden beneath kilometer thick ice these interactions are not yet studied, neither the flux quantified nor the faith of nutrients in the ocean is known. Yet processes, like mobilization of iron from fine glacial flower, could play a role in fertility of the polar ocean.

Changes in the extent of polar ice coverage exposes large areas of ocean floor to an open ocean or to semi perennial ice coverage as well as large continental areas. This exposes large areas to sun light and allows photosynthesis. Changes in the availability of light will change the food web and nutrient supply. Photosynthetic communities will likely replace chemotrophic communities. Unknown are the effect on the marine food web, global chemical cycles and feedback to the Earth Climate system. Especially understudied in this regard is the ecosystem of the polar oceans. To detect and quantify change here, a base line needs first to be established.

Glaciers and sea-ice at the poles also play a crucial role for the global circulation of the ocean. Increased melting at the poles will freshen the ocean impacting thermo hyaline circulation. A similar effect will have shrinking sea-ice extend and collapse of ice shelves. Yet many of these processes are not yet well understood. (see Global Water Cycle question)