Annualmeeting:2017 CSDMS meeting-050
Groundwater storage contributions to sea level at and since the Last Glacial Maximum
[[Image:|300px|right|link=File:]]Changing sea level and ice volume since the Last Glacial Maximum (LGM, 26-19 ka) has been an intensively studied topic for decades, and yet we have still not been able to adequately close the water volume budget at the LGM. At the LGM, global sea level was depressed by approximately 125-135 m relative to the present level. Past researchers have attempted to account for the storage of this water as an estimated 52*106 km3 of land-based ice. However, relative sea level, ice sheet morphology, and isostacy studies at local and regional scales have been unable to reasonably place high enough ice volumes to meet this global total, accounting for only approximately 120 m of sea-level change. This discrepancy has resulted in the so-called ‘missing ice’ problem. We propose that some portion of this ‘missing’ water was stored not as ice, but in lakes and groundwater. Thus far, no studies have attempted to determine the volume of water stored in lakes and groundwater at the LGM. Groundwater storage could potentially account for a large volume of water, reducing the missing water volume by a significant margin. Differing topography and recharge rates may have resulted in greater terrestrial water storage, which can help us to close the water budget. Indeed, many large proglacial and pluvial lakes are known to have existed and may indicate higher groundwater levels. Furthermore, assessing groundwater levels at 500 year intervals from the LGM to the present day can provide insights into changes in water storage and inputs to the ocean over time. It is challenging to assess groundwater levels with precision since various factors, including evapotranspiration, topography, and sea level all play a role in controlling groundwater level at a particular location. However, a recent model (Reinfelder et al., 2013) was able to estimate modern groundwater levels on a global scale. By using this model in combination with modelled topography and climate data for the LGM and each 500 year time step, we are able to compare the volume of water stored in the ground from the LGM to the present day to test whether groundwater would be a viable reservoir for LGM water storage. The model provides depths to water table, thus allowing computation of changing storage volumes. The model covers the entire globe at a resolution of 30 arc-seconds. The large datasets and iterative nature of the model require MSI’s computational power to perform the calculations. So far, preliminary results have shown that over a metre of additional sea-level equivalent water was stored in the ground at the LGM.