Towards Prediction of Arctic Sea Ice - Ocean - Global Climate Interactions at Seasonal to Decadal Scales
The Arctic Ocean has been warming during the 1990s and 2000s and appears to have accelerated during the last several years as observed by satellites and in situ measurements and as simulated by models. The main manifestation of this trend has been decrease of the ice cover, which through positive ice-albedo feedback may lead to further reductions with major consequences to the global ocean thermohaline circulation and climate. Our objectives are:
- to understand the present and past conditions of the Arctic sea ice and ocean with emphasis on variability in the ice volume and freshwater content and export into the North Atlantic,
- to predict future scenarios of seasonally / partially ice free Arctic Ocean in response to forcing from atmospheric model predictions or from extrapolated into the future combination of northern hemisphere weather indices,
- to address the general circulation model (GCM) limitations in representing Arctic climate through identification of physical and numerical requirements of future GCMs.
To advance these goals we will use a high resolution coupled ice-ocean model of the Pan-Arctic region forced with realistic atmospheric data and will validate/synthesize model output with available satellite and in situ measurements. This project will address the research topic #3: “Understanding of decadal changes in ocean, ice and related climate conditions” and #8: “Investigating the role of sea ice in the Earth system” of this NRA. It will also contribute to the research topic #5 and #6 through realistic simulation of coastal zones and through forcing of biogeochemical models. Findings of our project will provide insights to the fundamental questions of the NASA Earth System Enterprise research, including new information on how the global system is changing, what are the consequences of change in the Earth system for human civilization, and how the Earth system will change in the future.
The main science goals of this project are:
- to address the global model limitations in representing Arctic sea ice and ocean conditions through identification of the primary physical and numerical requirements of future/improved GCMs
- to understand the present and past several decades conditions in the Arctic sea ice and ocean with emphasis on variability in the total ice volume and freshwater content in the Arctic Ocean as well as on sea ice and freshwater fluxes into the North Atlantic
- to predict future scenarios of seasonally / partially sea ice free Arctic Ocean in response to atmospheric forcing derived from global/regional climate model predictions and/or using a combination of extrapolated into the future northern hemisphere weather indices
The primary hypothesis of the proposed research is that:
- the warming in the Arctic Ocean has accelerated in the last several years as represented by the dramatic decrease of the multiyear sea ice cover, which through positive ice-albedo feedback may lead to further reductions, or in an extreme case even to the collapse of the Arctic Ice Pack with major consequences to the global ocean thermohaline circulation and climate.
The following detailed hypotheses in support of the primary hypothesis are identified to advance the science
1. The rate of decrease in the sea ice thickness and volume based on our existing model results appears to be larger than the rate of ice extent/concentration as modeled (see Figure 1) and observed from satellite passive microwave data. We will verify this with better ‘tools’, including improved ice and ocean model physics/thermodynamics, high resolution, better atmospheric data for model forcing, and model validation with available data on ice thickness together with ice extent/concentration and motion.
2. The decrease of sea ice cover, thickness and volume is in part a result of thermodynamic interactions at the ice-ocean interface and the upward heat fluxes in particular, which are affected by the increased advection of warm Atlantic and summer Pacific waters into the central Arctic Ocean during the 1990s. We will improve model representation of Pacific and Atlantic water fluxes into the Arctic Ocean, boundary/slope currents, eddies, tides and surface mixed layer and quantify the oceanic contribution to the decreasing ice trends.
3. The decrease of the total sea ice volume and the subsequent increase of freshwater content determined by the air-sea-ice interactions in the Arctic Ocean, translates into the increased total freshwater export (i.e. solid and liquid phase) into the North Atlantic with consequences to the global ocean thermohaline circulation and global climate
4. Ensemble simulations of the Pan-Arctic ice-ocean model forced with predicted and/or interpolated into the future atmospheric conditions will identify the range of possible scenarios of Arctic Ocean response to climate change as well as its influence on the global ocean circulation and climate. This approach will provide a long term outlook on what changes to expect in the Arctic Ocean depending on future trends in the atmospheric circulation and in large scale weather indices.
The goals of this project directly address the research topic #3 – “Understanding of decadal changes in ocean, ice and related climate conditions” and #8 – “Investigating the role of sea ice in the Earth system” of this NASA Research Announcement. It will also contribute indirectly to the research topic #5 and #6 through realistic simulation of coastal zones and as potential physical forcing in biogeochemical models of the northern high latitudes. Finally, findings of our project will provide important insights to the (5) fundamental questions driving the NASA Earth System Enterprise research. In particular, they will provide new information on how the global system is changing, what are the consequences of change in the Earth system for human civilization, and how the Earth system will change in the future.
Determination of Changes in the State of the Arctic Ice Pack Using the NPS Pan-Arctic Coupled Ice-Ocean Model (1.6 MB)
This thesis provides an analysis of the diminishing sea ice trend in the Arctic Ocean by examining the NPS 1/12-degree pan-Arctic coupled ice-ocean model. While many previous studies have analyzed changes in ice extent and concentration, this research focuses on ice thickness as it gives a better indication of ice volume variability. The skill of the model is examined by comparing its output to sea ice thickness data gathered during the last two decades. The first dataset used is the collection of draft measurements conducted by U.S. Navy submarines between 1986 and 1999. The second is electromagnetic (EM) induction ice thickness measurements gathered using a helicopter by the Alfred Wegener Institute in April 2003. Last, model output is compared with data collected by NASA’s ICESat program using a laser altimeter mounted on a satellite of the same name. The NPS model indicates an accelerated thinning trend in Arctic sea ice during the last decade. The validation of model output with submarine, EM and ICESat data supports this result. This lends credence to the postulation that the Arctic not only might, but is likely to be ice-free during the summer in the near future.
On the importance of freshwater fluxes from the Arctic Ocean into the North Atlantic: the Nordic Seas versus Canadian Arctic Archipelago (6.3 MB)
We use a high resolution coupled ice-ocean model of the Pan-Arctic region forced with realistic atmospheric data to investigate the variability of sea ice and liquid freshwater fluxes from the Arctic Ocean into the North Atlantic during 1979-2004. Model results are analyzed to compare the relative contribution of the total combined liquid and solid freshwater flux through the two main pathways: Fram-Denmark Strait (FDS) and the Canadian Arctic Archipelago-Davis-Hudson Strait (CAADHS). Our results suggest the relative importance of the freshwater flux through CAADHS into the Labrador Sea. This implies the need for ocean models to adequately represent mass and property fluxes through the narrow and shallow passages of the Canadian Archipelago and Davis and Hudson Straits. We argue that this requirement must be satisfied to advance studies of the Atlantic Meridional Overturning Circulation (MOC) and especially its variability. Given the recent record sea ice melt in the Arctic Ocean, it is critical that global ocean and climate models improve their skill in simulating and predicting effects of changing exports from the Arctic Ocean into the North Atlantic. This talk will outline a possible approach to satisfy such requirements.